The -1 an D RADIO REVIEW (151P Year of Publication) \\`\\\ L No

$The -1 an D RADIO REVIEW (151P Year of Publication) \\`\\\ L No$

The -1 AN D RADIO REVIEW (151P Year of Publication) \\`\\\ l No. 405. WEDNESDAY, JUNE IST, 1927. VOL. XX. No. 22.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

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EMPIRE BROADCASTING. It appeals to us as almost pathetic that on the occasion of our recent celebration of Empire Day a request should ENCE the publication of our last issue have been addressed to the Dutch station authorities at matters in connection with Empire broad- Eindhoven for the Empire Day programme to be broadcasting have proceeded apace. The B.B.C. cast to the British Empire through that station. The have made an announcement to the effect that request was turned down, and with good reason, we con- they are immediately sider, for what possible excuse undertaking t h e ..- .+.- have we for asking a foreign erection of a short - - broadcasting station to distribute a CONTENTS. wave station at Daventry, and PAGE programme of that character to they excuse themselves for not hav- EDITORIAL VIEWS ...... 679 our own Empire, when it is merely ing gone ahead earlier on the score lack of enterprise on our part TELEVISION DEMONSTRATION IN that they did not feel justified in which has prevented us from spending public money on an enter- AMERICA. By A. Dinsdalc ... 680 being able to carry out such a prise which was only experimental PRACTICAL HINTS AND TIPS .. ... 687 transmission for ourselves? in character. If, that is the correct 0000 COIL- DRIVEN LOUD - SPEAKER IVITII explanation, it seems strange that TELEVISION. they arc now prepared to proceed PERMANENT MAGNETS with the station although, to the By H. Lloyd. . N this issue we publish the first still .1 detailed account of what is, best of our knowledge, they C URRENI TOPICS ... 693 have obtained no special authority without question, the first success - to authorise the expenditure. THE EXPERIMENTER'S NOTEBOOK 695 ful public demonstration of tele- However, even though the step By " Empiricist." vision. The article provides a fascinating story, indicating the .taken is so delayed, we are yet READERS' NOVELTIES ... 697 glad to see that action is being extent to which science has brought 698 taken. ('apt. Eckersley has stated NEWS FROM THE CLUBS us in the direction of achieving that it will be some six months NEW APPARATUS ... 699 what, a year or two ago, would have been regarded as an impossi- before the station is completed, BROADCAST BREVITIES ... 701 a very long time -perhaps bility. It is clearly pointed out by and EDITOR years -before Enipire broadcast- LETTERS TO THE those responsible in America that ing can be inaugurated. It seems READERS' PROBLEMS 705 this demonstration must not be to us that there is no justification regarded as a service which for such a delay. It snould only promises early commercial prac- take a comparatively short time to erect a suitable station, ticability. The demonstration was carried out irrespec- and no one expects that the results can be perfect all at tive of cost and complexity of the apparatus ; for the once. As we have pointed out before in our early appeals purpose of carrying out the experiments nearly I,000 men for an Empire station, the Colonies and remoter sections were employed, and when the transmission was conducted of the Empire would be well satisfied for the time being by wireless three wavelengths had to be utilised ; hut tele- if a station in this country could give them results equal vision has been successfully demonstrated, and the task to those they obtain at present from the Dutch broad- of the future is to simplify the methods by which it is casting station. achieved. A7

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Wksboo MpIlcl JUNE zsf, 1927.

A Successful Public Demonstration of Television between Washington and New York. By A. DINSDALE. OR some time past great interest has centred round Bell Telephone Laboratories the in New York, and were en- problem of television- seeing at a distance by abled to telegraphy, speak to, and simultaneously see, friends over either wire or wireless. haver since the the ordinary long -distance ciscovcry of telephone line to Washington, selenium by May in 1873 television has been zoo miles away. the dream of scientists all the world over, and of recent In his introductory years more remarks Walter S. Gifford, Presi- and more research workers have entered this dent of the American fascinating field, Telephone and Telegraph Co.,' until there is now an international race stated that " the elaborateness for final success along of the equipment required practical lines. by the very nature of The latest experimenters the undertaking precludes any pre- to enter the field are a group sent possibility of television being of engineers associated with available in homes aml the great American Telephone offices generally. What its and Telegraph practical use may he 1 shall Co., one of America's largest industrial leave to your imagination." companies, which depends for its scientific progress upon Mr. Gifford then introduced Dr. Herbert E. Ives, vast organised laboratories staffed by some of the cleverest under whose direction the research work on television has telephone and radio engineers in the world. been carried out. Dr. Ives then gave the party a brief A group of engineers attached to these laboratories lecture, in the course of which he outlined the details of (The Bell Telephone Laboratories, Inc.) have been the invention, working and gave a demonstration of its operation away quietly on the problem for some years, between onv until, end of the laboratory and the other. In this on April 7th last, they were able to give a public demonstration he demonstration was assisted by Dr. Frank Gray, who of television over kith wire and wireless is responsible for circuits. several of the developments which made possible the complete system. This demonstration was given before a party of guests Following this demonstration Mr. Gifford which included business executives, then talked newspaper editors, over the telephone with General John J. Carty, engineers, and scientists. The party assembled vice - at the president of the company, who was in Washington. and A

www.americanradiohistory.com WpeIl®00 os1 JUNE 1st, 1927. Wolaci Television Demonstration in America. - between the acts the announcer of the 'Whippany afterwards with Secretary Hoover, of the Department of studio made a television appearance during an- Commerce. nouncements. As Mr. Gifford talked to the General the latter's face An important feature of these demonstrations was that became visible on a small screen, measuring about two there was no difference in the quality of the reproduced inches by three inches, which was mounted in front of image, whether it was transmitted from one end of the Mr. Gifford's telephone. laboratory to the other, by wire from Washington, or by " How do you do, General? You are looking well," wireless from Whippany. said Mr. Gifford. The engineers responsible for this latest scientific de- The face of General Carty smiled and his voice velopment are well aware, and have made no secret of enquired after the health of the speaker on the New York the fact, that one of the serious problems in perfecting end. the invention for general commercial use is that of cost. " You screen well, General," said Mr. Gifford. " You For the purpose of the demonstration on April 7th, look more handsome over the wire." " Does it flatter me much ? " General Carty asked. " I think it is an improvement," was the reply. Loud -speaker and Large Screen. Mr. Hoover was then called to the telephone, and his speech was made audible to the assembled guests by means of a loud- speaker, whilst the (listant speaker was rendered visible on a large screen for auditorium use, measuring about two feet by three feet. This large illuminated transparent screen seemed some - what corrugated. This was clue to the fact that the squares which make up the picture are arranged in 5o rows, one on top of the other. As the eye became accustomed to looking at the screen in the darkened room the face was easily recognisable, although the features, which had been sharp and distinct on the miniature screen for individual use, had become considerably blurred by the enlargement. It was plain that, enlarged to the size of an ordinary motion picture film, the detail would have been completely lost. The invention is admitted to be far from the motion picture -house stage. The images reproduced upon the small screen have been described as being comparable to excellent daguer- reotypes which have come to life and started to talk. In these small pictures the detail of the face appears in Mr. W. S. Gifford, President of the American Telephone and clear -cut black lines against a shining gold background, Telegraph Co., talking from New York to Secretary Hoover in from the neon tube which Washington. The image of Mr. Hoover's face appears on the which is due to the orange light small framed screen. Behind Mr. Gifford is Dr. Ives, who was is used in reproducing the small images. mainly responsible for the development of the system. During this demonstration the pictures were projected only one way -from Washington to New York -it having when Secretary Hoover in Washington was seen and been considered unnecessary for the purpose to establish heard in New York, nearly 1,000 men were required. two -way television- telephone communication, but there is Furthermore, the transmission of television requires the no technical reason why this could rot have been done use of a large group of frequencies, and the transmission had it been so desired. of these frequencies requires a considerable number of ordinary telephone circuits. Television by Wireless. In the case of the transmission of television by wire- Following the wire demonstration between New York less, utilising the system under review, one wavelength is and Washington the visitors were entertained to a repeti- used for sending the picture and two for the synchronisation of the experiments, the transmission on this occasion tion process. Dr. Ives himself emphasised the difficulty being by wireless from the company's experimental here, in view of the congested condition of the ether. station, 3X N, at Whippany, N.J., about 30 miles from No new principles are involved in this latest television New York. development ; many old principles have simply been The first face to appear upon the screen was that of applied under the guidance of recently acquired scientific an engineer, who gave a technical description of what knowledge. Principal in all this has been the knowledge was taking place. Next came a vaudeville act by a obtained during the past few years in the research and comedian, followed by a regular radio programme item - development which has made it possible for the American a short humorous dialect talk by a lady. Before and Telephone and Telegraph Co. to augment its national A 9

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632 Wp@hoo iZ%.VE rsr, 1927 . WopIld. Television Demonstration in America. - Viewing a small portion of this scene at a time, it trans- telephone service by a transcontinental phototelegraphy forms the variations of light and shade which it " sees " service. into variations in the strength of an electrical current. The methods and apparatus used for this service have The next factor is the transmitting medium, which already been described in the pages of this journal by the may be either a wire or a wireless circuit. The third present writer.' factor is the receiving apparatus by means of which the Television and the transmission of pictures by wire or variations of current may be transformed back into terms wireless have many points in common. In an electro- of light and shadow, and the picture thus reconstructed mechanical system of picture transmission it is not pos- piece by piece. sible to send the entire picture at once; it lias to be sent The fourth and final factor is the apparatus used to over the circuit, or through the ether, piece by piece. keep the sending and receiving mechanism in step. Sintilarly, in television, the scene to be transmitted must be carried over the transmission circuit bit by hit, and the The Transmitting Mechanism. An essential feature of all television transmitters is that the scene to he transmitted must be illuminated. The intensity of the illumination depends largely upon the sensitivity of the light- sensitive device used to transform the light impulses into electrical impulses. With all systems so far developed it has been customary to flood the entire scene with light, and this light, in most cases, has had to be so intense as to cause con - siderahle discomfort to any person facing it. The intensity of the light has had to be made so great because, when an alkali photoelectric cell is used as the light -sensitive device, its response to light impulses is extremely feeble, the output requiring enormous amplification before it will perform the -work required of it. It must be borne in mind that the light which reaches the cell is reflected light, and some idea of the feeble- ness of reflected light may be obtained from the calculation of one scientist who estimates that, if the human face is illuminated with a r,000 c.p. lamp, the total amount of light reflected from it will scarcely amount to one cand le-power. In the matter of intense illumination the television system under review is no exception. Photoelectric cells are used to transform the light impulses into electrical currents, and a very intense illumination is employed, which is provided by means of arc lamps. Unlike other systems, however, the scene to be transmitted is not constantly flooded with this great light. Between the arcs and the scene there is interposed a re- volving disc which has drilled in it, near the circumfer- ence, a series of small holes which form a single spiral. General view of the television transmitting apparatus. The light beam is projected from the square aperture in front of the Through these holes. there shines, at any given moment, sitter, the reflected light being picked up by three photoelectric cells mounted behind grilles inside the cabinet. In the backgreun.l only one single spot of light. may be seen the associated amplifiers. The rotary action of the disc causes this spot to travel from left to right across the scene or individual to he received picture recreated bit by bit. In the case of transmitted, then the next hole, set a trifle nearer the television, however, and in contrast to phototelegraphy, centre of the disc, allows another spot of light to pass the details transmitted must follow each other so rapidly through, which travels across the scene on a parallel that to the eye and brain of the observer at the receiving track, but a trifle lower down than did the last one. end the effect will be that of seeing the scene reproduced As the disc continues to rotate, this action continues till as a whole, complete with natural movement. the entire scene has been covered, or " explored." This effect is rendered possible of achievement by what is called retentivity of vision, which means that the eye The Photoelectric Cells. retains for an instant the impression of an object which The disc rotates so rapidly that the whole scene or object it has seen after the object itself has been withdrawn is lighted up, a little spot at a time, in less than a from the actual field of vision. fifteenth of a second. There are fifty holes in the disc, Broadly speaking, the apparatus for television con- so that the scene has fifty illuminated lines traced across sists, first, of an electro- optical device, substituting for it. the eve, which, " looks at " the scene to be transmitted. By this method an intense illumination of the sitter can .' The Wireless World, April 27th, 1927. he obtained without undue discomfort. All that can be A IO

www.americanradiohistory.com WflmIl,go MAT rst, 1927. Wald 683 Television Demonstration in America. - portional to the light reflected to them, and hence propor- seen is a flickering spot of light which crosses and re- tional to the light and shade of the particular detail. crosses the sitters face at an incredible speed. Even As the beam of light swings across the scene, working its when using this method of illumination, however, it is way from top to bottom, the current from the cells varies said that the sitter begins to feel discomfort after a few correspondingly. minutes' exposure to the intense light spot. So swiftly does the beam sweep the scene that the cur- The lines, contours, and colours of the face of the rent variations are wide and rapid -sometimes correspond- sitter cause variations in the degree of brilliancy of the ing to a change from a maximum current to a minimum spots of light they reflect, and these, in turn, cause a and back to a maximum in a twenty- thousandth of a similarly varying effect tvhen they strike the photo- second. These variations, the so- called alternating cur- electric cells. In the photograph on page. 682 is shown a close -up of the transmitting apparatus. The backs of the panels up0.1 which are mounted thi associated amplifiers can also be seen. The light spot which covers the scene to be transmitted shines out from tbt cavity in the middle of the box -like arrangement before which the ligure is sittin_. Around this cavity, behind the metal screens, are placed three huge photoelectric cells. In the photograph in the title of this article Dr. Ives can be seen holding one of these. They are probably the largest photoelectric cells ever made. The ability of these cells to conduct electricity varies in direct proportion to the light falling upon them. As any particular part of the object is illuminated by the travelling spot of light, the fluctuations of current thus produced are transmitteit after amplification, to the Secretary Hoover before the television transmitter in Washington. receiving apparatus. As has already been explained, the total amount of rent components, comprise the electrical impulses which light reflected from a human face is very small indeed. are transmitted to the distant receiver. The speed of Coupled with this there is the well -known fact that the signalling is therefore about 20.000 per second. output of a photoelectric cell is extremely electrical At the Receiving End. minute, and requires considerable amplification before it can he utilised to operate a circuit. The current which Two forms of receiving apparatus have been developed. was sent out by radio at Whippany, for example, had to In both forms of receiver a neon gas tube is an im- be amplified 5,000 million million times before it was portant element. Such tubes, which the reader has no broadcast from the antenna doubt seen used in advertising display devices, are hollow glass vessels in which the air has been replaced by neon Increasing Sensitivity to Light. gas at a very low pressure. Electrical discharges pass- Hence the reason for such large cells. Three are used ing through such a tube cause it to glow, the brilliance in parallel, partly to augment the total response and of the light being directly proportional to the strength of partly to secure the effect, by virtue of their arrange- the current. ment, which would he obtained if the sitter were flooded It Neill at once be appreciated that, in regard to the with light from three directions-from above, from the relation between light and electricity, the properties of right, and from the left. a neon tube are exactly opposite to those of a photo- As each detail of the sitter is illuminated, the photoelectric cell. electric cells instantly respond, initiating a current pro - In the apparatus for use by a sirígle individual a small

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www.americanradiohistory.com 'Wpesom 681 Woiflll JUNE ist, 1927. Television Demonstration in America. - the eyes of the spectators. The grid may he viewed neon tube is used, and the entire tube glows in accord- directly or through a screen of ground glass or other ance with the strength of the current being received from translucent material. the transmitting station at any particular instant. The distributor consists of a brush contact which is re- Between the tube and the observer, who looks through volved in synchronism with the scanning disc at the send- a small aperture about two and a half inches square, there ing end. This brush, as it revolves, makes contact with is interposed a disc exactly similar to the one at the a commutator arrangement, composed of 2,500 segments, transmitting station, rotating in step with it. The result to which the leads to the neon tube electrodes are con- is that the observer sees at successive instants successive nected. portions of the field of view, each of which is illuminated Each segment picks up from the rotating brush the by the glowing neon tube, the brilliance of which is con- appropriate electrical impulse intended for it, and constantly fluctuating. ducts it over the connecting wire to the appropriate elec- So rapidly is the scanning of the field of vision carried trode -1 the grid. To each one of the 2,500 wires 15 out that the observer's sensation is that of seeing the impulses per second must be delivered. The most minute scene as a whole recreated just as it appears at the trans- error would scramble the portrait completely. mitting apparatus. What the observer would actually see if the mechanism were suddenly stopped dead would be Synchronism. a tiny spot of light, admitted to his line of vision through The question of synchronism is of vital importance in one of the holes in the disc. At each instant the posi- any television system. The mechanism at both the trans- tion of this spot of, light is caused to correspond to that mitting and receiving ends of the circuit must run exactly of the detail of the scene at the sending end. in step. In this latest system dots of light are put to- The entire scene, in successive details, is thus repro- gether at the rate of about 45,000 a second to give the duced for the observer, and the complete process of re- effect of a motion picture. Each dot has to he in its exact producing in proper order the light details of the scene place. occupies less than a fifteenth of a second. It is then The mosaic of dots, or picture elements, would be a automatically repeated, so that the observer views the jumble -the picture would be completely " pied "-if complete scene fifteen times per second, which, due to there was an error of r- 9o,000th part of a second in the retentivity of vision, gives a motion picture effect. synchronisation between the sending and receiving apparatus. The Large Screen. The moving parts at each end of the circuit are driven For the presentation of the image to a large audience by exactly similar motors, and, to ensure steadiness, two a different method must be employed. Instead of using motors are used at each end. One of each pair of motors a relatively small neon tube, successive. portions of which is a " synchronous " alternating current motor, the func- are viewed at successive intervals, a very long tube is tion of which is to control the speed of the main driving employed which is folded back and forth upon itself to motor. forni a grid. A near view of one of these grids, taken The main motor operates at a frequency with which during the pumping process, is shown on page 685. complete images of the scene can he formed. To prevent The tube is bent into fifty loops, corresponding with this motor from " hunting," that is, from varying slightly the number of holes in the scanning disc at the transmit- in speed alternately above and then below that correspond- ting end. Instead of being fitted with a single pair of ing to 18 cycles per second, the second and smaller motor electrodes, like the smaller tube, this grid is equipped assists the drive. with 2,500 electrodes, fifty per loop. Each electrode This synchronous motor, operated at 2,000 cycles, in .corresponds to a single elemental area of the picture plane the range of telephonic rather than power frequencies, which is scanned by the photoelectric cells at the sending ensures that the rotating mechanisms at the two ends of station. the system shall not be out of step with each other by These electrodes are connected by wires to a distributor more than the amount represented by half of one of the which, in turn, is connected to the circuit coming from small holes in the disc. This corresponds to an interval the transmitting station. The distributor revolves in of time of 1- 9o,000th of a second. exact synchronism with the rotating disc at the sending The two motors can be seen, together with the trans- end. mitting scanning disc, in the photograph on the front When a particular spot on the object at the sending cover of this issue. The main drive motor is on the end is illuminated, its position and light intensity are right, and the control motor on the left, close to the disc, transmitted, in the form of an electrical impulse, to the the control mechanism being in the centre. receiving station, as has already been described. In this case, however, the distributor selects the proper connec- Success the Result of Co ordinated Research. tion with the neon tube and lights a spot on the grid The successful development of this system of television corresponding with the spot on the original scene, the is not the isolated work of any one man; as already illumination of which set up the impulse. stated, many engineers took part in the necessary re- Only one spot on the grid is illuminated at a time, hut searches. and their method of attack and the record of these glowing spots follow each other with such rapidity progress forms an interesting story in itself. that the audience sees the entire grid lighted up, its de- Dr. Ives, who was put in charge of the work, has many grees of illuminatipn corresponding with those of the outstanding achievements to his credit, amongst them original scene, thus producing a complete picture before being the first practical lamp for producing artificial day- A 12

www.americanradiohistory.com JUNE ist, 1927. WbSISM, 685 Wo?Ilcl television Demonstration in America. - as the Vitaphone,' Mr. Stoller contributed the speed - light. Throughout his career his researches have many control and synchronising devices, embodying the first times touched upon photoelectric cells and their various commercial application of the thermionic valve for speed uses, and to him is due the work upon photoelectric cells regulation. This method has a much higher precision in connection with the development of television. than any other. Prior to commencing work upon television, Dr. Ives was engaged upon phototelegraphy, and it was he who The Development of Scanning Devices. developed the system which is now in daily use by the One of the next developments was that by Dr. F. Gray, American Telephone and Telegraph Co. for the trans- a member of the technical staff of the Laboratories, who mission of commercial and Press pictures to all parts of had previously been responsible for certain early forms the United States. of the experimental apparatus. He devised the method This method of directing the research attack to the of projecting a minute spot of very intense light upon elemental phases of the problem is illustrated by the the object to be transmitted, and of moving this spot back investigation of methods for producing currents in re- spouse to light variations and lights in proportional response to currents. This was separated from the other investigations (such as those of methods for synchronisation and of the characteristics of transmission channels) by driving on the same shaft the scanning disc and the similar disc for reproducing, and thus operating the transmitting and receiving equipment in close proximity. In a later form of experiment a stage of final accom- plishment was reached which might seem to have justified publication, but was with- held therefrom as being only a step in the research programme. Cinematograph Films Transmitted First. In this experiment a strip of motion picture film was projected from a standard projector upon a photoelectric cell, and the mug ing picture of this film was then recreated for an observer by Large -size screen used for demonstration purposes. It consists of a continuous glass tube containing neon gas into which 2,500 electrodes are sealed at the back. The photograph shows a means of a receiving equip- screen grid in process of pumping. ment involving the use of a suitable neon tube and a scanning disc as already described and forth to illuminate successively the details of the earlier in this article. entire area. This apparatus eliminated the problem of the illumi- Following the development of this method, Dr. Ives nation of the scene, for the photoelectric cell was influ- constructed and arranged the large photoelectric cells enced by directly transmitted light, which could he made which have previously been described. as powerful as desired. 'This line of experiment thus Other phases of the research problem were met in the permitted concentration on the other phases of television. development by Dr. Gray of the large neon tube for the Its adoption facilitated eery much the study of synchron- production of an image large enough to be viewed by a ous motors, which were then developed under the direc- considerable audience, and the development and use of tion of Mr. H. M. Stoller, whose work has for many such a tube, with its present total of 2,500 external elec- years been connected with the exact regulation of the speed of electric motors. I See " Wireless and the Gramophone," The Wireless World, To the apparatus for talking motion pictures, known Sept. 15th, 1926.

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Oa'd Wilmhoo JUNE rst, r927. Wacl'w1 Television Demonstration in America. - characteristic, special equipment for the equalisation of trodes, required the development also of the current dis- attenuation and of phase shift had to be devised. tributor from which 2,00 wires, like a gigantic optic Similar problems in radio equipment were also solved nerve, extend to the tube. by new designs and adaptations arising from the under- Dr. Gray is responsible also for the application to tele- lying researches, and these developments of wireless vision of the basic principles of amplifier design. equipment resulted in an operative radio- television system As the terminal apparatus approached its present forni of equal reliability to the wire- connected system. there were studied other problems which were to be en- \ \'hen, according to the most conservative judgment of countered in the transmission of the light- generated and the scientists concerned, and of the Laboratories' execu- synchronising currents over great distances, both by wire tives, the experiments liad progressed far enough to assure and by wireless. To transmit an image formed by 2. Soo operation over long distances both by wire and by wire- elements requires a channel capable of carrying without less, field experiments were undertaken, and these experi- distortion the entire range of frequencies from 18 cycles ments finally led up to the successful public demonstration per second to about 20,000 cycles per second. In order of long- distance television described at the beginning of to give a high -grade telephone line such an extended this article.

MR. A. W. WATT, the Editor of 3DA R. S. Dawson, 23, Kensington Rd., South " in Narra. Radio Australia and New Zea- 3DB Drewliegh Business College. land," has kindly sent us a list of Amateur Stations in 3EM H. WV. Doudnev, 7, Dickens St., Balaclava. amateur stations corrected to December 3ER E. H. W. Read, 147, Lygon St., East Bruns- 31st, 1926. Space does not permit us to wick. Australia. 3FA Nerang Motors, Scoresby St., Kcraug. reproduce this in full, but we give below (Dealer.) the stations which are not included in the 30G G. A. Garcon, 201, Page St., Mid. Park. R.S.G.13, Diary and Log Book, and any (Change of address.) 30N H. G. Selman, 35, Queen St., Geelong \\'est. alterations and corrections in addresses 2RE R. \T. E. Rees, 83, Northumberland Ave., (Change of address.) published therein. Staninore. 3GS G. S. C. Semrnens, State School, Queenstown. 2RM R. A. Macfarlane, Wak',en St., Griffith. (Change of address.) COMMONWEALTH OF AUSTRALIA. 2R.V R, V. Thomas, 18, Plowman St., N. Bondi. 3Hß A. H. Reid, 3, Kingston St., East Malvern. NEW SOUTH WALES. & 1'22, 2SA W. E. Salmon, Poldhu, Cor. Park Rd. an 1 31G Jones Clew, Tuorak Rd., Camberwell. 2BA Trawler " Bar -eu -Mal," Red Funnel Fisheries, Olympia St., Naremburn. (Dealers.) (Change of address.) Ltd., Killara. 2SH A. Short, Young St., Lambton. 31S J. Schultz, 24, York St., Glenferrie. (Change 2BC N. J Hurll, Northcote Ave., Killara. (Dealer.) 2SM H. W. S. Caldecott, 52a, Quint ton Rd., Manly. of address.) (Change of address.) 2111 Illawarra Radio Club, 75, Montgomerie Si., 3KM D. Kerr and Muir, Ltd., 241, Bay St., North 2BR Trawler " Brolga," Coastal Trawlers Co., Kogarah. (Change of address.) Brighton. (Dealers.) Goldsborough Chr., Sydney. 2WK W. D. Kennedy, 16, Mabel St., Willoughby. 3KN R.A.A.F., Victoria Barracks, St. Kilda Rd., 2DN G. E. H. Blanchard, 47, Foord Ave., Hurl - (Change of address.) Melbourne. stone Park. (Change of address.) 2XT Austr. Made Preference league Ex. Train, 25. 3LD Deal Island Lighthouse. 2FG F. Gibbons, 64, Thrupp St., Neutral Bay. Martin !'lace, Sydney. 3MH M. H. Stuart. 571, Mt. Alexander Ra., 2FK F. Welch, 1, Augusta Rd., Manly. 2ZU N. S. Gilmour, 161, 'Wycombe Rd., Neutral Moonee Ponds. 2HC II. R. Carter, The Armidale School. Armilale. Bay. (Change of address.) 3ND Police Patrol Car No. 1, Melbourne. 2HH II. H. Davis, Torrington Rd., Strathheld. 2ZY N. \Vollett, 33, Wolseley Rd., Masora. 3PD Police Dept. (H.Q.), Russel St., Melbourne. 2HT II. K. R. Thomas, Strathearn, Murdoch SL, (Special.) Neutral Bay. (Change of address.) VICTORIA. 3PX N. S. Taylor, 24, Dalgetv St., St. Kilda. 2J13 P. 1. Browne, 131, Avoca St., Randwick. 3AD J. A. Davey, 28, Cole St., Elsternwirk. 3RI Railways Inst. Wireless Club, Flinders St., 2LL L. S. Lane, ' Narbeth," The Avenue, Rand - (Change of address.) Melbourne. wick. (Change of address.) 3AH A. H. Faul, 3, St. Leonards Ave., St. Kilda. 3TM A. Ii. Buck, 7, Carrington St., Glenferrie. 2LM L. M. Wilson, 6, Kalima Flats, Reginald St., 3AL H. D. Kerr, 1214, Sturt St., Ballarat. (Change of address.) Cremorne. (Change of address.) 3AM A. Forecast, 22, St. George's Rd., Malern. 3TR W. S. Treagear, 22, Cule St., Upper ITaw thorn. 2LY R. H. Shaw, 120, Grafton St., \Voollahra. 3AU S. H. 9filtigan, Allawah, Nicholas St., Chilwell. 303 R. M. Dalton, 105, Murray St., Caulfield. 2N0 D. B. Knock, 1112, Cremorne Rd., Cremorne. (Change of address.) (Change of address.) 2PS P. G. Stephen, Mona St., Granville. ( Deahr.) 3CH H. C. Harris, Sherwood St., Birehip. (Dealer). 3WX VW. Cavanagh, 22, Mary St., St. Kilda. 2RC R. Chilton, co J. E. Siemer, Gloucester. 3CI Chilly Island Lighthouse. 3XW C. A. Cullivan, Bayview, Digger's Rest. (Corrected address.) 3CK Ernest Cook, Glenhope, Tresco. QUFESSLAND. 4AC A. C. Walker, Oxford St., Saudgate. 9AW A. B. \\'alz, Cor. Eton St. and Sandgate Rd N unda h. 4BD D. D. Grimes, Farragindi Rd., Anneslev. IBM A. B. Milne (Milrosc Motors), Mackay. (Dealer.) 4CR C. F. Kiel), London Bay Missionary Stn., Fife Bay, Papua. 4CW A. T. Buck, f eebung, North Coast Line. 4HL II. L. Miller. Cor. Ryan & Hoogley Strs Hill End, Brisbane. 4HW 14. D. Walsh, Vailima, Torak Hill I lamilton. 9LG The Grand, S.W., 7th Ave., Windsor. Brisbane. 4LJ I.. J. Feenaghty, Dickson St., AA-olnntrìu. 4MC M. J. 'rIcPherson, Merinela, via Bower. 4Rá H. J. Stephenson, Thorold St., AWoolo,,wirr. 4SM W. -G. Ikin, River Rd., New Farm, Brisbane. 4WE W. E. Vining, Brickland Rd.. Nuu,lah. 4WR H. D. Walsh, Dickson Terrace, Hautiltnn. 9YN I). J. Harkin, 101, Flight R.A.A.F., Bowen.

SC" II AUSTRALIA. 5AX A. H. Traeger, Brigalow Ave., Kensington Gardens. 5B0 H. A. K:mper, 6, Rothbury Ave., Tusinore. (Change of address.) 5BR Blackwood Radio Club, Waite St., Blackwood. (Change of address.) Y.: 5JA P. 1. Brewer, 21, Douglas St., Parkside. 5SA E. R. Turner. 111, Godfrey Terrace, Le.u+ronk. 5SR South Suburban Radio Club, Castle St., l'arkside. 5WI Wireless Institute (S.A. Division), lì, Bakewell Receiving station. BRS -38, owned by Mr. B. C. Bedwcll at 204, Swanshurst Lane, Rd., St. Peters. (Change of address-) Mosel -y, Birmi Iaham. Oa the left is a straight- circuited 0 -v -1 receivar with a tuning 5WP W. S. Pitchford, 318. Wakefield St., Adelai,le. of 140 rave -4,000 metres, and on the right a short -wave 0 -v -1 Reinartz with a r..nga 5WS West Suburban Radio Club, 4-1, King St., of 15 -200 metres. Mile God. A it

www.americanradiohistory.com JU.1'E rst, 1927. Wfip®Il®00 087 WOUIlc1

A Section Devoted to the Practical Assistance of the Beginner. HIGH- MAGNIFICATION VALVES The advent of the type of valve SELECTIVITY. IN AN H.F. AMPLIFIER. specifically designed for resistance A knowledge of the fact that the Although the majority of up -to- capacity coupling, however, leads one selectivity of a receiver may be im- date H.F. transformers are designed to doubt whether there is not some proved by increasing the ratio of its to work in the anode circuit of a valve justification for altering this atrange- capacity to inductance may be turned having an impedance of the order of nient and placing the filament re- to good account in the operation of 20,00o- 30,000 ohms, it is possible, as sistance in the negative lead of such perhaps the majority of receivers. In has already been stated in these valves. other words, the combination of a columns, to improve selectivity with- Fig. I shows that providing the small coil and a large condenser gives out introducing any great reduction grid return circuit is taken to a selective circuit. This being so, the in amplification, by substituting one L.T., the grid will be negatively beginner may wonder why designers having an impedance of 50,000 to biassed to the extent of the voltage go to the trouble of producing elabor- 70,000 ohms, with a correspondingly dropped across the resistance. Polari- ate arrangements when by simply increased amplification factor. Be- ties are marked in the figures to en- making a suitable change in values fore making this change, however, able the voltage drops to be appre- the desired results might be obtained. there are one or two points to which ciated. - Unfortunately, however, an increase special attention should be paid. The In this connection it may be borne in capacity results in a reduction of grid bias should be reduced, if neces- in mind that the anode current in a H.F. voltage built up across the cir- sary, to a maximum of I volts nega- valve with a megohm or more in cuit, and consequently signals will tive, although a lower figure is often generally be weaker. As to whether desirable. The high- tension voltage this reduction may be tolerated or not applied to the plate should be in- will depend entirely on circumstances. creased to the highest value avail- The principle may often be applied able, even beyond that specified by with advantage when working the the makers. Everyman Four " receiver on the By observing these precautions it long waves, for which no H.F. stage is possible to keep down the actual is provided, and a direct -coupled working impedance to a reasonably aerial circuit is used. Thus there low value, with the result that the may be interference on the Daventry transformer will be able to extract a wavelength from a powerful and good proportion of the available am- near -by short -wave transmitter. To plified H.F. energy in the anode cir- obtain the necessary conditions for cuit for transference to the grid of maximum selectivity, a small con- Fig. 1. -,, Free " grid bias. the succeeding valve. denser of about 0.0002 nail. or even. 0000 series is so small that adequate emis- less should be inserted in series with THE POSITION OF THE FILAMENT sion may be obtained with consider- the aerial, while the loading coil RESISTANCE. ably less than the normal filament should be of such a size that the par- 1'he present arrangement of battery voltage. For instance, one would allel tuning condenser is set nearly connections, in which H.T. - , expect a two -volt valve to work at maximum capacity for the recep- L.T. - and G.B. + leads are con- efficiently under the above circum- tion of the desired station. nected together and earthed and the stances at 1.5 to 1.6 volts, leaving, The "All -Wave Four" may also be filament resistance placed in the posi- say, 0.4 volt for grid bias. improved in selectivity by judicious tive lead, became standard some time Examination of the static char- choice of coils; when this quality after broadcasting actually com- acteristic curve of this type of valve is particularly necessary, both aerial menced, and has since been accepted will show that even with 120 actual and secondary inductances should be more or less without question as being anode volts this bias is as much as of the smallest size which can be the best, as indeed it is, except under can be used without lowering the tuned by means of the variable con- special circumstances. efficiency of the valve somewhat. densers to the wavelength required. A 15

Itirks7; : www.americanradiohistory.com r, , WAnIligog %Wad JUNE rst, 1927. THE BEST EARTH CONNECTION. giving passable results, is anything ments as to which is the best, since The advantage f a good earth con- but ideal, as it nearly always goes the course pursued by such conductors nection cannot be urged too often. to the street in front of the house, varies so greatly in different establish- The best aerial is wasted if the earth whereas the aerial generally extends ments. The best plan is to take connection is poor. The ideal earth backwards at the rear of the house. separate connecting wires to the consists of a number of good con- For this reason there must be many various possible earths and to try ductors buried just below the surface instances where better results could them one by one, in various combina- of the ground and extending under be obtained by burying two or three tions and all bunched together. In- the aerial very much as the roots of thick copper wires below the aerial discriminate bunching together of all a tree extend beneath its branches. and parallel to it. possible earths does not, however, in- Further, the lead from the earth tip Of the various conductors, such variably give good results, as there to the set should be as short and as water- pipes, etc., which are found are sometimes one or two earth con- direct as possible. The average available for earthing purposes, it is nections which make matters worse water -main earth, though usually impossible to make any general state- instead of effecting an improvement.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 72. -A D.C. High- tension Battery Eliminator. (To be concluded In next week's Issue.) The present series of diagrams is intended to show progressively, and in an easily understandable manner, the various points to which special attention should be paid in the design of typical wireless instruments, and at the sanie time to assist the beginner in mastering the art of reading circuit diagrams. The simple H.T. eliminator. shown below is intended to operate on direct -current supplies of from 200 -240 volts, and will give good results except where there is a heavy " ripple" on the mains current.

rn r" f' Z+ 7 } Zi á-- f.a- Cj ' s - +1 C' C3

(t) (2) (3)

A voltage- dividing resistance is connected Smoothing conde nsers and a low- trtquencq Output terminals tor the receiver are directly across the mains. choke are inserted as shown. added, with extra shunt condenser C. rf HE resistor should be wire - entirely in its function of suppressing age across the output terminals is a wound, and should have a re- irregularities. It should also have a proportional to the amount of resist- sistance of about 7,000 ohms, assum- low ohmic resistance. The reservoir ance in circuit, provided that no curing the supply to be in the neighbour- condensers Ct and C. may have rent is flowing. Thus, if the tap X hood of 220 volts, and that ordinary capacities of 2 mfds. each, although is joined to the centre point, on a 240 - valves are to be used in the receiver. a larger size may he desirable ; addi- volt supply there will be 520 volts About a dozen equally spaced tap- tional parallel condensers should he between - and + t. As soon as pings should be provided. Suitable connected if " hum " is loud enough current is taken, however, there will :oils are obtainable commercially, or to be annoying. be a voltage drop in the part of the they can be wound with No. 40 In (3) the output connections to the resistor still in circuit (that between Eureka wire, of which about 100 receiver are shown. The voltage ap- X and the end connected to the yards will be required. Note that it plied to the valve will depend on the choke), so it will he necessary to move is advisable to insert fuses in each position of the tap X ; this can only up the tap to a position slightly nearer lead, as close to the main input as be determined approximately unless to the positive end. possible. accurate measuring instruments are The condenser C3 should' have a The resistance specified above will available, but it is an easy matter to capacity of at least 2 mfds. This pass about ,,o milliamps, so the make a sufficiently accurate adjust- value may be found sufficient when a smoothing choke L, must carry at ment. comparatively simple receiver is to he least that current without saturation; Ignoring the resistance of the choke operated. but S mfds. may be neces- this is a very important point, as a (from a practical point of view it is sary in certain eases to prevent L.F. badly designed instrument may fail generally possible to do so) the volt- oscillation in the receiver.

A 16

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Vitpesg@O JUNE 1st, 1927 689

C MM -D0vEN LOUO -511EA I R

Reducing the Maintenance Costs of Coil = driven Loud =speakers. By H. LLOYD, M.Eng.

LL those who have heard an open diaphragm coil - ately becomes a more economical and adaptable instru- driven speaker will agree that the realistic quality ment ; it has only one pair of supply leads, and can, if of reproduction obtainable with this type of in- required, be installed at a distance from the receiver with. strument when operated under the best conditions is of out the necessity for relay devices for cutting off the field an amazingly high order. Many people are now using current when the set is not in use. or experimenting with this form of sound reproducer, The first attempts made by the writer to substitute but there must be a very large number who have reluc- permanent magnets for the electro- magnet commonly tantly decided that for them, at any rate, the maintenance used in this type of moving coil device were carried out of such a speaker is out of the question on account of in connection with magnetophones during 1923, whilst the energy consumed by the field windings. In the days in charge of the Sheffield Relay Station of the B.B.C. \lien receivers consumed as many am- In the early experimental stages of this peres as they possessed valves this pioneer relay station the arrangements additional drain on the accumulator were necessarily very primitive,' and in would not have represented a very particular the pressure on the battery - large percentage increase, but to -day, charging facilities was very great. A unless one is among the few who have Round -Sykes microphone was in use for D.C. supply mains, the prospect of local modulation purposes, and -this was increasing the L.T. con- the last straw of the battery sumption perhaps three- or load, so the writer decided four -fold is naturally viewed to try to produce something with dismay. at any rate approaching the In this article the results normal flux of 1,500 gauss by are. given of some experi- means of permanent mag- ments that have been made nets. Exceptional opportuni- with coil -driven. units, which ties were available, owing to show that quite adequate the fact that a good deal of volume for all domestic pur- special work had been done Fig. I.-Electro-magnetic micr oppone with permanent magnet in to produce mag- poses can be obtained with- fie Sheffield out any polarising battery. net steels of high coercive The characteristically high quality of reproduction is force. Several microphones were constructed privately, maintained, and the input can easily be provided by a and fully justified the trouble taken. The output in no medium -power receiver of modern design, such as the case was quite up to that of the battery- excited micro- " Everyman Four." phone, but the addition of another D.E.R. valve to the amplifier brought the strength up to standard, and a con- High Flux Density Necessary. siderable saving of energy was effected. A photograph in Fig. r. force on the moving coil is proportional to of one of the actual microphones is shown The axial modi- radial magnetic flux in the air -gap of Later the pole -pieces of one of these magnets was the density of the diaphragm the magnet, and to get the greatest sound output from a fied to suit the drive -coil of a large pleated more easily given diaphragm assembly the flux density must natur- loud -speaker,' but as D.C. " juice " became in favour of the rather ally be made as high as possible. The amount of available this was neglected electrical energy that it is necessary to dissipate in the more compact electro-magnet. Aindings of an electro- magnet in order to maintain this In order to give an idea of the flux that is necessary for a well - flux depends considerably upon the distance across the for reasonable acoustic efficiency, the curve is reproduced in gap, but since a rather wide gap, whilst requiring more known type of electro- magnet unit B in air -gap ampere- turns, at the same time greatly simplifies the Fig. 2. This shows the value of " " the different mechanical requirements in coil suspension, the electro- of a Magnavox field magnet corresponding to the excita- magnet generally is arranged to give ample clearance for currents through the windings. With normal Reducing the the moving coil. After all, if polarising current has to tion, the flux density is about 9,200 gauss. down to be used, it does not very much matter about the expendi- current to 0.75 ampere brings the flux density output as experi- ture of a few more watts for the sake of greater toler- 7,000 gauss, the diminution in sound serious in a ances in the matter of construction. The prospect of enced by the ear not, however, being very order can dispensing entirely with the polarising supply, however, room of ordinary size. Field strengths of this alters the question considerably. The speaker immedi- I The Wireless World, Oct. 14th, 1925, and Aug. 4th, 1926. A 17

www.americanradiohistory.com 690 WflpigIl@oo Wazll0 ;UWE 1st, 1927.

Coil-driven Loud -speaker with Permanent Magnets.- suspension must apply a minimum of constraint on the be obtained with permanent magnets of not too bulky movement, and must not be of such a nature as to intro- dimensions, and at a cost which is not excessive when it duce resonance effects appreciable to the ear. Fig. 4 is is considered that there is no maintenance charge. Steels a rear view of the movement of the speaker referred to óf the cobalt -chrome series have been used for the mag- above, with the magnet removed to show the method of nets in preference to tungsten steel on account of the centring the coil. The boss of the aluminium casting to saving in weight and dimensions, and in Fig. 3 is shown which the magnet is bolted carries three attachments one of these magnets applied to a coil -driven speaker arranged at 120 °. The two upper ones each consist of unit. Quite sufficient volume is obtained from this instru- a short strip of brass slotted, drilled, and tapped 3ß.A. ment for comfortable listening in a moderately sized to take a screw through the end of which is a small hole. The lower one is a similar sized strip, but of thin spring steel, again twitlt a small hole drilled through it near the B (GAUSS) end where it overhangs the slot in the aluminium. in 12000 the coil former, near the point of junction between the former and the diaphragm, there are three small holes about in. diam. so located as to be opposite the three attachments mentioned. Three threads of thin machine - 8000 silk are passed through these holes, each thread being passed through two holes, and each pair of ends coming out from the former are threaded through the small hole 4000 in the adjacent centring attachment and secured with a spot of melted wax. keference to the figure should make this clear : the threads are drawn only just taut, the weak spring at the bottom applying ever so slight a tension. if on plucking the threads with a in the diaphragm is 15 0 05 10 20 caused to emit a decided note due to the vibration of the AMPERES silk. the tension should be reduced by letting out a little more thread or by weakening the spring. After this adjustment is satisfactorily made the suspension is com- Fig. 2.- Variation of flux density with polarising current in pleted by serving the threads with a coat of rubber solu- air -gap of MIagnatox loud- speaker. tion, especially at the points where they pass through room, using a receiver with a 3,000 -ohm valve in the the coil former. last stage, and izo to 150 volts H.T. Modern gramo- With regard to the coil former itself, when this has to phone records are also very pleasingly reproduced, using be very thin the best material seems to be mica, built an electromagnetic pick -tip. The six magnets, one of which is shown separately in the photograph, are of the lame shape as those used in the microphone, being bent, heat treated, anti ground accurately to lit the pole- pieces. Fifteen per cent. cobalt steel was used, the 35 per cent. _obalt steel not showing sufficient advantages to justify the extra cost. The cross -section of each piece is 3.3 cm. x 1. r cm., giving a total flux of 130 kilolines at the (13H),,,,,, point. A gond deal of this is manifested as leakage field, but with the length of air -gap reduced to a minimum there is sufficient useful flux for the purpose for which this speaker is intended. As a basis of comparison for different magnets, the product (13 x r,D) was taken as a figure of merit. representing the force on a one -turn coil of diameter D centimetres. Thus for the Magnavox magnet normally excited the figure of merit was 57,700, whilst for a current of o.75 ampere it was 43,600. The permanent magnet just described was found on measurement to reach 3S,Soo. The length of air -gap (distance between pole -pieces) in this case was 0.14 cm. Fig. 3.- Complete loud -speaker unit. On the left is shown of 0.055 ", and the clearance between the moving coil and one of the magnet elements. the pole- pieces, inside and outside. was but to mils. tip to the tetluirecI thickness from strips split down Coil Suspension. to a thickness of about I mil. A few inches of brass To prevent the coil (luring its excursions from being rod or tube is turned up truly cylindrical and polished, able to come in contact with the magnet, it is necessary its finished diameter being about 6 mils less than the tchen using such small clearances to employ some form internal diameter of the coil former to be constructed. of suspension for the coil in addition to the usual dia- One end of the bras, should he faced up square so that phragm suspension of twashleather or stockinette. This it may be used as a guide for the blade when trimming A 18

www.americanradiohistory.com JUNE ist, 1927. Wt@Ilsoo 691 n%1P1 ç Coil- driven Loud -speaker with Permanent Magnets.- In the opinion of the writer, Seccotine, though excellent up the finished coil. The brass is heated to about for attaching the edge suspension and coil former, is not too° C., and one or two layers of paraffin waxed tissue so suitable for the seam as a form of mountant such as paper are wound tightly on it and bound with cotton to Higgins' or Grip -fix. Before applying the adhesive the keep the paper in position until the wax has cooled. After symmetry of the finished cone is improved by drawing the removing the cotton the diameter is checked, and if correct paper upwards Ivitli a curved sweeping motion from the winding of the mica strip is commenced. About four beneath the edge of a ruler held firmly clown in contact layers will generally be required, and they are wound as with the table top. This gives the paper a bias in the tightly as possible, filtered shellac varnish being used to direction in which it has to bend, and prevents hold the layers together. A binding of cotton should be the tendency otherwise present for the joint to pull put over the mica when the proper thickness is reached, apart during drying. In the speaker illustrated the and about 24 hours allowed for the preliminary harden- central portion of the cone has been left open. The ing of the shellac. Before proceeding with the winding it reason for this is so that the position of the moving coil is well to build up the portions of ,. within the air -gap can be seen, and the former which will not be centralisation by means of the ad- carrying wire up to the same justing screws easily carried out. The height as the wire will occupy. loss in the low register at moderate This will further strengthen the outputs is very small and to most former, at the same time support- people unnoticeable, although the ad- ing the end turns of wire during justment never needs attention except and after winding. Strips of in the case of accidents through trans- paper, accurately cut, and stuck ients in the moving coil. It is very round the mica with thick filtered iniportant that the entire moving mass shellac, are suitable for this. In should be very free; when displaced the coil illustrated the former is and allowed to return freely the din. in length, and the paper col- vibrations should be almost low lars at each end are respectively enough in frequency to count. Of ,bin. and hin. in width, leav- course, when the magnet is in posi- ing a winding length of yin. tion and the coil connected to the When the winding which should transformer the movement will be be of enamel -covered wire to pre- practically dead -beat. serve a high copper space factor - Straight Bar Magnets. is finished a final coat of varnish is given to the coil and the whole The magnet generally thoroughly baked. The effect used with the movement of this will be to melt the y.1N shown in Fig. 4 employs underneath the mica, and no dilli L- shaped strips of cobalt culty will be experienced in remov- I steel, but straight bars ing the coil from the brass tube. may be used with success. It is convenient at this point to In Fig. 5 are shown the coil former FIg. 4.-Rear view of loud- speaker with magnet removed dimensions of a magnet trim the ends of the showing moving -coil suspension with a razor blade, using the faced assembly giving equiva- end of the brass tube as a guide for the blade. lent results to the above type, whilst reducing to a mini- From Fig. 4 it will be seen that the flexible leads from mum the nachining to be done on the actual magnet steel. the coil are brought to terminal sockets fitted in insulat- Machining on this steel, even in the annealed condition, ing hushes in the casting. The leads consist of short is difficult, and in any case the finishing has to be done by lengths of 3/4o Litz wire, bound tightly to the coil grinding after hardening, so that the avoidance of foriner with silk thread, and carefully soldered to the machining justifies the apparent complication of the ends of the coil winding. Vibration between the strands clamping arrangements. The bars are of standard com- of the Litz is damped by painting it with rubber solution. mercial rolled section, heat- treated and machine- ground flat on one face, and can thus be obtained ready for use Constructing the Diaphragm. from the makers of the steel. The two end yokes and A few words in connection with the diaphragm con- the central core are of soft iron, the lower yoke being struction may he of interest to those readers who have bored to take the core, whilst the upper one is recessed experienced difficulty in turning out a really presentable and fitted with a brass bush. This holds the core pole - job with a professional air about it. Do not use the piece central, and is .secured to the core by two grub - heavy grades of cartridge paper ; thin drawing paper screws sunk in holes tapped through the yoke and bush ; gives better results and is easier to handle. The edges one of these can be seen in the sectional view. The which overlap to form the radial joint should he shaved magnet clamps are small brass castings, drilled to slide down with a safety -razor blade to a feather edge, so that on oB.A. studs screwed into three of the corners of each there is not a thick lump of paper at the seam ; a little of the hexagonal yokes. The earlier yokes were care- practice on some scrap pieces of paper will enable a joint fully slotted with the idea of reducing eddy currents in to be made which is difficult to discover with the eye. the pole- faces, a precaution recently pointed out to be A 19

www.americanradiohistory.com TMpisIligoo 092 , jUNE ist, 1927. Wolf Ed Coil -driven Loud- speaker with Permanent Magnets. - The magnets described do not represent the highest neither necessary nor even desirable, the eddy current stage of development possible in this direction, reaction at the higher frequencies tending rather towards but they are simple in shape and comparatively easy to an improvement in response characteristic than otherwise. construct. By employing more complicated forms, much The most important operation of all, upon which greater flux densities could without doubt be obtained, success or failure depends, is, of course, that of magnetis- and here is a possible field for the cast magnet, in which ing. It is no use magnetising the bars separately and the shape can be modified so as to use the material to then assembling them on the yokes ; the whole magnet unit the best advantage without having recourse to expensive must he magnetised at once, the air -gap being preferably machining operations. bridged during the process with soft iron. If a number of similar magnets were to he built, the best method to magnetise them would be to construct an electro- magnet of special shape for the purpose, but when only one or two are to be flashed the simplest way is to put a winding on the core of heavy - gauge cotton -covered wire. say No. r4_ filling the available space, and passing a very large current momentarily through the winding. A Job for Specialists. Not many constructors \will be in a position to obtain the sudden rush of current necessary for this purpose, and in any case the operation should in no circumstance lie Fig. 5.- Leading dimensions of magnet assembly using straight bar magnets. carried out except in the presence of someone thoroughly acquainted with the particu- The loud -speaker with moving -coil drive is begin- lar type of work. The magnet should therefore be ning to enjoy a well- deserved revival in popularity, and assembled after carefully removing all traces of metallic an effective permanent magnet system will remove what filings from the parts, and sent to a firm of repute who in the writer's opinion is the one serious drawback to a specialise in magnetising. It must not be dismantled device which, although in itself not new, possesses the after being magnetised, so that the winding must be left power, when used in conjunction with the recent develop- in situ, where it will at any rate be available in the ments in diaphragm technique, to set up a new standard unlikely event of remagnetising being necessary. of quality in broadcast reception.

ulunication on Sunday. May 15th, at about 1800 G.N.T. with Lieut. E. S. Earle, lchihan, Keppel Harbour, Singa- CATALOGUES TRANSMITTERS' NOTES pore, who is now using the call -sign VS lAB in place of SS 2SE and AM 2SÉ, RECEIVED. by which this station was formerly dis- AND QUERIES. tinguished. Electradix Radios, 218, Upper Thames ooco Street, E.C.4, 68 -page catalogue of all New Call.signs and Stations Identified. classes of Wireless Apparatus, Compo- Mr. A. (G .23, nents, and Accessories. J. Baker 6QH), Third G 2LW P. H. Lawrcucr, Ltvcroft, Albion Rd., Ave., Bush Hiil Park, Enfield, tells us Sutton, Surrey. (Transmits on S, 15 and Metrovick Supplies, Ltd., 155, Charing that he has received a report from a lis- an metres.) Cross Road, London, W.C.2. Broadsheet in who over- (This call -sign was stated, in error, in our of tener Bellerive, Tasmania, issue of May 15 to belong to Mr. \\'. E. descriptive the " Cosmos " Three -Valve heard his two -way communication with Benham.) Resistance Capacity Coupled Set. 1CW in Tripoli when using only 6 watts G 6LY (ex 2BVO) J. H. Blakeley, i, hazel Grose, Ward and Goldstone, Ltd., Frederick input. He has also worked with amateurs Blackool. (Transmits un I i and 4-19 Road, Pendleton, Manchester. List No. in metres.) 32 different countries during the past (This call -sign was formerly hcl,i by Mr. E /12, dealing with " Coltone " H.T. Bat- twelve months on 45 metres, the input H. \w. Sellars, at Chorley, Lanes.) tery Eliminators and Kits for the Radio never exceeding nine watts. Mr. Baker G 6WD G. A. Woods, Si, East Parade, Harrogate, Constructor. informs us that he is temporarily giving will welcome reports giving details of Tungstone Accumulator Co., Ltd., weather conditions, etc. St. up his station. 2APQ J. A. Cornell, 53, Trent Rd., Brixton, S. \v.2. Bride's House, Salisbury Square, London, Mr. Louis Era (Eß 4BC), 46, Avenue 2BHW B. T. Chapman, 3, Canton Rd., Sunbury -on- E.C.4. Folder describing the Tungstune Van Put, Antwerp, was in two -way conr- Thames. (change of address.) Pure Lead Accumulator. A 20

www.americanradiohistory.com WApe®EM JE7.\-E ist, 1927. VAnit 693

11] u; I III1111111111 .1 ' @1r. ,aun,. {1am MTh -u4i ..uy1 CZ.iRRFTTT TOPIC.J' News of the Week in Brief Review.

THE HAPPY WORKHOUSE. ORCHESTRAL ECONOMY. DOES IT EVER CLOSE DOWN ? A broadcast receiving system is being Broadcast receivers are displacing A broadcasting station controlled installed in the Marylebone Workhouse. orchestras on the boats of the Hudson entirely by women has been established 000o River Navigation Corporation. at Stephen's College, Colmbia. Missouri. 000p 000o STRAIGHT FROM THE UMPIRE'S MOUTH. UNWANTED. CALLS ACROSS THE ATLANTIC. on are to be used on the A temporary ban has been placed Up to 'Tuesday. May 17th, the number Loud -speakers by the at Wimbledon this year to mobile broadcasting stations of wireless telephone calls between this tennis courts American Federal Radio Commission. enable onlookers to hear the scores. country and the -United States amounted Stations of this type are said to have to 893. 0 0 0 0 caused " a considerable amount of inter- In a written Parliamentary reply, DERBY TRAFFIC CONTROL. ference." o000 Viscount 1Volmer, Assistant Postmaster- To-day's Derby traffic will be controlled General, stated that the receipts covered without the aid of wireless vans, which COLD COMFORT. working costs but not interest or depre- have been used in previous years. It has A recent cold spell in Lithuania has ciation. been found that the best arrangement is been attributed by a certain sect to the 0000 harmful influence of wireless aerials, a system of telephone posts in conjunc- SHORT WAVES AND SOLAR ECLIPSE. by the which picked up " waves of cold." tion with the facilities offered The Radio Society of Great Britain in- A.A. and R.A.C. The same phenomenon has been observed by a Wigan listener who states vites the general public to participate in 0000 that certain broadcast transmissions leave the experiments which the society will FREE STATE'S WIRELESS IMPORT him cold. conduct with short waves during the DUTY. 0000 period of the eclipse of the sun on 29th. the appeals of the Irish wire - GRIMSBY BEAM STATION. June Despite Details will be sent to non -members on .ess trade for the removal of the duty on On page 632 of our issue of May 18th wireless apparatus in the Irish the wavelength of the Grimsby beani receipt of one shilling in stamps. Com- imported should be to the a motion in favour of the step transmitting station (GBH) was erron- munications addressed Free State, its offices, 53, Street, has been defeated in Dail Eiramt. The eously given as 29.906 metres. The actual society at Victoria Minister of Posts and Telegraphs states wavelength is 25.905 metres. London, S.1V.1. 0000 that the duty is essential to cover the difference between the BOGUS WIRELESS expenditure upon broadcasting INSPECTORS. and the receipts from licence Three owners of broadcast fees. The question may receive receivers in 'Toronto were re- further consideration when a cently the victims of thieves substantial increase occurs in who represented themselves as the number of licences. officers of the radio service on ,000 a tour of inspection. The AERIAL DRILL TO MUSIC. " officers " confiscated the sets A novelty at this year's Royal and made their escape. They Air Force Display will he musi- have not been heard of since. cal drill by wireless telephony. 0000 Titis is a variation of an old THE WIRELESS TYPEWRITER in which complicated favourite A device for sending type- manoeuvres were carried out on radiotelephonic instructions. At writing by wireless is reported on Saturday, July 2nd, to have aroused the interest of Hendon Signor Mussolini, who will a series of popular tunes played by the R.A.F. Central Band shortly witness demonstrations and transmitted by wireless will between Rome and New York. provide the setting to which the The rights of the invention, aircraft will carry out a musical which is based on short waves, aerial ride. are stated to have been acquired new form of jazz will he by the Marconi Company, but This no carried out by No. 41 Squadron, at the time of going to press which is part of the Home De- information on this point had SUMMERTIME WIRELESS. This photograph, taken recently been received at Marconi fence Force, with headquarters on the River Lea, Is an effective reply to those who suggest at Northolt. that wireless is only a winter pastime. House, London. A 2I

www.americanradiohistory.com 69.E Wpe®00 'JUNE ist, 1927. Woirild WIRELESS ACROSS ARABIA. LATOUR PATENTS PROBLEM. cover, besides endowment, the erection of Wireless communication has been estab- There are indications that the Radio new buildings and the provision of new lished across Arabia between Rayad, Corporation is intending electrical and Mecca, to follow the lead engineering equipment. Huile, and Medina. King Ibn of the Hazeltine Corporation of America Cheques should be drawn in favour of Saud left Rayad on Friday, May 20th. and the British Marconi Co. by issuing the University College, London. Cen- after sending the first wireless message licences under its patents to manufacturers tenary Appeal Fund, between and crossed National his two kingdoms. who desire them, writes our New York Provincial Bank, and should be sent to 0000 correspondent. One or two large manu- Sir Robert Kindersley, G.B.E., Univer- THE FINISHING TOUCH. facturers have already acquired such sity College, London, Gower Street, Lon- licences, The importance of wireless as a recog- only to find that they are not don, W.C.1, who is the honorary treasurer enough, nised feature of modern home life is being in that the Latour Corporation (a of the Centenary Appeal Fund. more and more emphasised. and it is subsidiary of the Hazeltine Corporation) claims that certain Latour patents are 0000 significant of the trend in this direction WIRELESS AND THE CROWN that wireless essentially involved in a modern broadcast sets are being incorporated receiver. COLONIES. as an integral of housing schemes. It appears to have been over- part looked in An interesting is that, although the R.C.A. was The development of wireless the example of this the licensed Richings Park Estate at Ivey, Bucks. under these Latour patents, it Crown Colonies and Protectorates is one had not the of the questions When complete, this estate will com- power to sub -license. under discussion at the now Lon- prise 2,000 houses, some 200 of which o000 Colonial Conference meeting in don. During the past fifteen years about have already been completed. Each UNIVERSITY COLLEGE APPEALS TO house is equipped with a LONDON. thirty small stations have been erected, two -valve Ceco- being phone set. complete with loud -speaker and In used mainly for local requirements celebrating its centenary this year, and communication with Osram valves, the aerial being erected University College, shipping, but London, is making a they are regarded as the preliminary beneath the roof. special appeal to Londoners for funds to links in a chain of Empire communication o 0 0 o which may be -iltimately established. THE VOLTA CENTENARY. Ceylon has taken the lead in establish- The Volta Centenary Exhibition, to ing a broadcasting service, while the commemorate the death of the great possibilities of development in this direc- physicist in 1827, was opened by the King tion are hieing considered by Hong Kong, of Italy at the Villa Olmo, Lake Como, on Palestine, the Gold -.Coast, Cyprus, and Saturday last. Zanzibar. The exhibition includes an international 0000 section devoted to electrical communications, while the Italian Admiralty has IMPORTANT U.S. " NEUTRODYNE " erected a special 25- kilowatt short -wave JUDGMENT. transmitter which will work during the A legal decision regarded by many as period of the exhibition and will link up one of the most important in the history Como with Milan by wireless telephony of American radio has been handed down for the first time. by the United States Circuit Court of The national commemoration of Volta Appeals, writes our New York correspon- is to take place on September 19th in dent. Briefly, it is decreed that every Rome. and will he opened with a speech " neutrodvne " receiver involves infringe- by Senatore Marconi in the Capitol. ment of the neutralising patents issued to 0000 A STUDY IN CONTRASTS. The large Hartley and Rice. valve is one of tha latest Cossor trans The SATURDAY'S SHORT WAVE mitter type; its small brother is a sole licensee under these latter TEST in FROM WGY. Stentor Six. patents, the broadcasting field, is the Radio Corporation of America. If the On Saturday next, June 4th. the meet some of the essential needs of its decision stands -and it is unusual to carry General Electric Co.'s station, WGY, . at an appeal in such a case to a Schenectady, will work. still higher launch its second 24- court -its effect upon the American in- hour test, transmitting simultaneously University College, which is the Mother College of London University, dustry will be tremendous, as the Radin on 22.02 and 32.77 metres, both trans- Corporation will have very heavy royalties missions being modulated from the same was founded in 1827 to provide a centre of university education open to all with- to collect and will be in control of practi- source with voice and music. It is cally all the important radio patents. possible that both out distinction of race, class, or creed ; transmissions may not Possible exceptions are those of Latour, be heard at the same time. The test will moreover, it was I'm first university insti- relating, amongst other things, to a begin at 6 p.m. (B.S.T.). tution in this country to establish labora- method of neutralising and the usé The station director of WGY, Schenec- tories for the teaching of chemistry, of a physics, common battery. tady, is anxious to receive reports from and engineering. It was in the 0000 British listeners. It is pointed out that electrical laboratories of University observations between 10 p.m. and 6 a.m. College that Prof. J. A. Fleming invented " HOT STUFF." B.S.T. will be of particular interest. The the thermionic valve. An idea that station WEAF, New principal data required are time heard, The increase in the number of students York City, was about to broadcast some signal strength, quality, and amount of and the necessary expansion in buildings " hot stuff " recently brought a flood of fading. has laid nn the college a serious financial enquiries from newspaper reporters. 0000 burden, because its endowments have not They were disappointed to learn that the kept pace with its growth : actually the " hot stuff " was merely a talk on chem- A WORD FOR THE CONSTRUCTOR. college derives less than 15 per of cent. istry entitled " A Modern Inferno." , " Wireless does more than provide us its income from this source. £235,000 is with a supply of dance music and news needed for endowment, while only 0000 bulletins. It develops character, it £36,000 has as yet been raised. A large TRANSMISSIONS FROM HOLLAND. elevates, and it educates. It teaches us proportion of the sum already received As we go to press we learn of an altera- to be determined, resourceful, patient, has come from the provinces and abroad. tion in the times of transmission from and proud. You cannot build a set and Hence the special appeal to the business PC'JJ given on page 702 of this issue. . finish it without being a bit better than houses, industries, and citizens of London To-morrow evening (Thursday) trans- you were before you commenced, even if to help London's own university. mission will be from 5 to 8 p.m. G.M.T., the darned thing won't work. " -" Aerio " The total amount which the college is and the sane schedule will be observed in the Glasgow Weekly Herald. endeavouring to raise is £500,000. to on June 7th and 9th. A 22

www.americanradiohistory.com JUNE ist, 1927. WfiTg200 695 WopIM xperimenfers ófebook

By " EMPIRICIST." The Use of a Milliammeter in Receiving Circuits. discontinuities. such as dry joints and so forth. If the valve filaments have an abnormally high ikI,I, things considered, it is amazing how series resistance, which in the writer's experience little attention is paid by experimenters is a case not infrequently niet with, a milli- in general to the plate currents of the ammeter in the common feed circuit «-ill show valves they are using. AIillianrmeters that are suitable this up, if not in an individual valve, then as the for measuring these currents can he obtained quite yalyes are being successively put into circuit, the effect cheaply, and their utility seems to be as great for the being that the feed current, instead of rising, as valves purposes of experimenting as is a clinical thermometer are inserted in their holders, one after another, will fa11- to a doctor. owing to the decreasing voltage across the filaments. In the first place, it really is essential that experi- 'Phis point should always be watched for. in any case of menters should know the condition of the valves they are doubt, as it is an extremely easy matter to set it right. using Nowadays, when nearly every valve is a dull It is most frequently encountered with two -volt valves, emitter of a type which must some day or other lose its emission, the only means of checking valves in this respect is to measure the plate current under the standard conditions laid down by the manufacturer as appropriate for use with the particular type of valve. Plate currents of valves under working conditions vary from half a milli - amp. tap to zo milliamps. or even more, and it is therefore useful to have an instrument ,with two ranges, say. o to to milliamps., and o to 5o milliamps. ; this, however, is not essential, and we might quite vyell consider the experinienter as being in possession of a milliammeter of gored quality reading from o to zo milliamps. Checking Efnission. It is convenient, in order that the process of checking valves may be adequately carried out, to have a small valve testing hoard, arranged as shown, with either a pair of terminals or a jack to which the milli - ammeter can be connected. Valves when first bought should be checked against their published characteristics by the application of suitable H.T. and grid bias Volt- ages, and a record may advantageously be made of the readings obtained. It is naturally assumed that the M LLIAMMETER correct H.T. and L. T. voltages are applied to the valve ---- at the time that measurement is made, and it is very convenient to have some handy means of ensuring this. Assuming, then, that the valves are in order, we may next proceed to consider how the instrument may be employed in connection with reception experiments. First and foremost, provided that we can measure individual valve currents (and as a last resort we can do this by putting the valves into the receiver one at a time), we can ascertain first that the plate circuits of the valves are continuous, and, if the current is normal, we know further is not high. that the resistance in these circuits abnormally Simple testing board for measuring valve anode current under This serves as a check on continuity and also on partial standard conditions.

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www.americanradiohistory.com 696 Wpighoo WorM JUNE ist, 1927.

. The Experimenter's Notebook.-- - used the plate current of the detector valve will rise inasmuch as a small volt drop in the supply lead repre- when a station is tuned in. In general the deflection of sents a large percentage change in the filament voltages. the milliammeter will be less under corresponding con- A milliammeter used in the above manner is also a very ditions as this method of detection is comparatively in- useful check on the continuity of grid circuits. If we efficient, though on the other hand if the high- frequency are measuring the plate current of any one valve and amplifier used in conjunction with it is of really good vary the grid voltage we can see at once if the plate efficiency the change in current will he equally satis- current varies in conformity, or, in other words, if the factory and can he used just as readily for making valve " answers to bias." This is easy to arrange if the observations above described. grid return lead is connected to a separate terminal to which grid bias can be applied, but is, of course, impos- Grid Bias Adjustment. sible when the return is direct to the filament, unless the The last use of a milliammeter, namely, in the plate grid lead is disconnected. The latter course being per- circuit of a lower output valve, is of such importance haps advisable when tracing a difficult fault. The point as to be almost a necessity. Power valves, as is well of these tests which seems to be of outstanding importance known, are specially designed so as to have a large is that they include every possibility of error. We may range of " straight characteristic," and provided the test for continuity of grid and plate circuits in the ordin- voltages on plate and grid do not pass outside the limits ary way and then be misled by a had contact, either where this condition of straightness holds good, the between the valve holder and valve legs, or else within average value of the current passing through the milli- the valve itself. A test carried out as above described ammeter should not change and its pointer should in with a milliammeter tests right up to the valve electrodes. consequence remain steady. If, on Testing for Self -oscillation. the other hand, the limits of " straight characteristic " are exceeded a movement of the pointer will Another useful purpose to which a milliammeter can occur in one direction or the other in conformity with be applied is in checking whether a set is in a state of the signals being received. self -oscillation. When oscillation occurs, it is invariably The first use of the instrument is to get the value of accompanied by a rise or fall in the feed current to one grid bias correct. This can be clone by tuning in a of the valves in the circuit, and this will be indicated by strong station first of all at low volume so that no kick a change in the common feed current. The milliammeter on the milliammeter needle takes place, and then for a test of this kind is best connected so as not to gradually increasing the volume until the needle begins include the heavy current usually passing through the to move. If the movement of the needle under these power output valve. If the set is made to work with conditions is in a downward direction corresponding to the aerial disconnected, so that no signals of appreciable each signal impulse, then the value of grid bias is too magnitude are being picked up, the reading of the milli- low. If on the other hand the needle kicks in an up- ammeter may be noted, first with the set as it stands, and ward direction, the value of bias is excessive. By care- secondly when each of the grid terminals are either ful adjustment and observation the bias can he so set touched with the finger or else connected direct to their that the direction of movement of the needle, when over- appropriate bias points. If there is no change in feed loading just begins, is indeterminate, and this is the current in these conditions the set is not oscillating, but right setting. if a change occurs it certainly is. The tracing of the causes of oscillation in a set is too big a matter to be Locating Source of Distortion. dealt with here, but systematic analysis of the various The grid bias being correctly adjusted the'instrument possibilities with the aid of a milliammeter is the real can be used as a check on overloading and as a means method of attack. for differentiating between distortion which is taking We come now to the uses of a milliammeter in a set place at the transmitting end and that at the receiving which is functioning correctly under actual working con- end. The distorted quality popularly known as ditions, and in this connection there are two most useful " blasting " is quite unmistakable, but it is often a applications, the first being with the instrument in the matter of difficulty to determine whether the transmitter plate circuit of the detector valve, and the second using or receiver is at fault. The milliammeter used as just it in the plate circuit of the power, amplifier. described is a sure guide on this point. In the first case, the current will vary to a greater or A receiver with a milliammeter permanently connected less degree when a strong station is being tuned in. If in the plate circuit of the last valve has an immense the grid condenser and leak method of rectification is advantage, inasmuch as that not only can the question being used the tuning -in or a carrier wave will result in of distortion he checked, but also a watch kept on the a drop in the current which should he quite perceptible in state of the batteries. The course of discharge of the the case of a station of moderate strength, and will thus accumulator will he accompanied by a drop in the plate give an indication of a rough -and -ready character as to current of the valve, and the latter will be a guide as the signal strength of such a station. to the condition of the accumulator. A fall in plate A comparison between a number- of different stations current apart from this regular drop will indicate either (if this is possible according to the position of the re- a fall in H.T. voltage or else a loss of emission in the ceiver) will show whether the set is at fault or whether valve. These points can he separately checked up, hut certain stations are abnormally weak. the use of the instrument lies in the first warning which .1f the " bottom bend " method of detection is being is given that something is wrong.

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JUNE ist, 1927. WAp,8Il@go WOIlcIl s697

A Section Devoted to New Ideas and Practical Devices.

SHORTING -PLUG. trical contact with the case and also at each side of the spacers, the com- An emergency shorting -plug for with one side of the condenser. It mencement of the primary winding certain screw -in resistance holders desired, a plain washer may he as- being w ounrl in the hack-saw slot S. may he made from a burnt -out flash - sembled beneath the soldering tag in The end of the primary winding is lamp bulb by connecting a wire from order to raise it slightly to facilitate terminated at the small round -head the outer threaded casing to the centre soldering.. B. H. N. D. screw shoe n in the top of one of the contact, or by bridging the space be- O O 0 O spacers. C. S. tween them with solder. E. \V. W. H.F. TRANSFORMER 0000 0000 CONSTRUCTION. " ALL -WAVE FOUR " SPACERS. CONDENSER CONNECPIONS. Although the form of construction In the " All -wave Four " receiver a of square In many circuits -the Every- indicated produces coil the ends of the primary and neutralis- section it will he found that, as tar ing windings the transformers are man Four," for instance -it is advis- of able to earth the container of the anchored to screws in the ebonite to the pins of Mansbridge reservoir condensers. A spacers, and connection by of method of doing this whieb is ex- the coil former is made means ceptionally neat and which consider- an additional lead. The following ably simplifies wiring, is shown in the method dispenses with the screws :- diagram. Shall ebonite blocks about kin. The knurled terminal and lower square are cut from a spare spacer. locking nut are unscrewed from one Two saw -cuts are macle at right side of the condenser, and the Bake- angles on one side of each block. with lite insulating washer removed. The 1 hte little blocks are mounted face of the spacers, paint on the top of the -metal case is adhesive on the then scraped away over the area one at each end. The ends of the .E: covered by the Bakelite washer. Thy transformer windings can then be -cuts, soldering tag, or one of larger size. taken through the saw across

Plug -in former for interchangeable H.F. transformers. as actual results are concerned, the efficiency will he but little less than that of cylindrical or hexagonal coils. It will be seen from the diagram that two spacers are cut from ebonite sheet (yin. thickness is suitable) and halved " together in the manner of egg-box partitions. The spacers are Method of terminating primary and Simple method of earthing case of secured to a circular ebonite base with neutralising windings in " All -wave Four " transformers Mansbridge condenser. screws fitting into holes drilled and is then replaced so that it makes con- tapped upwards into the edge of the the windings, and so to the bins on tact with the metal case, and is spacers. the base of the coil former, as shown clamped in position with thè knurled The primary and neutralising wind- in the accompanying sketch. terminal. This provides a good elec- ings are supported on the strips left \V. R. P. A 29

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.. +s.,weti. .WS ,\. . ti ...... Sec- etartes of Local Clubs are invited to send in for publication club news of general interest. All photographs published will be paid for.

Remote Control. two stages of intermediate amplification. Remote control was the topic chosen at FORTHCOMING EVENTS. He explained that only one stage of L.F. an informal meeting of the Musweil Hill was required, owing to the very high and District Radio Society on May 18th, WEDNESDAY, JUNE 1st. amplification obtained in the intermediate Tot te nhnn, Winless Society. .I t 8 p.m. when details of the " Lotus " remote A 10, Bruce Grove. Business Alerting, amplifier. control, which had been sent for the followed by Discussion Evening. The receiver and its frame aerial were society's inspection, were discussed. Mr. THURSDAY, JUNE 2nd. housed in one case and the requisite bat- L. Hirschfeld, B.Sc., gave an interesting Golders Green and Hendon Radio Society. teries and loud- speaker in another. The -:1 t 8 p.,n. At the Club JI,o,,e. li'itli- impromptu talk, in which he described tìeld IVay, 1V.1 V.11. Exhibition of complete outfit was of fairly considerable practically every possible method of .Members' :1 pparat us. weight, and although an ideal set for the using remote control. He dealt with his WEDNESDAY, JUNE 8th. motorist it was certainly not the portable own ingenious system, whereby his mains ii,',li Hill and District Radio Soeiety.- for a country ramble. The construction At 8 p.m. At ToGinaton School, Tethrr- receiver could be switched " off " and down, n.10. Dem un strution and Leetere of the instrument was of an excellent " on " from any room. This was worked SO " Electric .1 c+, m aintors." by Mr. IV. standard throughout. S,a,orrld lot 11,.nsrs. The Hart A cru ma- by a " Weston " relay with a rotating lutor Go., Ltd.). Hon. secretary : Mr. W. R..Collis, 7, ratchet switch and mercury contacts. The Algar Road, Isleworth. device had given excellent service for 0 0 0 0 over a year. audience of the Hounslow Wireless Parti;'nlars of future meetings can be Society on \Tay 17th, demonstrating the H.F. Problems. obtained on application to the hon. Igranic Nentrosonic seven -valve portable Some useful tips were gleaned by the secretary, Mr. Gerald S. Sessions, 20, receiver. The lecturer said that, as its less expert members of the North Middle- Grasmere Road, Muswell Hill, N.10. name suggested, the Nentrosonic was a sex Wireless Club at the last meeting, 0 0 0 0 super -heterodyne receiver in which the when the erection of a new aerial was H.F. stages were neutralised. A stage undertaken, A Portable Super -Het. the work being carried out of ILF. amplification preceded the first under the supervision of Mr. \V. Mr. Alford, of the Tgranic Electric detector, while a separate valve was Gartland. Co., Ltd., lectured before a large used for the oscillator, and there were The club hopes to hold a field day on July 9th. The subject of high -frequency amplification was dealt with in a lecture by Mr. Gartland, who admitted that since a recent debate on the topic he had become converted to the idea that one stage of H.F. amplification plight be distinctly worth while. After relating his disappointing experience in H.F. amplification using the ordinary general -purpose valve, the lecturer opened a discussion on the advantage of the neutrodyne method of securing stability. He concluded with particulars of an efficient short -wave circuit using plug -in coils of a well -known make. In this circuit the aerial was coupled by a single turn, and there was no earth connection. The circuit had proved remarkably efficient in the reception of American signals. Hon. secretary : Mr. H. A. Green, 100, Pellatt Grove, Wood Green, N.22. 0000 Carrying on in Summertime. The summer season will not be an idle one for the Ilford and District Radio Society, which has decided to hold monthly meetings on the following dates : June 23rd, July 21st, August 25th and September 15th. In addition it is expected that the society will hold a FIELD DAY AT MILL HILL. Members of tha Golders Green and (tendon Radio Society photographed with their temporary transmitter at Mill Hill on a recent field day. Sunday, when communication was secured with amateurs in Nottingham, Isle of Hon. secretary : Mr. H. H. Carr, 39, Wight, Scotland, and Ireland. Lynford Gardens, Goodntayes. A 30

www.americanradiohistory.com ....41044.41§1 -TM - . *w9".

Wg7®Il®00 fr-.VE ist, 1927. MAZ 099

A Review of the Latest Products of the Manufacturers. STAPLE H.F. COUPLING UNIT. ary secondary winding. Adjustments H.A.H. JACK. the entire tuning are provided so that the extent of coupling In wiring up the extension points from Uniform stability over at maximum or range of the condenser can be obtained can be regulated either a broadcast receiver to the various rooms The primary winding is of plug in a high -frequency amplifier by care- minimum setting. of a house, the use of some form the neutralising and pri- centre tapped, so that neutralising can be and jack connector is to be preferred to fully arranging usual manner, whilst the mary windings so that the bridge which arranged in the fitting terminals elevated on ebonite. correctly balanced over user can carefully adjust the cam action Messrs. A. H. Hunt, Ltd., H.A.H. is formed remains the required increase have the range of frequencies to which the cir- so as to produce just Works, Tunstall Road, Croydon, secondary coupling as the form of jack tunes. This is accomplished by pro- in primary to recently introduced a useful cuit approaches a maximum to an ebonite viding a tight coupling between the tuning capacity with cover and secured windings, and in combination with the particular mounting plate. The jack is intended for primary and neutralising amplifi- exactly similar and so plac- type of valve adopted for H.F. mounting vertically against the wall, and making them usually ing the turns that both windings are cation. being only about zin. in width can equally influenced by changes in the be secure'd to the beading of woodwork so tuning of the winding forming the grid as to be quite inconspicuous and occupy very little space. circuit. If not balanced self oscillation o o n o usually arises when the tuning condenser is near the zero of its scale, owing FORMO GANG CONDENSER. to the reduction in damping. It is No provision is usually made when desirable, therefore, in an H.F. intervalve linking condensers together on a common transformer to increase the extent of shaft for the purpose of simultaneously coupling between primary and secondary tuning several circuits, such as is required as the capacity of the condenser advances. in a two -stage high -frequency amplifier This requirement is achieved in the new for making small adjustments individually to any one condenser. The Formo Company (Arthur Preen & Co., Ltd.), Crown Works, Crick le wood Lane, London, \ .W.2, v e evolved a u The H A.H. extension jack. ha

The Hammarlund H.F. intervalve The new Formo " gang " transformer, in which the coup- condenser. The centre dial ling between primary and operates all three condensers, secondary windings varies with the capacity of the tuning while individual adjustment is condenser. provided for two of the condensers, so that three tuned stages can ba critically brought into step. Hamntatlund Auto -Couple Coil obtainable of The tuning condenser is beautifully entirely new form of construction for from Rothermel Radio Corporation for 24 Maddox Street, finished and is practically perfect both linking together several condensers Great Britain, Ltd., -26, The main geared Regent Street, London, W.1, by fit- mechanically and electrically. The tuning simultaneous tuning. to he dial drives all three condensers, being ting a cam to the projecting end of the coils, which at first sight appear shaft, which, mov- self supporting and air spaced, are positively locked on to the shaft of the variable condenser subsidiary dials pro- a stop, alters the position of stiffened by attachment to a thin sheet centre condenser, ing against separate adjustment to the other the primary with regard to the station- of celluloid. viding A 31

www.americanradiohistory.com WIlpsIl@oo 700 Waal JUNE 1st, 927. t wo. By this means all three condensers The transformers made by Messrs. are rotated correct insertion of the transformer into on one knob, whilst small Wright & Weaire, Ltd., of 740, High its base. The latter is fitted' with a short differences in the setting of any one con- Road, Tottenham, London, N.17, are in denser brass rod, which, when the pins and can be readily made without dis- every way equal to the originals, and it sockets are registering correctly, engages turbing the settings of the others. It is interesting to note that this firm have is obvious in a hole drilled through a small trian- that even if correctly set in added a non -reversible fitting, in order gular piece one position the of ebonite screwed to the in- three tuning con- to minimise the risk of an accidental side of the tube. densers, unless the plates are shaped to short -circuit of the H.T. battery by in- follow a logarithmic The terminal points on the base are law, cannot for any marked with appropriate lettering which given movement produce a correspond - ing change coincides with that shown in the practical of wavelength in each of the and theoretical circuit diagrams published several tuned circuits. This new Formo condenser with the original descriptive article. makes provision for critically This feature adjusting each will help to simplify the of the condensers, at the wiring of the set. same time bringing all three dials roughly to the required position. The method of transferring the rotation from the centre condenser is ingenious, and makes use of two parallel ebonite bars.

0 0 0 0 INTERCHANGEABLE H.F. COUPLINGS. The H.F. transformers described in connection with the " All -Wave Four " were primarily designed for amateur home construction, and not for commercial production. It is, therefore, all the more gratifying to find that manufacturers are turning their attention to these coils, and, moreover, that they have apparently overcome the difficulties which must be encountered when attempting to produce them on a commercial basis.

' The Wireless World, April Wearite interchangeable transformers for use in the construction of the " All -Wave 27th, 1927. Four " receiver.

Cossor's Radio Mail. For the Radio Dealer. The current issue of Cossor's " Radio Mail " Houghton's " Radio News " for May, contains several topical articles of TRADE NOTES. intended particular interest to the for the radio dealer, is more dealer, and in- than a catalogue cludes a Useful contribution on the sub- of leading lines ; it is ject of resistance amplification. also the little magazine of topical trade Electrical Measuring Instruments. information. Houghton's " Radio News " noon is published by Houghton- Butcher (Great To obtain maximum receiver efficiency A Transatlantic Feat. no Britain), Ltd., 88 -89, High Holborn, amateur can neglect to pay attention to London, W.C.1. The Mullard Co. have received a letter the electrical adjustment of his set. from Mr. O. B. Kellett (G5KL), South- In this connection a booklet entitled 0000 port, giving details of remarkable low "Radio Control," issued by the Electric Soldering power transmissions. During these trans- Weston Electrical Instrument Co., Irons. missions Mr. Kellett used a Mullard Lid. (15, Great Saffron Hill, London, We learn from the Automatic Coil " 0/40 ;' valve as oscillator, and suc- E.C.1), is of special interest. This Winder and Electrical Equipment Co., ceeded in working the Canadian trans- little book includes some admirable Ltd., Winder House, Rochester Row, mitting station NC -1DM, owned by Mr. advice on the intelligent use of volt- London, S.W.1, that they have just been S. H. Appleton, Caledonia Mines, Nova meters, ammeters and galvanometers, be- appointed sole distributing agents for the Scotia, with the exceptionally low input sides illustrating and describing the " Zeva " electric soldering irons and of .925 watt and on a wavelength of 45 various instruments in the " Weston " crucibles. metres. range. Readers who are alive to the im- 0000 0000 portance of this subject would be well advised to obtain All About the " Clarostat." Valve Manufacture Forgotten a copy of " Radio -a Factor. Control " from the above address. " The Gateway to Better Radio " is So much attention is paid to the in- 0000 the title of a booklet describing the ternal construction of a valve that one " Clarostat," a special form of variable is inclined to overlook the care and New Offices. resistance manufactured by General Radio trouble involved in the manufacture of Mr. W. A. Appleton, M.B.E., Instruments, Cambridge, Mass., U.S.A., the glass container. The importance of M.I.R.E., advises us that he has resigned and obtainable in Great Britain solely glass as a valve constituent is the in- his directorship in Messrs. Radio Instru- from Messrs. Claude Lyons, 76, Old Hall teresting subject of an article in the ments., Ltd., and is not associated with Street, Liverpool. Besides containing current number of the " Osram " G.E.C. the present amalgamation between that useful information on securing the best Bulletin. The writer describes the pro- company and the Varley Magnet Co. He results from the " Clarostat " in the cesses under which " Osram " valve glass is now conducting business in his own elimination of distortion, regulation cif is obtained from the raw material com- name at Gloucester House, 19, Charing the plate voltage, etc., etc., the book in- prising sand, red lead, alkali and sundry Cross Road, W.C.2, where laboratories cludes some general advice on how to other ingredients. The Bulletin also and offices are equipped for the design obtain maximum receiver efficiency. The contains a contribution on the " Geco- and manufacture of radio and other book is obtainable from Messrs. Claude phone " H.T. battery eliminator. apparatus. Lyons at the price of ls. 6d. post free. A 32

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t. t 1 I , I .. 6cft <, a s o revittie, a .' , I , 1 NEWS FROM ALL QUARTERS. - 1 AUN, Ey Our Special Correspondent. To -day's Derby Broadcast. -Is " Daventry Junior " Delicate ?- Empire Broadcasting Queries.- Those Nightingales. -PCJJ's Schedule. -The Dying Oscillator. To -day's Running Commentary. A Point of View. The running commentary on the Derby FUTURE FEATURES. The B.B.C. announces that since the will be carried out this afternoon by Mr. London. end of 1925 it has indicated its desire Geoffrey Gilbey, while " local colour " will JUNE 5TH.- British Legion Service to co- operate effectively in any practicable be supplied in the form of a description from the Cenotaph. Chamber enterprise designed to interchange pro- by Mr. George F. Allison, who is already Music. grammes between various parts of the well -known as a broadcast commentator on JUNE 6TH.- -Thé Dansant and Empire or simply to make the B.B.C. pro- football. Clarkson Rose's Concert Party grammes available in other parts of the o 0 0 o from Westcliff. Popular Con- Empire. But it points out that senti- cert. mental considerations should not outstrip Special Microphones. JUNE 7TH. - " The Wandering practical considerations, and draws atten- Desensitised microphones fitted to Jew," a play by E. Temple tion to a paucity of funds and uncer- special headgear will be used, thus en- Thurston. tainties regarding technical efficiency. abling the commentator to keep the micro- JUNE 9Tx. -Light Symphony Con- 0000 phone at a uniform distance from his cert. Another Daventry? mouth while having his hands free to JUNE 10TH. -The Sea Symphony wield his field glasses. (Vaughan - Williams) relayed However, in the face of PCJJ's 0000 troni Cambridge. triumph and the undoubted fact that -wave the Dominions Signals from 5GB. Birmingham. short broadcasting to Weak is not an impossibility, the B.B.C. pro- A number of listeners report reception JUNE 8TH. -Liza Lehmann Pro- gramme. Promenade Concert. poses to erect a short -wave experimental of signals from " Daventry Junior." station at Daventry, though whether the The general impression is that these JUNE 10TH. - The " Tweenies " Concert Party. Light Operatic project will materialise very quickly is signals are too weak. a matter for doubt. " Daventry Junior " is to succeed Music. If 0 O O O it must have a reasonable power, and the Bournemouth. report -which reaches me from a reliable JUNE 7TH. -Speeches on the occa- Marking Time. source -that only 10 kilowatts is being sion of the visit of the Prince The impression I gained at Savoy Hill used is scarcely reassuring. of Wales to the University is that nothing fresh will be attempted 0000 College of the South West of England, Exeter. at Daventry until the new regional Flowers, by Request. station begins regular transmissions. No JUNE 10TH. -Comic Opera and Officially, time schedule of experi- this will not occur for three or No definite Bohemian Music. four months, but there are reasons for mental transmissions from 5GB has been Cardiff. the engineers being apparently supposing that the service will be opened issued, JUNE 7TH. -" La Serva Padrona," much sooner. content to rely on reception reports comic opera by Pergolesi. who have o000 from a few picked listeners Manchester. been provided with a secret time -table. Hopes and Fears. are engineers at JUNE 10TH. -An Evening at Black- Most of these listeners pool. The B.B.C. betrays extreme diffidence the different provincial stations. Newcastle. in pushing forward an Empire short- it seems that if you send in your So JUNE 9TH. -Neapolitan Programme. wave station, owing to the fear that it of 5GB's transmission to Savoy report JUNE 10TH.- Concert Performance might be impossible to realise a regular not be overwhelmed with Hill ynu will of " The Grand Duchess " and dependable service which would give bouquets and thanks. (Offenbach). satisfaction after the novelty had worn 0000 Glasgow. off. Well, the only way to combat these B.B.C. and PCJJ. JUNE 8TH. -" Once Upon a Time " fears is to experiment. The delicious enterprise -one might -a vocal and instrumental pro- 0000 the gramme. almost say the delicious audacity -of A 24 -Hour Service ? Dutch valve firm in rebroadcasting a 2LO JUNE 11TH. -The " Concord Fol- programme to the uttermost parts of the lies " Concert Party. The time problem is more formidable. British Empire throws a scorching spot- Aberdeen. There are gentlemen in the Himalayas light on the shortcomings of our own JUNE 10TH.- Scottish Programme. who might rise from their beds at any broadcast resources. Nevertheless, the Belfast. hour of the night to hear a speech by the King or the Prime Minister, but such B.B.C'., which has probably been just as JUNE 9TH. -" Clearly and Con- dazzled by the performance as everybody cisely " -a farce by Robert important items would be rare. else, has recovered itself sufficiently to Higginbotham. During the ordinary programme time in is in issue a dignified statement. this country half the Empire bed,

A 33

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702 Wilp4mo WoA(l JUNE 1.51, 1927. while a considerable portion is too busy to listen -in. which goes to show that an Empire -wide broadcasting service would have to last pretty nearly twenty -hour hours per diem. 0000 Finance. Then, too, the Aberdeen point of view must be considered. Would the money for an Empire service be derived from licence receipts? The Colonial Conference now sitting in London has been asked to consider the question of Empire broadcasting, and on the financial side I understand that two suggestions have been made. First, it is suggested that the Dominions should contribute towards the scheme, and alternatively that a regular interchange of programmes between England and the Dominions could be arranged so that the indebtedness would be mutual. 0000

What Not to Do . . . When the announcer intimates that the voice of the nightingale will be broadcast. from Oxted in an hour's time. Get out the car and rush off to Oxted. 0000 OPEN -AIR NEWS BULLETIN. An everyday scene In Soviet Russia, where the various Nightingales and Motor Cars. towns and villages are equipped with receivers and loud- speakers. Last week's nightingale broadcast would have been a greater success, Capt. where as many as twenty different bird Prince of Wales this Evening. West tells me. if the army of motorists songs might be picked up. Given a H.R.H. the Prince of Wales would has con- who invaded the district had been good naturalist as compère, the item sented to broadcast to all stations from make an Hour " enough to keep away. Apart from the excellent " Children's London (2L0) at 7 o'clock and would this evening fact that the birds are easily scared by give our hard -worked friends (Wednesday), speaking on the urgent need even the most magnificent motor cars, it at Savoy Hill a well- earned rest. for more public playing fields. is as well to note that an exceptionally 0000 His address will be in support of the sensitive microphone is employed -a spe- Dublin's Coup. £1,000,000 appeal of the National Play- cially designed magnetophone -which will It is interesting to learn that the ing Fields Association, which is to be pick up sound almost beyond earshot. Dublin Broadcasting Station first an- launched as from this morning. The Who Prince thirsts to hear a ticking motor ? As nounced the safe arrival of Capt. Lind- will be acting on behalf of his Capt. Eckersley brother, remarked : " The goods bergh over Ireland at 5.30 p.m. on Satur- the Duke of York, who is train liad President to pass, but . . . day, May 21st. A message to this effect of the Association, but who 0000 was broadcast from 2RN at 9.40 p.m. is not yet back from Australia to broadcast The Sensitive " Mike." This was the first definite message to be the appeal himself. .As demonstrating how sensitive the received by the public as to the airman's 0000 magnetophone whereabouts. was last week, it is inter- Some Hopes ! esting to learn 0000 that Capt. West and other Can it really be that the engineers at Oxted failed oscillator is to hear a Short Waves from Holland. flying out ? second nightingale Shall we yet hear, with a in the far distance, gulp in the tin-oat, " The although many listeners heard PCJJ, the Philips station at Eind- Last of the the lonely Howlers " ? songster quite clearly. hoven, Holland, will be transmitting to- 0000 morrow evening (Thursday) from 7 to Savoy Hill keeps a record of the 11 p.m. (G.M.T.) with a wavelength of number of oscillation complaints received Why Oxted P 30.2 metres. each week, and the following is an inter- If motorists are becoming so trouble- On Tuesday and Thursday of next week esting extract. some, why not shift the venue? Is Oxted the station will transmit from 6 to 10 p.m. Week Beginning the only place in this England of ours (G.M.T.). No. of Complaints where the nightingale can be cajoled into 0000 April 17th ...... 200 song? And is Miss Beatrice Harrison's ., 24th ...... 251 'cello such a very necessary stimulant Voices of the Past. 30th...... 187 after all? I have an idea that the poet Gramophone records of late music -hall May 6th ...... 145 Keats, when he listened to the nightin- stars are a feature of the programme en- gale, had neither 'cello nor saxophone, titled " Voices from the Past " to be M -yes, it looks pretty on paper ; but but only paper and pencil. broadcast from 2L0 on June 18th. a physician will be ready to admit that 0000 0000 fewer people suffer front indigestion through eating roast chestnuts in summer- An Idea. Another Debate. time because fewer roast chestnuts are Another attempt to broadcast the night- Major John Hay Beith (Ian Hay) and eaten. ingale will be made, I understand, within Mr. Douglas Woodroff (late President of 0000 the next few days. I think the B.B.C. the Oxford Union Society) will take part might do worse than transmit the notes in a broadcast debate on Friday next, June Perhaps . . . of other wild birds ; the microphone could 3rd, the motion being " That Sport is a Perhaps if detected offenders had their be taken to some secluded woodland - Menace." Lord Thomson will be in the licences endorsed in the Same manner as `here ire still some in this country- chair. the reckless motorists ... ? A 34

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The Editor does not hold himself responsible for the opinions of his correspondents. and address. Correspondence should be addressed to the Editor, "The Wireless World," Dorset Huse, Tudor Street, E.C.4, and must be accompanied by the writer's name

and grid leaks, to get most weird results from a resistance - BROADCASTING AND THE PATENT POSITION. capacity unit ; just as it is possible to get weird results from a Sir,---Our attention has been called to the Editorial entitled modern car by juggling with the carburetter. in " Broadcasting and the Patent Position," which appeared It is only fair to state that a properly designed resistance - The ll-ireless World for May 18th, in connection with which capacity unit can be made to give even amplification from 50 we should like to make the following remarks. to nearly 8,000 cycles per second. As regards the overall ampli- In the first place, we desire to point out that, although we fication it is recognised that for good results this cannot be as defined the valve holder (used as a basis of royalty) referred high as with a transformer. to in our broadcast licence as applicable only to a valve con- But after all valves are cheap, and it is doubtful whether taining the usual three elements, it is not our intention to a 2 -valve resistance amplifier would come to much more than a interpret this in a strictly literal sense. For example, we should transformer unit. E. A. ANSON. agree to count as single valve holders supports for certain London, S.W.5, May 18th, 1927. multiple grid or independently heated cathode valves, in view fact that the number of high -frequency or low- frequency of the of the we are able to reply to circuits and the extent to which they are employed remain in Sir, -By the courtesy Editor these cases the same as with the ordinary three -electrode valves. Mr. Anson's letter of May 18th. legal definition, however, we had to In our opinion, the unfairness commences in the vigorous For the purposes of which has been made adopt the wording as set out in our circular, but where the attack upon the transformer method above holds good we shall always be pleased by makers of resistance -capacity units and valve manufacturers. principle explained reasonable to state our favourably applications from holders of our amended We consider it to be quite fair and to consider we attacked. licence. case in advertisements when are to make is in connection with the Hollinwood, May 20th, 1927. FERRANTI LIMITED. The second point we wish General Sales Manager. concluding remarks of your article, from which it would seem R. H. Schofield, we are aiming at creating a mono- that it is apprehended that .a poly for this company. This is not the case. R.B.C. TRANSMISSION OF PIANOFORTE MUSIC. company as It is intended that the future policy of this Mr. has remain the same as in the past, that is, Sir, -I think your correspondent, Frank Smyth, hit regards licensing' shall head in his letter of May 9th, when he of licences to all bona fide and responsible British the right nail on the the granting poor quality reception of music is often due to manufacturers of broadcast receivers. suggests that I. SHOENBERG, slight heterodyning or local oscillation. I frequently get very Joint General Manager, poor quality of music and at the same time increased loudness Marconi's Wireless Telegraph Co., Ltd. on my crystal set and also on my 2 -valve set. (N.B. -The no for reaction and does not oscillate.) The London, W'.C.2, May 19th, 1927. latter has provision trouble is apparently due to a valve set with an aerial parallel to and about 20ft away from mine. CERTIFICATES OF MERIT. As in inane cases the owner does not realise that his set is Sir, -I have read Mr. Lyons' letter in the May 4th issue with just oscillating, this trouble is rather difficult to deal with. very great interest. Teddington, May 23rd, 1927. A. K. TAYLOR. I have no particular comments to offer, but am writing to say that such a scheme would receive our support, as we con- your control, it would do much to Sir, -I have been extremely interested in the correspondence sider that, carried out under of piano music from poor old 2I.O. give confidence to the public and stabilise the trade. about the transmission not a " highly technical gentleman," but I would add London, E.C.4, May, 1927. G. D. OZ AN N E. I am Wingrove and Rogers, Ltd. my voice to those who say " look to your set." In my opinion the key to the whole trouble is reaction ; not intentional reaction -that will spoil any music -but the very RESISTANCE OR TRANSFORMER COUPLING? slight degree of accidental reaction which is present in all but Sir, - --I rather take exception to the Ferranti advertisement in the most carefully constructed sets. The Wireless World for May 18th, 1927. I do not wish to offend your correspondents who have writ- Surely the makers of this transformer must themselves admit ten you on this subject; I do not doubt that their sets are that it is just a little bit unfair to compare a really high -class most carefully constructed ; hut if they will take the trouble transformer with a resistance -capacity unit that is obviously to go over them and eliminate absolutely all possibility of re- far from perfect. action in any shape or form -if necessary introduce a slight Just because a certain designer of a resistance -capacity unit amount of reverse reaction -and use a good diaphragm speaker is quite content to cut off at a frequency of about 1,000 it is with plenty of power, a super -power valve ill the last stage unjustifiable, in my opinion, to leave the impression that all and a choke filler, they will find that the engineers of 2L0 rre amplifiers of this type suffer from this complaint. not the sinners they are supposed to be. It is, of course, possible, by juggling with coupling condensers Croydon, May 18th, 1927. E. G. K EN N ARD. A 35

-', ,t'., www.americanradiohistory.com 704 Mmasoo JUNE ist, 102 7. GYIole Rcl LITZENDRAHT, The chief source of the trouble which some users experience Sir, -The writer has been interested in reading the question lies in the employment of excessivly small sacs ; obviously, and answer under the heading " Litz or Litzendraht," page 542 since wet and dry cells are the same thing in a slightly of the April 27th issue of The Tireless World, and in support different form, it is unreasonable to expect the wet cells to of reputable manufacturers who are out to supply the trade and give a very much greater output than the correspondingly small the public with reliable and proper material I shall be glad if dry cell. But large -size wet celle are comparatively cheap, and you can find space to publish this letter. it is here that the advantage of the fluid battery is found. For some time past it has been very evident to us that material In order to obtain good results it is, of course, essential to is being marketed by unscrupulous dealers under the name of use only best quality materials. The sac must be well tied, Litz or Litzendraht wire, the construction of which is as far and should contain no impurities. It is essential that the zinc removed from the proper construction as chalk is from cheese; be of first -class quality and, if possible, be amalgamated. consequently, it is not to be wondered at that people buying this Chemically pure zinc cannot be used on account of its very material are unable to obtain the results which are intended from high cost, but the best obtainable commercial material is satis Litz wire. factory. Care should be taken in purchasing, as the stuff sold It is obvious that the reason substitutes are marketed for by the ironmonger is often very impure. Litz wire is to swell the profits of unscrupulous dealers. When The strength of solution required varies between 2 oz. and quoting for what is known as genuine Litz wire, we have been 4 oz. to the pint of water, according to the composition of the told we are much too dear, and this, in cases where we have sac. The water should be distilled, or, at least, boiled. quoted only a very small margin over and above material and A little thin oil is preferable to paraffin for preventing labour costs, which is self -explanatory. evaporation, while a cork or other cover is desirable. Further, fo your explanation as to the origin and derivation The advantage of the wet cell lies in its lower internal resistance, which allows of a of Litz or Litzendraht wire : The word Litzendraht was the greater output, and in the fact name originally given to high - frequency cables some years that the solution can be kept at a constant strength, while the ago sac and by a German firm, and it has since become a generic term for zinc can be renewed as required. high- frequency cables in conjunction with wireless throughout London, S.W.11 R. S. SMETZER. April 27th, 1927. Europe and America, but, of course, high -frequency cable still remains the correct designation. W. W. NORRIS, London, W.1, The Standard Insulator Co., Ltd. LOGARITHMIC CONDENSERS. May 9th, 1927. Sir, -With reference to your article on logarithmic condenser design, we regret to find SMALL LECLANCHE that you have mentioned three firms CELLS. only as supplying this particular type of condenser, whereas Sir, -As there is a large number of pecple using wet or we have Leclanché been making an instrument of this type, conforming cells for H.T. supply, possibly a few hints may with your particulars, since 1924. prove of interest. Cambridge, May 18th, 1927. W. G. PYE & CO. WE often receive criticisms that Germany : -EK 4ABK. the extracts published from 4ABR, 4JL, 4i? AH. Holland : Readers' Logs are composed -EN OGA, OJB, OLY, : mainly of European CaIlIla ON \I, 2PZ. Italy -EI IDA, stations and the 1st, Neal./ 1DR, 1FC, 1\I A, 2nd and 8th districts of U.S.A. -in short, 1NO. 1PL, IUB, 1UU, 1WW. Jamaica : -NJ 2PZ. Japan the stations which any listener can receive. Extracts :- from Readers' JES. Mexico : 1J. Morocco Time does not permit of holding an -NM :- FM OCRB. New Zealand : 2BX. inquest on every list received and con- -OZ Logs. Norway : --EL LA1, sidering each individual " Call Heard " LA1A, LAIE, LA1X. Poland : on its merits; we would, therefore, ask -ET TPAI, 'TAR. Portugal and Madeira : 1AE, 3FZ, those who so kindly send us extracts -EP 3GB. Rumania : 5AA. Spain from their logs to keep their lists as short ßQ6, CB8, DB2, DE3, DR4, DT9, FC6, -ER :- EE EAR 6, 30, 48. Sweden : -EM as possible and to observe HG1, KA7, HD4. Uruguay : lAM, the following -SU SMUF, SMUK, SMUV, SMWR, rules : -(1) Write (or preferably type) on 1C'D. 1C'G, 1BU, 10A, 2AK. U.S.A.: - S \IWQ. Switzerland : 90C. Uru- one side of the page only; (2) start with NU 1ALR, lAKM. 111F, 1MV, 1AAO, -EH guay : -SU 1CD, 1CX, IOA, 2AK. the town in which your station is situate lABG, lADS, H R, 1ALA. 1BHM, and the dates between 1ABA, 1AXA, 1AOT, 1bIV, U.S.A.: -IAJF, 1AUR, lASA, 1\IDB, which the calls lASl. 1.YIV, lACI, 1BUX, IDEE, were heard; (3) only 1WBJ, 1DX. 1KKK, 2UKM, ZAGS, 1BHM, record foreign or 1CJC, 1N W,- distant stations sinless 2AVW, 2AMF, 2ASE, 2ASM, 2BUY, III, 1BFX, 1CNZ, 2AWX, there is any special 2CUQ, 2A Mil. 2AWQ, 2ATX, reason for including one 2AMJ, 2UW, 3GP, 3QW, 3CCU, 8BKM, 2APD, or two at short 2IHM. 2BUY", 2BUR, 2CX, range; (4) give the international 8AVD, 8ADG, 9ARA, KDO. Chile 3CPN, 3GP, indicat- :- 4JM, 4DIJ, 50A, 6BAV, SSG, 8XE. ing prefix once only, after the name of SC. 2AH, 2AS, 2BL. Morocco :- Austria : -EA PY, GP, MM, WY, MP. each country; arrange each group of calls FM 8VX, OCRB. Miscellaneous :- Miscellaneous : in alphabetical FO A9A, OH 3KK, SE B4, NC lAD, -WH4, SQAZ, ANC, order and in capital PCJJ ('phone), OCDJ, AGB, GBH, letters; (5) for the sake of FC F2, NJ 2PZ, FI 1CW, AS 11RA, WIK, uniformity we E'l' 2XA, EASL, 2XT (15 metres). prefer each group to be prefaced NR CTO. A. H. Broomfield. SUC, by the Vr IZ. A. F. Elton -Bott. name of the country and not the On 30 to 40 metres (0 -v -1 Reinartz). nationality On 15 to 50 metres (0 -v -1 Mod.. (e.g., " Holland " and not Hampton, Middlesex. Reinartz). " Dutch ") ; (6) end with nature of re- April, 1927. ceiver (e.g., 0 -v -2), waveband on which Argentine : -SA DB2, DE3, HB1, Pirbright, Surrey. the calls were heard, name, and (if a HD4. Australia : 2AY. transmitter) your own call -sign. -OA Belgium :- April 19th to May ist. EB 4AR,, 4AU, 4FT, 4DD, 4RK, 4WW, Great Britain : -G 5BY, 5 HS. Bel - London, S.W.11. 4XS, 4XX, K6, V9. Brazil: -SB 1AJ, gium : -B 4AU. Sweden : -SMUK. April ist to April 30th, 1927. 1AK, lAR, lAW, 1AT, 1130, 1BR, 1BU, France : -F 8110, 8CT. U.S.A.: - Australia : -OA 2TM, 2YJ, 5ES, 51-1G, 1BW, lIC, IID, 2AB, 2AD, 2AJ, 2AP, NU LAIR, 1CAW, 1CRA, 1RY, 1VK, 5LF, 5SM, 2S11. New Zealand : -OZ 2AR, 2AU, 2AV, 2ID, 2IG, SNI. 1ZD, 2ARM, 2BSL, 2CST, 6CC, 7AHC, 2BG, 2BX, 3AE, : 4AE. Brazil: - Cameroun -FQ PM. Canada : -NC 8BGX, 8BAU, 8CAN, 8CSR, 9CN. SB 1AJ, 1AK, JAL, lAR, lAW, : lIB, lAD. Czecho- Slovakia - EC 2YD. Brazil: -SB 1AK. Saigon : -AF 1B. lAX, 180, 1BU, 1BR, 1BK, 1BW, 1CK, Denmark : -ED 7ZG. Finland : ES Various : -ANF, AGC, GB \I, OXZZ, 1GW, 2AA, - lIe, 1I0, 2AB, 2AD, 2AG, 2C'O, 2N;1í, 7NB. France : -EF 8KX, PCRR, RKV, SS7, WIK. 2AM, 2AR, 2AU, 2AV, 2AX, 2ID, 2EG, 8ZB, 8WEL, 8MSM, 8XAM, 8TIS, On 20 -metre hand (0 -v -1). 2IG, 2IN, 5AA. Argentine : -SA AD5, 8SSW, 8ARO, 8AKL, 8BRN, SBMY. E. H. Robinson (G 51-M). A 36

www.americanradiohistory.com A

WflircpIl oo /UNL. ist, 1927. orIl 705

" The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed " Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply. in position. There is, how- The B.B.C. " Quality Four." the grid condenser of the valve as shown suitable this "Quality in the diagram, the earth and L.T. plus ever, not the slightest need to go to the I unn desirous of building the expense of purchasing a choke if you receiver described in connections being joined at the 50th turn Pour" B.B.C. be connected to the desire to experiment with one, since full your May 4th issue, since good and the aerial should I 75th turn; the other end of the coil go- constructional details of an excellent quality is my main consideration. on page 60 of our s'n'itch to ing to the reaction condenser. Using H.F. choke were given wish, hosierer, to add a be issue of 12th, 1927. It should and also this circuit reaction control will January rout out one H.1'. stage greatly be pointed out that this set is very to enable me to change found exceedingly smooth, thus another switch of distant economical to run, a 2 -volt accumulator crystal recfificatian if neres- facilitating the reception over to whilst the selectivity obtain- and an ordinary 30 -volt H.T. battery of sar71. Could you give me the neces- stations, able is equal to that of any other single the small cell type being all that is sary circuit diagram ? B. T. R. valve set, with the exception, of course, needed in the matter of fuel. so to It would be undoubtedly possible of single valve frame aerial receivers. 0000 recommended by the alter the circuit Owing to the fact that the single coil Eliminator Hum. B.B.C. that your proposed modifications required is quite easily made up at home, could be carried out, but we would point at 1 hare heard it stated that if a battery the instrument ;can be constructed is used on any given set out to You that the set would no longer to be eliminator quite small cost and is specially and hum and noises are experienced be in the sense of the word the B.B.C. recommended to those who wish for dis- even if you that it is often possible, after all " Quality Four." However. tant headphone reception at a minimum were intent on carrying out these modi- other attempts to cure it have failed, of expense and trouble. The H.F. choke to eradicate the trouble by running fications, after full realisation that the shown in dotted lines in the diagram is receiver would no longer be in accordance the detector calve from a separate entirely optional. It can be omitted if source of 11.7'. H. D. with B.B.C. specification, we should be desired, but if it is omitted then the con- doing you a disservice by providing you Your information is quite correct, and with such a circuit, since it would most it is often possible to remove apparently certainly not be one that we could recom- incurable troubles of this nature by run- mend. Briefy, if, as you say, quality is ning the detector valve from a separate your main consideration, we advise you source of H.T.. such as an ordinary small to give up complicated juggling with cell dry battery. The popular leaky grid switches in resistance- coupled ampli- rectifier does not usually require more fiers, and to confine yourself to a than 40 volts II.T., and since its current straightforward receiver specially de- consumption is not high, as in the ,case signed for quality, such as the one we of power valves, it is really quite a good have been discussing, or any of the plan to use a 40 -volt H.T. battery of special high- quality receivers described normal size for this valve. using the in this journal from time to time. mains for all other valves. The detector 0000 valve is an old offender in the matter of from Single Valve Circuit. preventing a battery eliminator having a really silent background. Some time ago I built up the single -coil 0 0 0 0 single -valve receiver whirl, was described in your columns and obtained Long Waves. great .success with, it. I have mislaid l' have commenced to ?nuke the "All - the issue in which this set was de- II"are Four " and should like to wind scribe:l, however, and should be glad an II.F'. transformer suitable for tun- if you would repeat the necessary ing to the Eiffel Turner aai.elength of circuit diagram together with details 2,600 metres:. I partiedurly desire to of the number of turns. S K. - receive this statosi, and rrad(l be Fig. 1.- gingle -valve long -distance receiver This receiver was first described on for headphone reception. trilling to sacrifice efficiency on the page 509 of our issue dated March 31st, 900- 1,400 -metre waveband. proved very popular. We re- denser shunting the telephones must also P. M. C. 1926, and the peat the circuit diagram in Fig. 1 here- he omitted. It should be pointed out As you presumably wish to use in the single tuning coil should C1)11- that the H.F. choke adds nothing to the commercial coil -formers adopted with. 'l'he suggest that slat of a total of 100 turns of No. 22 distance -getting properties of the circuit. original receiver, we would 320 turns of D.C.C. wire wound on a former of 3in. and is intended for the sole purpose of you wind the secondary with diameter, tappings being taken at the reducing capacity effects to a minimum. you 38 D.S.C. wire. There should be 50 60th and 75th turns. The commencement Needless to say, any of the commercial turns of No. 40 D.S.C. in the primary of the winding should be connected to H.F. chokes Upon the market will be and neutralising sections. A 37

www.americanradiohistory.com WApdsoo 706 Wadd JUNE 1s1, 1927. Reaction Condensers. eluded in the circuit, then the volts will be that magnetic saturation will set I am building a Hartley receiver to work dropped across R, will be less than for- in and cause distortion. from a centre- tapped frame aerial. merly. This will be seen from the follow- The modern power valve passes a fairly This will be followed by two trans- ing :- heavy plate current and supposing we wind a 20 henry choke which former- coupled L.F. stages. Can Volts across R,- of the supply will com- you tell me the correct value of the R +R,1+R, fortably accommodate the plate current reaction condenser? voltage of such a valve without getting magneti- T. R. B. 5,000 200 cally saturated, we shall find that if, for 91 volts. 10,000+500 any reason, we increase the number of The value of the reaction condenser +500 x 1 turns in order need not exceed It, will be seen from the above that if to raise the inductance 0.00005 mfd., and indeed value, we shall eventually usually an ordinary neutralising type the chokes A and B have a relative high come to a point of where the iron core becomes magnetically condenser is sufficient for the purpose. resistance, the omission of one will saturated. Doubtless you have noticed matc_ially affect the output voltage from If, however, we redesign our that in Hart- choke with a larger core suitable ley receivers described by us this type of fixed tappings on the potential divider for accommodating the plate current of the condenser has been used for reaction pur- R. power valve, poses in The then all will be well even conjunction with the usual above figures refer to the theoreti- though the inductance centre -tapped frame aerial. cal voltage developed across any be higher. Many This must portion of the 100 -henry chokes not be confused with the value of re- of the potential divider when no load is on the market designed for use after a action condenser usually advised in the taken from the eliminator. When the high impedance detector valve have quite a small core Reinartz type of circuit where the value device is used to supply H.T. to a re- because the plate current of the detector is much higher, being usually 0.0003 valve mfd. is small and they amply accom- 0000 modate it. They would be useless, however, in the plate circuit of a power Volume Control. valve. It would be quite possible to make I have installed loud -speakers in three a 100 -henry choke which would be capa- different rooms in my house and wish ble of being put in the plate circuit of a to fit some simple form of volume con- power valve. but the whole point is that trol so that each instrument may be such inductance is unnecessarily large, adjusted separately without interfer- 20 henries being quite sufficient, and, ing with any of the others, and moreover, it would lie cumbersome and should be grateful for any advice on expensive. On the contrary. a 20 -henry the subject. N. C. R. hoke capable of being put in the plate circuit of the power valve would be Provided that your loud- speakers are reasonably connected in series it will be a fairly small and inexpensive. It should not be assumed, however, that simple matter to obtain the desired con- every trol of signal strength without appreci- 20 -henry choke on the market is capable carrying ably altering the volume of the other of the plate current of a power valve because.there are many instruments. You should connect across cheap instruments each of them a variable non -inductive re- of foreign manufacture which will not do so. On the other hand, sistor having a maximum' resistance of it should about 100,000 ohms or even not be assumed that any choke more. exceeding 20 If they are not series -connected we re- henries inductance is incapable of being used after a power commend you to make the necessary valve; indeed, alteration, and would advise the inclusion at least one manufacturer has on the market a 32 -henry choke of a choke -condenser output filter in the Fig. 2. -D.C. battery eliminator circuit which, apart anode circuit of the last valve. showing resistances affecting final out- from being compact and put voltage. reasonably priced, will deal adequately 0000 with a plate current of 80 millamperes. ceiving set, An Eliminator Problem. current will be taken from it 0000 and the voltage will drop below the I have constructed o battery elimina- theoretical value. The actual voltage Overloaded. tor delivering output voltages of 60, will be governed by the current taken, I find that when my receiver, the circuit 120 and 200, and on adding an extra and for this reason it is difficult to deter- of which is shown on the attached choke in the positive supply lead mine its value by calculation. diagram, is accurately tuned to the find that the output voltages are now 0000 local station, signals are distorted and lancer than formerly. Can you please broken and the only -way to obtain explain the reason for this reduction? A Question of Henries. good reproduction is to more the con- R.. E. M. I ani building a receiver in which I shall denser dial several degrees away The voltage obtainable from any tap- incorporate the choke -filter method of from the point giving loudest results. feeding the loud be ping on the potentiometer in a battery -speaker. Can you I should glad if you could suggest tell vie the correct any possible cause eliminator as shown in Fig. 2 is inductance of the for the trouble. depen- choke? dent upon the ratio of the resistance R, P. R. A. G. W. C. to the total resistance across the supply It can he taken as a good rule that an Your circuit is a simple and conven- leads. For example, if the resistance R inductance value of 20 henries is sufficient tional one, and, although we note that is 10,000 ohms, and choke A has a resist- for all types of power valve, and a " super power " valve is used in the ance R, of 500 ohms, then the voltage naturally you will use a power valve of output position, it should be stated em- dropped across half the resistance R, some sort in your output stage. Not the phatically that at your very short distance which we will call R will be propor- slightest harm will be done by a higher from the local station it is very easy to inductance per se, but the point is that overload one of these valves, and we are tional to : of the supply volt - increase of inductance indicates an in- quite confident that this is the cause of R +R, crease of ampere -turns, or in other words your trouble. Unless you are willing nuze. We will assume in this case to that we may say that increase in the number go to the expense of using a valve with 200 volts are available across so a XY, that of turns on the coil to get higher in- still larger power -handling capacity you the volts dropped across R, will be :- ductance means that the magnetising must satisfy yourself with 5,000 200 weaker signals, x =95 volts. force exerted by a given current passing and it would, perhaps, be as well to fit 10,000 +500 1 through the choke windings will be in- one of the many forms of volume control If, now, another choke B having a _ creased, and if we do not increase also which have been discussed in recent D.C. resistance R, of 500 ohms be in- the dimensions of the iron core, the effect issues of this journal. A 38

www.americanradiohistory.com ,Th e AND r RADIO REVIEW (15Ih Year of Publication)

No. 406. WEDNESDAY, JUNE 8TH, 1927. VOL. XX. No. 23.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

Editorial Offices : 139 -4o, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone : City 4011 (3 lines). Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. Telephone : City 2847 (13 lines). Telegrams : " Ethaworld, Fleet, London."

COVENTRY : Hertford Street. BIRMINGHAM : Guildhall Buildings, Navigation Street. MANCHESTER : 199, Deansgate. Telegrams: "Cyclist Coventry." 7'4, grams Autopress, Birmingham." TrI Telephone: 5210 Coventry. g,ama: "liMe, Manchester." Telephone: 2970 and 2971 Midland. Telephone: 6970 and ö9î! City. Subscription Rates: Home, 17s. 4d.; Canada, 17s. 4d.; other countries abroad, sçs. 6d. per annum. As many 0/ tie circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy themselves that they would not be infringing patents.

VALVE PRICES. THE MARCONI LICENCE AGREEMENT. O doubt our readers will have noticed that N our issue of May 18th we commented editorially on the question of valve prices is being taken the modification which the Marconi Company seeks up by the daily Press following on the to make in its general licence agreement with manu- campaign conducted by The Wireless facturers of broadcast receivers, and in our issue of TVorld for a re- last week we published a letter duction in price. of reply from the Marconi Com- Our readers will CON TEN TS. pany. remember that in our editorial re- PAGE f In our opinion, that letter still ference to the subject in our issue EDITORIAL VIEWS ... 707 left certain points not clearly ex- of May r Nth we closed our cam- WIRELESS AND THE ECLIPSE ... 709 plained, and we therefore sought paign for the time being because By E. V. Appleton. i an interview with an official of the we were satisfied that a price re- REGIZAR TRANSMISSIONS 712 company. In conversation with us duction within a reasonable time SECRET RADIOTELEPIIONY SYSTEMS 713e the position was explained in more could be confidently anticipated. By O. F. Brown. detail. We were assured that the The daily Press is now going TWO -RANGE ALL STATION RECEïVER 717 Y modification in the agreement does over again the ground already By A. J. Bull. not indicate any change of policy covered in The T'Virejess- TT'orld, 4 on the part of the Marconi Corn. but apparently without having CURRENT TOPICS ... 723 the pany, but that its aim is merely to advantage which we have had of PRACTICAL HINTS AND TIPS ... I avoid misunderstanding and litiga- being closely in touch with the NEW APPARATUS .. ... 728 tion where, under a somewhat Valve Association and individual TItE EXPERIMENTER'S NOTE -BOOK 429 literal interpretation of the old valve manufacturers in this By " Empiricist." agreement, it might now have been country. No subject of this kind possible for manufacturers to INTERNATIONAL ASPECTS OF BROAD- can be fairly discussed unless one utilise a multiple valve such as CASTING ...... 731 is intimately acquainted with both the " Loewe " type, which is in By G. Rolland W illans. sides of the question. fact two or more valves combined In case there is any possibility BROADCAST BREVITIES 733 22 in one bulb, and yet claim to pay that our attitude in closing our LETTERS TO THE EDITOR 735 the same royalty of I2S. 6d. which campaign for the time being is not READERS' PROBLEMS ... 736 manufacturers of other sets would clear to our readers; we again em- pay on the use of a single three - phasise that our close acquaintance electrode valve. We were assured with the whole position leaves us satisfied that a sub- that, with the exec )tion of the " Loewe " multiple valve stantial price reduction in all excepting perhaps the and other valves of that type, all valves at present in exist- newest types of valves will come about within what we ence came under the old royalty of I2S. 6d., including the regard as a reasonable space of time when the difficulties four -electrode valve, the " Hull " screened valve, and involved are taken into consideration. Under these circum- refexing as at present used in various receivers. stances we see no purpose in pursuing a policy of criticism We were told that at one time the company had con- unless we should find that our confidence in the intentions sidered so wording the modification to the agreement that of the valve manufacturers has been misplaced. the basic unit, on which a 125. 6d. royalty would in A 7

www.americanradiohistory.com WiiT®Il®00 JUNE 8tlr, 1927. 708 WoIlc future be payable, should be a stage of amplification nient has not been disclosed, hut it would appear that, in equivalent to the use of a three- electrode valve. This return for permission to install microphones in the Queen's wording, however, would have precluded the use of re- Hall and to broadcast concerts and other events taking flexing, which it is the intention of the company should place there, the B.B.C. has entered into an arrangement still be permissible on the charge of r2s. 6d. per valve whereby they will run a series of concerts and, presum- holder as at present, and therefore the present wording, ably, contribute either directly or indirectly to the ex- although admittedly not ideal, was adopted. penses of Messrs. Chappell and Co. in connection with We were most emphatically assured that there is no concerts during the coming season. The lessees of the intention on the part of the Marconi Company to en- Queen's Hall have maintained for some time past that it deavour to create a new monopoly nor to impose a royalty was not possible to compete with the B.B.C. and they in excess of the present charge for the use of any new type contemplated having to give up the promenade concerts. of valve which may give special performance, unless 'Whilst the direct result of this agreement between the such valve is, in point of fact, a combination of two B. B. C. and Messrs. Chappell and Co. is a matter for con- or more valves, when the royalty would then he calcu- gratulation, yet there is. of course, another point of view lated on the basis of 25s. for a dual valve, or 37s. 6d. which may be taken. We have, in the past, on different for a triple valve. occasions expressed our disapproval of the policy of the We have submitted a copy of this, our interpretation B.B.C. in conducting their own concerts to which the of the amending clause of the agreement, to the Marconi public have been invited. In our opinion, the B.B.C. Company, and are informed that our interpretation is should not compete with organisers of concerts which are correct. open to the public, but should confine their Musical broad- 0000 casts to what is performed in the Studio or to the broadcasting of outside entertainments organised for purposes THE B.B.C. AND THE QUEEN'S HALL. other than broadcasting and not under the direction of /Q FTER months of negotiation between the B.B.C. and the B.B.C. As things stand at present we may expect \ Messrs. Chappell and Co., I.td., the lessees of the the B.B.C. to build its own theatre and, by using the Queen's Hall, an agreement has at last been reached microphone for publicity, get a very unfair advantage over which, it is stated, will insure the continuance of the other theatre proprietors; similarly, in almost every direc- Queen's Hall as a home for music and the resumption of tion there is the opportunity for the B.B.C. to compete the promenade concerts. in this way with other interests, unless the present policy At the time of writing, the precise nature of the agree- is checked.

In 1652 Admiral Tromp, the courageous Dutch commander, defeated the British fleet under Admiral Blake at Dover, and, according to tradition, sailed up the Channel with a broom hoisted to his masthead to denote that he hid " swept the seas." In 1927 the Dutch station of the Philips Company at Eindhoven "sweeps the ether" on short waves and again scores oft Britain, but this time in the friendliest spirit of rivalry. e8

www.americanradiohistory.com iT-?7"-","riv-. . `

vihp®Il®E@ JUNE ,Sth, 1927. 709 W RELESS AND THE ECLIPSE. How Experimenters can Assist in Collecting Data. By Prof. E. V. APPLETON, F.R.S. HE total eclipse of the sun in the early morning the sun from illuminating the moon. This type of eclipse of June 29th of this year will he a unique event is represented diagrammatically in Fig. 2. T in the lives of the majority of us. Thousands of Nov although we are at present unable to say whether people from all parts of the world will make the journey the moon has any marked influence on wireless propaga- to the North of England in order to witness one of the tion, we do know, thanks to the recent intensive study most awe- inspiring spectacles of all the varied pheno- of wireless propagation by many investigators, that the mena of Nature. Many wireless experimenters will, no sun has a very marked influence on transmission. A doubt, be among these thousands who, by going to York- solar eclipse is, therefore, likely to yield data of great shire, will see the rapid progress of the dark shadow interest and importance. crossing the hills just before the sun is completely hidden Path of the Solar Eclipse. and see the stars flash out as if at midnight. But there will also be many wireless enthusiasts who vwill lind the First of all, a few facts concerning the time and place cglipse a unique opportunity for studying the vagaries of the eclipse may be useful. The actual path of the of reception and who, throughout the eclipse, will be shadow of darkness is about thirty miles wide and ex- at their receivers making observations on the special tends fifteen miles on each side of a line drawn through wireless transmissions that will be taking place at that Criccieth, Colwyn Bay, Southport, and Hartlepool. The early hour. The American wireless experimenters had eclipse begins about 5.25 a.m. (summer time), and lasts an opportunity of making such observations on about no minutes, so that totality will occur about January 24th, 1923, when they experienced a total 6.2o a.m. to 6.3o a.m. The totality or time of darkness eclipse, and now such an opportunity has come to British will last about thirty seconds. Wireless observations will, observers. The present article deals with the eclipse from of course, have to begin very early, well before sunrise the wireless standpoint, and in it I propose to discuss on the morning in question, in order that the complete the possible types of observations which the amateur can series of phenomena may be studied. make. The facts given immediately above concerning the First of all I will say a few words about eclipses in general, in order that the later discussron of the effects on wireless may be the more easily understood. We experience eclipses of the heavenly bodies in two ways. In the first type of eclipse the obscuration of one body is brought about by the intervention of another between it and the eve of the observer. In the second type the body is eclipsed because another body intervenes between it and the source of its illu- Both of mination. these Fig. 1. -Solar eclipse in which the moon is interposed between the earth and the sun. types can he illustrated by the case of the sun, moon, and the earth. A solar eclipse place of totality have been calculated by the astronomers, is of the first type mentioned, in that it is due to the who are themselves making great preparations for ob- passage of the moon in front of the sun. serving the eclipse and photographing the sun during the 1 This state of affairs is illustrated in Fig. i (which, moments of totality. Until recently the astronomers were of course, is not to scale), which shows diagrammatically the chief scientific workers who found eclipses occasions how the light from the sun is completely cut off so far as of special interest, but now they are joined by wireless a small part of the earth is concerned. This small area observers, and the question arises whether the places of is called the area of totality. Round the area of totality totality predicted and calculated by the astronomers for there is a region where only a portion of the sun is visible, their photographic observations are really the best regions and here a partial eclipse is to be seen. for the wireless observer. This is a very interesting and The second type of eclipse is caused by the intervention important question, and to answer it I must first deal with of a solid body between the obscured body and the source one or two fundamental facts about wireless transmission. of illumination. This takes place when the earth prevents The enormous number of observations made on signal A 9

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710 WI E. @Il JUNE stir, 1927. WopIlca1 Wireless and the Eclipse. - of the Heaviside layer eclipse, as well as on the ground intensities during the last few years have shown very eclipse belt, to see if any difference in signal strength marked differences between day and night phenomena. can be detected between the two places. especially on the shorter wavelengths. For very long There are two further points in which the wireless waves the difference is not so marked, but for broadcast- observers «-ill work under different conditions from the ing wavelengths and ultra -short waves the differences are astronomical observers. Dr. Rayner and Dr. Comrie have very pronounced. The differences are curious in that they estimated that the eclipse on the Heaviside layer will do not always bend in the same direction. For example, take place a little earlier than that for the ground. They in the case of the broadcasting signals at distances of estimate that the centre of the shadow at a height of 200 miles or so the night -time signals are usually stronger sixty miles will have passed over England (between 6.2o at night than during the day. On the other hand, with and 6.22.a.m. B.S.'I'.) before the centre has arrived very short waves (e.g., 15 metres), which are used for from the west at the Welsh coast in its journey across the long -distance working, the signals are often stronger by North of England. In the case of the eclipse at the day than by night. It is not easy to give satisfactory ground, the centre of the shadow will travel across Wales explanations of all these phenomena, but it is obvious, and England from 6.23 a.m. to a.ni." from the marked changes in reception which take place A second and very important difference between the at sunset and sunrise, that the sun is a controlling factor. cases of the wireless and astronomical observer is that Recent experiments have shown that the sun exerts its the weather will not matter to the former, but will be influence via the Heaviside layer of electricity, which all- important to the latter. So far as Ave know, the is situated in the upper atmosphere and which is altered wireless observer will be able to make his observations in height and properties by the action of the sun. even if the sky were cloudy, but in such a case photographs of the sun's corona would be useless. There is, Track of the Heaviside Large Eclipse. of course, the possibility that atmospherics may upset Bearing the above facts in mind, we are in a position some of the wireless observations, hut, on the whole, this to appreciate an imperrtant difference between the eclipse seems unlikely, as the eclipse takes place at a time when from the points of view of the astronomer and the wireless atmospherics are not usually very strong. observer. This difference (which was first pointed out by Dr. E. H. Rayner, of the National Physical Labora- How to Make Observations. tory) is that the eclipse heft for the Heaviside layer at I n ïw turn to discuss a question which no doubt will a height of, say. sixty miles will he at an entirely dif- be uppermost in the minds of most readers of this ferent part of the country from the eclipse belt for the journal. The wireless experimenter Neill be asking him' photographic astronomical observations made at the self : HOW can I assist in ad ling a few observations to ground. The cone of darkness caused by the shadow of the great mass of data we hope will accrue from the the moon does not meet the earth's surface vertically, and special eclipse wireless transmissions? This question I the result is that the eclipse at the Heaviside layer is will do my best to answer. In the first place, I think along a track roughly parallel to the one on the ground we may rule out long -wave observations for the amateur. hut roo miles south -east of it. This very important These are best made using galvanometers and voltmeters and other measuring instruments. Ohsen.ations ought to be confined to wavelengths of the broadcasting range and below. Let us consider the broadcasting range first. Here accurate measurements of signal strength will be made by the Radio Research Board observers, and from these the height of the Heaviside layer will be estimated at various times. during the eclipse. But these observations can be sup- plemented very considerably by amateur estimates of signal intensity on other 2. -Lunar eclipse in which the earth's shadow is cast across the moon. stations which are modulating. But a very important difference suggests that if experiments are made on the factor comes in here. We may expect the eclipse to cause nature of reflection from the Heaviside layer the experi- a sunset and a subsequent sunrise after the normal sun- ments ought to be carried out near a line from Cardiff rise has taken place. Thus the eclipse is really a special to Grimsby. The Radio Research) Board of the Depart- opportunity of studying sunrises and sunsets. It, there - ment of Scientific and Industrial Research is, therefore, fore, cannot be too strongly emphasised that observations arranging for experiments to take place along the belt made on the day. of the eclipse will be of little value A 10

www.americanradiohistory.com JUNE Sill, 1927. Wflpd2ogi 711 WcTIlA. Wireless and the Eclipse. - mornings of the two days preceding and the two days unless they can be compared with normal reception succeeding the morning of the eclipse. Thus the experi- results. Thus observations of a similar character should menter will have plenty of opportunities of making ob- be made at least the morning before and the morning servations on short -wave intensities on a fair range of after the eclipse. Only in this way shall we be able to wavelengths. say what is the effect of the eclipse itself as compared A final word on small but important details may not with normal sunset and sunrise. In order to make similar be out of place. It is essential to record any observation observations from morning to morning and have the immediately it is made. Do not trust to the memory. results comparable, it is necessary to have the receiver sensitivity constant. Thus filament and anode volts should be kept the same, and the set should only CONE DS DARKNESS he used for stations which are comfort- CAUSED BY SHADOW ably received without strong reaction. OF THE MOON. The last point is very important, for a set on the verge of oscillating is useless for signal estimates, apart from the possibility of its interfering with other workers. Thus to the workers with a broadcast set I would say : Study the sunset (and, if possible, sunrise) characteristics of a station you can receive ?hill/ great case and note what extra phenomena you observe on the morning of tip' eclipse. Short wave Tests. TOTAL ECLIPSE' VISIBLE HERE I now turn to the question of ultra - short -wave observations. The Radio Research Board, in conjunction with the TRACK TRAVERSED/ Radio Society of Great Britain, are RV TOTAL ECLIPSE arranging for a series of transmission on various short wavelengths. A transmission on qo metres will take place TRACK TRAVERSED BY from Caterham and one on too metres HEAVISIOE LAYER ECLIPSE from Iceland. Arrangements are also 23 being made for signals on metres and 3. -The shadow cast by the moon passes through the reflecting surface of on 44 -46 metres. The two latter stations the Heaviside layer approximately 100 miles S.E. of the path of the visible eclipse and the path of totality for wireless observations will therefore pass will he situated one north and one south through Cardiff and Grimsby. of the line of totality for the Heavi- side layer. Amateurs will here find plenty of scope for Also it is important to time each observation correctly audibility estimates of signal intensity. In particular, with a watch or clock checked before and after the series they will be able to make the check measurements for a of observations by means of time signals. Sometimes normal day, which, I have pointed out, are so necessary, confusion arises between B.S.T. and G.M.T. The times for the above transmissions are also to take place on the relating to the eclipse have been given above in B.S.T.

Chloride Rugger Success. his " Everyman Four." " My reception," The Rugby team of the Chloride Elec- he writes, " is improved by about 25 per trical Storage Co., Ltd., of Clifton TRADE NOTES. cent. more stations, greater volume and Junction, Manchester, has distinguished purity, whilst my current consumption is itself by winning for the second time the greatly reduced. Now that I can reduce Workshops Cup Competition organised by the bulk of my accumulator I am think - pleted receiver covers both the Daventry ing of constructing a portable -a cross the Broughton Rangers Rugby Football wavelengths, and and normal band of between-the ` Everyman Three ' and the Club. In the final match the Chloride results a Municipal gives gqod loud- speaker on \-V ireless World Five.' " team defeated the Salford number of stations. a 0000 Employees team by 11 points, after The cost of the complete instrument, splendid display of high -class football by including all valves, batteries: etc., is Address Wanted. both sides. ,0o £21 16s. Alessrs. The Dubilier Condenser Co. 0000 (1925), Ltd., have received an enquiry Constructing an " M.H. " Portable. from Mr. R. King, of Torquay, for de- Owing to the success of the " M.H." Osram Valves and the " Everyman Four." tails concerning certain components. Un- five -valve Supersonic Block Unit, Messrs. In a letter to the General Electric Co., fortunately the gentleman has omitted to L. McMichael, Ltd., Wexham Road. Ltd., in appreciation of the new G.E.C. give his address, and the company is, Slough, Bucks, have issued constructional range of 4 -volt valves, Mr. F. Egerton therefore, unable to comply with his re- details for a six- or seven valve portable Parker, of Highgate, London, N.7. de- quirements. They trust that this para- receiver incorporating this unit. The corn- scribes how he embodied these valves in graph will come to his notice. A II

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-1 LS J¡I J , ° X RA.0M:007,0N3a Useful Data for Checking \Vavemeters and Calibrating Receivers.

OME constructors and experimenters generally who Mean Time. During the period of Summer Time it will, wish to calibrate their receivers will find the list therefore, be necessary to deduct one hour from Summer of Regular Transmissions which we give below of Time to arrive at G.M.T. considerable service. It is, of course, impossible in so Included in the list are the International Time Signals limited a space to give all the stations transmitting at transmitted simultaneously on 32 and 18,940 metres from regular times which may be heard in this country, but'we Bordeaux and Paris at o800 and 2000, the well- known think the following list gives all those of general interest. spark signals from the Eiffel Tower at 0925 and 2215,, The times of all transmissions are given in Greenwich and those from Nauen at 1155 and 2355.

Wave- Call Wave- . Call length. Name of Station. Sign. Times of Transmission. length. Name of Station. Sign. Times of Transmission. 20 Mourillon, Toulon .. OCPN 15:30.-1540. 1,800' Reykjavik ...... TFA 1030, 2005. 24.7 Bellevue D.C. .. .. NKF 2130. 1,84(1 Cherbourg .. FUP 0105, 0515. 33 Paris -Eiffel Tower .. FL 0755, 0801, 1955, 2001, 2250 1,850 Andover .. GFI f0700, 1000, 1300, 1800. .. IDO 1950. Bergen .. LGN 0950, 2050. 33 Issy- les- Moulineaux .. YZ 0940. 1;600 Utrecht PIMR 0710, 1310, 1810. Mourillon, 'ron1n1í .. OCTN 1545 -1555. 1,950 Danzig .. DG 0705, 1305, 1805. Paris ...... OCDJ o61í 2250. 1,980 Zurich .. HBK 0708, 0808, 0908, 1008, 1108, 36 Rabat ...... OCRB 0750, -2lí.., 1308, 1408. 50 Tunis .. .. . OCTU 051 2,000 Le Bourget .. FNB 0750, 1650, 1750. 51 Ain Bop!ja . . MN 06:30, 1!1:311. Stuttgart .. SIC 0850. 57 Mourillon, Toulon OCTN 7íi00 -1 61.0. 2,000' Revel .. .. AZA 0725, 1250, 2050. 58 Beyrouth .. OCBY 2015, 21110, 2145. 2,6511 Warsaw.. .. WAR 0200, 0550, 0815, 1115, 7 130 75 Paris -Eiffel Tower FL 0420, 0840, 1600, 2250. 1435, 1900. 270" Portland Bill .. FB9 0918, 2018. 2,100 Devizes .. GKU 0044, 0444, 0844, 1244, 1644, 300 N. Hinder .. .. PCN 0700, 1300, 1800. 2044. 400 Flushing .. PCD 0705, 13115, 181)3. Paris -Eiffel Tower FL 1200. Helder ...... PCB 0707, 1:307, 1507. Paris ...... YA2 0550, 1040. 600' Bergen . .. .. LGN 0755, 0950, 15:30, 18115. 2050. Rochefort .. .. FUR 0516, 0716, 1016, 1316, 1516, Blaavand .. .. OXB 0100, 0500, 0900, 1300, 1700, 1816. 2100. Sandhamm 0812, 1412, 1912. Copenhagen .. OXA 0300, 0700, 1100, 1500, 1900, 2,170(T) ORE 0740, 0945, 1(145, 1340, 1840. 2300. 2,:300 Norddeich ...... KAV 1205. Cullercoats .. GCC 0948, 2048. 2,400 Tripoli ICK 0750, 1850. Niton GNI 0930, 2030. 2,400(T) Monsanto ...... CTV 1140, 2310. Seaforth .. .. GLV 0S130, 2090. 2,450 Königsberg . KO 0805, 1030, 1905. valentia .. GCK (1948, 2045. 2,525(Tl Berlin (Wcolf's Bureau) - 1050, 2020. 6r,o' Borkum Lightvessel KBR 0015, 1245, 1745. 1,67,0 Libau ...... KCQ 0733, 1015, 1335, 1835. 800(T) Bergen .. .. LGN 0950, 2050. Madrid ...... EGC 0705, 0820, 0845, 1305, 1420, 800 Memel .. RYM (1145, 1245, 1745. 1445, 1805, 1920, 1945. 900 Air Ministry GFA 0750. Paris -Eiffel Tower .. FL 0220, 0.1m, 1715, 2130, 2235. Le Bourget .. FNB 0844. 2,150(T) Paris -Eiffel Traver .. FL 0040, 1115, 1000, 2210. 1,000' Monsanto .. CTV 11:30, 1350, 1850, 2300. 2,1150' Paris -Eiffel Toyer FL 0755, 0801, 0925, 2245. Terceira.. .. PQT 0030, 13:30, 183(1. 2,1377 Washington (Arlington) NAA 0300, 0330, 1530, 1700. 1,100 Lausanne HB2 0700, 1100, 1800. 2.800' Nantes ...... UA 1230. Swinemunde.. KAW 1030, 1300, 1120, 1800, 2145. 2,930 Scheveningen .. .. PCH 1115. Utrecht .. PIMR 1025, 1235, 1525, 1925, 1945. 3,000 Monsanto ...... CTV 08:35, 14:35, 1935. 1,100(T) Lausanne .. HB2 1200, 1555. 3,050 Vienna ...... OHO 0750. 1,100' Norddeich KAV 1015, 21:30. 3,100 Nauen ...... POZ 1155, 2355. Rame Head .. BYO 0018, 2018. Warsaw...... WAR (18:35, 1435, 1920. 1,130 Aldergrove .. GFH -10703, 1005, 1303, 1805. 3,300 Berlin . .. .. DL 0745, 1345, 1845. Cranwell .. GFC 1-0105, í0705, 1)05, 1305, 1(115, 3,350 Königswusterhausen .. AFR 07220, 11.20, 1820. 1 40 5. 3,400 Berne ...... HEB 0715, 1315, 1815. Leuchars GFD t0705, 1005, 1305, 1805. 3,500' So!3a ...... FF 0055, 1355. Renfrew GER 10705, 1005, 1305, 1605, 1805. 3 600 Brest ...... FUE 0455, 0900, 1500, 2000. Sealand GFO 10705, 1005, 1305, 11105, 1805. Bizerta ...... FUA 0810, 0910, 1130, 1410, 1910. .300 Calshot .. GFL 10705, 1005, 1305, 1605, 180 55. Casablanca ...... CNM 0155, 0800, 1400, 1000. Felixstowe GFF 10705, 1005, 1305, 1105, 1805. 3,700 1 uliauehaab ...... ORF 1200, 1800, :400. Guernsey GEY 10705, 0905, 1005, 1305, 18115. 4,100 Air Ministry .. .. GFA 0200, 0600, 0800, 0835, 0850, Plymouth GFM 10705, 1005, 1105, 1005; 1805. 0900, 1050, 1400, 1450, 1650, 1,330 List .. KAL 01'50, 0500, 0650, 10 -10, 1250, 1900, 1935, 2000. 1fí lu, 1750, 2220. 4,200 Karlsborg ...... SAJ 074(1, 1050, 1310, 1840, 2200. Wilhelmshaven KAN 0720, 130'1, 1810. 4,100 Budapest .. RAR 0835, 1315, 1845. 1,400 Air Ministry GFA 0715. 4,401) Washington (Arlington) NAA 0300, 0330, 1530, 1700. Le Bourget .. FNB 081,. 4,500 Porquerolles .. .. FUQ 0145, 0750, 1050, 1350, 1900. Riga . .. KCA 1350. 4,800 Leningrad ...... RET 0915, 1100, 1530, 1858, 2030. 1,4:0 Tromsö .. .. TUT 1030, 1513, 1015. Malta ...... OHA 0707, 1307, 1807. 1,460 \Vorthy Down GFG 70705, 1005, 1303, 1503. Moscow ...... RAI 0900, 1040, 2055. 1,500' Bilbao .. .. EON 0735, 1335, 1835. Rome . .. .. IDO 0850, 1950. 1,525 Marignane .. FNM 0504, 0704, 1004, 1304, 1504, 5,300 Lyngby .. .. OXE 0735, 1100, 1335, 1835. 1804. 5,400 Ismalia .. .. , . GHK 1100. 1,525(T) Toulouse .. FNT 0508, 0708, 1008, 1508, 1808. 5,454 Oslo .. .. LCH 0750, 1040, 1350, 1640, 1850. 1,550 Breslau .. .. BU 0755, 1420, 1855. 0,000 Belgrade .. .. HFB 0850, 1450, 1950. 1,575 Hamburg .. AEM 0140, 0540, 1440, 1940. Paris . .. .. YG 1600, 1921). 1,600 Barcelona .. EGE 0810, 1345, 1825. 0,120 Prague ...... OKP 0740, 1340, 1840. 1,650 Kiel .. .. KBK 07.20, 1010, 1320, 1615, 1820. 6,700 Gibraltar .. BWW 0705, 1805. Pillar .. KAP 0730, 1330, 1830. 7,300 Paris -Eiffel Tower FL 0820, 0810, 0910, 1420, 2100. 1,680 Air Ministry GFB 0536 and hourly to 16:36, 0800. 0,000 Nantes .. .. UA 1415. Cologne .. GEK 0716 and hourly to 1516. 10,300 Grudziadz .. .. ARK 0800, 1400e 1900. Le Bourget .. FNB 0728 and hourly to 1628, 0850. 10,500 Rome . .. .. IDO 1600. l.mdesibcrg .. AEQ 0125, 0150, and hourly to 1050. 11,000 Abu Zabal .. .. SUC 0955. 0900, 1030, 1350, 1850. Uccle . .. OPO 0622 and hourly to 1822. 11,700 Bucharest CVM Utrecht .. PIMR 0745 and hourly to 1445. 17,040 Washington (,Annapolis) NSS 0300, 0500, 1700. 1,800 Blaavand ...... OXB 1005. 17,631) Vorberg...... SAQ 0740, 1000, 1340, 1849. 1155, 2355. Lyngby .. . .. OXE 0123, 1005. 18,060 Nauen ...... POZ 1,800' Fir.uske .. .. LDW 0715, 1315, 1815. 18,040 Bordeaux ...... LY 0800, 1955. Spark Transmission. (T) Radio Telephony. All other transmissions are C.W. t Times approximate. A I2

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Ay1SJ\l-JRE1 , RADIOTELEPHONY11 JiONY -J'YS. FIB. A Review of the. Problems Involved and Solutions Suggested. By O. F. BROWN, M.A., B.Sc.

HE recent inauguration of the Transatlantic Tele- that the reflector or directive aerial systems employed at pPTI hony Service has directed attention to the problem the beam receiving stations are essential for the reception of secrecy in radio communications. Hitherto of the radiation from the corresponding transmitting comparatively little serious consideration has been station. These reflectors are extremely valuable, in that directed to this matter, partly owing to obvious difficul- they make the receiver more sensitive to radiation from ties of the problem, and partly owing to the fact that a particular direction, and by so doing reduce interference where telegraphic communication was concerned the dis- both by atmospherics and by signals from transmitting advantages of a lack of secrecy could be overcome by the stations arriving in directions other than that in which it use of code or cipher. Although code words can be emis desired to receive. It is not true, however, that with- ployed to a certain extent in telephonic communications, it out the reflectors the signals are so weak that they cannot is obvious that serious inconveniences are introduced by he picked up with suitable apparatus having a high factor their use. It seems probable, therefore, that the general of amplification. The long -distance communication ob- 'use of long- distance radiotelephone services is likely to tained by amateurs employing extremely small powers be prejudiced by the fact that at present portions of the affords good evidence on this point. The importance of conversations, at any rate, can be picked up by un- the reflector aerial lies in the fact that the ratio of signal authorised persons over considerable areas without great strength to atmospheric noise is increased, and thereby difficulty, and it is natural that the removal of this diffi- the number of hours possible per day for satisfactory culty should be receiving consideration. working is increased. Hence, without a complicated aerial system which could not Fundamental Principles. he erected surreptitiously, reception at long distances from a short -wave beam station The object of the present article is to review the diffi- would be possible only under comparatively favourable culties to be met in the problem of providing some adequate -atmospheric conditions, and without the reflector there degree of secrecy while at the same time preserving the would be periods at which eavesdropping would be ex- requirements of efficient radio communication, and to indi- tremely difficult or impossible. Except in this sense, how- cate the lines along which a solution seems likely to be ever, it can be said that present -day beam transmission found. It may be stated that little or nothing has been would be unlikely to provide any adequate degree of published on the matter, and the only source,of informa- secrecy. is study of patent literature. tion the Zones. Obviously, with line telephony the area over which the Silent speech can be picked up is limited to the region near the The use of short waves, however, has one advantage wire or cable conveying the current, and systematic eaves which must not be overlooked, namely, the fact that on dropping is only possible to persons having access to the short waves the energy is radiated for a considerable dis- wire in question. The case of a radio station is different. tance by waves travelling through the upper layer of the If the signals are capable of being received at one station earth's atmosphere, while any energy travelling along the they can, with suitably designed apparatus, be received ground is absorbed at a comparatively short distance from at another station. The only way in which radio com- the transmitter. Apart from a short distance round the munication could approach line communication, with re- transmitting station, therefore, there is a zone of silence gard to the area over which interception is possible, would of perhaps several hundred miles-the exact radius de- he to concentrate the wireless waves into an extremely pending on the wavelength used. After this distance the narrow beam. Now it has been suggested by writers in waves deviated from the upper atmosphere reach the the non -technical Press that the Marconi beam stations earth and signals become comparatively strong. In cer- radiate in a manner approximating to a beam of this tain particular cases the existence of the silent zone could nature. This is certainly not the case. A study of the no doubt be used to assist in providing a service which published data of the beam stations shows that the radia- could not be intercepted. tion is directed not in a narrow band, but in a fan several On the other hand, the beam system is proving success- degrees wide. The result is that at a distance of; say, ful in the main for telegraphic communication; and it 2,000 to 3,000 miles the radiation can he picked up over appears to be generally accepted that the variations in an ever -widening belt of not less than two or three hun- signal strength and fading effects due to the influence dred miles wide. In giving this value to the width of of the upper atmosphere on the propagation of short the belt it is assumed that the " cut off " at the edges wiretcss waves render it still desirable that long waves of the " fan " is sharp. No reliable evidence is available and comparatively high power should he employed in on this point, but it is extremely likely that the edges of such a service as radiotelephony over long distances the fan are not sharp, so that the area over which the where it may he essential for two subscribers to be put energy can be received with sufficiently sensitive appara- into communication at a prearranged time without delay. tus is greater still. Since there can be no possibility of guiding long waves in It has also been suggested in the non -technical Press a beam, the problem of securing secrecy resolves itself A 13

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Secret Radio Telephony Systems. - vibrations modulating it, the resulting carrier wave can into transmitting the speech in such a way that reception be considered at any moment as consisting of three waves becomes difficult without very complicated apparatus. whose frequencies are f, f .+ p, and f -.p. Now, in In using radiotelephony on long waves, one matter an ordinary system of radiotelephony, such as 'that used which has to be considered is the amount of interference in broadcasting, these three frequencies heterodyne in a produced on other communications. So great is the simple receiver so as to produce abeat note of frequency amount of signalling by wireless now taking place that the p. It is clear from this way of looking at the matter task of fitting in of new lines of communication on long that the carrier wave (frequency f) has no effect on the waves presents the greatest difficulty. One of the most transmission of the sound, except to provide a wave which important criteria by which a method of radio communica- will be of use in heterodyning the frequencies f + p and tion has to be judged is therefore whether it could be f - p, which really contain the sound to be transmitted. introduced into the existing crowded condition of the In the Western Electric Co.'s system a considerable saving ether. As will be seen later, many of the suggested of power is effected by not transmitting the carrier wave secret systems proposed can stand no chance of general at all, but by suppressing it along with one of the side - adoption on account of their failure to conform to this band frequencies f + p or f - p at the transmitting end, important condition. and in reintroducing the necessary frequency needed for Width of Side -bands. heterodyning the remaining side -band by means of a weak local oscillator at the receiver. It may therefore be desirable here to consider briefly Not only is there a saving of power of about 75 per the causes of the greater interference of radiotelephony cent. in transmitting only one side -band, there is a great services compared with radiotelegraphic services, and to reduction of the amount of interference. If both the side - indicate why the system developed by the Western Elec- bands are transmitted, frequency bands of between zoo tric Co. and the British Post Office for transatlantic and 2,200 cycles are present on both sides of the carrier - working ha; alone made telephony on long waves a prac- wave frequency ; thus a band about 4,000 cycles wide is ticabl° proposition. taken up by the transmission. If we put the shortest wave suitable for long- distance communication at, say, 4,000 metres, i.e., 75,000 cycles, L and the longest at 25,000 h-- 1 METRE --+1 metres or 12.000 cycles, the whole number of cycles N3 available for such communi Ìi cation is 6o,000, and it is clear that the maximum post sible number of radiotelephony services which can be got in between these wavelengths without direct '0000' ' ,06Òo overlapping is only fifteen. Even then no allowance has been made for the various telegraph services taking Lr' L2 place on long waves. The number of cycles occupied Fig. 1. -The system advocated by Tigerstedt (1918) makes use oI a continuous magnetised steel band. by a telegraph service is only a few hundred cycles. Probably every reader of The Wireless World is aware Comparing this with the 4,000 cycles required for that the essentials of an ordinary telephony transmitter telephony, it is clear that any proposal for starting are the production of a pure and steady continuous wave telephony services must have a difficult passage with the oscillation and the means of modulating this wave by the authorities responsible for the international allocation of audio -frequency vibrations due to the sounds it is de- wavelengths. Obviously the chance of fitting in such a sired to transmit. Now, the audio- frequency vibrations service is increased in the case of a system such as the corresponding to a sound can be shown to be made up present Western Electric system, where the band taken of a large number of waves corresponding to frequencies is only about 2,000 cycles, i.e., half of that required of between, say, zoo to 2,200 cycles in the case of by other systems. speech and perhaps roo to ro,000 cycles in the case of The Western Electric " side- band " system as at music. present used is secret only so far as speech cannot be The result of modulating the carrier by a complicated received on a simple broadcasting receiver, and cannot, speech form is the same as modulating the carrier wave therefore, be inadvertently overheard. The Western Elec- simultaneously with a number of simple component waves tric Company have, however, covered by patents several into which the ordinary speech can be resolved. If we schemes for making interception extremely difficult, if not assume the frequency of the carrier wave is f and that p impossible, and the principles of these will be described is the frequency of any one of the component speech in due course. A 14

www.americanradiohistory.com Ji YE 811z, 1927. WimDgto WOptcll 715 Secret Radiotelephony Systems. - and sections of it are continually being reserved before Before dealing with the Western Electric methods, reaching the coil N, through which it reaches the line. however, it .may be of interest to review briefly some The receiving arrangement is exactly similar to the trans- other suggestions that have been made. One of the most mitting apparatus. The received speech is passed through ingenious was patented by a Danish engineer named a transformer and is applied through rotating discs simi- Tigerstedt in 1918. His method is applicable both to lar to C and D, alternatively to similar transformers to line telephony or telegraphy and to wireless, and he pro- T1 and T2. If, however, in the transmitter T, is work- poses to provide secrecy by splitting up the Morse signs ing on coil N1, and T2 on coil N2, then in the receiver or words to be transmitted into sections which are re- T1 must work on coil N21 and T2 on coil N1 to get the arranged in different order so as to produce an unintelligible jumble which is transmitted into the ether. At the receiving end the components of the speech are automatically rearranged in the proper order so that speech becomes intelligible. In principle, the result is much the same as that achieved by the man who repaired his cuckoo clock so that it " cooed " before it " cucked." Tigerstedt's System. The method proposed in this invention is somewhat as follows : -An endless, easily magnetisable steel hand runs round the two rollers A and B in the direction of the arrow (see Fig. r). Mounted on the same shaft as the roller A are three circular discs. The edges of discs C and D are divided into alternate conducting segments so ¡^ . f ulu, arranged that when the discs rotate together an insulating 111 segment on C is opposite a conducting segment on D. 10i '1 11 T 111 í The conducting segments on C and D are connected with 4;l.... p IIIppIrÌIÌIMIa 11IIIIII111111111111111.NIIIIIIIIm a third conducting disc E on the same shaft. Conduct- ,lanai. 'dmIIIIIII111111111111P.m e ing brushes bear on the discs for making external con- WW1, uoanllallll111,1IIIaauk- nections. When the microphone M is spoken into the - A speech currents are conveyed across the brush on disc E and out through whichever of the brushes bearing on the Fig. 2.- Circuit and apparatus for continuously varying the carrier frequency in the method patented by R. Howe-Gould (1922). discs C and D is in contact with a conducting segment. If the current passes through disc C it flows through the speech rearranged correctly so as to be intelligible. A primary of a transformer T, ; if the current flows by circuit L is arranged to wash the steel band free from dise D it passes through the primary of a transformer magnetism before it reaches the coils N1, N2i and N,. T2. The secondary of the transformers T, and T2 are connected with coils N, and N2 respectively, and when Synchronisation. speech currents pass through these coils the magnetism The method, of course, depends on the velocity of the of the endless band round the rollers is altered, and moving hand and the discs being adjusted so as to be corresponding speech currents are introduced by the mag- identical in the transmitter and receiver, and suitable netic band in the coils _V whence the currents flow out methods must he provided for synchronising and- correctly into the line or to the wireless transmitting apparatus by adjusting the position of the discs C and D and their the terminals L1 and L2. The currents from the micro- segments with regard to one another. phone are thus conveyed to the terminals L1 L2 alterna- The accurate synchronisation required would probably tively by the coils N, and N2. be difficult to achieve and maintain in practice. No To show in a simple case how the speech could he doubt the exchange of sections of the speech could be made mixed up by this arrangement, let us assume that the at other rates than at the half- second interval described, distance between the rollers A and B is two metres, and and the best speed arrived at for confusing a listener. It that the band is running at the rate of 5o cms. per second. might be possible, however, for a determined eavesdropper Let us also assume that the distance between the coils to write down or record the sounds heard and piece them N, and N. is one metre, and that the conducting segments together correctly when the conversation interesting him and discs C and D are so designed that the current path was completed. If the mechanical difficulties could be is changed from one to the other after the band has run overcome this latter objection could be got over by cutting 5o ems. In other words, the current will cease to flow the speech up into three or. four sections instead of the through N, when the band has run 5o cros. forward from two described. Ni, i.e., half -way between N, and N2. The remaining A considerable number of methods proposed for secret 5o ems. of the band up to coil N2 is not magnetised, and telephony depend on the variation of the length of the is now affected by N2 for half a second, i.e., while the carrier wave. One of the simplest methods suggested is clean 5o cros. of the band runs under coil N2. At the to transmit alternately on two wavelengths. The aerial is end of this half - second coil N1 begins acting again on coupled to two identical generators of continuous waves the clean band running up to it, and the process is re- which are modulated in turn by the same .microphone peated. The general result is that the speech is cut up circuit. The exchange between the transmitters is ob- A 1j

www.americanradiohistory.com -zó WilmIlsoo IT-.\'E 3fk, 1927. Wor1lic1 Secret Radiotelephony Systems. - allows a similar clutch to engage and set the transmitting tained by a rotating mechanical switch. This is so ar- variometer in motion. If the speed of the'motors,in the ranged in one device that transmission begins on one wave- transmitter and receiver are the samei the receiver will then length before it has ceased on the other ; any interruption remain in time with the transmitter during its wavelength of the radiation during the change over is avoided. 'The variations. At agreed times cams of various shapes can receiving apparatus consists of two detecting circuits con- he substituted to make the wavelength changes more nected to the sanie audio -frequency amplifier leading to irregular. the receiving telephones. The receiving circuits are only Other Variable Wavelength Schemes. complicated by the double reception necessary, and apart from the inconvenience of this the method described does In another proposed system an electrical governing not appear to give real degree of secrecy. On the other arrangement is suggested. On the shaft of the motor hand, the occupation of two carrier waves in the ether driving the apparatus for varying the wavelength is for the sanie communication would for the reasons already mounted a balance wheel in the form of a disc. The stated probably render the practical development of the angular movements of the shaft are controlled by a spring system impossible. and sufficient external motive force is provided to make up Other systems vary the wavelength of the carrier by energy losses. The balance wheel has inset on its rim a regular or irregular variation small laminated piece of soft iron S (see Fig. 3). Mounted of the tuning arrangements close to the balance wheel is a small electro- magnet which of the transmitting circuits. is energised through a relay by energy from an auxiliary The means which have been receiver, as in the case of the solenoid shown in Fig. 2. suggested include the use of The auxiliary receiver is tuned to a particular wavelength, condensers with irregular - and every time this wavelength is reached in the ordinary shaped plates which are wavelength variations of the transmitter the electro- magnet caused to rotate mechanic- will he energised and an attractive force exerted on the ally, or the movement of the soft iron inset on the balance disc, provided this is ad- moving coil of a variometer. justed to be near the solenoid at the proper moment. In It has also been suggested this way it is suggested that any error in the time of rota- that the transmitting induct- tion of the apparatus in the receiver will he corrected by ance should be designed on the acceleration or retardation produced by the magnetic the principle of a concertina, force. so that by mechanical means In another method proposed it is suggested that the the coils of the inductance variation of wavelength of transmitter and receiver he could be brought close to- carried out by the motion of synchronised pendulums and together or separated, and its an arrangement is provided for stopping the pendulums self - inductance thereby Fig. 3.- Electrical governor by wireless means at any selected instant so that a signal for selecting predetermined be varied. In receiving the sig- message -bearing wave- can transmitted on a chosen wavelength which would nals the receiving apparatus length in the system due to be unknown to the intercepting station. In any of these L. D. G. Morrison (1923). nnist be fitted with similarly methods, however, the hand of wavelengths necessary variable condensers or inductances the moving parts of .would he so large as to make the method impracticable for which are synchronised with the transmitting instruments. actual communication, while if a smaller band were used In one method a motor A (Fig. 2) running at constant the signals could he easily picked up on a flatly tuned speed rotates, by means of suitable gears, an irregularly receiver. shaped cam 13, which, by an anti -friction roller and a lever (To he concluded.) C, imparts movements to the moving coil L, of a variometer L. A similar- variometer is provided at both transmitting and receiving stations. At the receiving station an auxiliary detecting circuit is provided in which is in- " EXPERIMENTAL WIRELESS." chided a relay R. The action of the relay causes the movable core M of a solenoid to be raised.. The upward The June issue of the above Journal includes articles on the following subjects in addition to the usual movement is controlled by a dashpot so as to occupy a features prearranged time. EXACT MEASUREMENT OF TRANSMITTING When starting a communication the variometers at the WAVELENGTHS. transmitting and receiving stations are set at the same point on their scales and an auxiliary signal from the trans- SELF INDUCTANCE OF STRAIGHT WIRES. mitting set consisting of a long dash is sent out. The SLOPE INDUCTANCE. throw -over switch \V-1 at the. receiving end is set so that L.T. AND H.T. SUPPLY FROM D.C. MAINS. the auxiliary receiving circuit is coupled to the aerial which DESIGN AND CONSTRUCTION OF A is tuned to the wave on which the long clash is being sent SUPERHETERODYNE RECEIVER. nut. The core of the solenoid is raised, but the termination of the long dash automatically releases the solenoid Copies are now available from the leading Newsagents, price 2/6 net, or from core, which falls so as to make the clutch T engage, which direct the Publishers, Messrs. Iliffe & Sons Ltd., Dorset House, Tudor Street, causes the motor to begin to rotate the cam C. Similarly, London, E.C.4, price 2/8, post free. at the transmitting station the termination of the long dash A 16

www.americanradiohistory.com JUNE 8th, 7927. WfiT@ESM 4'o lrll0 71;

A Three unit Set Covering the Entire Broadcast Band. By A. J. BULL. IT must not be thought that the receiver about to be followed by a detector valve and two stages of low described supersedes any of the sets recently put frequency are employed. For reasons which will be forward in these pages and which have attained such stated latr, the two H.F. valves and associated tuned widespread popularity. Each set fulfils particular re- circuits are in duplicate, so that in all there are seven quirements, and the aim of this " All Station Receiver," valves housed in the containing cabinet. as the name implies, is to provide a sensitive long -range Unit A, the short -wave amplifier covering the normal set without wavelength limitations. This instrument con- broadcast band of wavelengths, consists of two H.F. sists of three units, A, 13, and C, all of which are con- valves transformer coupled, the primary winding of which tained in one cabinet and connected together to form one is tapped for neutralising purposes, aerial coil, and three receiver complete in every detail (except L.T. and H.T. variable condensers, together with necessary valve batteries), and covering a wave -range from zoo to 2,000 holders, filament rheostat, etc. The tuning range of this metres. Two valves amplifying at high frequency unit is zoo to 600 metres. Unit R, the long -wave H.F. amplifier, consists of two H.F. valves, tuned anode coupled, aerial coils, and three variable condensers, together with filament rheostats and the neutralising condensers necessary. The wave -range of this unit is 600 to 2,000 metres. Unit (. consists of three valves, viz., one detector and two amplifying at low frequency, together with transformers, jacks, and filament rheostats, etc. Included as part of this unit, there is what might be termed a distribution `panel, on which are mounted, parallel with the three valves, six special spring terminals arranged in two groups of three and to Fig. 1. -This rear view shows the switch action by means cf which the output connections of either of the H.F. amplifiers is applied to the detector valve. which the output of the high- A 19

h- www.americanradiohistory.com "'`s 778 WAp®hOO MUNE Sth, 7927. WCOM

100 V. 120 V V H.T- 42 V. HO O O

Fig. 2.- Circuit diagram of two-range broadcast receiver comprising two stabilised high -frequency amplifying stages and valve detector followed by a power amplifier. C1, 0.0005 mfd. ; C2, C3, 0.0003 mfd. ; C4, 0.0005 mid. ; C5, C6, 0.001 mfd. ; C7, 0.0002 mfd. ; C6, 0.0002 mfd. ; C.,, 0.001 mfd. R1, R;1, 4 ohms ; R2, R4, 10 ohms. ; R5, R,;, 2 megohms ; R7, 30 ohms ; R8, R.,, 10 ohms. T1, T., T3 " Wireless World " H.F. transformers. T4, coupled plug -in coils. Lt, L., centre tapped plug -in coils 1,400 m:co- henries. T;, T6, low ratio L.F. transformers. Switch positions : Sw, and Sw2, a and c, 200 to 600 metres ; b and d, 600 to 2,000 metres ; Sw. e, battery " off " ; f, H.T. and L.T. batteries " on." frequency units A and B respectively are con- pivoted at the knobs of the lever of the switches and nected. These terminals are shown numbered i to 6 in extended to pass through a small hole in one end of the Fig. I and also on the valve platform Fig. 7. cabinet. It is free to move in a horizontal plane over a distance governed by the length of throw of the switch Two -range Switching System. levers (Fig. 3). By further inspection of the circuit dia- Referring to the circuit diagram Fig. 2 and also to gram it will be appreciated that by pushing the rod Fig. t (which is a back view of the complete receiver), slightly into the cabinet the aerial and earth connections there is shown dia- are transferred from the grammatically and lower H.F. unit to the top in photograph two one, and the detector valve " Utility " double - disconnected from the lower ll 0 le change -over unit and connected to the switches, one of upper one. Consequently, if which can be seen unit A is tuned to, say, mounted in an in- Hamburg (395 metres), and verted position on unit B to Radiola Paris unit B on the ex- (1,7Ço metres), a rapid treme right, and the change from one to the other other on unit C in can be effected by slightly a similar position. moving the rod into or out The two switches of the cabinet as required. are linked together For loud- speaker reception Fig. 4. -H.F. intervalve coupling for considering by a dia. wood of the local station up to, selectivity and amplifica- Fig. 3.- Method of mounting curtain rod eft. 4in. say, twenty miles, where an tion produced by various " Utility " switches for wave change ratios of inductance to switching. in length, which is average aerial is used, the capacity. A 20

www.americanradiohistory.com JUNE 8th, r927. Wflpghoo WopIlli 7ra Two -range All Station Receiver. - H. F. valves are not wanted, and they can be cutout of circuit by means of the switch on panel A seen to the right of the third condenser dial. This switch breaks L.T. and H.T. supply to that panel only. The aerial remains connected to the grid of the first H. F. valve of top panel, and the dials are set to the tuning of the local station, which will be received at full strength. No other adjustments are necessary. By making use of the jacks and switch just described, the following combination of valves are possible : (i) Detector and one I.. F. ; (ii) detector and two L,F. ; (iii) two H. F., detector, and one L.F. ; (iv) two H.F., detector, and two L.F.

- All Apparatus Easily Accessible. The instrument and containing cabinèt are designed to permit of the components of the receiver being inspected without removal from the cabinet and to enable each unit to be readily Withdrawn. For example, in order to with-

Fig. 6. -This view shows the terminal connectors for making easy connection with the leads from the adjoining units, one of the change -over " Utility " switches, the method of supporting the valve platform, the rheostat in the detector valve filament circuit and the two " fixed " filament rheostats connected to th L.F. valves. draw unit A, -all that is necessary is to depress the tops of spring terminals numbered r, 2, and 3 accommodated on unit C and thus release the three output connections of the unit. Aerial and earth plugs coloured red and black respectively are withdrawn from sockets correspondingly coloured, and the unit is free to be removed from the cabinet. Absolute stability is obtained over the enLre wave -range of the instrument, viz., zoo -2,000 metres, which is due mainly to the inclusion in the design of nothing but first -grade parts, a general layout giving liberal spacing between components, the disposition of the wiring, which is rigid, good insulation, and, what is of equal importance, the use of a good earth. Often the domestic water pipe does not constitute an ideal earth. Usually a good earth can be obtained by driving into damp ground one or a number of iron pipes about Oft. in length and zin. diameter, the larger the diameter the better, and where two or more are used they should be connected in parallel by copper wire. The connection to the receiver should be as short as possible and of insulated wire not smaller than 7 /.028in. (7/22 S.V.G.) Fig. 5.- Drilling details of L.F. amplifier panel. Sizes of holes The range, quality of reproduction, and selectivity is A, 3/8 in. B, 5/32 in. and countersunk for 4BA. C, 1/8 in. and countersunk for No. 4 wood screws. excellent. \Vitli an average aerial, say, zoft. abcve A 21

www.americanradiohistory.com PRIPTWIlitiorwmvp, !kra(l - ;_,? .:.,araer ax

Wflmilmg î'0 11-.VF S/71. 1927. WoYïiZ Two -range All Station Receiver. - ground, and situated about three miles from 2L0 good loud -speaker results from roost of the European stations have been obtained with four valves in circuit lvith a good reserve of amplification. A useful feature in the design of the instrument which may appeal to experimenters rather than to those whose primary interest is in listening to the programmes is the ease with which other circuits may be introduced into the cabinet and tried out. For example, supposing either as an experiment or because the component parts ire already possessed, anode rectifica- Fig. 7.- Constructio tal details showing drilling and assembly of the valve platform. Holes should be made at tha side of each terminal tag. tion followed by two stages of low - frequency resistance coupling is required, all that is large, L in consequence must he made small, and there- necessary is to mount the parts required on a i aseloard fore potentials lviIl be reduced and a less powerful signal and panel to the dimensions of unit C and to substitute result. "I'hat being so, what values of I. and C should for the one in use at the moment. Should this parti- be used in order to obtain selective reception from the cular experiment be made a o. 0002 mfd. fixed condenser principal broadcast stations as they are to -dav ? For loud- speaker results (with an aerial approximately zoft. high) no fewer than four valves should be employed, two of which must be H.N. (filter coupled) amplifiers, in which case the suitable value of the variable condensers (Cl) to cover wavelengths of zoo to 600 metres is o.0003 mfd. maximum. For wavelengths 600 to 2,000 metres (thus including Daventry, Radio -Paris, Hilversum, AVar- saw, etc.) a condenser value as high as o.00r mfd. maximum may be used and is recommended, as such a value stiffens the filter coupling and renders it less liable to shock excitation.

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Fig. 8.- Details of terminals and connector strips. Sizes of holes : A, 1/4 in. B, 7/32 in. and 2 megohms leak should be added to unit B, together with a biasing battery. Why the H.F. Amplifier is Duplicated. Let us now consider briefly whether duplication of the H. F: part of the receiver is justified. It is manifest that a receiver intended for reception of distant B.B.C. and Continental be J broadcast must 3%6 reasonably selective, and especially if one lives under the shadow of the local station. To obtain that result it is necessary to employ some form of filter and to include it preferably in the anode circuit, in which position it can also be made use of for coupling purposes (Fig. 4), [6_S vhich symbolically represents the ordinary tuned -anode cjy.: coupling consisting of a fixed inductance L (tapped __J for neutralising purposes) and a variable condenser C. LA .' As is well known, magnified oscillating potentials are developed across inductance L as a result of signals impressed at A B; the value of these potentials (the amplification factor of the valve and other factors considered) will depend upon the ratio of L to C, the greater L is made the greater thé potentials will be. If C is made Fig 9. -The location of the components on baseboard. A 22

www.americanradiohistory.com WAp®Il®ao JUNE 8th, r927. Wa'1 721 Two -range All Station Receiver. - cult to maintain the set in a stable condition when It may be asked why not make L variable as well as approaching the limits of inductance, owing to the slight C so as to cover the waveband 200 -2,000 metres and select resultant deviation caused from the original value of the for a particular wavelength those values of L and C counter reaction which gave stabilisation at the time of found most suitable for good reception. Theoretically balancing the receiver. it is possible to do so, but it has been the writer's experi- Where, however, the value of L is fixed arid no form ence that where two or more H.F. valves are employed of switching in the oscillatory circuits has been intro-

120.V. 1OO.v. 42.V. H.T-

Fig. 10.- Practical wiring diagram. in a multi -stage amplifier designed to coy -er a wide range duced, then there is no difficulty whatsoever in obtaining of wavelengths (either tuned anode or stabilised tuned a balance and maintaining it indefinitely. It was prin- transformer coupled) and L is made variable, unless cipally owing to contrast in results obtained and to the exceptional precautions are taken, it is extremely diffi- simple manner in which an alternative programme could A 23

- www.americanradiohistory.com Y , -, . - - i r

722 WflmIlgoo JUNE 81h, 1927. WozIica Two -range All Station Receiver. - be made instantly available, if a second H. F. panel was THE FOLLOWING IS A LIST OF PARTS NECESSARY adopted that led the present design. FOR THE CONSTRUCTION OF UNIT C:- Constructional Details. 1 Baseboard of -bin. wood, 6in.xSIin. Having obtained the necessary parts and compared 1 Ebonite panel 14 ¡in. x 6in. x ¡in. them with the working drawings, the process of 1 piece ebonite, R' in. x 3'rin. X ¡in. assembling can be commenced. It may be found most 3 Anti -microphonic Valve holders. convenient to construct the units in the following order, 1 seven- spring Jack, Cat. No. P67. (Igranic Electric Co., Ltd., 147, Queen Victoria Street, London, E.C.4.) C, B, and A, so that upon completion of C and B they 1 four -spring Jack, Cat. No. P68 (Igranic). can he put into service for reception of long -wave stations, 1 2.7 to 1 Transformer (Marconiphone Co., Ltd., 210¡212, whilst unit A is in course of construction. Tottenham Court Road, London, W.1). 1 4 to 1 Transformer ( Marconiphone). I Grid bias battery and plugs, 15 volt. I Fixed condenser 0.0002 mfd. 1 Grid leak, 2 megohms. 1 30 -ohm variable filament rheostat (Igranic Pacent). 2 10-ohm variable filament rheostat without dials (McMichael, Ltd., Hastings House, Norfolk Street, London, W.C.2). 2 Plugs and sockets, marked L.T.-, L.T.+. 4 Terminals, H.T. -, 1, H.T. +2, H.T.+3 (Belling & Lee, Queensway Works, Ponder's End, Middlesex). 1 D.P.D.T. Utility switch, lever pattern (Wilkins & Wright, Ltd., Utility Works, Kenyon Street, Birmingham). 6 Spring terminals (Grafton Electric Co., 54, Grafton Street, London, W.1).

In the list of parts included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should be used in preference to others, these components are mentioned in the article itself. In all

other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed . and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use.

screwing together to form the rigid arrangement, the three valve holders and six spring terminals should be fitted to the platform, also holes drilled in accordance with Fig. 7. The object of the holes is to enable short wire connection to be made between the valve terminals and components mounted below. It should be noted here that the sequence of the valves is as shown in Fig. 7. Immediately below the detector valve on the wood support a 30 -011111 filament rheostat controlling that valve is fixed, and below that the grid condenser is mounted. To Fig. IL- Another view of the L.F. amplifier showing output plugs and method of supporting valve platform. the right of the support (as viewed from back of instrument) a Utility switch controlling the output of the H.F. Having thus decided, the ebonite panel of C measur- units is mounted. For the method of fixing the switch ing f.}in. x 6in. x ¡in. should he drilled as indicated in see Fig. 9, which also shows positions, etc., of trans- the drawing (Fig. 5) and the two jacks and two filament formers. rheostats fitted to it. The panel is then attached to the Having fitted I.. T. and H.T. terminals and screwed base measuring 6in. x 8 in. x ir2ffin. by means of two two clips to the edge of valve platform near the detector 6in. x r }in. aluminium angle brackets. A piece of hard valve for the reception of the grid leak, the unit is ready wood Tin. x in. x -grin. is now attached to the base by for wiring (Fig. to). Do not rush the wiring, and means of one right -hand angle bracket (4in. x rein. wherever possible well space the leads, making aluminium), as indicated in Figs. 6, g, and r r, to form a symmetrical point -to -point rigid connections. The fila- support for one end of the valve platform, the other ment circuits are made with No. 22 tinned copper and end of which is attached to the main ebonite panel by Sistoflex laid snugly to the underside of the valve plat- screws and a piece of wood 31in. x ' in. square. Before form. A 24

www.americanradiohistory.com WipaIl@OT 1' 'T' 81b, 1927. 72,? C URRff-NT lÓPICS

N ews of +.e Wee R S ri ef IRe view

PCJJ SHORT -WAVE STATION. RUNNING COMMENTARIES. linquent was besieged with offers of mar- A slight change has been made in the The running commentaries upon a bull riage and loans from prospective fathers - times at which regular broadcasting is fight broadcast from Madrid do not in -law. Unfortunately for him, enquiries transmitted from Messrs. Philips' experi- appear to be as interesting or exciting were made concerning another of his ven- mental station in Eindhoven. On Thurs- as those of a football match, the Boat tures and these led to the discovery of the day, June 9th, Tuesday, June 14th, and Race, or the Derby, to which we are now fraud. Thursday, June 16th, the station will getting accustomed. If we may judge 0 0 0 0 broadcast from 5 to 8 p.m. G.M.T. from a letter from the Times correspon- AN INTERESTING EXHIBIT. dent in Madrid, the spectacle did not offer 0000 The of valves is. "in itself many chances for vivid word- pictures. The manufacture TESTS. a fascinating study, and many wireless SOUTH AFRICAN BEAM speaker at the microphone, we are told, public has completed critics enthusiasts as well as the general The Marconi Company was one of the best -known bull -fight have doubtless availed theinselVes of the the preliminary tests with the beam and described every phase of the fight, yet opportunity of witnessing - the and Bridgwater which that present stations at Bodmin at one time he warned his listeners actual processes through which a valve for G.P.O. for com- a one they are being erected the the show was such poor that passes in the course of manufacture. For munication with South Africa. During might soon be hearing the snores of the opening of the new wireless depart - speeds of between the these preliminary tests multitude. meut at- Messrs. AVhiteley's valve -making 200 and 250 words per minute have been 0 0 0 0 machinery has been transferred from the maintained with South Africa over long PIGEON FANCIERS AND AERIALS. valve works at Hammersmith, and the com- Osram periods daily. Further tests by Many inconveniences and discomforts, during the first ten days of this month ordinary traffic conditions are pany under such as a rainy summer, are often un- expert operators are working on these now being made. and if these prove satis- to the malign influence illustrating over justly attributed machines throughout the day factory the stations will be handed of wireless, but it is possible that there the intricate building up of Osram valves. General Post Office for the official to the may be some justice in the complaint of 0000 seven days' trial. 0000 pigeon fanciers that their homing birds are sometimes hampered by the number BROADCASTING IN JAPAN. THE ECLIPSE. of aerial wires encountered in their racing Listeners who delight in reaching out The Radio Association has made flights. for distant stations may be interested in arrangements for undertaking the collec- 0 0 0 0 learning the times at which stations iu tion of data in regard to the effect of the ATMOSPHERIC IDIOSYNCRASIES. Japan and Manchuria transmit, and for eclipse on wireless telephony and tele- The report of the Royal Meteorological their benefit we give the following par- graphy. They have issued a specially de- Society's Committee on Atmospherics and ticulars of these stations :- 'l'.okyo. signed log -sheet for this purpose, copies Weather, which contains a mass of useful JOAK, on 375 metres; Osaka, JOBK, on of which are obtainable from the hon. data obtained from observations by Mr. 385 metres ; and Nogoya, JOCK, on 360 sec., Mr. S. Landman. M.A., 22, Laurence R. A. Watson Watt and other observers metres : all transmit daily from 9. a.m. to Vountney Lane, E.C.4. in Europe, tends to show tha'. certain 10 p.m. ; Keijo, .IODK, on. 367 metres, The Siutlt African branch of the Asso- spoken words are more easily disturbed from 9.40 a.m. to 9.30 p.m. ; I-Iarbin, ciation, in conjunction with the Natal than others. Thus, of the two consecutive Manchuria, AOH, on 430 metres. from Astronomical Association and the Inter- words " for his " the disturbance on the 12.15 to 12.45 p.m. and from 7.30 to 9.0 national Union of Scientific Radio Tele- first word was strong, while that on the p.m. daily. These times are local and graphy, is also preparing to use this word " his " was only moderate. are nine hours ahead of G.M.T. 9.0 a.m. opportunity of collecting important wire- 0000 in Japan being midnight by G.M.T. less data. 0 0 0 0 0000 AN INGENIOUS FRAUD. THE N.B.C. EXTENDS ITS NETWORK. The French wireless operator who was WEATHER STATION IN GREENLAND The National Broadcasting Company of recently reported to have inherited a large Scientific meteorology is daily ex- America is rapidly extending the sphere fortune is doubtless repenting at leisure tending ; a permanent weather station of its activities and has now acquired the his wily scheme for obtaining almost un- is to be established in Greenland well-known station AVOW, in Omaha, limited credit, but it must be admitted by Dr. W. H. Hobbs, Professor of Gen - Nebraska, owned and operated by the he probably had a good tinte while it logy at the University of Michigan, and Woodmen of the World Life Insurance lasted. director of the university's Greenland Association. This station, which trans- Being anxious to infuse some excitement expedition. Dr. Hobbs expects to begin mits on a wavelength of 526 metres, will into a possibly dull and monotonous life, transmitting weather reports on short afford a large number of listeners in the he conceived the idea of sending out a waves this month. The Rumanian Middle West an, opportunity of listening message that he had come into a fortune Greenland expedition, headed by Dr. in comfort to the N.B.C. programmes in- of some 25 million dollars. The message Dumbrava. will also establish a liase at stead of being compelled to reach out for was picked up in mid- Atlantic by a ship AnmagsaIik, in South -East Greenland. the more distant stations controlled by coming to Europe and in due course re- " Segcondary depression " will therefore the company. transmitted to Rochefort, where the de- stand do chance of hieing overlooked. A 25

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721 Wgmgllsog Warllcl. JUNE 8th, 192j.

Amateur Stations in Australia and New TASMANIA. Zealand. 7BT E. C. Sheidrick 13, Richards Ave., Lamp TRANSMITTERS' NOTES teston. (Continued from page 686 of our issue of 7HL H. F. Lovett, 14, Summerhill Rd., West AND QUERIES. June 1st.) Hobart. WESTERN AUSTRALIA. 7M$ E. E. Cooper, Edgeley House, Youngtown. 6DH D. C. Hardisty, 2. Duncan St., Victoria Park. 7RS R. S. Hope, 210, George St., Launceston. 6GL G. A. Lorden, :30, Thomas St., Kest Perth. Nationality Prefixes. (Change of address.) In view of the fact that many amateur 6HR (not CHE) H. E. Cox, Marine Terrace West, NEW ZEALAND. Gerald ton. (Correction.) 1AN H. B. M. Arthur, 12, Clarence St., Berns transmitters have their call signs pre- 6JJ T. J. Jewell, Leithfield St., Victoria Park. Bay, Auckland. (Change of address.) 6,31. J. L. White, ceded by the nationality prefix G, GC. or Brookiands, via Grass Valley. 1AO R. G. White, 123, Grafton Rd., Auckland. GW, as the case may be, 6KM A. Saar. Post Office Building, Eucla. printed on their 6IiX H. T. Simmons, 75, Nicholson Rd., Subiaco. ^BB C. Ward, 63, Murray St., Relbum, Wellington. letter paper as well as on their QSL 5VP Victoria Park Radio Club (O. E. Kernick), (Corrected address.) cards, it may be advisable to remind them 70, Mackie St., Victoria Park. 3XB J. M. Bingham, 24, Carrington St., Christ- that according to the regulations laid 6WP W. R. I'hipps, 83, Carnarvon St., Victoria Pk. church. down by the G.Y.O. the use of the nationality prefix is allowed only when experiments are being conducted with stations abroad. We mention this matter as we have recently heard of cases in which amateurs using the nationality prefix before 3- letter call -signs or not being licensed for communication with foreign stations have been requested by the authorities to dis- continue the use of the prefix. New Call Signs and Stations Identified. 5XQ (ex YBI'B) J. Cyril Adams, Towerhill, Newton Street, Greenock, N.B. Transmits on 23.45 and 90 metres. AI 2AJ Lient. E. J. H. Moppett, " A " Cavalry Signal Troop, Roorkee, U.P., Lidia. Transmits on :3e and 45 metres. EB 9DP L. de ltruyn, 79 Ave. des Eglantiers, Antwerp. FM 8MC Dr. C. Vevre, 83 Ave. du Général Moinier, Casablanca, Morocco. 6 DP (ex 2 BQK) W. P. Dolphin, 53, Higham Road, Tottenham, N.17. Transmits on 23, 43, 90 and 180 -200 metres. 6 PP (ex 2 BZC) M. W. Pilpel, 38, Purley Avenue, Cricklewood, N.W.2. Transmits on 45 metres and will welcome reports from listeners outside 100 miles radius. 2 AZP L. Sanderson, 39, Bonham Road, Brixton 5 XQ. A new transmitting station in Scotland owned and operated by Mr. J. Cyril Hill, S.%V.2. Adams, Towerhill, Newton Street, Greenock.

A SIMPLE TEST FOR OVERLOADING. .14ANY an amateur. possessing no milliammeter, is to a higher value and takes longer to disperse, and, in left in doubt whether to blame ltis loud- speaker, consequence, the distortion produced is much more notice- his receiver or his valves when quality of repro- able. If, on the other hand, no overloading is taking ( uction is poor. Since the most tisual cause of poor place, the grid of the valve never becomes positive and quality lies in the overloading of the last valve, it becomes does not acquire a charge, so that the change of grid -leak necessary to apply some test to discover whether the value will make no difference whatever to the quality. signals applied to its grid are greater than it can handle If, then, it is found that this change of grid -leak without has distortion. The usual test of connecting a milli - an adverse effect upon the quality, one may quite safely ammeter in series with the loud- speaker and making infer that the last valve is being overloaded with signals, volume and grid -bias adjustments until the needle does and that it is necessary either to he content with not a smaller " kick " on loud signals is naturally not possible volume or to increase largely the high- tension voltage and When no milliammeter is to hand. There is, however, grid -bias on this valve. Where no change in quality another fairly satisfactory test that can readily be applied follows on the use of the high resistance leak, it is neces- when resistance or choke coupling is in use. sary to look elsewhere for the cause of inferior reproduction. Effect of Increasing Grid Leak Resistance. By a slightly greater temporary alteration to the If the grid -leak of the last valve is removed and is receiver, this same test can also be applied where the last replaced by one of very high resistance it will be found valve is coupled by means of a transformer. In this that any distortion due to overloading will be very con- case it is necessary to insert a condenser of about o.or siderably increased. This is so because if the valve is mfd. capacity between the grid of the valve and the being given too large a voltage input there are moments secondary of the transformer. A grid -leak holder is when the grid becomes positive, and (luring that time it then connected between the grid of the valve and the grid - collects electrons as they stream past it to the plate. bias battery and the test applied by inserting in the The negative charge so produced can leak away reason- holder, alternately, leaks of low and high resistance. ably quickly through a leak of low resistance so that The effects that may be observed and the conclusions to the distorting effect is not outrageously great, but if a he drawn from them are then exactly the same as those very high resistance leak is substituted this charge grows already detailed. A. L. DI. S.

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WATigmo JL-_l'r 81k, 1927. Walla 725

A Section Mainly for the New Reader.

of valves, which with a modern re- from the disadvantage that since the ceiver is likely to be heavy. condensers are in series, each must Fig. r (a ) represents what is now be twice the size of the one con- probably the standard circuit for denser used in the circuit shown in choke feed and has several advan- Fig. r to obtain the same tonal out- SOLDERIN3 NOT NECESSARY. tages over other arrangements. put characteristics. l' is a mistake to imagine that the It should be noted that the loud- o000 only way of obtaining a satisfac- speaker is at earth potential, and if tory connection is by soldering ; this is at any appreciable distance from the HOWLING DUE TO MICROPHONIC not the case. and for all practical pur- set only one extension lead is neces- VALVES. poses a wire fitted under a terminal sary if an earth connection can be T often happens in loud- speaker head or nut makes a junction of made at the loud- speaker. The A. sets that when one of the valves is equally low resistance, provided that larger the value of both the choke given a slight jar a low ringing note the surfaces are first cleaned with and the condenser, the lower the fre- is emitted by the loud- speaker. The emery paper or by scraping. It is as quency at which " cut off " or a sound from the loud- speaker reacts on well to have as large an area of metal diminution of output sets in. Good the valve and a continuous howl may in contact as possible, so the end of average values for first -class results be set up. 'Phis trouble, which is due the wire should be bent into an eye - are zo henries and 4 mfds. respec- to the vibrating of the electrodes, preferably with the aid of a pair of tively, although 2 mfds. is generally usually occurs in the detector or per- round -nosed pliers. sufficient. haps in the first L.F. stage. The Soldering has probably gained its The circuit shown in Fig. r (b) simplest and most obvious remedy is present popularity because a number may be used when it is desired to to have the set and loud-speaker in of connections may be made more different rooms. This is frequently quickly by this method than by the inconvenient, however, and another other alternative -a statement which remedy is to use a less microphonic, the beginner in the art may doubt, but valve in the offending stage. It is one which is nevertheless true. Pro- often our luck to find that our favour- vided that soldered joints are pro- ite detector valve is particularly perly made, they have an undoubted microphonic, and we are unwilling to advantage from the point of view of replace it by another valve, which, permanency. but a so- called " dry though less microphonic, is also less joint " is likely to be a source of sensitive. The remaining expedient trouble, and those who have not ac- is to surround the valve by some sort quired the art may do well to use of sound -proof enclosure ; much can screws and nuts or terminals, remem- be accomplished with a wrapping of bering that connections made in this cotton -wool and a valve box. The so- way should be cleaned and tightened called non -microphonic valve- holders up periodically. are not usually very effective by them- 000 selves, but may he very effective if the valves are artificially weighted THE CHOKE CONDENSER FEED by attaching heavy pieces of metal Fig. 1.-Alternative output filter con- CIRCUIT, nections. to them. This weighting may be P II 'HERE are certain undoubted ad- effected by fixing some sort of lead IL vantages in using a choke -con- isolate the loud- speaker from the set collar round the valve base ; this denser output circuit, the chief of entirely ; for example, when it is of weighting should he at least a quar-

which is that the windings of the-loud- a type with an electromagnetic field ter of a pound, hut, of course, not too - speaker are no longer subjected to the system which may be fed from house much for the springs in the valve - steady anode current of the last valve service mains. This circuit suffers holder to support. A 27

Af.,1:.? www.americanradiohistory.com Wflpe®EtT 726 JUNE stia, 1927. InOO IlC JACKS ON METAL PANELS. short circuit of the high- tension bat- fitted wherever this course is possible, AS has been previously stated in tery ; this disadvantage, however, is and in the case of such components these columns, the constructor of not peculiar to this special form of as L.F. transformers, filament rheo- a receiver with a metal panel must connection, the risk being present stats and variable condensers, etc., bear in mind the necessity of insulating with other arrangements. To reduce which are often provided with small those parts of components attached to the possibility of trouble a condenser terminals, it is a good plan to re- it which are not at the same potential. of good make should be obtained, move the heads, and to substitute two By taking a little care, however, and and it may be advisable to test it be- nuts. fore applying the battery voltage. Similar precautions should he ob- oaoo, served in dealing with bolts and nuts FLASHLAMP FUSES. which do not actually carry current, hut merely 1( 7 THEN bright -emitter valves, serve to hold the various components in position. \y / consuming about 0.75 amp., were in general use, there was com- 0000 plete justification for the frequent H.F. TRANSFORMER CONSTRUCTION recommendation that a flashlamp bulb .FAILURES with receivers using the should be inserted in the high- tension type of H.F. transformer having lead in order that it might act as a space -wound primary and neutralising safety fuse. Nowadays, however, windings are not infrequently traced to when few valves consume more than partial or complete short circuits of 0.25 amp., reliance on such a device is one of the windings. This is often apt to he dangerous, as the average due to contact between the wire and 3- or 4 -volt lamp will often pass as one of the terminal screws mounted on much as o.5 amp. for a considerable the spacing strips. It is important period. Before fitting such a fuse it is that each wire should make contact Fig. 2. -An " earth return" output as well to assure oneself that it will only with its appropriate terminal circuit. " blow'' at a lower current than that screws, and, moreover, it should be making one or two minor circuit consumed by the valves actually in emphasised that the silk covering of use. the alterations, it is possible to avoid the wire is not sufficient insulation ; 0000 air spacing is fitting of a number of insulating necessary. SOAP AND SECCOTINE. The bushes which would ordinarily be re- sketch given in Fig. 3 (A) has quired. ROM time to time experimenters been made from a transformer offered The majority of "on -off" switches may require to make parts which for sale as suitable for the " Every- man ; on the market are designed for have afterwards to be stuck together Four " receiver it shows what is distinctly mounting on an ebonite panel, while with Seccotine and which require lubri- the wrong method of con - structión. the output terminals or jack for con- cation during the making. An instance Sketch (B) indicates the amount of nection to telephones or loud -speaker of this occurs with the small conical spacing which should he allowed between will also need bushings if conven- washers required to attach a paper the winding and terminal screw. tional practice is followed. fit- diaphragm to a reed or similar The Although ting of these may be avoided if the mechanism. These small washers a defective transformer increasingly popular choke- condenser may be punched out or spun, but in filter output circuit is adopted in con- either case lubrication will be neces- junction with a jack, which, to save sary. the mounting of a switch, may be The natural inclination would he connected in such a way that the valve to use a heavy oil for the purpose, filaments are automatically lighted but if soap he used instead it will when the plug is inserted. The ar- be found that the parts twill, after a good rinsing rangement is shown in Fig. 2, from in cold water, take Sec - cotine quite well ; whereas if oil had which it will be seen that the ' ` speech current " circuit from the plate of been employed a special solvent, such the output valve is completed through as very good petrol or benzine, would the usual large condenser, the loud- be required to render the surfaces sufficiently Fig. 3.- Showing correct (A) and incorrect speaker (the plug of which picks up free of grease to allow a (II) relative positions for windings and contact reliable joint to be made. terminal screws on an H.F. transformer. with the longer spring), and 0000 the earthed frame of the jack, which may operate passably when it is per- is in metallic contact with the plug BUILDING A PORTABLE. fectly dry, it is almost certain that a shank. The proper jack for this pur- PORTABLE receivers, particularly fault of the nature under discussion pose is sold as a " single open, fila- those to be carried in a car, are will manifest itself when the atmo ment control " type. always subjected to a good deal of sphere is damp. This is because a A consideration of the circuit will vibration, and special precautions considerable difference of H.F. poten- show that a breakdown in the insula- must he taken to prevent the loosening tial exists across adjacent ends of the tion of the condenser will result in a of connections. A lock -nut should he parallel windings.

A 23

www.americanradiohistory.com JU,VE Stlr, r927. Wpisho 727 WopIlcol MEASURING THE OUTPUT OF An improved method of obtaining Experience shows, ' however, that ELIMINATORS. an indication of the eliminator's per- modern valves are extremely regular, 'jl"HE class of voltmeter likely to be formance is to place a milliammeter and a check is always available by found in the possession of a in the anode circuit of the last valve. the substitution of the valve by an- wireless amateur will have too low a With adequate filament current and a other having the sanie nominal char- sensitivity figure (in ohms internal re- known value of negative bias the acteristics. sistance per volt of full scale reading) usual family of static curves of the There is, on the other hand, a very to give a true idea of the voltage type of valve in use may be used to good point to be mentioned in favour produced by a battery eliminator, translate anode current into anode of this arrangement, and that is that whether such be a small generating volts. As a refinement, allowance the milliammeter, if left in the anode machine, a rectifying valve or valves, may be made for the voltage drop in circuit, serves as a distortion indica- or merely a potentiometer across the windings of the loud- speaker tor. The pointer of the instrument D.C. mains. directly connected in the anode cir- should at all times he steady, where- Such an instrument will probably cuit, since the resistance of the instru- as if the valve is being overloaded require at least 5 milliamperes to give ment is known, as is the current the instrument will waver in sym- a reliable reading, and the additional passing through it. pathy with the loud passages in the load thrown upon the eliminator by It may be said that this method is transmission, thus indicating that a the application of the meter will likely to be unreliable owing to the reduction of input to the valve or cause a serious drop in the output fact that the performance of the better working conditions are de- volts. valve is concerned in the reading. sirable.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 72 (a). -A D.C. High tension Battery Eliminator. (Concluded from last week's issue.) The present series of diagrams is intended to show progressively, and in an easily understandable manner, the various points to which special attention should be paid in the design of typical wireless instruments, and at the sarne time to assist the beginner in mastering the art of reading circuit diagrams. The simple H.T. eliminator shown below is intended to operate on direct current supplies of from 200 -240 volts, and will give good results, except where there is a heavy "ripple"- on the mains current.

:t1-.-:!-`: _ - 3 Lt= Lt L2 Y L-.. Y C3 X ,n +i +2 Z+¡n +2 Z+ Z-o C 4 Ci2 cit C2 Ct C2 Ct á_ Q+ ¢_ +2 Y t g t __ 2 2

C-1 3 C4 C3 ; (4) (5) (6)

An extra H.T. tapping is added at Y. Extra smoothing chokes, L2 and L3, are When the tositive main is earthed, the This section is shunted by an additional inserted in each output lead. smoothing choke should be inserted in condenser, C4. the " live " negative lead.

r HE position for the second H.T. " noisy," or possibly when the tion, will avoid this; but there will tapping is determined in the same receiver employs an elaborate circuit ; still be a difference of potential if a manner as is the first, while the shunt- their inductances should be as high second tapping is used. In cases ing condenser C, may have the same as is possible, compatible with suffi- where the positive main is earthed it capacity as C3. As the + 2 terminal cient current -carrying capacity and a is almost essential to use a coupled will probably supply current to the suitably low ohmic resistance. aerial circuit, as by doing so the fila- output valve, which generally requires The circuit shown at (6) is suitable ments of the valves may be earthed both heavier current and greater volt- evhen the positive main lead is only at one point. This coupled cir- age than the other, the tapping point earthed. The arrangement as shown cuit is highly recommended for any y will be nearer the positive end of will result in a difference of potential receiver working from D.C. mains, the voltage -dividing resistance to between the " mains earth" and the whether positive or negative is compensate for the voltage drop. positive tapping, while the connection earthed. If it is not adopted, a The addition of extra chokes L., of the output taps Y to the positive large condenser of high insulation re- and L3, as shown in (5), will only be end of the resistor, with a correspond- sistance should be inserted in the earth necessary when the mains are ing movement of the negative connec- lead from the set. A 29 i

611446.,; www.americanradiohistory.com ;28 Wflmhoz Walt]) JUNE Si k, 2-927.

NUIP C I RIO y TUS

A Review of the Latest Products of the Manufacturers.

CHAKOPHONE COILS. tains also The ll'ir,1,,? 11 "nr1r1 handbook " ALL -WOOD " LOUD- SPEAKERS. The coils required for constructing The giving full constructional details. There are many listeners who prefer to Wireless World " Everyman Four " re- 0000 ceiver use a loud- speaker fitted with a wooden are being produced by manufac- flare, turers in increasing quantities. A MULTI- CONTACT PLUG and a further development is to be The found in the All -Wood loud- Eagle Engineering Co., Ltd., Eagle CONNECTOR. " " speakers and horns manufactured by Walker Bros., Works, Warwick, are now making these In the case of a receiving set employ- Ltd., coils, and ail opportunity has been taken St. Joseph's Works, Brantley, ing several valves there are as a rule no Guildford, in which the neck, as well as of testing them for the purpose of endors- fewer than six battery connections to be ing their performance. the flare, is built of wood. The aim is, made. Owing to the trouble involved in of course, Even to the manufacturer many to reduce the resonances providing all the necessary leads and con- present in the metal type, and from the errors are likely to occur in building necting them up on to the terminals, with these coils, such as failing pick results obtained it is apparent that this to up the danger, perhaps, of joining the H.T. has been achieved. all the strands of the Litzendraht wire, battery to the L.T. terminals, many sets the use of inferior wire or formers, badly Apart from the acoustic merit of the constructed spacers for the primary, and " All -Wood " horn, these loud -speakers poor insulation between primary and are cleverly constructed, being built up secondary occurring from thin pieces of wood to produce the under the terminal required screws. All of these points were care- contour. Various models are fully examined, and, combined available, including the upright swan with a neck and the performance test, the Chakophone coils curved " U," each type can be recommended for building the being available in several sizes. It is understood that the manufacturers en- listed the assistance of Messrs. S. G. Brown, Ltd., when developing the designs, and several of the bigger models are particularly suited for use with the Brown movement, while the Lissenola, New multi-way plug connector in which T.M.C., Amplion, contact is made between the circle of bars Nesper, and other units and springs may be fitted. are built with leads instead of battery terminals. A further improvement is to use a multi -way plug- connector, and a connector of original design has recently been produced by the London Instrument Co., Ltd., 51A, Bridge Street, Cambridge. The connector makes provision for eight leads, the wires being joined to the plug and suitably labelled. Instead of using pin connectors, which are difficult to engage and render the withdrawal of the connector difficult, eight springs are employed, assembled round the inside face of an ebonite cylinder. These engage on eight bars secured to the walls of an ebonite rod. A particularly smooth action is obtained, with a liberal area Chakophone coils with constructional of contact, making an entirely reliable booklet for building " The Wireless electrical connection. Three specimen All- wood " loud-speaker World" Everyman Four receiver. Brackets are provided for baseboard horns. mounting, or, by means of bolts and " Everyman Four " receiver. As ell as screws, the connector can be secured to In view of the considerable work in- being electrically correct, the coils are the panel. A key -way prevents the plug volved in the manufacture, and the par- well finished, and, with the green silk - from being incorrectly inserted in the ticularly high -class finish, these horns are covered Litzendraht wire, are of particu- socket. The metal ring of the socket is inexpensive, and, together with a high - larly good appearance. nickel- plated, and the head of the plug grade movement, produce a reliable loud- 'I'he coils are suitably packed for is of polished ebonite, with the wires pass- speaker of pleasing appearance for a transit in a cardboard carton, which con- ing out at the side. moderate cost.

A 30

www.americanradiohistory.com Aama WEpSIlWO JUNE 811a, 1927. WopIld ,-9 Xperîrnen± ers otebookJ

By "EMPIRICIST." The Layout of a Wireless

Receiver. shown in Fig. r. This is a perfectly straight -

" )l forward valve- detector embodying reaction. (a) High= frequency Circuits. ` Referring to the figure, the various leads ` which connect up the components can be classi- E1PLRIME\TERS who have been accustomed fied first into two broad categories. Some of the from time to time to make up wireless receivers leads are entirely " dead," and the manner of wir- in accordance with constructional articles pub- ing up the receiver cannot be in any way* affected lished in the technical Press must very often have discovered by their disposition; other leads, however, are " live," for themselves by bitter experience the lamentable results by which we mean that they carry high- frequency cur- that follow from comparatively slight variations in the lay- rents or potentials, and in consequence are liable to affect out and wiring. The fact is, of course, that in designing a neighbouring leads and circuits by electromagnetic or receiver, especially one which embodies neutralised high - electrostatic induction. frequency circuits, all sorts of details have to be con- In considering the general layout of this or any other sidered which are very difficult to deal with in construc- receiver we therefore adopt as a first principle the neces- tional articles, as there is so much else which must be sity of taking care of the " live " leads and allowing the described. Readers of such articles, therefore, very " dead " ones to look after themselves. Thus, for ex- seldom arrive at the " true inwardness " of the design, ample, if it is possible, by running the filament supply but have to take the result in faith, and, as often as not, round the set in any manner however awkward, to enable pay the penalty for any attempted deviation from the high -frequency circuits to be wired up in a more standard. satisfactory manner, we should naturally adopt this The present article is an attempt to lay down some course. general principles of design in which the writer personally Classification of Leads. and most of which are matters of general experi- believes, Considering further the question of " live " leads we ence. It is not to be contended that a receiver is wrong may classify these according to whether they carry current if they are not followed out, nor right if they are, but it or potential, or both. :actually, of course, the effects can be said with certainty that they formulate a " safety will be mixed up in all cases, but there are some leads in and may lead to the avoidance of a consider- first " policy which the electrostatic effect is small enough to be negli- number of more or less well- known " snags." able gible and the electromagnetic effect quite considerable. It will be easier to consider this matter by taking first and vice versa. In other leads, both the electrostatic and all, as a particular case, a simple receiving circuit as of electromagnetic effects are present in full measure. We may make a further classification of both these types of lead according as to whether they are connected to a resonant or a non -resonant circuit, the necessity for such classification being due to the fact that the former require far more critical consideration in respect of the layout of receiver. In Fig. r -the leads marked [r] carry high- frequency current and are thus liable to set up an electromagnetic field, which interacts with other circuits ; on the other hand, inasmuch as they are connected together to the filament of the valve, the only high- frequency voltage at any point on them will be that due to the volt drop in the short length of wire constituting the leads themselves. For the purposes of our classification we thus describe these as " current leads." Since they are also embodied in a resonant circuit, this fact must be borne in mini Fig 1.- Classification of leads In a high- frequency circuit. (1) H.F. in classification, and we can thus describe them in an current resonant leads; (2) H.F. potential resonant leads; (3) H.F. current non-resonant leads; (4) H.F. potential non -resonant leads. abbreviated form as " c. r." (current resonant) leads. A 3r

www.americanradiohistory.com Wtpdsgo 730 Woífki JUNE 8th, 1927. The Experimenter's Notebook. - The consideration of p.r. leads (including c.p.r.) Reference [2] indicates a lead which carries practically more straightforward. Here we have to consider only no high -frequency current, inasmuch as it is connected to the electrostatic field, which is set up by a piece of wire the " live end " of the resonant circuit it ]will radiate a to which a high -frequency voltage is applied, and this strong electrostatic field. This may he described as a field is controlled simply by the length and thickness of " potential lead," and since it is connected to a resonant the wire concerned. Such leads must be kept as short as circuit we may denote it as. a " p.r." (potential resonant) possible, and the disposition of the various components lead. must be arranged with this end in view. It is amazing The references [r, 2] which apply to two further leads what can be done in this direction by merely careful indicate that the latter carry both current and potential ; thought, and it is equally so in respect of the greatly these may be denoted as " c.p.r." leads by analogy with improved behaviour of a complicated set. the two former cases. The thickness of p.r. leads in the average sets is also The leads connected to non -resonant circuits may he very often excessive, inasmuch as there is a kind of dealt with in a similar manner. Thus the leads [3] are vicious circle, the increase of the length of such leads c.n." (current non -resonant),. and those designated [3, 4] necessitating the use of thicker wire. This gives rise to are " c.p.n." (current potential non -resonant) leads. In a serious electrostatic field, with the possibility of induc- the figure under consideration there is no p.n. lead, but tion effects with other parts of the circuit. It seems from the foregoing such a classification is quite ohrious. really quite unnecessary to go beyond No. 20 S.W.G. In order to give further consideration to this classification and to consider its P n.I effects as regards the layout I--_ f of a typical receiver, a three - stage neutrodyne is shown in I c.P.n.I ESE Fig. 2, and the various 16. designations as above de- e scribed are narked against e bo o0 the respective leads. It will .

he noted in passing that there I c.n. áre two leads classified as a` p.n.: this is not strictly MI III correct inasmuch as a small ---I{ high -frequency current flows O H.T o through the neutralising condensers, but the electromag- Fig. 2. -Tbree -stage neutralised H .F. amplifier. Current flowing in neutralising circuits is so small as netic effect on this current to be negligible -leads are thus marked p.n. under practical conditions is so small as to be negligible. wire for interconnections of this kind if reasonable care is We may now proceed to consider what should be done exercised in arranging the components. in laying out a set of this type, having regard to the The problem of c.p.r. leads in themselves is difficult above classification, and for this purpose we may first inasmuch as they require careful treatment from both take the case of c.r. leads (including c.p.r.). These, as points of view, but there is no need to go to pedantic will be seen from the figure, constitute the interconnec- extremes in the matter of leads connecting a condenser to tions between tuning coils and their condensers. its coil, inasmuch as the stator of the condenser (which is normally Wiring Resonant Circuits. connected to the live side) has a considerable area, and must necessarily have a tendency towards Very frequently the coils in a neutrodyne, such as that induction effects which is perhaps greater than any reason- illustrated, are most carefully arranged so as not to be able wiring could give. electromagnetically coupled to each other, but it is often In considering the non- resonant leads the same prin- found that if the connecting leads to the coils and con- ciples apply to a large extent with the exception that in densers are traced out they constitute a loop of quite con- this case correct spacing is not so critical. Trouble will siderable area, and the presence of loops in each of the arise when a c.n. lead, attached, say, to the plate of the three circuits may give rise to interaction which will up- detector valve, is led round in the neighbourhood of the set the stability of the instrument. We may thus lay first circuit of a set like that considered in Fig. 2, but down as a first maxim : " Arrange c.r. leads in each there is no reason why this should be done, the obvious resonant circuit so that the area of the loop formed by course being the by- passing of the high- frequency current them is the smallest possible." by means of a condenser direct to the filament. If such In other words, " connect each condenser directly to a condenser is connected across the telephones or across the terminals of the tuning coil and keep the c.r. leads the primary of a low- frequency transformer, it has a close to each other." The circuits to grid to filament very great tendency to cause interaction with other c.n. respectively are then made by tapping these direct con- circuits, and this is not entirely taken care of by nections at any convenient point, and connecting them the customary large condenser across the high- tension direct to their destination. battery.

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INTERNATIONAL , ASPECTS BROADCASTING. Important Functions of Broadcasting Neglected by the B.B.C. By G. ROLLAND WILLANS. .444 N April ist and April 29th, 1925, the writer was average listener, who if not to -day will very shortly Le given the opportunity of outlining his views on cer- the average citizen, may well wonder why he is compelled tain aspects of British broadcasting, and on the to keep, feed and house a barkless dog. work of the International Broadcasting Bureau. At It is not intended merely to criticise the efforts of the the time of writing these articles the eventual control British Broadcasting Corporation in so far as these are and policy of what was then the British Broadcasting directed towards providing education and amusement for Company was assuming considerable importance, and it the public at large, but also to emphasise that their duties was then suggested that the future of broadcasting was are not merely parochial, and that their ultimate goal is the most important question of all, as it could lie con- not summed' tip in the announcement, " London will now strued in the light of a national institution. Emphasis take a little music." was laid in the first place on the necessity for providing A National Trust. adequate funds for the operation, maintenance. and, most Again referring to the writers previous comments on all, the development of the broadcasting important of the subject, British broadcasting has note, in fact machine and as in the course of time the writer itself, become something closely approximating to a nationa. seen no reason to change his views he may perhaps be has trust. Freed from commercial entanglements it is the permitted to quote a paragraph of the article in question more able to develop a policy directed towards the fur- what appears to him to be the with a view to emphasising thering of Imperial prestige and Imperial interests and of British broadcasting as it is to -day. lamentable failure to support and strengthen that vast concourse of men The reads as follows paragraph :- and women tvho by year carry with them to the wider issues affecting broadcasting year " The control of uttermost ends of the globe our national ideals. It would might well be considered as a national trust, and as such surely be better, now that our message can be accurately to the ablest speakers and doers of our should appeal transmitted, to concentrate on widening the boundaries of own or any future generation. Apart from this the door transmission rather than to expend technical energy in the any form of private or public should be left open to direction of making and demonstrating apparatus by which, under guarantees of a high standard enterprise, which, in the opinion of the Corporation, this message . of artistic and technical performance. would at the sanie can hest be received point which can vtell be left to the time the ultimate charge on the public to reason- -a reduce manufacturer. As to the educational and amusement able proportions." items, there is no reason to suppose that either as a com- Once more, as the Editor has recently pointed out in pany or as a corporation the I roacicasting authorities these columns, it has been left to our friends in Holland can afford to neglect the specialists in these two different to blaze the trail of development for us. They have lines of activity. It is not pertinent to the issue to en- shown that through their intervention the programmes of quire why the average man is willing to pay more to be the British Broadcasting Corporation, the Voice of Eng- amused than -to be educated, but it is certain that the land, can be flung to the most distant corners of the specialist in the art of amusement is able to command a Empire, and have emphasised for us the true significance markedly higher figure, and is not nearly so likely to be of broadcasting. impressed with the argument that it is an exceeding great An Opportunity Missed. privilege to be allowed to broadcast. The name of the To quote The Evening A7 c7c s of May 23rd : " The pedagogue can never be said to he a household word to the B.B.C., while welcoming the Dutch experiments, are sanie extent as is that of the organiser of prize fights, the taking no active part in them," and, to quote again, producer of successful musical comedy shows, or films with " It would be a wonderful thing if the Prime Minister's an international reputation ; and the ownership of a lecture voice were successfully rebroadcast in Australia and South hall or theatre of unlimited capacity does not necessarily Africa." It would be wonderful, indeed, if British imply the affinity to educate or amuse to a " full house " enterprise were responsible, but, with all clue respect to day in and day out. the British Broadcasting Corporation and our friends in In the particular article referred to the writer raised Holland, there is nothing wonderful, from a technical the following question : " Upon what will the future of point of view, in the achievement itself, which is merely broadcasting as a national institution depend ? " and has the ordinary and logical development of the art-a de- endeavoured to answer this question by saying, " Utter velopment which we in England have, as usual, been too confidence in those directly responsible for its develop- slow to take advantage of. It may he economy, though ment." probably parsimony is the better word, to allow others It can now safely be said that broadcasting has become to take the initial step at their own expense, but the an integral part of our national life, and that lack of

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International Aspects of Broadcasting. - stations is interfered with to a marked extent, not only vision, monopoly, or any other form of hindrance to its by German main stations but also by their relays. It obvious and logical development will eventually be swept is childish to disregard the importance of broadcasting as away by the tide of public opinion. a means of propaganda, and obvious that in our inter- To quote again, this time front the writer's article of national broadcasting relationships we cannot afford to April 29th, 1925: " Owing no doubt to the basis upon ignore the importance of holding our own and of being which our own services are founded, we do not appear represented on international conferences of this order by as vet to he sufficiently alive to the importance of broad- individuals who are really capable of safeguarding our casting as a vehicle for all forms of propaganda. Cer- interests. tain Continental countries, on the other hand, are actively The progress of civilisation, with all that it implies, aware of this fact, and will undoubtedly endeavour to depends upon friendly intercourse between nations and make use of the Bureau to further the commercial and individuals. Broadcasting, to be followed by television, other interests of their own national." It is interesting having no regard for time or distance, can be of incalcu- to note that, on the ordinary broadcast b:mas, German lable benefit to the human race, but in so far as we are stations appear to be most frequently received during human, in appreciating its possibilities, we must not as daylight hours and at night at excellent quality and a nation allow ourselves to lose sight of its importance volume, so much so that reception from other Continental to our national existence.

Portable Transmitter at Mill Hill. account of his own set, which had taken The new portable transmitter of the him several months to design and was Goldei:s Green and Hendon Radio Society intended to be the " last word." The was tried out, with remarkable success NEWS FROM set consists of a detector and three L.F. during a recent field day at Mill Hill. stages (two resistance and one trans- The set consists of a Hartley oscillator em- THE CLUBS.So former). Many questions were asked and bodying two L.S.5's in parallel, to which the lecturer's opinion was sought on the is coupled a resistance -capacity amplifier respective merits of resistance, choke and with the microphone across the grid and transformer coupling. He replied that recommended; the selectivity curve with filament of a valve ; each system had its uses, though " high mu " this H.F. amplifiers has comparatively he ob- valve is fed into a D.E.5 acting as a straight jected to the latest high value resistance grid sides and a leak. The high tension is supplied from flat top, whereas reaction coupling. gives a sharp peak to the curve. The ten 60 -volts " C.A.V. " accumulators. lion. secretary : Mr. G. S. Sessions, 23, lecture was followed by an animated dis- Grasmere Road, N.10. A working schedule had been arranged cussion. with the following on 45 : 0000 stations metres Visitors are welcomed 5CD, Nottingham; 5TZ, Isle of Wight; warmly to the Demonstrating Transformer Coupling. Society's meetings, pai t iavlars 6FR, Birmingham; 6MT.7, of which Ireland; 2IT. can be obtained from What was described as " astoundingly Ireland; and 6NZ, Glasgow. Each of the loon. secretary, Mi. H. T. I'. Gee, 51 -52, Chancery lane, fine reproduction " was obtained by these stations sent an excellent report. London, \V.C.2. means of a demonstration receiver reception from 5CD, 5TZ 2IT though and 0 0 0 0 operated by a representative of Messrs. was bad owing to jamming. During the Ferranti, Ltd., The "Ideal" Receiver. at a meeting of the afternoon 21.0's programme was received Hounslow Wireless Society on May 24th. and relayed to the Isle of Wight with Mr. 1'. K. Turner (of Messrs. Graham - The lecturer dealt with the questions con- great success. Amplion, Ltd.) gave an able lecture on nected with low -frequency amplification Among the party were representatives the design of broadcast receivers when he when using iron -cored transformers. He of the Muswell 11111 and District Radio addressed members of the Muswell Hill clearly explained the desirability and'District of using Society. 0000 Radio Society on May 25th. a transformer with a high primary induc- The ideal to be sought for in wireless tance, especially in the :Mode circuit of a D.F. Field Day. design, said the lecturer. was the produc- bight impedance detector valve, and tion of The next field of Golders a receiver which when heard in pointed out the consequent Necessity of day the Green an room, and Hendon Radio Society will be held adjoining would give sound in- a low ratio and a considerable quantity on distinguishable from the original. It was of suitable ii-oit in the magnetic circuit. near Elstree June 19th when some in- an teresting D.F. tests will be carried out. advantage to obtain reception as loud The demonstration set incorporated a as possible when seeking true reproduc- Hon. secretary : Lt. -Col. 11. A. Scarlett, valve detector followed by two L.F. D.S.O., 357a, Finchley Road, N.W.3. tion, for when transmission conies in at amplifying valves coupled by two A.F.3 half its original strength the ear does not type transformers. The volume obtain- receive it as such, and reproduction is not able was far too great and had to be con- Are H.F. Valves Worth While ? perfectly natural. It was desirable to have trolled to keep within the grid swing of " What is the Use of 11.F. Valves? " an output of at least a watt. a super-power valve. Mr. was the provocative title of a lecture Turner concluded with a detailed Hon. secretary : Mr. W. R. Collis, 7, given by Mr. J. \V. l'ukis, A.R.C.Sc., Algar Road, Isteworth. before the Croydon Wireless and 0000 Physical Society on May 16th. The FORTHCOMING EVENTS. R.C. Amplifier and the Gramophone. lecturer referred to the two schools of WEDNESDAY, JUNE 6th. The South Woodford and District Society of Muswell Rill and District Radio Society. thought on the subject. one which con- It 8 p.m. At Tofington School, Tether. has been studying resistance- capacity tended that the sole requirement for re- down. Demonstration on "Electric Accu coupling. At the last meeting Mr. J. E. ception was a sensitive detector mulato,,." by Mr. IV. Schofield (of followed .Messrs. Hart Accumulator Co., Ltd.). Nickless, 2KT, gave an interesting demon- by L.F. amplifiers, while the other school Tottenham tireless Society. :It 8 p.m. stration of the reproduction of gramo- of thought maintained that valves It 10, Brace Grace. Lecture by 11,. II.F. It. F. G. phone records using a resistance -capacity were necessary for DX work. After Holmes. THURSDAY, JUNE 16th. amplifier with excellent results. This summarising the position the lecturer sug- Golders Greco and Hendon Radio Society. Society meets at Holy Trinity Parish gested that while perhaps the use of H.F. It 8 p.m. At the Club house. IVilli/1dd Rooms on Monday ev gs. valves as was Way, N.W.11. Lecture: " Picture Broad - pure H.F. amplifiers not aiding," by tir. F. It. Haynes, Assistant Hon. secretary : Mr. S J. Turbyfield, altogether successful, yet the use of II.F. Editor, The Wireless World." 42, Alexandra Road, South Woodford, valves for selectivity was to be strongly E.18.

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The Daventry Hush. Comparing the Wavelengths. " Daventry Junior" shows no sign of Between 6 and 8 p.m. the transmission swamping the ether. In fact, since those ,11 32 metres was inaudible, while that on two furtive transmissions in May the 26 metres varied from fair to good. From station has been silent. Why tins hustle? 11.30 p.m. to 1.30 a.m., however, the no0o tables were turned, the 32-metre signals being much stronger than the others -in Failure ? fact, they were extremely good for the If the first tests are to be regarded as greater part of the time. full -blooded transmissions of the sort we At 9.30 a.m. both transmissions were shall hear under the regional scheme. the very good, but they soon faded, and station might as well be written off as a By Our Special neither was easily readable Ccrrespondent. until just failure. Many listeners within a hundred before 6 p.m., when the shorter wave- miles' radius have reported the signal length signals rose to good audibility as strength to be no greater than that of an the test concluded. average main station. FUTURE FEATURES 0 0 0 0 0000 London. A Useful Lesson. Warming Up ? JUNE 13TH.-Cornish Programme, While the results were erratic, the test However, as I hinted in these columns relayed from Sennen Cove. provided one useful lesson, viz., that 14st week, -there are reasons for suppos- JUNE 15TH. -'` My Programme," short -wave broadcasting of a reliable kind ing that an intentionally low power has by L. du G., of Punch. will probably be achieved by altering the hitherto been employed-somewhere in the JUNE 16TH.-Tunbridge Wells wavelength at predetermined hours of the neighbourhood of 10 kilowatts -with the Night. day to compensate for atmospheric idea, presumably, of " warming up " the JUNE 17TH.-" Philemon and Bau- vagaries. apparatus. cis," comic opeta by Jules This was abundantly demonstrated by Further tests are not likely to be made Barbier and Michael Carre. the fact that both wavelengths enjoyed of an for a week or two. JUNE 18Trr. -" Four Quarters their good periods as well as their bad ; 0000 IIour " (a Pierrotic Phrenzy). no doubt if four wavelengths had been Response to the Referendum. Birmingham. used good reception would have been possible throughout the greater part of At the time of writing the B.B.C. has JUNE 18'rir.- Military Programme the of test. had no cpportunìty of arriving at the in Commemoration Water- 0 0 0 0 results of the referendum, but I under- loo, 1815. Some Licence Reflections. stand that listeners have responded in Bournemouth. making the task of Is the listening public growing as their thousands, JUNE 15111-Songs and String collation a particularly heavy one. rapidly as it should'? Judging from the 0000 Music by Modern British Com- licence figures issued for the first four posers. months of this year, the pace is slacken- 2L0 the Favourite. JUNE 18TH. -The Saturday Medley ing. The- following list is illumin- A striking feature revealed by a pre- (Instrumental and Vocal Pro- ating :- liminary glance through the stacks of gramme). 1927. No. of Licences. postcards is the popularity of the London Cardiff. January ... 2.227,256 station. In one case, at least, a valve 16TH. The Banns of Mar - February ... 2.235,000 miles London indi- JUNE -" user residing 300 from riage, by Charles Lee (a March ...... 2,253,845 cates 2L0 as his favourite station. play), April ... 2,283,028 0000 Manchester. The last number includes 6,501 free How Far is That Station ? JUNE 18rx. -" On With the licences issued to the Wind. Another point revealed by the referen- Show," relayed from Black- dum is the ignorance of some people re- pool. Are We Near Saturation Point? garding the geography of their native Newcastle. It will be seen that the average country. In estimating the distance to JUNE 141x. -" A Racy Revue." monthly increase is in the neighbourhood of 20,000. During the corresponding their pet station quite a number of lis- Glasgow. teners were nearly a hundred per cent. period of last year the monthly increase wrong. No wander certain individuals JUNE 18äs. -" East, West, Hame's was over 50,000. Are we nearing satura- are disappointed at the strength of their Best," a Staff Programme. tion point? reception, and that others are correspond- Aberdeen. There is no reason why we should be

ingly elated ! anywhere near it. 0000 JUNE 13'1x. - Shakespeare in 0 0 0 0 Lighter Vein. The Transatlantic Short -wave Tests. That Five Million. The 24 -hour short -wave tests from Belfast. It is generally assumed that Great WGY last week were a little disappoint- JUNE 151x.- Original Programmes. Britain contains about seven million big, though they afforded a useful com- No. 1 : Reproduction of First families. The number of licences has not parison between the respective merits of Concert given by the Hallé yet reached two and a half million, which the 26.8 -metre and 32.77 -metre wave- Orchestra in 1858. world represent quite a small proportion lengths at different periods of the day. of the total number of potential licencees. A 35

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WAp®Il@g1g 734 JUNE 8th, 1927. WOO lsid Five million licences would be nearing From Cambridge University. interesting to note saturation point, and would allow in what way he con- for The Cambridge siders a broadcast programme two million families of the type who University Musical should be Society will broadcast on June 10, when made up. either "don't believe in this 'ere wire- 0 0 0 0 less " or prefer to take their entertain- their performance of the "Sea Sym- phony " is be relayed The Sound -range of ment without paying for it. to from the Guild- Gunfire. c 0 0 0 hall, Cambridge, to 2L0 and 5XX. An interesting test will shortly be con- Broadcasting During the Eclipse. 0000 ducted by the Air Ministry with the co- operation of the During the eclipse B.B.C. to determine the of June 29th the B.B.C. and the Queen's Hall Concerts. range at which gunfire can be heard. B.B.C. will transmit a special series of All lovers of music will rejoice at the Guns of different calibre will be fired at signals from Daventry and London as announcement, which was officially given Shoeburyness, and before the follows firing of :- out by the B.B.C. on June 1st, that after each gun the B.B.C. announcer at Daven- (a) Six dot seconds at 6, 6.15, 6.20. and a series of negotiations lasting for several try will count eight dot seconds. '1'he 5.30 a.m.; (6) single seconds continuously months an agreement has been reached gun will be fired exactly at the eighth from 6.22 a.m. to 6.26 a.m., missing each with Messrs. Chappell whereby the second, and listeners in various parts of 29th and 59th second to mark half - B.B.C. will give a series of Promenade the country will be asked to tote care- minute periods. In addition a verbal Concerts at. the Queen's Hall under the fully the exact time between the firing announcement, will be made every five conductorship of Sir Henry Wood start- of the gun and the hearing of the actual 1 seconds. ing on Saturday, August 13t1, and also sound. This time may be considerable, as the rumble of the gun may be audible many miles away and it takes from eight to ten minutes for sound to travel 100 miles. c000 Interference on 5XX. Quite a number of listeners are report- ing interference, chiefly of the spark satiety, with the transmissions from Daventry. Just why a 1,600 -metre transmission should suffer from ship interference is a little mystifying, unless it be that the few German ships using spark on 1,800 metres are the causo of the trouble. Strangely enough, several of the complaints come front listeners in Germany and France. ^000 5XX Abroad. This is a reminder that 5XX is still one of the most popular broadcasting; stations in Western Europe, despite the claims of giants like Koenigswusterhauser, Langen- berg, Hilversum, and others. Daventry's transmissions are listened to nightly in Northern France, Belgium. Germany, and even Holland, though I imagine that the astute Dutchmen will S0011 forget Daventry in the excitement of building their short -wave sets to hear PC JJ. 0 0 0 0 A POPULAR BROADCAST? Broadcasting a bowls match through the Melbourne Always With Us. station. Probably golf from 2L0 would draw more listencrs here. Last week it was tremblingly suggested that oscillators were a dying race. The " Saturday Night Revue." 12 special symphony concerts during next hope was based en the number of letters The third instalment of Graham John's sea sou. of complaint received at 2L0 during " Saturday Night Revue " will be given Thirty -seven Promenade Concerts will, April. 0 fatal optimism! Look at the on June 18th. This is the third revue therefore, IQ given, but not all of these figoros for May : which Mr. Graham John has written and will be broadcast, prohably about two in 1st week ... 187 produced for the B.B.C. Among his suc- each week. 21141 ...... 145 cesses have been the " Nine O'Clock 'l'Ire series of syittpliott' concerts at the 3rd ... 158 Revue " and " Whirled into Happiness." Queen's Hall will take the place of the 4th ... 175 He is also the author of the musical National Concerts broadcast last season Meanwhile two Post Office anti- oseilla- comedy " My Son John," now playing at front the :Albert Hall. tiara vans are roaming the country, the the Shaftesbury Theatre. The removal of the ban on the micro- B.B.C. is issuing anti- oscillation leaflets phone at the Queen's Hall will enable o 0 as fast as it can, and broadcasting has the B.B.C. to relay the speeches from been in existence for over four public meetings and, when years. Straight from Cornwall. possible and And still the oscillator is in our midst. ".4n Hour at a Cornish Inn " will desirable, to at-range for the broadcasting o 0 0 0 of other concerts that may be given form the subject of a broadcast from 2L0 there. A German o 0 0 0 Conductor. and 5XX on June 13. The programme Herr Scherchen, who conducted one of will consist of a fishermen's sing -song. with Arnold Bennett's Night. the most successful of the B.B.C. national touches of the Atlantic breakers and the It is expected that Mr. Arnold Bennett concerts at the Albert Hall last winter, " atmosphere " of Laud's End thrown in. will provide one of the " \ly Pro- is coming to the London studio on The inn front which the broadcast is to gramme " series on June 22. Mr. Arnold .lune 9 to conduct a light symphony con- take place is situated near Sennett Cove, Bennett lias expressed very decided views cert in which the Wireless Symphony on the Cornish coast. on broadcasting, and it will therefore be Orchestra will take part. A 36

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The Editor does not hold himself responsible for the opinions of his correspondents. name and address. Correspondence should be addressed to the Editor, "Tae Wireless World," Dorset House, Tudor Street, E.C.4, and must be accompanied by the writer's ;e EMPIRE BROADCASTING. station in each country. There is no doubt whatever that people internationally if we are ever to have world Sir, have read with great interest the articles in your must think -I peace, and a good start towards it is to get them li toning issues of April 27th and May 4th on Empire Broadcasting, and the internationally. Since listening to American broadcasting i I certainly think it is time the Government woke up to mentality. programmes from the Old Country, have got an entirely different idea of the American necessity of broadcasting the Germans and for our colonies, but also for the benefit of Britons and I am also beginning to understand not only Spaniards. Listening to French stations has merely confirmecí residing in foreign countries. By this I mean duplicating the a programme that the opinion I had formed of France from personal experience. success of the Philips station in transmitting bare in broad- enjoyably in practically any part of the world. I am convinced that national mentality is laid can be picked up and the wider the range of the pro- before the advent of PCJJ it was distinctly dishearten- casting programmes, Even grammes the sooner " foreigners " will become " fellow- citizens ing_ striving on a 7 -valve receiver to pick up a B.B.C. station only to be met of the world." in the hope of hearing Big Ben chime midnight, they realise that Morse; and yet a few minutes later to The "DX-hounds " will, I am sure, when with a roar of X's and other side of the world for other 3 set and with the greatest of people actually listen to the change over to a simple -valve consider before they switch on, and ease (and apparently any old aerial) tune in 2XAF -3,000 miles than test reasons, just " keep off the grass." JOHN WILLINGS. away, twice the distance of our nearest B.B.C. station -with and clearness really astonishing. As for 5XX, the Ilandsworth, Birmingham. a strength 25th, 1927. super power station, the less said the better. Now PCJJ comes May in at " phones -on- the -table " strength in broad daylight using

only 3 valves. B.B.C. TRANSMISSION OF PIANOFORTE MUSIC. . of number of Britishers who, in the hope of 1 census the of the poor recep hearing intelligible programmes from outside the 1,000 -mile Sir.- Referring to Mr. Snryth's complaint in I should like to say that the same radius of any B.B.C. station, have spent money on costly tion of 2L0 the provinces, be illuminating. trouble is experienced here (six codes east of Ipswich). and receivers and then been disappointed, would by few on this little island. that I believe I have definitely traced it to heterodyning There are quite a in and consists of broadcasting the Englishman's voice Leipzig. This interference varies severity, Apart from the effect note, some- it is duty of the Mother Country sometimes of a definite and steady heterodyne throughout the world, the sometimes of programmes, and above all, news items, for her times of ' nasal " distortion of speech and to provide by snatches of horribly dis- colonies and sons overseas. In how many different countries sharp fading accompanied stations been heard? torted speech or music from Leipzig followed by tolerable of the world have the American short -wave very adjust- Palmas. Canary Islands. M. V. BLAKE. reception of 21.0 for a few moments. A slight Las as large as life only equally May 17th, 1927. ment of tuning will bring in Leipzig distorted. These different types of distortion may be due to slight differences in my tuning from time to time, but I think the question of possible distortion in my own set can be ruled Sir. --Would you be good enough to intimate, through your out. as I have three stages of neutralised H.F., detector and admirable publication, to the brass- pounding fraternity the 2 L.F., and do not use any reaction for London. Outside in- fact that they have no monopoly of the ether after the B.B.C. terference is practically non -existent as I am well out in the closed down. Those of us who listener s regularly country, while other stations of less power and greater distance stations have and to 2XAF as we do to the local programme may be few and far come in quite undistorted. The set is reasonably selective between, but surely it is easy not to pitch exactly on 32.77 separates Cardiff from London easily. metres for the purpose of discussing counterpoises with some It is a great shame that yet another station should be denied " ham " in the Antipodes. Zez Confrey was playing magni- to us in this benighted spot. Defining a station worth listen- ficently last night at WGY when some merchant started his ing to as one that will give full volume ors a cone speaker " blibetty-blah, blibetty -blah " and spoiled reception for a solid practically every night with no fading whatever, no distortion, half -hour. It often happens so. little or no interference from Morse or atmospherics, and all Talking of " blab," when are the B.B.C. going to drop that this without much reaction being needed; all we have here are hoary joke about low -wave work not being reliable and give Daventry and Hilversum, and in a lesser degree Radio Paris not is badly the Colonies a chance of hearing the Mother Country. Broad- and Langenberg. Hilversum more often than is impressive and fascinating as the square of the dis- jammed by Morse. London often provides a symphony concert casting rough stuff, tance of the source of emission from the receiver. It is only or chamber music when Daventry is handing out of this country that this medium of inter- and that is just when one would listen to London direct. I be- fair to the people it change of ideas should he opened up to them also by the lieve the B.B.C. have already protested to Leipzig once; establishment of similar stations overseas. seems as if further action is needed. P. J. R. KING. It should not be difficult (through the T.eague of Nations, Woodbridge, Suffolk. probably) to arrange a limitation of one short -wave high -power May 24th, 1927. 37

www.americanradiohistory.com W'p@ll@gg Vrodd1 JUNE 8th, 1927.

The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. / Questions should be concisely worded and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply. Litz Wine. Grid Bias for H.F. Valves. formers have secondaries of extremely I should be glad if you would examine 7 here constructed a receiver with, two low resistance it will be necessary to the enclosed sample of "Litz" mire. H.P. stages rather on the lines of bridge each bias battery with a large It appears to differ considerably from the " Il'rireless condenser, as shown in the the World Five." The circuit dia- stranded conductor which. I hare loco- potential ends of the gram (C1 and C,). If, on the other seen used in trans- certain 11.1'.' trans - former's are earthed hand, you are using transformers with formers, and to the screen I fancy its et.?e may ac- through the frames of the tuning secondaries of fairly high resistance, it count for the poor result, I am get - eon.densers and thus is unlikely that the extra internal resist- ting from my rrceirer. the grid is P. H. R. working at zero, as the screen is also ance of the dry cell will cause a notice- We have, as requested, examined your connected to L.T. negative. I now able reduction in amplification, but you sample of wire, and in our opinion it wish. to add negative grid bias, but should, of course, replace the cells fairly could not fairly be described would prefer, if possible, frequently. as " Litz." to avoid 0000 It is made up from a number of strands the necessity of retuorinq the con- (not a multiple of three) twisted togethet densers and fitting insulating bushes Keeping Out H.F. Currents. apparently at random, and we to their spindles . Can gate think it male 1 notice that in probable that it has a higher H.F. resist- any suggestions? several recent issues you W. F. have shown resistances of about ance than solid wire of equivalent cross - sectional area. The simplest way of making the pro- stegohnn connected directly in the 0000 posed alteration would be to connect one grid circuit of the first L.F. amplifier, or two dry cells directly between the the idea being to prevent, or rather An Economical Project. grid of each valve and the tuned trans- to restrict, the development of H.F. here former. It is, however, bad practice to potential across the L.F. simplifier. I I often hearer it stated that anode insert a mass should be glad to know bend rectification of metal at the high if this is considerably less potential end of the circuit, arrangement may be applied when sensitive than although in an the leaky grid type. I practice this arrangement may be L.F. transformer couples the detector line 30 Writes per- from Darentry, and am missible, as it is possible to to the amplifier. C. H. D. desirous of receiving obtain ex- this station at tremely small cells which are sold as re- moderate loud -speaker volume with The stabilising resistance may be used placement batteries for the so- called in a transformer -coupled set, and it will the least initial oietlaq and the " fountain pen " flash lamps. Another smallest cost of upkeep. My certainly do no harm. It is doubtful, how- friends method is shown in Fig. 1, and this is tell me that I shall need a leaky grid ever, whether its inclusion is worth while, probably the sounder of the two. You and in any case the difficulties of detector with. reaction followed by will see that the necessary a transformer- coupled biassing cells separating the H.F. and L.F. components stage, and are inserted in the low -potential end of have thrown cold water on are less pronounced with transformer my idea the tuned circuit. If your H.F. trans- coupling than when a of using an anode bend detector fol- resistance is used. lowed by a resistance- coupled stage with reaction. T. R. B. We have no hesitation in saying that, H.T.+ provided you can erect a reasonably efficient aerial, your proposals are perfectly in order, and your friends' advice is non- sense. Furthermore, always provided your locality is not a bad one, and the aerial is reasonably good, you will have N C. N.C. cs no need of reaction or H.F. , but merely need to use a simple anode bend detector followed by one resistance -coupled stage such as was described with full con- re structional details in our October 27th issue last, under the title of " Economy Two." This will assure you of good H.F. H volume coupled with very good quality. From the economy point of view, we advise 2 -volt valves, one of the new high - magnification valves such as the Milliard DET. P.M.1A. or Cossor 210 R.C., etc., being L.T.- 8 SCREEN used as detector, and in the output stage i go. a power valve. such as the Marconi or Osram D.E.P. 215 or a similar 2 -volt Fig. 1. -Grid bias connections in H.F. amplifier in which the tuning condensers are power valve by other makers. mounted on a metal panel.

A 38

www.americanradiohistory.com VfpeQog JUNE S'1 /t, 192 7. MAJ. 737 An " All Wave " Alteration. ductance. On the other hand, it must valve; by other manufacturers. Users of grett interest and not always be assumed that because a 4 -volt valves have a similar range of 11tave read with eery inductance as 20 valves at their disposal, such as in the appreciation your cuticle describing cho..e has as low an easily carry the plate cur- Mullard series V, and V., I'.M.3. V, the ".All-Wave Four " receiver, and henries it will rent of a power valve, because a cheap P.M.3.A, V, P.M.4, or preferably have decided to build it. I intend, valves nre the Marconi however, two alterations, 20 -henry choke will not necessarily do P.M.234. Other to make this. With regard to the blocking con- D.E.L.410 for V. The D.E.II.41C one. of which you countenance in your not be of less value should make an excellent detector with use a transformer denser C,, this should article, that is, to it is the D.E.P.410 as the output valve. It resistance coupling in that 2 mfd. if possible, and prefer- in place of the no means necessary, should not he forgotten that many readers the last L.F. stage. My second sug- able, although by two 2 mfd. condensers be used in prefer to use a 2 -volt valve as anode bend gestion, which you do not mention in that parallel here (or, of course, one 4 mfd. detector; owing to the fact that usually the article, is to use a choke filter' condenser) in the interests of quality. a 2 -volt valve makes a better anode output circuit. I should be glad if is not much object, however, in detector than those of greater filament you would gire me a recised diagram There this condenser of larger value voltage. Thus, using 6 -volt valves, we showing me the connections for making no harm will be could use a 2 -volt 0.l.ampere valve such retaking alterations, and also than 4 mfd., although these choke filter circuit, the as the Mollard P.M.1A as detector, but the -valves to use in done. Using the most suitable of the loud -speaker with rein this case it must not be forgotten that the 2, 4 and 6 colt classes. connections its positive and negative ter- a resistor of at least 40 ohms value C. F. T. gard to minals is immaterial, as no plate current should be placed in series with R,, and in Your proposed alterations to this re- will be passing tnrough it. the case of using a 4 -volt accumulator ceiver are perfectly sound in every way. It should he realised that, if desired, the fixed resistor in series with R, must Tl.e transformer which you should use the single -wire extension system for be at least 23 ohms. No harm will is

o V H.T, t i H.T.+ 2 04 0.P. o I L1 l. P.

N.C. vl R6 B H.T.- P A LS. 0 0 Bo 0 Ol -G B.3 IN H.F.T. O.B. r

R L.T. n 2 3 R1 POTS"_ ' SWITCH

Fig. 2.- Modified .. All -wave Four " circuit with transformer coupling for the second L.F. valve and choke filter output circuit.

should be of a good make having a high using the loud -speaker at a remote dis- doue in exceeding these values slightly inductance primary (50 to 80 henries). tance from the receiver may be used here in order to obtain an instrument marketed In a case where a reliable manufacturer if desired. In this case one terminal of as a stock resistance by a manufacturer, makes his transformers in more than one the loud- speaker will connect via the since ive do not necessarily want full ratio, von should choose the lowest ratio single extension wire to the terminal emission, and therefore need not have which will be 22: 1, or thereabouts. marked A in the diagram, the other ter- full filament voltage on the detector, With regard to the output choke L,, this minai of the loud- speaker connecting to owing to the high resistance in its anode need not have a greater value of induct- the remote earth. Terminal B in our circuit. ance than 20 or 30 henries. There is no diagram being then left blank. Having 0000 harm in using a higher inductance pro- made this alteration the valve at V, will vided that the manufacturers specify need to be changed, and one of about A Single Stage L.F. Amplifier. of choke is so de- 20,000 to 30,000 ohms impedance and of that the iron core 'h" +e me the coupled factor as possible l'1,,- tell if transformer- signed that it will cope with the heavy as high a magnification designed for adding to 30,000 ohms impedance is L.F. amplifier plate current of the output valve without (provided a the `Nuclrus " receiver which was magnetically saturating. Thus, the 32- not exceeded) shotild be used. Suggested described in your issue of March, G. valves in the 2 -volt class then are : V, henry choke made by Messrs. W. 23rd, would be suitable for ase in or Pye, Ltd., is suitable in every way, al- Mullard l'.1I.i.H.F., Cossor 2101I.F., conjunction with a crystal set, and though of slightly higher inductance than similar valves by other makers; V, Cossor also if any modifications would be we have mentioned. The point is that, R.C.210, Mullard P.M.1.A., or similar; necessary. C. L. all other things being equal, higher in- V Mullard P.M.1.H.F. or Cossor which you ductance means that . the choke will 210H.F. ; V, can be Mullard P.M.2, Mar- The L.F. unit to refer would saturate at a much smaller value of plate coni or Osrant D.E.P.215, or similar be quite suitable for the required purpose current than would be the case if it were valves. Those who favour 6 -volt valves and no modifications are necessary. It of a lower inductance. can use for V, and V, Marconi or Osrani could, however, be improved slightly from Since we shall use a power valve in D.E.5.B or Mullard P.M.5.X, Mollard the point of view of neatness if instead this last stage in any case, there. is not P.M.5.B. for V,, and for V, D.E.5.A or of fitting battery sockets on the face of the slightest object in using a high in- P.31.256, or, of course, similar types of the panel you were to mount a terminal A 39

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WAp®hoo 73b JUNE 8th, 1927. `lofilLta strip mi the baseboard and pass out the for aerials of different dimensions, pro- interference from the London Station. connecting leads through a hole in the vided always, of course, that all the An added advantage back of which this receiver the cabinet. aerials are of the average type, and not possesses over those previously described 0000 exceedingly long or exceedingly short, lies in the use of interchangeable H.F. such, for instance, in the latter case, as transformers, thus enabling the frequency Problems of Aerial a small indoor aerial. In the latter case valve to be employed for Coupling. it the reception would be more efficient to connect the of stations working on the longer wave- I have been care /ally reading your small indoor aerial direct to the top of lengths. article on the " All - 1172re Four " the grid coil. receiver, and, in discussing the ques- 0000 0000 Lions of " aperiodic" or fully tuned aerial coupling, it would seem that Constructing a Home-made Cone A Misapprehension. aperiodic aerial, coupling is not of Loud -speaker. great use above 600 metres, whilst on I hare Genii remltnq with some interest the normal broadcast band both I possess a loud -speaker unit and under- the " Extracts from Readers' Logs" fortes of coupling work very well. I stand that some time back you pub- published in recent issues, and as am building a short wave receiver, lished an article on the construction they seem to be able to receive from however, and am desirous of know- of a cone loud -.speaker using a unit practically any part of the world, I ing whirh, system to tise. The re- similar to that in my possession. should like your advice as to where I . ceiver will be for wavelengths below Unfortunately I have mislaid this could buy a suitable receiver to gire 200 m.etre-e. D. D. issue, and should be obliged if you equally good results. I am an abso- would give me the lute beginner may be date of the pub- and do not propose to It said that on short wave- lication in which this construct my lengths aperiodic aerial coupling is the article ap- own set. R. W. S. peared. R. P. only system to use, and the shorter the S. We think that you are mistaken regard- wavelength the more does this rule hold We think you refer to an article en- ing the signals heard by our readers. The good. On the normal broadcast band titled " Loud- speaker for Ilome- Construc- published call -signs relate not to tele- between 200 metres and 600 metres both tion," which appeared in our issue of phony stations, but, in the vast systems of coupling will work very well, November 10th, 1926. Excellent results majority of cases, to short -wave and there is not a great deal to choose were obtained from the loud -speaker amateur transmissions of Morse, for between them. Possibly, on the lower described, and the quality of reproduc- the reception of which, naturally, part of the broadcast hand, aperiodic tion compared very favourably with that a knowledge of the code is essential, aerial coupling would be the best to use, given by commercial types. The construc- and, as you are a beginner, you probably although, when approaching 600 metres, tion of a horn having good acoustic quali- have no experience of Morse signalling. the fully tuned method would show a ties would be outside the capabilities of If we are mistaken in this and you really marked superiority. Either system may the average home constructor, whereas do wish to receive Morse transmissions, be used with good effect, however, for the cone diaphragm presents little we should be pleased to give you the the broadcast band of wavelengths. difficulty. addresses of one or two manufacturers of Speaking generally, a fully tuned aerial satisfactory short -wave sets. should he used above 600 metres, and the longer the wavelength the more does O 0 0 0 this rule apply, so that a fully tuned BOOKS FOR THE aerial is Long Waves and Short Aerials. the only thing to consider on HOME CONSTRUCTOR very long wavelengths, just as on very My three -calve receiver, a detector short and wavelengths aperiodic aerial coup- Issued in contundion with" The IVireless World." two stages of low- frequency amplifi- ling is the only thing to consider. cation, gires fair loud -speaker recep- "TUNING Many people working on a very long COILS AND METHODS OF tion of the London Station 30 miles. wave station may find that a TUNING," by W JAMES. Price 2/6 net. such station By a away, but although I am less thait may come in loudly with Post, /ro: apparent '. THE 100 miles from Darente!, this station aperiodic coupling, since there is no HOME CONSTRUCTOR'S tun- WIREJ.ESS GUIDE,' by W. JAMES. is indifferently received. My ing condenser across Price aerial the aerial tuning coil, 3/6 net. By Post, 3/9. is 35ft. high and 50ft. long, the domen but, in reality, it is probably not aperiodic "MAST AND AERIAL CONSTRUC- lead being taken front the aerial coupling TION rentre of at all which is being FOR AMATEURS," by F. J. the horizontal portion. Can you used, AINSLEY, A.M.1.C.E. Price r/6 net. By Post, 1/8. the actual facts being that, owing ,hake any suggestions that will enable to broad tuning on long wavelengths, the Obtainable by post (remittance with order) from unproved reception of Daventry aerial capacity and the self -capacity of to be ILIFFE & SONS LIMITED, obtained without impairing the re- the coil give the effect of a fully tuned Dorset House, Tudor ception aerial. St., London E.C.4, of the London station. Aperiodic aerial coupling can be or of Booksellers and Bookstalls made to work on long waves, but usually J. S. the primary winding must be designed The poor reception of the Daventry for the aerial it is to be used upon, and Station is without doubt due to the type the wavelength it is to receive. Eliminating 2L0. of aerial employed, and we think a Thus it was found, when first designing I ant situated three miles from the Lon- definite improvement would result if an the " All -Wave Four," that an aperiodic don Station, and wish to construct aerial of the inverted "L " type were aerial coil could be designed for Daventry a receiver which will enable me to erected. Actually the effective length of when the set was used on a given aerial tune in some of the more distant wire in use is only 60ft., this being the and maximum efficiency was obtained, broadcasting stations while London length of down lead plus half the length brit it was is found also that using an aerial working. I should be obliged you of the horizontal portion. If, now, you of different dimensions the if number of would inform nie which of the re- were to connect the down lead to one end primary turns no longer held good, or ceivers recently instead of to the centre of the horizontal using described in your the sanie aerial, the same number paper would most satisfactorily portion, a total length of 85ft. could be of primary turns no longer held good on answer my requirements. W. E. P. obtained, which would result in a longer Radio Paris, for instance, as he was of fundamental wavelength. Under these longer wavelength. Radio Paris was still The best advice we can give is that conditions less loading " of the aerial receivable at good strength, but not any- you make up the " All -Wave Four " re- would be necessary to tune it to the thing like at maximum efficiency. On the ceiver described in our issue of April 27th Daventry Station's wavelength with a other hand, as you know, aperiodic aerial last. Exhaustive tests have been carried corresponding increase in signal strength. coupling need not be changed over the out at varying distances from 2L0 and Also we should expect a slight improve- normal broadcast band for different wave- at three miles it was possible to tune -in ment in the reception of the London length stations, nor need it be changed a station on 385 metres with no sign of Station. A 40

www.americanradiohistory.com rei AN D RADIO REVIEW (15q, Year of Publication)

No. 407. WEDNESDAY, JUNE I 5TH, 1927. VOL. XX. No. 24.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES. : City 4011 (3 lines). Editorial Offices : 139 -4o, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. Telephone : City 2847 (13 lines). Telegrams : " Ethaworld, Fleet, London."

: : Street. MANCHESTER 199, Deansate. COVENTRY : Hertford Street. BIRMINGHAM Guildhall Buildings, Navigation Cyeliet Coventry." Telegrams: " Autopreee, Birmingham." Telegrams: "IllIIe, Manchester." Telegrams: " 8970 8971 City. Telephone: 3210 Coventry. Telephone: 2970 and 2971 Midland. Telephone: and Subscription Rates: Home, 17s. 4d.; Canada, 17s. 4d.; other countries abroad, ios. bd. per annum. to themselves that they As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, satisfy would not be infringing patents.

RECEIVER DESIGN. be able to achieve the desired increase in selectivity. The reduction in the cost of valves will also, no doubt, HE design of receivers for broadcast recep- result in a very large section of the public hitherto tion in this country is, of course, governed satisfied with a crystal receiver acquiring valve sets. to a very large extent by the policy of the We have at the present time several commercial B.B.C. and the distribution, wavelengths, receivers which are admirably designed and will meet and power of their the alternative programme require - stations. In the early H ments, but these sets are in the days the wavelengths minority and are very high priced. CONTENTS. through our policy of of the transmitting stations were PAGE In carrying confined to one band, and de- EDPIORIAL ...... 739 reviewing commercial receivers of signers had a clean -cut line on DITTON PARK RESEARCH STATION ... 740 interest we deal in this issue with which to develop their receivers. By J. F. Herd. a set of American origin which is Then came the Daventry station, THE WORLD'S LARGEST VALVE ... 743 I now being sold in this country under licence from the Marconi w hieb complicated matters very TWO-RANGE ALL STATION RECEIVER Company at a price which makes it much for the set manufacturers, (Concld.) . 745 who found that the public demand By A. J. Bull. a keen competitor of a large mini- her British sets, because it has was for receivers capable of re- HINTS AND TIPS ... .. 751 of and range ception on both the short band and THE" EXPERIMENTER'S NOTE -BOOK 754 the required selectivity the Daventry wavelength. By "Empiricist." to make it admirably suitable for regional The policy of the B.B.C. up CURRENT TOPICS ... 756 the requirements of the it has the further till now has been to induce listeners BROADCAST RECEIVERS - CROSr.EY scheme, and viewed in thé to concentrate exclusively on their JLODEL 5 -513 ...... 758 advantage that, the local station, with Daventry as an REGULAR BROADCAST TRANSMISSIONS 760 light of present equivalents, is right. alternative, though as things have SECRET RADIOTELEPHONY SY STEAL S price worked out Daventry has very (Gondel.) 763 We would urge manufacturers seldom been an alternative pro - By G. F. Brown. here to get ready for the foreign is bound to gramme to London. Now that BROADCAST BREVITIES ...... 766 competition which as a result of the regional scheme seems likely NEW APPARATUS ...... 768 come about when, the regional to go through, having as its oh- LETTERS TO THE EDITOR ... 769 the introduction of the recep- ject the provision of alternative READERS' PROBLEMS ...... 771 scheme in the autumn, programmes from different tion conditions of the British stations, the set designer must, in listener will compare so closely many instances, turn his attention to modifying his with those of America. Some drastic reductions in price may existing models. Once the regional scheme is in opera- and important modifications in the majority of what receivers of to- tion the interest in receiving alternative stations will he he described as the standard broadcast extended, and this will require that receivers should he day will have to come about, even at a cost of sacrificing of more selective than the average receiver of to -day, and in appearance and many of the refinements characteristic selectivity many cases it will be found expedient to add an H.F. the British set, the requirements of range and must be met at the right price if the stage where this is not already provided ; in fact, it seems with good quality likely that the H.F. stage will be necessary in order to future of British sets is to be assured. A5

www.americanradiohistory.com :,1+F!°'' MININTM.PwIrliPe.) AimPrE` . - 147

In Vllpa@oo WopIla, JUNE 15th, 1927.

Apparatus That Will Be Used During the Eclipse for Studying the Propagation of Waves and Atmospherics. By J. F. HERD, A.M.I.E.E.

which is mounted in the tripod structure below the frame. The set is for work on the broadcast band and is used exclusively for making directional measurements on broadcasting stations. A special hut lias been constructed to house the direction - finder. The hut is supported on large porcelain insulators, and is electrostatically screened by wires passing over THE radio research station at Ditton Park is maintained by the Department of Scientific and Indus- trial Research, and the work is principally in connection with wave propagation and atmospherics. The station is divided into two sections, one in each of two large fields on the estate of Ditton Park, near Slough, an historic site which is now the home of the Admiralty Compass Observatory. In one field the work done con- cerns problems of wave propagation -i.e., absolute signal strength measurements, fundamental problems of direction - finding, including measurement of the electric and magnetic components of the arriving waves and their respective states of polarisation, night errors, and other factors due to the ionised upper layer of the atmosphere. The other section of the station is devoted to the study of atmospherics, and is possibly unique amongst wireless stations in its affection for what are mostly regarded as undesirable visitors.

. Wave Propagation. The characteristic feature of the " propagation " side of the station is the wide separation of the different buildings, which house the various measuring apparatus to prevent any form of interference between the sets. The need for such precautions will be realised when it is mentioned that four or five separate measurements are frequently being conducted simultaneously on the same signals for complete correlation of the various effects to be measured. In one hut there is a direction -finder specially designed for measurements of the magnetic elements of the arriving Crave. This instrument was described and illustrated in the issue for August r rth, 1926. The frame aerial is rotatable about both vertical and horizontal axes, and screened leads are carried in a brass apparatus, 1.- Portable direction -finder to be used during the eclipse tube to the for measurements on each side of the path of totality. e6

www.americanradiohistory.com W pgIl@go 74, JUA'E 1511/, 1927. WopIlc1 cathode ray oscilkigraph. When no signal (or atmospheric) is being received nothing is visible but the normal green fluorescent spot on the screen of the tube. 'Che arrival of a signal voltage opens out the spot into a line which makes the sanie angle with the vertical axis on the screen of the tube as the line of the transmitting station makes with the true north south line. The screen of the tube can thus be used as a direct -reading wireless compass. This holds good even with individual atmospherics lasting only a thousandth part of a second. In this case the indication is in the form of a momentary " streak " of fluorescence, giving the direction of the single atmospheric in the same manner as a visual direction- finder. Fig. 2.- Testing the new wireless compass which makes use of the signal. small porcelain reel insulators mounted on an external framework. In Fig. r is seen a portable direction -finding set mounted on the top of its screened amplifier. The front of the screen is shown open while the observer is making adjustments preparatory to directional measurements. The direction -finding apparatus shown will be used for observations during the forthcoming eclipse, similar apparatus also being employed to make measurements in the region of totality. A set for the measurement of long -wave signal strength is also available. Signal strength is measured by comparison with a known local input, the measurements being effected on a string (Einthoven) galvanometer. This set and similar apparatus at other places, operated by observers working in conjunction with Ditton Park, will also be in use for special observations during the eclipse. Atmospheric Recorders. On the " atmospherics " side of the station the notable external feature is the extensive aerial system. One system of large crossed loop aerials is employed fer the visual direction- finder, while another large " T " aerial of about J,600ft. total horizontal length is used for other purposes, including the study of atmospheric wave forms. The main aerial system is shown in the title of this article. The central mast seen is about zooft. high, of wooden lattice; the out -masts are about r55ft. high, of box construction, each being 600ft. from the centre mast. The two out -masts visible are respectively north and south. Similar masts, east and west, complete the crossed loops, while two other box masts support the outer ends of the " T " aerial. The main laboratory building is seen at the foot of the central mast. visual direc- Fig. 3.- Visual direction -finder. The observer is watching the The large crossed loops are used for the fluorescent screen upon which the direction of the atmospheric tion- finder, the directional indication being given on a is indicated by a line of green light. A

www.americanradiohistory.com ;2 Vt,shoo JUIVE r50i, Waiad 1927. observer left inside to deter mine the direction of a signal, afterwards check ing the accuracy of th e hearing by the position o f the hut as read on the larg e circular scale visible on th e ground. The visual direc tion -ender in the interior of this hut is shown in operation in Fig. 3, where the observer is demonstrating the use of the fluorescent line to indicate the direction of a transmitting station. The photograph of Fig. 4 shows apparatus recently developed for recording the atmospheric disturbance on each of six wavelengths. Six separate sets, each using nine valves, are used, the recording instrument being the double- thread recorder seen to the Fig. 4.- Apparatus for recording atmospherics simultaneously on six different wavelengths. right pf the picture. The There are nine valves in each of the six receivers. The observers are calibrating the apparatus at Fig. 2 shot-s- a rotating hut which is being used for the input and output ends respectively. testing the performance of a similar apparatus working The atmospherics apparatus shown will he in use for on smaller loops for the direct reading of the direction special observations during the eclipse period, \\-hile a of wireless signals. The loop aerials are wound round visual direction -finder and an atmospherics strength the outer framework, on the grooved porcelain insulators recorder will also be in operation at a point north of shown. The hut can be rotated to any azimuth and the totality for comparison with Ditton Park results.

Low =power Signals Heard in the Anti= General Notes. podes. Mr. G. G. Livesey (2BZT), Stourton Since the preparation of the note on TRANSMITTERS' Hall, Horncastle, Lincs, has been experi- page 692 of our issue of June 1st, in NOTES menting with a receiving aerial consist- which we recorded the report of recep- ing of 60ft. horizontal wires arranged in tion in Tasmania of transmissions on a AND QUERIES. " V " shape 9ft. above the earth, with 6 -watt input, we have received letters which he has received U 2XAD at good from other correspondents on a similar loud- speaker strength on an 0 -v. -2 Schnell matter. receiver. 2XAD, which relays the WGY Mr. D. B. Fry (G 5UY), Mayfield, programme at 1.0, B.S.T., in the small hours of Sussex, has received a card front Mr. C. from one or other of the stations during Monday morning, is, like 2XAF, Harrison, of Bellerive, Tasmania, report- the whole 24 hours on a 2 -valve set. crystal controlled. ing the reception A correspondent in of his signals on He states that during it China, writing on April 22nd at 7.39 p.m., the time when May 19111, asks if any reader Tasmanian time, was daylight all across the Atlantic can give with an 0 -v. -1 receiver. was him the power used by PCTT and Mr. Fry at 2XAD on 22.07 metres was received much PCPP, that time using a hand generator which he has picked up there good giving better than 2XAF on 33.77 at an input 9 metres, the strength on an 0 -v. -0 receiver. of watts. latter being at times inaudible. During Mr. F. N. Baskerville, on the other the hours of darkness all across the ocean New Call= signs and Stations Identified. hand. reports having heard OZ 2AR 2XAF was much -Mr. better and stronger than 2AZP L. Sanderson, 30, Bonham Rd., Brixton A.. M. Rennie. 67, Campbell Street, Wan- 2X A D, though both stations came through Hill, S.\\'.2. ganui, New Zealand -last November on well 2BQA .4. Cawley, " Sunnybank," Church St., 34.5 metres when Ile was using only Frodshain, Nr. Warrington. 2BQH G. G. F.. Bennett, 26, Blenheim Part: Rd., 2.5 watts input. When it. was dark at the receiving end Croydon. and light in America 2XAD was louder GW 18C W. H. Benson, 46, Dutferin Ave., Dublin. American and more consistent Transmits on 23 and 45 metres, usually Short -wave Tests. than 2XAF, but when between 1900 and 2:300 G.M.T. the conditions of light were reversed ED G. Bramslev, Laboratory A 7ZM of Telegraphy correspondent in Birmingham reports 2X AF was stronger, 2XAD being in- and Telephony, Royal Technical College, that during the short -wave broadcasting audible 6 11.7 Farimagogade, Copenhagen. (Change of front to a.m. on Sunday ,el,i ress.) tests from 6 p.m. B.S.T. on Saturday. morning. For 18 out of the 24 hours June 4th, to 6.12 p.m. on Sunday, June every word of speech was clearly heard QR.A.'s Wanted. 5th, he was able to receive the programme front one station or the other. G 5F0, G 6LP, NU 1X1, ZAX. A8

www.americanradiohistory.com `71pie@§o 743 JC.\'E 15th, 1927. WorIlc1

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New '100 kW. Valve Used by WGY. 7111:, highest powered transmitting valve in the world is now being used by R-GV, the General Electric Company's big i,roadeast transmitter at S henec- ta lys N.Y. The valve is one of the latest developments of that company's research laboratories, and is ratel at loo k\ \'. The utilisation of this valve, Avhieh takes the place Of eight 20 kW. valves, marks the occasion of the first

practical use of a valve of this size for broadcasting. Mounted in its water jacket, ready for use, the new valve stands 7ft. high and weighs about too lb. The tungsten filament is Sft. long and has a diameter almost equivalent to that of the lead of a pencil. It contains two ounces of tungsten, or about 750,000 times as much of this metal as an ordinary bright- emitter receiving valve. lit order to keep the filament straight, several pounds tension is necessary, and this is obtained by means of a spring, N. which resembles an ordinary screen door hinge. To heat the filament 6.;5 kW., or about it h.p., is required. This is equivalent to the power used to light one hundred and seventy 40 -watt lamps. The leads carrying current to the filament are as large in diameter as a lead pencil, and the terminals used on these leads are similar to those ronunon in switchboard construction. In the development of the too kW. valve the engineers had to devise an entirely new structural design to provide the necessary strength and durability. Details of Construction. Outside its water jacket the valve stands five feet high, and. as can he seen in the photograph, two -thirds of this height consists of the copper envelope H, which is four inches in diameter. The envelope serves a double purpose, for it contains not only the elements of the tube, but is itself the anode or plate of the valve. The tipper third of the valve D is made of glass, through which the filament and grid leads snake their insulated entrance. 'l'he glass bulb is 22in. lung and 4in. in diameter, and it is sealed at E to the open end of the Internal construction of the IN kW. valve. copper anode tube by a machine process, in such n way as 9

www.americanradiohistory.com -

711 VAp®Ilmo JUNE 15111, WOyIlcI 1927. The World's Largest Valve. - construction to prevent short- to make circuiting due to swaying the junction F of glass and copper mechanically or sagging. A minimum strong of metal in the grid structure as well as vacuum tight under varying tempera- facilitates the exhausting tures. of the valve and mini- mises the possibilities of " softening " Two copper cables, at a later date B, of a size capable of carrying a due to the release, under working conditions, current of several hundred of occluded amperes act as leads to the gas. The state of the vacuum is estimated during pump- filament, and are connected to tungsten rods, h, which, in ing by means turn, of the ionisation gauge A, which is really pass through the pinch seal I to the ends of the an ordinary receiving filament. valve to which meters are attached Three lengths of tungsten wire, M, each roughly for measuring grid current. r6in. long, connect to each of the filament leads, where The grid connection C inside the valve is brought they come through the pinch, out thus forming six parallel through a special arm part way up the high- tension glass filament spans. These pass within the grid and meet at bushing to a flexible outside grid terminal wire. a common point at the filament spring suspension in the A uniform flow of water around the anode of lower end of the tube, which the valve is held in position by a is necessary to prevent unequal heating, and for this pur- quartz insulator, O, and spacer disc, P. pose a new type of water jacket has been The grid within the copper designed. envelope is cylindrical, and This consists of an ordinary jacket with an inner has an overall length of aft. flexible sin. In design it is a jacket secured to the flange G to direct the water past spiral. The grid frame L is a most ingenious structure the anode. of molybdenum and tungsten and is clamped to the glass The valve is now being operated as a plate- modulated at J. Bracing such as is common in steel bridge con- power amplifier at \VGY, where, due to the limitations struction, is used in the design to provide - maximum of the circuit, the output is normally held at the compara- strength with a minimum of metal. tively low value of so kW. Engineers are thus securing Sufficient rigidity and strength are necessary in this valuable operating data on the new valve. A. D.

USING BURNT -OUT TRANSFORMERS. Conditions Under which the Secondary Winding may be Used as a Choke. ONE fairly frequently sees suggestions in the tech- attained; as much, in fact, as can be had, for the same nical Press to the effect that the secondary of an quality, with transformer coupling, using valves of lower intervalve transformer can be pressed into service impedance and amplification factor. as a choke after the primary winding has " burnt out." Used in this way, the burnt -out transformer need not Provided that the limitations imposed by the fineness of be regarded in any way as a makeshift, for the wire it will prob- with which the secondary is wound, by the very ably prove a better instrument for this purpose large number than the of turns, and by the comparative smallness majority of commercial L.F. chokes, the inductance of the iron of core are duly respected, such a transformer which in many cases is deplorably low. can be made of great use. The fineness of the wire is a drawback chiefly insofar Avoiding Saturation. as it raises the D.C. resistance of the winding; the trans- The remaining purpose for which it is usual; in wireless former secondary is therefore unsuitable where heavy cur- practice, to employ a choke is as output choke where choke - rents have to be carried, on account of the large voltage - condenser feed to the loud -speakeris employed. drop across For this it. As a smoothing choke in any type of purpose the secondary, as it stands, is battery quite unsuitable, eliminator, for example, it would be utterly out but in cases where the disadvantage of the of place for D.C. resistance, this reason alone. Further, owing to the with its accompanying voltage drop, is not large number serious, it may of turns, and the smallness of the core, the be converted into a tolerable makeshift by providing iron will an become saturated if any attempt is made to pass air -gap in the core, which has the dual effect of reducing a heavy current through it. the inductance to a more suitable value and of preventing Choke Coupling. saturation of the core. The air -gap is introduced mOst easily by dismantling the core, and rebuilding it This latter limitation without must be borne in mind, too, if allowing the stampings to overlap. Normally the T stamp- it is desired to use the transformer in a choke -coupled ings are pushed in alternately from each end of the bobbin, amplifier ; if the valve that precedes it is of comparatively but if an air -gap is required it is necessary to put them low impedance the plate current would almost certainly all in from the same end, and to bring all the U stamp- saturate the core, for, with the average secondary, one ings round the bobbin from the other end, clamping them milliampere is about the maximum permissible current. so that there is a small gap between the ends of the U and Owing, however, to the very high inductance, which is the cross -bar of the T. usually well over 400 henries, there is no objection on the It is hardly advisable to use a transformer converted score of quality to using before it a valve of high imped- in this way as output choke after a " super -power " valve, ance (say from so,000 to roo,000 ohms), and the plate because the voltage drop is likely to be considerable in this current will in this case be too small to cause trouble from case, owing to the large plate current ; after a power valve saturation. Further, the high amplification factor of such of some 8,000 ohms impedance, however, it may prove ,valves enables considerable amplification per stage to be very serviceable. A. L. M. S. A 10

www.americanradiohistory.com JUXE 15/71, 1927. 't S

0 °RAN ICIVSTAT

A Three =unit Set Covering the Entire Broadcast Band with Switch Action for an Alternative Programme. By A. J. BULL. (t'amGalad from page 722 of previous issue.) to the baseboard the unit comprising the a1ve- detectar anti panel, and the remaining components (Fig. 14). low-frequency stage completed and in opera- in positions indicated in the working drawing the Igranic coils Nos. 150 tion on the local station, attention can be turned Upon completion of that work coils should be inserted to the long- and short-wave high- frequency amplifiers. and zoo and the two Gambrell and wiring commenced. Unit. B. long-wave unit (Fig. 12) covering a tightly in their respective plugs -The the filament circuits, which tyave -range of boo tu 2,000 metres is prulally- the most Begin the wiring with 22 tinned copper and simple of the three to construct. With working draw- should be connected up t'.itli \o. connections with No. -16 ings and component parts to hand, the unit can be Sistoflex (Fig. 17). flake other short as possible. A \There, assembled ready for wiring in about two hours. Care S.W.( ;., the leads being as lend is needed, arrange it so. must be exercised, however,. to ensure that the Utility for example, a 9o-degree a goad job of the wiring, and, as a result, switch is mounted on the baseboard in line with the one In short. make is stabilised it will remain so in- Mounted on unit C, so that when, at a later stage of when later the receiver connections shown at b (Fig. assembling, the rod connecting the switches is added, it definitely. The two input output leads shown by the dotted lines to shall operate smoothly. The ebonite panel (Fig 1,3). 1 5) and the three are made with 23/.007in. rubber -covered after drilling, is attached to the baseboard by means of 4, 5. and 6, soldered to their respective components two angle brackets and a piece of wool ?,in. square by tleville wire ; they thus become an integral fastened to the base immediately leluind the mounted on the baseboard 16in. long. remaining ends of the input which the panel is screwed. 'part of the unit. To the panel and to coloured red and black, The next step is to fit the three variable condensers, wires Clix plugs are attached, respectively, and to the out- terminals, i filament rheostat to the representing aerial and earth aerial and earth n put wires tags are soldered. Unit .1 .- Turning now to Fig. 16, it will be seen that unit _1 is in many, respects similar to 1t and that the tuned anode coupling between the valves is substituted for H. F. transformers. These are similar to the H.F. inter - valve couplings adopted in The 1Piicless World Every- man Four receiver. As the 'principles underlying the design of H.F. transformers have so often been explained in the pages of this journal, the writer does-not feel justified in introducing theoretical consideration of transformer design in this constructional article ; he will therefore comment, in passing, that it Fig. 12. -Unit B. The two -stage high- frequency amplifier, covering a waveband 600 to 2,000 metres. is essential to the successful

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Fig. 13.- Details for drilling the panel of B. Unit Sizes of holes: A. 1'2in.; B, 1'4ín.; C, 532ín.; D, 5/321n. and countersunk for 4BA screws. E, 1181n. and countersunk for No. 4 wood screws. design of H.F. transformers to give good selectivity, to may be mounted rigidly by means reduce to of brass rods a minimum the electrostatic coupling between Sin. long threaded 4BA and passed through the windings. Consequently, small the distance between the holes in the cylindrical formers, as shown in primary and secondary windings, Fig. 17 ; the number of primary 4BA nuts are placed on either side of each rod, where turns, spacing between turns, and diameter of wire em- they pass through the holes and grip the wall ployed. is of great importance. of the An examination of the cylinder. In a similar manner the ends of the rods coils designed for the " Everyman are Four " will reveal that secured to a baseboard measuring sin. x rin. x gin. due consideration has been given to these points, and Following the construction of the H.F. therefore, in view transformers, of the fact that the coils can be ptir- the ebonite panel should be drilled chased ready made to receive the three from most wireless factors, it is variable condensers, filament rheostat, and recommended that they Utility switch be adopted in this unit. (Fig. r8). The dimensions of this panel and baseboard If the coils are to be constructed minor modifications are identical with those of unit B, and the position may he made to simplify of mounting. The coils the components on the panel are the same. There are,

Fig. 14. -The baseboard of Unit B, showing the positions ut the components.

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www.americanradiohistory.com Wfipa.®00 1L'.1'T 15th, 1927. . WOOF'iild.

Fig. 15.- Resistance coupling has been substituted for transformer coupling previously shown in the low-frequency stages. In this valve becomes an anode bend rectifier when connected to the short -wave H.F. amplifier. Rio, 150,000 ohms. instance the detector 0.1 mfd. (mica dielectric). R,,, 100,000 ohms ; R12, 0.5 megohms ; R,;,, 0.25 megohms ; C9, 0.0001 mfd. C,o and C,,, however, no A and F, terminals. The panel is attached Utility switches mounted on B. and C linked together by to the baseboard by angle brackets and wood strip in a means of the wooden rod. similar manner to that of unit B. An inspection of the receiver at this stage should re- The H.F. transformers and remaining components are veal eight rubber- covered wires with free ends, six of now screwed to the baseboard in accordance with the which are fitted with tags and two with plugs coloured particulars on the working drawing (Fig. i9), and red and black respectively. Having connected the former wiring commenced and car - ried out on similar lines to the long -wave unit, using the practical wiring diagram (Fig. zo) as a guide. 'l'he three output connections (to be made to terminals N(3. I, 2, and 3 of unit C, see Fig. 15) are made with 23l.007 robber- covered wire soldered to their respective components, tags being provided for the other ends. Testing. The three units having been constructed and wiring checked with the diagrams, they should be placed on a convenient table in their normal working positions (hut without cabinet) and with the Fig. 16. -Unit A. Two -stage H.F. amplifier with a wave range of 200 to 600 metres. A 13

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Fig. 17.- Practical wiring diagram of Unit B. LIST OF PARTS. UNIT A. 1 piece of Ebonite 21in. X lin. x tin. 1 Baseboard of ply -156 wood, 21in.x S.'1in. 2 Neutrovernia condensers (Gambrell Bros., Ltd.) I Ebonite panel, 21in. x Tin. x tin. 1 pair bin. Angle brackets. 2 Variable condensers, 0.0003 mfd. (Igranic). UNIT B. 1 Variable condenser, 0.0005 mfd. (Igranic). 1 Baseboard of Ain. ply wood 21in. x Si in. .3 Slow motion dials (Igranic Indigraph. Cat. No. 2296;24 1 Ebonite panel, 21in. x Tin. 2 Anti- x tin. microphonic Valve holders. 2 Anti- microphonic Valve holders. 3 31-in. x Bin. dia. Paxolin or ebonite tube. ) or 3 "Wireless World" 2 Variable condensers, 0.001 mfd. 60 yards Litz (Igranic). wire 27142. tcoils (1 aerial coupler 1 Variable condenser, 0.0005 mfd. (Igranic). 4 pieces Ebonite rod, é dia. 1ft. long. and 2 H.F. intervalve 3 ordinary 4in. dials. 2 1ft. Lengths of brass rod threaded, IBA. 1 couplings). 2 Gambrell E.1 centre tapped coils. 39 4BA Nuts. 1 Igranic coil, No. 150. 1 Utility switch, D.P.D.T. lever pattern (Wilkins & Wright, 1Igranic coil, No. 200. Ltd., Utility Works, Kenyon Street, Birmingham). 4 Coil sockets. S Lengths of 16 S.W.G. wire. 1 Terminal marked H.T.+. 3 231.007in. ft. rubber covered wire. 1 Utility switch D.P.D.T., lever pattern. 1 4 -ohm Filament resistor and mount (Burndept). 1 Fixed condenser, 0.0002 mfd. 1 10 -ohm Filament rheostat (Igranic Pacent). 1 Grid leak, 2 megohm. 1 H.T.+Terminal. 11.5 -voll Dry cell, " Ever-Ready," Cat. No. UW1. 1 1.5 volt " Ever -Ready " dry cell, Cat. No. UW1 (Portable 1 4-ohm Filament resistor and mount ( Burndept). Electric Light Co., Ltd., 120, Shaftesbury Avenue, W.1). 1 10-ohm Filament rheostat (Igranic Pacent). 3 Clix sockets coloured Red, Blue and Black respectively. 2 Neutrovernia condensers (Gambrell). 2 Clix plugs, Red and Black. 3 6in. Angle brackets. Cabinet with hinged lid and removable back sections. (Carrington Manufacturing Co., Cameo Works, Sanderstead Road, South Croydon.) ERRATUM. Cy referred to on page 718 of the previous issue should be o.000x mfd. and not o.00x mid. as given.

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www.americanradiohistory.com 312

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E, 118in. 1 and countersunk for 4BA screws. D, 1/81n.; Fig. 18. -The panel of Unit A. Sizes of holes: A, 1/2in.; B, /4in.; C, 5;32in. and countersunk for No. 4 wood screws. with plug inserted in first to the terminals r to 6 on unit C, and the latter to (6) \lake a further test similarly coloured and mounted on the aerial coil L.F. stage. sockets remove the top of unit A, the receiver is ready for test. (7) If the tests prove satisfactory, two H.F. valves, and Proceed as follows unit and insert in the lower unit :- stage, a " general (1) Connect L.T. and H.T. supply to receiver. in unit C one H.F. in the detector a " power " valve in (z) Insert loud -speaker or telephone plug in the jack purpose " valve in first L.F., and aerial and earth to the of the second L.F. valve, and adjust all filament rheo- second L.F. stage. Connect an in first L.F. stage tune stats to the " on " position. receiver and with the telephones metres), adjusting the neutral- (3) Set wave- change switch to lower panel. in Radiola Paris (1,750 are found where a move- (4) By means of a voltmeter check voltage at each ising condensers until positions or anti -clockwise) produces valve socket. ment either way (clockwise to a 600 -metre station, (5) Continue to check valve filament potentials with evidence of oscillation. Now tune a slight adjustment of one of the wave- change switch set to upper panel. and it may be found that

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Fig. 20.- Practical wiring diagram, Unit A. the neutralising condensers is necessary to obtain a The short -wave balance. panel should now be replaced complete If that adjustment is carefully made it will be with two H.F. valves and found that the effect of valve capacity the unit is stable over the whole range of neutralised. This can be accomplished the tuning condenser. by tuning in stations near limits of tuning condenser, say, It is advisable, when 25o and making these adjustments, to 500 metres, and adjusting the neutralising condensers employ an aerial the height as of which is only a few feet just described. All that now remains is to fit the above ground, as the strength units of the received signals in the cabinet and to calibrate the receiver from broadcast are distressing to the ear. transmissions of known wavelength.

CURING "BOOM." ERTAIN loud -speakers of the horn type, especially ments by connecting the two bobbins in parallel instead - the earlier models, give a pronounced " booming " of in series, which tends to lessen the intensity of the low effect, which gives speech, more perhaps than music, notes. Really, this is curing one fault by introducing the appearance of emanating from the bottom of a deep another, and is, from the modern point of view, a well. In some cases that have come under the writer's thoroughly heretical proceeding; but, nevertheless, the re- observation, this effect has been so marked that speech sulting reproduction, though very far indeed from being has been very nearly unintelligible. perfect, is often more pleasing after this alteration has Some improvement can generally be made to such instru- been made.

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www.americanradiohistory.com ; ,._a : > -. .. , , WipgIl®00 JUNE 15111, 1927. Mplie 75,

Aids to Better Theoretical Diagrams Reception. Simplified.

VOLUME CONTROL. of either detector or L.F. amplifying this arrangement a suitable proportion is 7 SHIN dealing with a receiver valves. of the total L.F. voltage available j of taken from the grid leak. As resist- / V/ primarily intended to give It is probable that the methods high -quality reproduction, the pro- volume control which depend on a ances of this type are not generally blem of controlling signal strength is reduction in the input to the L.F. available, it will be necessary to con- not always quite such an easy one as amplifier are least open to criticism. nect two or more single leaks (Ri, R., might be imagined. Of course, it TWO alternative systems whereby this etc.), in series, totalling the resistance is does not exist when the set depends effect may be obtained in a resistance - required. The L.F. amplifier grid for its sensitivity on the use of re- coupled amplifier are shown in Fig. connected by means of a plug -and- action, provided normal volume is r. The first (a) is particularly ap- socket arrangement or a switch to one B, small, but this method of increasing plicable when the normal values of or other of the junction points A, as is, of course, ob- response is not operative in every case. coupling components are used, or C. Full volume is made It may sometimes be possible to re- tapped wire -wound resistors are tained when this connection resulfs in the duce intensity by detuning; this is not readily obtainable. When the coup- to the point A, which all the available resist- quite so bad a plan as is often sup- ling condenser is joined to that end inclusion of posed, but is not altogether desirable of the resistance which is connected ance in the grid circuit. Av under certain conditions and cannot to the anode, full volume will he pro- -0000 be generally recommended. duced ; this will he reduced progres- VOLTMETERS. is moved to- Another method of obtaining re- sively as the tapping II `H E normal purpose of a voltmeter duced intensity is by dimming the wards the end joined to H.T. posi- JL is to read the electrical potential filament of the high- frequency ampli- tive. differences between two points, and in fying valve. This, in practice, is At (b) is shown a scheme of con- this capacity it is extremely useful to convenient, but has its limitations. It nections which is generally more con- a wireless amateur. should be definitely stated that it is venient when a high ohmic resistance All types of voltmeters except the quite incorrect to dim the filaments is inserted in the anode circuit. In electrostatic, which relies on the affinity of two .electrodes at different potential, and the valve voltmeter, which relies on the change in anode current in a valve circuit following on the application of a potential to the grid, require current to give a deflection of the pointer. The amount of current required to send the pointer to the highest reading on the instrument (known as full scale deflection) varies in different classes of instrument, and it may almost be said that the smaller this current, the better the instrument. A superfine meter costing six or seven pounds would possibly take only one - tenth of a milliampere, whereas a cheap pocket instrument might easily absorb one -tenth of an ampere, or one thousand times as much. The range is given to an instru- Fig. 1.- Alternative methods of volume control. The usual damping resistance may ment by increasing its internal re- be inserted at the point marked X. A 19

www.americanradiohistory.com WipISIl®00 752 JUNE 15th, 1927. WOpIl4 sistance so that when a voltage lack of sensitivity is due to the pres- small change in intensity is applied more easily to its terminals corresponds ence of excessive resistance or damping appreciable. If the insertion of the to the highest marked voltage on the in the H.F. transformers or the cir- artificial resistance in series with scale, the the current required to give cuits associated with them. The aerial -grid transformer secondary re full scale deflection is flowing. easiest way of carrying out the opera- sults in a considerable decrease in It follows that since, with a given movement, the actual current required to give full scale deflection is always the same, the volts reading H T.+ is dependent on the internal resistance, e.g., of two instruments having the same pattern movements, but one scaled 0-12 volts and the other o -6 volts, it will be found that the internal resistance of the former is N.C. twice that of the latter. We have in this way a fair and useful way of comparing the relative merits of voltmeters -we say that the H.F. sensitivity of a certain meter is so many ohms per volt. The higher this figure (which is independent of actual "--AAA.A.A.V-- -il scale reading) the better. With a cheap pocket meter the figure may be as low as 30, while 200 may be taken as a reasonable figure for a good all - round instrument. Fig. 2. -The Insertion of artificial resistances as an aid to the location of damping in 0 0 0 o a receiver of the " Everyman Four " type. . TRACING FAULTS. tion is deliberately to insert an arti- strength it may be assumed with some T is probably safe to say that it is ficial resistance in each circuit in turn, confidence that this coil, with its con- .11. an easier matter to locate the more and then to notice if this addition re- denser, etc., is in order. The resistor serious faults, of the kind which give sults in an appreciable falling off in should accordingly be transferred to rise to a complete or almost complete signal strength. If it does not, then the intervalve transformer. If in this failure to receive signals, than to find it may be assumed that the circuit in position its presence appears to make the small leakages and resistances question has already an excessive re- no difference in signal strength, it may which merely reduce the total H.F. sistance, which must be removed justly be assumed that we have prac- amplification obtained from a receiver. before the best possible results can be tically located the source of the Indeed, it is always difficult for the obtained. trouble, which may be due to a com- less experienced amateur to tell This simple method of testing ap- pletely or partially short -circuited turn whether his instrument is or is not plies only, of course, to modern -re- on one of the windings, to broken working as it should. He may be dis- ceivers using efficient coils, and par- strands in the Litz cable, or to an ex- appointed as to the strength of distant ticularly to sets on the lines of the cessive H.F. resistance in the tuning signals, but, realising that local receiv- popular " Everyman Four " ; this condenser. It should be noted that ing conditions play such an important may be taken as an example, to indi- none of these possible faults would he part in determining the range of any cate the method of procedure. The indicated by-the ordinary tests. set, and lacking a standard of coml. essential H. F.- detector circuit is given If negative results are obtained, we parison, he may assume that results in Fig. z, which shows the position have at least the satisfaction of know- are as good as can be expected, al- for the artificial resistors R, and R2. ing (assuming the valve itself to be in though actually there may be avoid- These should be of some 3 to 5 ohms, order) that in all probability our H.F. able losses which should be elimin- and must be non -inductive ; they can amplifier is working properly, and that ated. conveniently consist of a short, straight this part of the receiver may safely be Poor H.F. amplification is gener- length (about r in.) of No. 45 Eureka passed over in our further search. It ally traceable to resistance in tt:e tuned wire, which has a resistance of ap- should be emphasised that this test is circuits, or to some form of damping proximately 2 1 ohms per inch. This applicable only to receivers with which acts in more or less the same should be mounted on a narrow strip lightly- damped circuits. way as a resistance in the wrong place. of ebonite, fitted with screws and nuts 0000 The actual measurement of high -fre- at each end, in order that it may be GRID BIAS PRECAUTIONS. quency resistance is a matter of con- supported on the wiring of the DUE to the fact that " super- siderable difficulty, requiring a fairly receiver. power " valves are now coming extensive laboratory equipment, but it It is advisable to carry out the test into more general use, it may be per- is extremely easy for an amateur, even when listening with 'phones to a dis- missible to repeat the advice, previously without any measuring apparatus, to tant station whose signals are weak, as given in these columns, to the effect obtain a very good idea if an apparent under these conditions a comparatively that the grid circuit of a low -imped- A 20

www.americanradiohistory.com JUNE 15tlr, 19_7. 753 WoPIlco1 ance valve, with probably a consider- usually brings us very nearly to the make one which will tune to goo metres by able voltage on its anode, should required result in the case of single - we can do this either winding the never be broken, even momentarily, layer coils wound on ordinary cylin- same number of turns of the same while the filament is lighted. This drical formers. In the first place most gauge of wire on a former of 7 } in.. means that, while adjusting grid bias of us are not so much interested in the or use the same diameter of former as voltage it is necessary to switch off the actual inductance of a coil as the wave - used in the original coil and wind it toils filament current before each alteration length to which it will tune with the with 120 turns. In making to is made. condensers at our disposal. Now we reach very different wavelengths it is Neglect of this precaution will cer- usually have on hand some coil with often desirable to alter both the num- tainly result in the passing of a heavy which we are familiar and we know ber of turns and the diameter. Perhaps we down to metres. anode current ; while this in itself from experience to what wavelength wish to tune 45 may not do much harm to the bat- this coil can be tuned when inserted in 1f we have a coil which we know for tery, provided it is of momentary our set and the tuning condenser set certain to tune to 45o metres we are duration only, it is possible that the 10 a certain mark. Such a coil may pretty sure that a coil half the dia- valve may he damaged. Certain be used as a basis for the design of meter and having one -lifth of the num- valves are found to he particularly other coils to tune to other wave- ber of turns will tune somewhere in of susceptible to harm from excessive lengths. The wavelength to which i the .15 -metre region. This method anode currents. coil will time in an ordinary receiver is reckoning is admittedly rough, but is 0000 very nearly proportional to the number u ry useful when one is rather puzzled as to what size Of coil to try. HOW MANY TURNS? of turns, outer things reinaining the 0000 rrH ESE questions are continually same, provided that the length of the confronting everybody who has winding space is not greater than the A CORRECTION occasion to wind tuning coils for him- diameter of the coil. Or, if the num- `H E letters A and B on the two self. Without going into any of the ber of turns and gauge of wire are kept I sketches showing H.F. Trans- formule for calculating the inductance the same, the wavelength twill be pro- former construction appearing in these of a coil from the thickness of the portional to the diameter of the coil columns of last week's issue were in- wire, diameter of the former, number former. Thus, if our known coil advertently reversed ; the correct of turns, etc., we can give a method tunes to boo metres and has 4o turns method was shown at B, and not at of making an intelligent guess which on a 2!, in. former. and we want to A as stated.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 73. -An A.C. High- tension Battery Eliminator. (To be concluded in next week's issue.) The present series of diagrams is intended to show progressively. and in an easily understandable manner, the various points to which special attention should be paid in the design of typical wireless instruments, and at the same time to assist the beginner in mastering the art of reading circuit diagrams. The eliminator shown below uses half-wave rectiffcatio'n and is probably the simplest pattern likely to give satisfactory results.

-0

;1) 2)

The double -secondary transformer, the 'rhe low -voltage winding is connected The plate circuit is completed through the primary of which is connected across the across the rectifier filament, a controlling high -voltage secondary winding to the A.C. main;. rheostat being interposed. negative output terminal.

irHE transformer should be de- resistances, \rill give about i 20 volts valves are available; amongst others signed for working on mains of output. The filament-lighting wind- are the DU.5, DU. Io, U.4, the voltage and periodicity of the ing must supply a voltage correspond- S. P.4tU. Where a small output is supply (which twill be shown on the ing with the rating of the valve ; if it required, an ordinary bright -emitter meter). Its high- voltage winding exactly coincides it will be possible receiving valve, such as the R.5V., should deliver about 120 volts; this, to eliminate the rheostat. with grid and plate connected to allowing for drop in the various series A number of suitable rectifying gether, will give good results. A si

www.americanradiohistory.com Wfip@Ilsoo 754 JUNE Worl'Il(1 rStlr, 1927. jhe xperimenter:s ófebook,

"EMPIRICIST." The Layout of a Wireless i . By Receiver. ing of this transformer should be connected to a " dead " point in the circuit, (b) Low= frequency Circuits. usually L.T. j It should be noted that the well- known choke- - . condenser method of connecting N our previous a loud- speaker to article we considered the precautions a circuit, while offering many which advantages in other re- were advisable in laying out and connect- spects, does not reduce the electrostatic ing up a high- frequency field of the amplifier, and it is now output leads, and if these are long there desirable to apply is just the the same line of argument to a low - same likelihood of distortion and oscillation frequency layout. being set up in the receiver as in the case where The classification no such coupling becomes more simple, inasmuch as device is employed. The use of the choke- capacity unit the distinction between resonant and non -resonant cir- is outside the scope of the present article, but it is hoped cuits becomes somewhat meaningless. Admittedly, a that it may be dealt with in another connection at a transformer has inductance and self -capacity, but since subsequent date. there is no connecting up of condensers_ in any critical manner the same tendency towards interaction is not in Jacks and Switches. general obtained. Furthermore, since the external wir- Possibly the principal troubles that arise in low -fre- ing of transformers has a negligible electromagnetic field quency amplifiers are due to attempts at incorporating in comparison with that passing through the core, the switches or jacks for cutting out a stage of amplification. precautionary measures outlined in high -frequency circuits This necessitates a considerable lengthening of " poten- become somewhat superfluous. tial " leads, and the consequence is almost inevitably a Troubles arising from potential leads remain, as before, distortion effect, if not actual oscillation when two stages a source of difficulty. are being employed. One is almost inclined, as regards stage switching, to take Grid Condenser and Leak Connections. up the attitude of a well -known authority and say : " Don't do it Foremost '' Other means of among these is the grid lead of the detector controlling volume can be adopted, such as a variable high valve, when the " grid condenser and leak " method of resistance or potentiometer across the secondary rectification winding is employed. This lead is the first point in of one of the transformers. Even this device necessi- the circuit at which a low- frequency potential appears, tates care in laying out, as it must be arranged so that and, owing to the impedance of the condenser, there is a the leads from it to the secondary of the corresponding very strong tendency for electrostatic pick -up at this transformer are short and not of unnecessary thickness. point. This may take the form either of a tendency The layout of the amplifier, apart from these considera- towards reaction, giving a resonance or even an actual tions, is not a difficult matter, bearing in mind what is oscillation on some audible frequency, or else a pick -up normally a necessity in respect of " potential " leads. of induction from A.C. mains or other source of audio - Subject to a suitable arrangement of the components, the frequency disturbance. It is of the first importance to leads to grids and plates may be made very short, and connect the junction of grid condenser and leak to the the return leads may be taken in any desired manner to grid terminal of the valve holder by the shortest possible their appropriate terminal connections. The stability is lead. Not infrequently it is possible to connect both the sometimes improved, though not always, by earthing the condenser and grid-leak clip direct to the valve- holder shrouds of the transformers, and occasionally the sense terminal, and if this can be arranged it is very satis- of the transformer windings has a controlling influence factory. upon performance. Inasmuch as the grid condenser and leak must be in It may be said, however, that a reversal of one of the the circuit somewhere, however, it is essential that par- transformer windings, except in the particular case of ticular attention should be paid to the wiring of the rest impedance in the H.T. circuit, is not a satisfactory cure of the amplifier. The worst trouble arises from the leads for instability, and a set which is properly laid out connecting the set to the loud- speaker, and it is frequently should not \vork differently when the windings are of advantage to employ a step -down transformer on the reversed. output of the set, so as to reduce the electrostatic field A word would appear to be necessary on the subject of on the output leads. Some point on the secondary wind- resistance -capacity amplifiers, inasmuch as these have cer-

A 22

www.americanradiohistory.com IL'.\'/: 1511r, 1927. 755 Wopllcsl The Experimenter's Notebook. - tion with the longer wavelengths, however, brings these tain special- feature, which it is desirable to consider. troubles into increasing prominence as the wavelength 'l'he principal trouble with these amplifiers is that radio - is inricased, though with simple radio- frequency circuits, frequency currents get through them to a really alarming embodying not more than one stage of high- frequency extent, and in consequence it is necessary tither to employ amplification, the effect of the radio- frequency passing rigorous means of filtering out such currents at the detec through the resistance amplifier %yill he merely as if a for valve stage, or else to apply the same Fart to the certain aimant of reaction of an accidental character leads of the amplifier as has been recommended for ',tigh- had crept into the circuit, thereby necessitating a slight freiluency circuits. The following out of the latter mollification of the existing reaction adjustment. policy is made very easy by the extremely compact nature A resistance amplifier which follows a supersonic of the components used in these amplifiers, and it is receiver operating on a waxelvngth of about 6,000 metres probably due to this that in practice there is frequently almost invariably gites rise to serious trouble, and nothing no trouble experienced, at any rate on the shorter waves. but careful filtering out of the intermediate frequency is l'he use of a resistance -capacity amplifier in cornice- of any use.

Captain Round's Short -wave Set. ciIL's transmitting station and to report on the effect of surrounding objects on President, ('apt. Il. .1. Round. The -ignal strength. Ten parties will start entertained members of \L('., \LI.E.E., NEWS FROM3OM off from predetermined points and each the Mus well Hill and District Radio group will be equipped t. ith a receiving at his house un Wednesday, .Tune Sudety set. frame aerial. magnetic compass, pro- 1st. when a very pleasant evening tt'as THE GLUM. tractor, map, lunch, a iid a ca'. A super -heterodyne was installed spent. Operations will begin at 12 noon, but in one rouit. while in another was a ltice - letter front Epsom reported fine signals a general stand -by will be observed for Kellogg loud -speaker and amplifier, ail elec- 115. lunch between 1 and 2 p.m. Operation's gramophone, and a highly efficient trical Among tr'ansmitter's present "ere 61.L. will cease at 3.30. Transmission will be short -wave set with two Il. F. stages. null 51'1'. Members 150 metres, interrupted C.\V., from instrument was operated by Jlr. Tre- on Titis voted it the best field day ever held, and station 5( ''I' sending ten -second dashes mayne, and signals were received. from another will be arranged soon. f v, minutes alternated by five- utiutte North and South America, Australia. lion. Secretary, Mr. L. -T. Fidler, 13, viva , and India -those f South Ai Neagry Road. \ \'anstead. Esse* ng the broadcast programmes from the new beam day emanating 0000 lucked up from Hilversum, Radio station. At 9.30 Capt. 1'. P. Eekersley Finding a Hidden Station. l' 2LO. and of her stations, awhile :'rived tu amuse the cumpaly with many fiudin, l game.; have been arranged for songs and jests. Before the gathering anti itious "direction- a .i n Sunday t l a I,t e a fteruoou. The r, moats broke up at midnight thine honorary scheme has been arranged for by green are in the hands of the Ho Ia;V, thoniers were enrolled. viz.. Mrs. Il. J. nest. .Tune 19th, the Guiders Society. The object Lt. -Col. 11. A. Scarlet t, I I 3.57a, Round. Capt. P. P. Kckersley, aucj Mr. and Hendon Radio to lucite the Pinckney Road, N. \V.3. '1.111 o'ne. of the nmnneuvres twill If, The Society is making excellent head way. bit vacancies still exist for new mends is. lion. Secretary, \f r. herald S. Ses- sions, 20, I:rasincre Road, \Iustwell Hill. N .10. ooco Q.R.P. Transmitters' Field Day. Permits having been procured, the Q.R.P. Transmitters' SIR' t iy met at. 6LL's bungalow un the banks of the River Lea near Royden, Hertfordshire, for a field clay on \lay 29th. A lase station using call 6LL was installed in the bungalow and used a " Hartley " circuit on the 180 -metre band with grid modulation, the antenna being a 'I'. 15ft. high and 25ft. long. The portable station, conveyed by car and motor cycle, and using the call 6LB, was a choke control set for which 6TA was responsible. Input at both stations averaged 6 watts, H.T. being supplied in both cases by either a 1).0. hand generator or two 120v. \i -L anode converters in

Connuunieation was m a i n t a i n e d IInuughout the day between both stations. speech being exceptionally well received over distances up to ten miles. In one case speech from 6LB, the aerial of which was stiitcheil n!o)n.! !Fie grotutd, was received at 6LL, eight miles away, 114. station 6LB in action during a field day Later 5111) at twenty utiles and 6.1 L) at AN IMPROMPTU TRANSMITTER. Portable held recently by the Q.R.P. Transmitters' Society near Royden, Herts. Note a portion of ten utiles were worked from 611. speech the aerial which was stretched along the ground! Speech was heard R4 at a distance of being perfect according to 6.1.D. Also a 8 miles. A 23

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News of the Week in Brief Review.

NOT A NOISY INSTRUMENT. SHORT -WAVERS, PLEASE NOTE. LISTENERS IN JAPAN. " Wireless does not cutue under the de 'l'he Philips short -wave station PCJJ, Approximately 300,000 people now hold scription of a ' noisy instrument.' "- at Eindhoven, will broadcast to- morrow receiving licences in Japan. Each set is Clerk at the Willesden Police Court. evening (Thursday) from 5 to 8 o'clock licensed at 2s, per month. This is rather discouraging to owners of 0000 power amplifiers. 0 0 0 0 0000 (HARD) LABOUR OF LOVE. WIRELESS SET FOR STORMS. \Vhen Clifford Roberts was found guilty DEVELOPMENTS AT CROYDON. A ship's 2,000 -watt wireless transmitter, of stealing wireless parts to the value of specially designed to A new v, iteless station is shortly to be provide a stable £43 ils. 2d. at Wolverhampton last. week, erected at Croydon Aerodrome to super- wavelength adjustment independent of his defending counsel pleaded that it was sede the present installation. :Messages variations which might be caused by the simply a love of wireless that had macle rolling or will be rcieived and despatched over a pitching of the vessel, has been his client commit the offence. much large,: area than is possible to -day. installed on the U.S. coastguard cutter The magistrates, who were unmoved 0000 North hoe Mier /and. by titis tender appeal, sentenced Roberts The equipment, produced by the to three months' hard labour. APPEAL THAT CARRIED. General Electric Co. of America, em- 0000 in respo,c' to a broadcast appeal, a bodies " dead front " panels, so that the A TIME OF CHASTENING. gift of five dollars for the church hostel operator is not exposed to dangerous volt- The present tinte is one of probation if has been received bv the vicar of St. ages thrown against the set during for the American broadcasting stations Martin-in-the-Fields from it listener in heavy seas. which have been allocated new wave- Amouica. O 0 0 0 BRITISH ASSOCIATION MEETING. The ninety- seventh annual tweeting of the British Association for the Advance- ment of 'r deuce, is tu be held in Leeds from Wednesday, August 31st, to Wed-

nesday, . ..'eptenilier 'th, 1927, inclusive. 0 0 o L1GII'CHOUSE LISTENERS. The installation of a broadcast receiver in the Inchcape lighthouse, near Arbroath, marks the completion of the Dai /i1 New.; Wireless for Lighthouses Fund. Lord Iuchcnpe contributed £1,200.

0 0 O 0 DISTANCE NO DIFFICULTY. An inauguration coteutony conducted over a distance of two thousand miles took place in Paris recently, when officials in the French capital opened the new colonial wireless station at Brazzaville, in the French t_'ungo, O 0 0 BROADC:AS t DESCRIPTION OF THE

An oye t:itwe:;ï act-,1.-.ut of the Senio, moor ,-cle rare in the Isle uf \I will be .1;. t, ::ll r-tatious at .June (the clay 0 I' the r,ice) at 9.20 p.m. flowt Liverpool. 'l'i: c muuentator wil! lae " lxiou.' unr ri-,tcr I,nur.ul, The J1vh. G;,tClr. lie will Irave the island innwe- mt - \\ I \G COMMENTARIES IN GERMANY, A scene at the aerodrome near Berlin during the wait for Messrs. Chamberlin and Levine, Atlantic flyers. diatelv ; tici tho ;ace iu ,nrder to reach the The com- mentators had the unenviable task of " filling time " with lengthy descriptions the Liyt.i thl:c to htoadcitit. during the prolonged wait for news.

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www.americanradiohistory.com Fat-Tti.. gre7

JUNE 1111, 7927. Wpd@go 757 WokIld! lengths by the Federal Radio Commission. less. They were convinced that wireless its use at KDKA-A- the station tuned very The test period covers sixty days from was a sound proposition for fire brigade sharply at near -by points, although radiat- 3 a.m. on June 1st. purposes and could be easily worked. ing as much as 50 kilowatts energy. Stations which satisfy the Commission Observers at 1llichigau. New York, and that they are not causing interference will Massachusetts have reported that the be granted a three -year licence. FORTHCOMING EVENTS. .ig i iI strength is even ;trouger than when 0000 the ordinary- transmitting system was WIDE -AWAKE FARMERS. WEDNESDAY, JUNE 15th. used. There has, at the same time, been Totnnhann Wireless Soviet 8 p.m. On May 7th, according to the U.S. De- . -1t 10, Br,, e Grove. Competition for a great saving in the number of valves partment of Agriculture, 1,252,126 Ameri- t ao -ral,e long-distance receivers. requited in transmission and the amount ,IIionrll 11111 and flint riet Radio Society. All valves can farms were equipped with receivers -:1 t 8 . 1 ( Tolling(on1 , School, of power necessary. modulator for picking up market and weather re- Teti erdoien. Lee( are and demonstration are eliminated, and this, in the case of by Messrs. A. C. L'ossor, Ltd. ports. KDKA, means 12 10- kilowatt water - o000 THURSDAY, JUNE 16th, cooled valves. SWEATED LOUD -SPEAKERS. (folder., Green and Hendon. Radio Society. 0000 --AI 8 p.m. At the ('I ub House, 11. Oh- The man who can never switch off is field tiny. N. n'.11. Lecture " Pict are STOCKTAKING IN AUSTRALIA. Broadcasting," by Mr. F. II. Haynes, the of a trenchant article by John The existing order of broadcasting in subject Asst. Editor " T)ae n i retins 11' arid... may undergo striking changes Wallace in the June Radio Broadcast, SUNDAY, JUNE 19th. Australia New York. polders Grreu and Hendon Radio ,Society, at the ]rands of a Royal Commission " When you open the door of his house -Field dan. which has been appointed to enquire into for a friendly little call of an evening," WEDNESDAY, JUNE 22nd. the position of wireless and broadcasting says the writer, "you are immediately Radio 5'oriety of Great Britain. -Ordinary throughout the continent. All aspects Meeting. At 6 p.m. (I ea at 5.301. At greeted by a resounding blare from a loud- the Inst it at ion of Electrical Eli ainrcrs, of the subject will be considered, the speaker in the next room. And whether Savoy Hill, 11..C'.2. Lent art r "Fading in most important questions relating to wire- Radio con: pared 'with at her slat oral the order of the evening he bridge or phenol, ena,'' by lie. H. .1. P. L.ittic- less and national defence, broadcasting poker, ping -pong or conversation, that in- dale, F.R. Met.. Soc. and the Press, Government administra- fernal loud- speaker continues to vibrate tion, experiment and research, besides patents and copyright. viciously the evening through. It vibrates NEW SYSTEM TRIED BY KDKA. from string quartet to brass baud, from 0000 election speech to bed -time story, from The engineers of the Westinghouse NEW AMERICAN PATENT wheezy soprano to musical saw player, Electrical Co., in an endeavour to reduce AGREEMENT. from stock market report to bee- keeping as far as possible the interference and An important agreement lias been instruction, and Lack again-and all over improve the efficiency of the well -known entered into between the Crosley Radio again." high -power station in Pittsburg, have Cerporatiuu of Cincinnati and the Radio This type of listener is not uncommon developed a system of " frequency modu- Corporation of America, whereby the it is much in this country, but here, of course, we lation " which, claimed, gives Crosley concern is licensed to use patents pay for the entertainment, and to miss sharper tuning and employs considerably held by the P,.C.A., General Electric Co., any of it would be a pity. the American Telephone and Telegraph 0000 Co., und the Westinghouse Electric and WIRELESS " LIGHTHOUSES " FOR Manufacturing Co. Henceforth the ALL SHIPS ? Crosley Corporation will be permitted to 'Wireless beacons giving a service of use 100 basic patents, with the exception protection to vessels which are not of those covering the super -heterodyne equipped with special D.F. apparatus is and superregeueration.0000 the latest project of the Board of Trade. Experiments with such a device are THE SUPPLANTED SHEPHERD. already in progress, and if they are suc- The weather forecasts of the Air Minis- in cessful a most important step forward try which are broadcast daily have will have been made in the interests of Many country districts supplanted that small ships and cargo boats which cannot born weather prophet, the local shepherd. carry elaborate apparatus. It is said that even he now gets his in- 00o9 formation from 5XX, but many of the FIRE BRIGADE WIRELESS. oldest inhabitants of our villages still " Wireless Communications and the stoutly maintain that his old -fashioned Fire Service " was the subject of a paper forecasts were more0000 accurate. by Fireman Tom Knowles, of Bir- read ON FADING. nmingham, at the conference of the In- A LECTURE stitution of Fire Engineers at Liverpool " Fading in Radio " is the title of a on June 2nd. lecture which will be given by 11ír. Since 1920, when successful experiments H. A. P. Littledale, F.It.Met.Soc., at th.. in wireless communication had been con- ordinary meeting of the Radio Society of ducted between a fire engine and brigade Great Britain on Wednesday, June 22nd. headquarters in Loudon over a distance The lecturer has discovered a definite typo of seven miles, interest in the matter had of periodicity in the fading of wireless keen spasmodic, said the lecturer, but signals which he finds only to exist in several brigades had experimented on decliuluion t shies, earth -air potential their own account. He was convinced ROYALTY IN THE STUDIO. The tables. and in sunspot cycles. He will Queen of the Netherlands photographed analyses of of luis records that sooner or later wireless would be before the microphone of PCJJ, Eind- exhibit n10 used to a very- large extent to keep various hoven, while broadcasting to the Dutch and a number of original charts made colonies. With Her Majesty is H.R.H. during a period of four years. units of a fire brigade in touch. Princess Juliana. 0000 Chief Superintendent Wilson, of Roch- dale, said his brigade had experimented less power than " power modulation." A CORRECTION. with wireless and held transmitting and Briefly, the new system of transmission, In the valve data sheet which accom- receiving licences. At a recent display one instead of varying the amplitude or panied our issue of April 6th, it was of the engines was fitted with wireless and strength of the signal, maintains an even stated in error that the A.C. resistance communication was maintained with head- constant strength of signal and varies the of the S.S.13 valve, a product of the Elec- quarters on the way to and from the frequency by a very small amount, tron Co., Ltd., Triumph Rouse, 189, Regent ground and throughout the display -in usually not more than .5 to .8 kilocycles. Street, London, W.1, was 4,000 ohms. fact, they actually received a call by wire- It is stated that during the few weeks of The figure should read 74,000 ohms. A 25

www.americanradiohistory.com sr, 4w.,_ ,`: .!?-r.:.4

WilpIlc7o jL.\'E 15th, 1927. 1N O11

An Inexpensive Long distance Receiver of American Origin.

HE Croslev 5 -5o receiver is of American origin tuning circuit, and efficient screening prevents direct and is produced on mass production lines by The coupling between the two circuits. Croslcv radio Corporation of Cincinnati. This Stability in the H.F. stages has been attained not by organisation has been at the forefront of the movement any of the fashionable neutrudyne balanced circuits. but to pro\ idc " radio for the million," and may be said to by efficient screening and weak coupling between -the have a unique experience of the requirements of the primary and secondary windings of the H.P. trans- average ht'ondca.,t listener. formers. With this system less than the optimum ampli- American radio " fans " have an innate love of " get- fication per stage is obtained, but this is immaterial, since ting distance." and a high degree of sensitivity is essen- with two stages there is in mple margin of amplification tial in any receiver which is to capture the popular above the requirements for average conditions. A far imagination. At one time the single -valve reacting circuit more important consequence of loose coupling in the H.P. or " hinoper " supplied this need, but of late it has transformers is the very considerable increase of selec- fallen into disrepute. not only on account of the inter- tivity which it gives, a quality which alone would justify ference it causes. but because it dot's not possess suffi- this method of coupling apart from consideration of cient selectivity to disentangle the maze of stations which stability. has congested the American ether since tile inception of broadcasting. High- frequency amplification l,efore de- Fine Tuning. tection supplies the necessary sensitivity and selectivity, Of course, with such highly selective circuits it is ino- hurt multiplies the number of tuning controls, so that perative that they should each he tuned exactly to the with two stages there are three tuning condensers which same wavelength. otherwise the overall selectivity of the live to be operated simultaneously. To master the con- set will not he s. o high as that of the circuits taken in- trols of such a set would require more time and effort dividually. To unsure exact tuning small variable com- than the average listener would he inclined to devote. pensating condensers are fitted to two out of the three Unified control of condensers is, therefore, a sine qua circuits. So well, hi,wecer, do the main logarithmic con- non of any popular receiver employing more than one densers function that the compensating condensers are high- frequency stage. superfluous for 75 per rent. of the stations received, and The I'roslev set has been developed along these lines, need only he brought into action when experiencing severe and the use of logarithmic interference from a near -I,y AERIAL enndenscrs has i ìade the station. unified control a complete Two stages of audio - success. The two high - frequency amplification are frequency stages are trans- PM.5X P.M.5X incorporated to bring sig- former coupled and are fol- o nal. up to loud- speaker lowed by a reacting detector 2nd H.F. DET. strength, and provision is valve. There is no fear of made for the use of a re- radiation. however. as L J power output valve in the the H.P. stages act as an L--- S. last stage. effective filter between the `o much for the electrical Layout of H.F. and L.F. stages in the Crcsley 5 -50. Dotted lines detector and the aerial indicate screened compartments. circuit; let us now consider A 26

www.americanradiohistory.com JUIVE rstfr, 1927. ';'firnIlig00 WiNsIla 759 Broadcast Receivers- Crosley Model 5-50. - The tuning controls are clearly visible in the photograph the layout and constructional details. Here considerable in the title of this article. The main tuning control is ingenuity has been shown in combining convenience and seen near the right -hand top corner of the panel. The efficiency with low cost of production. All the components compensating condensers are operated by levers working in are mounted on a metal " chassis " which can be with- two vertical slots lower down on the panel. They are drawn from the cabinet after removing the two small tuned "acuminators " since their principal function is to ebonite control knobs on the front panel. sharpen tuning by bringing all circuits to the same wave- The " chassis " consists of a metal box the top of which length. The small knob on the right -hand side operates slopes downwards from the front panel and supports the the reaction coupling device, which consists of a small coil tuning condensers and valve holders. The interior space controlled by a quick- thread screw. It is known as the below this panel is divided into three compartments by metal partitions running from back to front of the set. The distribution of components in these compartments is well thought out. The first compartment, starting from the aerial, contains the 1st H.F. and 2nd L. F. stages ; the second compartment, the znd H.P. and 1st L.F. ; and the third the detector and reaction circuits. The introduction of L. F'. transformers into the H.F. compartments in no way interferes with the functioning of the H. F. valves, and Plan view of interior as seen from the rear of the set. Note the tuning drum with detachable the extra spacing between paper scale. partitions which results from the use of this method is a great advantage inasmuch as " Crescendon," since it is used to increase volume on dis- the H.F. transformers can be mounted farther away from tant stations. Incidentally, the judicious use of this the metal partitions. control will greatly improve selectivity on wavelengths close If further evidence were required that the designers to the local station. Finally, there is the left -hand 'ebonite understood their business the method of wiring the set knob, which controls the rheostat for the valve filaments. would suffice. All H.F. wires are direct and pass through The performance of the set is very convincing. Imme- clearance holes in the partitions, and battery and grid bias diately after connecting up and without any manipulation leads are collected in groups at the back of the set and of the " acuminators," stations were picked up at intervals tied together in the manner of telephone exchange wiring. of two or three degrees all round the dial. At least 3o The valve -holders are arranged immediately over their stations were received at good loud- speaker strength in this respective components in the compartments below, with the way, but interference from 2L0 (361 metres, 3¡ miles dis- result that H.F. and L.F. valves alternate as shown in tant) was experienced on wavelengths between 325 and 410 the diagram. Mullard valves with special U.X. American metres. By careful adjustment of the " Crescendon " and bases are used throughout. " acuminators," however, the width of the interference band can be considerably reduced, and outside a radius of Unified Condenser Control. five miles Cardiff (353 metres) can be tuned in sufficiently The plan view of the interior shows the mounting of the clear of London to be enjoyable.- Proof of this was logarithmic condensers, which are coupled through insu- established by a daylight test during one of the afternoon lated flexible joints and operated by a large diameter drum. transmissions, when Cardiff's signals were rather weak. A knurled flange on this drum projects through a slot in Generally speaking, the quality of reproduction is not the front panel, and a small square " window " with indi- up to the standard of the best British sets, but by careful cating pointer reveals a small portion of the paper scale adjustment of the controls it can be made very pleasing. upon which calibration particulars may be entered. The In our opinion the most striking feature of the set is the paper scales are detachable and may be renewed. There remarkable way in which distant stations fall in as the is very little friction in the system, and only a light touch tuning drum is rotated ; it is virtually a single- control set. is required to rotate the drum. European conditions in the ether now approximate to those The sane photograph also shows the ebonite terminal in America, and the performance of this receiver is well strip let into a recess at the back of the metal sub -panel. suited to current requirements in this country. Here a minor criticism is possible. Since the metal panel The sole distributors are the Wholesale Wireless Co., is earthed a short- circuit will result if any of the H.T. + 103, Farringdon Road, London, E.C.1, who carry out the wires are allowed to touch it when pushing the bared ends final assembly of the parts. The set is licensed under through the terminals from the back. The obvious remedy Marconi patents, and the price, without valves or acces- is to bare the wires only for a distance of u to in. sories, is .20, including royalties. A 27

www.americanradiohistory.com 760 wp@Ils,00 1U21/E 15th, r927. WopDcol REGULAR BROADCAST'CAST' TRANSROSSROHSo List of Stations Likely to be Heard in England. if N preparing the following list of broadcasting stations have chosen those in Canada and the United States which IL we have spared no pains to make it as complete and are most likely to be of interest to our readers, and have accurate as is possible under the ever -changing conditions. given a fairly comprehensive list of those in British pos- In selecting the principal stations outside Furope ur sessirms throughout the world. Nominal Present Nominal Present Station. Call- Power II'm-elewith Station. Call- Power Il'a+:elengtic sign. (K lonolts), (,lletre.3). sign. (Kilowatts). (Metres). EUROPE. Novosibirsk, Russia 1{A3:3 4 700 {4,000 Saratoff, Russia 1 700 Komigswusterhausen .1 FL' '2,91M 1 Moscow (Soviet Workers' Union) RA4 675 Eiffel Tower, Paris (Time -signals Stavropol, Caucasus RA20 I IIJ./ in code 09.26 and 2226 G.M.T.). FL .i 2,650 Moscow, Popoff, Russia MSK ° lí:al Berlin (Wolff's Bureau) - 5 2,525 Kharkov, Russia 1{A4:3 4 6414 Momtesanto, Portugal ('TV 1.5 2,4511 Grenoble ( Radio Club of Grenoble, Kovno, Lithuania - 2 2,01N1 France) - 1 585.2 Scheveningen, Holland 21 1.950 Freiburg, Germany (relays Stutt-

Koszice, (Kassa) ('zeeho- Slovakia. - 1.8711 577 - - gart) - 2 Norddeich, Germany -- -_ 1.8111) Vienna (Radio Wien) - 1.4 577 Paris (Radin Paris) CFI{, 3 1.7:111 Berlin (\lagdehurger Platz) 566 Daventry, England (Time- signals Bloemendaal, Holland - - .51113 10.30 a.m., 6.30 p.m., 9.0 p.m.) 5XX 25 1,11()4.3 Mikeli, St. ylichel, Finland (relay AIoscow, Komitern, Russia ...... RD\1' ez 40. 1,4:d) station) á 566 RAI Ilniepropetiovsk, Russia 560 Nijni- Novgorod, Russia 1(AI:3 1 - 1,4011 Hamar, Norway 55 13 urlsborg, Sweden SA1 5 1,:31i.5 Itudafxst, Hungary :3 :xw.6 Motala, Sweden 30 1.305 Sundsvall, Sweden S ASD 545.6 Irkutsk, Russia 1,:3110 NI ankh, Germany 1.1 535.7 Konigawus_terhausen, Germany Riga, Latvia 526.5 (relays Voxhaus) A I°r 1 1,250 Vienna ( Rosenhügel) 5 517.2 Hjürring, Denmark (relay station) 1,225 Krasmxlar, Kuban, Russia RA38 1 :513 Boden, Sweden (relays Stockholm) SASE 11 1,200 Brussels SBR 1 R I108.5 Luxemburg 4 1,201() Porsgrund, Norway 504 Sorii, Denmark (relays Copen- Palermo, Italy (projected) IC'P S4 501) hagen) 1' 1,1:53.8 Tromso, Norway - 501) Ryvang, Denmark 1,1:111 Aberdeen 2BD 1.1 500 Kallundborg, Denmark (projected) 71 1,151) Uppsala, Sweden (relays Stock. Warsaw, Poland ANO 10 1,111 holm) 500 Kbely, Prague, ('zecho- Slovakia.. OK 1' 1 1,110 Valencia (Heine Victoria Hotel, Viburg, Denmark (relay station) . 1 1,110 Spain EAJ 14 500 Basle, Switzerland 4 1,100, Linkaping, Sweden (relays Stock- De Bilt, Holland PUFF l; 1,100 holm) SMUW i 497.5 Hilversum, Holland H DO 5 1,071 Zurich, Se itzerland N BZ 4913 Veliky Ustjuk, Russia R_1113 14 1,010 Bournemouth 61331 ]t 491.8 Leningrad, Russia 1{A42 10 1,11(N) Berlin, 11'itzleben 4- 483.9 Moscow (Central) lI1 1,000 Lyons (l.a Doua) (relays Ecole Odessa, Russia R A40 1¡ 1,000 Superieure P.T ) VN 1 478.1 Ust- Syssolsk, Russia 1{E1; 1; 1!NNI Kharkov, Russia I{A24 4 475 Tver, Russia RA44 It 9115 I.angenburg, Germany 25 468.8 Minsk, Russia RA18 l'4 9:111 Paris (Ecole Superieure) FPT'r 4134 Voronesh, Russia RA12 11 !1511 Barcelona (Radio l'atalana) EA.J 13 11 462 Leningrad, Russia RA13 ., 9411 Oslo, Norway It 461.5 Hamel, Russia 1{ A39 I ¡. 925 Vladivostok, Russia RA17 l' 4.513 Tiflis, Russia 4 b711 Stockholm SASA 11 4:rt.5 Artemosk, Russia (relays Moscow Rome 1R1) 3- =WM 44a4 and Kharkov) `;:d1 Moscow (Trades Union) I{A2 -450 Lausanne, Switzerland HB2 Y511 Notodden, Norway (relays Oslo) 447.8 Rostov -on -Don, Russia RA 14 8211 Rjukan, Norway (relays Oslo) ... 443 ( (dense, Denmark (relay station) . 1+111 Bruno, I'zeeho- Slovakia 441.2 Ivanovo Voznesensk, Russia .... 1{07 81111 Bilbao (Radin llab de 'Vizcaya). Sevastopol, Russia RA9 tMNI Slain EA.J9 4:36 Tashkent, Russia RA27 4 fMMI Fredrikstad, Norway (relays Oslo) 434.8 Kiev, Russia RA5 775 Frankfort -on -Main 44 428.6 Baku, Russia 1{A45 760 Cracow, Poland I!. 422 ( :eneva, Switzerland H Rl 1 760 Moscow (Peredacha) 4.21) Hogorndsk, Russia 1{A8 7511 Bordeaux (Lafayette) 419.5 Ekaterinburg, Russia RA 15 751) Bilbao (Radio Vizcaya) Eä311 418 4113.7 I )stersund, Sweden 7211 Gotebcrg, Sweden SASB astrakhan, Russia RA_'13 700 Berne, Switzerland 1113.4 J 411 A28

www.americanradiohistory.com JUNE 1 jtTt, 1927: WIlpg®00 Thifam 761 Nominal Present Nominal Present Station. Call- Power Wavelength Station. Cell- Power Wavelength sign. (Kilowatts). (Metres). sign. (Kilowatts). (Metres). EUROPE -continued, Lyons (Radio Lyon), France - 14 291.3 Glasgow 5SC 11 405.4 Lille, France - 4 287 Salamanca, Spain EAJ22 1 402.5 Tallinn (Reval) Esthonia - 2 285.7 Cadiz, Spain EAJ3 1 400 Edinburgh (relay station) 2EH 4- 288.5 Cork, Irish Free State 6CK 11. 400 Dortmund, Germany (relays Miin- Bremen, Germany (relays Ham- ster) - 4 283 burg) - 11 400 Cartagena, Spain EAJI6 1 279 Falun, Sweden (relay station) SMZK 11 400 Caen (Radio Club of Caen), France Mont de Marzan (Radio Club (relay station) - 11 277.8 Landrais), France - .4 400 Leeds (relay station) 2LS 4 277.8 Plymouth (relay station) 5PY 4 400 Stavanger, Norway - 4 277.8 Seville (Union Radio), Spain EAJ17 1 400 Trodhättan, Sweden (relay station) SMXQ 4 277.8 Tammerfors, Finland (relays Jacobstad, Finland - - 275.2 Helsingfors) - - 400 Nottingham (relay station) 5NG 4 275.2 Hamburg (Morse) HA 4 394.7 Norrköping, Sweden (relay station) S11IVV 4 275.2 Madrid (Radio Espana) EAJ2 3 393 Angers (Radio Anjou), France - 1 275.2 Toulouse (Radio du Midi), France - 2 389.6 Posen, Poland - 11 273 Manchester 2ZY 1-1 384.6 Sheffield (relay station) 6FL 4 272.7 Stuttgart - 4 379.7 Danzig (relays Konigsberg) - 11 272.7 Helsingfors, Finland - 2 375 Genoa, Italy (Projected) 11 272.7 Madrid (Union Radio) EAJ7 3 373 Klagenfurt, Austria (relays Vienna) If 272.7 Bergen, Norway - 11 370.4 Cassel, Germany (relays Frank- Leipzig, Germany - 4 365.8 furt) - 2. 272.7 Nice - 1 362 Malmö, Sweden SASC 1 260.9 London 2LO 3 361.4 Hangö, Finland (relay station) - 4 260 Graz, Austria (relays Vienna) V ,F 357.1 Toulouse P.T T 5 260 (Morse). Linz, Austria (Projected) - - 254.2 Cardiff 5WA 11 353 Kiel, Germany (relays Hamburg). - 4 254.2 Paris, (Lucien Levy) - 4 350 Pori, Finland 4 254.2 Prague, Czecho Slovakia - 5 348.9 Venice (Projected) - 11 254.2 San Sebastian, Spain EAJ8 2 346 Bradford (relay station) 2LS 1 252.1 Barcelona (Radio Barcelona), Kalmar, Sweden (relays Stock - Spain EAJI 11 344.8 hohn) SMSN } 252.1 Seville, Spain EAJ8 1 344.8 Montpellier, France - 1 252.1 Paris, Petit Parisien - 340.9 Stettin, Germany (relays Berlin) - 4 252.1 2 Copenhagen - 337 Sallie, Sweden (relays Stockholm) SMTS If 252.1 Naples INA 11 333.3 Eskilstume, Sweden (relays Stock- Reykjavik, Iceland - - 333.3 holm) SMUO 4 250 Limoges, France (relay station) 4 330 Gleiwitz, Germany (relays Breslau) - 4 250 Konigsberg, Germany - 4 329.7 Uleaborg, Finland (relays Heis- Birmingham 5IT 1:1 326.1 ingfors) 4 250 Malaga, Spain EAJ25 1 325 Lemburg, Poland (projected) - 11 247.9 Saragossa, Spain EAJ23 11- 325 Trondhjem, Norway - - 243.9 Milan 1MI 1- 322.6 Münster, Germany (relays Langen- Dublin 2RN 1- 319.1 berg and Dortmund) MS 11 241.9 Lahtis, Finland - 318 (Morse) Breslau, Germany - 5 315.8 Bordeaux (relays Paris, PTT) - x 238.1 Newcastle 5N0 1} 312.5 Vilna, Poland (projected) - 2- 234.4 Björneborg, Finland (relays Boras, Sweden (relay station) SMBY 4 230.8 Helsingfors) - 311 Juan -les -Pins, France - 1 230 Zagreb, Yugo -Slavia 1 310 Helsingborg. Sweden (relays Stock- Marseilles P.T T 1 309 holm) - SMVE 4 229 Paris (Radio Vitus) - 1 308 Umea, Sweden (relays Stockholm) SMSN ¿ 229 Belfast (3.0 p.m. onwards) 2BE 11 306.1 Belgrade, Yugo Slavia - 2 225.6 Madrid (Radio Madrilena) EAJI2 2 306 Leningrad, Russia 2 223.9 Nuremburg, Germany (relays Strasbourg, France - 4 222.2 Munich) 4 303 Karlstadt, Sweden (relays Stock- Bratislava, Czecho- Slovakia -- 300 holm) SMXZ 4 221 Tomsk, Siberia RA21 4 300 Orebro, Sweden (relays Stockholm) SMTI 4 218 Cadiz (Radio Lehera) EA,I10 1 297 Luxemburg LOAA 4 217.4 Liverpool 6LV 2 297 Halmstad, Sweden (relays Stock- Hanover, Germany (relays Ham- holm) SMSB 4 215.8 burg) s 297 Viborg, Finland - c 214.3 Jyväskylä, Finland (relays Hel - Kiev, Russia RA5 2 211.3 singfors) 4 297 Dijon, France - 1 207.5 Agen, France 4 297 Gävle, Sweden (relays Stockholm) SMXZ' 4 204.1 Varborg, Sweden (relays Stock- Reims, France - 1 204.1 holm) SMSO 4 297 Kristinehamm, Sweden (relays Dresden, Germany (relays Leipzig) - 4 294.1 Stockholm) SMTY 4 202.7 Hull (relay station) 6KH 4 294.1 Jönköping, Sweden (relays Stock- Dundee (relay station) 2DE 4 294.1 holm) SMZD :'. 201.3 Innsbruck, Austria (relays Vienna) - 1 294.1 Karlskrona, Sweden (relays Stock- Stoke (relay station) 6ST 4 294.1 holm) SMSM 4 196 Swansea (relay station) 5SX 4 294.1 Reziers, Franco - i 178 Uddevalla, Sweden (relays Stock- Eindhoven, Holland (Philips Lamp holm) SMZP 4 294.1 Works) PCJJ - 30.2 A 29

www.americanradiohistory.com WALPcIlisgg JUNE 151h, 1927. t MAO Nominal Present Nominal Present ,Station. Call- Power Wavelength Station. Call- Power Wavelength sign. (Kilowatts). (.Metres). sign. (Kilowatts). (Metres). PRINCIPAL STATIONS IN DISTANT COUNTRIES. Baltimore, Md. (Consolidated Gas & Power Co.) WBAL 3 285.5 Canada. Columbus, Ohio (American In- surance Union) WAIU 5 282.8 Calgary, Alberta (W. W. Grant, Council Bluffs, Iowa (Mona Motor Ltd.) CFCN I Z 434.5 Oil. Co.) KOIL 11 277.6 Montreal, Quebec (Canadian Batavia, Ill. (People's Pulpit National Railways) CNR.II 1 411 Association) WORD 5 275.1 Montreal, Quebec (Canadian Mar- Batavia, Ill. (Richmond Harris coni Co.) CFCF 11 410.7 & Co.) WTAS 31 275.1 Burketon Jet., Ontario (Canadian Atlantic City, N.J. (Municipality Broadcasting Corpn.) CKCW 5 329.5 of Atlantic City) WPG 21 272.6 San Antonio, Tes (Alamo Broad- U.S.A. casting Co.) KTSA 2 265.3 Mount Des Moines, Iowa (Bankers Life Prospect, Ill. (Zenith Radio Corpn.) WJAZ 5 263 Co ) WHO 5 534.4 Chicago, Ill. (Westinghouse Elec- Fort Worth, Texas (Lone Star Broadcasting Co.) KFQB 1 260.7 trical Co.) KYW 21 526 Hastings, Nebr. (National Broad- Spokane, Wash. (North West Radio Service) KGA 2 260.7 casting K FKX 2 521 Co.) Rossville, N.Y. (People's Pulpit Omaha, Nebr. (Woodman of the Assn ) WBBR 1 256.3 World Insurance) WOW 1 508.2 Chicago, WOK 5 252 New York (National Broadcasting Ill. (Trianon Inc.) Portland, Oreg. (Western Broad- Co.) WEAF 5 491.5 casting Co.) KEX 21- 239.9 Portland, Oregon (Oregonian Publ. St. Louis, Mo. (Benson Broad- Co.) KGW 1 491.5 casting Co ) KFVE 1 234.2 Atlanta, WSB 1 475.9 Ga. (Atlanta Journal) Minneapolis, Minn. (l:adison Washington, D.C. (Radio Carpi Radio Corpn.) WAMD 1 225.4 of America) WRC 1 468.5 Pittsburg, Pa. (Westinghouse Co ) KDKA -- 64 Los Angeles, Calif. (E. C. Anthony) KFI 5 468.5 Bound Schenectady, N.Y. (General Elec- Brook, N.J. (National tric Co.) 2XAF 32.77 Co.) WJZ 30 454.3 - Broadcasting Schenectady, N.Y. (General Elec- Pontiac, Mich. (Detroit Free Press) WJR 440.9 2XAD 22 WCX} tric Co.) - Harrison, Ohio (Crossley Radio Corpn.) WLW 5 428.3 South Africa. San Francisco, Calif. (San Fran- Johannesburg (African Broad- cisco Chronicle) KPO 1 422.3 casting Co.) JB 450 Chicago, Ill. (Radiophone Broad- Durban (Durban Town Council) 400 casting Corpn.) WHT 5 416.4 Cape Town (African Broadcasting Minneapolis, Minn. (Washburn Association) - 1} 375 Crosby Co.) . WCCO 5 405.2 Cleveland, Ohio (Willard Storage Battery Co.) WTAM 32 399.8 Northern Africa. Chicago, Ill. (Atlass Investment Tunis (Radio Carthage) TNV 5 1,850 2 Co.) WBBM 1 389.4 Algiers, PTT. - 310 Oakland, Calif. (Edgewater Beach Morocco, Radio Casablanca (Radio Hotel) KGO 5 384.4 Club de Maroc) CNO 21 305 Schenectady, N.Y. (General Elec- tric Co.) WGY 30 379.5 India and Ceylon. Detroit, Mich. (Evening News Colombo, Ceylon - ]} 800 Association) WWJ 1 374.8 Calcutta (Indian States 8e Eastern Chicago, Il!. (Edgewater Beach Agency) 5AF - 425 Hotel) WEBH 2 365.6 Bombay (Bombay Residency Cincinnati, Ohio (U.S. Playing Radio Club) 2FV - 375 Card Co.) WSAI 5 361.2 Rangoon, Burmah (Radio Club of Devonport, Iowa (Palmer School Burmah) 2HZ 350 of Chiropatic) WOC 5, 352.7 - Seattle, Wash. (North West Radio Service Co.) KJR 21 348.6 Australia and New Zealand. Chicago, Ill. (Sears Roebuck Co.). WLS 5 344.6 Perth, W. Australia (Westralian °Zion, Ill. (W. G. Voliva) WCBD 5 344.6 Farmers, Ltd.) 6WF 5 1,250 Springfield, Mass. (Westinghouse Sydney, N.S.W. (Farmers, Ltd.) 2FC 5 942 Co.) WBZ 15 333.1 Auckland, N.Z. (Radio Broad- Denver, Colo. (General Electric casting Co. of N.Z.) 1YA - 420 Co.) KOA 5 325.9 Christchurch, N.Z. (Radio Broad- Richmond Hill, N.Y. (Atlantic casting Co. of N.Z ) 3YA - 900 Broadcasting Corpn.) WABC 21 325.9 Adelaide, S. Austr. (Central Pittsburg, Pa. (Westinghouse Co.) KIKA 30 315.6 Broadcasting Ltd.) 5CL 5 395 Lincoln, Nebr. (Nebraska Buick Brisbane, Queensland (Queensland Auto. Co.) KFAB 2 309.1 Radio Service) 4QG 5 385 Chicago, Ill. (Chicago Tribune) WON 15 305.9 Dunedin, N.Z. (Radio Broad- San Antonio, 'Tes. (Southern casting Co.) 4YA - 380 Equipment Co.) WOAI 2 302.8 Melbourne, Victoria (Broad- St. Louis, Mo. (Voice of St. Louis) KMOX 5 299.8 casting Co. of Australia) 3L0 5 371 A 30

www.americanradiohistory.com JUNE 15111, 1927. WAIFigh@O 763 WOThIld SECRET RADIO i["Fif ,EPHONY SYSTEMS. The Side =band System as Used for Transatlantic Telephony. By O. F. BROWN, M.A., B.Sc. (Concluded from page 716, June 8th issue.) THE practical difficulties referred to in the first part small power of a few watts developed in the first pair of of this article are absent in the methods for secret balanced valves is amplified in stages up to a hundred or telephony covered by the series of patents held by more kilowatts, which is the power applied to the aerial. the Western Electric Co. (Standard Telephones and In the example described, the band of frequencies emitted Cables, Ltd.). The arrangements proposed are based on from the aerial is 55,700 to 57,70o cycles. To make the principle of " side -band " telephony already in use the speech intelligible on the receiving station it is neces- in the transatlantic service. As already stated, in this sary to heterodyne this band by a frequency of 55,500 system this main carrier wave is suppressed and only one cycles. When this is done it is clear that frequencies side band is transmitted. The principle of the apparatus included between zoo and 2,200 cycles, i.e., frequencies used for this purpose is shown in Fig. 4. The apparatus corresponding to the voice frequencies, will he produced consists of two balanced thermionic valves, V1 and V2. which can be detected in the usual way. A carrier wave of a suitable frequency, say 33,000 cycles, is developed by means of the valve generator and Speech Unintelligible in Ordinary Receivers. applied at the middle of the system, as shown. When It is clear that this system is secret to the extent that the microphone M is not being spoken into, equal and no intelligible speech can be received unless incoming opposite potentials will be applied to the grids G, and waves are heterodyned with local oscillations of correct frequency. Nothing, for example, could be picked up by an ordinary broadcast receiver. FILTER The object of the second modulation by the frequency PASSING ONLY 88,5oo cycles is the further separation of the two side 30 800 TO 32 800 CYCLES bands, so that the practical elimination of one side band is made easier. In what follows, therefore, it will be assumed that the second modulator is omitted. The principle involved in the methods for securing greater secrecy now to be described depends on what is known as " inverted voice transmission." This means that the low notes in the speech band, or a portion of it, are turned into high notes, and vice versa. Obviously the voice will be completely distorted and the speech rendered unintelligible unless apparatus is provided in the receiver to re- invert the sounds transmitted. It is not much use to invert the whole speech band because all that is necessary to re- invert it is to hetero- Fig. 4.- Schematic circuit of Western Electric side -band transmitter. dyne the transmitted frequencies of the side band with hence-the currents and potentials in the two halves of the one single frequency at the receiver. Thus, provided transformers connected to the plates of the valves will be this local heterodyne frequency is correctly selected, there balanced out. Thus the carrier frequency supplied by is no difference between the reception of a completely the oscillator will be suppressed. When the microphone inverted voice and a non -inverted voice, and no gain in is spoken into, however, the balance will be destroyed secrecy is achieved. To get over this difficulty the voice and the carrier frequency will be modulated by the voice band is divided into three or four portions, the frequen- frequencies ranging, as we have seen, from, say, zoo to cies in one or more of which are inverted as desired. As 2,200 cycles, hence the balanced system will deliver to a first example, let us suppose the speech band is divided the secondary of the plate transformer the two side bands, into three portions comprising frequencies between zoo to one containing frequencies between 30,800 and 3z,800 Soo cycles, 800 to 1,5oo cycles, and 1,500 to 2,200 cycles. cycles, and the other frequencies between 33,200 and To do this, all that is necessary is to apply the voice 35,200 cycles. These two bands are then passed through currents from the secondary of the transformer T1 (see filter circuits, consisting of condensers and inductances, Fig. 5) in the microphone circuit to three filters F1, F adjusted to pass only frequencies ranging from 30,800 F3 designed to pass bands of zoo to Soo, 800 to 1,5oo, to 32,800 cycles. The selected side band is then passed 1,500 to 2,200 cycles respectively. The currents from through a second pair of balanced valves supplied by an these filters are applied to the centre of three balanced oscillator generating a frequency of, say, 88,5oo cycles. valve modulators Mt, M2, M3. In the input windings The frequencies developed in the plate circuit are thereby of the modulator Ml is introduced, by means of the further separated by filters passing frequencies between generator G1, currents of frequency r,000 cycles (i.e., 55,70o and 57,7oo cycles. These frequencies are then zoo plus Soo cycles). This current modulates the portion passed through a series of amplifying valves until the of the speech currents passed by F1 so that at the output A 31

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F1 200 -800 a M1 OZ 100 -800

TM 800 -1500 F2

800-1500

2 M2 G C) 1111 1500-2200 e, F3 411.

1500-2200 (11)G3 M3 F3

Fig. 5.- Filter circuits for dividing speech -frequency band in the western Electric system.

end of the modulator two hands of frequencies are de- hand 1,5oo to 2,200 is also inverted by modulation with livered, one Soo to 1,200, the other 1,200 to 1,800 cycles. a frequency of 3,700 cycles provided by G3. The cur- The higher and is cut out by a second filter F11 similar rents from the filters F1', F2', F3' are re- combined to- to the filter F1, passing only frequencies between 200 gether in the primary of the transformer T2 and pass to and Soo cycles. After the currents leave it will be the aerial through a balanced modulator TM in whicn seen, however, that the frequency band has been inverted. is introduced, by the generator, the radio frequency oscil- A sound of frequency zoo conies out having a frequency lation at which it is desired that the transmission should Soo, while a high note of Soo cycles comes out as a low take place. The apparatus between T2 and the aerial note of zoo cycles. would be of the type already described for ordinary side In the same way the hand Soo to 1,500 cycles is in- hand telephony, but the additional filters and amplifiers verted by the modulator M2, and the filter F2' by modu- are left out in the diagram for the sake of simplifying lation with a frequency of 2,3oo cycles from G2, and the the drawing.

100 -800 RA RG RF1

DM1 1111 0000, 100-800 T 0000 `--1 I1I1I1I RF;

800-1500 .J R F2

800 1500 RG2 DM2 RF2

1500- 2200 RF3

1500-2200 RG3 DM3 RF; á it '. - Fig. 6.- Receiving apparatus used In the Western Electric side -band system.

A 3 ,

www.americanradiohistory.com JUNE f5111, 1927. WIp@ Ilam WopIlol 765 Secret Radiotelephony Systems. - four portions or sub -bands of the speech are possible The diagram of the receiving apparatus is shown in which are incapable of yielding more than one of the Fig. 6. The radio- frequency carrier wave suppressed by sub -bands in its normal form in a simple heterodyne re- the modulator TM in the transmitter is supplied from the ceiver, the others being present as unintelligible noise. local heterodyne RG, and by the usual detecting action of It would be possible to change from one combination to the valve D the low- frequency waves applied to the trans- another'simply by switching arrangements. The changes former RT2 contain components similar to those impressed would be capable of being introduced rapidly at pre- on the modulator TM at the transmitter. These compo- arranged intervals, and thereby a very high degree of nents are passed through filters RF1, RF2, RF3 and de- secrecy could be provided. The number of possible corn- modulators DM17 DM2, DM3, etc., which are exactly binations is worked out in detail in British Patent Speci- similar to the corresponding apparatus in the transmitter. fication 219,987, while the principle of the system is The output from the demodulators is applied to the re- more fully described in British Patent Specification ceiving telephones R. 218,282. It appears to the writer that the development By switching out any of the modulators M1, M_, M3 a of such methods of inversion of portions of the speech portion of the band can, by arrangement with receiving band before transmission on the lines described in these station, be transmitted in an uninverted or normal con- patents is most likely among the methods with which he dition. In this way, even if an intercepting station is acquainted to lead to a satisfactory solution of the possessed a complete demodulator, reception could be problem. In what has been written it has been assumed rendered very difficult. that the inversion methods were to be used with the side - By employing the same principle a still greater degree band system of transmission. This system requires the of secrecy can be provided. If the speech frequency use of a comparatively low radio frequency (i.e., a long band is divided into, say, four parts, any one portion of wavelength), otherwise the two side bands are so close the speech frequencies Can be shifted into any other part together that the suppression of one band by filters be- of the speech band by introducing the correct frequency comes very difficult. There appears to be no reason, into a balanced modulator and using a suitable filter. however, why the inversion apparatus should not be With a system in which the speech band is divided in applied, if desired, to ordinary carrier -wave telephony four parts it can he shown that 125 combinations of the on short waves.

NOVELTIESS F oO i OUR READERS. A Section Devoted to New Ideas and Practical Devices.

PUSH -PULL AMPLIFIER. secondary terminals. Grid bias is be made from the lid of a metal Experimenters who may wish to applied between the common filament shaving stick container. If the lid acquire experience with the push -pull connection and the centre point on does not fit tightly on the end of the system of L.F. amplification can do this resistance. cell the edge of the metal should be so without purchasing special trans- The output circuit operates on the first drilled and then V- shaped pieces formers by following the accompany- " filter feed " principle, and consists ing circuit diagram. of two chokes in series between the An ordinary intervalve transformer two anodes. The H.T. feed is con- is used in the input circuit, the elec- nected to the centre point between the chokes and the output terminals are fed -through two r mfd. condensers. R. H. A. 0 0 o GRID BIAS MOUNTING. A convenient mounting for the new cylindrical type of grid bias cell may

VALVES FOR IDEAS. Readers are invited to submit brief details, with rough sketches, where necessary, of devices of experimental interest Shaving tin lid used as grid cell holder. for inclusion in this section. A dull emitter receiving valve will be despatched Push-pull amplifier making use of standard components. to every reader whose idea is accepted cut as shown in the diagram and the for publication. projections pressed inwards to grip trical centre of the secondary winding Letters should be addressed to the Editor, " lVirc- the sides of the cell. The finished less World and Radio Review," Dorset House, being located externally by connecting Valor St., London, E.C.4, and marked" Ideas." holder is then screwed down to the two 0.5 megohm leaks across the baseboard. E. T. W. A 33

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JUNE z5tlr, 1927.

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Savoy Hill Topicalities : By Our Special Correspondent. An Important Debut. -The Referendum.- Justifying the Regional Scheme. B.B.C. and the Eclipse. -Giant German Station. Stravinsky at 2L0. Famous Conductor's Broadcast Debut. Anyway, there seems little doubt that The R.A.F. Display. our `Fb Sir Henry Wood, whose engagement grandihildren will have alternative Listeners who wish to hear the sounds with the B.B.C. started on June 1st, programmes, especially if they live to a of an aerial combat will have an opportu- good old age. may make his first appearance before the o000 nity of realisipg their desire on July 2nd, microphone at 2L0 on June 30th. He is when a portion of the Royal Air Force down to conduct the Wireless Symphony Broadcasts From Wimbledon. display at Hendon Aerodrome will he Orchestra in a Wagner programme, but The Centre Court matches of the broadcast. there is a feeling that the first of the Wimbledon lawn tennis meeting will be The broadcast items will include the de- " Proms." on August 13th should be broadcast on .June 29th, from 4 to 5 p.m. ; struction of a kite balloon, an air fight, made the occasion of his broadcast debut, on Jule 30th, from 4 to 5.15 p.m. ; on the rescue of a beleaguered British to give a more " spectacular " effedt. July 1st, from 4.45 to 5.15 p.m. ; and on population from a barbarian town by 0000 July 2nd., from 2.30 to 4.45 p.m. In means of aircraft, and the destruction of Arnold Bennett's Night. addition descriptive comments will pro- a fort and bridge. Quite a lot for one Owing to unforeseen circumstances the bably be transmitted between 6 and afternoon ! 6.30 p.m. on these days. 0000 programme which was to have been pro- oodo vided by JIr. Arnold Bennett on June B.B.C. and the Eclipse. 22nd has been postponed. Dominion Day in Westminster Abbey. The B.B.C. are to be commended for 0000 On Dominion Day (July 1st) the special the very carefully arranged schedule of Valve v. Crystal. morning service will be relayed from tr:ulsmissions which has been prepared in The listening public bas responded Westminster Abbey to 2L0 and 5XX. connection with the eclipse on ,June 29t1í. nobly to the 13. B.C. appeal for information as to the most popular station, with the result that thousands of postcards still await checking at Savoy Hill. In the main the expectations of the engineers have been fulfilled, i.e., the postcards show that the number of crystal sets is decreasing, 50 per cent. of the listening population now using val ves. 0000 Regional Scheme Justified. The main purpose of the referendum has been served, because t.lie results show that the regional scheme, involving fewer stations and Higher power, will he justified. 0000 A Long Wait ? So far so good. All that remains is to set the regional scheme into operation ; hot here we are gazing into the dim and I fear) distant future. The Daventry experimental station has yet to win its spurs, and even if it is transmitting regular programmes by the .lilt nnnnn, sites for the new stations will have to be found and similar experiments carried out before the present stations are superseded. coon Our Fortunate Grandchildren. An optimistic prophet at Savoy Hill FLYING TO BROADCAST MUSIC. A rehearsal of a fascinating stunt to be given tells me that we may see the scheine in at the Royal Air Force display at Hendon on July 2nd, when a squadron of new planes operation by the end of next year. will carry out aerial drill to " instructions " by music by the Royat Air Force Band. A 34

www.americanradiohistory.com JUNE 15th, 7927. WAp®Ilig0 767 `1`O ifIld Various time signals will be trans- selection of lectures will be given. It is Great things may be expected of the mitted from London, Daventry, Bir- felt that the present power of 8 kWs. is new station, which is situated rather mingham, Manchester, and Newcastle, inadequate if a wide circle of listeners is more than a mile from the Königswuster- and the carrier waves of all except 5XX to be appealed to, especially as the other hausen site. will be radiated continuously. commercial aerials at Königswuster- 0000 0000 hausen tend to absorb the transmissions A Midsummer Fantasy. from the broadcasting station. Before and After. A fantasy, " with music for a mid- The experiments are to be carried out summer night," entitled " Pixie Led," on June 27th, 28th, 29th, 30th, and July FUTURE FEATURES. by L. du G., of Punch, will be broadcast 1st, so from 2L0 on June 24th. Pixie songs that listeners may have an ample - London. have been specially composed by Kenneth opportunity of studying conditions before JUNE 19m.- Programme of works and after, as well as during, the eclipse. by Stravinsky, conducted by A. Wright, who used to direct the Man- On each morning except June 29th a the Composer. chester station when it was first established by Metropolitan- series of dot seconds will be broadcast, JUNE 20T11.-Concert of New Com- Vickers. the sixth dot occurring precisely at every positions, and a Play. o 000 half -hour from 4.30 to 8.30. These JUNE 21sT. - " A Midsummer Stravinsky at 2L0. signals will be sent out from London and Night's (All Sta- Dream." A programme of works by the well - Manchester at 4.30, 5, and 5.30 a.m. and tions.) from London only for the rest of the known composer Stravinsky, which he JUNE 23x.1..- Concert relayed from will conduct from 2L0 on June 18th, will period. the Kingsway Hall. 0000 feature the first performance in England JUNE 24TH. -" Carmen," Act 2, re- of his Concerto for Piano with accom- Continuous Carrier Waves. layed from Covent Garden paniment of wind instruments. For this On June 29th London and Manchester Opera House. item Stravinky will be the soloist, while will transmit the dot seconds at 4.30, 5 Cardiff. the orchestra will be conducted by 19TH. his and 5.30 a.m., and London and Daventry JUNE -Don Pedro and Edward Clark. will give them at 6, 6.15 and 6.20. Mexican Band and Watcyn 0000 Watcyns (baritone), relayed During the six minutes from 6.20 to 6.26 About the a.m. London and Daventry will broad- from Llandaff Fields Pavilion. Compère. cast single seconds continuously, missing JUNE 22ND. -The Super Six in a Is the compare idea being overdone? the 29th and 59th seconds, while the Summer Revel. When this omniscient individual first announcer will call every fifth second JUNE 25TH. -A Neapolitan Night. came into favour he had at least the throughout the period. London and Manchester. virtue of novelty. Now that the virtue Daventry will radiate dot seconds on the JUNE 19TH.- Special Evening Ser- has departed the question arises : Dues day of the eclipse at periods of half an vice relayed from Manchester the compère fill a róle which could not be hour between 6.30 and 8.30 a.m., while Cathedral. undertaken by the trained announcer? London and Manchester will also keep JUNE 20TH. - Vaudeville Pro- 0000 their carrier waves going continuously. gramme. His Privileges. 0000 JUNE 23RD.-" On With the Show Many listeners must be ready to answer of 1927," relayed from Black- Varying Wavelengths. the question in the negative. pool. In the majority of cases -there have From the London station broadcast ex- JUNE 25m.-" A Country Cot- been planations will brilliant exceptions -the compère be given of the dot signals tage," a Play by Patience succeeds merely in bringing to the that are transmitted between 6 and 6.30 Raymond. microphone an air of amateurism which a.m. In each case the normal wavelength Glasgow. the professional announcer has been of the station will be used, except that on JUNE 19TR. -The Band of the 28th, 29th trained to avoid. June and 30th Birmingham Second Battalion, Argyll and The compère and Newcastle, in transmitting their Sutherland Highlanders. can be facetious without getting slapped ; it matters not to him carrier waves continuously, will vary JUNE 22ND. Pro- -A Highland what high official of the B.B.C. may be their wavelengths over a range of 10 gramme. listening. He may drop his voice or metres, i.e., 5 metres on either side of JUNE 23RD.-Symphony Concert. without the normal. raise it being cautioned by the oó00 Birmingham. engineers, and he can take liberties in JUNE 20TH.- French Music and the matter of free speech which are P la A German Giant. ys. debarred the ordinary. artist. JUNE 22ND.- Philip Con- A Berlin correspondent sends further Ritte's In a word, the compère enjoys all the details of the giant broadcasting station cert Party. privileges of the amateur who is not now being erected at Zeesen to supersede JUNE 24TH.- Chamber Music. required to come up to professional stan- the present station at Königswuster- JUNE 25TH. -Military Band Pro - dard. Who wants the compare? hausen. From all accounts Zeesen will gramme. 0000 outpace Langenburg as well as Daventry. Bournemouth. Ideal Length for a Talk. The power of the new transmitter will JUNE 20TH. -Opera Comique : Vocal be 35 kilowatts, i.e., four times that of and. Instrumental. Perhaps it affords no intense excitement Königswusterhausen, and use will be JUNE 24TH. -A Midsummer Day to British listeners to know that Mr. D. made of Telefunken water- cooled trans- Concert. Lawrence is broadcasting a series of talks mitting valves rated at 20 kWs. such as Belfast. on the American Government from the are already used at Langenburg. The JUNE 20TH. -Vocal and Orchestral " Red Network " of stations of the wavelength will remain at 1,250 metres, Programme and Two Plays. American National Broadcasting Com- and, as in the case of Königswuster- JUNE 23rn. -A Welsh Programme. pany. But it is interesting to note that hausen, the modulation will be carried JUNE 24T11. -An Up -River Concert. each talk is limited to eight minutes' out at Berlin. 0000 Newcastle. duration. Eight minutes seems an ideal JUNE 22ND. -The South Moor Col - length for a talk. A Move for Independence. liery Band and the Prudhoe Some speakers can bore in less than The principal reason for the removal Gleemen. one minute ; others do not begin to bore and enlargement of the Königswuster- JUNE 24TH.- British Composers, after fifteen minutes. But eight minutes hausen transmitter is that the station is Instrumental Programme. gives an average speaker time to bring intended to take foremost rank in the Aberdeen. out his main points without wrapping broadcasting of educational talks. Every JUNE 23Rn.- Scottish Programme. them in frills. It is the happy medium afternoon from 3 o'clock onwards a varied between long and short. A 35

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A Review of the Latest Products of the Manufacturers.

WESTON METER SWITCH. and special transformers for use in wire- Milliard type DU.5 two valves may have One sometimes hesitates before fitting less transmission. their filaments connected in series for full a voltmeter to the panel of a receiving A new series of transformers has been wave rectification. Transformers are set when the instrument is arranged only produced for use in the construction of supplied with special windings to suit the to determine possibly the maximum bat- battery eliminators, the windings being. Mullard DLT.2 aucl DÚ.10 valves. On tery potentials. A single voltmeter can. suitable for supplying loth filament heat- circuit the transformer is perfectly silent, by moans of a switch, be arranged to and can be operated for many liours con- determine the voltages applied to the tinuously without any apparent tempera- filaments and anodes of all the valves oi ture rise. Other transformers are avail- a multi--valve receiver, as well as the able with windings arranged to give L.T. grid biasing potentials. For determining 4 volts at 2.2 amperes with H.T. 120 +120 L.T. and H.T. battery potentials, it is at 50 milliamperes; 4 volts at 2.2 amperes only necessary to have a single -pole multi - with 180 +180 volts at 50 milliamperes; 4 contact switch, which in turn connects volts at 2.2 amperes with 200 +240 volts the meter with the filament and H.T. at 50 milliamperes ; 7 volts at 3 amperes valve connections, though it is necessary with 200 +200 volts at 80 milliamperes to introduce a series resistance when de- 7 volts at 7 amperes with 400+400 volts termining the anode voltages in order to at 150 milliamperes, tappings being pro- read on the high -voltage scale of the vided at 200 +200 volts. In addition to meter. this range, all suitable for use on various The Weston Electrical Instrument Co., primary voltages and frequencies, there Ltd., 15, Ureat Saffron Hill, London, is another type giving 4 volts at 0.8 am- E.C.1, now supply for use with their peres for supplying heater current for Model 506 voltmeter a multi- contact Marconi and Osrant valves of the K.L.I. switch in which is incorporated the series type. resistance for taking readings on the 0000 high- voltage scale. Being provided - double The new Hamilton Wilson battery elimi- NEW DIIBILIER DEVICE. pole contacts, voltage readings can be nator transformer. taken on H.T., L.T., or grid biasing bat- To make provision for connecting the teries, irrespective of whether the H.T. - ing and anode current to the rectifying grid leak either directly across the grid is normally connected to the L.T.+ or valves. Although very moderate in price condenser or to return the connection to L.T. -. The dial moves with a snap these transformers are of massive con- the filament, the Dubilier Condenser Co. action, and the settings a ro aliown on an struction, and the general build at once (1925), Ltd., Ducon Works, Victoria reveals that experience in transformer Road, North Acton, -London, R'.3, has design not always possessed by wireless recently introduced a new form of inount- manufacturers who have found it neces- ing clip. sary to extend the scope of their products to include the manufacture of power transformers. The specimen transformer examined laid a core cross -section of about 14in. square, and the frame, which had a single opening, measured about 3áin. x4zin. The windings were built up on a mica wrapping, and sub - stantial angle pieces compressed the core stampings tightly together. By winding The Weston switch for determining al as receiver voltages with a two -range volt- the primary two sections with the ends meter. brought out to four terminals the transformer was suitable for use on 100 to 125 indicating card viewed through apertures volts, or 200 to 250 volts. The filament in the dial. Several indicating cards are gave 7 heating windings volts at 1.5 am- Dubilier clip mounting for use with grid supplied to meet various requirements. peres when connected to a 110 or 220 condensers. 0000 volt supply, and the step -up winding gave 120 +120 volts at 50 milliamperes. These It is suitable for use with Dubilier con- WILSON ELIMINATOR windings are suitable for operating most densers type 610 and 620, and consists of TRANSFORMER. of the small rectifying valves requiring 6 a small insulated extension piece carry- Win. Hamilton Wilson, of 125 -127, Red volts or less, such as the Marconi or ing terminal and clip. It is supplied Lion Square. Surbiton, Surrey, has long Osram " U.S " or two " U.4s," or the without extra charge with the condenser been known as a manufacturer of power Baradept 4` U.695." In the case of the as well as being obtainable separately. A 36

www.americanradiohistory.com JUNE 15th, 1927. Wp@Il@g0 WOTrid. 769

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iilm 11 'Iljllniil iIII The Editor does not hold himself +' iì responsible for the opinions 1j11mmmfi11111d111 40 of his correspondents.

Correspondence should be addressed to the Editor, "Tae Wireless World," D3rsat H3use, Tudor Street, E.C.4, and niast be accompanied by the writer's name and address.

BROADCASTING AND THE PATENT POSITION. a public demonstr:ctiou of television to over forty members Sir, -I have read with a great deal of surprise the letter in of the Royal Institution on January 27th, 1926? your issue of June 1st from the Marconi Co. with reference. to Professor Andrade, who witnessed a demonstration, states as broadcasting and the patent position. follows in the Encyclopcedia Britannica under " Television " It is just another example of the policy, or lack of policy, " Mr. J. L. Baird, who has already succeeded in producing of the Marconi Co. that an explanation of its decisions should a crude but convincing representation of a moving object be made to a periodical only when attention is drawn to it, through the agency of Hertzian waves, and has so achieved when surely that explanation should have been given in the a true ' vision by wireless.' first place to the parties mostly concerned, the actual licensees. "In February, 1926, Mr. Baird had succeeded with quite As a result of my refusal to accept a pere nptory 'modifica- crude apparatus, constructed on the lines laid down, in trans- tion my licence has been determined by the Marconi Co. mitting recognisable pictures of moving objects such as a living . without the slightest possibility of negotiation or explanation. face. The licence which I hold entitled me, amongst others, to the ".Synchronism is secured with the help of an alternating use of patents Nos. 147147 and 159984, both of which are current generator mounted on the same shaft as the scanning for multi- electrode valves giving several stages of amplification, disc. The slow alternations so produced are superimposed on and yet, to read the Marconi Co.'s statements, licensees were the carrier wave which is used for conveying the variations never meant to use these particular patents -what an anomalous of intensity which produce the picture. At the receiving end position the synchronising wave is separated from the light modulations by a wave filter, and is to The facts of the case, I suggest, are as follow : The par- then made control the speed of the ticular patents referred to above were put into the original slit and the spiral disc." licence as " make -weight," the Marconi Co. attaching little Dr. Russell, Principal of Faraday House, states in Nature. importance to them, but when multi- electrode valves are mn,cie of July 3rd, 1926 :- a commercial product by another company the Marconi Co. " We saw the transmission by television of living human see the possibility of cheap receivers being placed on the market, faces, the proper gradation of light and shade, and all move- and accordingly set about to stop this at all cost. ments of the head, of the lips and mouth, and of a cigarette The lot of a Marconi licensee is indeed a sad one, as he is and its smoke were faithfully portrayed on a screen in the bound hand and foot and has to pay all ways, as instance the theatre, the transmitter being in a room at the top of the following examples : If an amateur constructor applies to the building. Naturally, the results are far from perfect. The Marconi Co. for a licence to cover a set he has built he is image cannot be compared with that produced by a good leine- supplied with a licence on payment of 12e. 6d. per valve nmtograph film. The likeness, however, was unmistakable, and holder, a licence plate being thrown in free of charge; but the all the motions are reproduced with absolute fidelity. This is poor manufacturer licensee has to purchase the plates in addition the first time we have seen real television, and, so far as we to paying the outrageous royalty of 12s. 6d. per valve holder. know, Mr. Baird is the first to have accomplished this mar- This charge for licence plates, no doubt, is a paltry thing, vellous feat." but is another instance of grab. A vast American organisation, employing about one thousand A non -licensee may make and sell transformer- coupled ampli- men to do this one demonstration, appear to have repeated Mr. fiers (as admitted by the Marconi Co.) without paying Baird's early results, with the difference that they transmitted royalties, while another company (a licensee) can supply a 200 miles, while Mr. Baird, at his first demonstration given single valve detector to go with such an amplifier, with the nearly eighteen months before the American experiment, trans- result that the user can purchase a three -valve set, paying only mitted from one room to another. This, however, does not 12s. 6d. royalty; yet if the unfortunate licensee wishes to do affect the point that television was first demonstrated in the same thing he has to pay 37s. 6d. royalty. England. The whole thing is manifestly absurd, yet the Marconi Co. The authorities of the Science Museum, South Kensington, cannot or will not see it, and it is high time that licenses after careful investigation, are exhibiting Mr. Baird's original banded themselves together to demand better and more equit- apparatus, and describe it as follows :- able terms " UNDER NOTICE." "Original Television _Apparatus, made by J. L. Baird, Esq. June 2nd, 1927. Lent by Messrs. Television, Ltd. " This is the transmitting portion of the original TELEVISION. apparatus used by ì\1r. J. L. Baird in experiments which led him from the wireless transmission of outlines in 1925 to the Sir, -In your issue of June 1st the statement is made that achievement of true television nine months recent later, when, en the demonstration of television by the American Tele- January 27th, 1926, the transmission of living human faces, phone and Telegraph Co. was the first public demonstration of with light, shade and detail, was demonstrated television. before members of the Royal Institution, this being the first demonstration of May I draw your attention to the fact that Mr. Baird gave true television ever giren. A 37

www.americanradiohistory.com 4ktlt:;:ç t 1960'whI4t,'W*',74R17yew". ATIW.-Q7VITTIF911L :Y?-?"Pr!!1"i?>4: tTs yt1 ET,wis Fnef,, Wigigmg 70 MAL JUNE 75th, 1927. " The original apparatus here exhibited was used by Mr. TRANSMITTERS. Baird at a demonstration given a London store in April, at Sir, a member of what your correspondent, _llr. John 1925, when the wireless transmission of outlines was ahcwn -As Willings, chooses to call " the brass -pounding fraternity," I publicly for the first time. This apparatus was developel, write to take exception to the sarcastic tone of his letter pub- tiubles with the light -sensitive device were overcome, and lished in your issue of June 8th, and also to suggest that he an improved optical device was evolved with the result stated towards the Ihove." might be a little more courteous in his attitude transmitting amateur as a community, even though he may. as With regard to of is noteworthy the question distance, it I have no reason to doubt, have very good grounds for objecting í\1r. between that Baird has recently demonstrated television to the inconsiderate attitude of certain transmitters who may London a and Glasgow, distance of over 400 miles, employing be interfering with his reception of distant stations. for the purpose of the demonstration a staff of three operators. Mr. AVillings also suggests that the ''brass -pounding frater- Professor of Taylor .Tones, who holds the Chair Natural nity " might be told that they have no monopoly of the ether Philosophy at Glasgow University, commenting on the test, after the B.B.C. stations have closed down. As a whole, the said :- transmitters would not consider that they had a the images certainly " I think of those in London were remarkably monopoly of the ether at any time, but if they are not to work clear. I recognised Mr. Baird immediately. The televisor closed down, then, please, may has after the B.B.C. stations have great possibilities, and it is a remarkable achievement that we know when they should carry out their transmissions, a face transmitted from London can be clearly seen in Glasgow, hours, although not pro- and its movements because to work during broadcasting followed in detail." in the terms of the transmitters' licences, is still re- face of hibited In this evidence I think you will agree that the garded as " not done " amongst respectable transmitting assertion made in your issue of June 1st that the American amateurs ? "PRE-WAR TRANSMITTER." demonstration was the first is in error. London, BAIRD TELEVISION DEVELOPMENT CO., LTD. June 9th, 1927. O. Cl. Hutchinson. Joint Managing Director. London, \W.C'.2. ,Tune 3rd, 1927. RECEPTION OF PCJJ. Sir, -I give below some details of the reception of I'CJJ which may be of interest to readers. The receiver is a two - valve Bowyer -Lowe short -wave set. Tuesday, May 10th, 1927 : Tuned in on closing remarks. Next transmission Thursday, 19.00/23.00 hours. Sig. strength R4 -5. Steady wavelength (by Stn. wavemeter -29 metres). Thursday, 12th : Tuned in at 19.15 hours. Held PCJJ till they closed down at about 23.00 hours. A few of the items from the programme are :- (a) "Somebody Loves lle." Gramophone Record. (b) " Nobody Knows \Vhat a Red- Headed Mummer ( ? ) Can 1)o." (c) Selection from " Rose Marie." (d) Selection from " No No Nanette," including " I Want to Be Happy," etc. It was announced that there would be a special transmission at 18.40 till 20.40 Hours on Saturday, 14th, to the Dutch East Indies and West Indies, when the 'Minister of Colonies would give a special address and the Philips' Band would play special Dutch selections. The announcer called the world mentioning among others British India and Calcutta. Sig. strength R4 -5 intermittent fading. PCJJ announced wavelength as 30.2 THE STUDIO AT PCJJ. Mr. A. F. Philips broadcasting " to metres. the world" from the Eindhoven station. Saturday 14th : Tuned in at 18.50 hours and held till 20.55 hours when PCJJ closed down. Music excellent. All announce- "Philip EMPIRE BROADCASTING. ments in Dutch but recognised the announcement Radio Laboritorium," Sig. strength R5. Fading in groups Sir. -The letter over the signature of Mr. M. V. Blake, in of 10 second intervals. A. T. DEWAR. the Time 8th issue, makes out a strong case for the Empire broad- Rangoon, Burma. (Al 2KD.) casting station which you have so consistently called for May 16th, 1927. through the columns of your journal. Here. we have the case of a Britisher resident abroad who an Dutch listens with comfort to American and a station, but OPERATION OF RECEIVERS. yet with a set employing more than twice as many valves fails INEFFICIENT to get satisfactory reception front a B.B.C. station. Is it merely Sir, -With reference to W. Carr's letter in the May 25th apathy on our part, or is there some definite reason, not apparent issue. This raises rather an interesting subject, namely. the to the layman, wily broadcasting from England to the Colonies percentage of sets in use which, through the lack of wireless should not take place? The B.B.C. is, perhaps, only naturally knowledge of their owners are never extended to their full rather timid to spend phoney on a station which it is really out- abilities. By which I mean, apart from technical values, such side their province to maintain, unless a definite authority for things as correct high tension to each valve, suitable grid bias, that expenditure is forthcoming. transformers applicable to the valves in use, and numerous It would seem to me that the only way that this short -wave other adjustments known to the experienced amateur, but of station can be brought into existence is by joint action from the which the average listener fails to make use. A leaflet from Dominion Governments. with a request to the Mother Country manufacturers would help, but I think that this is where the to make the necessary arrangements. Tt seems hardly possible numerous wireless societies could be of greater assistance, apart that if such a request were made collectively that the station from their experimental work, to instruct the average listener mold still be denied to the Empire. "EX- COLONIST." ill the intelligent operation of their receivers. South Norwood. Croydon. H. W. HURLEY. June 8th, 1927. June 1st, 1927. - A 38

www.americanradiohistory.com ]UNE 15th, 1927. 7/YEyA®oo W®pIl1. 771

" The Wireless World " Information Department Conducts a Free Service of Replies to Readers'Queries. Questions should be concisely worded, and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply. Super 18th, -regeneration. 1922, Major Armstrong acknow- tional details of the Armstrong super - I am very interested in circuits of the ledges the work of Capt. John Bruce regenerative circuit have appeared from super -regenerative type, and under- Bolitho, an Englishman who preceded time to time in The 'Fireless World, such stand there are two variants of this him in the production of super- regener- as October 21st, 1922, and, to come to circuit upon the market, namely, the ative circuits (British Patent No. more recent times, December 16th, 1925. Armstrong and Flewelling circuits, 156,330), and also acknowledges the work In the latter receiver two valves are and should be glad if you could give of another Englishman. Lawrence B. shown, but the final valve is merely an me the circuit diagram of these in- Turner (British Patent No. 130,408), who L.F. amplifier. It should be pointed out struments and also information as to preceded Bolitho. that many readers, owing to the loose use when they were first invented and Many experimenters to-day use the of the, expression "super" or " Arm- what improvements have been made Bolitho form of circuit. although it is strong super," are apt to confuse the since. very difficult to draw the dividing line " Armstrong super -regenerative " circuit I understand that it is quite between possible by means of one switch to these circuits since Armstrong with the " Armstrong supersonic- hetero- convert himself has produced more than one dyne " circuit. The latter circuit, of these circuits from ordinary super -regenerative regeneration to super- regeneration as circuit, his original cir- course, is a very well -known and popular should cuit using two valves, a rectifier, with a circuit, and is thoroughly reliable, but it desired, and like the necessary separate arrangements included in valve to produce the " quench- cannot be said that any great progress the dia- ing " oscillations. gram. M. D. D. His best known cir- has been made towards removing the cuit, and the one usually accepted, is stigma of lack of reliability from the The two best known super -regenerative that which we publish in Fig. 1 (a), where latter circuit. circuits are undoubtedly the Armstrong the valve acts both as a rectifier and as The Flewelling circuit, which was and the Flewelling, the former being the the producer of the " quenching oscilla- brought out by Mr. E. T. Flewelling, of older circuit. There are, however, a tions." Referring to this figure, the New York, is of much greater simplicity large number of other types of circuit frame aerial, of course, requires to be in appearance, but even to this date no upon the market employing the super - of such specifications that it will cover circuit employing the super-regenerative regenerative principle which are mainly the band of wavelengths required when principle can be classed as a really stable variations of the Armstrong and Flewel- used in conjunction with C,. The coil and reliable circuit, and such circuits are ling circuits, although employing the same L, in series with the frame is necessary suitable only for the experimenter. The basic priûciples. Major Edwin H. Arm- for the purpose of coupling the reaction original Flewelling circuit, which we show strong was not, however, the originator coil L, to the grid circuit in order to in Fig. 1 (b), did not make its appearance of the super -regenerative circuit, nor produce ordinary regeneration. Alter- in the U.S.A. until the latter part of has he ever claimed to be so, and, natively, it i.s possible to use an outdoor 1922. and in this country until the early indeed, in a paper read before the Insti- aerial in the ordinary manner, but it is part of 1923. The circuit was, as a tute of Radio Engineers on .Lune 7th, not advised as the circuit is a strong matter of fact, published in the issue of 1922, which was published in the issue re- radiator. The 'Fireless World for April 21st, 1923, of The 'Fireless World dated November We would point out that full construe- a full constructional article being given

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1. -Three typical super -regenerative circuits. A 39

www.americanradiohistory.com 772 WApeiS20 JUNE 15t1í, 1927. I`oTIld. in our issue of September 12th, 1923, the a high H.F. resistance. You do not give over half a. watt, and so it is less eco- actual receiver published being, curiously details of your H.F. transformer, but we nomical to use it. It must be remem- enough, built as a portable receiver. suggest you try one wound on the lines bered that there are comparatively few Later, the Flewelling circuit was greatly of that used in the " Everyman Four " four -electrode valves upon the market at simplified, and we illustrate this circuit receiver, but with the omission of the present, although manufacturers will prob- in Fig. 1 (e). neutralising winding, which will be un- ahlv produce them with various charac- With regard to your desired switching necessary in this case, as the sequence of teristics in the 2 -, 4 -, and also in the arrangement, we would inform you that tuned grid and plate circuits is broken by 6 -volt classes when such a demand arises. in the case of the Armstrong circuit a the interposition of the resistance- coupled In the matter of economy, of course, NI double -pole switch will be necessary. A stage included in the first valve. If this are only taking into consideration the moment's glance at the figure will show does not put matters right we suggest question of L.T. supply, since economy in you that the effect of this double -pole that you test carefully for high resistance H.T. supply will depend upon the par- switch is merely to short -circuit the two connections and leakages, which may be ticular characteristics of the valve, irre- quenching coils and their condensers; giving rise to your present flatness of spective of whether it is a 2 -, 4 -, or 6- thus, with the switch at position A we tuning. volt valve. have an ordinary regenerative set using 0000 a frame aerial; with the switch at B we have a super- regenerative set. In the Protecting the H.T. Battery. A Rising Resistance. case of the 1 always make a practice original Flewelling shown of disconnecting ,Some time qgo I built n t,mr -raire rein Fig. 1 (b), only a single -pole switch the - batteries from my rereirer after switching ceiver, ond, on connect'ng op, nil was is absolutely necessary. Positions A and off each night, and notice well. The receiver appeared to B when reconnecting give us a regenerative or a super - tlìe high tension jtnution vorvttally, and excellent re- leads that et regenerative receiver as desired. spark is prodt;ced. Doc..; sults were obtained. Gradually, how- this indicate poor insulation It perhaps would be better, however, in the ever, the receiver seems to luore de- to include a set! W. B. double switch in order that. veloped a pronounced whistling noise R, may be short -circuited when using On the assumption that you are using of a rather low pitch. This pitch is the receiver as an ordinary single valve the usual large by-pass condensers across constant, set, and does not appear to since otherwise we must turn this to each section of the H.T. supply we think change, but, on the contrary, is its position of minimum resistance in that in all probability the spark is caused growing louder. Can you tell. no, the order to prevent it as acting an additional by the flow of charging current into these cause of this trouble, and horn to series grid leak. The -simplified Flewel- condensers, and if so the effect is quite remedy it.' R. T. ling shown in Fig. 1 (e) is really the only normal. It may be added that if the in- system in which a single -pole switch can sulation of the receiver is above suspicion It is not improbable that you are using be used for rapidly converting the re- (as it should be) there is no real need to H.T. batteries of a capacity inadequate ceiver from regenerative to super- regener- disconnect the H.T. battery each night, to meet the needs of your set ; the result ative, A being a simple regenerative set, as the flow of current from it should cease is that more current is drawn from them and B a super -regenerative, as in the case as soon as the valve filaments are ex- than the makers had in view when de- of the other circuits. It is claimed by t ingui shed. signing them, and so gradually the bat- experimenters that the simplified Flewel- 0000 tery resistance has been rising. It must ling circuit is much the easier to operate, be remembered that some portion of this although it is somewhat less sensitive An Expensive Mistake. battery at least will be common to the than the Armstrong form of receiver, all I recently canteetecl 1,y accident a 4 -volt plate circuits Of all four' vales, even other things being equal, and conse- accumulator to the L.T. t emintds of though a separate H.T. tapping be used quently we show it with a normal aerial my set with 2 -colt 'maire.s in the on each valve. As the resistance of the and earth system, although a frame can sockets, and did not notice the error battery rises, then, we shall have a resist- be used with a series coil for the pur- .until the filaments had been alight ance common to the plate circuits of all pose of reaction if desired. Needless to for about ten minutes. All the four valves, and this will act as a say,. L.F. amplification can be added in filaments .Mill glow, but results are coupling between the valves, due to the the- normal' manner by inserting the very poor. I presume that they have fluctuating potentials set up across it by primary of an L.F. transformer in the been harmed by the excessive u- oitoge each valve, and a howling noise will be place of the phones, but separate bat- applied to them? T. R. R. built up. As the battery grows older teries are advised: Yes, in all probability the emission of and the resistance greater, the noise will It cannot be too strongly- urged that your valves has fallen off very consider- be increased in intensity. super -regenerative receivers of any de- ably, due to the application of this ex- Undoubtedly you. could cure it for the scription are not suitable for the ordin- cessive voltage for a comparatively long time being by putting larger shunting ary listener or home constructor, and period. It may- he, however, that some condensers across the battery, but it is owing to their vagaries and difficulties in other fault has developed, and it would advised, if you are using small cell bat- operation -are really only suitable for the be worth while to test your valves with teries, that you abandon them in favour serious experimenter. a millianuneter. of others of adequate capacity. You may 0000 e o o o argue that you are already using large cell batteries; if this is the case we Four -volt Economy. Multiple Valves. should imagine that there exists in your 1 am attempting to build the three -calve amplifier magnetic or capacitat ive I have obtainer] taco of lire foreign multi- potable set described in your .flay coupling, so that the amplifier is already ple valves (the 11.1. and detector- llth issue, bat, in the interests of unstable, and not very far from the point combinations), and Icare made economy, I am. going to use 2 -volt of L.F. oscillation. If this be so any them tip into a receiver on the lines valves instead of 4 -volt valves, as I little extra cause of instability. such as .suggested by the ntahers. The set invariably n,se 2 -calf real +es. lVill, a slight rise in resistance in your H.T. seem to be lacking in .selectivity, and you ?lame tell me which rcdre.s battery, would be sufficient to cause the I should welcome any .suggestions lion the 2 -roit class will be .suitable? amplifier to howl, this slight extra re- methods could make oit snilabt, far R. D. sistance being, as it were, the bust straw, improving it in this respect. We are afraid that you will be quite and the amplifier consequently commences R..S.S. unable to obtain great economy in this to oscillate. Of course, even the largest The circuit recommended for these case by the use of 2 -volt valves instead dry cell batteries have a certain internal multiple valves should certainly lie of 4 -volt valves. The filament wattage resistance which rises as the battery moderately selective, and we can only of the 4 -volt valves was not quite half a grows older, although this rise does not think that you are using in your aerial - watt, whilst the most economical valve occur so soon as in the case of the small grid and intervalve couplings coils having in the 2 -volt class consumes somewhat cell batteries. A 40

www.americanradiohistory.com t TheWl reles AND sì 3> RADIO REVIEW (151f Year of Publication)

VOL. XX. No. 25. No. 408. WEDNESDAY, JUNE 22ND, 1927.

: F. H. HAYNES. Editor : HUGH S. POCOCK. Assistant Editor : City 4011 (3 lines). Editorial Offices: 139 -4o, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone LONDON, E.C.4. Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, : " Fleet, London." Telephone : City 2847 (z3 lines). Telegrams Ethaworld, Navigation Street. MANCHESTER : 199, Deansgate. COVENTRY : Hertford Street. BIRMINGHAM : Guildhall Buildings, "Antoprees, Birmingham." Trkprmna: "hide, Manclieetee" Tekgeeme: "Cyclist Coventry." Telegram: Telephone: 0070 and 0971 city. Telephone: 5210 Coventry. Telephone: 2970 and '2971 Midland. Subscription Rates: Home, 178. 4d.; Canada, 17s. 4d.; other countries abroad, 898. 6d. per annum. are advised, before making use of them, to satisfy themselves that they As many of the circuits and apparatus described in these pages are covered by patents, readers would not be infringing patents.

of the staff of The Wireless OF EMPIRE BROADCASTING from 2NAD. 'Members POSSIBILITIES 11. oriel also listened in to this reception, and although at PROVED. times a little fading did occur, yet with a two -valve re- the Correspondence columns of this issue ceiver the speech never became unintelligible 'at any period \7e publish four letters under the heading throughout the transmission. of " Empire Broadcasting." Frankly, we This broadcasting of Lindbergh's arrival was a truly must confess to hav- national affair in America, and the ing read these letters psychological effect amongst have been with a feeling of American nationals must CONTENTS. broadcast was shame that England PACE very great. The the biggest ever organ- should have been left so far 1)e- EDITORIAL ... _. ... 773 probably in the States. it hind in the race for supremacy in 774 ised United MAKING SYNTHETIC GALENA ... and world broadcasting. We were continued for Several hours, By G. H. Tatham. in told the other day by the B.B.C. microphones were placed H. T. FROM TIIF. MAINS of New York where that it would be a long time, per- 179 various parts celebrations haps years, before we could have By H. L. Kirke. the procession and Y84 could be described. Considering satisfactory broadcasting to the READERS' NOVELTIES ... Empire from the Mother Country. how excellent was the reception PRACTICAL HINTS AND TIPS ... 785 feel that the Does this mean that we are going here, we cannot but CenRENT TOPICS ...... 788 a great opportunity to sit down and watch whilst B.B.C. missed America, and other WIRELESS INSTALLATION AT THE in not rebroadcasting at least part Holland, Can countries develop short -wave NEWCASTLE INFIRMARY ... 790 of the 2 XAD transmission. made a public broadcasting in order that we may By L. A. Sayce. it be that, having themselves re- copy their methods when we have statement that they THE EXPERIMENTER'S NOTEBOOK 794 short wave made quite sure that there is no gard broadcasting on By " Empiricist." stage element of uncertainty or experi- as only in an experimental 797 satisfactory about the undertaking? Are MANUFACTURERS' NEW APPARATUS and not possible of ment for years," we correct in looking upon short - BROADCAST BREVITIES 798 achievement " perhaps they hesitate to let the listening wave world- broadcasting to -day LETTERS TO THE EDITOR 800 for themselves the only in a very experimental public hear as Z HEADERS' PROBLEMS ... 802 which In the letters already re- true state of development to stage? broadcasting has been ferred to above, one correspondent. short -wave writing from Calcutta of Hol- brought? In making our case for a short -wave station we are not land's rebroadcast of London, says : ee I received the outset, but a performance transmission almost word perfect. It was like being home expecting perfection at the short -wave stations in other again to hear the same old announcer's voice. Holland comparable with that of in our opinion, ample proof I listen to every night he works." countries which have given, is no longer in the very In another letter from a reader in England, Mr. H. that short -wave broadcasting would have us believe, Whittaker, we are given an account of how he received experimental state that the B.B.C. expenditure to establish the wonderful broadcast in connection with Lindbergh's but has reached a stage where the amply justified. arrival in New York, which was relayed on short wave such a station can be A7

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WfipigIl®00 771 MALI I UNE 22nd, 1927. - MAKING J - . SYNTHETIC GALENA . ÌlillllllllllllllllllIIII; 31111111111111111111111T t T:.sÌíi i}y ?i=

Processes for the Preparation of Sensitive Crystal Detectors. By G. H. TATHAM. PRIOR to the days of broadcasting galena was very the amorphous form. The roll sulphur, which has a little used as a detector, and it is only in recent melting point of 112 deg. C., is first slowly melted in the years that it has achieved such a widespread popu- enamelled iron basin with a gentle heat, taking care that larity. Practically every crystal used for broadcast recc ? - it does not ignite. 11 hen entirely molten the temperature tion is galena or one of its modifications, and in conse- is slowly raiscl, the colour changes from yellow to quence it is now manufactured in con- a dark red, the viscosity rapidly siderable quantity. Natural galena, increasing. This change takes plaçe at one time fairly commonly used, has Although of a practical nature, this article at 15o deg. C., and as the temperature been replaced by a manufactured describes for the first time lead the actual processes employed for is raised to 162 deg. C. the liquid sulphide which in crystalline forni is the preparation of wireless detecting becomes so thick that it can scarcely usually described as " synthetic gal - crystals. he poured, reaching a maximum vis- ena," as it The formula: are of special im' closely resembles in struc- cosity at 'So deg. C. If the tem- ture the portance. They have been developed natural product. from perature is raised still higher the By theories held by the author on a series of experiments it was the operation of crystal detectors, liquid becomes less viscous, found although that a pure synthetic galena and will be found to produce par= its dark colour still remains. 'l'he could be produced by the fusion of titularly sensitive crystals when used in the manner described sulphur should be allowed to cool powdered lead with sulphur, using down soon after maximum viscosity only an ordinary gas -ring or Primus has been reached, until it resumes a oil -stove and taking advantage of the considerable heat quite liquid state, when it should be poured off into the generated by the chemical combination of the lead and enamelled When quite cold it can be crushed into sulphur. dish. A feature of the process is its simplicity, and small pieces, and by repeating this process twice again the interest attaches to the vivid sulphur reduced display can be to a which takes place tine amorphous powder. The upon the chemical combina- powdered lead required must tion of the powdered lead be both pure and dry, and with the amorphous sulphur. can be obtained from dealers Several pounds of synthetic in chemicals with a purity of galena can be produced for cent.' a few 99.99 per shillings. According to the weight of Materials Required. the fusion required the enamelled iron basin should An enamelled iron basin vary in size, and as a guide measuring about 43-in. in dia- it may be mentioned that for meter 5!7-in. by deep, together a small fusion of about one with an enamelled iron soup l.- Layout of the bricks for the foundation of a small furnace. pound a basin of the size of plate about gin. in diameter, The construction of the fireclay cone for supporting a small crucible is shown. It is a teacup is most suitable, will be retained in position by a projecting brick . large enough for while for a fusion of 20 lb. making some seven pounds of synthetic galena, the weight the basin should measure about 7,1,-in. in diameter by 4?in. being that of the final fusion. Best enamelled ware is not deep, thus holding about two quarts. required A wooden paddle for stirring the plastic A table is given showing the various combining weights sulphur can be cut from a piece of dry wood, and should of lead and sulphur to produce different weight fusions, measure about one foot long by an inch wide and din. in and as the heat of combination is very considerable the thickness. Sulphur is usually purchased in the form of sticks known Townson and Mercer, Ltd., 34, Camomile Street, London, as roll sulphur, and the Furst step is to convert this to E.C.3.

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www.americanradiohistory.com Wfill'asSEgi JUNE 2zrzd, 1927. 775 Woplic1 Making Synthetic Galena. - galena can be easily removed. It is very important that height of the flame Nvhich will be produced is also the gas should be turned off directly the flame starts on stated. the surface of the mixture, or otherwise the fused product will be found to contain innumerable small cavities. As a rule the enamelled basin cannot be used again for a Powdered Prepared Weight of Approx. height fusion on account of the surface being destroyed. When Sulphur. Fusion. of Flame. Lead. a fusion of 18 to 20 lb. is made any attempt at lb. oz. lb. oz. lb. oz. large 1 ft. in. will result in the 1 0 0 3!,V. 1 0 3 using the basin for a second charge 3 9 0 0 3 8 3 .. metal being completely burnt away. A small quantity of 7 0 0 ., O 0 1 u synthetic galena prepared in the manner, described will 1 14 0 10 12 1 13 be found to be very rich in sensitive spots. 15 3 2 3 18 0 16 ., 17 9 2 7 20 0 18 Making Larger Quantities. When undertaking a large fusion of 18 to 20 lb. the Making 1 lb. of Galena. surface of the liquid, which is at first quite even, after The smallest quantity recommended is the one -pound a while sends up small mounds, and from each a flame is reaction continues the jets unite to fusion, requiring r lb. of lead and 3 oz. of sulphur. ejected, and as the illumination After the sulphur has been prepared in the manner de- form one large flame. The flame has good to the burning scribed it is again placed in the basin. (which should have power and colour, and is somewhat similar zinc. The large fusion a capacity of about 6 to 8 oz.), preferably on a gas -ring, of a mixture of magnesium and being con- and the heat gently applied until the sulphur reaches the gives a good demonstration of the lead vapour the chemical state where it is so thick that it will hardly pour. It is sumed by the oxygen of the atmosphere, and the com- then removed from the flame, the gas turned off, and combination is so rapid that from the start to the powdered lead added quickly, stirring until thoroughly pletion of the reaction the time is only about 55 mixed. If a Primus oil -stove is being used owing to the seconds. need for working out of doors it is advisable to take the basin off the stove when mixing the lead with the sulphur as well as taking care to he ready to open the air valve directly fusion starts. It ;s inadvisable to attempt the B fusion of more than about 3? lb. from an oil- stove. \\Tien thoroughly mixed it is replaced over the gas flame, which should well surround the bottom of the basin. After E two or three minutes it will be observed that the sulphur is starting to combine with D F the powdered lead, and a flame which is bluish -white in colour first appears on the surface of the compound. The flame increases in height to about 15in., giving off a light grey smoke of lead oxide, the flame making a noise similar to a blow -lamp. The chemical combination of and sulphur raises the lead E temperature to between 95o and r,000 deg. C., and it will be seen that the basin becomes a bright cherry colour. Directly the flame ceases a cover should he placed over the basin and the fusion allowed to cool down slowly. ; vent pipes ; C, fire - Fig. 2.- Section of first tier of furnace. A, brick supporting cone B, air By gently tapping the basin ; F, floor of furnace shown in previous figure; clay cone; D, fireclay filling; E, brickwork bricks forming the door. when cold the synthetic G, filling stoppers ; H, half brick for supporting the five movable

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www.americanradiohistory.com l. i:164'

77e. Vnipshoo JUNE 22111'', 1927. Wofllc.l Making Synthetic Galena. - In use the charged crucible is brought to the desired In considering the most suitable quantity for one temperature (deep orange, which is about 1,125° C.) and charge it may be mentioned that the larger the quantity maintained at this temperature for a period of twenty to of lead and sulphur the greater will be the temperature twenty -five minutes. The fire should be allowed to burn reached. The small enamelled basin becomes unsuitable out before the crucible , is removed. The for a 28 lb. D- shaped charge unless the bottom is supported by a muffle may be used in a similar manner thin iron plate upon a smith's so as to avoid the basin being burnt forge, being heated and timed as just described through and the greater part before of the galena being lost by allowing to cool. The crucible should be covered by burning away into the atmosphere. Uniform synthetic pouring into the muffle dry powdered charcoal so as to galena crystals can usually be obtained from a 14 lb. prevent the crucible cooling too rapidly. With a small fusion. A 28 lb. fusion gave very large crystals, while crucible, such as size " A " or " B," a smelt can a 4o lb. fuse proved to be be the maximum that can be con- carried out in a Bunsen flame. A simple method veniently handled, inasmuch consists that the heat generated was of employing a D muffle supported hori- so great that over 15 lb. of lead was burnt away. The zontally upon two bricks. In the centre temperature in this instance of the approaches 1,2oo° C. muffle a fireclay support about run. Although the synthetic high is galena as now prepared can be provided to support the crucible. used for detection purposes, further treatment of the crystal is desirable, and the galena forms an excellent Building a Small Furnace. hase for the production of wireless crystals. As some readers may prefer to build the Furnaces for Treating the Galena. small furnace out -of- doors, constructional de- It is generally thought that for the tails are given of a portable assay further treatment of the crystal an furnace which has been used with electric furnace is necessary. As considerable success for pro- a matter of fact, there are ducing crystals. The fol- several objections to the use lowing materials are re- of the electric furnace, prin- quired :- cipally that of heating too I5o common yellow bricks. quickly, overheating and cwt. fireclay. cooling down too rapidly. A sheet of Uralite r8in. x In certain types of furnace, 28in. x gin. however, these troubles have 6ft. of iron pipe to form been eliminated, but the de- the chimney. signs are elaborate and Six pieces of iron gas - costly. barrel each 6in. long x The process consists of diameter. further fusing the synthetic The materials are galena not ex- and introducing other pensive, and the substances furnace, if to render the a muffle is included, crystal may br more sensitive. As used for other purposes. the principal difficulty is Constructional that details ar of providing a suitable given in the accompanyin furnace for this . purpose yrüv 111- diagrams, where constructional o the founda- details are V+ tion is shown in detail. The given so that the experi- Idwr bricks forming the founda- ments can be carried out by N tion (Fig. r) are laid flat and the experimenter in an eco- tv_ close together, nitmu and are not nomical manner. A tern - 4t, cemented in any iwav by porary furnace may, of Fig. 3. -The completed furnace. B, air inlet pipas for regulating the use of fireclay. In th course, be fixed up in the fire with the use of the the stoppers G. K, the five movable centre the brick A (Fig. 2) kitchen stove, providing bricks forming the door to the furnace. L, Uralite sheet for is seating the door and kept in position by fireclay. M, Uralite stood on end so as to pro- there is a good draught and cover plate. N, cover to fuel feed hole. P, semi-circular opening for chimney fixing. R, 6 ft. chimney of cast -iron pipe. trude about zin. above the a good coal is used. A level of the floor. If a small D- shaped muffle with a closed end supported muffle is to be used the projecting portion of the brick by two pieces of brick so as to allow space for the fuel should be coated with paraffin wax. to gravitate under the muffle can be satisfactorily used Fireclay is prepared by working together one part with a small Battersea round crucible with lid such as with three parts of water, and should be as stiff size which " A," is 2Rin. in height by rein. in diameter, as possible. A fireclay cone about 4in. in height or " B," Sin. in height and rein. in diameter. The and 6in. in diameter at the base and zin. at the D- shaped muffle should be used in a vertical position with apex is built round the projecting brick. Two pieces the flat of the D facing the back of the stove and the of round wood j in. in diameter are laid in the fuel fed round the muflle.2 fireclay, and if coated with paraffin wax can be easily Reference should he made to the lists of chemical apparatus removed when the clay sets. It is for this pur- manufacturers for details of muffle and crucibles. pose that the supporting brick is treated with wax, so as A IO

www.americanradiohistory.com - . : . i ; 1. . ,77707 ' . . r 7 .

WilpA@Eg JUNE 22nd, 1927. MAO 777 cool in Making Synthetic Galena. disturbing the lid. The crucible may be left to - in the case to permit of the removal of the cone. The pieces of the furnace, and particularly is this desirable be closed wood can, of course, be left in position, as they are soon of the 7 lb. charge. All the air inlets should the crucible is re- burnt out, and the openings left assist in keeping the and the fire allowed to go out. If as quickly as pos- bottom of the crucible hot. The projecting brick, of moved while hot it should be placed unslacked builders' course, keeps the cone in a firm position. sible in an old iron pail half full of lid should not be The six pieces of iron pipe are arranged in the first lime and completely covered. The is cold. tier of brickwork as shown, and project about ',kin. out- removed until the crucible perfectly side the brickwork. The fireclay should be sifted before being mixed, and it is an advantage to soak the clay in FORMULA No. I. water for two or three days before using it. By doing 7 Ib. Charge. 2 oz. Charge. this the fireclay will give a more smooth finish, and to a lb. oz. dr. oz. drs. gr. certain extent prevent clinkers adhering to the walls. By Synthetic Lead Sulphide (PbS) 6 12 0 2 0 0 the air supply can be regulated. Silver Sulphide (Ag2S) 1 3 t) means of fireclay stoppers 8 2 are Iounded off with fire- Zinc Sulphide (ZnS) All corners inside the furnace Copper Sulphide (CuS) 10 21 clay. Other constructional details can be seen in the ac- Mercury Sulphide (HgS) 1 0 4 companying illustration (Fig. 3). Amorphous Sulphur 11 3 By placing a brick in the back of the furnace a D- Temperature. -Deep Orange, about 1,125° C. shaped muffle, size " J," can be introduced measuring Tinte.-20 to 25 minutes. should show very small crystals with long by 6in. wide by 4in. in height, and is capable of Remarks. -When fractured 12in. bright faces. Use a soft catwhisker of gold or soft copper. holding eight small crucibles. The best fuel is coke pieces and used dry, or charcoal broken up into small FORMULA No. 2. A of hand bellows will be useful to can be used. pair 2 Charge. is introduced 7 lb. Charge. oz. assist in lighting the furnace. The fuel lb. oz. dr. oz. dr. gr. in the top of the furnace. When through the feed hole Synthetic Lead Sulphide (PbS) 6 12 0 2 0 0 the wood is well kindled replace the fireclay stoppers Silver Sulphide (Aa2S) 1 8 6 and introduce the coke, etc., moving the stoppers as Copper Sulphide (CuS) 4 1 21 to regulate the air. When the coke is red -hot Mercury Sulphide (HgS) 10 necessary 4 1 the charge may be placed in posi- Nickel Oxide (Ni0) the crucible containing Cobalt Oxide (Co304) 8 2 tion on the cone either through the opening made by Amorphous Sulphur 14 3} of tongs through moving the loose bricks or with a pair Temperature. -Light Orange, about 1,150° C. the fuel feed hole. The crucible should be well packed Time. -20 minutes. round with fuel and covered over to a height of gin. or Remarks.--When fractured small crystals incline to the cubic made of very fine soft iron which has Sin. above the lid. By sliding the cover plate the ignition system. Use a catwhisker been magnetised, or a nickel or silver catwhisker. of the fuel can be checked, and if at any time one side he given tó the is found to he turning dull attention should FORMULA No. 3. air regulating stopper or a few blasts may be given with 7 Ib. Charge. 2 oz. Charge. the bellows through the air channel. lb. oz. dr. oz. dr. gr. Crystal Formulae. Synthetic Lead Sulphide (PbS) 6 11 8 2 0 0 Silver Sulphide (Ag2S) 1 10 6i The several formula; given here for the production Mercury Sulphide (HgS) 1 2 5 of synthetic crystals are all based Upon the use of syn- Uranium Black Oxide (U203) 12 3 galena produced by the chemical combination Zinc Sulphide, Pure (ZnS) 8 2 thetic Sulphur .8 2 already described. The galena should be broken up in Amorphous Bright Cherry Red, about 1,000° C. an iron mortar, or it may be crushed to a powders with Temperature.- dry Time. -20 minutes. a flat hammer upon an iron plate. The various Remarks. -Crystal hard but very sensitive. Use with very fine chemicals should be well mixed together, and it is only wire catwhisker, three or four strands bunched together, of copper by thoroughly mixing that the best results are obtained. or silver. A light contact only is required. In the formuhe the weight of sulphur given is -for the FORMULA No. 4. amorphous variety powdered with pestle and mortar. the amorphous 7 lb. Charge. 2 oz. Charge. 1- lowers of sulphur may be used in place of oz. dr. oz. dr. gr. sulphur, though it will be necessary to double the weights lb. (PbS) 6 10 11 2 0 0 proportions are given for a 7 lb. charge Synthetic Lead Sulphide given. The 1 4 5 " G " size crucible, Silver Sulphide (Ag2S) such as can be fused in a Morgan Mercury Sulphide (HgS) 1 8 6 also for a small charge of 2 oz. such as can he contained Zinc Sulphide (ZnS) 8 2 in the No. I crucible and heated in the muffle. Lanthanum Oxide (La20,) 4 1 When the charge is placed in the crucible it should be Yttrium Oxide (Y20.3) 4 1 the sides and bottom of Praseodymium Oxide (Pr.,( )21 2 O tamped down by gently tapping Amorphous Sulphur 8 2 and the lid should he luted on with a little the crucible, Bright Cherry Red, about 1,000" C. a smelt it is most important that Temperature.- moist fireclay. After Time. -20 minutes. the crucible should he cooled-as slowly as possible without Remarks. -Thoroughly mix the yttrium and praseodymium oxides before introducing the other compounds. Catwhisker of soft silver or gold. 9 Powdered to pass through a 60 -mesh sieve. A II

ii www.americanradiohistory.com Wilpgwo WopJ1c1 ./VAE 22nd, 1927.; Making Synthetic Galena. - FORMULA No. 7. FORMULA No. 5. 7 lb. Charge. 2 oz. Charge. -7 lb. Charge. 2 oz. Charge. lb. oz. dr. oz. dr. gr. Ib. oz. dr. oz. dr. gr. Synthetic Lead Sulphide (PbS) 6 10 4 2 Synthetic Lead (PbS) 0 0 Sulphide 6 10 0 2 0 0 Silver Sulphide (Ag2S) 2 0 8 Silver Sulphide (Aa2S) 1 10 6} Mercury Sulphide (HgS) 1 8 6 Mercury Sulphide (HgS) 1 4 5" Cobalt Sulphide (CoS) 4 1 Black Uranium Oxide (U205) 1 8 6 Nickel Sulphide (NiS) 8 2 Thorium Dioxide (Th02) Selenium 8 2 Sulphide (Se2S) 4 1 Zinc Sulphide (ZuS) 8 Zinconium Oxide (Zr02) 10 2.'1 Amorphous Sulphur 10 Amorphous Sulphur 21 " 10 2.'E Temperature. -Deep Orange, about 1,125° C'. Temperature.- Cherry Red, about 900° C. Tinge. -20 to 25 minutes. Tine. -45 minutes. Remarks.- Thoroughly mix the silver sulphide with the uranium Remarks. -Place 8 drachms of the mercury sulphide in the black oxide. Mix the thorium bottom dioxide with the mercury sulphide of the crucible. Mix the cobalt sulphide, nickel sulphide and and then grind altogether in a mortar. Catwhisker of fine tinsel selenium sulphide together, then add the copper, gold plated. mercury sulphide, followed by the zinconium oxide and blend altogether. Catwhisker, silver or fine gold. FORMULA No. 6. 71b. Charge. 2 oz. Charge. FORMULA lb. oz. dr. oz. dr. gr. No. 8. Synthetic Lead Sulphide (PbS) 6 10 3 2 0 0 7 lb. Charge. 2 Silver Sulphide (Ag2S) oz. Charge. 1 8 6 lb. oz. dr. Mercury Sulphide (HgS) oz. dr. gr. 1 6 51,- Synthetic Lead Sulphide (PbS) 6 10 Thorium Dioxide (Th02) 6 2 0 0 5 1; A Silver Sulphide (Ag2S) 1 15 Tellurium " Metal 8 Crystals " l Mercury Sulphide (HgS) 1 3 A (T1003) 6 4 Uranium Black Oxide (U205) 8 2 Uranium Black Uxide ((5205) -9 2t- Thorium Dioxide (Th02) k 6 11 Zinc Sulphide, Pure (ZnS) 6 B lt Lanthanum Oxide (La203) 4 1 Lanthanum Oxide (I.aO) 5 1 Yttrium Oxide (Y203) 4 1 B Yttrium (Y203) 5 li Praseodymium Oxide (Pr203) 2 01 Praseodymium Oxide (Pr203) 3 1 C'-Amorphous Sulphur 1 0 4 Amorphous Sulphur 10 3 Temperature.- Temperature. -Cherry Red, about 900° C. Cherry P.ed, about 900° C. Tinte. -35 minutes. Time. -30 minutes. Remarks.- Remarks. -Place 8 drachms of the mercury- sulphide in bottons Thoroughly mix A and B separately. Place 8 drachms of the crucible. Well of mercury mix A and B separately, then mix A, B and C sulphide in bottom of the crucible for a 7 lb. charge. together. The praseodymium 3 grains extra for a oz. acts as an exciter of the phos- 2 charge. Catwhisker of four or five soft phorescence of lanthhnum and yttrium. flexible strands of copper tinsel or fine silver wire. Catwhisker of fine soft Hex or copper tinsel, silver wire very fine, three or four strands.

New Marconiphone Catalogue. cent technical developments in the United An attractive art, catalogue has recently TRADE States. .An interesting piece of apparatus been issued by the Marconiphone Co., NOTES. dealt with is the type 388 Vacuum Tuhe Ltd., 210 -212, Tottenham Court Road, Reactivator, an instrument for testing and London, Wß'.1, covering in 72 pages the restoring thoriated valves. The two complete range of " Marconiphone " wire- General Radio Factory this little periodical methods of achieving this end, viz., less apparatus. Among the noteworthy contains much useful information on re- "flashing" and "cooking," are described. items in these pages must be mentioned the KLI transformer and power choke, the new potential divider and new " Marconiphone " valve switch. The catalogue incorporates a useful list of Marconi valves with prices and operating data. e o o o Burndept Portable Five. ST ARr On page 660 of our issue of May 25th NC-RE' the price of the Burndept Portable Five receiver was erroneously given as £30. The correct price of titis instrument is 30 guineas. O o o 0 From America. From Messrs. Claude Lyons, 76, Old Hall Street, Liverpool, sole concessionaires for Great Britain fur General Radio Li- struments of Cambridge, Mass., U.S.A., we have received cumbers 10 and 11 of the 6'e ne rol Jindio T.rperimenter a monthly publication, copies of which, we understand, can be .forwarded to any reader making application to Messrs. HOW VALVES ARE MADE. At the recent opening of Whiteley's wireless depart- Claude Lyons. ment a successful demonstration was given of the manufacture of Osram valves In dealing with stage by stage. The photograph shows how skilfully the exhibit was arranged in a the productions of the comparatively small space. A I2

www.americanradiohistory.com WIT@hoo JUNE 227nß, 792; . 779 pilcd H.T. MOM THE MARNSu Some Notes on Mains Units and their Application to Receivers. By H. L. KIRKE.

UCH has been written on the subject of mains system of the H.T. unit, causing the whole L.F. portion units for supplying H.T. and L.T. to broadcast of the receiver to oscillate at some low (audio) frequency receivers. There are many types on the market which depends upon the constants of the whole circuit. simple at the moment; some good, some poor. It is the purpose Fig. 1 shows the essential connections of a 3- of this article to point out some of the pitfalls in the valve receiver, consisting of a detector and two resistance - design of such apparatus. The article will he confined capacity- coupled L.F. amplifying stages, together with chiefly to apparatus for obtaining H.T supply. the connection of a normal H.T. mains unit. One of the great advantages of obtaining H.T. from A system containing condensers and inductance, such as imped- mains -in particular A.C. mains -is that fairly high shown in the smoothing system in Fig. 1, has an obtainable by this method with little extra ance which varies with frequency both in amplitude and voltages are resonant expense. 'The advantage of high H.T. voltage is that phase. The circuit acts at frequencies above the below good volume is obtainable with freedom from distortion. frequency as a condenser, at some frequencies at the re- That is to say, the valves -in particular the output stage the resonant frequency as an inductance, and Slightly above -may be operated on the linear portion of their charac- sonant frequency as a high resistance. high resistance teristics, even when using sufficiently high grid negative the resonant frequency the circuit acts as a -slightly below the bias to prevent grid current with very loud signals. in series with a small condenser, while and large Despite this great advantage of the mains unit there are resonant frequency it acts as a high resistance manner similar very few giving Outputs greater than about 120 volts at inductance in series. In fact, it acts in a except that it is less 10 -r5 milliamps. One wonders why. Is it that the to a simple tuned anode circuit, of the choke and importance of high H.T. for good volume with good sharply tuned, due to the high resistance valves. quality is forgotten, or is it that mains units have been the damping effect of the rectifier designed simply to replace dry H.T. batteries where 120 volts was considered to he quite a high voltage. Broadcasting loses much of its charm if the volume is insufficient, even if the quality is good. For reasonable volume in a medium -sized room at least 3o milliamps at about 200 volts is required ; while really loud results require at least 5o milliamps at about 30o volts. The Receiver. The next point to he considered is for what type of receiver the unit is to he designed, and in turn for what loud- speaker the re- 1.-Simple 3 -valve receiver with H.T. unit working from A.G. mains. been designed. ceiver has will be For instance, if the loud- speaker reproduced frequencies The natural frequency for such a circuit only down to 206 or 25o cycles, as some do, there is no I a receiver -which is efficient down to, Î object in designing 2n CiC2 say, 5o cycles or even 20 cycles. As will be seen later L v Cl C2/ the type of loud- speaker and its method of connection to - choke and the damping as well as the receiver itself, all affect the Neglect the resistance of the the receiver, consider what happens the supply unit. effect of the rectifying valves, and design of H.T. through the re- It frequently happens that when a mains unit is con- when an alternating E.M.F. is passed of the receiver under normal nected up to an ordinary receiver and loud- speaker only ceiving circuits. The action and need not be described an unpleasant noise results. This noise is often referred circumstances is well known to as " squeggering," or " motor- hiking." This is due here. that the E.M.F. has arrived at to low- frequency reaction introduced by the smoothing Consider, therefore, A 13

www.americanradiohistory.com 780 Wpishoo WopIl 0 JUNE 22nd, 1027. H.T. from the Mains. - methods; one frequently adopted is to reduce the value the grid of the last valve; the changes of grid potential of the intervalve condenser, so reducing the magnification will cause changes of anode current The magnitude and of the amplifier at low frequencies until the amplification phase of the changes will depend upon (a) the valve is sufficiently low to prevent oscillation. This method is internal resistance, (b) the impedance normally in the out- cowardly and robs a resistance -capacity amplifier of one put circuit, such as the loud- speaker, L.F. choke, etc., of its most important features, i.e., its ability to amplify and (c) the impedance of the smoothing system. (if properly designed) very low frequencies equally with There will be a certain back E.M.F. across the smooth- the high. A second method is to reduce the value of ing system due to the alternating current through it ; the grid leak or increase the value of anode resistance in

+ H.T. + H.T.-4 o L L

U2LL LLU Q:

-H.T. H.T. o

Fig. 2 and Fig. 3.- Reducing impedance of smoothing circuit at resonant circuit by connecting resistance in series with C.,. magnitude of this back E.M.F. will be I Z There I is the the first interstage circuit, the latter method being current and usually Z the impedance of smoothing system. more effective. The effect is to alter the ratio of P.D. There is, therefore, instead of a steady high -tension across the valve to that across the anode resistance,. so supply, one which is modulated or varying at the fre- reducing the value of P.D. applied to the second grid. quency of the magnified impulses in the receiver. This The more scientific method is to alter the varying smoothing H.T. supply causes the anode current in the first system by increasing C Ct and /or L until its impedance valve to vary in magnitude. Part of the variation will is so low that there is very little back E.M.F. across it. occur across the anode resistance and the remainder across The effective capacity of the system at frequencies well the valve Any changes of potential at the anode of the above the natural or resonant frequency will be very nearly first valve will be applied through the intervalve condenser the capacity of C. At frequencies just above the re- to the grid of the next valve, and will be magnified by sonant frequency the effect of the remainder of the circuit the remainder of the system, adding to or subtracting (i.e., Ct and L) will be to decrease the effective capacity from the original impulse according to the phase angle. of the system. Increasing C, will therefore decrease the If the secondary impulse happens to be as large as the impedance at frequencies above the resonant frequency original impulse would have been had there been no and also tend to reduce the impedance at the resonant fre- secondary impulse, and of the same phase, the whole quency. Increasing C Ct and/or L will decrease the system can oscillate at that frequency. It frequently floes. resonant frequency and so lower the impedance at what How can this he prevented ? There are various was the resonant frequency.

L S.

Fig. Another method 4.- of reducing low- frequency reaction ; separate smoothing circuits are provided for each valve. A I¢

www.americanradiohistory.com àd Wt@hoo 781 11-YE 22nd, 1927. Watcll H.T. from the Mains. - receiver and its bearing on the working of the receiver follows : It is frequently found that, however much C C, and with a mains unit. The effect is as -The the L increased (within practical limits), the receiver still amount of reaction is proportional to alternating are the to oscillate, but at a lower frequency, this is current from the last valve which flows through continues This current true of a good resistance -capacity amplifier. smoothing system for a given grid voltage. particularly internal resistance This is because the impedance of the smoothing system is depends, as stated above, upon the always high round about the resonant frequency, the increase of C,,, C1 and L causing a lowering of the resonant frequency. The impedance at the resonant frequency can be reduced by inserting resistance in series with C_ or by IN dividing C2 into several parallel paths and connecting OUT various values of resistance in the various condensers, as shown in Figs. 2 and 3. T resonant frequency is i T O The decrease in impedance at the usually at the expense of an increase of impedance at a higher frequencies. It is possible, however, to make Fig. 6.- Multiple- circuit smoothing system. compromise. of the valve, the loud- speaker impedance, and the smooth- A further method of tackling the problem is to use impedance. Therefore, if we increase the separate smoothing systems for the various valves: This ing system loud- speaker impedance we shall reduce this reaction is not so expensive as it may seem. High resistance effect. This method, however, is not efficient, as there is of very little consequence in the smoothing circuits is optimum loud- speaker impedance for maximum for the resistance- capacity valve, as the current is an efficiency. A method of connection commonly known as parallel or choke feeding may be employed. This is efficient as far as the set and loud -speaker is concerned, and has the effect of reducing the reaction effect considerably. The connections are shown in Figs. 7 and 8; Fig. 7 showing how the circuit may be used when the loud- speaker impedance is correct for the valve; Fig. 8 where a transformer must he used to change the effective impedance of the loud- speaker to suit the valve. It is important that the loud- speaker or transformer should be connected as shown and not between the blocking condenser and + H.T., as is frequently done. In both these cases the current which actuates the loud- speaker flows through the blocking condenser and loud- speaker to earth, while only a small portion of the current flows through the choke, smoothing system, etc. This Fig. 5.- Resistance- capacity smoothing system for use when a latter current may be made as small as desired by in- reduction in H.T. voltage is required. creasing the inductance of the choke. The maximum value by its resistance; small. Very high inductance chokes can therefore be of inductance of the choke is limited so reduce the H.T. at with smaller condensers. The circuit is shown in which if too high will considerably used and.thus reduce efficiency. Fig. 4. It is not, however, always necessary to use the anode of the last valve separate smoothing for each stage. Where the H.T. to The value of condenser C3 points, a particular valve can be considerably less than the maxi- depends upon three mum H.T. a resistance- capacity smoothing system may viz., the impedance of the be used. This is shown in Fig 5. loud -speaker or output cir- im- Some smoothing systems consist of more than one sec- cuit, tree valve internal fre- tion, i.e., three or more condensers and two or more pedance, and the lowest chokes, as in Fig. 6. While the smoothing for a given quency it is desired to repro- total capacity and inductance may be greater than for a duce. As a rough guide 2 single circuit, as shown in Fig. r, the circuit has more mfds. per 6,000 ohms is of than one natural frequency, and the natural frequency about right, the increase will be higher due to the reduction in inductance and capacity being proportional for given values of to the decrease in valve in capacity per stage. This means that Fig. 7.- Choke-capacity out- intervalve condenser, anode resistance and grid leak, etc., ternal resistance. put circuit for use when the found that loud- speaker impedance is the circuit is more liable to self- oscillate with a multi- It is generally suited to the valve. filter, due to the increased impedance and higher with a good receiver the stage and inductance required frequencies. values of smoothing condenser resonant -frequency are usually Reference was made in the beginning of this article to prevent self -oscillation at audio to the method of connection of the loud -speaker to the sufficient to provide good smoothing. A 15

www.americanradiohistory.com NWTp®Il@00 wóIC>A JUIVE 22nd, 1927. H.T. from the Mains. - well known that the impedance of a choke is proportional It is sometimes found in such systems that, however to frequency. For the sake of simplicity in Fig. io con- much smoothing is used, a certain amount of hum re- sider that the grid leak resistance R is high compared with mains. This residual hum may he due to causes other the resistance of the valve V,. than lark of smoothing. One of these causes is rather peculiar. Referring to Fig r it twill be seen that there is a path H.F. CH^KE for a high -frequency alternating current from the earth +H.T. vvvv O terminal of the set to - H.T. and thence via condenser C,. the rectifying valves, the capacity between windings _L FROM of the power transformer to the mains, and via the capa- RECTIFIER city of the mains to earth. If the earth lead is not very short or the earth not good, the earth terminal will -H.T. .4.49Q9/ o not be actually at earth potential, i.e., there will be a H.F. CHOKE difference of potential between the earth terminal and earth proper ; this difference of potential will cause a FYg. 9.- Chokes in.erted in supply leads to keep II.F. off the current to flow through the above- mentioned path to earth. rectifying salves. This path is intermittent, as rectifying valves are only conductive during part of the L.F. cycle; therefore. H.F. If we apply an alternating E.M.F. across a, b, Fig. ro, a current will flow through L. and V,. At very low frequencies the impedance of the choke will be negligible, and therefore the main P.D. will be applied in effect across c and a, there being no drop of potential across the choke "2. In the circuit considered in Fig. r there was a considerable drop of A.C. voltage in the anode resistance, thereby reducing the voltage across the first valve, as it is this voltage that is magnified and causes reaction. It will be seen that the circuit shown in Fig. to will be more liable to oscillate than the circuit in Fig. r. The above is not strictly true, but illustrates the general Fig. 8.- Combined choke -capacity and transformer output principle that choke circuit for use with low-impedance loud-sp:akers. coupling is more liable to give trouble than resistance coupling. Here again, however, it is pos- current can only flow (luring this portion of the IA:. sible to use a separate smoothing system for the first cycle, with the result that the current is intermittent. valve. With transformer coupling the case is again \Ve thus have part of the carrier current in the aerial different in that the reaction effect of a receiver depends going to earth via the earth lead, and part via a circuit upon the P.D. developed across the primary of the first which is intermittently conductive. This results in the transformer and the frequency characteristic of the re- aerial current being modulated at the frequency or double mainder of the amplifier. The amount of reaction in the the frequency of the supply, according as to whether amplifier will decrease as the resistance of the first vale single- or double -wave rectification is used. is increased, as this increase of resistance will decrease This effect may be reduced to a negligible amount by inserting H.F. chokes in the rectifier system as shown in Fig. 9.

Effect of Various Types of Inter -stage Coupling. So far we have considered merely the simple case of resistance -capacity coupled receivers. While most of the remarks above regarding the design of mains units apply when various types of receivers are used, the type of receiver has considerable bearing upon its working \\'lth a mains unit. Fiß 10. -A choke -coupled amplifier with sing ;le -circuit smoothing system is more It Is well known that a high- niagnifi- subject to L.F. reaction than a resistance- capacityamplifler operating under the 'ation I.. F. amplifier will not work tvitlt same conditions. a high- resistance H.T. battery. The same applies to the alternating current through the primary of the trans - mains units; a mains unit can be considered as a high- former, due to the back E.I.F. across the smoothing resistance battery shunted by a condenser, except at its s}'stem. resonant frequency. If, for instance, choke -capacity The reversal of the transformer connections will reverse coupling is used, we have the circuit in Fig. 1o. It is the phase of the reaction, and may in some cases stop A 16

www.americanradiohistory.com WATasto JUNE 22nd, 1927. WoDa 783 H.T. from the Mains. - changes 18o degrees for each valve. It is, therefore, pos- the oscillation; but what generally happens is that the sible that, by adding a stage of magnification, the re- frequency of the oscillation changes to one which suits action may be reduced. This is only true when the phase the new arrangement. angle of the smoothing system does not change with fre- In general, however, with the high voltages obtainable quency, and is nearly zero. from mains units, very little advantage can be gained by In practice, however, the phase angle at frequencies using transformer coupling, as reasonably high magnifica- above resonance is nearly - 90 °. The angle of reaction tion consistent with gookl frequency characteristics can be frill vary, therefore, between - 9o° and + 90° nearly, obtained from resistance or choke -capacity coupling. unless the smoothing circuit is designed so that the phase A point which must he borne in mind in direct -coupled angle is nearly zero for all frequencies that matter. Most amplifiers such as resistance or choke coupling (particu- of the above remarks apply (in particular the use of H.F. larly the former) is that the phase of the reaction effect chokes) to smoothing systems for D.C. mains H.T.

SOLAR ECLIPSE TESTS. Short =wave Transmissions by the Radio Society of Great Britain. IT is thought that many experimenters would like to Following the transmission of the station call signs for participate in the tests which have been organised live minutes the Morse signals should be noted, and if by the R.S.G.B. This Society is confining its at- there is any doubt a blank should be indicated. tention to the shorter wavelengths, and arrangements Abbreviations have been prepared for use on the log have been made for stations using wavelengths as indi- sheets, and these are as follow :- cated to transmit signals on June 27th, 28th, 29th, 3oth, S.- Statics. and July 1st, commencing each day at 5.4o a.m. B.S.T., S.E.S.-Statics extra strong. and closing down at 6.4o a.ni. B.S.T. F.- Fading. G5YG (Glasgow) 100 metres ; steady unmodulated I. S.- Increase in signal strength. carrier wave. G.I.S.-Great increase in signal strength. G2NM (Surrey) 90 metres ; ditto S.G. -Great interference by statics. G2W'.7 (Palmers Green, N.) 46 metres ; C. W. Morse code words. D.- Distortion. 44 metres ; ditto (:6W\W (Leicester) state G2OD (Gerrard's Cross) 32 metres ; ditto S.I. -Interference by other stations (here also ; I :14Z (Aberdeen) 23 metres ditto call of interfering station if possible.) The following scheme has been devised in order to All reports and log sheets should be forwarded to the ensure that all stations receive a certain amount of atten- Hon. Organiser, Solar Eclipse Tests, Radio Society of tion from listeners and others interested. A map which Great Britain, 53, Victoria Street, London, S.W. r, -after shows your nearest town or village is obtained, and then the tests, and any deductions or theories formed as a upon a piece of tracing paper or tissue paper a circle divided into six equal segments is drawn as shown in the sketch. It will he noted that each segment forms an angle of 6o °, which can he marked out from a pro- tractor or' by means of a pair of compasses. The drawing is now placed over the map so that the line ZZ inter- sects Borth (Cardigan Bav) and Birmingham and so that the point A comes immediately over Birmingham. From the following table the station to observe is selected :- Station Station z Sector No. Wavelength. Sector No. 1Wavelenrth. Sl 23 or 90 Nl 23 or 99 S2 44 or 100 N2 44 or 100 S3 46 or 32 N3 46 or 32 Will any R.S.G.B. members who have received the " T. and R. Bulletin " kindly note that the wavelengths of sectors S3 and N3 have been altered as shown above. Members of the general public taking part in the tests head of the report their sector should insert at the This diagram should be redrawn on tracing paper and used number, County, town and street, and house number in according to instructions to indicate the stations to be observed. that order from top to bottom, and the report is best of observations will in due course be communi- prepared on a sheet of paper squared in tenths. Any result the Press by the Society. Readers phenomena occurring during the tests should be noted cated to the technical any information apart from that speci- as nearly as possible to the nearest five seconds, and in should note that be sent on separate sheets of paper, this connection the time signals being transmitted by the fied above should in the daily lóg sheet of the receiving 11.ß.C. will be of great assistance in correcting time- and not included station. pieces. - A 17

www.americanradiohistory.com _. _ rIMPII.,1541144111- .. irriRrtfilrIn rra.-' . ...

784 WEpesoo Mpild JUNE 2211d, 1927.

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A Section Devoted to New Ideas and Practical Devices. battery leads and the internal connec- current, and the neutralising con- tions to the set are soldered to tags denser adjusted until the signals from at the back of the socket, while the the local station are at a minimum. battery lead itself is brought out The bulb is then replaced and the through the socket. The mouth of process repeated for the second H .F. BELL CIRCUIT. stage. When the loud -speaker is working In addition to providing a con - on full volume on the local station venient method of breaking the H.T. difficulty may be experienced in hear- circuits the bulbs also act as a pro- ing the electric house -bell. Some- tective fuse and may be fitted with times when the bell wiring runs advantage to the detector and L.F. parallel to loud -speaker leads the valves. For convenience the adaptors electrical disturbance due to the bell should be mounted outside the screen, may be heard in the loud- speaker. but in all cases they should Extending be con- this idea one can make nected in circuit on the battery side certain of always hearing the bell in of the Mansbridge by -pass con- the loud- speaker by connecting in the densers. A. R. bell wiring a circuit LC tuned to A neat method of terminating battery 0000 leads. the wavelength of the local station. CONDENSER SPINDLE. When energised by the bell, this cir- the socket is usually bevelled or The sectional drawing shows an cuit will radiate in the same manner rounded which prevents fraying of excellent method of increasing the as a buzzer wavemeter and will effect the insulation. F. P. diameter of obsolete condenser the aerial circuit 0000 of the receiver so spindles for use with modern slow - that the vibration of the bell will be NEUTRALISING " THE WIRELESS motion dials. Most of these old con- reproduced in the loud - speaker. The WORLD FIVE." densers were provided with spindles 'l'he trouble of taking off the back of the copper screen, disconnecting BUSH FOR the H.T. leads and resoldering when DIAL neutralising this receiver may be Nffareomm ` obviated by including two flash -lamp ói1,llIN;Iu11111IilNNh9i1Ìll ü IVPu, adaptors and bulbs in the H.T. leads ri,d.,rr ti to the set. , When the set has been tuned to the GRUB CONDENSER local station the bulb in the first SCREW SPINDLE Tuned circuit for making house -bell audible in loud-speaker. high- frequency transformer lead is unscrewed, thus breaking the H.T. Increasing the diameter of condenser tuned circuit may be introduced at spindle to fit modern slow -motion dials. any point in the circuit, preferably consisting of a length of 213. A. near the receiving room or aerial VALVES FOR IDEAS. rod, whereas plain }in. spindles are lead -in. H. J. S. stan- 0000 Readers are invited to submit brief dard on modern condensers. details, with rough sketches, where neces- A length of -iiin. BATTERY LEADS. sary, of devices of experimental brass rod is drilled interest throughout its length, preferably A convenient method of anchoring for inclusion in this section. A dull in emitter receiving valve will be despatched the lathe, and tapped 2B.A. To fix battery leads when it is desired to to every reader whose idea is accepted this bush on the spindle use is made dispense with ternilnal panels for publication. is of a small internal grub screw driven shown in the diagram. " Clix " or Letters should be addressed to the Editor, " Wire- down inside the bush on to the head similar sockets are fitted to the panel less World and Radio l,evie,e," Dorset House, Tudor St., London, E.C.4, and marked " Ideas." of the condenser spindle. or the back of the cabinet. Both the F. J. W. T. A IS

www.americanradiohistory.com WIp@Ilsoo JUNE 22nd, r927. 785 W©111

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A Section Mainly for the New Reader.

ARTIFICIAL RESISTANCE. containers will serve not only to in depth, and should be made of wood pre\ cat damage to instruments at least flin. or, better, in. in thick - T may not he generally realised the These dimensions represent the that the method of testing the themselves loot will also act as nes.c. minimum size recommended. There effectiveness of an H.F. transformer a support for the other com- is no real reason why the boxes should by the insertion of an artificial re- ponents, which may be mounted on he larger, and indeed a slight sistance, as advocated in these notes the top, or even on the back, and not sometimes of the increase is sometimes necessary to in last week's issue, may he applied on one or both give a for the vanes of cer- the Everyman- Four " receiver sides. When the circuit calls for two clearance to " which without the necessity for altering any or more condensers the boxes may be tain S.L..F. condensers, by generally occupy a good deal of connections. A consideration of the placed side side, a baseboard of suitable size being screwed to their space when the condenser is in the circuit diagram will show that a load- middle of its scale. ing coil socket is inserted in series upper surfaces. This gives solidity 0 0 0 0 with the tuned H.F. transformer to the whole arrangement, and the secondary. If the coil is replaced edge of the hoard serves as a point and A SOLDERING TIP. by a plug, the terminals of which are of attachment for terminal strips soldered joints are made joined together by a loop of fine small pieces of elsetite carrying such in a wireless set with every- resistance wire, the conditions neces- components as filament rheostats, etc. thing in situ it is often difficult to sary for a test will be realised when If necessary, the baseboard may be prevent the flux becoming spluttered the short -circuiting switch, primarily of such a size that it overhangs the on to the panel or surrounding com- intended for the long -wave change- condenser boxes both at the back and ponents. Killed spirits may be the over, is " opened." sides, thus giving ample space for worst offender in this respect, but 0000 the mounting of a large number of components. even the so- called non -corrosive fluxes EXPERIMENTAL SET CONSTRUCTION. If all the parts are secured to the are apt to wander into places where ' HE majority of wireless compo- removable 'aa.se it is possible to detach it is undesirable. Even if this does r nents are intended to be perma- it without disturbing the wiring, ex- not give rise to noisy operation in nently mounted on a panel or base- cept, of course, that joined to the the finished set it looks very bad. A board, and it is always a matter of condensers, and to use the latter for cleaner way of doing the job is to tin some little difficulty to arrange them other purposes, reverting to the ori- each component separately at the conveniently when connecting up a ginal circuit at short notice. points where the soldered connections temporary receiver, either for experi- The use of screening, which is so are to be made before the final mental purposes or for testing some necessary in many modern H.F. am- assembly is carried out. All traces new circuit. Variable condensers are plifying circuits, is not precluded. as of superfluous flux are cleaned off and assembled in their probably responsible for the greater metal sheets may he introduced 1- the components part of the trouble; even if a rigid tween containers. It has been found various positions. A touch with a support is devised, noises are likely to when connecting up receivers of this clean soldering iron then serves to develop in a few days' time, due to kind that it is most convenient to sweat the various joints together the accumulation of dust between the screw each container (with perhaps an effectively. This procedure has the vanes. inch or so of spacing between adja- advantage that one can use one's Those who undertake the construc- cent ones) to a wooden strip running favourite flux and hold each compo- tion of receivers in the manner under along the back. The H.F. valve nent in the most convenient position discussion will find that it is an ex- holder, together with its coupling de- to ensure thorough tinning, instead of cellent plan to mount two or three vice, is then mounted on the top of having to do the most critical part of spare variable condensers in stout the associated tuning condenser. the soldering in awkward positions _1 wooden boxes, fitted with an ebonite The boxes may conveniently amongst the components of an assem- front panel and terminals. These measure about Sin. by .sin. by fin. bled set. A 21

www.americanradiohistory.com Z86 Wflp®Il,S00 - JUNE 22nd, 1927. íOOTs'Ca. VALVE INSULATION. in The IFireless World for October voltage than that provided by a WHEN searching for the leak- 27th, 1926. It should be pointed tapped bias battery. In point of fact, ages which are often respon- out, however, that the average aerial, the majority of them operate best at, sible for poor H.F. amplification and particularly of the kind which, of very roughly, two volts negative. flat tuning, the possibility of faulty necessity, is generally erected in a This means that two dry cells should insulation in the valves themselves town, has a very considerable H.F. be used, the excess negative voltage should not be overlooked, and it is resistance, and that the easiest way being offset by moving the- potentio- advisable to test (by means of phones of compensating for the reduction in meter slider towards the positive end and a dry battery, if no more exact signal strength caused by this resist- of the winding. method is available) between plate ance is to fit an " untuned " aerial Finally, it should be pointed out and filament, grid and filament, and coupler. It is no exaggeration to say that the substitution of a coupled grid and plate. that under certain 0000 conditions the ap- aerial circuit for a direct connection parent loudness of signals will be is least likely to result in an appre- A LOCAL STATION RECEIVER. almost doubled by this change, while ciable gain when the aerial is exces- T has been suggested from time in the great majority of cases a very sively short. V to time in this journal that the appreciable gain will result. The cir- 0000 simple arrangement of an anode rec- cuit diagram of a complete receiver of SWITCHING OFF THE H.T. - tifying detector valve followed by this type is given in Fig. 2. fROVIDED that the insulation of a single resistance -coupled low - This is one of the cases where the a receiver is as good as it should frequency amplifier makes a perfectly good effects of a highly efficient coil be, there is no real need to disconnect adequate receiver for loud- speaker re- will be felt, and it is recommended or switch off the high- tension battery ception up to distances of five or even that an aerial -grid transformer of the when " closing down." As soon as ten miles from a main station. It is design included in the " Everyman the filaments of the valves become essential, however, that the detector Four " receiver (and in several others cold, the current flow from this bat- valve should be of the " high- magni- recently described in this journal) tery Ivill cease entirely, unless there fication " type, and, moreover, that should be used. The anode resist- is leakage across its terminals. a considerable high -frequency volt- ance R, and the grid leak R, will In spite of this, however, there may age should be applied to its grid. have conventional values suitable for be cases where it is desirable, as a Even in the immediate vicinity of a the comparatively high impedance of safety measure, to arrange for corn- transmitter, this latter condition may the valve with which the former will plete disconnection of the high- tension not obtain unless the aerial -earth be associated, while a damping re- battery, and the most certain way of system is moderately effective. sistance R, of about 0.25 megohm doing so is provided by the insertion of a switch in each positive lead. Alternatively, a single -pole switch may be inserted in the lead joining H.T. - to L.T. - , although it should be realised that this plan will not preclude the possibility of short - circuiting sections of the battery between any alternative tappings which may be connected up. It is sometimes recommended that a multi -pole switch should be fitted in order to switch off both batteries, but if this arrangement is adopted the switch should, strictly speaking, be of special construction, its contacts being arranged in such a way that the H.T. circuits are completed before the filaments are lighted, and broken after they are extinguished. In other words, the anode circuits should not Fig. 2. -A detector -L.F. combination with resistance capacity coupling and untuned " aerial -grid transformer. be interrupted while the filaments are glowing. A simple receiver of this descrip- may be inserted as shown. An anode From the foregoing it will be seen tion has so many advantages that a by -pass condenser, generally of not that the switching on or off of the hint as to possible methods of improv- more than o.000r mfd. capacity, is high- tension battery is not altogether ing its sensitivity and range may be as a rule desirable ; it should be con- a simple matter, and probably the of interest. It is generally recom- nected as shown in dotted lines. best advice to the average wireless mended that, to avoid complications, As a refinement, a grid potentio- user is that this battery should be a direct- coupled aerial circuit should meter may be provided ; many of the permanently in circuit, being discon- be used, and a set on these lines was modern valves require for best detec- nected only when the receiver is to be described with constructional details tion a more accurate adjustment of out of use for a prolonged period. A 22

www.americanradiohistory.com tWfimhogi JUNE 22nd , 1927. 7d'7

THE CHOICE OF A CIRCUIT. will give sufficient magnification of This is because the ratio of signal LTHOUGH the construction of any signal to which it is worth while strength -even when amplified enor- a receiver, including a single listening. This does not apply, how- mously -to extraneous noises will be *o(, stage of high- frequency amplification, ever, when local receiving conditions 1. 0000 'does not present any very great diffi- are bad -perhaps due to the use of a culty, due largely to the fact that the poor aerial -earth system -or when ELECTROLYTIC RECTIFIERS. r r' windings of up -to -date transformers high selectivity is necessary to "HOSE who work with aluminium are arranged so that a "balance" may eliminate a powerful near -by trans- JIl electrolytic rectifiers for H.T. easily be obtained, the less experi- mitter. supply are often troubled with exces- enced amateur should be warned that It may be added that there are com- sive corrosion of the aluminium elec- a " two -H.F:" set is a much more paratively rare occasions when a set trodes at the point where they enter ambitious project, and that the of almost unlimited sensitivity may the solution. This may be avoided chances of complete success are be used with advantage from the by making the aluminium electrodes remote unless a good tested design is point of view of long -range reception, of round rod and fitting them with a followed implicitly. even under the almost ideal condi- tight sleeving of rubber tubing where It is certain that an efficient single tions which sometimes obtain in they enter the solution. This rubber stage will give more satisfaction than country districts. Such circum- tubing should extend at least an inch two stages which are not working stances are likely to arise when the above and below the surface of the properly, and, moreover, under good waveband on which it is desired to solution.. When rubber tubing is thus receiving conditions, it is probable receive happens to be particularly used it is not practical to use a layer that one high- frequency amplifier free of interference and " mush " of oil as is sometimes suggested, as (always provided that it is effective) and when atmospherics are absent. oil ruins rubber after a short time.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 73 (a). -An A.C. High tension Battery Eliminator. (Concluded from last week's issue.) The present series of diagrams is intended to show progressively, and in an easily understandable manner, the various points to which special attention sh9uld be paid in the design of typical wireless instruments, and at the sane time to assist the beginner in mastering the art of reading circuit diagrams. The eliminator shown below uses half-wave rectification, and is probably the simplest arranfemen! likely to give satisfactory results.

C1 02 C3

_ ...._. = A.C. + 1 A.C. I A.C. i _- f + t2

(4) (5) (6)

The positive output connection is taken A smoothing choke is inserted in the A lower voltage ( +1) output is obtained by from the centre tap of the filament - positive output lead, and two large inserting a series resistance and another lighting winding. " reservoir " condensers are added. smoothing system. HE smoothing choke in the but, in the interests of economy, a The series resistance should have high -voltage output lead should capacity of as little as 2 mfds. may a current-carrying capacity of two or have an inductance of at least 3o he tried for C C2 and C3 should three milliamperes and a maximum A henries -preferably more -and an be of 4 or 5 mfds. value of about ioo,000 ohms. ample current -carrying capacity. The choke in series with the low - wire -wound resistor with some five or This latter will depend entirely on voltage output terminal (+ r) should ten tappings is suitable. It is im- the consumption of the set. Two be of high inductance. This ter- possible to give an even approximate chokes may be connected in series if minal will presumably feed the valves idea of the actual proportion of the necessary, and it should be remem- consuming only a small current, so total resistance required in circuit for bered that they should have a reason- a fairly large D.C. resistance and a a given voltage without knowing the ably low D.C. resistance. low saturation current value are per- current which will be consumed. It is hardly possible for the missible. An inductance value of too The tapping point is best determined smoothing condensers to be too large, henries is suggested. by trial and error. A 23

www.americanradiohistory.com 783 WÌp@R@go. WopIlcl JUNE 22nd, 1927.,

up,L witiul 4d' ;liiól; - ! : nniI gtlln .,1111ÌÌ11111i11111 am: 1,1.! niúvi nur.n : IIC :t--- .I{ïi ' CL1RREîTT TOPIC.J' Events of the Week in Brief Review.

SCHOOL WIRELESS. WIRELESS GEOGRAPHY. TELEVISION IN FRANCE. Over 3,000 schools now receive the " This station is in Moscow, now a part France has come into line with other B.B.C. nations lectures from London and of Poland . . . it manages to get across by duly producing her inventor Daventry. Of these schools 372 came on in good volume. " -Northern Echo. of television. He is M. Valensi, chief the register during the last term. And it seems to have taken Moscow with engineer of the French Post Office. M. 0000 it ! Valensi makes use of the cathode ray IN FRANCE, oo00 in his experiments. TOO! 000o Wireless amateurs in the south -west of RADIO SOCIETY OF GREAT BRITAIN. France are complaining bitterly of inter- " Fading in Radio " is the title of a NEW MARCONI OFFICE. ference to broadcast transmissions by the lecture to be delivered by Mr. H. A. P. A new Marconi telegram office has been opened Government high -power station at Croix - Littledale, F.R.Met.Soc., at this even- at 3, Charterhouse Street, Lon- d'Hins, near Bordeaux. ing's (Wednesday) meeting of the Radio don, E.C.I. 0000 Society of Great Britain at the Institution 0000 NEWS FROM ABERDEEN. EXIT THE of Electrical Engineers, Savoy Place, S.A. PIRATE 1 W.C.2. This meeting In South Africa, will be the last of Official figures show that an increasing which recently the present session. number of receiving licences are being appeared to hold the world's record in 0000 the matter taken out in Aberdeen. This proves that of trireless . " pirates," the ` ALL WELSH " STATION. wireless is not an expensive hobby. number of licensees is increasing. A resolution 0000 According asking for the erection of to the latest census, licences an " all Welsh " broadcasting station was RADIO AND THE AURORA BOREALIS. are held by 13.093 people. passed at the conference of the National The influence exerted on wireless recep- 0000 Union of Welsh Societies held recently tion by the aurma borealis has forme i SIGNALS AND THE ECLIPSE. at Oswestry. the subject of researches by the director A specially designed log sheet for registering signals received during the eclipse on June 29th has been issued by the Radio Association. Copies are obtainable from the hon. secretary, Mr. S. Land- man, M. A., 22 and 23, Laurence 'Pount- ney Lane, London, E.C.4. 0000 TRACKING A MOBILE TRANSMITTER. A direction- finding test with the object of plotting the route taken by a mobile transmitter is to be carried out on Sunday next, June 26th, by the Leeds Radio Society in conjunction with the Sheffield Society. The experiments will be conducted within it radius of ten miles from Penistone. 0000 NATIONAL BROADCASTING IN BELGIUM. .A national broadcasting company, State -owned to the extent of 60 per cent. of its capital, is the latest proposal in connection with Belgian broadcast ing. The scheme provides for a board consisting of eleven members, the chairman and five other members to be appointed by the Minister of Posts and Telegraphs and the remainder to be appointed by general meeting. The company would be granted authority to continue for ten years with AIRCRAFT RADIO BEACON INAUGURATED. Dr. G. Burgess, of the U.S. Bureau the right of extension for another five of Standards, with the wireless beacon which has been erected at College Park, Mary years. land, for the guidance of civil aircraft. This installation is the first of 40 to be erected at 200mile intervals on the American civil airways. A 24

www.americanradiohistory.com 1927: W$P@Il®00 JUNE 22nd, WoAd 789 of the Goodhaon wireless station, in 7.30 a.m. to 7.31 a.m. -61 rhythmic Greenland. He states that tests over a time signals. TRANSMITTERS' NOTES prolonged period have not revealed any Special transmissions of a similar nature AND QUERIES. increase or diminution in signal strength will also be made on the previous two which could be attributed to the days, June 27th and 28th, at 6.30 a.m. Transmitters in I.F.S. " northern lights." and 7 a.m. (B.S.T.). 0000 0000 Amateur transmitters in the Irish Free WHEN "BIG BEN" ERRS. LOOKING AHEAD. State are taking an active part among those engaged in experimental research Those who rely on the broadcasting of Commenting on the progress likely to on this side of the Atlantic. 'l'here are "Big Ben " for the correct setting of be made in wireless picture transmission, their household clocks may be interested Mr. David Sarnoff, now seventeen stations licensed and most of the Radio Cor- of these can be heard working nearly to learn that certain discrepancies in the poration of America, suggests that at the famous timepiece every evening on about 45 metres. Re- performances of some time in the future " newspapers " ports will be greatly appreciated. have been noticed by the Astronomer will be printed at home, each household 0000 Royal. In his report covering the year being equipped with a photo -radioscope. ended May 10th, 1927, the Astronomer 0000 Also in Jamaica. Royal reports that " Big Ben " was more WHAT THE COLONIES SAY. On the other hand, we understand that than three seconds fast on nine days, Colonial wireless papers, without excep- NJ 2PZ, the station operated by Mr. J. between two and three seconds fast on tion, are enthusiastic over the reception F. Grinan, Kingston, is the only one 122 days, between one and two seconds of short -wave programmes from PCJJ, licensed in Jamaica and that other calls fast on 164 days, and less than one second Eindhoven. purporting to originate from that island fast on two days. For a time the clock The South African Wireless Weekly should be regarded0000 with suspicion. was kept purposely about two seconds writes : We would heartily welcome -" American fast, as its chimes were used as a warn- an efficient short -wave station in Eng- Short -wave Tests. .The second 24 -hour test, on June 4th ing for the Greenwich broadcast time land. . . We can only once again ex- press hope soon something will to 5th, when the General Electric Com- signal' the that 2XAD were 0000 be done in England, which at the moment pany's stations 2XAF and ECLIPSE SIGNALS ON THE CONTINENT. seems to be only important transmitting continuously, has aroused the country interest. No opportunity is being lost on the without a short -wave station." considerable is to experiment during the Describing the reception of in Among the reports received one from Continent PCJJ Messrs. of Bir- eclipse on Wednesday next, June 29th. Australia, Western Wireless writes:- Stratton and Co., Ltd., At the time of going to press we learn " The strength and clarity of the repro- mingham, who send us a copy of the that the following stations will send test duction, though only gramophone records, actual log of signals taken with a two - valve 1815 on Satur- transmissions :- was remarkable." receiver from B.S.T. Parie. tole Supérieure. W.L. 458 day to 1812 B.S.T. on Sunday. Some -1 What a pity it isthat the B.B.C. " has trouble was experienced from atmo- metres. Transmits from 6.15-6.35 a.m. not been convinced that any of the pro- Madrid. -Union Radio (EAJ7). W.L. spherics from about 2200 to midnight on posals so far made are likely to be pro- Saturday and during Sunday afternoon. 373 metres. 6.10-6.35 a.m. : Dashes indi- ductive of that degree of efficiency which These appeared to affect 2XAF on 33.77 cating wavelength. would justify the expenditure involved." ljarrelona.- (EAJ1). 344 metres. 6 0000 metres more than 2XAD on 22.02 metres. Concert, " Serenata Española " WIRELESS AT THE R.A.F. DISPLAY. The results generally were consistent with a.m.: expectations, with the exception that fora (Albeniz), 3 minutes' duration ; "Mal- The R.A.F. display at Hendon on period of five minutes between 4.40 and lorca " ( Albeniz), 4 minutes' duration Saturday, July 2nd, will furnish abun- 4.50 the signals came in with unusual Rondalla Aragonesas " ( Granados), 5 " dant interest to wireless enthusiasts. strength and clearness. During the hours minutes' duration ; " La Gran Via," The most novel event will be time aerial (Chueca- Valverde), 10 minutes' of daylight time carrier wave from both selection drill to music, briefly referred to in our stations kept strong, but became very duration ; " from " Dolores" Jota," issue of Joie 15th. For obvious reasons sharp and the tuning critical. (Bruton), 8 minutes' duration. 6.30: the pilots would be unable to hear music 0000 English talk. 7: Close down. from the ground in the ordinary way. Madrid.-San Sebastian (EAJ8), 297 As these stations are now attracting The music will therefore be broadcast. considerable attention, it may be con- metres. 6A0-6.35 a.m.: Dashes indicat- A microphone slunig over the band posi- ing wavelength. venient to remind our readers that tion will pick up the music, whence it NU 2XAF transmits the Tuesday, Thurs- Merlin. -1,250 metres, 577 metres, 484 will be transferred by means of a land metres, and 215 metres. 6-9 a.m.: day. and Saturday evening programme of line to a central control room containing WGY on 32.77 metres, and NU 2XAD Musical and gramophone programme. powerful amplifying apparatus. There it Pittsburgh.- (KDKA). 309 and 62 the evening programme on Sunday, Mon- Will be amplified and broadcast from 24 day, Wednesday., and Friday on 22.02 metres. 4.35 a.m. : Revue from the loud- speakers erected so as to serve all Grand Theatre, Pittsburgh. metres every week. In addition, 2XAD public enclosures. At the same time a special programme from Schenectady, N. P.- ( \VGY). 379.5 transmits the land line will carry the music to a radio WGY every Tuesday from 4.0 to 5.0 p.m. metres. Programme relayed by 2XAF on telephony transmitting station, whence it 32.77 metres. 3.30 -4.30 a.m.: "Radio Eastern American Time (10.0 to 11.0 p.m. will be transmitted to the air. Spectators B.S.T.), and at 6A5 p.m. E.S.T. each Cavalcade." will, therefore, be able to follow changes The times mentioned are B.S.T. Saturday (12.45 a.m., Sunday, B.S.T.); the 0000 of manoeuvre consequent upon changes u omplete schedule for time ensuing week of tune. Iu addition, as tunes change, EIFFEL TOWER SIGNALS DURING is transmitted by IC\\' (Morse) from 2XAD ECLIPSE. the squadron leader in the air will give and by telephony from 2XAF. Special transmissions will be made by the words of command involved by 0000 the Eiffel Tower station in Paris under changes of fomation to his squadron by \Ve understand that reports received at the direction of the Bureau Inter- radiotelephony. His transmission will Schenectady from Europe and South nationale de l'Heure. Using the well - be received by receiving stations situated America indicate that the shorter wave. known call sign FL, the Eiffel Tower at remote points of the aerodrome and 22.02 metres, is more effective when it is will transmit on 2,650 metres, spark or time signals transferred by land lines to daylight at either the transmitting or re- interrupted C.W. The following is the the control room, where they will be ceiving end, but that when the whole schedule of transmissions, the times amplified and broadcast to the spectators area covered is in darkness the longer being B.S.T.: - by means of the loud- speaker system. wavelength proves better. 5.30 a.m. to 5.35 a.m. -306 rhythmic The installation of input and output 0000 time signals. circuits for wireless stations and the loud- QRAs Wanted. 6.30 a.m. to 6.35 a.m. -306 rhythmic speaker system involves the laying of HZA 1, EN ()DK. ER 5AA, EI 1DR. time signals. some twenty miles of buried cable, EAR 59, NT 8AF, EA MM. A 25

www.americanradiohistory.com 7:7fpcDsoo Wallca 11'.Vr. 22nd, 79:7.

E., . M...R_.MrM SI ,.g..,.....M

fipVCASPITTOTIFIU

Receiving Equipment for 250 Phones, with Semi= automatic Battery Maintenance.

By LEONARD A. SAYCE, 11.Sc., Ph.D.

CRITIC! of unit ersity " rags is ti (Apt 1.1 and not always undeserved, but netcr lia1 students a better excuse fia' their hih spirn- th:ut that which nt:ule them turn New cast l: upsi,le down in February. last ye.r. It all bean in the Union Refectory at a lunch -tine conversation concerning, wireless in h,spitals. \ \-hw sltrrald the Newcastle Rn:tl Victoria infirmary Ise behind the London hospitals. and why should not the students of the two Newcastle rolle;_e. (.1 the University of 1)u: ha m of the district, and the placing bn,xcs organise an Appeal:' Surely Nt e'tle was wealthy of collecting in many w'f the shuts. enough to equip its own infirmary' (These were days 'rhos the people of Newcastle were well before the Coal Stoppage !I And so a committee got to acquainted twidi the students objects when work tu put into practice their slogan " Radio for the the rag took pace :it the end of the week. Women Royal' " This slogan, by the twat. tuas the outcome of students in academic dress were " on duty " with collecting -boxes in all a competition, the prize for which was two tickets for a the college dance. principal streets of the city throughout the day, whilst the men students, in fancy costumes which were anything but academic, held How the Funds were Collected. a mock coronation of " King Radio," after which they dispersed to empty the pockets of the Twelve hundred pounds was the estimated requirement. Novorastrians. How successful they were may le and. inexperienced as were the students in the annual judged from the fact that they collected over nine- charity " rags which are su StICCU,s -IulIy e.irrird oat in pounds in this one days effort, bringing the total Glasgow and Manchester. it appeared a difficult enongl for the whole Appeal t'n over sixteen hundred pounds. task. An " Appeal \ \'eck was set aside. and Ncwa- It fell to the lot of the present writer to design tle castle was prepared for this special effort by rneans of installation and supervise its erection. and with the ample circulars and I'rcs; notices. The activ itir . i t the week. funds available the task has been a pleasant one. which were to culminate in a " ua_ " on the Saturday. In the library of Newcastle Infirmary, a large room included a broadcast appeal. a daily l,roression in the beautifully panelled in unpolished oak, was a handsome main strec is of Newcastle of students wearing sandww ich- fireplace which had never been used as such, for the room boards and heralded by a drum -and pipe band. an appeal was centrally heated by hot-water pipes. So the fire- 1,w means of printed dips to patrons of city restaurants. place became the home of the radio installation. and the the exhibition of special lantern slides in local kinemato- illustration in the title of this article shows how com- f,ralrü theatres, a rullrrtion in the workshops and factories plete has been the transformation. The radio panel, A 2'

www.americanradiohistory.com JUNE 22nd, 7927. WfipsIlsoo 791 Wow lico1 Wireless Installatfon at the Newcastle Infirmary. - filled with " Sorbo " rubber soaked in oil. A metal at the right -hand side of the upper ebonite panel, is a cup, F, 1R in. in diameter, lined with carbon and half full straightforward two -valve set employing high -frequency of very fine carbon granules, is held near to the dia- and detector valves. The aerial circuit is loose -coupled phragm by means of the insulated steel bar, G, and a to the grid circuit of the high- frequency valve, which, in ring of soft felt, H, prevents the leakage of granules turn, is coupled to the detector input by the well -known and further assists in damping the diaphragm. The " tuned anode " method. The circuit is shown in detail sound -waves are thus received only by a small annulus. in Fig. r. Stability rather than efficiency is required, so In spite of its small dimensions this microphone is most the grid circuit of the first valve is stabilised by means responsive. It requires only one stage of amplification to of a " damping resistance " of high value, as shown. deliver normal " phone strength," and it is remarkable The microphone amplifier panel at the left -hand side of the upper ebonite panel contains a one -valve amplifier MIC. o fed from microphones situated either in the Infirmary INPUT chapel or the library itself. The circuit of this panel o is shown in Fig. 2. These microphones are as used in COM- the Marconiphone Public Address system, and are so and a brief description may be of 2 V.+ simple effective that Su.h.l a granule interest. Experience has shown that carbon MIC GRID 6V++ BIAS

MO. 0675-00 TUNED 0 ANODE MIC. COIL TEST o GRID 6 TES T MIC 'AERIALO- Fig. 2.- Circuit of microphone amplifier panel. EARTH

COM for.its excellent pick -up. It is shown in its shock-absorb- ó ing mount standing on the top of the instrument cabinet. zr 6V J O O The Main Amplifier. IC7 U WO W The output either of the radio panel or of the microphone panel is taken via the "control panel " situated RECaI H T. between them to the lower amplifying panel. This is the main amplifier, and it provides two transformer - frequency amplification, the first o coupled stages of low- PHONES by one D.E.5 valve and the second by eight D.E.5A valves, whose grids and filaments are all in parallel. (0414: / \ Each of these " second -stage " valves can deal comfort- I o o ably with at least 25o pairs of 4,000 -ohm telephones connected in parallel and fed from its output through a AERIAL ANODE step -down transformer. Each of these valves is provided with a milliammeter in its anode circuit as a check on distortion and grid bias. It is controlled by an " on and o off ". switch and a variable graphite resistance across the COUPLING REACTION DAMPING as a volume RESISTANCE secondary of its output transformer to act " control." There is also a pair of telephone plugs across each output circuit, so that an operator " tuning in " may 1.-Circuit diagram of receiver unit. microphone of the ordinary type can be made suitable for the faithful transmission of speech and music by two important modifications : (r) by damping the diaphragm very heavily, and (2) by the use of very fine granules. Both these objects are fulfilled by the microphone in question in the manner shown in Fig. 3. The body of the microphone consists of a piece of steel tube, A, of 2in. external diameter and Ihin. internal diameter and gin. long. At one end of this a thin gilt diaphragm, B, is securely stretched by means of the ring, C, and the nuts, D. To the other end of the tube is fixed a steel disc, E, and the little box so formed is Fig. 3.- Section of carbon granule microphone. A 27

www.americanradiohistory.com 477 . ti , - Who@lisoo 792 opill JUNE 22nd, 1927.. Wireless Installation at the Newcastle Infirmary. - The many miles of lead -covered wire needed to distri- hear exactly what is going to the wards. The circuit bute the output of the amplifier to the bedsides of the diagram of this amplifier -Fig. 4 -has been simplified patients run, as far as possible, upon the external Avails by the inclusion of only one of the second -stage valves of the buildings. Nothing of the installation is to he and its associated meter, switch, etc. seen inside the wards but the telephones themselves and The control panel, already mentioned, can be recog- a neat Bakelite fitting upon every alternate window- frame. nised in the title photograph by its two volt -meters for Each ward is provided with a two -way switch which, when .checking H.T. and filament voltages. Its circuit is in the " off " position, puts a " dummy load " upon the shown in Fig. 5. Below the voltmeter dials are two switches, one on the right marked " Radio -Microphone," for connecting the amplifier input to the output of radio +2V +60V. MIC. 2 MIC 3 o o 0 set or microphone respectively. The other switch, on the COM - +6V GRID leí't, is for switching the microphone +120V OUTPUT amplifier input to MIC. O- any one of the three microphones. Below these two INPUT switches again are two variable resistances acting as " volume controls " to the outputs of microphone ampli- COM. fier and radio set respectively. 2V

6v GRID 120V 6V. COM. GRID 2 INPUT + + 6 7 8 O o o p O O o o O MO 2 3 3 4 4 5 5 6 7 8 O O O O C TEST MIo C.

GRID

COMMON GRID COMMON -

FILAMENT VOLTS

+120 V TEST COMMON PHONES Fig. 5.- Control panel connections for checking volume and H.T. s and L.T. voltages. amplifier equal to that of the telephones themselves. in this way the signal strength in the other wards on the same circuit is left unaffected. The telephones were selected with great care, for pre- z vious experience of hospital installations had shown the o writer that the roughest and most inconsiderate treatment must be expected in such institutions. The following mA requirements were therefore laid down as essential r. They must have no external nuts. Fig. 4.- Circuit diagram of main amplifier. 2. They must have no adjusting screws or external screws of any kind that could be loosened without The cabinet containing all the above gear is supported the aid of a screwdriver. on concealed castors, and when pulled out of its normal 3. The head -bands must have no leather or fabric position discloses the original " fireplace." This is now coverings (for hygienic reasons). a veritable telephone exchange, for all the input, output, 4. The ear -caps must he able to withstand frequent and battery wiring is concealed in this space, and even falls upon the hard floors. the aerial lead -in comes down the chimney ! Thus to 5. The flexible connecting cords must be provided with external appearance, at least, the installation is truly " tension tags " to relieve the electrical connec- " wireless." tions from all mechanical stress. A 28

www.americanradiohistory.com NYE 227ld, 1927. 7Ap®Ilsm ViopIlcal 793

Wireless Installation at the Newcastle Infirmary.- I20 -volt and 6 -volt accumulators respectively. At a given 6. The stirrups, swivels, and headbands niu-t Le very time each Clay these are connected to the instruments robust and not be likely to work loose. by mean; of a time -switch and contactor. At the end These conditions, necessary as they undoubtedly were of the day's programme the time -switch again operates for the installation under discussion, were satisfied lx and the instruments are switched off. In falling to the scarcely any of the mane types of headphones upon tl:e t' oft position the discharge contactor starts up a motor market. In fact, manufacturers have been slow to de- generator %%hick commences to recharge both high ami velop telephones really suitable for use in public institr.- low tension batteries. But during the discharge period tions. They do not seem to realise the amount of misuse the filament current was taken through an ampere -hour which mist be borne by t teir productions at the hands (.f meter, commencing at zero. The charging current also people v hat' not themselves paid for them : Nor í14I passes through this meter, but in the reverse direction. '1'hus, when the peter has got back to zero. a contact is made inside the meter, the " charge contactor is re- leased. and the motor -generator switched off. If this were all. the batteries would receive exactly the same amount of energy as they supplied on discharge, and. seeing that their efficiency is not too per cent.. they would run down in the course of tinte. The meter contacts are so arranged, however, that a small overcharge is given automatically. Batterycharging Plant. The batteries and their charging anti control equipment are contained in a large cupboard in the basementment of the infirmary immediately under the instruments which they operate. 'The cupboard is divided intu two compartments by a vertical partition. The right -hand compartment contains the batteries anti is painted with anti -sulphuric enamel ami provided with Venti- lation holes. The left -hand compartment contains the charging anti switching gear, trhich was made to order by Messrs. lgranic Co., of Bedford. The two contactors are at the top of the slate panel. Beneath them are centre -zero charge -discharge meters for the two batteries. lower still are the special meter and the time switch, whilst the nintor- generator is screwed to the floor. The two wheel -like controls in the middle of the panel are for the purpose of controlling the respective charging rates of the two batteries. The foregoing de.scriptinn of this installation lias been given in the hope that it may be of some assistance to these who may be responsible for future hospital installations. The benefits of " wireless " for invalids is so great that radio facilities will soon be regarded as an essential part of the equipment of a hospital. Fig. 6.- Switchboard of automatic battery -charging plant. in conclusion. i shntlltl like to pay tribute to the excellent workmanship of Messrs. \farconiphone Co.. Ltd.. they realise that 90 per cent. of the maintenance charges who were the contractors to the installation. of a hospital installation is in telephone repairs. The makers of the " ('laritnne " headphones, however, hare in the opinion of the writer, ciune nearest to the ideal, Next Week.- and their telephones have been used throughout the SPECIAL SHORT -WAVE ISSUE. installation. An Article on HOW TO BUILD A 45 -METRE TRANSMITTER. Inexpensive and easily constructed for key or telephony transmission. A further requirement of a hospital installation is tint Can t'e operated from dry cells on small input, giving a world-wide it should require a minimum of skilled attention, for it Morse signalling range. Constructional Details for Building a SHORT-WAVE RECEIVER, must be remembered that to many hundreds of people it covering a wave -hand of 20 to ro metres. Mane novel fcatnres for the reception of short -wave broadcasting is their only relief from monotony and suffering, and reli- are included. Suitable 2XAP, :XAD, KDK.\, l'CJ 1 (Eindhoven). and long -distance ability must have first consideration. For this reason the amateur transmissions. HOW TO BUILD AND CALIBRATE A WAVEMETER (ia Newcastle Infirmary installation lias 1icen made entire -y bt 2.0 metres). This wavemeter is of simple design, and a working calibration can be obtained without comparison with a automatic. anti. except ft,r the use of the microphone ar(i standard. It can be used for tuning both transmitter and receiver. the occasional 't topping up " of the batteries, the on.y The sets described have been developed over a long period to meet the clock special requirements of the short -wave enthusiast and embody well-tried attention it requires is the winding of a once a practice. month. High and low tension current is supplied by

A 29

www.americanradiohistory.com 311°; -we`!K9`6 ..,. _ -, ' Vfllp@hoo 791 Wor JUNE 22nd, 7927. xperimenfer:s - ofebookJ

The Causes of " Howling." By "EMPIRICIST."

T is a vexed question yhether a wireless set possibly be dealt with in any detail in the present which refuses to utter a sound or one 1 article. The oldest method consists of applying which refuses to remain silent has the damping in sonic shape or form to the aerial cir- most shattering effect on the morale of the operator. cuit. usually by means of a potentiometer controlling Possibly silence is more easily explained away than the flow of grid current. A far more satisfactory way. shrieks, should the necessity for explanation exist; is to employ one of the many circuit arrangements in ` silence is golden," it has been said, but certain noises which the capacitative coupling due to the valves is neutral- produced by receivers can only be described as brazen. ised. More recently again we have the various methods In considering the causes of " howling," which is the developed in America for stabilising receivers, of which purpose of the present. article, we must give careful the Loftin -White circuit is a good example. thought to the different kinds of oscillation which can If one of the above .methods of controlling oscilla- be produced ; these are many and various, and are all too tion is embodied in the receiver there is still plenty of frequently confused Nyith each other. opportunity for snags in carrying it out. Only Let us take first the most generally familiar case, two tips can be given here : first, look after the high - namely, that of a pure continuous wave oscillation on frequency component of current flowing in the detector the wavelength to which the receiver is tuned. This is, valve circuit and see that it is led in the right direction, of course, the most anti -social form of oscillation, and e.g., by a by -pass condenser from plate to filament ; and, one which is very rightly condemned in all quarters, in- secondly, do not forget the by -pass condenser across H.T. asmuch as it affects not only the user of the receiver, but batteries. Apart from these considerations, the factors also his neighbours for a considerable distance. A dealt with in a previous article on the layout of the set receiver in a state of oscillation will give no evidence of should be borne in mind. its condition unless it is tuned in to a wavelength closely A second form of " howling," which is essentially due corresponding to that of a signal, when the characteristic to the high -frequency circuits, is fairly often met with. heterodyne note will he heard over a certain range of the tuning condenser. 'A number of points on the dial will give such notes corresponding to various broadcasting stations, but in general no audible effect will he produced except by the aid of external signals. Uncontrollable Reaction. The causes of oscillation of this kitid depend on the type of circuit which is being employed. If a valve detector without a high -frequency stage is used, there should, of course, not be the slightest difficulty in controlling oscillation, though on occasions a highly efficient valve used in conjunction with too large a reaction coil may be impossible to stabilise. The golden rule is always to use the smallest value of reaction coil that will Fig. t.- Howling was experienced in a circuit of this type and still persisted when the H.F. valve V, was switched off. give the desired effect ; such a course not only makes the set absolutely certain as regards oscillation, hut also The symptom in this case consists of a squeaky note, the largely negatives the necessity for retuning the receiver pitch of which is constant over a fairly considerable range after an adjustment of the reaction coil. of the tuning condensers, or, when there is more than In the case of circuits embodying stages of high -fre- one high -frequency circuit, on bringing the latter into tune quency amplification Ave are on more difficult ground. with one another. The effect is traceable to the high - Sets of this type have a general tendency towards oscil- frequency circuit by short- circuiting any tuning con- lation when the aerial and high -frequency circuits are denser ; if the howl stops under these circumstances it brought into tune with each other. The cures for self - must he due to high- frequency effects. o. cillation of this kind are many in number and cannot Two main causes of this form of howling are well A 30

www.americanradiohistory.com ;JUNE 227fd, 7927. Wfip@hoo G`opIl 795

The Experimenter's Notebook. - anode was connected to L.T. - , instead of to its normal known; first, the excessive use of reaction (or a state of H.T. tapping, the howl at once ceased. The H.F. excessive accidental regeneration) when one of the circuits valve, it should be mentioned, was removed for both of has a grid condenser and leak ; and, secondly, the modu- these tests, so that the circuits were essentially as in Figs. lation of the high- frequency currents by oscillations pro- r and 2 respectively. duced in the low- frequency amplifier. The trouble was thus traceable to the transfer of the Howls of the first type are simply due to exces- alternating voltage set up in the H.T. battery back on to sive instability and yield to the treatment outlined for the grid of the detector valve, and in this particular case the first class of oscillation. Howls of the second it was cured by a choke -capacity output unit connected as type open up larger questions. In reflex circuits they in Fig. 3, the bulk of the alternating current being are very commonly encountered, and are not infrequently diverted through the loud- speaker to the filament, and due to the use of a valve for double magnification pur- thereby not giving rise to any appreciable alternating poses which has an insufficiently straight characteristic. voltage in the H.T. battery. However, it is worth noting Another cause of this trouble is interaction between the that this defect exists in a tuned -anode circuit, and it is high- frequency and low- frequency circuits through the as well to consider the great advantage in this respect medium of the H.T. battery or through a leakage path offered by a high- frequency transformer. of some kind to the receiver. It may be mentioned, in passing, that by -pass condensers across the high -tension are of amazingly littte use in curing a howl of this character when there is a serious resistance in the H.T. battery. The choke -capacity output device seems to offer a far more fundamental and satisfactory way of safeguarding a receiver in this respect. " Motor -biking." A fourth class of oscillation which may be considered for the sake of completeness as a howl consists of a pulsating effect not unlike the sound of a motor bicycle. The writer. in fact, fell into the habit of talking about this effect as " motor- biking " as long ago as 1923, and it is of interest to note that the term " motor- boating " Fig. 2. -By connecting the tuned anode circuit to L.T. -with the H.F. valve switched off the howling produced in the circuit in is now in common use in American radio journals to Fig. i was cured. describe the same symptoms. The third class of oscillation with which it is proposed The trouble is always due to H.T. battery impedance. to deal is that which consists of a persistent note, which and was first encountered when using a resistance shunted does not alter in pitch when the high -frequency circuits by a condenser in the H.T. circuit of an amplifier to are adjusted, and which persists when the tuning con- produce " automatic " grid bias. A reversal of one of densers are shorted out. This is due to low- frequency the L.F. transformers in the amplifier cured the trouble regeneration pure and simple, the most common form of which originates from a grid lead of excessive length connected to the detector valve. Any unnecessary length of lead or complication in the wiring of the low- frequency circuits is apt to lead to trouble of this kind, and it is well worth while, in laying out the low- frequency amplifier, to pay careful attention to the points raised in a previous article. There is, however, a totally distinct cause of audio -frequency oscillation which must not be forgotten, namely, that due to impedance in the H.T. battery, which gives rise to a transfer of voltage from the output to some point in the input of the receiver. A good test in order to check whether the trouble is due to the latter cause is to take a condenser bank of Fig. 3.- Howling may frequently be cured by the use of a choke - capacity output circuit as the choke prevents the flow of A.C. considerable size, say, 4 to 6 mfds., and apply it across from the last valve through the H.T. battery. the various H.T. tappings in turn. The oscillation may not be cured by this means, but a change in its fre- at the expense of a certain amount of audio- frequency quency will infallibly indicate that the trouble is due to distortion, and ultimately grid bias batteries were resorted impedance of some kind in the H.T. battery. to as being safer. The writer came across a most unexpected trouble of " Motor- biking " is also extensively found in ampli- this kind in the case of a set which had a stage of fiers that are supplied from mains units, hut as this is tuned -anode amplification followed by two I.. F. stages. the subject of an article by Mr. H. L. Kirke _appearing The 'set howled persistently with the circuits in 'heir in this issue it would be superfluous to go further into normal state, but when the return path of the tuned the matter. A 31

www.americanradiohistory.com Wf6Ilisto 796 JUNE 22114, 1927. WoreM The Experimenter's Notebook.- be identified by the loud noise produced on tapping it The last form of howling that has to be considered with the finger. is that due to the impact of sound wages on one of the A curious case of microphonic howling is sonietimes valves Of the receiver. 'hile nature of the howl is experienced in the case of receivers, e.g., of the super - usually quite apparent from the outset, inasmuch as it sonic type, which give a great deal of high- frequency builds up very slowly from a faint noise to a consider- amplification. In this case a horns clearly micro - able volume, can be made to vary in intensity, and phonic in character is sometimes produced on tuning -in may even be completely extinguished by moving the loud- a very strong carrier wave. As a rule, such howling only speaker about the room or pointing it in different direc- occurs when the station is being received at such strength tions. as to cause serious saturation of the detector valve, so The cure for howling of this type is the employ- that when the volume is reduced to manageable propor- ment of a proper shock -absorbing mounting for the de- tions the effect disappears. The use of a shock- absorb- tector valve of the set, and maybe for other valves as ing. valve- holder is, however, indicated in such cases, well. The valve which is giving the trouble can usually particularly on the first detector of a supersonic receiver.

Making the Most of Summer. accumulators, including those of the type The present summer is proving a. used on submarines. " bumper " season for field days and Hon. Secretary : AIr. Gerald S. Sessions, other outdoor activities. No doubt NZWS FROM 20, Grasmere Ruud, Aluswell Hill, N.10. favourable weather conditions are partly 0000 responsible; at the same time there are THE CLU3So An Active Society. undoubted indications that the clubs are The Thornton Heath Radio Society, recognising the value of maintaining en- r which holds its meetings every Tuesday thusiasm among members during the evening throughout the year at 8 o'clock misnamed " slack " season by means of FORTHCOMING EVENTS. at St. Paul's Hall, Norfolk Road, Thorn- well- organised field days. WEDNESDAY, JUNE 22nd. ton Heath, has ;('ranged a number of Radio Societ, of (Inn( Britnix.-- órdinurg summer events of special A 0 0 0 0 I11105. :I( 6 p.r,r. leur at 5.301. At interest. de- the Luit ueion of 1Slrct ricut lirutinerr5, monstration by \lr. Atkinson of the vari- Portables in the Field. SSrou Ylan., ti.5 2, Lecture: "Fading ous kinds of valves on the club's set on )lndi o 5r pnr,1 'Pith other Not oral In view of the programme of direction p'nl), now, lot,- by Mr. If :I. P. Lit (h- June 28th will be followed on July 12t1í finding d l,. F.11.Ilrt..ti'c. by a demonstration for beginners in the to be carried out on the field day North. 11 iddi .er ll' ìraless Club.- Lecture: of the North Middlesex Wireless Club Elect rolylie Rrehiliers,' by 11r. a. .1. efficient use of grid bias and reaction. next month, the last meeting of the club paon. Features of the society's meetings are Tottenham Wire?,,,,) Society. -At 8 p.m. was partly devoted to the examination of :It 10, Bien 6'ro.e. ,Lecture: " Work the elementary evenings and open discus- 05 Short 14ur¢s," a 4- electrode valve portable set, con - by 11r. S. F. Smith. sion nights. The society has an energetic SUNDAY, JUNE 26th. experimental section, and every endeavour structed by Mr. W. Gartland. The com- Tot tcnha IS. fl- irrless Soci, t Dug/. is made to cater for all radio enthusiasts. plete receiver (2- valve) weighed only TUESDAY, JUNE 28th. 12 lb., and was contained in an ordinary Thorntno Phut lr 115)115 Society.-.1t 8 Enquiries as to membership are cordially attaché case socket for 11.5). :It ,S't. l'ans', HnA. Norfolk !loud. invited by the Hon. Secretary, Mr. with 'phone plugs U,rnnS st rut iota for Beginner',, bu Mr. and tuning control on the outside. Tile ll'el,tend. C. H. Piper, 77, 'Porridge Roars, 'Thornton removal of the 'phone plug automatically Hen t11, Surrey. cut off the L.T. battery. It is hoped to have a number of portable direction finders in the field on July 9th. A large receiver which was not giving the results expected of it was exhibited by sIr. G-. L. F. Martin, and in the search to discover the trouble members obtained more information than would have been gleaned if the set had been working perfectly. While the selectivity of the instrument was beyond reproach, it was found that the L.F. side was inefficient, distortion and overloading being noticeable. After careful experinielt and adjustment the set functioned satisfactorily. Hon. Secretary : Mr. H. A. Green, 100, Pellatt Grove, Wood Green, N.22.

Advice on Accumulators. A large number of accumulators and components was on view at the last meet - ing of the AIuswell Hill and District Radio Society on .Iuue 8th, when Aft.. W. Schofield (of Messrs. Hart Accumulator Co., Ltd.) lectured on " Electric Accu- mulators." Many valuable hints were given on the choice of an accumulator and especially its maintenance, G. 5DC, owned and operated by Mr. W. T. Aked at Victoria Road, Thornton -le- Fylde. while .special The transmitter has a tuned grid circuit with grid modulation. Telephony tests from interest was slmwn in the construction of this station have been heard in Brazil. A 32

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WAp®Il200 JUNE 22nd, 1927. Worllt 797

A Review of the Latest Products of the Manufacturers.

AN L.T. ELIMINATOR FOR through a smoothing circuit, the leading speaker this new production is unlike the loud- A.C. MANS. feature of which is a large -capacity elec- other commercial models, as trolytic condenser. It is necessary only speaker stands vertically instead of being Hitherto it has been a perfectly simple to dissolve the salts supplied by the turned to produce a horizontal cabinet, matter to purchase or build a reliable manufacturers in warns water and to which is the common practice. H.T. battery eliminator for A.C. mains pour this into the condenser to render the The specimen examined was built which, when connected to almost any eliminator ready for use. The instru- throughout of mahogany. and measured receiver, lias proved a more than satis- ment requires no other attention than 16 in. high x10 in. wide x7 in. deep, and the " topping up " of enclosed a properly supported papier- the electrolyte with mâché horn. The grill was of particu- water at prolonged in- larly open design, and had a pale blue tervals to compensate covering resembling silk. for evaporation. The The cabinet is a specimen of high -grade rectifying valve has a work, is well finished, and can be normal life of 1,C00 recommended where a loud-speaker is re- hours and is renewable quired io harmonise with other furnish- at a cost of 12s. ód. ings. It might be mentioned that, mangy: The eliminator is of the cabinet loud -speakers at preset suitable for use with either 2, 4 or 6 volt valves, and has been tested by us with various types of set, perfectly satisfactory results having been obtained, the background b e i n g quite silent in every rase, irrespective of whether the II.T. supply was delivered from an H.T. eliminator or from batteries. In one case the instrument was used for 24 hours constantly without ill effect. If desired the instrument may be used for the charging of L.T. bat- Longton L.T. battery eliminator for use on A.C. supply. teries, and was satisfactorily tested for this purpose. The charging rate of a 6- for any type of battery, volt battery is about 1.2 amperes or a factory substitute 2 -volt batte 1.5 but it has not been possible to do the y amperes. same in the case of the L.T. battery, and 0000 be either to the resort has had to had LOUD- SPEAKER CABINET. use of special valves or to a trickle charge. Many amateurs prefer to construct a Messrs. Longton, Ltd., of Guildford, loud- speaker by fitting a loud- speaker Surrey, have now made it possible, how- movement to a horn either of home con- ever, to dispense entirely with the use of struction or one of the special papier- the L.T. battery if A.C. mains are avail- miiché types for which they may have a able and no special valves or circuit preference. Loud -speakers constructed arrangements are called for. The device in this way, although being sensitive and consists essentially of a transformer producing good results, are usually of The new loud- speaker cabinet of W. & T. which. in conjunction with an arc somewhat ugly appearance. Lock. It Is fitted with an enclosed papier- rectifying valve, produces a rectified cur- Messrs. W. and T. Lock, 15, St. màcbé loud -speaker horn. rent which is more than adequate to Peter's Terrace, Bath, well known as supply the L.T. current for a large manufacturers of wireless cabinets, have on the market are fitted with an encl ,sed set using modern dull- emitter recently introduced a cabinet containing horn, as this form of loud- speaker is multi -valve dia- valves of the 0.1 amp. type and a 0.25 a loud- speaker horn so that a good loud- usually more sensitive than the amp. super -power valve in the output speaker is produced merely by fitting a phragm type anti is suitable for opera- stage. This rectified current is passed movement. As a cabinet type loud- tion on small input.

A 33

www.americanradiohistory.com 3'r "Trk..")'-'1[illá$.N1ik.,4.,{^y1'...'' Wp®llisoo 798 JUNE 22nd, 1927. Wopllcl

1 NEWS FROM ALL QUARTERS.

By Our Special Correspondent. A Running Commentary Triumph. -Keston's Lost Opportunity. -Sir Henry Wood's Debut. Oscillation : A New Move. -De Groot Again? - Best Commentary of the Year. excited comments of the crowd could lhe best running commentary I have FUTURE FEATURES. often be distinguished. yet listened to carne over the Atlantic on London. 0000 Monday of last week in the afternoon JUNE 26TH. -Military Band Pro- Keston's Lost Opportunity. and evening, when 2XAD, on 22.02 gramme. Service S.B. from The broadcast was a memorable one. metres, broadcast the arrival of Colonel Liverpool. It raised this question : Were the B.B.C. Lindbergh in New York. JUNE 27TH. - Murray Ashford's engineers listening? If only the B.B.C. had been listening ! Concert Party, relayed from 0000 (Keston, by the way, might have Fe] ixstowe. Query. attempted to relay this truly remarkable JUNE 28TH. The Belle of New broadcast.) -" \V-ho was the wireless official who 0000 York," a musical comedy by decided to appraise the qualities of the Hugh Morton. female staff at Savoy Hill in terms of Many " Points." JUNE 29TH.- Harrow Speech Day. " Mi]livamps "? No effort had been spared to give the Variety Programme and 0000 American listener a complete bird's -eye Chamber Music. A Delysia Item. view of the progress of Lindbergh's car JULY 1sT.- Dominion Day Pro. Miss Alice Delysia is to broadcast from from the time he landed until arriving in gramme. 2I.0 on July 1. Central Park to receive the official wel- JULY 2ND. -Military Band and 0000 come from the Governor of New York Variety Programme. To- night's Programme. State. Indeed, it is doubtful whether a Birmingham. A " Musical Man -in- the -Street " will bird could have seen as much in the time, JUNE 26TH. --Light Symphony Con- provide the items for another of the " My fer the description came through from a cert. Programmes " series to be broadcast from dozen or more " points," the microphones JULY 2ND.- Popular Orchestral and 2I.0 this evening (Wednesday). It. takes being changed over with a swiftness Vocal Programme. the place of the " My Programme " which which was almost bewildering. 0000 Bournemouth. it was expected Mr. Arnold Bennett would arrange for this date. Lindbergh's " Business Suit." JUNE 27TH. - Instrumental and 0000 Vocal Programme. At about 8 p.m. (B.S.T.) the announcer I\lodern Saturday's Variety. was JULY 1ST.- Concert of heard describing the scene at the British Compósers. A variety programme will be given on War Memorial, with its " Eternal Saturday next by Sydney Fairbrot her `. Flame," where Lindbergh placed a Cardiff. JULY 2ND.- Orchestral Programme (Cockney humour), Barney O'Reilly (Irish wreath. " Colonel Lindbergh is wear- ballads), Harold Harvey (syncopated ing his business suit," said the relayed from Weston -super Mare. songs with guitar and ukulele accompani- announcer, leaving the listener to con- ment), Ann Penn (impersonations), and jecture what type of garment that might Manchester. JUNE 27TH.- Sonatas and Charles Heslop and Cyril Smith (enter- be. Then the listener heard the impres- Spanish tainers). sions of an announcer on the 27th floor Songs. 0000 of the Metropolitan Building as the pro- JUNE 29TH. -" Eclipse." a topical Safety First. sketch by J. L. Hodson. cession passed and proceeded by the new 'l'he adoption by the British Broadcast- building of the National Broadcasting Newcastle. ing Corporation of kilocycles instead of Company up Fifth Avenue. It was also JUNE 27TH. -Choral Singing and wavelengths elicits a timely warning from stated that the crowd lining the street 'Cello Solos. " Vigilant." was twenty -five deep, that the streets JULY 1ST.- Orchestral Concert re- " Remember," he says -" remember the were impassable, and layed from Whitby, and a play. that showers of therm ! " -" Beachcomber," The TJrrilf confetti and streamers were falling from Glasgow. Expre ,a. all the surrounding buildings. JUNE 26TH. -List rumental and 0000 0000 Vocal Concert. Sir Henry Wood. In Central Park. Aberdeen. It has now been decided, as hinted Governor Smith's speech of congratu- JUNE 27TH. Variety Programme in The TV-ir,less World last week, that lation on the platform in Central Park and two plays. Sir Henry Wood's broadcast debut will was heard clearly, but unfortunately the Belfast. lie postponed until August 13tlí, when saute can hardly be said of Lindbergh's JUNE 27TH. -Military Band Pro- he will conduct the first of the " Proems." reply, which came through badly. 'This gramme and a play. This will be a much more auspicious be- may have been due to fading or to the JUNE 2911-I. -Orchestral Programme. ginning than if the fanions musician fact that the microphone was badly " Black Out," a Telescopic Re- opened his broadcasting career by con - placed. view. ducting the Wagner programme on June )'During the address of welcome the 30th in the studio. A 34

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VRp@Esto Jl'.VE 22nd, 1927. WUlad 799 Curbing the Conductor. New Pill for the Oscillator. In the caseof de Groot, as in the case who engaged in . in Tormented br a local oscillator, a friend of other celebrities have It is fortunate that most conductors " hotel broadcasts," the B.B.C. negotiates the studio are unaware of the restrictions of mine recently wrote to the B.B.C. for comfort and consolation. In reply he only with the hotel proprietors. not with that surround them. Most conductors the individual artists. In the rase of goes out from received a questionnaire which the Cor- imagine that the music de Groot the question of his return to the 2L0's aerial just as played. Sometimes poration has prepared with the object of getting at the facts systematically, and microphone has been raised by the Picca- it does. But if the conductor has an idea dilly Hotel, and although nothing has concerning the rendering of a piece differ - with a minimum of irrelevant detail. These interrogatory forms, which contain materialised, there is a strong probability ing from that of the composer, the odds that the famous Dutch conductor and his are that the composer's idea will be more five important questions, are to be issued send in complaints of orchestra may broadcast again. faithfully represented in the music broad- to all listeners who 0000 cast. oscillation. cono 00o0 Russian Exiles in Chiswick. The Questionna`re. A programme by Russian exiles is to be Controlling by the Score. The questions are as follow relayed from their English hoine at This is one of the mysteries of I. Is your set a valve or crystal ? Chiswick on Saturday next, June 25. " control," the department at 2L0 which 2. Does the distortion take the form of Besides M. Vladimir Polunin, the scene is now presided over by the erstwhile (a) howling, (b) sudden variation in signal painter to the Diaghileff Russian ballet, B.B.C. Director of Music. Mr. Stanton strength, or (c) complete ces "sal ion of who has taken a leading part in organising Jeffries. signals? the show. those who will assist in the (a) if the howling is continuous . The official in charge of control during If state programme are DIme. Edezi, _lime. Marie or a symphpnnv concert is furnished with a for periods of ten minutes at a time Rabinek, M. \icholi Rabinek, M. Ivan c ipy of nl, score. It is by this that the loger. If (b) is the variation or cessa- Ivautich Barnett. Dame. Rabinovitch. Mme. Ustinov, Mme. Duska Benois. 112. t'ürlo Norway, W. H. Stanton, and M. Strachovsky, The ronpèrrs will be A. P. Herbert and L. de G. Sieveking, who will make their announcements in English. 0000 Kilocycles. The decision of the B.B.C. to talk in kiluryrles instead of wavelengths provokes the comment which so often hovered on the lips of Victorian maidens : " Oh, George, this is so sudden ! " If the decision had been taken last autumn, when the British public was in the mood to grasp the Geneva scheme, with its dependence upon kilocycle calcu- lations, it would have been more compre- hensible. Coining at the present moment, the decision tempts one to think that an effort is being made to keep our minds occupied on any matter other than short -wave Empire broadcasting.0o00 The British Stations. recalled The following is a list of the British LONG BEFORE BROADCASTING. The early days of wireless are being and kilo- by the Volta Centenary Exhibition. now being held at Como. The two exhibits seen stations with their wavelengths In the photo are replicas of Marconi's first experimental apparatus using parabolic cycle. equivalents :- reflectors for the transmission and reception of wireless telegraphy. That on the left by side with a modern " beam " Çii, ¡Iaa. i['.oe1ea ^I h. Kzlonr/es. is the transmitter. The replicas stand side 1,604.:1 187 transmitters f Dareutrv- Aberdeen 51111.11 6011 is mainly guided in the task of adjusting tion continuous for several days at all Bourne:ma:ih ... 491.8 6111 times when you attempt to listen? Glasgow .... 495.4 740 for volume. Consequently, a conductor Plymouth 400.11 ¡dl who seeks for extravagant effects " not in 3. Is your set in perfect order? Manchester :384.5 780 the score " may waste his fragrance on 4. Are there any particular times or London 351.4 sao of the week or types of programme Cardiff ... 353.0 8511 the desert air, and his purple passages days Birmingham 326.1 920 will get no farther than the purple pas- during which the interference is more Ncwcloth' 312.5 9110 noticeable? Belfast 306.1 980 sages of Savoy Hill. 1,010 0000 5. Could you in confidence name any Liccrpu 1 297.I1 Hull .. 294.1 1,020 person who, in your opinion, is likely to 1,020 Control Room " Tyranny." Stclie - 294.1 be causing the disturbance. Swansea .. 291.1 1,0211 Whether the control room should exert 0000 Dundee .. '294.1 1,020 this " tyranny" over the studio is a Edinburgh 288.5 1,040 seriOus question. Let's Hope So. k 277.8 1,1180 0 o o o Nottingham 275.2 1.090 The abovo should sate ranch futile 1,100 Sheffield ...... 272.7 ; will Where Danger Lies. correspondence whether it lead to Bradford 232.1 1,190 of offenders is another No artist will give a piece of music the detection 0000 matter. precisely the sanie interpretation on two o000 A Yodelling Programme. different occasions. And it is precisely of their of approach and treat- De Groot Again ? Yodel songs have an attraction this spontaneity sung by a native ment (within limits) which makes a per- Statements have recently been made to own. especially when effect that Mr. de Groot had been of Switzerland. On July 7th Martins former an artist rather than a machine. the will The control room idea of following the approached by the B.B.C'. with the object Hugentobler, the Swiss yodeller, Dundee station, in a has its of regaining 1 s services. I understand broadcast from the score rather than the conductor airs. dangers. that the statements are untrue. recital of old Swiss yodel A 35

www.americanradiohistory.com WAp@Eigog Roo JUNE 22nd, 1927. Wm-RA

The Editor does not hold himself responsible for the opinions of his correspondents. Correspondence should to addressed to the Editor, " The Wireless World," Dorset Rouse, Tudor Street, E.C.4, and must be accompanied by the writer's name and address. EMPIRE BROADCASTING. year because of the prevalence of atmospherics. In any case Sir.-May I take advantage of your offer to write you in such relays from home would of necessity be infrequent, as regard to Empire broadcasting? Doubtless you have heard of they world interfere with the working of the proposed beam the Holland station's (PCJJ) recent success. London was re- telephone services. What is waned is a regular programme on broadcast last Friday night, and I received the transmission a wavelength its the. 26 -35 metre band, which (if of the same almost word perfect; it was like being home again to hear power as PCJJ) would not be interfered with by anything the same old announcer's voice. Mine is a three -valve home - short of a local thunderstorm. E. J. H. \LOPPETT. constructed set, and I use an aerial of only 30ft. Holland I Roorkee, U.P., India, May 25th, 1927. listen to every night he works, but the sjx hours' difference in time makes many fans prefer to stay in bed rather than Sir, -I» your issue of May 4th you ask for opinions from turn out at 1 or 2 a.m. overseas readers regarding short -wave Empire transmission. If by your efforts a short -wave station should be erected at The London programme which has recently been received in home, 1 hope you will put this matter forward. The best India ria Holland has been the subject of enthusiastic notices time for them to broadcast, in my humble opinion, would be in the Press out here, and I am convinced that if a regular from midday, so that it would be received here in the even- short -wave transmission could be instituted it would be a ing, 6 p.m., our time, and a wavelength of 30 metres should source of great delight to us exiles. be used, this being most free from static. I believe I am right in saying that short waves travel as There is an enormous interest in India. I know of hundreds well, if not better, by day than by night, and also that they of keen fans; many spend hours listening to 'Morse, there are not nearly so liable to interference from atmospherics. being little else to listen to. Think what it will mean to At present out here to listen in to Europe one has to wait many lonely souls, miles from anywhere, if they can only till about midnight, and, except during the cold weather months hear a few words from home. The stuff is here in the shops, the appalling atmospherics which prevail render reception prac- everything of the latest to be had, but what is the use of tically impossible. Both these disadvantages would be done building or buying sets if there is nothing to listen for? This away with by short -wave transmission. is the usual cry. Think what it will mean to the trade at As far as the residents of this station are concerned we home if we had enough encouragement to build sets. The would be very grateful for anything you could do to bring millions of folk here who would buy sets like hot cakes if about this transmission. England would only wake up to these facts. MAJOR C. W. P. MONEY. Calcutta, M. S. HALES Almora, U.P., India, May 24th, 1927. May 26th, 1927. (T. E. Bevan and Co.. Ltd.). Sir,-As I ails writing this letter I ant listening to what, in soy opinion, is an excellent argument in favour of England Sir, -You will be interested to hear that PCJJ continues having a short wave station. It is a transmission relayed by to be received very well here on his 30.2 metre wavelength. 2XAD on 22.02 metres from WMYC of Lindbergh's reception On May 20th, with characteristic enterprise, the Philips Com- in New 'York, with a continuous running commentary by pany carried out a relay of Daventry through this station, announcers in various parts of Ilse city. thus demonstrating in a convincing manner the possibility of The transmission was first picked up at 6.50 p.n. B.S.T., Empire broadcasting. Practically the whole of this trans- when the announcer was heard to say that about 50,000 people mission was listened to here, and although the strength was were massed in Broadway alone. At about 7 p.m., a band in wonderful the quality was open to criticism. There was a the parade was heard, and at 7.5 p.m. Lindbergh arrived seated definite cut -off of the higher audio- frequencies, for the sibilants on the hood of his car. The cheers and clapping were clearly were missing from a man's voice, and a woman speaking or heard. \Ve were then switched over to the City hall, where singing was very difficult to follow. As this fault was not fragments of various speeches were heard. At about 7.45 p.m. noticed m speech actually from Holland. but only in that re- Lindbergh left the Hall amidst frantic cheering. Next announce- layed from Daventry, it would appear that the fault was in ments were heard from the 25th fluor of the Municipal Build- the amplifier between the Daventry receiver and the PCJJ ings. After this a. big fade took place, lasting till about transmitter, and not due to any effect caused by the use of 8.15 p.m. Since then signal strengths has increased until now, such a wavelength for telephony No doubt our Dutch bene- 8.45 p.m., every word can lie heard. I have just heard that factors will have remedied this defect before very long. Lindbergh has put a Inge wreath on some memorial in, I think, I wish you all success in your endeavours to create an Fifth Avenue. interest at home in broadcasting to the Dominions. I should Two or three more announcers in various streets have been like to add that the suggestion that the beam services may heard. The description of the vast crowds and the double lines be utilised for sending programmes to the Dominions and Colo- of police and soldiers provides intensely interesting padding nies for retransmission on the normal broadcasting wavelengths to the rest of the account. would be only a half- measure. In this country at least the America is letting the world listen to the way she greets her range of broadcast stations is very limited for most of the heroes, why cannot we. do the same? A 36

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Wpishoo JUNE 22nd, 1927. WwIld Bot Although reception is far from perfect, yet it is good enough There is one point about your description of the A.T. and T. to have kept me, with the earphones glued to my ears for two Company's demonstration that needs explanation. What did hours, intensely interested. they do with their thousand men? I cannot conceive how they I could tell you a great deal more of what I am hearing, but employed them all unless, as one illustration suggests, two or I think I have told enough to make you realise how interesting three looked on while one man worked. Perhaps they used this reception is. them as a sort of chorus to come in at appropriate moments Now, at 9.10 p.m., I am able to get the transmission through and sing " Who invented television ? We invented television, a loud -speaker. H. WHITAhER. the great A.T. and T Company." Of course, the figure may Illingworth. have been quoted to give a false idea of the difficulty of work- June 13th, 1927. ing television, particularly as the A.T. and T. Co. have carefully copied some of Baird's patents and have not acknowledged VALVE NOMENCLATURE. the use of them. Baird's demonstrations never required more than two people Sir, -The Radio Manufacturers' Association of America have - to one to act as " subject "- unless, of course, you include the formed a Vacuum Tube Committee to consider attempts commissionaire station have approached three at the door, the lift man, the power standardise valve nomenclature. They hands, the who of apparatus he who have been closely asso- people made the various pieces radio engineers in this country uses, and so on. Then, of course, you can produce as imposing a a view to co- operation in ciated with valve development with total as the regiment that the A.T. and T. Company wasted this matter. requesting the hospitality its money on. As one of those approached, 1 am Reading between the lines, it rather looks as though the A.T. of your columns to invite from valve manufacturers, radio towards the and T. Company were fishing to get the key invention to tele. societies and members of the public suggestions vision by trying to make it appear impossible or at least very solution of the problem of classifying in a convenient manner suggestions sent costly. Colour is given to this idea by the fact that a British the different types of valves used to -day. Any company was floated some weeks ago the purpose of in the United States. for put- to me will be forwarded to the committee ting television apparatus on the market and television to the large number of starting How far it is practicable classify broadcasting. W. C. FOX. Kay. fact however, British valves it is difficult to The remains, London, N.W.11. June 8th, 1927. that nearly all types convey no information whatever regarding the filament voltage, filament current and voltage amplification factor or impedance. The nearest approach to satisfactory Sir,- Following your Editorial comment in the issue of June nomenclature is that applied to Burudept valves, but obviously 1st on the first successful demonstration of television, one reads more can be done to indicate the vital factors relating to with interest the observations made by the Baird Television voltage amplification and impedance. Development Company in your issue of June 15th. As the The problem is a difficult one, and perhaps a satisfactory statements made might be convincing in support of the priority solution would be too complicated for general use by the public. as well as the success of the Baird system, might I suggest that in The question, however, deserves full investigation. and, my a demonstration of the Baird apparatus should be given before private capacity, I shall be only too happy to forward any the Radio Society of Great Britain which could be fully British suggestions to an American industry which has honoured reported on in the pages of The Wireless World? As a wire- us by an invitation to co- operate with them. less enthusiast who is distressed by the sensational statements JOHN SCOTT-TAGGART. which appear in the daily Press on scientific matters and on 2, Melbourne Place, Aldwych, London, W.C.2. wireless in particular, I feel that you were right in your comment. The importance of the matter now demands a well TELEVISION. authenticated demonstration, not before non -technical newspaper Sir, -Tour Editorial of June 1st on Television surprised me men or general or journalistic scientists, but before those who considerably. Surely you have seen the Press of the country have kept a keen watch on television progress -the wireless during the past two years and have read that a British in- amateur's. ventor has given not one but many successful public demon- One has not forgotten, of course, the paper read before the strations of television? Radio Society of Great Britain on the Baird system, but among However, we will let that pass, and instead I would refer those who have studied the problem of television this paper you to a hook .vratten by your contributor, Mr. A. Hinsdale, was far from complete and was subsequently commented on entitled " Television," published in 1926, and purchasable on by M. Mihaly in the pages of Experimental Wireless, and many almost any bookstall. amateurs still await with interest a reply to the points raised. In it, having referred to the various systems of television, The paper was not accompanied by a demonstration, although has he says of Baird, on page 49 : " Baird was not discouraged. In Mr. Baird frequently stated through the daily Press and the obscurity of his attic laboratory he worked on -money was illustrations have appeared in publicity pamphlets indicating that becoming scarce results had to be achieved -and achieved they the apparatus is of simple construction and can even be used in were. conjunction with our broadcasting service for the home recep- " On January 27th, 1926, a Ftrange gathering thronged the tion of moving pictures. stairs leading to the little attic laboratory in Frith Street. In spite of the progress which Mr. Baird has undoubtedly Baird had at last achieved teleri.+ion." The italics are mine. achieved, the wild statements which he has permitted to appear The paragraph refers to a demonstration given to over 40 in the daily Press leaves considerable doubt in the mind of the members of the Royal Institution, and further down it is enthusiast as to the merit of the apparatus with which Mr. stated, " Living human faces tvero transmitted between two Baird claims the distinction of having given the first successful rooms by television. . As one of the members said (of the demonstration of television. A. J. DIXON Royal Institution), ' He has got it. Development is now Ponders End, Middlesex. June 15th, 1927. (G6PD). purely a matter of L.S.D.' A footnote to this part of the book refers to accounts in The Electrician of June 28th, 1926, and Nsture of July 3rd, 1926. TELEVISION -A SUGGESTION. This, I think leaves little doubt as to who was really first Sir, -May I make a suggestion for what it is worth? Tele- to demonstrate television successfully and in public. vision will probably never be an accomplished everyday fact until I am inclined to think that you, like other Englishmen in the the problem of synchronisation has been solved. I suggest that past, are ignoring the sterling and basic work of your country- a great wireless station should be set up to transmit, on a men and lauding the efforts of foreigners who have copied and specially reserved wavelength, a signal at equal intervals of time, exploited British discoveries. It happened with aniline dyes like a great clock ticking across the world. The signal sent out and again with wireless, in which the key discoveries of, I think could be of any desired frequency, and, by its use, not only it was Hughes, were discountenanced by members of the Royal television apparatus, but also clocks, could be synchronised Institution, wile told him his discoveries could be explained throughout the world. The station would be supported by users by existing electrical and natural laws. They were, but never- of the service. G. CHAPMAN. theless he had discovered wireless. Hockley, Essex. June 8th, 1927 A 37

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VIT®Il®E0 Sn, JUNE 22uá, 7927. WoId,(01

" The Wireless World " Information Department Conducts a Free Service of Replies to Readers'Queries. Questions should be concisely worded, and headed " Information Department." Each separate ques'ion must be accompanied by a stamped addressed envelope for postal reply. Transformer Ratios. Uncontiol'.able Oscillation. We strongly recommend you to rebuild I hare two L.F. transformers, one of 1 hare a four -valve rrceirer (IL to a more up -to -date circuit, but if you which has 0 5: 1 ratio and one a 2 L.F.) of -which the circuit dia- do not care to do so it might be worth 3: 1 ratio, and I intend to incor- ,ram i.s et iren on the attached sheet. while to try the effect of short -circuiting porate these in a four-valve receiver. This set 'worked quite satisfactorily the reaction coil holder and'or altering 1l'/ le/e ratio should be used in the with /might- rn,itter valves, but since the relative positions of grid and anode first stage? V. T. I hare changed over to dull emitters coils. The application of a positive gril it has impossible bias to the H.F. valve by means of n From the point of view of ratio alone been almost to prevent oscillation, which is potentiometer would certainly it is quite immaterial which instrument produced stabilise when a .station is turned in. I had the set, but this is only a palliative, and is used in the first stage. We presume a bad one at that. from your gathered from rations remarks in letter that you are building your journal the o e c e a four -valve set with one H.F., that new rolres arc detector, in ereiy/ -u-ay an improvement over Background Noise. and two L.F. stages, and are going to the old ones, and must admit that I I make use of valves of about 20,000 to understand that it is possible to have um disappointed. Can you make any what is known as 30,000 ohm impedance in the first three a " noisy" rare suggestion? A. D. L. in one's set. please explain positions. with a good power valve of Cent you about 3,000 or 4,000 ohms impedance in The circuit you are using (of which the this.' -T. L. V. the output stage. If this is the case, H.F. detector portion is reproduced in In the average loud- speaker set there is of course, both transformers should have Fig. 1) includes no stabilising device, and always a certain unavoidable background we not, a high -inductance primary which (owing are surprised to hear that uncon- of noise, although in a properly c,in- trollable oscillation is when a to difficulties of manufacturing a high - produced strncted set this, is negligible. Iu some ratio instrument with a high -inductance modern H.F. valve of higher efficiency is cruses, however, the noise is excessive, primary) means that the transformer will substituted for the bright emitter. There and it may be found that it is not traceable set have a ratio not exceeding 3 or 3.5 : 1. to any defect in the itself but If you could state the primary inductance is due to one of the valves. Modern of your instruments, we can help you valves are of a very high standard, and better, but as it is we do not suppose do not usually suffer from this defect, that your 5: 1 instrument has a high- although one may still occasionally come across a. specimen which inductance primary. Possibly, the 3: 1 has accidentally instrument has a much higher primary slipped through the exhaustive tests inductance, although we have had cases carried out by manufacturers without this defect being detected. brought to our notice of transformers of coco 3 : 1 and 5 : 1 ratio respectively having the same primary inductance, the smaller Logarithmic Condensers. ratio being obtained by the rather use- ! am. building the ''All- Ware Four " less procedure of pulling off a number rereirer. I hoer, however, several of the secondary turns. In such ca variable Condenser.: of tli't new of course, it is immaterial which trans- loguiithrnU' type, and .c/u,ll like to former comes first, but, acting on the enquire 'Whether I can use these in assumption that your 3 : 1 instrument has the receiver or whether it is neces- a higher inductance primary than the sary to purchase the S.L.F. type as 5: 1 ratio, we, should suggest the lower used by thee authors? N. P. ratio in the first stage, whilst you might It would be quite in order for you to try the higher ratio one in the last stage, a,-e these condensers in the receiver in using, however. a valve of lower imped- Fig. 1.- Circuit of H.F. and detector question. and thus save yourself thé ex- ance, say 7,000 to 10,000 valves In the receiver referred to by ohms impedance A. D. L." pense of Buying the ones used. We would in front of it. This should give satis- point out that an additional saving of factory results if your transformer is by is normally a. good deal of coupling be- expenditure can be made by using a plain a good maker. but if otherwise there is tween plate and grid circuits, oscillation dial on the aerial condenser, since the considerable risk of it saturating under being checked only liy the load of the tuning of the aerial is naturally compara- the normal plate current of a 7,000 ohm direct- coupled aerial: this is evidently in- tively flat. and an expensive slow- motion val ve sufficient when a better valve is used. movement would be rather superfluous. A 33

www.americanradiohistory.com JU.VE 22ttd, 1927. V/fipe®@0 80,E

Neutralising Unnecessary. charge, and by using very large con- 30,000 ohms, but the detector valve must be a lower resist- wish to modernise my receiver, the cir- densers indeed one could arrange for the one of much internal I ance. do recommend a valve of cuit diagram of which is attached, by programme to carry on for quite an ap- We not substituting the present H.F. coup- preciable time without any apparent higher A.C. resistance than 20,000 ohms, tuned source of H.T. and a Cossor 610 H.F. or Mulland ling by either a neutralised 0000 of anode or transformer. Do you think P.M.5X would be a typical example be worth the type specified. One low- frequency that the change would Three -valve Receiver. accord- while? K. St. J. F. valve only is shown, and we must I propose to construct a three -valve re- ingly have a power valve in this position, We think it would be a mistake to go ceiver capable of giving good loud- such as a Mollard P.M.256 or one with to the trouble of putting in a neutralised speaker reproduction from the local similar characteristics. coupling unless at the same time you station and possessing sufficient 0000 change your aerial tuning circuit, which sensitivity to enable a number of the at present is direct -coupled with a more distant stations to be received. When Jacks are Undesirable. parallel tuning condenser. As you do not It is desired to use the receivers for I am constructing the ".-111- 11-are Four," complain of lack of stability, we expect the reception -of long -wavelength but wish to insert jacks in order to that the H.F. valve is stabilised by the stations such as Daventry and Radio use the H.F. and detector only, or aerial load, and there would be no advan- Paris. Can you recommend a circuit to use one or two L.F. valves after tage gained by neutralising as suggested, which would answer my require- the H.F. and detector valves as re- although it is possible that a more efficient ments? J. M: quired, and shall be glad if you will H.F. transformer would improve sensi- A three -valve receiver consisting of one give me an amended diagram to tivity. J. M. 0000 H.F. amplifier, a detector valve and one embody this. transformer -coupled L.F. stage would be We should be doing you a definite dis- Indoors or Outdoors ? most suitable in your case. If you con- service to recommend you such an I have built á four -valve receiver, using struct a receiver on the lines indicated arrangement, for many reasons. In the one H.F. stage, and am making use in Fig. 2 you will have an excellent three - first place, we would point out that both of the high- efficiency aerial -grid and valve set capable of efficient performance L.F. stages are of the resistance coupling intervalce H.F. transformers de- on both the medium and the long wave- type employing high anode resistances, veloped by THE WIRELESS WORLD. lengths. This is a modification of the and the stray capacities associated with Results have been excellent in evert) way on the normal aerial, but the results on an indoor aerial do not satisfy me. I hare 15 turns in the aerial coil, with a tapping at the 8th turn, but on connecting the indoor aerial to either of these ter - minals results are poor. I should mention that the aerial consists only of a length of flex slung across the room. J. C. B. R. The trouble which you are experiencing will probably disappear entirely if you connect your small indoor aerial direct to the top of the grid coil of the H.F. valve instead of to terminals A, and which should be used only in conjunction with an outdoor aerial or a very large indoor aerial ; you will then, of course, be using a direct coupled aerial circuit with the indoor aerial, but owing

to the - smallness of the indoor aerial you should not lose in efficiency. 0000 A Mystery Unmasked. In my receiver I hare separate switches Fig. 2.- Three-valve circuit for long- and short -wave reception. for switching off either the H.7'. or Four " receiver in which the jacks would very effectively reduce niy source of H.T. being accu- " All- Wave L.T., interchangeable aerial coils and H.F. the efficiency of the L.F. amplifier, quite mulators. I find that when I switch transformers are employed, and accord- apart front the instability which would off the H.7'. the programme carries Another point is short ingly this portion of the receiver will be probably be caused. on for a period without any identical with that of the "All -Wave that, in any case, the high resistances are H.7'. supply whatever, and then dors Four," constructional details of which in the anode circuits of very high im- not cease abruptly, but gradually were published in the April 27th issue. A pedance valses, and if jacking were fades away. What is the cotise of modification is recommended to the detec- arranged to substitute phones or loud- this strange phenomenon? tor valve circuit and the resistance -capa- speaker for the high resistances terrible C. E. T. R. city coupling has been replaced by an quality would be obtained, owing to the The behaviour of your equipment is L.F. transformer. It will be necessary to fact that the valve used is of very high perfectly normal, and it is caused by the have a transformer with a high primary impedance, and. consequently, we should presence of the large condensers across impedance owing to the retention of anode lose all our low notes. It would be use- the various tappings of your H.T. bat- bend rectification, and the Ferranti less also to attempt to use the telephones tery. When the set is in use, of course, A.F.3 would be a suitable component to in series wish either of these resistances, these condensers are all the time fully employ. In view of these modifications, owing to the very small percentage of charged. On breaking the H.T. supply, the valves recommended for use in the volts dropped across the telephones as the condensers commence to discharge " All -Wave Four " will nOt be the most compared with the volts dropped across themselves, of course, and so supply the suitable and we accordingly recommend resistance and telephones combined. In valves in the set until their charge is ex- the following. The H.F. valve will re- other words, nearly all our volts would hausted. The larger these condensers are main as formerly, namely, one having an be dropped across 'the resistance, leaving the greater time will they take to dis- A.C. resistance between 20,010 and practically nothing for the telephones. A 39

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Wllp@Rigoo 801 !EWE 22nd, 1927, WopIlcal Wiring the " Everyman Four." Simplicity or Selectivity. A " Reflex " Difficulty. In the " Everyman four " booklet it is I should be obliged by your criticism of I am using a " Roberts Reflex `'eutra- staters that three earth. wires are con- the enclose circuit diagram. The re- dyue " receiver, and find that with nected to the screen, but 1 can Only c, leer gices real fair results, but is the detector valve switched off it is see two in the practical Wiring plan. neat at all .selective, and it is in this possible to hear signals front the As I can in difficulties with the con- lie 'i on that the suggestions for im- local station at almost loud -speaker necting up of this receiver I should prorcmcut would be appreciated. strength, and should be interested to appreciate elucidation on this point. W. T. A. know how this can happen, as it S. M. F. alone could Junction as a dual ampli- Your circuit diagram shows a tapped We consider is fairly fier. G. S. that this matter aerial tuner directly coupled a de- from to clear both practical and theoretical tector valve followed by two stages of L.F. It would appear probable that your re- diagrams. The positive side of the grid - amplification. Now flex valve is over biassed and, indeed, bias this tuning arrange- battery is earthed to one point on ment has many advantages from the point the only way it can give signals without the screen, while the earth terminal is of view of simplicity and quick change the detector is by acting as a bottom bend joined to another. Both these wires con- of wavelength, but it must be lacking rectifier. It is quite feasible that on a nect to that side of the screen next to the selectivity, as judged by modern standards, very large input you should obtairi loud aerial -grid transformer. A third lead conn- and we are signals with the arrangement, but as you ing afraid that very little can from one side of the by-pass condenser be done to improve it, short of entirely suggest the valve cannot he operating as Cs and also originally from L.T. -, joins remodelling the receiver. a reflex amplifier. io Our only sug- the other side of the screw to which gestion is that you should try the effect 0000 the last -mentioned connection is made. of connecting a fixed condenser of from Gas or Water ? 0 0 O o 0.0001 to 0.0002 mfd. (the best value is I have the only to be found by test and may be choice of two alternative earth Valve Filaments in Series. connections, the gas pipe or the somewhat larger than that indicated on water I hare constructed a two-calve portable the long wavelengths) pipe. No doubt the latter would in series with the prove the receiver, and, to economise in current aerial. When selectivity is required more efficient owing to the consumption, have wired the filaments you will adjust the tappings on your superior conductivity of water. In in series in accordance with sugges- aerial coil so that the my case, hou e 'er, the gas pipe takes tuning condenser the shorter tions I have seen from time to time across it is set at a fairly high value. path to earth, and I at in your journal. Both the valves undecided which to use. Gould you are raters at 1.8 volts, 0.1 amp., but please advise me on. this point? they are of different manufacture. T. H. Perhaps this accounts for the fact BOOKS FOR Under no conditions should a gas pipe G+ that the set seems to be absolutely THE WIRELESS STUDENT be used as an earth connection for a " dead," and I can hear no signals wireless receiver. Any length of wire, whatsoever. V. M. Issued in conjunction wills "The IV ireless1Vorld." such as an aerial, is likely to accumulate an electric charge, this being more prob- The fact that your valves are of dif- THE PERRY AUTO TIME MORSE ferent make does not able during the summer months. Strong account for your SYSTEM " by F. W. PERRY. Price 6d. net. " atmospherics " might quite possibly failure. When connecting filaments By Post, 7d. in charge an aerial sufficiently to cause series all that one need concern oneself " WIRELESS VALVE RECEIVERS AND minute sparks to occur at any joints in with is current, at the same CIRCUITS IN PRINCIPLE AND time bear- PRACTICE " by R D. BANGAY and the ing in system. Should these sparks take mind the fact that the total volt- N. Asn RIDGE, B.Sc. Price 2/6 net. By Post place leaky joint in a age applied at a gas pipe un- must equal the sum of that pleasant results are likely to be en- at which individual valves are rated. " THE OSCILLATION VALVE THE ELEMENTARY PRINCIPLES OF- ITS countered, and we therefore strongly dis- Your valves will require a total of 3.6 APPLICATION TO WIRELESS TELE courage its use as an earth lead. volts across their filaments and will, of GRAPHY " by R. D. BANGAY. Price 6/- net. course, consume 0.1 amp. As you are By Post, 6/3. 0000 probably using a dry battery of 4z volts "ELECTRONS, ELECTRIC WAVES AND WIRELESS TELEPHONY " by Dr. Leaky Insulators. we suggest that you include a filament J. A. FLEMING, M.A. Price 7/6 net. By Post, I can using a crystal receiver in a large rheostat of 10 ohms maximum. manufacturing Obtainable by post (remittance centre, and during the 0000 with order) from last six months my reception the ILIFFE & SONS LIMITED of No Switching. Dorset local station ha8 become progress- House, Tudor St., London, E.C.4 weaker. or Booksellers The receiver has re- Please give we et circuit diagram showing of and Bookstalls mained unaltered, and although how one of the L.P. stages in the various crystals hare been purchased " ue e Four " receiver may be no improvement. results. I should be of The Cure for Overloading. switched out by means a jack. obliged if you could suggest a pos- is to to to the This enable me listen r think that your suggestion (nude in a sible explanation. A. P. S. local station without the necessity of previous reply) as to the cause of The atmosphere your is using all foau' mines. C. C. R. my trouble in district no with distortion must be doubt heavily laden with soot and other correct, as I find the needle of We think that it would be a great mis- that impurities given off from factory chim- take to recommend you to insert a jack a In ¡Unlit! ter inserted in the anode neys. circuit of the lost These impurities will be deposited for this purpose, as in our opinion this valve fluctuates on aerial insulators, and owing to the form of switching (or, indeed, any other) violently when signals are being re- ccired: this presence of carbon in soot will result in should be used only with the greatest care thus l take it that valve surface leakage. In time the surface rein any amplifier employing high ohmic is being overloaded. How ron I remeclq sistance of the insulators will be lowered resistances in the anode and grid circuits'. it H. W. and serious losses will occur. An increas- For local station work it would certainly We are afraid that there are only two ing percentage of the aerial energy will be be better and much simpler to switch out courses open to you. The first is that by- passed to earth, this being accom- the H.F. valve, and to partially deneutra- you substitute in your output position a panied by a decrease in the strength of lise. Under these conditions you should valve with a greater voltage -handling broadcast signals. obtain adequate volume and the current capacity, and also with a suitably in- We suggest you take down the aerial, I onsumption of the whole set will be less creased grid bias voltage, or else you must remove any deposit from the insulators, than that of many 2 -valve receivers, be- satisfy yourself with the weaker signals and before re- erection connect three or cause both detector and first stage L.F. obtainable by reducing signal strength to four of the bobbins in series, thus mini- amplifier consume very little current from the point where distortion is no longer mising the possibility of this trouble re- the batteries. produced. curring.- A 40

www.americanradiohistory.com [he»H AND RADIO REVIEW (154h Year of Publication)

, { No. 409. WEDNESDAY, JUNE 29TH, 1927. VOL. XX. No. 26.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

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Subscription Rates : Home, 17s. 4.d.; Canada, 17s. 4d. ; other countries abroad, 19s. 6d. per annum. As many o/ the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy themselves that they could not be infringing patents.

THE EMPIRE STATION DELAY work of an experimental kind before the first B.B.C. - stations were established was undertaken by the big wire- A REMEDY. less companies, and when a long wave station was decided S this issue is chiefly concerned with matters upon it was first established and all experiments con- of short wave interest, including articles ducted in connection with it at the Marconi Company's giving designs for a 45 -metre transmitter works at Chelmsford. and a short wave The Solution. receiver, it is only We sympathise with the attitude natural that our CONTENTS. of the B.B.C. that it is not justi- thoughts should PAGE fied in incurring heavy expenditure turn once more to the question of E DITORIAc VIEWS 805 on experimental work, but such ex- Empire Broadcasting and the need work, we believe, EMPIRE BROADCAST RI.c1:PTIaN 806 perimental for a British short wave station. would readily be incurred by one Letters continue to arrive from By H. F. Smith. of the commercial companies if the overseas impressing upon us the PRACTICAL HINTS AND TIPS ... 813 station, when established in going urgent demand for Empire broad- SHORT- \V:1V-E TRANSMISSIONS 816 order and after having passed casting, and unless Britain intends specified tests, could be handed TRANSMITTING to turn a deaf ear to the supplica- ON 45 'METRES 817 over to the British Broadcasting tions of those who people our dis- By F. H. Haynes. Corporation at an agreed price, tant units of Empire it is impera- CURRENT TOPICS ...... 824 just as in the case of the beam tive that we should act quickly. stations the Post Office gave to the THE EXPERIMENTER'S NOTEBOOK 826 Our main concern is that a station Marconi Company the contract for should be established without any By "Empiricist." their establishment at an agreed unnecessary delay; it is a worthy ABSORPTION WAVEMETER 829 figure and the Post Office was not nl;ject, in the way of which the By H. B. Dent. committed to take over the stations Government -including the Post and pay for them until they had Office authorities -would place no BROADCAST BREVITIES ... 833 passed the required tests. obstacle. \Vrittle, the first broad- LETZ -ERS TC THE EDITOR 835 We do not expect the B.B.C. to cast transmitter of a regular char- I1Et.ENT INVENTIONS ... 858 have at its disposal the same facili- acter in this country, and the fore- ties as a commercial wireless corn- 1 runner of the established transmis- Ii}_.{pFRS' PROBLEMS 879 pany for the building of a short sions of the British Broadcasting N4--N NÑ wave broadcasting station at short Company, was an undertaking of notice, but this work could un- private enterprise conducted by the Marconi Company, doubtedly be clone on their behalf, and our suggestion the authority for which was obtained from the Post Office is that the B.B.C. should invite tenders for a station by the Radio Society of Great Britain. such as is required and place a contract with one of the The British Broadcasting Corporation has given as its commercial companies. There would then be no excuse excuse for not proceeding earlier with a short wave broad- for delay and the B.B.C. could stipulate a time within casting station that it is not justified in spending public which the station was to he ready to be taken over by money on experimental work unless a satisfactory result them. The matter is urgent and we see no reason or from that work is already in view. The preliminary excuse for delay. A 5

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JUNE 291Ir, 1927.

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-411.1%. A Receiver for Wavelengths from 20 to 70 Metres. By H F. SMITH

NOW that the efforts of The Wirclèss World seem recei\ ed from across th Atlantic. Gone are the days likely to be rewarded in the not - too -distant future %hen it was necessary to ` sit up for America " into the by the inauguration of a British short -wave broad- early hours of the morning. One of the greatest charms (' (sting scryic ?, amateurs both at home and in the over- of reception on the ultra -short waves is that the necessary seas Dominions and Colonies are turning their attention apparatus is neither elaborate nor expensive ; indeed, the

to this specialised branch of the wireless art. The in- complex and so- called " powerful " multi -valve set seldom - terest of the former is aroused not so much because they seems to put up a performance sufficiently good to justify themselves expect to gain any great benefit from the its initial cost. British station, but because the fact has been emphasised Interesting as the subject may be for the amateur in as never before that short -wave transmissions have an the British Isles, we must not lose sight of the fact that extraordinary range, considered in terms of power input, the proposed transmissions are primarily intended for the and because, if the wavelength is suitably chosen, these benefit of those of our own race living at great distances ranges are attained when daylight exists over the greater from the Mother Country, and that our own interest in part, or even over the whole. of the signal path. Under the matter is purely a subsidiary one. The description these latter conditions good signals are not infrequently of an Empire broadcast receiver may possibly appear to be premature, but even now there are signals to which it is worth while listening, and many will wish to gain experience of this forni of reception. This is neither the time nor place to enlarge on the subject of Empire broadcasting, hut it may be permissible to make a few observations as to the results which ran be obtained at the present state of development. In the first place, it should be emphatically stated that the user of a short -wave receiver must not expect to receive consistently signals from a transmitter- perhaps thousands of miles away - t. -The circuit diagram. Cl. C2, Ct, 0.0002 ofd.; C,, 0.0001 mtd.; C - 0.001 nild.; Co, C;, 2 mfd;.; Lt, aerial grid coil; L., reaction coil; R;, 5 megohms. which will be comparable A 6

www.americanradiohistory.com JUNE 29th, 1927. WIpIS11@00 807 W(DpllZ Empire Broadcast Reception. - with those from a local station. This statement should be unnecessary, but it is observed that some enthusiasts are apt to think that the system is a complete solution of the problem of long- distance work. It is not; signals suffer from most of the disabilities of those on the normal wavelengths, with the addition of a peculiar trouble of their own, known as high -speed fading, but in spite of this they are received with some reliability at greater distances than by any other system, excepting the beam, which for obvious reasons is of limited interest to the amateur. Daylight Range. At the present time of year, under summer conditions, when atmospherics are at their worst and when daylight covers the greater part of the path across the Atlantic, the chances of receiving intelligible signals from either of the two American stations on 32.77 or Fig. 2. -The containing case, with lid open. 22.02 metres at any given time during their periods of transmission are distinctly in favour of are occasions when the signal- strength to atmospheric the listener. This statement is made as a result of care- ratio is better on American short -wave transmissions than ful observations under what may be described as average on those of a broadcasting station 5o or roo miles away. conditions, and gives a fair idea of what may be ex- As has been suggested above, there is no need for pected. There are, of course, times when signals fail elaborate apparatus, and a detector-L.F. combination, of altogether, and others when fading or atmospherics the type which it is proposed to describe, is the most render reception impossible. It is a fact, however, that generally favoured receiver. As pure high -frequency atmospherics are generally less troublesome on the short amplification is almost out of the question at present, waves, and this is particularly true in tropical climates. we have to depend on the use of reaction; provided that Evert in this country, incredible as it may seem, there really critical control of this invaluable aid to sensitivity is obtained, and hand- capacity effects / 3`\ are minimised, the problem of design is -i r-- practically solved. The first requirement is met by introducing capacity -controlled 3 regeneration with a well-proportioned reaction coil, together with é a careful choice of H.F. choke, grid leak, and condenser values, and the provision of a detector grid voltage adjustment. The second is .18/1a/'1 assured by arranging for the spindles of the variable condensers to be at earth

3, potential, by fitting an H.F. choke in 30 oy o 30%; the phone leads, and by thoroughly screening the apparatus. The circuit is 31; 2'B 1i conventional, as will be seen from Fig. r ; it comprises the usual grid de- 234. tecting valve, followed by a transformer - coupled low- frequency amplifier. An is FRONT BACK additional by -pass condenser, C added, in effect, to that already included in the transformer, in order to dispose of H.F. currents in the anode circuit; this addition to the transformer would hardly be permissible in a receiver de- 16% 6% 8 signed for the normal broadcast wavelengths, but it is legitimate in this case. Fig 3.- Constructional details of the front and back sections of the metal case. Positions for the panel holes are shown. A, 9 /16in.; B, 3 :Sin.; C, 5/321n. The complete screening mentioned s7

www.americanradiohistory.com 808 WApsIl@oo JUNE 29th, 1927. Wo11cl Empire Broadcast Reception. - bending at the dotted lines. above is obtained by mounting all the apparatus in a The seams are riveted to- containing case made of sheet aluminium; No. r6 gauge gether, small brass pins was actually used, although it is probable that No. 18 being used as rivets. To would be heavy enough for ordinary requirements. It is avoid the need for another not essential, however, that this method of construction bend (which would give should be followed; many readers, no doubt, will hesi- sufficient rigidity) a stout tate to embark on sheet -metal work (although it is by no wooden batten measuring means difficult), and may substitute an ordinary wooden in. x ¡in. in cross -section is cabinet, but it . is suggested that they should retain the screwed to tie rear upper aluminium front panel in any case. It seems likely, edge of the front panel. however, that short -wave design will tend towards the Two screws, the projecting sise of these metal containers, which lend themselves heads of which engage with Fig. 4.- Mounting for the particularly well to the construction of a set intended slots in the lid, thus forming L.F. transformer, reservoir condensers, and by -pass for tropical climates. Thus, in all probability, boxes a catch, are passed into the condenser C4. similar to that illustrated will become available com- ends of the batten. Another mercially. slot, of the dimensions shown in Fig. 3, is cut to receive the connecting leads, and a hole, which is preferably Constructing the All-metal Case. bushed with ebonite, is drilled to take the phone cords. The case is made in two similar parts, which are A wooden base, tin. thick, and of full internal hinged together, the construction being shown in Figs. 2 dimensions of the case, is secured to it 'Icy wood screws and 3. The latter shows the exact dimensions to which passing through the bottom, which is raised on four small the sheets forming each section should be cut before rubber buttons (sold by ironmongers as " cupboard

Rear view of the receiver, showing hinging of the lid.

www.americanradiohistory.com W11p @Ilse@ JUNE 29th, 1927. MpH Empire Broadcast Reception. stops "). Those who have had no previous experience of i+-1 2 4 2 2 13 work of this kind and who doubt their own capabilities are recommended as a pre- 1578. ,. liminary to make a full-size R'... 2 /4 model of cardboard. case -µ The aerial -grid coil L, 1., - t -i consists of nine turns of 3 " ..., I 2g ^ F4""__---t r-----.7-77-- -i No. i8 tinned copper wire, -'..a`r. :: ' {^ i :; r ----i which I are wound with I úin. J i H F. C. }t-.-; I ` J. \ u = N °'S , 1 - L . I r spacing between the centres ,rS , 4_1_, ,r __ç._,?r ...i_ r ,1".".e,--i ` on a ribbed former Sin. long s \..... ' i ry T ^ 1-* L2 ., i , ti + Zr zazizi by Sin. in diameter. The re- 9 ,F _ ; v, -''' , i _n .a action coil L2, having 5 J..., ( - y _í-3C..Z ) n. is 2 5 4!43--f,¡ ------zlt turns of No. 3o D.S.C., C /g `'Ái5'ì i IF.-4,4 . I I Ll wound in the same direction, _ _ J' í,.3L: Tr*' 1. 2L ÿ. i 1 i a a= ¡9 r- f I 1 4:: if L with adjacent turns touch- 1 t !I ,' rT ` iiT_._+ .,1 .. t ing, and is spaced gin. from 1- # r;.__.lt l .._

}, ', F`i1Jw C8 that end of L, which con- .:[ R _.. ..-..J Y I.:: j nects to the grid condenser. Ì hw 1 n , 1 1 ` a: o are I The ends of this winding , , 1 ; ,+_: , [- :_ J secured to soldering tags C5 z ; .,`^^r

L., I ( i 1¿ G 1 .! screwed to the ribs, while ; .- A--- r_--, , those of the heavy wire coil f-= . are passed through holes in 1/4,. ,-Ì. 4 3 the body of the former, 12 is raised on two ebon- which ; in. length , ite pillars i in Fig. 5. -The disposition of components on the baseboard. these are attached to an ebonite hase. on two small wooden strips, the 2 mfd. by -pass con- The H.F. choke in the anode circuit of the detector densers Cs and C, being mounted underneath it, while valve is wound on an ebonite rod ein. in diameter and C, is attached to the side, as shown in Fig. 4. Porcelain Sin. long, which is mounted vertically, being secured connectors are used in place of the more conventional in position by a screw passing through the bottom of the terminal strip, and they are secured to the baseboard as case. Its winding is a single -layer solenoid of No. 42 shown by aluminium strips, drilled so that access may D.S.C. wire, with turns touching, and a length of zain. be had to the heads of the inner screws. Both in this The choke in series with the phones is of similar con- matter and in the mounting of the valve holders, which struction, except that the former is tin. in length and is in the receiver, as illustrated, are supported on shock - mounted horizontally on two brass brackets. The ends absorbing sponge rubber hases, the constructor may follow of the windings of each of these coils are soldered to the his own ideas. heads of small brass screws inserted in the formers ; If a rheostat and potentiometer of different construc- these serve also as points of attachment for the leads tion are substituted for those specified, it may be neces- spindle to the external circuit. sary to bush the panel, as it is essential that the To economise in space, the L.F. transformer is raised should be insulated. With the particular type shown

LIST OF PARTS.

2 Variable condensers, 0.0002 mfd., with slow -motion dials ( Utility). 2 Valve holders (Excelsior Motor Co.). 1 Filament rheostat, 6 ohms (Igranic Pacent). 1 Grid leak, 5 megohm (Dubilier). 1 Potentiometer (Igranic Pacent). 1 Porcelain base (A. F. Bulgin & Co.). 1 L.F. transformer (Ferranti A.F.3). 1 Ribbed ebonite former, 3in. (Becol). 1 Fixed condenser 0.0001 (with base), (Igranic Freshman). 2 Spring clips (Baltic). I Fixed condenser, 0.0002 (with base) (Igranic Freshman). 3 Three -way porcelain connectors. 1 Fixed condenser, 0.001 (Igranic Freshman). 1 Two -way porcelain connector. 2 Fixed condensers, 2 mfds. (T. C. C.). Sheet aluminium, ebonite rod, wire, screws, etc. Approximate cost t5 0 0. In the " List of Parts" included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should be used in preference to others, these components are mentioned in the article itself. In all other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use.

www.americanradiohistory.com Wñp@ Sro Ilwo JUNE 29th, 1927. WopPc Empire Broadcast Reception. - 20,000 to 30,000 ohms impedance, with an amplification this is prevented by drilling a central hole with an ample factor of, very roughly, from 55 to 2o, is difficult to clearance, and also by enlarging that in the indicator disc. beat. Among representative specimens in this class we As an additional precaution, a thin tube of insulating have Cossor 65o H.F., Marconi and Osram D.E.8 material may be slipped over the spindles. H.F., Mullard P.M.5X, and a number of others, mostly The remaining points regarding assembly and wiring with their counterparts in the 2- and 4 -volt ranges. It is will be sufficiently clear from the various diagrams. Par- recommended that an H.T. voltage not greatly in excess ticular note should be made of the fact that the rotors of 40 should be applied to this valve. As for V2, we of both condensers and one end of the potentiometer have a still wider choice, as any "L.F.," "general winding are in metallic connection with the case; this purpose," or " power " type will work well. The contact is obtained automatically by making use of the maker's instructions as to anode voltage and grid bias one -hole fitting on the former components, but it should should be followed. he pointed out that the large brass washer supplied with the make of condenser shown should not be removed, as Operating Details. it would he were the instrument to be fitted on a thicker The operation of any receiver, be it crystal set or panel. The potentiometer connection is made by a strip superheterodyne, can only be mastered by practice, and of metal clamped between the porcelain base and the it is as easy to give really definite instructions on the panel. subject as to prepare a correspondence course on the Suitable Valves. painting of a masterpiece or the composition of a symphony. While the set under discussion is no exception The disposition of the more important connecting wires to the rule, its design is such that operation is a com- (those to the variable and grid condensers, the grid and paratively simple matter. It is suggested that, for the reaction coils) are shown clearly in the photographs. It 20 -40 -metre waveband, the earth clip should be set to in- will be seen that the leads to the valve holders are made clude about 61 turns of the inductance, starting from the with short lengths of " flex," as otherwise the advan- grid end. The IKrial tapping may be made on the next tages of rubber suspension would be lost. turn down, remembering that its exact position should The choice'of valves for a receiver of this description be a subject for experiment. The potentiometer may be 's not a difficult matter; as a detector (V1), one of some set at a central position, or perhaps a little towards the

CASE AERIAL

EARTH

C, + LT.

- L.T. + G.B. ILi11 ,-- --- r.. I,!NEf - G.B. C -H.T.

POTE Ira usia

+ H.T.2

TO CASE

H F.C. 2

H. F. C.

TELEPHONES

CASE

Fig. 6. -The practical wiring plan. Tha olate of V1 is joined to the end of the reaction winding nearest to the grid coil. A IO

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Wizamo Bur JUNE 29th, 1927. WopIlc1 Empire Broadcast Reception. - For the longer wavelengths, up to 7o metres, the earth negative side, particularly if 6 -volt valves are used. The tap should be made to the extreme end of the coil remote reaction condenser (C2-the right -hand dial) is now from the grid, the aerial being joined to a point about moved slowly from zero towards its maximum position 2 turns above it. With this adjustment the Pittsburgh until the valve is on the verge of self- oscillation. Pro- station, KDKA (64 metres), is tuned in at about 145 vided that signals or atmospherics are now heard, it is degrees. Incidentally, this station is " corning over " probable that no serious fault exists, and searching may very indifferently at the time of writing, and is, as a

Plan view of the receiver, with lid completely removed. mornin`. be commended, by rotating the tuning condenser (C,) rule, not receivable till the early hours of the amateur trans- slowly and following up each movement with the reaction The condenser setting corresponding to these afford control in such a way that the set is always near oscilla- mitters on 45 metres is about 90 degrees; to be heard tion and thus in its most sensitive condition. good practice in tuning and are generally same tappings As a guide to the rocation of the different wave- working during the week-ends. With the it is lengths, it may be useful to know that, with the coil 2XAF should be heard at about 3o degrees, but on this wave- tappings as indicated above, the tuning condenser is set generally better to work with more capacity at about 3o degrees for the Schenectady station, 2XAD, length. a useful aid to the finding on 22.02 metres, while the adjustment for the companion A wavemeter is admittedly 2XAF (32.77 metres) is 90 degrees. The of a desired wavelength, but it is by no means essential. transmitter, elsewhere in this Dutch station at Eindhoven, PCJJ, on 3o metres, The absorption instrument described of a particularly suitable kind will be found at about 75 degrees. issue is, unfortunately, not A II

www.americanradiohistory.com -.

812 WIpIShE0 JUNE 29111, 1927. InOO TIld. Empire Broadcast Reception. - particularly in tropical countries. Naturally, under these for use with a totally screened set, as to make a measure- conditions, the most economical valves will be chosen - ment it is necessary to open the case, and, when closing probably those rated at 2 volts o. r amp. This consump- it, to allow for the resulting decrease in inductance. "I'his tion is not beyond the capabilities of dry cells, which, decrease, however, is not very great and is compensated however, are apt to deteriorate in transit and stock, so for by an increase of a few degrees in condenser reading. " inert " or large- capacity wet primary cells (of which The conventional type of aerial, as used for broad- improved types are now available) are generally prefer- cast reception, is quite suitable for short -wave work, but able. An H.T. voltage of 45 is sufficient ; this may be it should be taut and well- insulated, particularly at the derived from about thirty small " inert " cells. Ordinary " free " end. Any swinging will cause a variation in dry H.T. batteries are quite out of the question. Need- signal strength. A short earth connection is particularly less to say, where there are facilities for recharging, the desirable, as any appreciable drop in H.F. potential in use of accumulators for both high- and low- tension is this lead will give rise to capacity effects. the best solution of the difficulty. The best adjustment of the potentiometer can only be In conclusion, the writer would stress the point that the found by trial; the general idea should be to make the reaction condenser should be regarded as a " volume con- grid as positive as possible, consistent with good reaction trol," and not as a tuning adjustment. In other words, control Its setting is, to a certain extent, dependent on its direction of rotation should always be from minimum the resistance of the leak, and it should be pointed out towards the point where oscillation is about to be pro- that if trouble is experienced with " threshold oscilla- duced. This remark may be superfluous, but, due pos- tion " (the production of an L.F. howl as the valve goes sibly to the fact that the reaction control dots have some into H.F. oscillation), an increase in the value of this effect on tuning (only very slight, however, in this par- resistance may help to put matters right. ticular receiver), it is noticed that beginners almost in- A few suggestions as to batteries may be of value to variably handle this condenser in the wrong way, inci- those situated in localities remote from civilisation, and dentally to the annoyance of other listeners.

Those 200 Yards ! being investigated, and compared their One of the most exciting and profitable respective advantages and defects. The Field Days yet held by the Golders NZVV3 FROM Society having devoted special attention Green and Hendon Radiò Society took to the selenium cell method, the lecturer place on Sunday, June 19th, when six conducted a number of chemical experi- parties each equipped with a receiver, THE CLUBS.So ments demonsirating the nature of frame aerial and a motor car engaged in a selenium and its manufacture. Ile con- hunt for a concealed transmitter. cluded with an interesting display show. Zero hour, which was 12 noon, found Another Field I)ay will probably be ing the variations in the electrical resist- the different parties distributed over a held early in September. ance of a selenium cell when exposed tc 'arge area of country extending to Hon. secretary : Mr, J. Levy, 19. Lans- light of varying intensity. Harpenden, Redbourn, Chorley Wood downe Road, West Didsbury, Mau - The Society hopes shortly to proceed an l Chipperfield. Transmission began chester. to actual television tests. from the concealed station 5CT on o 0 o o Visitors and new members will be wel- 150 metres (interrupted C.W.) sending Mysteries of the Selenium Cell. comed at 8 p.ni. on any Tuesday at the 10- second dashes for five minutes, fol- Lecturing on " Television " at the last Society's headquarters, Holy Trinity lowed by a five minutes pause and con- meeting of the Hounslow and District Hall, Hounslow. The hon. secretary is tinuous repetition in this order. Four Wireless Society, Mr. Huntingford gave Dir. W. R. Collis, 7, Aigar Road, Isle of the six parties succeeded in coming a brief account of the various systems now worth. within a mile of the secret transmitter before the close of operations at 3.30 p.m., while special credit is due to Mr. Maurice Child's party, which finished up within sight of the transmitter only 200

yards distant ! Considering that the party had started operations at a distance of 10 miles, this result was noteworthy. The general opinion was that if a little more time had been allowed the results would have been still more satisfactory. Hon. secretary : Lieut. -Col. H. Ashley Scarlett, 357a, Finchley Road, N.W.3. 0000 Tottenham Society's Competition. A competition for two -valve receivers, which will be judged according to the quality of reception from 2L 0, will be held this evening (Wednesday) by the Tottenham Wireless Society at eight. at 10, Bruce Grove, o'clock, 0000 N.17. Manchester Society's Field Day. The Radio Experimental Society of Manchester proposes to hold a Field Day on NEAR THE END OF A PERFECT DAY. Members of the Golders Green and Hendon at Coombes Edge, near Mottram, Radio Society photographed at tea alter a strenuous and exciting day in pursuit of a Saturday, July 2nd. hidden transmitter. A r?

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`IñpIgIl®@@ JUNE 29th, 1927. 813 Wo;filcl 1 Q 4 P_R AC T ICA ( )) ' AN

Aids to Better Theoretical Diagrams Reception. Simplified.

SOME SHORT -WAVE HINTS. ohms -depending on valve imped- The accumulation of dust between ''HERE is no real need to use ance -will be best. condenser vanes is often responsible special valves -those of the 0 0 0 0 for noises. The set should be mounted ordinary " four -pin " type are gener- When using resistance coupling it in a case, while dust may be removed ally quite satisfactory. In any case, is necessary to take precautions with the aid of a bicycle pump or a there is no point in using low- capacity against the application of H.F. Bunsen gas flame. valves as L.F. amplifiers. potentials to the L.F. amplifier. On 0 0 0 0 0000 short waves the easiest way of doing A SIMPLE WAY OF CALIBRATING Capacity-controlled reaction, al- this is to connect a quarter- megohm SHORT -WAVE WAVEMETERS AND though popular, is not the only possi- resistance of the grid leak type RECEIVERS. ble system. The swinging coil method directly in the grid circuit of the first HEN we turn our attention for works well, but mechanical difficulties L.F. amplifier. the first time to a new short are often encountered. Resistance 0000 wavelength -and some of the most control depends for its effectiveness A taut aerial is necessary for the interesting wavelengths lie below qo on the smoothness of variation in the best possible results ; in spite of the metres -we are at a loss to find our resistor. Few types are consistently fact that the open circuit is almost in- way about unless we possess a reli- satisfactory. variably of the so- called " untuned " able wavemeter or some other means 0000 type, variations in its capacity will of ascertaining with certainty the A reaction coil may with advantage be communicated to the closed circuit, wavelength to which our receiver is be wound with very fine wire, in and an apparent fading effect will be tuned. One of the simplest and yet order to reduce the capacity between produced if the aerial sways with the most reliable methods is to make use it and the grid inductance. If this wind. precaution is taken, changes in re- o000 action coupling will make compara- Short -wave chokes should be of tively small changes in tuning. low self- capacity and small physical 0000 size. It is difficult to better a single - Tuning will be extremely difficult layer solenoid winding of fine D.S.C. if large variable condensers are used, wire on an ebonite former about one even if a high -ratio reduction gear is inch in diameter. fitted.. A maximum of o.000z mfd. 0000 is suggested ; a slow- motion dial hav- The majority of those who receive ing a step -down of about 5o : i is de- the short waves successfully do so sirable, and is much better than a with a simple detector -L. F. combina- separate " vernier " vane. A direct tion. Do not attempt the construc- drive is almost impossible, even with tion of a more elaborate set without Fig. 1. -A crystal set as an aid to the a maximum capacity of as little as having had experience of this arrange- production of harmonics. o.000r mfd. ment. 0000 0 0 0 0 of the harmonics of our local broad - The majority of short -wave lis- A " noisy " short -wave receiver is casting station. The fundamental or teners content themselves with head- an abomination, and no pains should main wavelengths of the B.B.C. phone reception, and accordingly use be spared to remove the causes of this stations are now pretty accurately only one L.F. amplifier. If two trouble. They may most easily be fixed and widely published. The stages are desired, it is suggested traced by putting the set into an oscil- harmonics have frequencies corre- that the first (that following the de- lating state with aerial and earth re- sponding to wavelengths which are tector) should be coupled by a resist- moved. Faulty condenser bearings exact simple fractions of the funda- ance, followed by a transformer. should always be suspected ; a " pig- mental wavelength. Thus if the Very high anode resistances are tail " connector to the rotor is gener- local station has a fundamental wave- generally out of place; about roo,000 ally preferable to a rubbing contact. length of 36o metres the harmonics A 13

www.americanradiohistory.com sr WATighom JUNE 29í1a, r927. Warilc11 will have wavelengths of exactly ¡, THE REACTOR VALVE ON SHORT A consideration of the diagram 4, ', etc., of this wavelength, WAVES. will show that the steady voltage of that is, râom., r2om., vom., 72m., ''HE advantages gained by the the detector grid (V2) is determined etc. If we can pick out these har- 1l use of a separate reactive valve, by the setting of the potentiometer, monics on a receiver or oscillating which are often sufficient to justify as it is insulated from the bias bat- wavemeter we have a number of use- its inclusion in a receiver designed for tery G.B.1 by the grid condenser. ful points which at once show us the normal broadcast waveband, are This battery serves to bias the reactor where we are as regards wavelength more pronounced when receiving on (V1), and should be of such a voltage on various tuning settings. the short waves. As far as the former that it is working on the straight part Harmonics beyond the second and are concerned, it must be fairly obvi- of its characteristic curve. A 20,000 third are, however, often difficult to ous that better use may be made of ohm " H.F." valve is suitable for pick up directly, even if the station the extra valve by making it operate this position; it will be operating cor- does actually radiate them at all, and as a pure H.F. amplifier, although rectly with r¡ volts negative on its they are apt to be confused with other signals. An excellent plan for getting the harmonics strongly and free from other signals is shown in the figure. All that is needed is a simple crystal receiver connected to an outside aerial and tuned to pick up the local broadcasting station in the ordinary manner. Nearly everybody has the where- withal to fix up such a crystal set. It is the property of a crystal detector to generate strongly the whole series of harmonics of the signal to which the aerial is tuned so that when the short -wave wavemeter is placed near the tuning coil of the crystal set the harmonics can be tuned in quite easily as reasonably strong carrier waves. Do not couple any closer to the crystal than is absolutely essential to pick up the-harmonics with certainty. Starting with the second harmonic (half the fundamental wavelength) we follow the harmonics downwards, taking the utmost care not to miss Fig. any harmonic or lose count. The 2.- Smooth control of reaction on the short waves. greatest care in this respect must be admittedly this course will necessitate grid and an anode voltage in the exercised when we come to the mini- another tuning control. On the very order of roo. mum of our tuning condenser and short wavelengths, however, such 0000 have to change to a shorter wave- amplification is impracticable, and length coil. Much the best way of any device which will improve reac- LOOSE CONTACTS AND SHORT -WAVE avoiding difficulties here is to use an tion control should not be neglected. RECEPTION. auxiliary oscillating wavemeter to To obtain smooth regeneration with WHEN an oscillating receiver is " hold " a particular harmonic while the ordinary arrangement it is, as a being used for the reception the change of coils is being effected. rule, necessary to effect a compromise, of signals below 6o metres it is essen- The lower the wavelength, of course, as the best grid voltage adjustment tial to avoid variable contacts not only the more crowded do the harmonics from the point of view of detection is in the set and aerial circuits them- become and the greater is the care not always best for reaction. selves, but also between any two ad- required in following them. Within The circuit diagram of a short- jacent metal bodies anywhere near the five miles of a powerful local broad- wave receiver, including a separate set. Two objects, such as a pair of, casting station it is quite easy to. fol- reactor valve, is given in Fig. 2. All scissors and a screwdriver, touching low the harmonics down to about zo the components may have conven- eacli other lightly within two feet of metres. Needless to say, a short- tional values, while their disposition the receiver may easily give rise to wave receiver must be calibrated ex- may follow standard practice. The distracting scraping noises in the tele- actly as it is going to be used. If inductances of the aerial -grid coil L, phones. The lower the wavelength the aerial is to be tapped directly on and of the reaction coil L2 will, as the more pronounced is this sort of to the grid coil, then the set must be usual, depend on the waveband to be effect, and on wavelengths as low as calibrated with an aerial on, and a covered,. and are similar to those used zo metres one may have to look quite supplementary aerial must he used for in a reacting detector set, except that far afield for the cause of scraping the crystal set. extra turns may be necessary on L2. noises. A 14

www.americanradiohistory.com WIpigii®00 JL:1'r 29t11, 1927. Bis MpIlCo1 COMPARISONS. When testing apparatus associated grid leak detector valve is most sensi- r l `HE human ear is notoriously un- with H.F. circuits, care must be tive to the smallest leakage of this iL reliable, and unfortunately re- taken to retain a reasonable degree nature, and very perfect insulation is tains its impressions for an extremely of electrical symmetry in the connec- needed in the condenser, both in the short space of time. Most of us have tions to the components under test; dielectric itself and the casing in found this out when changing over otherwise totally misleading results which the condenser is enclosed. It alternative pieces of apparatus in may be obtained, due to variation in is safe to say that the best insulation order to judge their comparative tuning or other causes. in the whole of a tuned anode set effectiveness either from the point of 0000 should be in the detector grid con- view denser. The dielectric should be of quality or signal strength. USE GOOD GRID CONDENSERS IN ex- mica or at least as good. Unless the change is made with TUNED ANODE RECEIVERS. something treme rapidity, it is found that, by 0000 the time the second component is in -r, last coupling condenser in the ordinary form of tuned - SOLDERING TO NICKEL -PLATED position, there remains but a hazy METAL. impression of the conditions prevail- anode H.F. amplifier is also the grid TrT occurs sometimes, but fortunately ing with the first. condenser for the detector valve which not ofen, that we have to make a To facilitate the making of a functions on the leaky -grid principle. connection to a nickel - quick change, it is strongly recom- Now one side of this condenser is at soldered article. Nickel is not a very mended that the apparatus should lie full H.T. voltage while the other plated good metal to solder, and nickel -plat- wired to a double -throw switch with side is connected to the grid of the is ing often does not adhere any too a suitable number of poles. The detector valve, and since this grid the metal below. For this slight extra trouble involved will be isolated except for a grid leak of one firmly to reason is advisable to file the sur- compensated for by the more definite or two megohms the slightest leakage it the joint has to be made results obtained by the test. Single - on the part of the condenser will face where main metal (usually brass) and double -pole switches, mounted on cause irregular positive charges to until the is before attempt is made stout porcelain bases, are suitable and flow on to the grid. This will give exposed any are readily obtainable at a low price. rise to hissing or crackling noises. A to tin the surface.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 74. -An H.T. Eliminator with Full -wave Rectifier. (To be concluded in next week's issue.) understandable The present series of diagrams is intended to show progressively, and in an easily points to which special attention should be paid in the design of typical wireless manner, the various circuit instruments, and at the same time to assist the beginner in mastering the art of reading diagrams. The eliminator shown below operates on A.C. mains, and gives full -wave rectification by the use of a double -plate valve.

.. .., ,1 A.C. A.C. A.C.

...:

(2) CO (3) connected in The ends of the high- voltage secondary The primary winding of the transformer is The low- voltage winding is to the anodes. A.C. supply mains. series with the filament and a controlling winding are connected connected across the rheostat. to the 'HF transformer must be de- valve is actually rated, in order that but only half of this is applied 1 signed to work on the voltage a minimum value of series rheostat pates. and supply mains. may be necessary. Several ma nufacturers produce periodicity of the of The filament lighting winding should It is suggested that the voltage he- double -plate valves for eliminators filaments generally have from to 6 volts across its ends, tween the centre tap and each of the this type; their 4 one according to the type of valve to be ends of the high voltage winding consume rather more than used. This voltage should approxi- should be about 150. There are thus ampere and give a working emission mate closely to that at which the boo volts across the whole secondary, of about 40 mA. A 15

www.americanradiohistory.com 1`,

S t.) Wbghea JUIVE 2911, 1927. WOpIld

5lli0RT°WAVE T.SUANSRI<.,55i3OH5a

ÌN compiling the following list of stations which transmit fairly regularly on short waves, we have selected those which are likely to prove of service to experimenters in this country. Many other short -wave stations heard are engaged only on tests of a temporary nature, and these have been omitted.

Waae- Ware - Wave- length. Call- Stitt inn. length. Call - Station. length. Call. Station. (Metres). sigli. (Metres). sign. (Metres). sign. ) 2.25 AGA Nauen. 30.0 GBL Leafield. 46.0 OCMY Mont Valerien. r 13.5 AGA Nauen. GBM Leafield. PCLL Kootwijk, Holland. 14.09 U 2XBC Rocky Point, N.Y. U 2XI Schenectady, N.Y. 46.5 TSB Norwegian s.s. " Hel- 14.28 F FW Ste. Assise. 30.2 PCJJ Eindhoven, Holland. der." 14.93 U 2X5 Rocky Point, N.Y. 30.6 NAL Navy Yard, Washing- 47.0 POZ Nauen. 15.0 GLS Ongar. ton, D.C. ICX Massawa. U 2XAW Schenectady, N.Y. 32.0 FL Eiffel Tower. SPI Rio de Janeiro. 16.0 AGA Nauen. ANE Malabar, Java. SUC2 Abu Zabal. Cairo. WSS Rocky Point, N.Y. IDO Rome. 49.5 KRP Salt Lake City, Utah. 16.02 U 2XT Rocky Point, N.Y. HVA Haniii, Fr. Indo China. TFA Reykjavik, Iceland. 16.57 WLL Rocky Point, N.Y. VIS Sydney, N.S.W. 50.0 OCTU Tunis, La Casbah. .. 17.0 SPI Rio de Janeiro. 32.77 U 2XAF Schenectady, N.Y. WBZ Springfield, Mass. NKF Bellevue, Anacostia, 33.0 OCDJ Isly les Moulins. SAJ Karlsborg, Sweden. D.C. OCTN Mourillon, Toulon. 51.0 AIN Ain Bordja, Casablanca. 18.0 POF Nauen. 33.5 AQE S.S. " Sir James Clark TSB Norwegian s.s. " Hel- :. 20.0 AG K Nauen. Ross." der. NAL Navy Yard, Washing- 34.0 NAJ Great Lakes, Ill. 51.5 WQN Rocky Point, N.Y. ton, D.C. XDA Mexico City, Mex. VIS Sydney, N.S.W. OCTN Mourillon, Toulon. 35.0 BW 1V Gibraltar, North Front. 52.0 VAS Louisburg, Nova Scotia. PDX Nauen. BXW Seletar, Singapore. WKK Ceiba, Porto Rico. GFR h'lowerdown, Hants, BXY Stonecutters Isld, Hong - WGW Vieques, Porto Rico. R.F.A. Kong. 52.02 WLW Cincinnati, Ohio. GI.SQ. S.S. " Olympic." BYB Whitehall, R.C. 53.0 ZWT Bremerhaven. J 1PP Tokyo. BYC Horsea. NPU Tutuila, Samoa. 20.8 NKF Bellevue, Anacostia, BYZ Binella, Malta. 54.0 NBA Balboa, Canal Zone. D.C. BZE Matara, Ceylon. 54.4 NKF Bellevue, Anacostia, 21.0 PCTT Kootwijk, Holland. BZF Aden. D.C. 21.4 WDJ Harrison, Ohio. VKQ Garden Island, Sydney, 54.5 WQN Rocky Point, N.Y. 21.48 WIK New Brunswick, N.J. N.S.W. 56.0 GBL Leafield. 21.8 KEB Los Angelos, Calif. NPM Honolulu. GB9I Leafield. 22.0 VIS Sydney, N.S.W. .I 1PP Tokyo. ANF Malabar, Java. VIT Townsville, Queensland. 35.03 1VQ0 Rocky Point, N.Y. U IXAO Belfast, Maine. 22.02 U 2XAD Schenectady, N.Y. 36.0 PCMII Kootwijk, Holland. 57.0 OCTN Mourillon, Toulon. 23.0 PKH Soerabaja, Java. LPZ Buenos Aires. WQN Rocky Point, N.Y. 23.25 FFWV Sainte Assise. OCRB Rabat, Morocco. 58.0 OCBV Beyrouth. 23.3 1VBQ Schenectady, N.Y. 36.8 NPM Honolulu. 58.79 KDKA East Pittsburg, Pa. 24.0 GBL Leafield. 37.0 PC1111 Kootwijk, Holland. 60.0 U 1XAO Belfast, Maine. GBM Leafield. 38.0 PCUU The Hague, Holland. 61.0 NK l Bellevue, Anacostia, 24.3 KF D Denver, Colo. U 2XI Schenectady, N.Y. 24.5 GLQ Ongar. 39.0 OCMV Mont Valerien. 65.5 U 2XK South Schenectady, 24.7 NKF Bellevue, D.C. 40.0 NAJ Great Lakes, Illinois. N.Y. 25.0 PCMM The Hague. NAS Pensacola, Florida. 67.0 U 8XS East Pittsburg, Pa. PUY Nauen. NOSN Coco Solo, Panama. 68.0 NPO Cavite, Philippine HZA Saigon. WNU New Orleans, La. Islands. 25.5 AGB Nauen. 40.2 AGC Nauen. 70.5 NQG San Diego, Calif. 25.6 NKF Bellevue, D.C. 40.5 J IAA Iwatsuki, Japan. 70.54 WRP Pinecrest, Florida. 25.728 VIZ Melbourne (Beane Stn.). 41.5 OCBA Bamako, Sudan. WFV Poinciana, Florida. 25.906 GBH Grimsby (Beam Stn.). 41.6 NKF Bellevue. Anacostia. 70.74 WRB Miami, Florida. 26.0 AGA Nauen. 41.95 FEW Ste. Assise. 71.25 NKF Bellevue, Anacostia. VIS Sydney, N.S.W. 42.0 VIS Sydney, N.S.W. 74.0 WIR New Brunswick, N.J. 1VNU New Orleans, La. VIT Townsville, Queensland. 75.0 F 8GB Ste. Assise. 26.086 GBK Bodmin (Beam Stn.). 42.5 TFA Reykjavik, Iceland. WGN Rocky Point, N.Y. 26.269 CG Montreal (Beam Stn.). 42.98 WIZ New Brunswick, N.J. FL Eiffel Tower. 26.6 AGB Nauen. 43.0 NPG San Francisco, Calif. 80.0 NEL Lakehurst, N.J. 27.0 PCPP Kootwijk, Holland. JOC Oteh:shi, Japan. 83.0 RDW Moscow. RCRL Central Lab., Leningrad. 44.03 WAQ Newark, N.J. 84.0 NKF Bellevue, Anacostia. 27.5 PCMM Kootwijk, Holland. 44.5 SPI Rio de Janeiro. 90.0 KIO Kahuhu, Hawaii. 29.3 KEL Bolinas, Calif. 45.0 NPG San Francisco, Calif. 100.0 LT 2XI Schenectady, N.Y. A 16

www.americanradiohistory.com WIpisIlgoo JUNE 29th, 1927. WortIl

Building an Inexpensive Long =range Transmitter. By F. H. HAYNES. (2DY, 2DZ.) -HE increase in the numler of transmitting permits efficient. It is merely a matter of convenience of control during recent months reveals the growing interest that has led to the several circuit systems. stands in the rI in transmission. That thousands of amateurs are The part played by unwanted capacity on -short waves no limiting their activities to broadcast reception is way of using the same methods the ultra of loo metres and evidenced by the popularity of certain short -wave trans- as were adopted on wavelengths need for feeding the circuit missions. Much interest attaches to short -wave recep- upwards, emphasising the of radio - frequency poten- tion, Loth telephony and Morse signalling, and when a only through nodal points zero use of choke coils. working knowledge of the code has been acquired the tial and placing less reliance in the a arrange- amateur feels that the scope of his experimental work It should be the aim therefore to devise circuit depend for its correct operation upon can be greatly extended by the setting up of a small ment which does not owing to their self - transmitter. the performance of H.F. chokes, capacity, while the points of connection of the battery Starting in Amateur Transmission, leads can he conveniently adjusted so as to prevent The new field for experiment thus opened covers the stray earth capacities forming a path for radio- frequency study of fading, long- distance communication in rela- current.

r aerials and tion to wavelength and onditions, short -wave Modified Colpitts Circuit. directional effects, circuit systems for ultra- short waves, the tuned oscillatory circuit crystal control, as Nvell as methods of keying and modu- In the circuit diagram I,,, I, bridged lating, all of these considerations involving principles comprises the series connected inductances (grid poten- not to he found in the development of apparatus for by the series conneted condensers C,. (',. is reception purposes. tials are determined in respect to the filament which between the two condensers. The circuits in most general use to -dav for short -vv av c connected to the mid -peint potential passed to the work are modifications of the Colltitts oscillator. On The feed -Lack. radie- fro;acnry is increased, it hieing obvious the longer waves of 150 10 200 metres and .14o metres grid is increased when (', in value of used until recently by amateurs, Hartley and tuned grid that for a given wavelength an increase the he compensated for by a coil oscillating circuits were generally favoured. Funda- one of the condensers twist so the resultant mentally, all of the oscillating systems are similar inas- redo 'lion in the value of the other that much as the oscillating voltage at any moment applied capacity remains unaltered. condenser and choke the grid of the oscillating valve is of the opposite sign I'o dui id the need for Hocking to circuit, the that existing on the plate, while each of the circuits such as are commonly fitted in the Hartley to connection gives exactly similar performance and all are equally tuning inductance is divided and the battery A 17

www.americanradiohistory.com 818 WIp@Il®oo JUNE 29th, 1927. WWs Ill Transmitting on 45 Metres. - oscillatory circuit, but these made at only serve as a safeguard the nodal point of zero radio -frequency potential. until the correct adjustments of coils and condensers are The condenser which is interposed, C has little influence made. Obviously there is no difference of radio - frequency potential between the mid- points of the condensers and coils which are connected across by the keying lead between L.T. - and H.T. -, and the chokes shown become unnecessary when the best relative values of condensers and coils have been found. Other details of the circuit require little comment. The aerial load is critically adjusted by a variable coupling Lt, while the negative grid biassing potential is created by a resistance R. shunting a condenser C4. Constructional Hints. The few components required for this transmitter render construction easy. Building is simplified by mounting all components on a litseboard in preference to the use of a vertical front panel. The design is readily modified, however, and if desired the tuning condensers and filament rheostat can be carried by a panel without the need arising for any change in wiring layout. With the addition of the aerial ammeter and plate current niilliammeter Modified Colpitts transmitting circuit. The H.T. and L.T. to the upper part of well above batteries as well as the key are at zero radio -frequency potential the panel the condenser and changes of earth capacity do not affect the operation of the dials a more portable set canbe produced. circuit. I'he choke coils Lt and L3 are not required when the circuit is correctly adjusted. It is always the case when constructing a transmitting set that certain of the parts must be of new design and on the oscillation constants of the tuned circuit providing are not to be found among the. component apparatus on its capacity is large compared with the resi ltant capacity the market. In this instance the transmitting inductances, of the two series connected tuning condensers. It serves as a barrier to maintain the D.C. potential on the anode of the valve, and should therefore be capable of withstanding the H.T. voltage as well as being suitable for handling a. comparatively large high -frequency oscillating current at low potential. TAPPED 6 B A Nodal Points and Earth Capacity. 316 PITCH Assuming the correct adjustment of th. relative values of C, and C then the operation of the circuit will he un- influenced by the large earth capacity of the L.T. battery. Similarly no . difficulty will be experienced when the H.T. supply, which is always virtually earth connected, is joined to the mid- point of the tuning coil. Both sides of the bridging condenser Cn are at zero radio- frequency potential, as its capacity is large compared with the tuning capacities. It is this consideration with regard to the battery connections having no effect on the tuning of the circuit that so strongly recommends the THIN WOOD adoption of this circuit for transmission OR 3 PLY on wavelengths below Too metres, and no longer is it necessary to space the L.T. battery from earth or introduce an elaborate arrangement of H.F. chokes in the high- tension supply. Actually choke coils I,4, L,, are provided between the high- tension terminals and the Details for making and mounting the transmitting inductances. A 13

www.americanradiohistory.com WilmIlcvggi JUNE 291/i, 1927. WorIl0 819 Transmitting on 45 Metres. - brackets. Small pieces of angle brass or angles bent choke coils, and gril leak resistance are not standard. from strip secure the coils in position, and are fixed to The drawing of the coils shows the use of two ebonite the ebonite rings by 6 or 8BA screws and nuts. rings Ain. in thickness, supporting three gin. pieces of The choke coils are wound upon seven -peg formers, ebonite rnd. Small brass strews. such as 6 or SBA, lin. tied round with cotton, and then transferred to the ebonite bases with supporting pegs. As there is a differ- 1 ence of potential equal to the H.T. voltage between the two choke rails it is advisable to make use of the ebonite disc bases as shown in the sketch giving the constructional details. Almost any form of short -wave choke coils can

WOODEN PEGS 3/16 DIA X 13/4 LONG

EBONITE BASE 2 OA, XY4THICK.,

DIAMETER OF PEGS FOR. WINDING 13/8" Constructional data of the H.F. choke coll. be substituted, as these coils serve no useful purpose when the set is properly adjusted. Plan view showing the arrangement of the components. The The grid leak is wound upon a piece of ?in. ebonite by short direct leads. radio-frequency circuits are connected measuring Iin. x j in. It carries to slots 4in. wide by in length, secure the rods to the rings, and the turns of Ain. deep, into each of which are wound too turns (about wire are carried in slots. As the turns are spaced by an tz yards) of No. 44 D.S.C. " Eureka " wire. Before amount roughly equal to twice the diameter of the wire winding seven pieces of No. IS tinned wire are inserted (No. t4 S.W.I .), it is necessary to move the positions in pairs of holes, as shown in the diagram of the layout of the slots in the three rods by an amount equal to the thickness of the wire when passing from one rod to the next to allow for the spiral formation. After being straightened by stretching, the wire is wound tightly with turns touching upon a former about ?.in. smaller than the required coil diameter. The turns are lifte', into position and adjusted, thel ends being terminated by bends which grip the bars. All windings are, of course, in the same direction, the two outside coils (1.2, 1.3) being identical. The two ends of any coil ter- minate on the same crossbar, and reference should be made to the drawings showing the apparatus and wiring layouts The finished transmitter. The key may be connected by a flexible lead to the terminals provided, while no special precautions are necessary in regard to earth capacity created by the before fixing the supporting batteries. A 19

www.americanradiohistory.com WAlfigh00 820 JUNE 291Ií, 1927. InopIld Transmittinv on 45 Metres. - In this instance the condensers are supported on short of components to serve as terminal and tapping points. ebonite stems as usual, but are inverted, while the holes Whether or not the direction of the turns is reversed on are carried right through the dials, giving the arrange- passing from one section to another is unimportant, for ment shown in the illustration on page 822. Three the winding is certain to be inductive, and in other forms small holes are drilled in the normally top end -plate of of transmitting circuits the use of an inductive leak may each condenser and the ebonite supports are drilled for be necessary. The leak is mounted with screws and 6BA screws. spacers. All other details of construction, including the setting When a baseboard layout is adopted the mounting of up of the coils, are shown in the drawings. There is tuning condensers generally presents difficulty, particu- very little wiring, and convenient routes which may be larly as regards setting up the indicator for the scale. taken by the leads are indicated in the practical wiring diagram. Thin strips of copper foil connect the bridging condenser C3 with the coils, plaited 'braid connects the clips to the tuning condensers, and the condensers are bridged with three strands of No. 16 tinned copper soldered together. Both condenser spindles are at zero radio - frequency potential. 45 m. Aerial Dimensions. Before proceeding to test the set a few observations on aerial dimensions may be useful. Although harmonic and Hertz aerials are in common use for ultra -short wave transmissions, it will as a rule be found best to work the aerial near its fundamental. The aerial arrangeaient and dimensions should therefore be governed by the wavelength it is intended to use. This observation has no bearing, of course, upon aerial arrangements for short -wave reception. The relationship between the height of the typical amateur mast, the usual length of ground available at the back of the premises, and the height of the first floor window to 45 metres is a happy one. Thus the length of wire between the lead -in and the aerial insulator should be just less than a quarter of the wavelength, and the length required for 45 m. is therefore 36 feet. An exactly similar length is needed for the counterpoise, and should NIM1MI be measured off with care before erecting. The best wire to use is No. 12 S.W.G. Scale drawing showing the arrangement of the components on the board. copper. The aerial is excited A 20

www.americanradiohistory.com /UNE 29th, 1927. vArnIlmo S27 WoTilcl Transmitting on 45 Metres.- by means of the coupling coil thus connected at the exact centre. Sources of H.T. Supply. As an inexpensive transmitter and to suit the needs of the amateur who has not yet made provision for using supply mains as a source of H.T., it is pointed out that quite good work can be con - ducted with dry H.T. batteries of the " super - capacity " class giving 300 volts. The load taken from these batteries is no greater than that taken by the average power amplifier, and they are not, of course, in continuous use. This set has been tested with dry ccl k. using an L.S.5A valve, giving a feed current of 25 mA. Stations have been easily

worked in Central Europc . Northern Africa, and Pales- tine, the low- power input from dry cells giving a steady wave without involving keying difficulties. If higher power is used, such as rectified A.C. or direct current from an H.T. machine, a D.E.T.r valve may take the place of the L.S.5A. When D.C. mains of 220 -240 volts are available the best arrangement is undoubtedly to charge an H.T. accumulator of roo or more volts and discharge it in series with the supply voltage. Before attempting to bring the set into operation an absorption wavemeter, com- wiring diagra m. The filament wiring is arranged beneath the baseboard. prising coil, condenser, and Practical pea lamp, should be constructed. The calibration can inductance end of the coils. With the aerial coil dis- be checked by comparison with the receiving set when connected the tuning capacities are varied to give the tuned to the many transmissions indicating the 43 m. minimum feed current, an increase on one condenser being wavelength allocated to British amateurs. American compensated for by a reduction on the other when amateur stations work on wavelengths of 37. 5 m. and adjusted correctly for wavelength. The key terminals 42.8 m. are, of course, short -circuited while adjusting, and the grid leak resistance should be increased in value in the Adjusting the Transmitter. process of tuning. After connecting the aerial and A milliammeter with a scale reading of 5o or roo mA. counterpoise leads to include the entire aerial coil, further will be found helpful when making adjustments. It adjustment of the condensers is necessary, and it will should be connected in the H.T. positive lead and the be found that the maximum reading on the aerial ammeter 11 coil L, will serve to protect its winding from damage will be obtained on the correct wavelength providing that by high- frequency currents. Each of the tapping clips no error has been made. in measuring off the aerial should be connected at one turn down from the maximum wires 4 21

www.americanradiohistory.com 822 Wilmhog JUNE 291Iz, 1927. WoTIlcö1

LIST OF PARTS. Set of 3 transmitting inductances (Pero- Scott). 2 "Deckorem " dial indicators (A. F. Bulgin). 1 Baseboard, 18 x 12. 6 Ebonite shrouded terminals (Belling & Lee). I Fixed condenser, No. 620, 0.001 (Dubilier). oz. No. 47 " Eureka" wire. 1 Fixed condenser, No. 577, 0.001 (Dubilier). 2 oz. No. 26 D.C.C. for choke coils. 2 Variable condensers 0.00025, 8,1122 (Ormond). 2 Bases for choke coils (Pero- Scott). 1 Rheostat, 6 ohms (Ashley). I ft. Phosphor bronze strip, á "x No. 30 S.W.G. I Valve holder (Pye). In the " List of Parts " included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should be used in preference to others, these components are mentioned in the article itself. In all other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use.

A chéap aerial ammeter is connected in the lead to the counterpoise with a maximum scale reading of o.5 or even up to 2 amperes. The meter will have appreciable

Symmetrical arrangement of aerial and counterpoise for short wave transmission on the aerial fundamental. resistance, and should be short- circuited after everything has been adjusted. Method of mounting the tuning condensers so as to provide good It should be insulation and to permit of the condenser scales being read borne in mind that all the tuning adjust- against pointers on the baseboard. ments are more or less locked together, and a change at one point in the circuit may call for a compensating adjustment at another. A double -pole switch should be arranged to readily disconnect the H.T. supply so that a variety of adjustments can easily be carried out. Telephony Transmission. Remembering that the set is intended for use where a liberal H.T. supply is not available, grid modulation may be adopted if telephony transmission is required. The only merit of modulation in the grid circuit is, of course, economy in K y P H.T. supply, and a cir- ' cuit arrangement is given showing 0 the modulator + LT. -o valve functioning as a variable grid leak. The battery used to supply Gltcult of grid modulated transmitter with two -way switch for telegraphy or telephony transmission. filament current to the A 22

www.americanradiohistory.com JUNE 29th, 1927. 823

Transmitting on 45 Metres. - modulating valve must be well insulated from earth, and its capacity should be as small as practicable. Although excellent results have been obtained with grid control, choke modulation is to be preferred, and may be introduced by inserting in the H.T. supply an iron -core choke coil of liberal current -carrying capacity and an inductance value exceeding zo henries such as a secondary winding of a small H.T. transformer. The plate of the modulating valve is connected to H.T. positive, the filament is connected in parallel with the oscillator valve and between the grid and filament is the secondary of the microphone transformer with grid biassing battery. Performance. As an indication of the range which can he expected from this transmitter, it may be mentioned that working from station 5YZ telegraphy communi-

cation has been established with the following : -- British, GI6MU, GISZY, 6PU, 6HZ, and.32 others; French, SJZ and to others; German, S stations; Italian, iCW, Tripoli; while speech has been exchanged with 6PU, 5DC, GTÔ\IU. 6JK, CISZY, and 42 others, using a Mullard 0-20 valve as the oscillator and an H.T. potential of 25o volts derived from wet cells. These stations have reported very Compact transmitting set (5YZ) employing the circuit system described with the addition of grid modulation. A switch is favourably on the quality of telephony w hen using the introduced for changing over from telegraphy to telephony as grid method of modulation. shown in the diagram on the previous page.

WEARITE PLUG AND JACK. NEW FEATURE OF THE SIEMENS To avoid the use of an " on and off " GRID BATTERY. switch a plug and jack loud- speaker or NEW telephone connector is now commonly To avoid the difficulty of fitting up some employed in which contacts are provided form of mounting for the grid battery for closing the filament circuit when the such as metal clips or strips of wood with plug is inserted. APPARATUS. screws, Siemens Bros., Ltd., of Woolwich, A new jack of this type is among the have introduced a very simple form of recent products of Wright and Weaire, fix Ltd., 740, High Road, Tottenham, future, Siemens grid batteries will be London, N., and differs from the usual provided with a cardboard cover over the miffing of the use of the auxiliary con- sockets. On breaking the seal the card- tacts in a high- frequency circuit if desired, while the contour of the insulating piece gives a good snap action. The frame of the jack is of nickel - plated angle brass, and the plug is fitted with a turned ebonite mount with simple provision for connecting the loud- speaker or telephone leads.

C C C O

T.C.C. CONDENSER MODIFICATION. The Telegraph Condenser Co., Ltd., Wales Farm Road, North Acton, London, W.3, will in future supply a small bracket with their fixed capacity condenser to permit of them being mounted horizon- Siemens grid batteries are now fitted tally. Sometimes when building a re- with a flap for use in securing the battery ceiver it is inconvenient to stand the H.T. to the inside of the cabinet. bridging condenser vertically, and by means of the new strapping piece the con- board piece is folded back, and, by means Wearite loud- speaker Jack. The local cir- denser can be turned on its side and of two brass eyelets, the battery can be cuit contacts are insulated by an ebonite screwed to panel, baseboard, or on one of readily attached to the interior of the of thickness. spacer liberal the inside wails of the cabinet. The wireless set cabinet with a pair of screws form in that an ebonite face spring is straps vary in size according to the thick- or more simply by drawing pills. With used for making connection with the addi- ness and capacity of the condenser, and this easy attachment the battery hangs tional- contact. By this means a liberal are finished with green enamel similar to securely in position and fits flat against thickness of insulation is obtained, per- the cases of T.C.C. condensers. the wall of the cabinet. A 23

www.americanradiohistory.com Wilpghoo S21 JUNE 29111, 1927 WosIlco1

Events of the Week in Brief Review.

FIGHTING THE HOWLER. DEARER LICENCES IN GERMANY. An anti -oscillation league has been .tlany protests are being made in Ger- formed at Southend. many at the decision of the Postmaster - 0000 General to raise the wireless licence fee NEXT SATURDAY AT HENDON. from two to three marks a month. 0 0 0 0 Wireless telephony will play a leading STILL GOING STRONG. TRANSATLANTIC TELEPHONY pant at next Saturday's R.A.F. display at " This noted pianist has just completed QUESTIONS. Hendon Aerodrome. The aerial to his drill centenary for the B.B.C. " -Wireless An average of three broadcast music will provide the principal Paper. calls per day from novelty. this country is being maintained 'on the He must have many quaint recollec- Transatlantic Telephony service to 0 o O 0 tions of broadcasting in pre-Victorian America, according a days. to statement in the REGULAR WIRELESS PICTURE 0000 House. of Commons last week by the SERVICE. Postmaster- General. From the American AUTUMN WIRELESS SHOW IN PARIS. A regular service of wireless picture side there is a daily average of four calls. A hiti,m transmission will be inaugurated between Faris wireless erl is to be Asked whether there liad not been a held in the Berlin and Vienna on Friday next. July Grand Palais from October very considerable loss on the service, the 28th to November 13th inclusive, under 1st. The . Telefunken-liarolus- Postmaster- General said, No, the work- Siemens the system w-il1 be used. auspices of the Syndicat Professionel ing expenses are covered." des Industries Radio Electriques. 0 0 0 0 0000 0000 EIFFEL TOWER WIRELESS FATALITY. IN THE " WILD AND WOOLLY." INTERNATIONAL RADIO TELEGRAPH At a joint conference of Australian wool A young wireless engineer, M. Jean CONFERENCE. Herr, was accidentally growers and wool workers at Adelaide a killed at the Eiffel Tuesday, October 4th, has been fixed Tower broadcasting station early last as resolution was passed urging the estab- the opening date of the International lishment of wireless stations and aerial week. M. Herr had just switched on the Radio Telegraph Conference transmitting current when at Washing- services to link up isolated parts of the he carne in ton. continent. contact with a lead carrying 10,000 volts and was killed instantly. 0000 MODESTY UNVEILED.

. The use ,of - indoor aerials failed to secure the privacy- sought -for by three Dublin wireless " pirates " who. with twenty -four others, were fined in the Dublin District Court last week for con - travening the Wireless Telegraphy Act, 1926. In one case the fine amounted to £5. 0000 FREQUENCY FEVER. Apropos the proposal of the B.B.C. to talk in kilocycles instead of wavelengths, it is interesting to note that the sanie step has been insisted upon by the Ameri- can Federal Radio Commission. The U.S. newspapers have been diligently engaged in defining " the new radio ter- minology."

o o O O FISHING FLEET WIRELESS. Wireless telephone apparatus is being carried on Hull trawlers which are now proceeding to Greenland to explore new fishing grounds. Successful telephony- tests have been conducted between two of the vessels, one lying off Grimsby and one AMATEURS AND THE ECLIPSE. To ensure accurate observation during the in St. Andrew's Dock, Hull. Solar Eclipse the Incorporated Radio Society of Great Britain calibrated the apparatus The apparatus will permit of closer used by members by means of the wavemeter shown above. This instrument, which touch between the vessels of the fleet fur was designed and constructed by members, was calibrated at the National Physical Laboratory and is probably the most accurate instrument in the possession of any the purpose of discovering the most suit- radio society. Note the Weston thermo- coupled galvanometer, the plate milliameter able fishing grounds. and filament voltmeter. A 24

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Wflp@ll@go JL-.VE 29tIa, 1927. %nOlI ild, SOUTH AFRICAN BEAM TESTS. CLYDE LIGHTHOUSE WIRELESS. TRANSMITTERS' NOTES At the time of going to Press it is The Cumbrae and Toward lighthouses understood that the Post Office tests with ni the Clyde have established wireless AND QUERIES. the new beam service to South Africa iiterc-i)tiliisiiil nut un for the purpose ut have been highly successful. facilitating shipping reports and giving The R.S.G.B. Wavemeter. directions during fogs. On the oink ,-;itc page appears a photo- 0 0 0 0 0000 graph of the wateuteter used by the In- PCJJ ENCIRCLING THE EARTH ? corporated 11.S.Cl.Il. for calil,ratiug the WIRELESS BOOMING IN TURKEY. wavemeters and other apparatus used by On Thursday last, June 23rd., PCJJ, members during the eclipse. is, per - the pro- A sudden and remarkable interest in It Eindhoven, was heard relaying wireless haps, one of the finest instruments of its grammes of Daventry, Langenberg, and is being evinced in Turkey, where the number of listeners during the kind in existence. It was designed and Radio Paris. ,,u,structed by members of the Society interesting announcement was past year has increased front a few indi- The viduals nd calibrated at the National Physical made that many listeners to PCJJ had re- to gnaw thousands. According to a wireless dealers Laboratory. ported an echo effect. No echo was pre- Tins:: correspondent, in ('oitstatit,pople themselves 'l'Ire wavemetet, It-hit-It is "crystal sent in the studio, said the announcer, are finding unable to cope with the demand for radio checked" to cassure high accuracy, tunes and it was thought that the effect night to exceedingly high frequencies. The signals were material. be due to the fact that the valve is an 1..S.5 with a plate voltage of travelling once or twice round the earth. The only broadcasting station -" Radio St;unbul," Osmanií, gives a daily pru- 200 volts. 0 0 0 0 granmte on 1,200 metres, consisting of Oriental and Occidental music in judi- Fey over a year 2XAF has broadcast cious proportions. time signals the times a week to Mr. Because of their prohibitive cost wire- F.-G. Smith, who was in unexplored parts less sets are not vet within the reach of of Brazil, and it is expected that these all, but hotels, restaurants, caf(ts, chem- ists. barkers' shops and the like have installed loud -speaker sets. The annual receiving licence (for ordinary listeners) costs about 30s.

WIRELESS AT WESTMINSTER.

By OUR l'Atil.l.Anie.N'r.alty Coltrt ESN )N DENT. Post 'Office Advertisements. Rt. Iultil tsV1i Broadcasting Iu the House of Commons last week .> 'gt:;,.,r i,d,Pi N M ' Sir hurry Brittain asked the Postmaster- General whether, seeing that many facilities of the Post Office in the matter of telephone service, aerial mail, etc.. were A HANDSOME PRIZE. The R.C. Three- not fully known or by mem- some, with accessories, constructed by appreciated the Birmingham No. I Branch of the bers of the public, he would suggest that British Legion on behalf of the Children's the British Broadcasting ('orooration Outing Fund. occasionally made known these facilities for the financial benefit of his depart- R.S.Ç.B. SUMMER MEETING. ment and ut the public generally. An interesting fixture for August 1st Sir William Mitchell- Thomson said that (Bank Holiday Monday) is a " Conceit- services the telephone service and other A BIRMINGHAM STATION. G 2AK, tionette," in the foret of a lunch and tea conducted by the Post Office had been owned and operated by Mr. C. H. Young, and a visit to 5XX, to be held by the broadcast on a fete occasions as matters of at 52, Maidstone Road, Handsworth, of Radio Society showing the short -wave transmitter and Mid- Britain section the general public interest; but he did not receiver. of Great Britain, consider that it would be advisable to use Any member of the Society, and the broadcasting service regularly as an will have proved of great assistance in friends, will be welcomed to the " C'on- advertising medium for Post Office the preparation of accurate maps. The yentionette," tickets for which (5s.' per facilities. explorer is now on his way back to the head, inclusive) are obtainable 'front Mr. 0000 United States, and it will be interesting G. A. Jeapes ((l2 YET), " C'llandos," to learn how these signals were received Great Shelford, Cambs. Applications Telephone Wires and Aerials. by hint. 11th. should be made not later than July Mr. Hove- Belisha enquired whether it 0 0 0 0 The rendezous for the " Conventionette " was the intention of the G.P.O. to issue New Call-signs and Stations Identified. will be the Cock Hotel, Kingsthorpe, instructions that, wherever possible, tele- 2C% J. D. Chisholm, 27, Gresham R'l., S.W.9; Northampton. phone wires should not be run across, transmits on 40 and 180 metres and will 0000 welcome reports. either abut e or below, wireless receiving 230 J. L. Summertìeld, " Poldhu," 2a, Salisbury AUSTRALIAN WIRELESS PATENT aerials. Rd., Seven líings, Esses. (Change of CHALLENGE. Sir William Mitchell- Thomson said that a(ldress.) 5PR H. farter, 141, Waterloo Rd., Wolver- Several large firms in Australia have there was already . standing instruction hampton. challenged and have refused to pay the which provided for tlte altetation of tele- 5QP (ex z BPP) J. V. Parsons, Holland House, Rd., C'oldtìeld, Birming- patent royalties charged by Amalgamated phone wires on ì- rivate property which in- Holland Sutton ham. Transmits on 8, 23, and 45 metres. Wireless (Australasia), Ltd. (says Ti" terfered wit-lt wireless reception, and he 6PB H. Berry, 156, Lea Rd., Wolverhampton. Times). Giving evidence before the did unt consider that further instructions GW 16B H. J. Duncan, 2, Albert Rd., Sandycove, Co. on mem- Dublin. (Change of address.) Royal Commission on Wireless June were ne'ess;uy. If the hu:,nurable Dufferin Ave., South of would furnish hint with GW 16C G. Horander, 44, 15th, Mr. Fisk, the managing director ber particulars Circular Rd., Dublin ; transmits on 45 the company, declared that the company of any case in which reception was haut- metres and will welcome reports. spent on patents and re- he would he happy to see what GW 17C J. B. & R. D. Scott, 9, Upper Garvillc Ave., had £200,000 peted Rathgar, Dublin. search and had only received £76,000 steps could be taken to remedy twitters 2AWJ P. Lacon, 19, Merridale Lane, Wolverhampton from royalties. without ineurting undue expense 2BQK J. M. Wilkie 102, Stanley St., Aberdeen. A 25

www.americanradiohistory.com ..K- -.. a * a6Pk:03kp . 41-?-,7101,"

WßpCIl@gg 826 JUrVE 29111, 7927 WoTIlcal xperimenters oteb o ok.

Interference in Wireless By "EMPIRICIST." Reception.

IT may safely be said that there is no o will receive also a small band of wavelengths on problem in connection with wireless re- either side of this, we know that it must also ceiver design more important than that of receive just that band of elementary wavelengths eliminating interference. In these days, when it is a which form part of the whole spectrum corresponding matter of no difficulty to attain any degree of sensi- to any atmospheric impulse, and that therefore some tivity that is required, it may well appear as if the effect must necessarily be produced in the receiver by owner of a really powerful seven- or eight -valve set the latter. should be able to receive any station at will ; actually The narrower we make the hand of wavelengths which those who have used even the best instruments of this is efficiently received, the less will be the effect of the kind very soon discover that the basis on which one must atmospheric, hut, on the other hand, curtailment of this consider the problem of what is, and what is not, ,pos- hand to too great an extent will result in distortion in sible bears little relation to the potentialities of the re- telephony, or even in the wave -form of Morse signals. ceiver, but is rather settled automatically by the relation There is thus a limitation to what can be done by simple between the strength of signal to that of interference. tuning, and it is one which is very soon encountered by In saying, therefore, that the problem of eliminating anybody who attempts to design a receiver which is to interference is of such great importance, we do so with operate an automatic recorder from high -speed Morse. a slightly pessimistic tone; there is so much interference, Serious atmospheric disturbance is far more of a and has been so much since wireless telegraphy was first problem on very long waves than on the short ones, and invented, and so very little of it has ever been really this is one of the contributory reasons for the extra- eliminated. ordinary success which has attended recent developments Atmospherics. in short -wave reception. Therefore, in considering estab- Let us first consider the large class of interference lishing communication between two points, one would which originates at some source of electrical disturbance. naturally give a lot of thought to the selection of the In this we include both natural sources, such as those right wavelength for the purpose, but such considerations electrical discharges which are held to be the origin of are not very helpful when it is a matter of receiving to atmospherics, and also artificial sources which occasion the best advantage a transmission which already exists. so much trouble to the users of sensitive receivers in Electrical Machinery. town areas. Elimination of atmospherics in telephony is very much Coming next to the sources of disturbance which are more difficult than in telegraphy, and the latter problem, artificial in origin, we are on ground which is in a certain in spite of numberless attempts, has not yet been solved. degree more hopeful, seeing that, to some extent at any Engineers are slowly coming to the conclusion that there rate, the sources themselves are capable of being con- is really no satisfactory means for cutting out atmo- trolled. The nature of the interference consists in spherics, simply by virtue of the fact that they must general of impulses of arbitrary wave -form which are necessarily partake of the same nature as a signal which just as difficult to get rid of by tuning as are atmo- is being received, whatever be the character of the latter. spherics. A helpful means of visualising the problem is afforded The sources which are troublesome are most diverse in by the conception of an impulse, such as an atmospheric, their nature, and, peculiarly enough, those which at first as consisting of a " spectrum " of continuous waves, sight appear highly trivial are often the worst in actual spread all over the whole band of wavelengths. Any practice. Within the writer's experience the most per- impulse, of whatever wave -form, can be resolved into nicious of all is a fan motor, though there is no doubt such a spectrum, and the distribution of the various that other small motors of kindred type would be equally component waves which form this spectrum will vary troublesome'; fan motors, for some reason or other, according to the nature of the atmospheric impulse which appear to have a greater tendency to sparking at their is being received. commutators ; at any rate, one fan motor in a building If, therefore, we arrange that our receiver is tuned -in can most certainly " poison " the latter quite effectively to a certain wavelength and thus, by implication, that it as far as long- distance reception is concerned. A 26

www.americanradiohistory.com VApeno 827 JUNE 29111, 1927. Wolflll The Experimenter's Notebook. - purpose of telegraphy or telephony, are designed to oper- Another troublesome source, apart from the large class ate on a very restricted band of wavelengths, and, in of motors with sparking commutators, which are always consequence, if reception is not desired on the particular a plague to wireless, is afforded by telephone systems. band on which the interference occurs, there is every hope Interference of this character is very bad sometimes when of being able to " tune out " the undesired station. there is a branch exchange in the neighbourhood of the In considering this question it is, of course, of great receiver, as the insertion and removal of the plugs and importance to know the difference in strength between ringing of the various bells seem to make a great deal the station which it is desired to receive and that of the of disturbance. It is not absolutely clear what the exact interfering source. For instance, we may have a receiver nature of the trouble is, and, fortunately, it does not which will cut out a station separated 5 metres from the seem to afflict the user of a wireless receiver who has wavelength of the desired station, provided the signal an ordinary telephone line connected to his house. It strengths of the two are equal. If, however, the un- is, however, as well to arrange that the receiver is as desired station turns out to be within a radius of 5 miles, far as possible from the telephone and that the aerial whereas the desired station is at a distance of zoo miles, does not run parallel to the telephone wires. the case is very different, though the problem is by no The cure of motor disturbances can be undertaken to means insoluble. a certain extent, but with somewhat varying fortune. Not There are two main lines of attack in respect of the infrequently a pair of condensers connected in series elimination of a powerful near -by station. First, we across the brushes of a motor or dynamo, and having may sharpen up the tuning of the receiver itself until the centre point connected to earth, will produce a great it selects the desired band of wavelengths and rigorously improvement in the interference; such an arrangement excludes all others, or, secondly, we may employ a re- is shown in the circuit diagram. ceiver of average good selectivity and use in association Reverting once more to the receiver itself, the only with a device which will cut out the particular band of really hopeful method of minimising interference of an wavelengths on which the undesired station is operating. impulsive character is based on the directional properties Devices of the latter type have been frequently described of various aerials, of which, of course, the simple frame in the technical press under the name of wave -traps or aerial is the best known. Statistically, one would expect rejector circuits. frame aerial which is non -receptive in two direc- that a Supersonic versus Neutrodyne. tions in the horizontal plane would, on an average, pick When radical improvements are desired in the selectivity of a receiver one is led almost inevitably to supersonic heterodyne methods, but a receiver built on this principle lays itself open to special kinds of interference from which other types are immune. First there is the well -known fact that a " super " will accept two bands of wavelengths separated by equal frequency intervals from the wavelength of the heterodyne oscillator ; interference of this type has been described as " second TO FRAME OF on account of the two channels of MACHINE channel interference " wavelength to which the instrument responds. Secondly, 2 mfds - a highly sensitive ampli- OR MORE owing to the instrument having fier operating on a relatively long wavelength, it is peculiarly liable to pick up interference on stations which operate on this wavelength ; for obvious reasons this is Interference from a dynamo or motor can often be cured by connecting Large condensers in serles across the brushes and generally known as " intermediate frequency inter- earthing the mid -point to the frame of the machine. ference." up less atmospheric disturbance of the type which origin- The design of a supersonic heterodyne receiver so as ates at a distance. Furthermore, any specific source of to avoid, in the greatest measure possible, the disadvan- interference can be cut out, or very greatly reduced in tages which tend to be present is a matter of the greatest intensity, provided its direction is not the same as that interest and importance, and, subject to success in this of the station which it is desired to receive. A combina- respect, which in the writer's opinion is obtainable in a tion of a frame and open aerial will enable a station to very large degree, the results obtained are amazingly be received at optimum strength when it is in a direction good. 180° apart from a source of interference which is simul- When the question of selectivity is not of such extreme taneously cut out. This corresponds to the well- known importance, there is no doubt that " straight circuit " re- " heart -shape " diagram of reception. ceivers embodying any of the well -known methods of neutralisation offer many advantages over the average Interference from Other Stations. supersonic heterodyne instrument, and there seem to be Coming next to the question of the interference, occa- immense potentialities in the direction of combining such sioned by other wireless stations, we are confronted by a receiver with a device which selectively rejects any un- in a problem at once more complicated and more hopeful wanted powerful station. The only real disadvantage of solution than that of atmospherics and impulsive inter- connection with such receivers appears to lie in the diffi- ference in general. Wireless stations, whether for the culty of obtaining really adequate strength of reception A 27

www.americanradiohistory.com 828 Wgp@Il@g0 MAC]. YUNE 29th, 1927. The Experimenter's Notebook. - leak is short- circuited. The easiest way of checking this when using a frame aerial. This precludes the use of defect is replacement by another leak, which offers no directional methods of reception, which are of such great difficulties, owing to the readiness importance with which these com- in connection with eliminating interference of ponents can be removed from their clips. all kinds. In some cases it is difficult to say whether interference A word should be said on the subject of interference originates within the receiver or outside it. There is a from spark stations. The transmissions from the latter general tendency for distant telephony stations to be are of peculiar character, inasmuch as they tend to accompanied by extraneous noises of ill- defined character spread over a band of wavelengths, and will thus have popularly known by the suggestive name an impulsive of " mush." effect upon a receiver similar to that of an The difficulty lies in the fact that this interference be- atmospheric, even though there may be a wide separation comes apparent only when the receiver is tuned -in to the between the nominal wavelength of the transmission and carrier wave of a broadcasting station, and as a result it that to which the receiver is tuned. Interference of this is not easy to settle the origin of the trouble. class is very troublesome on the coast when it is desired A few pointers may not be out of place indicating to in receive broadcasting stations inland. Here the how a problem of this kind may be attacked. " heart -shape diagram " yielded by the combination of a frame aerial and an open aerial is of the greatest service, Locating Mush. inasmuch as it enables the receiver, as it were, to " turn First, it is worth checking that the mush does not its back " upon the sea and receive only from inland. originate in the microphone of the transmitting station; this can be ascertained by making a careful Set Noises. observation when the station starts up, and comparing the noise with The last class of interference with which it is pro- that which occurs when the microphone is switched on. posed to deal consists in that which originates within the There is almost invariably a difference, and in some cases receiver itself, or the apparatus connected to it. This is a serious additional noise has been perceived. Secondly, almost invariably due to some definite trouble such as a or as an alternative to the former, the set may be dis- bad contact, a faulty component, or a defective high - connected from its aerial and a local oscillator set up so tension battery. Bad contacts need not receive any special as to imitate the carrier wave from consideration the distant station. here, as they are usually readily traceable If the mush originates within the receiver it and can, of will " come course, be easily put right. In the matter up " when the set is tuned -in to the local oscillator, of faulty components and the most frequent offenders are low - a comparison between the conditions when the local oscil- frequency transformers and grid leaks; the former have lator is used and when the set is receiving normally will a regrettable tendency towards a breakdown in their give a good indication of the true state of affairs. A primary winding, occasioned by corrosion, and during method of this kind is of great value in improving the their last few hours of life this results in the production design of supersonic receivers. of most alarming crackles, which start usually after the Lastly, it is worth noting that a set which receives a receiver has been turned on for a few minutes. This wide band of wavelengths is more liable to certain fault can identified a be as occurring within the receiver type of mush than one which is very sharply tuned. Here by short- circuiting the grid of the detector valve to the we are in a difficulty, as some of the interference may be filament, the noise originating in a transformer persisting external in origin and occur on frequencies which are under these conditions. Trouble from a defective H.T. desirable for the true reproduction of battery the sibilants in occasions interference of much the same character, speech. Under these conditions, owing to the prevalence and the only satisfactory way of distinguishing between of external interference, a sacrifice of theoretically correct the two is by interchanging components and batteries. quality by sharpening up tuning may result in more A defective grid leak will give rise occasionally to pleasing reception, particularly in the case of certain crackles of a character, but more similar usually results musical items in which the very high harmonics are not in the production of a hiss which disappears when the of such great importance.

Walker Bros., Ltd., St. Joseph's Works, The Wet H.T. Battery Co., 12, Brown - Brantley, Guildford. Illustrated price list low Street, High of W.B. " All -Wood " Loud- speakers and BOOKS Holborn, London, Hórns. AND W.C.1. Booklet relating to " Standard " 0 0 0 0 Wet H.T Batteries, including price list CATALOGUES and full particulars, instructions for use Weston Electrical Instrument Co., Ltd., and working 15, Gt. Saffron Hill, London, E.C.1. hints. Leaflet illustrating and describing Weston RECEIVED. 0000 pin jack and panel voltmeters. 0000 " Les Lampes ìb Plusieurs laectrodes et leurs Applications en Radiotechnique," Ruubaken Magneto Company, Tipping " Le Poste de L'Amateur de T.S.F." by J. Groszlcowski. Street, Ardwick, - Translated from Manchester. Pamphlet New and revised edition, by P. Hémar- Polish into French by G. Teyssier, (illustrated) dealing with the Raubaken dinquer. with a A simple textbook for the preface by René Me.sny. A treatise on Radio charges for H.T. and L.T. Batteries. amateur, describing and 0000 explaining the the theory and practice of two -, three -, functions of aerials, crystal receivers, and four -electrode Graham Amplion, valves employed as de- Ltd., 25, Savile Row, valve receivers, amplifiers, typical circuits, tectors, amplifiers or generators, with London, ßi'.1. Catalogue of Amplion cone loud- speakers, recording instruments, bat- notes on typical valve speakers; also catalogues Amplion circuits. pp. 348, of horn teries, etc. pp. 328, with 347 illustrations with 207 illustrations and diagrams. Pub- speakers and gramophone attachments and diagrams. Published by Etienne lished by Etienne Chiron, Paris, price 40 respectively. Chiron, Paris, price 20 francs. francs.

A 28

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By H. B. DENT. For Use on all `l'have= Between 14 and station to enable those more distant, lengths but closely related in wavelength, to 200 Metres. be received. It will have been noticed that the rejector circuit had to be tuned to a definite wavelength for ex- signal, and THI? wide publicity recently tinction of the unwanted accorded the short wave that this tuning was sharply defined. transmissions has led to a Now, if facilities had been available of this circuit, the considerable increase in the for the calibration have noticed that the number of experimenters explor- reader would when the " rejec- ing this interesting waveband. It is quickly realised, how- greatest diminution in signals uc .erred as that of the ever, that reception on 3o metres is a vastly different pro- tor " was tuned to the same wavelength be seen that this simple position from that on 300 metres, and owing to the very unwanted station, it will therefore a wavemeter. For high frequency the short wave represents, careful design piece of apparatus actually constitutes and ease of operation an ab- the receiving equipment becomes necessary. The tuning simplicity of construction of if we couple must have a small maximum capacity, with the sorption wavemeter is perhaps unrivalled, and condensers of accuracy sufficiently high for the result that only a limited waveband can be covered with with this a standard needs of the average short -wave listener we have an instru- any one coil. Apart from this, the very few stations having occupy the place of honour second only regular schedules of transmission adds considerably to the ment which should to of receiver. difficulty of determining the tuning capabilities of the that the these con- receiver. Searching for 2XAF or KDKA under The Circuit. is like looking for the proverbial needle in a hay- ditions columns and many weary hours have to be spent " knob The circuit of the wavemeter described in these stack, a coil, a variety of coils before results are forth- is given in Fig. r, and from this it will be seen that twiddling " with lamp This waste of time, labour, and a variable condenser, and a small coming. necessary components. The mental fatigue could be obviated if a reli- comprise the lamp is included so that the instrument can able short -wave measuring instrument was The reference to a wavemeter be employed for wavelength measurements available. as re- conjures tip visions of an in- of short -wave transmitters as well immediately omitted if the embodying a valve with its accom- ceivers ; hown'er, this can be strument only for reception panying high- and low- tension batteries, or wavemeter is required alternatively one employing a buzzer and purposes. assembly of the wavemeter dry cell. It might be advisable to mention The actual a matter, but the calibration at this stage that a buzzer wavemeter is as parts is simple instrument presents certain good as useless on the very short waves, of the completed obstacles unless access can be gained to one owing to the " flatness " of the wave gene- Fig. 1. The circuit diagram. from a standard. To rated, with the result that accurate readings previously calibrated This, however, does not constitute the overcome this apparent difficulty, a Cyldon 0.0003 mfd. are impossible. for " alpha and omega " of wavemeters, and those function- logarithmic condenser is employed, and the reason when the instruc- ing on the absorption principle have not in the past been -this will he more readily appreciated which is their due. tions for calibrating the wavemeter are read. given that consideration his heart The reader has no doubt occasionally made use of a The experimenter always has a warm corner in in the rejector circuit for the elimination of the local broadcasting for anything constructed with his own hands, but A 29

www.americanradiohistory.com Wp®llimo N3o 'JUNE 291h, 1927. - WopN1 Absorption Wavemeter.- preceding chapters reference has been made to " simplicity D C B A of construction," and to justify the use of this expression 180- 68- Igranic short -wave coils are employed in this instrument. 66 25 170- 64- Three of these are required, one 4-turn coil, one 6 -turn 62 24 ' coil, one No. I.25 XLLOS coil, and a Gambrell " A " 160- 60- coil (new series), these together covering the wavelengths 58 23 r4 metres to 200 metres. 150- 56 N It has been previously mentioned that a small lamp w 54 22 140- 52- A B, I is included in the circuit for the purpose of measuring Ñ the W wavelength of a short -wave transmitter, but the photo- 50 21 graph 200-130- 4$- of the instrument clearly indicates that two such ? 46 20 lamps are employed. Actually, one only is " live," 190-120- 44 namely that occupying H 42- 19 the top right -hand corner of the c instrument ; the Z 180- 110- 40- other is a spare to be taken out and in- D serted in the " live " holder should at any time the original J 38 18 w 170-100- 36- occupier endeavour to rival the performance of a 6o -watt < o lamp. ' 34 17 This departure to the land of the setting sun may 3 180- 90- 32- be brought about by inadvertently coupling the wavemeter 30 16 too tightly to the transmitter, and every amateur who 150- 80- 28- oscillates violently with P.M.G.'s permission knows to his 26 15 chagrin that when this happens a spare lamp is difficult 70- 24- to find. The holders employed are flush panel 22 14 mounting 60- 20- type, made by Messrs. the Grafton Electric Co. The lamps used should have a small current consumption, and 0 20 40 60 80 100 120 140 160 180 in this instrument 3 -volt o.r5 amp. flashlamp bulbs have CONDENSER DEGREES been used. Fig. 3. -The Calibration chart. To obtain a pleasing appearance of the completed instrument a slight departure is made- from standard practice, and sawing through. to the top edge of the opposite side. and a sloping cabinet is employed. This may be home - When the case was obtained the base overlapped the sides constructed if desired, but in the model described a 6ín. x by ¡in. all round, and to enable the case to be used on its 6in. x 4in. deep case was obtained from Messrs. Carring- side this overlap was trimmed off, after which the entire ton Manufacturing Co., Ltd., and modified in the follow- base was removed. These alterations naturally left ing manner. First, a wedge- shaped portion was cut scratches on the polished surface, and accordingly the back away by measuring down one side to a depth of tin. was temporarily fixed in position by four screws and the case rubbed down with fine glass paper. When all the polish had been removed the whole was given a thin coating of stain, and when this had a - 2V4 dried coating of car riage varnish was applied. Whether the cabinet is entirely home constructed or a modification made to a commercial article must be left to the tests and capabilities of the reader, so we will now turn our attention to the front panel. This should be cut from iin. ebonite, and if the particulars given for the construction of the cabinet are faithfully followed the size of the panel required will he 6in. x 6Hin. The top and bottom edge's 1vill require chamfering to give a neat appearance to the finished instrument. This is then drilled for the mounting of a Cyl -- d,m o.0003 mfd. log -line condenser, a template for this purpose being supplied' with the carton. Two Ain. holes must now be drilled -one at the top right -hand corner and one at the left -hand corner, these being required for the purpose of mounting the lamp -holders, which are held in position by hexagonal nuts on the underside of the panel. The left -hand Fig. 2.- Details of the panel and cabinet. holder is to accommodate the spare lamp, A 30

www.americanradiohistory.com JUNE 29t11, 1927. Wflpecoo 831 WOyIlA Absorption Wavemeter,- care being taken to guard against any tendency to slip. and no connection will be required, but the other is in The back of the cabinet can now be fixed in position by circuit with the condenser and coil so that before assemb- four countersunk brass wood screws tin. long. ling this a loop of wire should be placed between the fixing nut and the panel, leaving a short length protrud- Advantages of Logarithmic Condensers. ing to act as a soldering tag. Before assembling the The actual construction of a wavemeter embodying condenser and lamp- holders it will be necessary to drill either S.L.F. or S.L. condensers does not present many four holes to take the wood screws which hold the panel difficulties, but an impassé is invariably reached when in position and scribe a line midway between the two lin. attention is turned to the calibration. When a logarith- holes. This line can be filled in with some suitable white material, such as plaster of Paris or white paint, and is intended as an indicator for positioning the dial. Should any difficulty be experienced in following the above. a reference to Fig. 2 will enable these instructions to be more easily followed. The panel can now be fixed on the front of the cabinet, using four ¡in. countersunk brass wood screws, and the few necessary wires soldered in position. One wire should be taken from the condenser to the centre contact of the " live " lamp - holder and one from the end of the wire loop under the lamp-

' holder fixing nut, through the hole

- in the cabinet, to the coil plug. A third lead is now Fig. 4. The logarithmic scale of wavelenths. taken from the remaining coil plug soldering tag and through mie condenser' is employed the usual difficulties encoun- the case to the remaining contact of the variable tered in obtaining a true calibration immediately dis- condenser. The two wires which pass through the holes appear for the reason that the required wavelengths can in the wooden case should be covered with sistoflex or be engraved on the dial. These will be correct irrespec- other suitable insulating material. It is advisable to fix tive of the coil used, provided, of course, these wave- the dial on the spindle before screwing home the back of lengths are within the tuning capabilities of the coil. It the cabinet so that the moving plates can be correctly will be seen, therefore, that any slight discrepancy in the positioned. When these are fully interleaved with the inductance of commercially made coils will not affect the fixed plates, the r8o° mark on the dial should be upper- calibration of the instrument for the reason that this can most-that is to say, the same position as the figure 12 be compensated for by adjustment of the dial. on a clock face, The dial must now be securely fixed to ' See " The Logarithmic Condenser," by F. H. Haynes, the condenser spindle by means of the fixing screw, The -Wireless World, May 18th, 1927. A 31

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LIST OF PARTS. I Cyldon 0.0003 mfds. variable condenser. I Igranic short -wave coil (4 turns). i Wooden case, 6 x 6 x 41 in. deep (Carrington Manufacturing 1 Igranic short -wave coil (6 turns). Co., Ltd.). 1 Igranic XLLOS No. L25 coil. 2 'Lamp holders, 11a21 (Grafton Electric Co., Ltd.). I " Mandem " 4in. dial (McLeod & McLeod). 2 Small bulbs, clear, 54'87 (Grafton Electric Co., Ltd.). I Ebonite panel, 6 ¡x 6x +in. thick. 1 C9i1 plug (Wright & Weaíre, Ltd.). i Gambrel " A" coil (new series). In the " List of Parts " included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should be used in preference to others, these components are mentioned in the article itself. In all other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use.

Calibrating the Wavemeter. coil. The 6 -turn coil should now replace the 4 -turn Before proceeding with the calibration, the logarithmic and the alcove procedure repeated ; however, in this case scale (Fig. 4) should he either cut out by following the the line scribed will be marked " B." Before consider- dotted line, or a very careful tracing taken. The con- ing the calibration of the next range it will be necessary denser dial must now he removed and this scale placed to have available a " check " signal on a higher wave- over the spindle, after which the dial can be replaced, length, and the 4th harmonic of 2I.0 can he advantage- leaving sufficient clearance between it and the panel for ously employed ; this is to be found a little over go metres the easy rotation of the scale. The scale would have and is receivable at fair strength. greater rigidity and be more robust if, before assembling The Igranic XLI.OS coil No. T.25 must be inserted in on the condenser spindle, it was glued to thin cardboard the wavemeter, and having correctly tuned or " rejected " or a piece of celluloid cut to the same diameter. To this station a line should be scribed in accordance with accurately calibrate the wavemeter it will be necessary to the instructions previously given. The tuning curve for time in on the receiver a station whose wavelength is this coil is marked " C " in Fig. 3. With these three known, and with an Igranic short -wave coil No. 4 in the coils the instrument covers all wavelengths from 14 metres wavemeter loosely couple this to the receiver inductance. to aSo metres, but if desired this range can be extended The wavemeter should then be tuned to the setting where to considerably over 200 metres by the use of a Gambrell the signals are rejected, and the coupling loosened to the " A " coil (new series). The tuning curve correspond- point where the rejector tuning is sharply defined. ing to the wavelengths covered by this coil is marked T.et it be assumed that the " check " station received " D " on the chart. If the wavemeter has been con- is 2NAD (22.02 metres), then by rotating the log scale structed strictly in accordance with the instructions given, until 22.02 coincides with the 18o° mark on the bakelite then the curves in Fig. 3 will he sufficiently accurate for dial the wavelengths covered by this coil can be read off employment as a guide to readers whose short -wave re- the log scale by using the r8o° line as the pointer. The ceivers are tuning to some unknown wavelength. It is log scale must remain stationary during this process, and strongly urged, however, that when the receiver has been to facilitate the correct positioning for all future occasions brought to heel and is functioning on the desired wave- a line must he scribed on the panel opposite the " arrow " lengths, no time should be lost in correcting the wave- on the log scale. The scribed line should then he marked meter by check readings on known stations and using the " A," which represent the 4 -turn Igranic short -wave logarithmic scale.

Darimont and General Radio. Receiver Cabinets. An agreement concluded on June 8th Owing to the expansion of their busi- between Darimont. Electric Batteries, TRADE NOTES. ness, Messrs. W. E. Manson, Ltd., makers Ltd., and General Radio Co., Ltd., places of scientific instrument cases, have been the sole and exclusive manufacturing and compelled to remove to more _extensive selling rights relating to Darimont Patents premises, their address now being Windus on electric primary, cells, appliances and Valve as Golf Ball ? Works, Windus Road, Stamford Hill, N.16. , accessories in the hands of General Radio The astonishing robustness of a Dlul- The new works are fully equipped with Co., Ltd., who will hereafter produce lard valve picked up from the sea at Hoy - the latest types of machinery, special the well known Darimoht Batteries and lake is commented upon in a letter which facilities being available for the develop- charges, etc. 0000 the Mollard Co. has received from Dlr. ment of the wireless cabinet section. W. S. Booth of Daresbury, nr. Warring- 0000 Cossor's Trade Monthly. ton. " It may interest you to know," The Igranic Neutrosonic Seven. " Does the Impedance Matter? " is an says the writer, " that I have in my pos- " The Giant Stride " is the title of a important question dealt with in a novel session one of your bright emitter valves new publication of the Igranic Electric manner in the current issue of Cossor's which was recently salved from the sea Co., Ltd., dealing with the Igranic Neu - Radio .ifnil. The question is answered at Hoylake, and the surprising thing is trosonic Seven Receiver. The booklet in the course of an imaginary interview it still functions although the bulb is a contains useful information for the ordin- between a salesman, and his customer. little loose, no doubt, owing to the ary purchaser regarding the general prin- The Radio Mail contains several other thorough soaking it had got.'' On test- ciples of this receiver together with a features of special interest to wireless ing the valve the' Dfullard Co. have found technical description and illustrations of dealers. It is published by A. C. Cossor, that the emission was only slightly under the set in various types of cabinet. Neu - Ltd., Ifighbury Grove, N.5. that of a new specimen. trosonic accessories are also described. A 32

www.americanradiohistory.com WIT@ IlgtO JUNE 2913, 1927. 833 Woo lfîl oC1

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! -. , 1 uiiiu, , n Correspondent. News from All Quarters : By Our Special Dominion Short -wave Programme. -Alternative Programmes in August. -B.B.C.'s Director- General.-Listening Post for Brussels. -" S.B." by Wireless Link. -Poor Sets in Schools. a may cover a multitude of sins. It is This has not yet exceeded 10 kW., Empire Broadcasting. which power which, in the light of the present towards the quite possible that the five stations The first serious step will ultimately comprise the regional tests, appears to be inadequate. realisation of Empire broadcasting not include the present ex- 0000 Britain, but from one scheme may comes, not from perimental station. and the Post Office. of the Dominions. 0000 Daventry July 1st, when The new equipment at Daventry pro- On Friday next, The Power Question. celebrates the Jubilee of Federa- vides for a power of at least 20 kW., Canada or rather frequency, to know tion, an effort will be made to broadcast The wavelength, and it would be interesting is still unsettled. During the is work to to other parts of the Empire the speeches of 5GB exactly what. influence at -General and Prime past few weeks the engineers have been prevent 5GB from operating at its maxi- by the Governor advantage of silent periods to Minister. The transmission will be made taking mum efficiency. Marconi beam utilise the wavelengths of many of the The last word in matters concerning from the high -power wireless station at Drummondville, Quebec, on the licensing of experimental The B.B.C. will endeavour stations lies, of course, with the Post 26.18 metres. Office giving 5GB to pick up the programme at Keston and Office. Is the Post while similar every opportunity to justify the hopes relay it to all stations, for the regional efforts will be made in South Africa, of those responsible other Dominions. scheme ? New Zealand, and0000 0000 The Time Table. Does 5GB Interfere ? a to inter- Nvi11 begin with a If 5GB exhibited tendency The broadcast the working of official and fifteen- minute inauguration programme at fere with Summer 'Finie), fol- commercial stations, the Post Office 5.15 p.m. (British offer objection to 8.30 p.m. (B.S.T.) by the cere- could, quite rightly, lowed at of a licence for the higher monial speeches. At 3.30 a.m. (B.S.T.) the granting power. But has 5GB interrupted any a three hours' national all -Canadian pro- ? Such news has yet to reach gramme will be broadcast. service will be provided me. And if 5GB on 10 kW. is per- A stand -by receiver not a possi- Company for use in the fectly innocuous, is there by the Marconi the same station might still be of failure being experienced at bility that event harmless on 20 kW. Keston. 0000 0000 Brightening the " Dog Days." The Ether Policeman. The introduction of regular pro- The desirability of establishing some grammes early in August from the sort of etheric policeman to keep a Daventry Experimental Station, 5GB, watchful eye on the wavelengths used should exercise a tonic effect on the by the European broadcasting stations broadcast ether. The " dog days " are has already been emphasised in The inclined to make their presence felt just Wireless World, and the decision to inas much in the broadcasting sphere as stitute such an authority was referred - in other directions, but the exciting pros- to in the issue of May 25th. pect of an alternative programme should I understand that this official listen- help to break the spell. ing post, which will be controlled by 0000 the Union Internationale de Radio - 5GB's Limitations. TRIALS 0V TILE BROADCAST LIS- phonie, is to be set up at Brussels. TENER. Two " Wireless World " readers 0000 It is extremely unlikely, I am afraid, photoy?raphed at a somewhat awkward) anything like a complete alternative moment. 'I-he wire halyard had slipped that The choice The Technical Hub. bill of fare will be provided this side of down the side of the pulley. as the of a suitable halyard and pulley when the While Geneva can be regarded . Christmas. The new station will not erected would have saved European broad- and aerial was administrative hub of start up at three in the afternoon tizne and trouble. Brussels can be looked upon as to give us " something dif- casting, gaily proceed without any de- the technical pivot. It was in this city, ferent " all the while until 11 p.m. The other B.B.C. stations, of M. result. under the careful supervision transmissions will remain for the time cisive the Geneva wavemeters experiment, The real mystery attaching to 5GB is Braillard, that being in the nature of an were calibrated. and the mere mention of " experiment " in connection with the power employed. A 33

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Wflp@hoo 834 JUNE 29111, 1927. WaeIlcd A Wavemeter Tragedy. Programmes in Strips. July 4th, 5th, and 6th and during the Mention of these wavemeters reminds A handy type of wireless programme afternoons at times when no interference me that several of the instruments dis- guide is being issued by the American will be caused to any important trans- tributed to the European stations in Westinghouse Company, which controls missions from the studio. In the case of November have already shown signs of KDKA and 'other broadcasting stations. the Eton v. Harrow match the comment- falling from grace. At one station, It takes the form of a perforated sheet ary will take place between 2.30 and which shall be nameless, the engineer - in which a strip is devoted to the pro- 5.15 p.m. on July 9th. in- charge protested loudly against the grammes for each day of the week. 0000 charge that he was " off " his correct As each day's programmes are com- Your Turn Next ? wavelength. According to his Geneva pleted, a strip is torn off, and the wavemeter he was An SOS message of a new sort is " dead on," and in being out the politest manner possible he sug- sent every Friday night from FUTURE the New York broadcasting station, gested that not he, but his accusers, were FEATURES. WOKO. " off." London. It consists of the names of heirs to unclaimed estates ; consequently Finally, the wavemeter was sent to JULY 3nn.- Albert Sandler and this weekly Brussels, where it was found to have the Grand Hotel, Eastbourne, item comes in for a good deal of attention front optimistic strayed from the paths of virtue to the Orchestra. listeners. extent of several metres. JULY 4TH. -" Abraham Lincoln," a 0000 play Among the missing heirs announced by John Drinkwater. on the first Prince 5TH. night, says The Manchester Henry to Broadcast. JULY -Mass in B minor. Part Guardian, was Prince II. Bach. Relayed from York the son of a German im- Henry's speech at the opening migrant who died in New of the new Leas Cliff Pavilion, Minster. York in 1880 and left an estate then valued at nearly Folkestone, on July 13 will be relayed to JULY 7TH: -Wireless Military Band £2,000. and Another heir who is missing 2L0 and 5XX. Vocalists. could claim an 0000 Jt-LY 9TH.-Concert Party from estate0000 worth £100,000. To- night's Variety. Folkestone. Birmingham. When the Anchor's Weighed. Donald Calthrop is appearing before Newcastle the microphone JULY 4TH. -Eye- witness account of listeners will hear a novel this evening (Wednesday) programme on July 9th, in a sketch entitled " Archie and the County Cricket Match -War- when the wick v. Hants. pleasure cruiser, Stella Polaris, leaves the Lawyer," by R. Guy -Reeve. Variety Tyne for turns included JULY 8TH. -" Royal Quixotes the Norwegian fjords. Micro- in the same evening's pro- phones will be placed gramme are by the Ramblers, Wish Concert Party. on board prior to Bournemouth. the sailing of the ship, and a commentator Wynne, the Musical Avalos, and Charles will hold the Heslop and JULY 7TH. -Light Concert of the captain of the vessel and Cyril Smith. A concertina other officials in conversation act will be given by Harry Morton. Moderns. on the o00o JULY 9TH.- A Saturday Soufflé. bridge. At the sane time the various sounds connected with the ship's A Gipsy Programme. Cardiff. parture, de- JULY 5TH. -A Request Programme. leave- takings, etc., will be ab- In memory of George Borrow, the gipsy sorbed by the microphone, writer, JULY 7TH. -" The Powdered and a short who immortalised the gipsies orchestral concert provided by the by such books Player " Concert Party. ship's as " Lavengro " and Manchester. orchestra will be broadcast from the " Romany Rye," a gipsy programme saloon. will JULY 7TH. -An evening at Black- be broadcast from Newcastle station on 0000 the 124th pool. " On with the Show of anniversary of the author's 1927." Inferior Sets in Schools. birth. July 5th next. Many 000o JULY öre. -" Sonia," a farcical factors go towards making or play by Victor Smythe. marring a broadcast lesson intended for Trouble with the Wireless Link. Newcastle. schools. Much depends Manchester on the subject listeners have been com- JULY 5TH. -A Gipsy Programme. chosen, and much depends upon the abili- plaining at the poor quality of the JULY 9TH. -Norwegian Programme. ties of the broadcast teacher. Daventry transmissions when relayed to Glasgow. Iu the opinion of that pioneer 2ZY via wireless. of school That the wireless link JULY 5Trr. -Mr. G. F. Luke on wireless, Mr. R. J. Hibberd, who writes is used for any inter -station communica- on Aviation. " Oscillations " : a the subject in The Teachers' World, tion may corne as a surprise to some radio revue. the reason why many readers. educational authori- JULY 7TH. -Offenbach Programme. ties have been reluctant to encourage wire- Certain provincial stations occasionally Aberdeen. less in schools is that they dispense with the have heard land line for their Juts 8TH. -Inverness Wool Fair school demonstrations where inferior morning transmissions, but the practice Concert. amplifiers and loud -speakers is not have been encouraged in official quarters. JULY 9TH. -Variety Programme. used The wireless relay may be very useful Belfast. 0000 for special running commentaries and JULY 7TH. -Military Band Pro- The Useless Lesson. other outside broadcasts, but it lacks the gramme. reliability The B.B.C. endorses this opinion while and freedom from interference JULY 9TH. -A Novelty Programme. acknowledging enjoyed by the land line. that the technique of wire- 0000 less teaching is still in an evolutionary state. Its Use in Emergency. listener avoids the embarrassing possi- " Unless reception In more is reasonably good,' than one emergency, when a bility of mistaking to- morrow's pro- writes an official of land line has suddenly the Corporation, " the failed, the use gramme for that of the day before wireless. lessons should be stopped, for the Of -the wireless link has saved the situa- yesterday. prejudice against tion. For this reason 0000 this form of teaching in- each of the B.B.C. duced in the young mind by a practically stations is equipped with a receiver Cricket Commentaries. which unintelligible lesson may do irreparable can be tuned into a distance trans- Running commentaries on the Gentle- harm." mission and connected up to the control men v. Players match on room. July 6th, and Few will quarrel with this statement of of the Surrey v. Lancashire ; Emergencies match on the case but the other factors are equally of this sort, however, are July 16th, will be relayed from Kenning- important. The clearest rare. The last occurred, reproduction will I believe, at ton Oval. Commentaries will also be not compensate for the waste of a pupil's Glasgow during the general strike. broadcast on the Oxford v. Cambridge in Usually when time laboriously listening to a broad- a land line fails the Post. and Eton v. Harrow matches at Lord's. cast lesson which could Office engineers can just have easily instantly resort to In the former case descriptive comments been delivered by the teacher in the class- an alternative line. are to be given in the mornings of room. A 34

www.americanradiohistory.com WAp®Il®03 835 JUNE 291h, 1927. Woplld

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. `^h^.-iS.':ì.,.5;^.,r.::`;:_ ,. w.ra ,,.e - claw does not hold himself responsible fir tile opinions of his coi respondents. be accompanied by the writers name and address. Correipondenae should be addressed to the Editor, " The Wireless World," Dorset House, Tudor street, E.C.4, and must simply general uplift; but all the busybodies feel that they EMPIRE BROADCASTING. listener, who to reach me really should do something for the poor, dear Sir, -In the most recent copies of your journal Now comes this last -wave broadcast only thinks he knows what he wants. I notice a growing demand for a British short proposition that an important function of all parts of the Empire. and most terrible transmission voiced from the B.B.C. is to cater, not for their own customers, subscribers I feel that we in the less accessible parts of the Empire politics, Imperial of broad- or financial supporters, but for Imperial would derive a greater benefit from reliable reception Imperial interests, Imperial commerce. In short, we in older Colonies. Our news is for the prestige, cast than those the -a paltry two and a quarter million people, paying for and most part three weeks old, and musical entertainment is con- value for our money-are The comparative unimportance of expecting reasonable entertainment fined to the gramophone. to uplift and inspire the rest of the universe; to fill the all - our appeal from the numerical point of view will surely be as a Prime Minister's voice per individual. pervading ether with such wonders balanced by the benefit at stake delivering messages of truth and majesty to .the inhabitants I have with me here a five -valve neutrodyne set (3 H.F.), Africa. reception of Bournemouth and of Australia and South with which I obtained fair For the moment we will agree with the Evening News what London up to the end of March. Since then, however, atmo- " it would be if one of our chief worse. At the present a really " wonderful thing spheric conditions have become steadily could be heard talking all over the Empire at once. time to put on the headphones is sheer pain fair imitation politicians -a We will even admit that it may cement the Empire more of 'a battle fitly describes the noise. closely ; that it may bring us more trade ; that it may make the I have with me also a two -valve Reinartz set with short- what fine fellows we are; and that, hear 2XAF on 32.77 metres rest of the world realise wave coils. With this set I can ultimately, it may bring us that universal freedom from wars on any Tuesday, Thursday, or Saturday -if I can keep awake broadcasting can accom- KDKA which we all so much desire. But, if long enough -at " phones on the table strength." miracles, then is it not time that the nation slightly from X's. plish all these suffers (and not merely its listening -in population) pulled itself to- I wish particularly to stress the point that the 32 -metre band own Empire Propaganda Broadcasting atmospheric disturbances in a gether, erected its suffers practically nothing from did its own duty, without expecting to get the locality where just now are about as violent as any in Station, and stcrms job done for nothing by the B.B.C. the world. (I have continued 'listening to 2XAF -at reduced only should be taxed, and suffer Further, on To suggest that licensees strength -during a storm, with aerial removed.) and voluntarily bore themselves, for the benefit this wavelength fading is very slight, and daylight seems to inconvenience, of the whole nation and Empire, is as ridiculous as suggesting have only a small effect on signal strength. entirely supported by the inhabitants beard PCJJ as that the Navy should be Last night-very near midsummer now -I towns. as ever about 6.30 p.m. i.e., broad day- of coastal strongly at G.M.T., Should the Board of Trade, or the Foreign Office, or the light in Holland. It is dark about 6 p.m. G.M.T. here. or the House of Commons wish I presume high -power stations are constructed with distance Admiralty, or the War Office, to give the world inspiring messages from time to time, to show as the object. Then why in the world are they fooling around and vigorously kicking, then want that the British nation is still alive with 50 kW. on 400 metres when we can hear all we and work their own station on its own particular a 32 metres, using only let them erect throughout the year of transmission on wavelength not unnecessarily interfere with the innocent a And with a set which costs -and fraction of the power? rereiving and healthy enjoyment of the people of these islands. After a fraction of that required to hear the 400 -metre transmission here do not want to be continually listening to a fraction of all, we over for the year only! our own backs being scratched. Now, then, England ! be more than two years behind Don't If it is simply a question of the rest of the world sitting the U.S.A. this time. G. A. MOUNTAIN, the programmes we want (and get) A.M. I.E.E. by its fire side enjoying Nigeria. ourselves, then the matter is easy of solution. Let the Govern- May 31st, 1927. ment relay from the B.B.C. and rebroadcast from its own 'ether- penetrating, high -power station, just those items which INTERNATIONAL ASPECTS OF BROADCASTING. it considers most desirable for foreigners to hear. The Govern- Sir, -Mr. G. Rolland Willans' article in The Wireless World ment (or a special authority acting on its behalf) could inter- of June 8th is a very fine example of the colossal amount of sperse items of its own, additional to the relays of such mun- loose thinking and talking that has been done almost ever since dane stuff as song and music. Incidentally, the nation should the first wireless licence was issued. Stripped of its high - pay the B.B.C. for any material so used from the latter's pro- reason why sounding phrases, the purport of the article is this : " Broad- grammes. This is common justice. There is no casting is of world -wide importance. As such, it is, therefore entertainments provided for a section of the community (and a national trust. But, do not expect the nation to pay for the definitely paid for by them) should be pirated by the nation administration of this trust. Instead of that, make merely as a whole for purposes of national or international benefit. -two- and -a- quarter millions of its population pay -and also suffer There is not only too great a tendency to regard the B.B.C. much inconvenience and boredom for the sake of the rest of as a national milch cow, but there is also a constant endeavour the Empire and the world." to bully or persuade it into performing specific work in which We are getting used to hearing, via the loud-speaker, nice the average listener is not interested. loud gentlemen -and, worse still, dear old ladies -with bees The broadcasting of those weighty and stereotyped utter- buzzing in their wireless bonnets, that we are apt to overlook ances by prominent politicians, for instance, is a novelty at the elementary justice of the axiom that the people who pay first, but the time will soon come when it will be a bore. the piper should be the people who call the tune. The licensee Most listeners who can understand German would far rather pays mainly for entertainment. He should get it. listen to an opera or a running commentary on a Rugger match The B.B.C. are besieged by clever people who know just in Berlin than they would listen to von Hindenburg explaining what we ought to have. It may be religious propaganda, or precisely how important was some particular theory or project high -brow music, or dry and dusty educational discourses, or of his own countrymen. A 35

www.americanradiohistory.com Wfipa@og S36 JUNE 2911:, 1927. WofIld It may be argued that licensees should be proud to support from 2L0 states that he most frequently listens to that station.. financially the performance of work of international import- May I suggest that care should be taken concerning those ance. Possibly; but they are merely taking on their shoulders listeners who, when asked to what station they generally listen, a responsibility which rightly belongs to the nation, or its will reply, " London," whereas really they are listening to the appointed representatives --the Government. Why should a London .programme through 5XX. I have often met listeners nation shirk such responsibilities and the expense they entail? who seem to be under the impression they are hearing the The B.B.C. is a monopoly which, unless we are very careful, London programme direct from London, whereas in reality will tend to degenerate into a hunting ground for cranks, up- they are hearing itkfrom Daventry. lifters, and No doubt this is due to bores. It is vital that listeners should never lose the announcement so often heard through 5XX-" London sight of the fact that it is they who pay the piper and they calling." GRAHAM HUNT. who should consequently call the tune. Torquay, June 9th, 1927. Let the cranks, uplifters, bores, nationalists, and inter- nationalists get together and formulate and broadcast their own programmes. But let them leave us alone. Then we shall SMALL LECLANCHE CELLS. all be happy. BERTRAM MUNN. Sir,-I imagine that your correspondent, Mr. R. S. Smetzer, Twickenham. has had but little experience with primary sal- ammoniac cells when he refers to the wet cell as having a greater output than MUSICAL INTERPRETATION IN THE CONTROL ROOM. a dry cell. Sir, -In connection with the establishment of the proposed If he is referring to ampere -hour capacity, this depends regional broadcasting scheme, there is one point I hope will largely on -the volume of zinc and the consistency of the electro- receive attention, and on which I believe all music- loving lis- lyte, and it is possible to put just as thick a zinc in one type teners would welcome information. as the other. One of the principal artistic defects of the present low -power But the dry cell, by virtue of its lower internal resistance, broadcasting system is the absence of what one might call a maintains a higher voltage on a given rate of discharge, and " volume datum." The searcher after good quality spends the watt -hour output (or B.T.U.'a) is therefore greater than much time and money in bringing his set to a high standard with a wet cell. of tonal reproduction and then finds that he is deprived of one If, on the other hand, Mr. Smetzer refers to rate of dis- of the essential requirements of satisfactory musical performance charge, the dry cell always has the advantage and comparative. by circumstances over which he has no control. I refer, of course, figures for internal resistance, for two cells approximately the to the control of modulation at the transmitter, which, in alter- same size can be represented by 0.4 ohm (wet) and 0.2 ohm ing the true relative loudness of the various musical passages, (dry) taken on an ohmic value of two. detracts from the enjoyment of items where great differences in I have yet to be convinced that wet cells are at all suitable, volume take place. This was very evident to me on a recent and my own experience is that, however well regurated a Sunday afternoon when the crescendos in Schubert's " Un- receiver may be, the H.T. currents are usually too heavy. finished " Symphony actually came through as diminuendos and Manchester, June 4th, 1927. M. E. HAYES. all sense of musical climax was entirely lost. Much of this control at the transmitter is obviously done for the benefit of the crystal user, but I hope that Sir, -We have read with interest the reply of Mr. M. E. under the new Hayes scheme a minimum field strength will be chosen so as to give to the letter of Mr. R. S. Smetzer, which you were every listener an adequate volume on the very soft passage kind enough to forward to us for comment. The contention whilst still keeping "hands off the controls" throughout musical that the capacity depends on the " volume of the zinc " is items. My view is that this will ultimately be the only satis- quite wrong. The output is proportional to the size of the factory state of affairs and that it is now time for the position depolariser and the quantity of oxygen it contains. When to be reviewed bearing in mind both the receiver and its dis- the whole of the oxygen in the depolariser is used up it is tance from the transmitter On the other hand, the listening necessary to have a new sac. Mr. Smetzer is quite correct public require to be educated to the fact that unless in saying that the output depends on the size of the depolariser. a receiver Again, is capable of handling an impressive volume, enjoyment of big we cannot agree that a dry cell has a lower internal orchestral works and the like is out of the question. May we resistance. On the contrary, the internal resistance of a dry also hope that receivers will ultimately be sold according to the cell is higher than that of a wet cell. Further, the output of power -handling capacity of the last valve and not merely labelled a wet cell is greater than that of a dry cell using the same "loud- speaker receiver " size of sac element. A simple proof of this can be established Some day, perhaps, we shall have much larger power valves, by obtaining a 9 -volt, 6 -cell grid bias battery and removing cheap in price, and, when the new Electricity Commission gives the sacs from three of the cells. Put these sacs in small us a uniform public supply we shall be able to feed them jars with a circular zinc, and use an electrolyte of zinc chloride cheaply without trouble and obtain a really adequate re- 2 oz., sal- ammoniac 3 oz., water i -pint. Connect the six production from a whisper to the full volume of an orchestra or cells in series and discharge through a resistance to give about organ without continual adjustment at the receiving end. This ten milliamps at the commencement of run. It will be found is a question which should engage the combined attention of that the wet cell has a very considerably increased output over musician, broadcaster, manufacturer and listener. the dry cell, taking the output either in ampere -hours or watt - hours. After all, what is the use of engaging a conductor of world- wide fame if the control engineer makes it impossible for his The remark also that the H.T. current may be too heavy for interpretation of the score to be transmitted ? a sac leclanche cell is incorrect. Take a super -het. receiver Lofthouse, June 11th, 1927. F. HARTLEY. requiring 35 milliamps ; it is quite possible to make a sac leclanche cell that will run for twelve months without renew- ing the elements. are DAVENTRY AND SPARK We now making a sac leclanche cell that INTERFERENCE. will be suitable for L.T., and will last twelve months without Sir, -I note in the issue of your valuable paper for June 8th attention. two paragraphs upon which I should like to comment. If Mr. Hayes would like to have any technical data on wet Your note on page 734 as to spark interference on 5XX sug- batteries we shall be pleased to supply it. The facts regarding gests that this interference is due to ships, but I am informed Standard Wet H.T. batteries can be briefly stated as follows :- by an expert telegraphist who has made notes upon this trans- (1) By reason of the improved electro- chemical action which mission that it is due to a high -power spark land station at takes place in a fluid to that which takes place in a paste or Madrid. This interference frequently occurs between 9.45 and jelly the output of a wet battery of equal size sac element 10.30 p.m., and is extremely irritating, as it often spoils the is increased by at least 50 per cent. best part of a good programme. There has also of late been (2) The containing jar, tray, and rubber insulating bands are an almost continuous undercurrent of what appears to be the permanent. Only sacs, zincs and electrolyte are consumable. harmonic of a high- powered arc station. No need to throw away a battery with half its material still My second comment is on the report, on page 733, that, in unused. Couple this with the increased output, and you see reply to the B.B.C. referendum, a listener living 300 miles the obvious economy.

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www.americanradiohistory.com V/Ip®ll®Em 637 JUNE 29th, 1927. WoreIlcal Would it not have been better to give the call -sign of the (3) The cells of a Standard Sac Leclanche battery are always do not leak. Consequently the causes of offending station? fluid, and the jars in this country and U.S.A., has done a noises practically always experienced when a dry 'The amateur, bcth crackling amount of pioneer work using high frequencies, and battery is becoming exhausted do not arise. The Standard Sac considerable free from extraneous noises is to a large degree responsible for their use in the long- distance Leclanche battery gives a current enjoys. the whole life of the elements. transmission your correspondent throughout ? am it is not M. E. WATES. Why send out a general complaint I sure (The Wet H.T. Battery Co.) justified. Mr. Willings refers to I must confess - London, W.C.1, June 9th, 1927. The " hoary joke " I am inclined to think, after years of listening to U.S.A. broadcasting on short and medium wave, has quite a lot of truth AMATEUR SHORT -WAVE TRANSMISSIONS. in it Sir, -As an amateur transmitter, I write to take exception Can your correspondent get consistently good -quality music to the remarks of your correspondent, Mr. John Willings, in or speech from American S.W. stations ? I have received excel- The Wireless World for June 8th. Li the first place, it is lent results sometimes, but to say such transmissions are reliable extremely unlikely that the interference complained of on is another matter. 2XAF emanated from an amateur station. There are few The B.B.C. engineers are not ignorant of the possibilities of stations in England operating on that wave, and at the time such frequencies, and I believe programmes will be available 2XAF is audible they would certainly not be louder than 111, in the near future from this country using short waves for their if that, owing to skip distance effects. There are no Ameri- propagation. There is a considerable amount of experimental cans licensed for that wave, and Australians and New Zea- work yet to be done before short waves are a certain means of landers, who are the principal occupiers of that band, are not long- distance broadcasting, and I suggest that amateur trans heard till much later in the morning. It is far more likely mitters be helped, not hindered, in this field. that the interference was caused by one of the numerous com- Allow the B.B.C. engineers time to complete their experi- there, who operate without, seemingly, mental work on these high frequencies. It is better than erect- mercial stations down something any pause day or night, and who never sign any call. ing a 100-kilowatt 20-metre station only to find that that amateurs should keep off the better could have been done a month or so after. Mr. Willings' suggestion system air after B.B.C. hours -for that is what his remarks re mono- We have something to be proud of in our broadcasting poly imply -is at least very unfair. British amateurs keep off when compared with that of the U.S.A. hours purely from a sense of sportsman - Melton Mowbray. C. R. CHADFIELD the air during B.B.C. (G6 AS) ship and fair play, not because they have to. How, then, are June 10th, 1927. they going to do any work if they must give up non- B.B.C. hours? And is it reasonable to expect them to do so? K. E. B. JAY SMALL ADVERTISEMENTS. Amersham, wonder if you would care to mention the following June 16th, 1927. (G2HJ). Sir, -I points in The Wireless World for the guidance of small adver- comments, so detrimental to the tisers? Sir,-I regret reading such Goods should not be sent on unsolicited approval. Recently a " brass -pomading " fraternity, as recently suggested by your me that he had received no less think I am correct in stat- despairing advertiser informed correspondent Mr. John Willings. I copies of a particular number of a periodica4 for which (in this country) are at present than 50 ing that the 32 -metre permits he advertised. only issued to a few transmitting members of the R.S.G.B., through the post the stamps are well -known In forwarding fragile articles " Special Research Section." These members a " tie -án " label, not on the package itself. a wavemeter, and should be placed on amateur research workers, each must possess a valve which only just escaped being is above the average. I have just received their knowledge of transmitting apparatus smashed to smithereens by the lilow from the stamp obliterator. had to listen for a -solid half -hour to raises a curious As your correspondent not A correspondent, Mr. Shaul], of Brixton, " blibetty blah," otherwise Morse telegraphy, why did he refers to the good will existing among adver- the offending station? If point when he give in his letter the call -sign of tisers in your colemns. He is quite right. There is never any he can only read " blibetty blah " (letter V ?), then why suggest have any qualms about sending cash at all? I know quibble, and no 'one need that the Morse was from an amateur station on apl -rcval to your readers. This is a very pleasant to stray unintentionally or goods it is an easy matter for a transmitter state of affairs, and I hope it may long continue. from his licensed wave. If this had so happened with the H. BRAITHWAITE. a better policy on the Southbourne. offending station, would it not have been June 18th, 1927. part of Mr. Willings (if lie reads Morse ?) to have notified the station concerned, thereby keeping the said station " off the grass " for future uninterrupted programmes? Evidently ULTRA-VIOLET RAYS. DX to your correspondent, nor is he a " DX- Sir, -in amongst your readers who have heard me NU 2XAF is not -Listeners may hound." I would now like to know what a " DX -hound " really speak at one time or another about the value of sunlight is? Is it not a general tendency on the part of B.C.L.'s to label be interested in a novel and arresting piece of independent every scrap of Morse interference they receive as originating testimony. It has just come to me from Kew. stations, mostly without justification on their part? Some weeks ago two boxes,' each containing six lettuce, were from amateur the other Your correspondent may or may not be aware that amateur sown on .the sane day, one beneath ordinary glass, to mention three more countries-Australia. beneath the special glass which admits the sun's ultra-violet- transmitters, just manner, New Zealand, and South Africa -use the 32 -metre waveband. A rays. They have been tended in exactly the same tuned to a wavelength near 32.77 metres, and situated and they have been plucked on the same day and weighed. transmitter weeks in any of these countries, could be " brought in " by the carrier And with what result? The weight at the end of six ; of the six wave of NU 2XAF. Why accuse only the " brass- pounders " of the six grown under ordinary glass was 82 lb. in this country? grown under vitaglass 9; lb. -that is to say, the ultra- violet I suggest that Mr. Willings might be a little more considerate rays, and any others of value which vitaglass may transmit, transmitter; try and help him, not throw un- have added 1* lb. to the weight of six lettuce in six weeks. to the amateur shade of necessary criticism about because he may not read Morse or Under them their grew up much sturdier, of a deeper the difficulties the transmitter has to contend with green, and with bigger hearts. understand to in his research. J. O. J. HUDSON 'The authorities, very naturally, are now proceeding test other plants of economic and dietetic value on the same lines. London, N.18. not June 17th, 1927. I for one should be very much surprised if the results do give added proof of the value of ultra- violet rays in the cultiv.- and children. Sir, -I read with interest Mr. John Willings' letter in your tion of plants as of animals very old experimenter I consider his London, N.W.6. C. W. SALEEBY. June 8th issue. As a M.D., F.Z.S., F.R.S -. remarks rather hasty. June 18th, 1927.

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www.americanradiohistory.com Wpsiligmg 838 Walla JUNE 2gtII, 1927.

The following abstracts are prepared, with the permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Palen! Office, 25, Southampton Buildings, London, W.C.2, price is. each.

A Multiple Tuner. are connected together, while the inner at 3 and earthed through a blocking con- (No. 254,338.) ends are brought out for connection to denser K,. The anode circuit is tuned some circuit. - ob- Contention date The same method of con by a condenser K2, while reaction is (France): .lime 29th, struction may 4 1925. also be employed for coup- tained by means of a grid. coil coupled ling inductances together, or for to the section 2 of the anode inductances. .Au arrangement of tuning induct- transformers The illustration shows two ances for long and short wavelengths inductances coupled together according to 0000 forms the subject of a patent granted to the invention, while a wavemeter circuit Compagnie pour la Fabrication des Comp- employing this type of coil is also ind= teurs et Material d'Usines à Gaz. The cated. The first inductance consists of A Low Voltage Amplifier. invention relates to an arrangement of two portions A and B, wound on an in- (No. 267,198.) long- and short -wave tuning coils so that sulating former F. The extremities of December 3rd, 1925, the short -wave sections are not appreci- these windings are X, Application dates: connected at while 4th, 1926. ably influenced by the long -wave sections. the adjacent ends P and Q are brought and January The short -wave tuning coils shown in the out for connection purposes. An insulat- A. H. Midgley- describes in the above accompanying diagram are divided into ing layer L is placed over the two wind- British patent a form of amplifier which two equal portions A and B connected in ings A and B, while another similar works at a very low high- tension voltage. of a inductance consisting of two portions C The invention either makes use and D is wound upon it, the whole being special valve with two sets of electrodes connected to a framework R. An induct- or two ordinary valves. The accompany- of ance of this type is also shown connected ing diagram shows one arrangement the circuit in which the ordinary aerial tuning circuit L, C, is connected to the first grid and filament G, F,. The anode A, is connected through a resistance R to a low voltage obtained by means of a potentiometer P working in conjunction with a filament battery B,. The anode A, is connected directly to the grid G, of the second valve or set of electrodes. The

Multiple tuner circuit. No 254,338.) series and spaced some distance apart. The two sections A and B are so arranged that the directions of the windings are opposite. The longer wave coil C is connected electrically in series with the two portions A and B and is placed between them in the manner indicated. The aerial tuning condenser is shown at K and the aerial and earth terminals at X and Y, while a multiple switch S is used to connect the varions portions of the tuning coil in circuit. The specification states that the effect of the coil A upon C will be equal and opposite to the effect of the Dual valve for tow-voltage amplification. coil B upon C, and, therefore, since the (No. 267,198.) two coils A and B constitute' the short- wave portions, the long -wave portion will have no appreciable effect. second anode A, is connected in the ordinary manner through telephones T to a 0000 normal high -tension battery. B,. The value of the resistance R may be between Inductance Construction. a half and two megohms, while the posi- given to the anode A, and (No. 267,196.) wavemeter coil construction tive potential (No. 267,196.) grid G, through this resistance may be Application date: November 30th, 1925. of the order of three or four volts. It A particular form of inductance con- to a wavemeter, the advantag of the is also mentioned that the value of the may, be increased to five meg- struction suitable, for example, for wave - system lying in the fact that the earth or resistance meters, is described in the above British filament connection to the inductances ohms, in which case the voltage should patent by I. E. Edgeworth. The inven- renders the system less liable to the in- he increased to about forty. Another tion consists in making the inductance in fluence of capacity effects. The outer feature of the circuit is the connection of in series. two portions, the extremities of which ends of the anode coils 1 and 2 are joined the two filaments F, and F, A 38

Converting a D.C. Battery Eliminator. ready made. The names of manufac- Detector Bias. turers of small power transformers can be I should be obliged if you would clear up My high -tension is at present drawn from obtained by reference to the miscellaneous but I mn a misunderstanding regarding the a D.C. battery elimi:,.ator, advertisement columns at the end of this " Everyman Four" set. On page 29 now informed that very shortly a journal. made. of the booklet describing this instru- change over to A.C. will be With reference to Fig. 1 it will unnecessary ment it is stated " If 2 -volt valves Not wishing to incur be noticed that the filament winding on is necessary to remove a new unit, I are used it expense in purchasing the transformer has a centre tap, this the resistors R, and R, and to propose to convert my present elim- two being necessary to locate the " electrical the wires, etc. . On page inator into one capable of being used -join centre" of the rectifying valve filament 31 it says " As the Cossor 0.1 R.C. is on an A.C. supply. Unfortunately, from which the H.T. is taken. In cases 2 valve taking 0.1 amp. the my knowledge on this subject is very a -volt where this winding has no centre tap, resistors R, and R can be of 15 and be, obliged if limited, and I should the desired effect can be obtained by con- ohms respectively." These state- you me with a circuit 30 would supply necting a potentiometer of about 400 ments seem to be contradictory. diagram showing the necessary altera- ohms across the valve filaments and tak- D. N. tion. ing the H.T. lead from the slider. misunderstanding D. H. W. supply We think that this The fuses shown in the mains will be cleared up when we say that the not be a difficult matter to con- leads to the primary winding are not M applies only when It will advisable. statement on page vert your D.C. battery eliminator for use essential but are nevertheless a 2 -volt detector is used in conjunction load is on an A.C. supply, actually this can be as they will blow if an excessive with 6 -volt valves elsewhere. It refers accomplished by the construction of an imposed on the circuit, due to a short - back to the preceding paragraph, in which unit which can be attached to circuit of either of the secondary windings. of 2- and 6 -volt valves is additional is a combination your present eliminator. You will re- Unless a safety device of this nature suggested. When using 2 -volt valves quire a special rectifying valve and a incorporated, damage may result to the throughout, it is no longer possible to take grid bias from the drop in voltage across one of the resistors, and for further information on this subject you are referred to a reply given to another reader o in our issue of April 13th. SWITCH D.C. BATTER) ELIMINATOR 0 0 0 0

MAINS -O o Below the Broadcast Wavelengths. SUPPLY INPUT / am thinking of constructing a receiver o for covering the band of wavelengths SWITCH + below 200 metres as far as 90 metres, and am intending to use a stabilised i5 type of plug -in roil. Could you tell me what you consider the best circuit for my needs? P. S. R. In our opinion the best circuit to con- circumstances is a detec- an A.C. rectifier. struct under the Fig. 1. -Using a D.C. eliminator as a smoothing unit after tor and L.F. We should advise that the transformer having a primary winding primary, or excessive heat be generated, aerial be coupled to the grid tuning coil of aperiodic coupling wound and secondary windings for the high - which will " char " the insulation of the by means tension and filament heating. The con- coils. This will bring about short - over the grid coil, or by an auto -tapped transformer circuited turns and various complications grid coil, which are, as you may be struction of a suitable power to is not recommended unless the home con- will arise, the least serious of which aware, upon the market. With regard structor is experienced in the making would be an unnecessarily heavy con- reaction, we think that one of the usual of such components, and we think you sumption of current in the primary wind- merhoda of capacity control of magnetic would be well advised to purchase one ing. reaction may be suitable. . A 39

www.americanradiohistory.com Wpds@o 840 JUNE 29111, 1927. W0rR.al Black or Blue? aerial -grid transformer of the " Every- a similar value of grid bias, although one 1 am a new reader, and notice in your man -Four " receiver if you are going to amplifies and the other rectifies. This is journal reference to a receiver confine your work to the 200- to 600 -metre arranged for in the construction of the named the "All-Ware" Four. Can waveband. On the long wavelengths, valves, as the negative potential on the you supply me with a blue print of however, it will be desirable to use the grid of the H.F. valve will bring the this circuit? P. T. ordinary system of loose coupling with operating point on to the straight part of This receiver was described, with full plug -in coils, the aerial coil being tuned the operating curve, whilst in the case of constructional details, practical and theo- by the condenser shown in dotted lines the rectifier valve it will bring the work- retical wiring diagrams published, and as in the case of the " All -Wave Four." ing point on the bottom bend. Grid bias dimensional drawings of panel and base- The intervalve transformer preceding the in the case of the second H.F. valve is board, etc., in our issue dated April 27th, detector valve may consist of the " Every- arranged for by the potential drop across 1927, which may still be obtained from man Four " or the " All -Wave Four." the filaments, which are in series, the the publishing department at a cost of types of intervalve transformer, except valve being so constructed that this auto- 4d., post free. The practical wiring that no neutralising winding will be matically puts the correct bias on the plans, etc., are printed in black and needed as the set will be automatically grid. Similarly, in the case of the first white, as is our custom, and not in blue stabilised, due to the fact that the L.F. valve, the valve is so arranged that and white, although naturally this has sequence of tuned grid and plate circuits the correct bias is put on the grid when no effect on their efficacy. is broken by the interposed resistance- it is joined to L.T. -. The filaments of

`.I / 2mfds 10.0003 c`T 1=; mfd 0'0003 mfd

00005

ó /S2

1 mfd

O 0 O o _ O 0 i.B.+ H.T t+ H..1: H.T.- + +L.T- H.T.3 H.T.4+ G.8.2

Fig. 2. -A practical arrangement making use of Loewe multiple valves.

Multiple Valves. coupling. Thus we have a tuned input cir- the detector and two L.F. valves are, it I hare o1,tain, d two of the Loewe multiple cuit followed lty a stage of resistance will be noticed, connected in a series - valves, one marked H.F. and the coupling, and then we follow on again parallel arrangement. other N.F., and desire if possible to with another tuned circuit uniting the use then. with H.R. transformers of second H.F. valve with the detector. 0000 the " Everyman" type, and also wish The L.F. choke in the output stage may to run my loud- speaker from a choke be of the usual type advocated for this Hand Capacity. filter circuit. D. G-. purpose, and a fixed condenser may be I am using a straightforward two -valve

These two valves consist of a complete connected across the loud - speaker in the det. -L.F. receiver and get good re- high- frequency amplifier enclosed in a usual manner if it is so desired. sults from the local atation, but if glass bulb, the H.F. bulb containing two By connecting the aerial and earth an attempt is made to true in distant complete four -electrode valves coupled to system to the points which we show in transmissions, hand- capacity effects each other by means of resistance dotted lines, nu will be able to use at once become troublesome, and in coupling. The terms H.F. stand actually the detector and two L.F. valves on the fact; to receive any other station is for the German words Hoclr. Frequenz, local or Daventry stations with good an extremely difficult natter. Will and the symbols N.F. of the other effect. In the case of the local station, you please gire nue your adrice as to instrument stand for the German words the grid coil, of course, will be a No. 50, how matters may be improved? Nieder l'rcgnen:. The N.F. instru- and in the case of Daventry a No. 200, G. E. H. ments contain an anode bend detector depending on aerial capacity. etc. It should We think it probable that you are using followed by two resistance -coupled L.F. be pointed out also that if using plug - one of the more modern tuning con- st ages, the complete amplifier being built in coils preceding the H.F. valve, and densers, in which the rotor is connected or the bulb. using ordinary plug -in coils with tuned to the frame. Now it is intended that We give in Fig. 2 a diagram for using primary, you will need a 50 -turn coil in the moving plates of these condensers these two valves. Each " valve " has six the primary and a 50- or 65 -turn in the should be connected to the earthed side legs, which fit into a special socket, and secondary on the normal broadcasting of your tuning coil, and we think if you from our diagram both internal and ex- wavelengths, with a 200 -turn coil in the make the necessary alteration, hand - ternal connections are seen clearly. We primary and a 250 -turn coil secondary on capacity effects will no longer be trouble- show the ordinary system of aerial the long wavelengths. some, as the spindle and frame will be at coupling which may be aneriudic and It will be noticed. that the first H.F. the same potential as the hand of the may consist i4 you so desire of the valve and also the detector valve receive operator. n 40