No. 971. THURSDAY, APRIL 7TH, 1938. VoL. XLII. No. 14.

Proprietors : ILIFFE & SONS LTD.

Editor : EDITORIAL COMMENT HUGH S. POCOCK. Editorial, relayed by wire fairly satisfactorily, Advertising and Publishing Offices : Television in the Home and it is for this very reason that so DORSET HOUSE, STAMFORD STREET, concern has been felt by listeners LONDON, S.E.I. Relay Reception Impracticable ? much and by the radio industry over the Telephone: Waterloo 3333 (5o lines). Telegrams: "Ethaworld, Sedist, London." HEN the television service attitude of the Post Office in proposing was started the fact that to establish a nation-wide relay system CovENTRv : Hertford Street. Telegrams: Telephone: high ground had to be which would gradually mean the dis- "Autocar, Coventry." 5210 Coventry. chosen for the transmitter, appearance of manufactured wireless BIRMINGHAM: and that at that time it was necessary sets, except in comparatively small Guildhall Buildings, Navigation Street, 2. for the cameras to be located very near numbers and, therefore, at vastly en- Telegrams : Telephone : itself, meant hanced to the public. "Autopress, Birmingham." 2971 Midland (4 lines). the transmitting apparatus prices that the B.B.C. had no alternative but At the same time that the proposals MANCHESTER : 260, Deansgate, 3. to accommodate the television trans- for a sound -broadcasting relay organisa- Telegrams: Telephone: Biffe, Manchester." Blackfriars 4412 (4 lines). mitter and studios on the same site tion on a national scale are being and at a spot remote from other B.B.C. pushed, statements have been made GLASGOW : 26s, Renfield Street, C.2. Telegrams: "Biffe, Glasgow." Telephone: Central 4857. centres. that the ultimate distribution of tele- As improvements have been made vision may also be by wire to individual PUBLISHED WEEKLY. ENTERED AS SECOND CLASS MATTER AT NEW YORK, N.Y. and it has been found possible to homes. televise from a considerable distance Subscription Rates : by means of special television cables Technical Considerations Home, LI is. 8d. ; Canada, LI Is. 8d. ; other countries, LI 3s. Iod. per annum. or a short-wave wireless link, the posi- tion is gradually developing where it An article in this issue discusses the As many of the circuits and apparatus described in these possibilities of distributing television pages are covered by patents, readers are advised, before is no longer so essential for television making use Of them, to satisfy themselves that they would to be regarded as a separate unit. by means of a_ relay system, and a not be infringing patents. study of facts there revealed leads us Merging Television and Sound to the conclusion that the chances of a television service by wire to individual Broadcasting homes are extremely remote. If this CONTENTS We think there is no doubt that the is so, and the article leaves very little doubt on the matter, then to encourage Page technical directors of the B.B.C. will be anxious to merge sound and tele- a sound -relay system will not contri- Editorial Comment .. 301 vision broadcasting more and more as bute in the least to popularising tele- Testing PA Equipment .. 302 time goes on. Television must ulti- vision, as television receivers will still Return from Malaya .. 306 mately become the means of illustrating have to be designed for reception by wireless, and once we are faced with Unbiased .. .. 308 the sound -broadcasting programme. this necessity, the addition of the small Television Relay Systems 309 If we accept this view, a first step made towards planning the amount of further apparatus for sound Broadcast Programmes .. 310 has been future of television on a satisfactory reception as well will add very little Timing London's Buses . . 311 basis and, as far as wireless transmission to the cost. If, then, for television Practical Aspects of Design 312 is concerned, we anticipate that pro- we must continue to depend on wireless Ambassador Superheterodyne Re- gress in this direction will be rapid. transmission, and if we agree that viewed .. .. , 314 television and sound -broadcasting must ultimately merge as one service, it News of the Week 316 The Relay Position is only logical to enquire what benefit Television Topics 318 Let us now turn to a consideration it can be to listeners to pay for a relay Random Radiations .. .. 320 of relay possibilities in relation to service for sound when a wireless re- Principal Broadcasting Stations 322 sound and television. Experience has ceiver for television remains a Recent Inventions.. 324 shown that sound-broadcasting can be necessity ? 2 30 The Wireless World, April 7th, 1938 Testing PA Equipment Checking Amplifier Performance By P. H. WALKER, B.Sc. (Eng.)

THE best can be got out of an amplifier only by designing it specially to fulfil a particular purpose, and it is interesting, if not always necessary, that has given very satisfactory results. to know its technical performance in some detail. In this article it is Turning now to the methods of measur- ing the proposed (a) to mention briefly the details of design of one of the PA performance of the equipment, we shall deal first amplifiers used at University College, London ; (b) to describe with the frequency - at least one response from method of determining the most useful characteristics, the pick=up terminals of and lastly (c) to give the tone control stage actual results of tests to the secondary made upon the University College equipment. terminals of the output transformer. The input impedance is a volume control, or A pasratu inlled U pensive moving -iron milliammeter as the grid leak of 0.5 M0, say, and the connec- I. sityap College «wassta designed toniver-give output meter (with series resistance) or tions between the oscillator and ampli- really high -quality reproduction, anode current meter as required. A ten - fier are arranged as in Fig. i. Next, the and was built by Sound Sales, volt accumulator is Ltd., to our specification. This specifi- used for micro- cation was briefly as follows.: -Two I2 - phone polarisation, watt amplifiers to a design based on The mounted inside the Wireless World Quality Amplifier, micro- cabinet in a lead phone amplifier with independent treble box. The superio- o8C. and bass tone controls, local -station re- rity of this method ceiver, volume controls on, and mixing over dry batteries of, all inputs, headphone monitoring is very marked, jacks, output meter, output valve anode - particularly in re- MICROPHONE MICROPHONE current meter, twin turntables with record gard to cost. TRANSFORMER TRANSFORMER groove cue scales on the pick-up arms. The radio set is a (a) (b) The use of two small amplifiers made simple affair, con- the equipment much more flexible, and sisting of an RF complete breakdown Fig. 3:-When the input is applied to the microphone transformer almost impossible pentode feeding a primary the arrangement when compared with a of (a) should not be used. For correct single 24-watt am- power grid -detector results it is necessary to load the transformer properly as in (b). plifier. They were arranged so that two and thence to the completely independent ` programmes " tone control amplifier. The tone control output impedance into which the ampli- could be dealt with at the same time, such circuit is similar to that designed for The fier is designed to work must be known as stage - effects and a load resist- noises, independ- ance made up of ently of our stage - g a )'ilI this value and con- greenroom micro- / AMPLIFIE'--_ 2 ---- nected to the out - phone system.' 2'° ------p u t transformer When required, a B AMPLIFIER \ - secondary in place switch parallels the I I 1 1 1 l t s of the speech coil. amplifiers to give a a There are two combined output of FREQUENCY IN CYCLES PER SECOND ways of measuring over 20 watts un- the input to the distorted, though Fig. overall response amplifier z.-The curves of two amplifiers are given here ; the differences are - with a each amplifier is quite small. valve voltmeter or capable of coping with a thermo- with most situations when operating alone. Wireless World i2 -watt PA Amplifier, ex- milliammeter. The first method is always Provision was made for headphone cept that bass attenuation is provided in preferable if it can be made to read low monitoring with the assistance of an out- addition to the other ranges. It is not voltages accurately and the instrument put meter : speech needs much more care- often required, but it becomes particularly should be connected as shown by VV in ful monitoring than music, and the rela- useful for improving the intelligibility of Fig. r. If, however, the load resistance tively low fundamental frequency of speech at very high volume and also safe- R is made up as a fixed potential divider, guards the loud the voltmeter may be connected as shown speakers from dotted and the voltage injected into the damage. amplifier will be a known fraction of the Marconi - Reisz VV reading. carbon micro- Measuring the output is much simpler, phones are used, and valve or metal -rectifier voltmeters while at the other may be úsed. end of the chain we have a number of Output Level for Measurements baffle speakers, also PM Standard Fig. r.-The connections between the AF oscillator and the input of Rola Gil practice with receiver mea- the amplifier are shown here. speakers which can surements asks us to show the frequency be bolted rapidly, response as the decibel ratio of the input speech made it possible to use an inex- either on to baffles or horns, and for our voltage. at all audio frequencies to the in- ' Described by the Prompter in the London more important work we are equipped put voltage at 40o c /s to give a constant Evening News of 16th December, 1936, and else- with a Voigt twin diaphragm double -power output of 5o milliwatts. where. unit working into a 4 -foot straight horn, To the PA man, however, an output APRIL 7th, 1938. Whehog 3O3 ?IopIld Testing PA Equipment- false readings as the transformer is not it is advisable to take exceptional care in of 5o milliwatts is very uninteresting, and correctly loaded, but Fig. 3 (b) shows a the preliminary preparations, to avoid in any case in practice it is extremely circuit that can be relied upon to give " dud " runs. a difficult to adjust the oscillator voltage to accurate results. . If V is the voltage read Fig. 5 shows the effect Marconiphone give exactly that output at every fre- by the valve voltmeter, then the voltage type 7A pick-up has on B amplifier's re, quency, not to mention the difficulty of injected into the microphone transformer sponse (Fig. 2). Though poor in compar- measuring 5o milli - ison, the solid curve gives the response as being within ± db. between 5o c /s watts across a 7.5 - + o 4.5 ohm load. De- 6 and 5,50o c 's, a fair result for a moving - In n b cide on some fairly 2 iron pick-up. An adjustment of the tone 0 _--w - e useful output, say O controls gave the curve shown by the a quarter to half ó ---`' _'a ------dotted line. the maximum un- 08,9,8 - `ee.....º.Ç The last test we can make in this class is distorted power, ¿ ó to find the effect the radio receiver has on The test and keep as near to FREQUENCY IN CYCLES PER SECOND our amplifier response curve. this as possible at will, however, be beyond. the means of all frequencies by Fig. 4.-Curve (a) shows the response of the amplifier and microphone most people unless expensive test gear is varying the input transformer, and (b) one effect of using the tone controls. available. It will be evident that the voltage. Changing audio -frequency response of a straight -RF the range of an instrument during a fre- 200 and detector receiver will be dependent will be : x V volts. queñcy run is responsible for many 2,000 + 200 on the radio frequency to which it is peculiar curves, so choose the output so This test carried that a preliminary frequency run shows out on the U.C. W you to be within the range of input and amplifier gave the S - -y- s `... output meters whenever possible. curve ` a " shown 4 --. It is often more convenient to keep the in Fig. 4, 'with the 2 D input voltage constant and to measure the tone controls in the .2 ----f^\. ; the various voltages developed across normal position, 8 output load, and this method is just as but the curve " b " S 1 a2 accurate and has the advantage that it is shows that the 0 ' f to have the input voltmeter not necessary drooping nature of FREQUENCY IN CYCLES PER SECOND calibrated. ` a " can be cor- method is adopted, it is very Whichever rected if necessary Fig. 5.-The response curves including a gramophone pick-up are important to see that overloading does not by an adjustment shown here. occur at any frequency. This may easily of the tone controls occur with an amplifier including a tone - The third test that we can make in re- tuned, and several tests at varying wave- control system. gard to frequency response is to play a lengths must be made to get a true im- Actually, when the characteristic is standard frequency record on the gramo- pression of the performance. such that the gain falls off at either end of phone turntables to determine the effect The apparatus required consists of a the range of audible frequencies the con- the pick-up has on the curve previously - variable radio-frequency oscillator, an stant input system is less likely to lead to obtained. audio-frequency oscillator, a meter for overloading than the constant output. These records can be obtained with a showing the carrier intensity, and another The converse is true, however, when the pure sine wave tone from 5o c / s 'up to for showing the percentage modulation of gain rises at the ends of the frequency 8,000 c/s with both steady and gliding the carrier wave by the audio -frequencies, spectrum. This assumes, of course, that' the whole equip- the input is chosen ment forming a for a reference fre- standard signal quency at the generator. middle of the band, T h e oscillators as is usually the and receiver should case. be taken to a com- Carrying out this mon earth while the test on the Uni- link between the versity College am- " transmitter " and plifiers shows the the receiver must result given in Fig. be via an artificial 2, where it will be aerial, which has noted that B ampli- been standardised fier (solid curve) is as consisting of a flat within ± 1.5 db. condenser, induct- between 4o c/s and ance and resist- 30,000 c/s, includ- ance in series as ing the output shown in Fig. 6, on transformer. which the required The next test is values are given. that of the micro - Resistance R is that of the output cir- p hone amplifier A view of the complete equipment upon plus main ampli- which the tests described in this article were cuit of the RF fier, including input carried out. oscillator which, in and output trans- series with a resist- formers. The output circuit will remain note. The output response curve is ance r must make a total of 25 ohms. as before, but precautions must be taken plotted on the assumption of constant in- The procedure is much as before, it be- with the input circuit. put against a reference frequency of r,000 ing necessary only to see that the carrier If the microphone transformer is de- c/s. intensity remains steady and the percen- is signed for an input impedance of zoo12 ; As standard frequency records are tage modulation 30 per cent. through- the circuit shown in Fig. 3 (a) would give guaranteed accurate for zo playings only, out the audio range. The AF oscillator 304 Whe@m3 APRIL 7th, WopIl. 1938. Testing PA Equipment- the fall of signal on either side of the rent flowing frequency in the output valve. This, is varied while noting the read- humps will be rapid. of course, assumes that the ings of the output output valves meter. Selectivity curves for the London are correctly biased and operated with the The London Regional and National National and Regional frequencies are correct load wavelengths impedance. With other were selected for test on the given in Fig. 8. It will be seen that there types of output stage, notably pentodes, U.C. equipment ; the curves with tone is a slight out -of-balance between the two the grid current does not determine the humps, due to errors in trimming. Un- distortion point. For such circuits a 0.0002 less cathode-ray and automatic frequency, simple R r .,Ia and interesting method consists of OSC nor) N--ORECEIVER wobbling equipment is 20.H available, how- plotting input voltages against output ever, it is extremely difficult to obtain voltage developed across the load, and so greater accuracy of balance than that shown except by Fig. 6.-For radio -frequency measurements chance, and in the RF oscillator is connected to the re- this particu- ceiver through an artificial aerial which con- lar case the discrepancy is sists of the network shown. probably insufficient to cause audible distortion of controls in the normal position were as the received programme. shown dotted in Fig. 7, while application Returning to the amplifier of tone control produced the responses proper, a figure frequently shown by the solid curves. asked for is the overall gain. As a matter of interest it will be noted Readers of The Wireless that in the case of the Regional curves a World know now, if not step-up of 14 db. is provided by the tone before the recent discussion, (a) (b) (c) control at io,000 c/s, a figure which is that this term can be quite Fig. 9.-These oscillograms show (a) the waveform of the output with no grid current in in very close agreement with the figure arbitrary when expressed in the output valves; (b) with published by 244A grid current in the output stage; and (c) with heavy The Wireless World for the decibels, and if I may quote overloading. step-up for that frequency on their tone - from an anonymous poem, control amplifier. " We can make it what we will- long as the amplifier is distortionless, the While we have the RF oscillator in By discreet approximation." result is a straight line, but when distor- mind we might deal with selectivity Though a method of dealing with the tion occurs the output does not rise so curves. These again are dependent on subject has been explained, using decibel rapidly, and there is a marked flattening the frequency to which the receiver is notation, the best method, long since of the curve when the overload becomes tuned, as is well demonstrated if curves adopted by The Wireless World, is to ex- serious. This method has the advantage at more than one frequency are taken. press the gain, not in decibels, which are that it shows up any non -linearity at In this case the small inputs, and also any distortion audio -frequency is introduced by valves other than those in kept constant at, R the output stage. say, 40o c / s, while Since Class A triodes were used in the the radio -frequency, -. tests described, the grid current method produced by the was used throughout. L6 '- oscillator is . With B amplifier og ``NR and a 15.3 -ohm load "wobbled" on on 15 s 08 the -ohm transformer secondary the either side of the 's e input was increased until just FREQUENCY short of the "transmitter " fre- IN CYCLES PER SECOND grid current point in the output stage. quency in as small A voltage of 13.6 was read, which Fig. 7.-The overall response curves at the is steps as possible, National and Regional equivalent to an output of 12.1 watts. usually between wavelengths, without tone control (dotted lines) and with tone control 1 (solid lines). In practice it may be found that a and 5 kc/s per slightly different result is given depending step. Either constant input or constant essentially a function of power and not on which output valve output of the grid -current can be used to 'determine the selec- voltage, but in millivolts or volts input meter is inserted. The difference should tivity curve, a fairly low constant output required to give maximum undistorted be small, but if grid current is found to being preferable , owing to the great output. There is some doubt as to the be flowing much earlier in one valve than change of signal strength that takes place. method of determining the distortion the other, the anode currents reading should be A of millivolts input is taken for point accurately, but when quality is a checked for balance, and if satisfactory, each step and the decibel ratio found with primary consideration, grid current is then it is advisable to substitute reference to the power to the input required to give the be avoided, particularly in RC amplifiers. valve with one that more closely matches same output at resonance. If band-pass A micro -ammeter in the grid circuit of one its partner. If perfectly matched tuning is valves employed, a tendency towards of the output valves will show when grid are used and the trouble still persists, double-humping will be noticed, while current flows, and we can assume that then it indicates that the amplifier is un- (for triodes) the maximum undistorted balanced, and this can be checked by output is + 2 reached when there is just no connecting a pair of headphones in series grid current. with a good condenser 6 ssiia11z:i3 between the out- Using the circuit shown in Fig; 3 (b), put transformer primary centre -tap and 2 %IFl\ /tiaIEMM ilI1 simply increase the input volts till grid earth. Anything more than a faint signal 4 current flows á and then reduce the input shows unbalance, and the input balancing 6 till the current just ceases. The input potentiometers, if provided, should m o be M voltage for this condition is the adjusted accordingly. w \\Ï value c y N!11 required. 18 MI To conclude the tests it was decided We now come to 12 tin to the determination of find what effect grid current had upon Iai what, with the YC1 the possible exception of fre- output 14 3111111113113111133331111111111Z1 waveform. Either a Dudell 11n quency response, is the most interesting mechanical oscilloscope -16 or cathode-ray -20 16 12. 4 0 4 12 figure of all where PA tl\78 S 1 + amplifiers are con- equipment is required with synchronous KILOCYCLES OFF TUNE cerned-the maximum undistorted power motor or linear time base respectively. output. It was stated earlier that for The voltage output required will depend Fig. 8.-The selectivity curves at the National triodes the maximum undistorted output upon which equipment is used, and Regional wavelengths. but with is obtained when there is just no grid cur- a cathode-ray tube it will usually be found APRIL 7th, 1938. TITA@Og '305 `'IopDd Testing PA Equipment -- prisingly little distortion is noticeable. On or puzzles one's brains to find some means of loud speaker the sound was unbearably utilising them. This difficulty will no longer that the maximum voltage available will a and my tests, leads were loud, and an aural test for distortion arise if sapphire needles are employed, be needed. For this is now possible, as an American firm has taken from the 15.3 -ohm load on the rendered almost impossible. A further just marketed play-back needles for ordinary secondary of the transformer to the Y increase of input sent the grid current up pick-ups consisting of a genuine sapphire tip plates of a cathode-ray tube, while the to 83 microamps, giving the highly dis- on a bronz8 shank. The price is 3 dollars time base was connected to the X plates. torted waveform shown in Fig. 9 (c). each (about 12 shillings). A life of at least The time -base frequency should be Finally, three more useful hints:- 3,000 playings is claimed for these needles, made as high as possible to give a well (a) Do not take it for granted that the combined with the advantages of reduced spread -out waveform, and if photographs calibration of a valve voltmeter will re- surface noise and record wear, due to the on the be to main constant at all frequencies. fact that no steel filings or burrs are to be taken, care must exercised needle can embed in and damage the ensure the stability of the time base. (b) After a frequency run, always re- grooves. Fig. 9 (a) shows the waveform of a turn . to the starting point -400 c / s, to The Telefunken pick-up, released in Eng- 400 c / s note as given by the amplifier check that no drift has taken place. land some months ago, is believed to be the just before grid current started to flow, (c) Keep a watch on the mains voltage. only commercial model using a sapphire that is, at about 12 watts. Increasing the My grateful thanks are due to Professor needle (other than the Western Electric input sent the valves into grid current, R. O. Kapp and to Dr. Monteagle Barlow Company's " hill -and -dale " reproducer that and when this had reached 24 microamps, for permitting me to use the University has a permanent diamond or sapphire), but, of is an integral part of the whole equivalent 16 watts, the College Communications Laboratories course, it to a little over pick-up. This is probably the first time a photograph 9(b) was taken, where sur- and apparatus for these tests. replaceable sapphire needle has been made available to the public at a moderate price. The reason for the price of these needles, apart from the cost of the raw stone, is at- tributed to the work of the skilled lapidary Combined Detector -Loud Speaker required to shape and polish the tips, which can be done only with diamond dust. rFHE piezo-electric crystal is better the surrounding air, and, having regard The of the American firm making " under address I known as a high -frequency oscil- also to their " mean free paths these needles is Electrical Laboratories Co., lator than as a detector of wireless ordinary atmospheric pressure, to create 49, East 21st Street, New York City. signals, though it seéms that it can be mass movements of air at the frequency of made to serve both purposes simultane- the audible signals, in much the same way For instance, the idea of rectify- as the piston strokes of an ordinary loud ously. PRECISION 840 METER ing high-frequency signals directly by a speaker diaphragm when subjected to the is, in effect, the diaphragm action of audio -frequency currents. THE Precision 84o meter is handled by crystal which of Strathyre, Perth- forms the subject of a The necessity of using crystals of differ- 1 L. A. MacLachlan, of a loud speaker shire. It is a multi -range AC and DC volt- meter and milliammeter and ohmmeter. The voltage ranges are ro, 15, 25o, r,000 and 2,500 volts at r,000 ohms. per volt for AC and DC, while the current ranges are ro, In order that a single crystal "speaker " may deal 5o, 25o mA and r amp. AC and DC. There with incoming signals over a range of wavelengths, are three ohmmeter ranges giving useful of the crystal is made to corre- the natural frequency indication from about r ohm to I megohm. spond with that of the IF amplifier ; signals are converted to that frequency by the normal super- A single rotary switch enables the desired heterodyne process. range to be selected, and another two-way switch gives a change -over for AC or DC measurements. A variable resistance is pro- vided for the adjustment of the ohmmeter ranges.

RF FREQUENCY AMPLIFIER CHANGER

recent patent (No. 477623) issued to ent size for receiving programmes on Standard Telephones and Cables. different wavelengths is avoided by cutting The incoming signals, after RF ampli- a single crystal to respond to the fixed fication, are applied to a crystal approxi- intermediate frequency used on a superhet mately II inches square and *th of an inch receiver, as shown in the accompanying thick. The natural frequency of a crystal diagram. The inherent frequency of the of this size is roughly one million cycles crystal being stable, this helps to increase a second, so that it is resonant to a carrier- the overall selectivity of the set and to cut wave of 300 metres. A close analysis out all forms of interference. shows that, in addition to vibrating at the In order to pass the necessary side - carrier -frequency, the crystal will also bands, the crystal is deliberately damped Precision multi -range AC and DC volt- milliamp-.ohmmeter. follow audio -frequency variations in by inserting shunt and series resistances with sufficient fidelity to repro- as shown at R and RI. There is also a cer- amplitude with a duce the original voice' or musical fre- tain amount of frictional damping where The meter is a good instrument, end. the crystal is clamped to its mount. scale length of some 2¡in. across the arc of quency imparted at the transmitting the voltage and current scales. The resist- In other words, the necessity for a separate ance scales, being outside these, are longer, detector or rectifier disappears. and the decibel scale, being inside, is The mechanical movement of the crystal SAPPHIRE NEEDLES shorter. surface is sufficient, having regard to the problem of how to dispose of worn The instrument is contained in a black effective diameters of the molecules of THEsteel gramophone needles is ever-present, leatherette case with a compartment for test oxygen and nitrogen which go to make up and generally one either throws them away leads. - The Wireless World, April 71h, 1938

MORE than two years have elapsed since the Return from publication in " The Wireless Malaya World " of a survey of Empire Broadcasting from the Receiving End E mp ir e Broadcasting in Malaya by the author of this article. URING the last year or two it has Department to the best advantage. There On his return home after four years' come to be generally acknow- appears to be lack of co-operation between absence he now records the progress ledged that Empire broadcasting these two departments at the B.B.C. The that has been made in this increasingly is an essential service which stated policy of the Programme Depart- important should be given gratis to the Empire by ment is to give each part of the Empire B.B.C. activity and offers the Mother Country. It was gratifying to a transmission primarily intended for it suggestions for the development of overseas listeners that this principle was during the early evening. In pursuance of the Empire Service endorsed by the Ullswater Committee. this policy, Transmission II is directed to From the radio engineering point of view, Malaya so as to be heard there between British short-wave broadcasting leads the 6.3o p.m. and 8.3o p.m. local time. Re- world. ception of the Empire Service is always By " HEPTODE" The B.B.C. Engineering Department better after 8.3o p.m., when the pro- has carried out a policy of steady develop- gramme for Malaya has concluded-. ment and has not hesitated to invite the Broadcasting then continues in Transmis- At present the B.B.C. relies upon co-operation of listeners during protracted sion III (for India), and is usually official organisations and broadcasting tests of aerial arrays and frequencies. This received- very much better than is Trans- bodies overseas for its reception reports. period of development culminated in the mission II. It is particularly annoying to There is reason to believe that in many bringing into service shortly before the have the News Bulletin in Transmission II instances these reports are based on ob- Coronation -of the new transmitters which marred by bad conditions, which then servation bÿ unskilled personnel with are now giving greatly improved strength improve to very good perhaps half an inadequate apparatus. In any case there of reception and greater choice of fre- hour later. The next bulletin is not given can be no consistency or uniformity in quency. The excellence of the service until nearly midnight, local time. reports from many diverse bodies. The amazes listeners from England who are next step in the development of Empire accustomed to the erratic reception there Programme Times Need Revision Broadcasting must be a thorough investi- of American stations. gation of receiving conditions in all parts The strong and reliable reception ob- The Engineering of the Empire. The Engineering Depart- tained Department must be of the Empire Service in Malaya well aware of this state ment has admirably fulfilled the first part would seem of affairs and yet incredible to anyone who had the 'Programme Department continues of its task and it must now be allowed to not experienced it. There its is never a night 'efforts to reach Malaya two hours too take to the field. Qualified men with full when reception of the B.B.C." Service is early. If similar experience of short-wave technique should not possible conditions prevail in at some time during the even- other parts of the Empire be sent out to give reliable and compre- ing and there (and the writer's are few nights when recep- experience in the earlier days hensive reports of reception. They would tion on an adequate receiver of short- falls below wave development in North America and also make contact with local listeners India leads him to suppose they do), then who would continue to carry out ob -

Since new transmitters were installed at Daventry just before the Coronation, British short-wave broadcasting, judged from the viewpoint of a listener abroad"leadsthe world"

entertainment value. Although it is diffi- the Programme Department would do well servations after they had left. Many cult to imagine so progressive a body as to reconsider the hours at which pro- the listeners who are competent and equipped B.B.C. Engineering Department being grammes are directed to particular parts of for making satisfied that finality observations and who have had been reached, the Empire. Rather than arbitrarily decid- long since ceased there seems little left writing to the B.B.C. to be done by way ing that every part of the Empire must be would be only too willing of technical improvements. Perhaps to co-operate if the reached in the early evening and expect- they were placed in personal touch in this provision of sufficient channels for alter- ing the engineers to defeat Nature, it manner. native It is emphasised that the per- programmes may be considered? would be better to get the engineers to dis- sonnel of the Empire It is Departments field certain that the Programme cover at what time they can best reach force must be engineers and not,publicists. Department do not use the facilities placed each part of the Empire with the If the use of a field force as at their disposal by the envisaged Engineering apparatus at their disposal. is not possible, then there exists, in the - APRIL 7th, 1938. WheIl@g0 307 íOpIlc Return from Malaya- in the local papers, making it much easier dude a tuned RF stage for all wave- many holders of amateur transmitting to regard events in their correct perspec- lengths covered, two IF stages with an IF licences throughout the Empire, a body of tive. One defect is the growing tendency of the order of at least 465 kc/s, non - men who are fully versed in short-wave to include items of news originating from delayed AVC and power output sufficient technique. These amateurs are capable of the region to which the transmission is for large rooms and open verandahs. For sending worth -while reports to the B.B.C. directed. So far as Malaya is concerned Malaya the receiver must tune down to and have the means at their disposal to such items are unnecessary because the 13.9 metres because this wavelength is send them rapidly. If the P.M.G. could local papers and local broadcast news well received during the greater part of the be persuaded to allow amateurs to pass bulletins cover all local events adequately. year. Reception on waves of this order 'messages addressed to the B.B.C., then The B.B.C. should avoid any tendency requires good stability of oscillator fre- the Empire's amateurs would have a use- to give the Empire to the Empire-what quency. There is nothing more exasper- ful and interesting work to carry out and the Empire wants from the B.B.C. is ating than reception of 13.9 metres on a live traffic to handle, while the B.B.C. Britain. set with oscillator creep. would be able to obtain reliable reports The question of broadcast propaganda The best British receiver the writer was from overseas with great rapidity. is very much to the fore at the present able to test before leaving Malaya was During the last two years there has been time. Malayan listeners get full measure the G.E.C. " Fidelity All-Wave Eight." a steady improvement in the Empire pro- of tendentious news in English from This receiver gave results under Empire grammes, but they are still very, very inferior to the fare of Home listeners. Re- corded programmes are employed more than they were, but they are still almost invariably recordings of special Empire Department pro- grammes which have been given in the original in some pre- vious period of Empire transmission. Desperate efforts to avoid controversy spoil nearly all talks

Photo courtesy The Malayan Information Agency. Street scene at Kuala Lumpur, Malaya. foreign stations. There is no doubt that conditions fully comparable with American the Empire News Bulletins are an ex- ten-valve sets, and the specification and cellent antidote to some of this foreign finish are really tropical. It is an interest- " news." The broadcasting of these ing point that the set is fitted with valves and what is left of interest is spoiled in bulletins in foreign languages would cer- of the so-called International Range delivery by the kindergarten diction im- tainly increase their antidote value, but it which are equivalents of American types. posed upon the speakers. This slow diction is to be hoped that this can be carried out It is a curious fact that some British re- is also practised by the announcers. No without seriously curtailing the time avail- ceivers which appear to be as good as doubt, under bad conditions or with poor able for normal programme matter. American sets from specification do not receivers, slow speech helps listeners to compare favourably with them on actual understand what is being said, but when Scope for British Enterprise test. the periods of transmission are intended Malayan listeners still suffer badly from for reception only in areas where the A few British manufacturers have interference by commercial stations with service is of programme value at the time, entered the Empire market with effective short-wave broadcasting. This is a it seems illogical to legislate for poor con- apparatus, but the bulk of the receivers in matter which might well receive the atten- ditions. Under normal conditions of recep- use in Malaya are still of American origin. tion of the B.B.C. engineers if they are tion of the Empire Service in Malaya, it is The success of Empire broadcasting in sent out to study receiving conditions. just as easy to follow a talk on a good that part of the Empire has undeniably Many complaints of interference can be receiver after 9 p.m. as it is when listening been built upon a solid foundation of traced to poor receivers, but there is still in England to a medium -wave non -local American receivers. It is fortunate for far too much real interference from com- regional station. the reputation of British receivers that mercial telephony, telegraphy and facsimile The Empire News Bulletins are still by none of the small all -wave sets now manu- transmissions. The Berne list still shows far the best and most widely appreciated factured in England have as yet been stations with frequency allocations within part of the programmes. Their greatest tried in the Empire market. It is to be the short-wave broadcast bands. Perhaps merit is their excellent continuity from day hoped that manufacturers and exporters the Cairo Conference will evict these sta- to day, reflecting very great care in pre- will continue to show restraint in this tions ? The operation of very high- paration. In the local Press, only too matter. This small type of set with no powered stations just outside the broad- frequently is some event mentioned in a RF stage, low sensitivity and a limited cast bands should also be restricted. brief cable and then nothing more is heard wave coverage is quite unsuitable for Em- Singapore appears to be in the maximum of it by those interested until the papers pire listening. It fails in two essentials ; signal zone of the aerial array of station arrive from England three weeks later. it allows second channel interference on PLF in the Netherlands Indies, for at In the Empire News an event is followed the shorter waves and it cannot give some seasons its signal, just outside the up daily until there is nothing more to be proper control of fading. sixteen -metre band, causes a wipe-out of said about it. All the news is given much The fundamental specification of a re- everything on that band, no matter how more fully than in the cables published ceiver for Empire broadcasting must in - selective the receiver may be. The Wireless World, April 7th, 1938

garden by their indignant owners, and I fear that the 'social standing of Mrs. Free Grid and myself in the neighbourhood, which was already somewhat shaky, underwent a still further decline. UNBIASED Eventually, however, the sack of rats was safely dumped in the hole dug in the Encouraging Crime are broadcasting receivers to be made to field and I put the ferrets down the garden cover trawler wavebands? Merely for the hole in order that they might commence SUPPOSE that one of the most I despic- purpose of eavesdropping on private con - their great work in the cause of applied able traits our frail human nature science. Unfortunately things went wrong exhibits from time to time is that of eaves- right from the start, as the first dropping. ferret to To my mind, it has nothing in BY be released seemed a badly trained common with the bold buccaneering spirit animal, and, instead of commencing his of olden days which made men murder FREE GRID allotted task of tunnelling, promptly took their mothers-in-law and set sail in a tiny refuge in my trouser leg. The immediate ship to attack the big treasure galleons of versations as far as I can see. What is worse,' many listeners may be tempted to effect of this was that I received a very the Spanish Main. Not, mind you, that I severe bite, but this was by no means the am trying to defend piracy, but there is retail some of the trawler conversations to at least something wholesome about it their friends as they often are, as I can which cannot be said of eavesdropping personally vouch for, very entertaining and similar underhand pastimes. indeed, although unintentionally so. It is because I hold these sentiments so This would, of course, constitute a strongly that I have always deplored the definite breach of the terms of a wireless fact that set manufacturers have never licence, and make the offenders liable to fitted muting arrangements to their pro- prosecution under the provisions of the ducts so that the set is silent when tuning various Wireless Telegraphy Acts. These past wavelengths reserved for ship and rumoured trawler -band sets would thus other commercial services. In the course act as a deliberate temptation to a breach of tuning, a set inevitably does pass over of the law which, as ' all right-thinking such wavelengths, more especially in these people will agree, is a very bad state of all -wave days, and, although I feel sure affairs indeed. I trust, therefore, that the that all of my readers discreetly hurry by manufacturer concerning whom I have them, there are some people who, I fear, heard these rumours will either reconsider " ... took refuge in my trouser leg." are base enough to stop and listen to his decision or write to reassure me that it private conversations even though they is only a rumour, on receipt of which I worst as, in my pain, I accidentally may not break the letter of the law and shall be very pleased to apologise. kicked over the ferret box, this causing the terms of their wireless licence by dis- the lid to fly open with the result that all closing what they hear. the animals escaped into neighbouring As I have said, it has always troubled One Thing After .Another gardens and are still at large. For the past my spirit that manufacturers do not fit few days the whole district has been in a A GRATIFYING large number of you this form of muting to their sets, . but I state of siege, the women not responded daring to realise that it would mean extra produc- to my recent appeal for venture into their gardens and the men- tion expenses, and in these hard times, of advice as to the best method of tunnelling folk being compelled to search underneath their re- course, when the cost of keeping race- neighbouring gardens in order spective houses thoroughly at night before horses has risen to the pitch it has, manu- to link my house, by means of a low - the household retires to impedance rest. facturers have to look at every penny. It transmission line, to an aerial To crown all, when I went to erected in the hole a nearby field. in the field, I found that the rats had eaten The suggestion which I eventually their way through the sack and had adopted was that I should dig a hole in spread themselves over the adjacent farm my garden and a corresponding one in buildings. Needless to the say, my social field. In the latter I was to dump a status in the neighbourhood has now sunk sackload of rats, a number of ferrets being to the absolute zero mark, but it has released in at the garden hole. The ferrets, any rate had one good effect, as it has which my informant was willing to sell enabled me to re -erect my garden me, aerial, as possessed, he said, a very keen direct - it is quite obviously impossible for it line scent and to would at once commence to cause my prestige in the neighbourhood to tunnel through to the rats in the other hole, go below absolute zero. as it would not occur to their limited intel- ligence to climb out of it and travel over- land. The ferrets duly arrived, but owing to Bouquet for Manufacturers the difficulty of getting a quantity of rats is gratifying to find that my words Private conversations. I was compelled to keep them for a few ITcarry so much weight with manufac- days in the house, a fact which caused the turers. This is strikingly exemplified by has, however, come as a very deep shock strong disapproval not only of Mrs. Free their promptness in responding to my re- to me to hear a rumour that one important Grid but also of neighbouring residents, as cent appeal for the marketing of a " play- manufacturer is contemplating putting out these animals possess to some extent the ing desk " fitted with an automatic his standard all -wave models fitted to well-known properties of the skunk. In record changer. Two prominent firms cover the trawler band of wavelengths. the end I was able to obtain some rats by have already produced these articles in Now, by no stretch of the imagination negotiating with a local ne'er-do-well who response to my request, and I understand can it be argued that wireless telephony was recommended to me as a specialist in that a third is making plans to market transmitters are established on trawlers for this sort of thing. The delivery of the one which will deal also with the popular the purpose of radiating Entertainment as sackload of rats on my doorstep gin. records. As yet, however, there are in the case of broadcasting stations. If, occasioned great excitement among the no signs of the 12 -guinea radiogram which therefore, no entertainment is being dogs of the neighbourhood, many of them I asked for, but I realise, of course, that ràdiated from trawlers, for what purpose having to be dragged forcibly from my this takes somewhat longer to design. The Wireless World, April 7th, 1938 309 Television Relay IS "WIRED" TELEVISION PRACTICABLE ? Systems T is often argued that the cost of a provide at least a high -voltage unit similar IT has been suggested that tele- sound broadcast relay system to the to that included in all present television vision programmes might be individual listener is less than that sets. distributed to viewers by methods involved in the use of a receiver, for In addition to these steady voltages and similar to those adopted in certain the only apparatus he requires is a loud currents the CR tube requires saw -tooth areas for relaying sound broad- speaker. If the standard of quality is of voltages or currents with basic frequencies casting by wire to listeners. The a mediocre order, this may be true, but of 5o c/s and 10,125 c/s for scanning. technical possibilities of this sug- it is doubtful whether it is the case when The channels over which such frequencies gestion are critically examined in a high standard of quality is maintained. are passed must have an even frequency this article. The relay equipment must then be of response up to some ten times the funda- much higher quality, and, more im- mental frequency. That is, two channels portant, the relay lines are much more must be provided for the scanning, one of costly. All this increase in cost must he 50-500 c /s and the other of 10,125-101, 250 output of some 10-30 volts p -p., and the borne by the subscriber in his regular c /s, and these channels must exhibit frequency response must be such that fre- payments. remarkably little frequency and phase quencies from zero to 2,000,000 c/s are Now in respect of television the sug- distortion over these bands. For electro- evenly reproduced ; the phase distortion gestion is sometimes put forward that a static deflection the saw -tooth waveform must also be very low. similar distribution scheme might be must have a peak -to -peak amplitude of In addition to the purely television adopted, presumably with the idea that signals there is also it would enable a great saving in cost to the sound channel tc be effected. Those who favour such a be considered. Fot LOW-PASS o scheme seem to believe that because in FILTER this a frequency re- LOUD CUT- OFF a sound relay system it is only necessary FREQUENCY SPEAKER sponse _ of, say, 30 for the subscriber to have a loud speaker 10,000 cf, o c/s to 10,000 c/s is connected to the incoming two -wire line needed for high it would in a television system be necessary quality.

only to have a cathode-ray tube connected BAND-PASS An eight -wire FILTER DETECTOR AMPLIFIER FRAME to the line. This is actually very far from 195-20.0kt'a SCANNING cable system is the being the case, and it will be instructive obvious suggestion to examine the possibilities. for the linking of the To produce a picture the cathode-ray relay station to the tube must have a heater supply of some BAND-PASS individual houses, - FILTER DETECTOR AMPLIFIER LINE 2 to 4 volts at I to 2 amperes, a high 50-250k:ß'. SCANNING voltage supply of 3,000 to 6,000 volts at a few microamperes, and lower voltages at Fig. 2. -The re- negligible current if electrostatic focusing ceiving apparatus if is used, or some 5o mA. at 5o volts BAND-PASS needed for the FILTER DETECTOR VISION . focusing is adopted. SIGNAL carrier system is electromagnetic 350 - 2,350 k cis the depicted in this With the exception of heater supply, diagram. these must all be direct current, and it is obviously impracticable to supply them directly from a relay station. In prac- tice they would have to be derived- from about 1,000 volts, whereas for electro- but it is very doubtful whether this would the lighting mains with the aid of the usual magnetic deflection a current amplitude of _ be satisfactory for more than quite short transformer, rectifier and smoothing about ioo mA. p -p. is needed. distances. The signal levels on the lines equipment. In addition to the CR tube, For modulating the tube there must be would be of quite large values, and it therefore, each subscriber would have to a vision channel capable of providing an would probably be very difficult to avoid cross -talk. Even for short distances the necessary cables would be very expensive. An alternative method would be to use a single pair of wires only and to adopt the carrier system. There are many pos- FRAME LINE SCANNINO SCANNING sible ways of arranging this, and the most obvious is to transmit the sound at audio - frequency, as in any other relay system,

30 -10.000 c! s 50 - 250 k U-35-2 35M;s with three carriers for the three necessary vision signals. A band of 30-10,000 c/s would thus be reserved for sound.

2 be used SOUND 20k Os 150 kt s VISION 35 Mc;s The frame -scanning wave would CHANNEL CHANNEL to modulate a carrier, and a band -width of not less than I kc/s would be neede"' The carrier might have a frequency di Fig. I. --The bands of frequencies which would be needed for the distribution of sound and vision by the carrier system are indicated here. 20 kc/s. 3zó APRIL 7th, ñpcDcogWould 1938. Television Relay Systems- These would be generated locally by sible for cable links to pick up interfer- The line -scanning wave would modulate time -bases just as in present-day receivers, ence. The avoidance of such pick-up is another carrier, but this time- the band- and the vision signal would include syn- quite a difficult problem in wide -band width would have to be 200 kc / s. The chronising pulses. Only two channels cables of the type necessary for television carrier could then hardly be- lower than would then have to be provided, i.e., for purposes, and it is doubtful whether the 15o kc/s. sound and vision. The sound channel few cables of this type in existence have The vision signal contains frequencies. would be at audio -frequency, and quite been in use long enough, to give 'a full up to 2 Mc / s, and for double-sideband a simple filter would suffice to separate the knowledge of their capabilities. working a band -width of 4 Mc / s would vision signal from it. The vision signal We must conclude, therefore, that a be needed. Single-sideband working is would include sync pulses of the present television relay system hardly seems a feasible, however, and would reduce the type, and could be transmitted in a band practicable proposition, and it is very band required to 2 Mc/s only. A certain of 100-2,100 kc/s, and possibly at a level doubtful whether it will become so in the gap must be left between the edge of this sufficient to modulate the tube directly future. If we accept this conclusion, as band and the upper sideband of the line - after detection. Quite a simple filter we must, it brings us to another point in scanning channel. The latter is 250 kc /s, would suffice to cut out the sound. connection with sound relaying. The and the minimum gap is probably about An amplitude filter for separating the time will come, and sooner than many ioo kc / s for reasonably easy separation of sync pulses from the vision signal would think, when sound broadcasting without the signals in the receiver. This makes be necessary, however, as well as the line vision will be considered as much of an the vision channel extend from 35o kc/s and frame scan time -bases, their power anachronism as a silent film is to -day in to 2,350 kc/s. supply unit, the CR tube, and its high - the world of the cinema. The evolu- voltage supply unit. tionary process of the talkies will be The Receiving Equipments It will be seen, therefore, that the reversed, and people will demand that apparatus required in the home would in sound broadcasting be accompanied by The arrangement of the channels is reality consist of a present-day television vision. probably most easily visualised from the receiver less the aerial and pre -detector Vision, as we have seen, cannot be con- drawing of Fig. z, which is not to scale. stages of the vision and sound receivers. sidered a practicable proposition on a The relay system must have a level The mains equipment could also be re- relay system, and so those who take their response from 3o c / s to 2.35 Mc /s to duced in size, because there would be sound programmes via such systems will accommodate all four channels. The fewer valves to operate. In place of this be obliged to install wireless equipment energy level of the transmissions cannot apparatus, there would be special filters for the reception of vision signals. be very high if cross-talk is to be avoided, and the special cable to the relay station. and, consequently, amplification at the In general, the vision and sound re- Books Received receiving end is likely to be needed. ceivers are the least expensive parts of the The At the receiver the minimum National Physical Laboratory : Report equipment television equipment. It is in the CR for the Year 1937.-A survey of the activities is shown in Fig. 2 ; this is, of course, in tube, the high -voltage unit, and the time of the N.P.L. in various fields. In our own addition to the CR tube and high-voltage bases that the major portion of the cost particular sphere the work of the Radio De- supply unit. This minimum equipment lies, and it is just these parts which would partment covers a wide range of fundamental supposes research, mainly concerned with propagation that the signal level is sufficient have to be provided by the viewer in a and its relation to communication and direction for operating the loud speaker directly and relay system. On the whole, therefore, finding. The measurement of field strength, for modulating the CR tube after detec- it would seem that there is little to choose the design of RF oscillators of stable frequency, tion. If it is not, additional visual indicating direction -finders, and other amplifiers in the matter of cost between the relay matters, are discussed in would be needed on these channels: the Report. Pp. 15o ; system and the present wireless methods. published by H.M. Stationary Office, Kings - The arrangement obviously does not In the matter of interference, however, way, London, W.C.2. Price 2s. 6d. lead to the use of very simple receiving there may be some benefit, particularly at The Broadcaster Radio and Gramophone apparatus, and it is probable that in a a considerable distance from the trans- Trade Annual, 1938. Pp. 224, with numerous practical case no attempt would be diagrams. The Wireless Retailer and Broad- made mitter. This benefit, however, should not caster, 29, Bedford Street, London, W.C.2. to transmit the scanning waveforms. be overstressed, for it is actually quite pos - Price 5s., post free.

THURSDAY, APRIL 7th. FEATURES TUESDAY, APRIL 12th. Nat., 6.20, " Forgotten Anniversaries" OF THE Nat., 7, Anna Neagle in " Star - -talk by the Hon. Harold Nicolson Broadcast Programmes WEEK Gazing " (repeat). 9.20, America on Dick Turpin. 7.30, The Band Speaks. 10.15, " Cabinet of Dr. of H.M. Scots Guards. 8, Geraldo SATURDAY, APRIL 9th. Reg., 6, Eugene Pini Caligari "-an adaptation of the and his and his Tango Concert Orchestra. 9.20, Orchestra. early film thriller. Weather Talk Nat., 2.25 and 4.45, Commentary on 6.30, Sir Adrian Boult by Lord Dunboyne. conducts Sunday Reg., 6.35, " Stop Dancing "-for Reg., 7.30, the Motor -racing at Donington Orchestral Con- " Cotton "-how the new tunes and old. 8, Variety from industry Park. 2.55, England e. Scotland- cert, with Clifford Curzon, piano - is managed. 8.15, The the Holborn Empire. 9, Handel Royal Philharmonic Society's Con- commentary on the International f. Abrorteoad. Programme relayed from Stuttgart. cert at the Queen's Hall, Association Football Match. 8, conducted Radio -Paris, 8.30, by Sir Music Hall. 9.20, American " La Croisade des Abroad. Thomas Beecham. Enfants Abroad. Commentary. "-oratorio (Pierne). Milan Group, 9, " Cleopatra," opera Naples Group, 4.30, " La Marseilles, 7.30, The Elizabethan Reg., 7.30, The Perth Theatre Gioconda," (La Rosa Parodi). Song-Shakespeare, Company in " The Barretts of opera (Ponchilli) from the Royal Ben Jonson, Opera, Rome. etc. Wimpole Street." 9, Peter Yorke WEDNESDAY, APRIL 13th. and his Orchestra. 9.30, The Pig MONDAY, APRIL 11th. Nat., 6.40, Band Waggon. 8, Skittles FRIDAY, APRIL 8th. and Whistle-a rural episode. Abroad. Nat., 7, Monday at Seven. 8.20, Commentary. from Tower Hill: Nat., 8, Commentary on the Snooker 8.15, Prague, 7, " Kerbside Music-makers. 8.40, Stanelli's Bachelor Party. World Championship Final The Gipsy Baron," at operetta (Johann Strauss). " The Gang Smasher "-serial, No. 9.40, Boxing Commentary-the Thurston's Hall. 8.20, Dave Frost Bordeaux, 2. 9.20, World Affairs. final stages of the Imperial Services and his Band. 9.20, B.B.C. 7.30, " Faust," opera Concert (Gounod). Reg., 6, Montague Brearley and his Boxing Association Tournament. of Contemporary Music-VII. Orchestra with Alan Paul, piano- Reg., 7.30, " The World Goes By." Reg., 8, Scotland - life in the forte. 8, Discussion on the Future 8, Gounod's opera " Faust "-the SUNDAY, Cromarty Firth. 830, Aileen APRIL 10th. of Lancashire Cotton. 9, Anna B.B.C. Chorus (C) and the Theatre Bransden at the B.B.C. Organ. Nat., 5.20, Constant Lambert con- Neagle supported by Herbert Orchestra, conducted by Stanford 9, The Fol -de -Rois. ducts B.B.C. Orchestra (E) with Wilcox, Stuart Robertson and Kay Robinson; narration spoken and Abroad. Jean Pougnet, violin. 6.30, Troise Stammers in " Star Gazing." written by Wilfrid Rooke-Ley. Brussels, 7, " The Daughter of the and his Mandoliers. 9.50, " Over- Abroad. Abroad. Regiment," operetta (Donizetti). ture and Beginners, Please "-pro- Brussels, II, 8, " Black Violets," Beromunster, Berlin, 8, Film Music." 8.10, " Titus," opera gramme by the Theatre Orchestra opera (Leo Fob). Rennes, (Mozart). 830, Beethoven and Wagner with singers from the Chorus. Paris, P.T.T., 8.30, Basque Folk Lore. Concert from Nantes. 'The Wireless World, April 7M, 1938 377 Timing London's Buses

RECORDING MOVEMENTS BY INDUCTION SIGNALLING

THE recording of the " headway," or picked up from a passing bus are trans- distance between successive ve- mitted via telephone cable to the control hicles, is an important detail of pas- station, where, after further amplification, senger transport organisation, and in the they are passed through a selective tuned case of tube trains, trams and trolley - amplifier and made to actuate the relay of buses, clock -driven recorders have been the headway recorder. This instrument successfully employed by the London Pas- may be installed at Headquarters or any senger Transport Board for some time. All other point ; moreover, duplicating dials these vehicles, however, have some electri- can be connected as required. cal connection with a rail or power wire, The recorder is very similar to that used but a bus is a completely independent unit. for tube train working, and is fitted with This makes the recording of its passage a powerful clock mechanism which rotates past any given point-and consequently a paper -dial. Each impulse causes an the organisation of an evenly spaced ser- inked hammer to imprint a bar -shaped The recording apparatus, as installed at vice-a much more difficult matter. With marking on the dial margin, and, as the headquarters. the object of overcoming this handicap, a system of induction signalling, which is now in experimental use on Route 44, has been devised. \. LINE Although radio is not used as a link with AMPLIFIER the moving bus, wireless technique is em- ployed in the associated amplifiers, etc. The signalling equipment on the bus com- prises a 15 -turn coil mounted in the roof, \NERGISED COIL which is energised by a vibratory genera- tor actuated by the 12 -volt accumulator of the vehicle. The vibrator is of the tuned reed type, matters being so arranged that Circuit diagram one pair of contacts interrupt the current of the inductive through the primary of a trans- signalling sys- passing tem. Sparking former, which is tuned to the frequency of at the contacts the reed. is prevented by At appropriate points along the route a resistance - receiving stations com- capacity sup- are installed " " pressor. prising a pick-up coil (with Ioo turns of wire) which, in the case of the experi- mental installation, covers the full width BUZZER of the road. This is because the pick-up coil is installed in the forecourt of 'Victoria 12V BUS BATTERY Station, where one-way traffic is in opera- tion. A half-width loop would, of course, BUS EQUIPMENT HEAD OFFICE be used on two-way roads, in order to avoid the recording of vehicles travelling in both directions. hammer is in line with the " correct time " be tuned to a characteristic frequency, In association with the receiving loop is pointer on the recorder, the marking indi- and the headway recorder for a given an amplifier, through which impulses cates the exact time at which a bus passes route would be actuated only by received under the coil at impulses of the frequency to which its the checking point. associated amplifier was tuned. By making pro- Twenty -four-hour dials are used on the vision for selective recorders, and at the end of the day the tuned amplification paper disc is removed and filed for refer- of the received im- ence. Thus any irregularities in the ser- pulses, it becomes vice can be studied in detail, and such possible to use a matters as recurring delays on certain days single pick-up coil can be discovered and their causes for recording the investigated. passage of buses The apparatus on the buses is designed on more than one to stand rough usage, and is mounted in route. The vibra- a heavy cast aluminium case. An am- tor generators on meter is fitted, as shown in the accom- each route would panying diagram, to provide a check on feed current to the roof coil. A bus passing The accompanying illustrations are re- under the pick-up produced by courtesy of the L.P.T.B., to coil ; the " trans- which thanks are also due for information mitting " coil is mounted in the and assistance in the preparation of this roof. description. 312 The Wireless World, April 71h, 1938 Practical Aspects of Design II. -MECHANICAL COUPLING AND GANGING be necessary to mount it on rubber and yet to fix the slow-motion drive rigidly, the use of the coupling shown in Fig. 2 By R. H. ß ALLACE will permit a relative movement of as much as one -eighth of an inch, while still, if it is carefully made, giving correct THERE is a tendency-quite a prising if the electrical side does not angular drive. Where, natural however, the error one-for many electrical require more frequent attention. may be of the kind where the spindles engineers and wireless enthusiasts The wise designer and builder will use may be slightly inclined to each other, the to avoid, as far as possible, both the methods, each where it is the most coupling shown in Fig. 3 is the one to use of mechanical devices where an elec- efficient and t h e use; this is also of trical method can be used, even if the result will be both value when it is latter costs much more and is far more a cheaper and a the first necessary to insu- complex. This viewpoint was no doubt better design. It is IN instalment of this late the fostered in the article two drives earlier days of wireless by the intention of the the author discussed the from one another. the very flimsy devices then produced, writer to show in general design of a wireless In cases of and the clumsy appearance of them ; this article how the the apparatus from . the purely spindles earliest at right - ganged condensers measured any- mechanical devices mechanical point of view. He angles which have thing up to a foot long by six known to engineers inches now goes on to describe the less to be connected to square, and were even then subject may best be ap- to common applications of mechanical each other, two al- large errors. plied. There is one ternatives Experiences important principles to receiver construction. are pos- with components of this feature sible, according to nature of led many wireless technicians to the mechanical whether they are to suppose that backlash, bulk and lack of coupling which is rotate by an equal reliability often of great value, were essential concomitants and that is the amount or a change of movement is re- of mechanical couplings. That this fact that the whole of it may be earthed quired. Where equal ratio is desired if desired. then should not be the case will be obvious if This makes it possible to the conventional type of bevel gear will carry the control through, or into places perform the change, but if where a change of conducting wires could not be ratio is wanted then a crown wheel used, and makes it possible and to avoid pinion is the right gear to ; the use the ratio loss due to the screening of leads. of movement is inversely as the number A good example of this is the ordinary of teeth on the gears. radio -gramophone It must not be switch. Unless great forgotten that where the power to loss of sensitivity is be accepted the leads transmitted is small, as it usually is for this cannot be screened, and it in wireless work, the ' gears is frequently most need -not be convenient to place toothed if some slip is not objectionable, the valve in the grid circuit of which it is thus it is quite permissible to use wheels located at the rear of the set. Many, faced with rubber or cork people therefore put where the knob the switch at the does not indicate, as in a tuning drive. back also, and put up with the incon- venience of this position, although it is Skew and Worm An early ganged. condenser; although satis- easy to keep the switch by the valve and Gears factory enough for the " semi -ganged " sets extend the control to the of its panel-the period, the frame and vanes were natural place to find it. Where the spindles do not intersect, as liable to distortion. Note absence of'splitvanes This may not be they possible by means of a straight rod, must for the cases just quoted, then for adjustment. as skew gears can there may 'be components in between the be used, but, since they require designing specially thought is given for a moment desired position of the knob and the best for each par- to the ticular case, are costly unless more -familiar machines of everyday life. position of the switch.. Here the device used in quantity ; the familiar worm gear Take the watch, for instance; a com- known as a universal coupling comes in, can paratively permitting the two spindles to be inclined take their place if a large reduction can cheap one will keep time. be permitted, otherwise within half a minute and yet coupled effectively to each other. it is often possible a week, an accuracy by repositioning the component of 0.005 per cent. What would Thus the switch may be placed at an to incline be the them so that their axes do intersect. cost of an electrical oscillator of similar angle, so that its extended spindle passes performance? Nor are all electrical cir- between the components, the coupling cuits free from such evils as backlash. being used to connect it to the knob. The ordinary reaction circuit comes to Note that the spindles must be so arranged mind in this connection, as, if great pains that they would intersect if produced. are not taken, there is considerable back- The drive can, if necessary, be taken lash. It should not be forgotten that, in right round a component by the use of two general, the electrical equivalent to a of these couplings. simple mechanical coupling will be a much more complicated affair. Another Compensating Couplings objection often raised against mechanical methods is that regular oiling and atten- Where it is desired to connect two tion is needed, which it is implied the spindles, nominally. in line, which may be electrical substitute does not require. somewhat out of alignment, then two This is definitely not the case, and pro- devices are available, according to the perly designed and lubricated bearings nature of the error ; these are shown in Fig. x.-Universal coupling for spindles in- clined to will run for years with the use given to Fig. 2 and Fig. 3. In the case of a each other by angles between 18o them in a wireless and 145 degrees. The crosspiece may be of set, while it will be sur- ganged condenser, for instance, should it insulating material if necessary. APRIL 7th, 1938. 1313 WOptd Practical Aspects of Design- purpose " school for this and other, Cord drives have their particular uses, reasons, the coupling of too many con- chiefly for slow-motion dials. They have trols does lead to mechanical complica- Club News the advantages of lightness and cheap- tion, and is generally less reliable than Kingston and District Amateur Radio Society ness, and can be very easily ; independent controls, and also more arranged Headquarters: The Three Fishes Hotel. Richmond wire is better for them than cord, and some awkward to repair when out of adjust- Road. Meetings: Alternate Wednesdays at 8 p.m. form of tensioning device must be adopted ment. Hon. Sec.: Mr. D. N. Biggs, 44, Pooley Green Road, to take up the stretch which occurs even Finally, a word about lubricants. Egham. with steel wire. There is no reason why the purely On March 16th Mr. J. F. Stuart -Williams gave a lecture on the oscilloscope. Modulation A coupling that the writer has rarely mechanical devices should not be treated patterns of many amateur and commercial tele- seen applied, but which has its special with a good clock oil, -so long as it is kept phony stations were studied by members. virtues, is the cam. This is used where On April 13th a lecture on quartz crystals the relationship between the two devices will be given by Mr. Didagan, of the Quartz Crystal Co. to be ganged is not a simple ratio, and may even obey no definite law. London Transmitting Society Headquarters: 90, Raeburn Road, Edgware. Meetings: Thursdays at 8 p.m. Correcting Errors Hon. Sec.: Mr. G. Yale, 40, Raeburn Road, Edgware. On March 24th members visited the Golders it Green Society and enjoyed a lecture by Mr. For example, for special apparatus Blake. may be desired to correct the residual error The Society now has fifty members. of a ganged condenser, or to ensure equal band -width or constant reaction at dif- Exeter and District Wireless Society Headquarters: 3, Dix's Field, Exeter. ferent frequencies, all of which require an Meetings: Mondays at 8 p.m. Hon. Sec.: Mr. W. J. Ching, 0. Sivell Place, Heavitree, irregular compensation ; a small condenser Exeter. operated by a cam on the main spindle On March 28th Mr. H. A. Bartlett conducted and small de- Fig. 3.-Flexible coupling for spindles very a " Questions and Answers " evening. The will permit this to be done slightly inclined. This is the usual commer- partures to be corrected. This method is questions were chosen from a recent examina- cial pattern, generally made with a paxolin tion paper set by the New Zealand Govern- particularly easy for the amateur, as the disc. ment for intending amateur transmitters. cam is easy to make and can be calibrated The subject of the next lecture is " Tele- in situ; the rest of the parts of the control to them, but bearings which carry a cur- graphs, Wire and Wireless." Mr. H. Ridge should be made and a piece of card affixed rent should be lubricated with something will be the lecturer. to the spindle in place of the cam, the that will not increase the resistance of Croydon Radio Society main dial is then rotated step by step, the the circuit. Vaseline is often used, but Headquarters: St. Peter's Hall. Ledhury Road, South a much better choice is something which Croydon. subsidiary condenser being set to the best Meetings: Tuesdays at 8 p.m. is an actual conductor, namely, graphite, Hon. Pub. Sec.: Mr. E. L. Cumbers, 14, Campden Road. more commonly known as blacklead. South Croydon. his lecture Progress in Com- These observations do not by any At entitled " t mercial. Receiver Design " Mr. Marks stated means exhaust the field of inquiry, but it that only five manufacturers produced a really is hoped that they will be sufficient to reliable receiver. In. one case, hè said, a re- indicate the principles, and the reader can ceiver arrived from the factory duly passed as " O:K." but with no loud speaker fitted. apply them to the various cases that con- He emphasised these points to bring home his front him ; intelligently used with due .views on the defects of mass production. Ile regard to the other considerations in- envisaged the time when only giïalified engin- improve both the relia- eers would be employed' by manufacturers. volved this will Sets at nine guineas were far too cheap, he bility and the ease of operation of the said, as the amount of knowledge involved was LOOSE COUPLER apparatus. not saleable at that figure.

Fig. 2.-Coupling for parallel spindles misa- ligned, with parts dismounted to show action. The dogs must be a good sliding fit in the guides. position each time, and the position of the roller marked on the card. When the job is completed the cam is cut to the marked line and then fixed on the spindle in the correct angular direction corresponding to the original marking. The grub screw, simple as it is, may often be responsible for trouble. When used on round spindles the screw fre- quently slips, even if pointed, and it is the author's practice to countersink the spindle with a small drill at the right place so as to afford a proper seating for the screw. This is a little more trouble than simply screwing it in, but is well repaid afterwards. Although the suitable ganging of con- trols is of great value this should not be carried out indiscriminately. As has often been pointed out in The Wireless World, the ganging of the on -off switch to the volume control subjects the latter to The use of a cam for obtaining constant reaction. An insulated cam is fixed to the spindle of the an undesirable amount of use." The writer main condenser, while the small condenser spindle carries an arm having at its end a roller is a strong adherent of the one knob one which runs on the edge of the cam and is kept in contact by gravity or a light spring. The Wireless World, April 7th, 1938 Ambassador MODEL 6778AC Four -Waveband Superheterodyne Tuning Down to 12 Metres

FROM the technical point of view, the chassis which has been de- FEATURES. Waveranges.- veloped by this Yorkshire firm has (1) 12-35 metres. (2) 34-95 metres. many features which indicated that (3) 200-550 metres. the designers not (4) 800-2,000 are content to follow too metres. Circuit. Pentode slavishly the - RF current conventions. As far amplifier -triode hexode frequency as the RF amplifier, frequency -changer changerpentode IF amplifier-diode- and IF stages are is concerned the circuit triode second detector pentode output straightforward. is It worthy of note .that valve. Full-wave valve rectifier. Con- the RF amplifier ins tuned on all four wave- trols.-(1) Tuning. bands, and (2) Volume. it will be seen that AVC is (3) Waverange. (4) Tone and on -off applied to all three valves except on short switch Price.-(Console) 14 guineas. waves, when the frequency changer is (Chassis, including valves and loud uncontrolled. -cored Iron IF transformers speaker) 10 guineas. Makers.- with Litz windings are employed and the Ambassador Radio Gramophones, final adjustment is made moving by the Hutchinson Lane, Brighouse, Yorks. cores under the control of opposed springs. It is when we arrive at the second detec- 1 - tor stage that the principal deviations from standard practice are to be found. A single of its advantages for the first AF ampli- diode is used for both signal and AVC fier in a receiver in which the HT line volt- rectification and the second diode of the age is likely to be affected by the fluctua- DDT4 valve is tied down to earth. The tions in anode current of the large single the matching conditions in - impedance single output valve. The single cell the anode dr of the diode was found used is of a cuit of the output valve, remain to give the special type and both mechanically therefore, just right damping for the IF and reasonably constant. A measure of nega- response required when the diode was con- chemically is designed to last at least as tive long as the feed back is applied by making a part nected across the whole of the output IF useful life of the receiver it- of the cathode bias self. The resistance common to transformer secondary. open circuit life is, in fact, not both grid and anode circuits. There is no less than 40,000 hours. delay on the AVC circuit A loin. moving -coil loud speaker with and the designers are of opinion that the an energised field -magnet consequent of moderate di- elimination of threshold distor- Negative Feed Back mensions has been developed for this re- tion more than outweighs the disadvantage ceiver, and the cone is of graded thickness pf possible reduction of signal strength on Tone control is effected by a shunt with a comparatively rigid weak level centre. The stations near the of background capacity on the diode load resistance and balance of tone is in favour of the noise. bass and It is unusual to find battery bias in a A single diode is used for mains receiver, signal and AVC rectification and the bias for the first AF amplifier is but there can be no doubt provided by a special cell.

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I APRIL 7th 1938. Wfip@hoo r315 WopIlc1

treble which suits the volume level at sible on all stations with the exception of and the 9 : i reduction for the slow-motion which best quality of reproduction is ob- the locals, and the comparatively wide tuning control which is integral with the tained. With the overall magnification spread of four channels on either side of condenser assembly is through a single provided, the output stage can be over- the London Regional station was attribut- pinion and gear wheel with opposed loaded when the volume is tuned to maxi- able to some cause other than selectivity springing in the gearing to avoid back- mum on any station of programme value, -possibly the effect of overloading in the lash. and although the volume obtainable frequency changer. The semi -circular tuning dial is printed before distortion sets in is more than No second channel whistles were to be in three colours on a black background enough for normal domestic require- found on the medium-wave band, and on and is framed in a chromium -plated ments, it does not quite carry the con- long waves the few which were present escutcheon. Station names are indicated viction of the 8 or 9 watts mentioned in were located below the wavelengths at on medium and long waves and are the instruction leaflet. There is plenty of unoccupied space in the console cabinet, and a fairly wide the back serves to give fillet surrounding FREQUENCY CHANGER VALVE more enclosure of air than usual. Any 2nd DETECTOR VALVE T X 4 expectations of bass resonance were, D D T 4 however, doomed to disappointment, and the lower register was, in fact, quite free is from boom. The plywood cabinet OUTPUT VALVE reinforced at many points, and from the APP4E method of application it is evident that wood resonances have been carefully studied and adequately dealt with.

Sensitivity R F AMPLIFIER I F AMPLIFIER The overall sensitivity is good, and the VALVE VALVE is at its best on the two short- set probably V P 4 B V P 4 B wave ranges. We were particularly im- pressed with the manner in which the sensitivity is maintained down to the bottom of the shortest waverange, and reception on the 13 -metres broadcast band was much better relative to the i6 - and 19 -metre bands than usual. American stations were well received, and second -channel repeat tuning points RECTIFIER were absent, indicating good preselection. VALVE on the Microphony was only experienced A P 4 V strongest carriers and with the volume control turned deliberately and unneces- sarily to maximum. On medium waves, the reception of distant Regional stations was notable for the excellent programme value and good signal-to-noise ratio, but between stations background noise was prominent, due to the high sensitivity. From the character of the noise we infer that some degree of regeneration is permitted in the IF ampli- fier. Adjacent channel selectivity is pos-

E.rEaN .L i'hOWireless World ÖAÖ COPYRIGHT

The power pack is mounted separately from the receiver chassis, and the ro -inch loud speaker has a special graded diaphragm. Extension loud speaker plugs are mounted on the output transformer.

present used for broadcasting. The viewed through an aperture in the split LC OUT - Deutschlandsender could be received pointer. In the console model the dial comfortably clear of Droitwich and Radio- is nearly vertical and a fair distance back Paris with the tone control at minimum, from the front glass, is not too well placed and from its strength it could be inferred for comfortable tuning except from a low that the sensitivity on this range was well stool-that is, unless one is prepared to up to standard and only slightly less than tilt the instrument as a whole, which is that of the medium- and short-wave in fact quite practicable, as it is of com- ranges. paratively light weight and the centre of From the constructional point of view gravity is low. the receiver is sound, and there are several As well as the console there is a hori- points which indicate that a moderate zontal type table model at 12 guineas, price has not been obtained at the expense and radiogramophones with and without of efficiency. All three sections of the record changers at 26 guineas and 20 gang condenser have widely spaced vanes, guineas respectively. '316 The Wireless World, April 7111, 1938 CABLE CRISIS AT A.P. Boat Race Television Triumph four hours before the For some time before " zero FORstart of the Boat Race Post hour " Philip Dorté; at Mort- Office engineers struggled to lake, sent messages to D. H. NEWS repair a line breakdown, which Munro, Productions Manager at OF completely isolated Alexandra Alexandra Palace, by means of Palace from the telephone ex- hastily scribbled notes held in. WHAT THE B.B.C. IS AND DOES change, Broadcasting House and front of the television camera. the mobile unit at Mortlake. Meanwhile, the Mortlake micro- A Review of 1937 At noon on Saturday it was phone being " dead," Howard decided to pick up the National Marshall was being rushed to THE most notable events and An analysis of the distribution commentary on the Boat Race Alexandra Palace to comment developments in the fifteenth of wireless licences throughout by radio, the receiver being a on the picture on the studio year of the British broadcasting the seven regions is very inter- standard table -model superhet monitor. service is presented in the esting. This shows that through- installed in Mr. Gerald Cock's The pictures from Mortlake B.B.C. Handbook, 1938, which out Great Britain and Northern office. This, incidentally, were completely free from inter- is just published. Island 68.3 families in every seemed to give a better " top " ference, due to the use of a new After a brief review of the hundred hold wireless licences, to the National quality than the receiving point at Highgate, two year's work, the address of the a ratio which is only exceeded line signal, which eventually miles from the transmitting King on the occasion of Their in the U.S.A. and Denmark. came through just before the station, the signals being sent by Majesties' Coronation and His The regions with the highest start of the race. line to A.P. message on Christmas D:.y are ratio are the Midland and West, printed in full. The intricate where there are as many as arrangements for the Coronation seventy-six licences per hundred RELAY OR RECORDS? RADIO -NATIONS broadcasts are well described, families. A Considered Opinion on A New Schedule of English following which are chapters on The hope is expressed in the Transatlantic Relays Broadcasts television and the foreign news foreword of this book, " that it RECORDS arc cheaper than LAST Sunday a new schedule service. will be of practical use to those Transatlantic relays, and came into operation at the Some interesting data are given many members of the great more satisfactory in practically League of Nations station at in the miscellaneous information listening public who are in- every respect. This is the Prangins, near Nyon, on the section, which occupies over terested in what the B.B.C. is B.B.C.'s considered opinion north side of the Lake of seventy pages of the total 128. and does and has yet to do." after a series of experiments in Geneva. Each transmission will relaying well-known dance bands include an account of the latest direct from New York. It is activities of the League and the realised that what thrill remains International Labour Office. GLASGOW EMPIRE go back to the time when the in hearing a band playing on the The complete schedule (in EXHIBITION big drum was literally beaten other side of the Atlantic is G.M.T.) of the English trans- Regular Broadcasts outside bear pit and barn. neutralised by uncertain recep- Will sponsored missions is as follows :- A PERMANENT O.B. station programmes be tion conditions and . the inevit- 1. Sunday, 3.45-4.30 p.m. included in this survey? able distortion. 11511 on 18,480 kcfs. is being established by the On the other hand, recordings 2. 6.45-7.30 p.m. B.B.C. at the Empire Exhibi- 1151 on 14,535 tion "STUNT" of American bands show off the HBQ on 6,675 in Glasgow, and this will be BROADCASTING performers best, and as 3. Monday, midnight -12.45 a.m. in almost constant use from the THE return of " stunt " broad- at their HBO on 11,402 kc/s. opening the records can be broadcast 4. 7-7.15 a.m. date (May 3rd), whdn casting in the B.B.C. pro- immediately they are landed in HBO on 11,402 the King's inaugural speech is grammes, such as the recent 5. 7.30-7.45 a.m. broadcast this country, little time need be HBJ on 14,535 from Ibrox Stadium, under - water commentary by lost in keeping jazz fans au fait Transmission r should pro- until the Exhibition closes at John Snagge and the Trans- with latest developments on the vide the best 'reception in the end of October. On the atlantic Spelling Bees, is a wel- other side. During the quarter India; r or 2 in South Africa, evening of the opening day come indication that broadcast- from April to June the late - Egypt and the Near East; 2 listeners will be taken on a ing is emerging from a long night record sessions on Mondays (HBQ) in England and North- microphone tour of the Ex- spell of lethargy. In the early (National) are being devoted to ern Europe; 3 in North America, hibition. days stunts were common, and discs made by crack American and 4 or 5 in Australia and Prior to the opening of the ex- did much to stimulate popular dance bands. New Zealand. hibition a " documentary " pro- interest in the new medium of Reception reports will be wel- gramme will be broadcast giving entertainment, but a humdrum comed by the Information Sec- an impression in sound of how period set in, marked by the this vast display has been built THE INDUSTRY IN tion, League of Nations, Geneva, unwillingness of the engineering Switzerland. up, and recourse will be had to GERMANY branch to take risks or depart recordings being made by the from the established routine. Authorised Dealers Only B.B.C.'s mobile unit. Much could still be done to B.B.C. DEPARTMENTAL is hoped THERE has been a general It to broadcast at test the possibilities of ultra - reorganisation of the radio UNIFICATION least one programme daily from short and micro -waves. In industry in Germany. The independence between the Exhibition throughout its many outside broadcasts the Ministry of Economics has THEB.B.C. departments has run. Many of the programmes commentators would have freer issued regulations whereby only long been a point of wonder ,will be dovetailed into special scope than at present if they recognised dealers will be allowed with the listening public, which transmissions from the new could use micro -wave transmit- to sell radio apparatus. has, in the course of years, Scottish Broadcasting House in ters installed in knapsacks. Examinations are to be attributed the peculiar internal Glasgow. A broadcast of a parachute arranged whereby it is hoped to organisation of the Corporation descent could be carried out Substantially reduce the num- to conditions so complicated as "ADVERTISING " AT THE without difficulty. Gliding ber of dealers from the present to be beyond ordinary under- would make an excellent sub- 30,000 and to raise the standard standing. MICROPHONE ject for a summer afternoon of efficiency. This complimentary view of THE ban on advertising at the broadcast, especially if a com- Discounts in the trade have the situation is crushed with the B.B.C. microphone does mentary could be given by also been revised, and the grant- news that departmental unifica- not prevent the Corporation micro -wave from a glider in ing of a discount other than tion is to be established. The from broadcasting a feature pro- flight. that prescribed makes the manu- readjustment is said to have gramme concerned with the The scope for technical ex- facturer liable to prosecution. been made for practical and technique of advertising through periments with a popular appeal Discounts for dealers vary, economic reasons, and it is ex- the ages. Accordingly, National is still enormous, and it is to be according to the annual turn- pected that an influx of new listeners are to hear " Banging hoped that, with television loom- over, from 23 per cent. to 36 per names and new ideas from the the Big Drum " on April 29th. ing ahead, the sound -broad- cent., while wholesalers are Empire department will appear This four -century survey of casting officials will not adopt a allowed from 36 to 45 per cent. in home programmes. British publicity methods will defeatist attitude. The Wireless World, April 71h, x938 377

Cables to the West Cabarets from Abroad BROADCASTING to the West A FRENCH cabaret and music- Country will be improved with the hall show will be relayed from completion of new cables which Paris for British listeners on May the General Post Office is now lay- 13th. Many of the artistes taking ing. The first section, which runs part are prevented by contracts or E EEK from Broadcasting House via Wig- pressure of engagements from more Street and Kensington Gar- coming to England. Archie dens, has just been finished. Campbell, of the B.B.C. Variety SINGAPORE TO N. Taxing the Industry Department, will produce the pro- MALAYA VIA DAVENTRY A SUB -COMMITTEE of Congress in Pocket Transmitter gramme in Paris. If the experi- U.S.A. has proposed the repeal of VIENNESE police are experiment- ment is a success, it is hoped to THE Empire Department at 25,000,000 dollars' worth of excise ing with a small portable trans- visit each of the European capi- Broadcasting House has taxes on various kinds off merchan- mitter which is slung from the tals in turn. thrilled over reports received dise, but radio is not included. policeman's shoulder with the bat- from Malayan amateurs who According to Radio Retailing, teries in his coat pockets. This Photographing Lightning listened to the Daventry broad- wireless manufacturers are making transmitter, which operates on a BEFORE a visible flash of light- casts of the opening of ,the a strenuous effort to persuade the pre -determined wavelength and is ning occurs an invisible discharge 5 for CW only, weighs just' over Singapore Naval Many Government to repeal the per runs along its line of path. This Base. cent. excise tax which is levied 1a lb. complete with batteries. preliminary disturbance is enough of the listeners were tin miners upon the industry. to affect a wireless set, and when and planters situated in out-of- Agony on the Air amplified it can be made to the-way spots in Northern Gift to Scientist's Widow ROAD accidents have assumed actuate the shutter of a camera. Malaya, only roo miles or so THE widow of Heinrich Hertz, such alarming numbers in the In this way photographs of from Singapore itself. Yet, be- who before his death in 1894 U.S.A. that the authorities have lightning which takes place in cause Malaya has no powerful demonstrated the practicability of resorted to gruesome descriptive semi -daylight can be obtained. broadcasting station of its own, Clerk Maxwell's theory of wireless broadcasts in an endeavour to waves and laid the foundation for frighten the public into caution. Another Television Miracle they tuned in Daventry. The Marconi's experiments, was last broadcast ` A GREAT part of the Boat travelled from the week presented with a gift of £250 School Broadcasting in Italy Race, which will be televised, may Naval Base via fourteen miles by Canon Marshall, of Cambridge, ACCORDING to official figures be rowed on the Alexandra Palace of landline to the Singapore on behalf of the Pope, to whom there is a total of 2,627,262 Lake, as I hear that the actual race station, which transmitted it to one of Hertz's manuscripts was children who are taught by school cannot be followed by the camera, Java, whence it was relayed to recently given. broadcasts in Italy, where more and only the finish will be the real than 17,000 sets have been in- thing."-Bowes Park Weekly Holland, conveyed by submarine Aberdeen Wireless Beacon cable stalled in schools. News. to Canterbury, relayed to THE Northern Lighthouse Com- London and so to Daventry, missioners, after considering the Radio Service for Aircraft Turkish Broadcasts from Daventry ? where it was finally re -broadcast question of the large number of AT the International Conference THE South Slav Herald, Yugo- to the Empire. fishing vessels wrecked near Aber- in Dublin on the Atlantic Air Ser- Slavia, reports that, according to deen, have come to the conclusion vice, it was decided to establish the Arab Press in Palestine, the that the solution: of' the problem an elaborate organisation covering Daventry station will shortly CAR RADIO might be met bÿ>the establishment wireless communication, DF and broadcast in the Turkish language. of a wireless beacon at that port. meteorological reports. AN increase in the sales of The B.B.C. will be interested to learn that " the Turkish Govern- car radio sets is forecast ment will itself probably arrange by radio manufacturers who are the programmes." This piece of striving for the same percentage news will be welcomed by the of radio motorists in England hard -worked producers at Broad- as is prevalent in America, casting House, who will no doubt where 17 or 18 per cent. of the seek similar assistance from other cars on the road are fitted with Governments who can spare the wireless. time. Investigations by Philips Stratosphere Investigations show that cat radio is no longer IT is proposed, in the United confined to the large car, since States, to make regular meteoro- 43 per cent. of the sets sold logical observations by aircraft in during the last six months were the sub -stratosphere and pilot- fitted into cars of the 10-12 h.p. less balloons carrying automatic radio-meteorographs are to be em- class. ployed with a view to investigat- ing stratosphere conditions up to SPONSORED PROGRAMMES a height of 50,000 feet. FROM ICELAND LEE. Summer Meeting THE Cairo agitation directed THE Council of the I.E.E. has against European sponsored accepted the invitation of the programmes in English has South Midland Centre to hold its caused advertising agencies to summer meeting in the area from July 4th to 8th. The programme seek fresh stations which they TWO-WAY COMMUNICATION is being maintained during the Spanish includes visits to the works of the could turn to in the case of war by the use of ultra -short-wave transmitter-receivers. As can be G.E.C., B.T.-H., and the Austin necessity. seen from this picture the complete apparatus is easily carried on the Motor Company. Broadcast Advertising is re- back of an infantryman. ported to have approached the N.R.E.A. Election Icelandic programme director AT the recently held annual of Reykjavik with a view to New Radio-Paris Music from Lithuania general meeting of the National radiating sponsored programmes THE building of the Radio - RECENT frequency tests on the Radio Engineers' Association the from the new roo -kW station. Paris super-station at Mehun-sur- new telephone lines from Lithu- following officers were . elected : Yévre is progressing apace. The ania have revealed so great an im- T. F. Nicholson, chairman ; Reg. erection of the aerial mast is provement- that it is now con- A. Loader, hon. secretary ; and almost complete, and the hope is sidered possible to use them for H. W. King, editor of the Asso- FROM ALL expressed that the station will be musical relays. Accordingly, the ciation's journal, Radioman. testing in June. B.B.C. will take an Easter pro- QUARTERS gramme from Kaunas, the Lithu- Miscellaneous Advertisements Free Sets in Egypt anian capital, on Easter Sunday. and Easter Echoes from the Stratosphere ? THE Egyptian Sovereign WITH the approach of the Easter THE Daventry announcer's ordered that 3,000 wireless sets Service holidays slight alterations are voice, according to the Sydney should be distributed amongst the Two German wireless experts necessary in our printing arrange- Bulletin, has recently been accom- poor people of the Nile Valley.. At flew from Berlin to the Antarctic ments. Miscellaneous advertise- panied by a series of strong the same time instructions were in order to remedy a defect which ments intended for the issue of echoes. The favourite evening issued to the effect that educa- had developed in the wireless in- April zist must be received not wavelength in Australia appears tional broadcasts should figure in stallation on the Walter Rau, base later than first post on Thursday, to be 49.59 metres, used by GSA. forthcoming programmes. ship of a large whaling fleet. April r4th. j rcS The Wireless World, April 7th, 1938 ,,,Television Topics FLY -BACK TIME The effects of a slow fly -back time are off and there is also a bright line down more serious. The deflecting voltage the extreme left of the picture. might then have the form of Fig. i (c). With electrostatic deflection the time - The sync pulse and the following interval base circuit is usually of the form shown F TER the spot on the cathode-rayy occur during the fly -back as usual, but it in Fig. 2. The saw-tooth waveform is tube has traced out one scanning is easy to see that when the vision signal generated by the gas -triode VI in con- line it must fly back from the commences (D) the scanning spot is still junction with CI and RI, the voltage right-hand side -of the picture to flying back to the left instead of starting appearing across CI. This is applied to the left before it can start to trace out on the traverse to the right. The result V2 through an RC coupling in the usual the next line. Although the fly -back is is that the left-hand side of the picture way and if C2 and R2 are large enough very rapid in comparison with the line appears to be folded back on itself, for they have little effect. The input capa- traverse, it nevertheless occupies a finite the picture modulation appearing on the city of V2 has no harmful effect for it is time and gaps are fly -back is very in shunt with CI and merely increases its accordingly in- nearly superim- capacity somewhat. cluded in the trans- posed on the pic- The output of Vz is developed across mission of vision (a) ture modulation on the coupling resistance and one deflector signals in which it BLACK the normal line plate is fed from the anode. A portion must occur. LEVEL when the spot at of the output voltage is tapped off at the In Fig. r is shown length starts to junction of R5 and R6 and fed to V3. a portion of the move to the right. This valve produces an output. across R7 vision signal wave- On many trans- which is fed to the other deflector plate. form at (a) ; start- missions there is The conditions 'are such that the outputs ing at the beginning little detail in the at the anodes of V2 and V3 are equal and of a line we have I (b) extreme edges of of opposite phase. Assuming R3 is very the subject and the large compared with R6 this is achieved B i Fig. r-The tele- Iól main effect is then when I + R5 / R6 equals the gain of V3 vision signal wave- E a band of light on and R7=R5+R6. form is shown at the left-hand side. (a) and the correct shape of scanning The effect is dis- The Time -constants waveform at (b). If concerting on pann- the fly -back time ing shots, however, At line frequency the stray capacities exceeds that for the for then an object have an important effect. sync pulse and In thé anode black edge (c) and instead of moving circuit of V2 the capacity represented by

(d) . the left-hand out of the picture C4 includes the anode-cathode capacity side of the picture appears to move of V2, the CR tube capacity and wiring will be folded back. over the edge and capacities, and in the anode circuit of V3, then backwards! C5 represents a similar capacity. The the vision signal transmitted for 85 per A different effect is observed when the absolute value of these capacities is cent. of the complete line period. This is fly -back waveform is as shown at (d). naturally unimportant. What is im- represented in Fig. I by the waveform be- Here the initial fly -back is very rapid, but portant is their value relative to the tween the dotted lines A B. Then the there is an excessive interval after the circuit resistances and the effective resist- synchronising pulse comes along and lasts fly -back before the commencement of the ance is the coupling and valve resistance for io per cent. of the line time ; this is scanning stroke. The folding over of the in parallel. the part B C. Next there is an interval picture does not then occur, but it In the input circuit of V3 the capacity of 5 per cent. of the line time with -a signal appears as if the left-hand side were cut is C6 and includes the Miller effect in this level corresponding to black, and this is shown by C D. The time represented by A D is that of one line with its fly -back. It is I /10125 second for the present trans- missions. For an undistorted picture it is neces- sary that the deflecting voltage should rise linearly during that portion of the time A D devoted to the picture modulation A B and fall back again to its original value during the time B D. The deflecting volt- age (or current with magnetic deflection) should thus have the form of Fig. I (b). It does not matter, however, if the fly- back is quicker than this. For instance, it might occur in io per cent. of the total time instead of 15 per cent. ; if it does this, the remaining 5 per cent. of the time will appear on the left to right scanning stroke and give a black band on the left-hand edge of the picture. This is no disadvan- tage and the presence of such a band is proof that the fly -back time is quicker Fig. 2.-The circuit of a typical time -base for electrostatic deflection is shown here. Tiìe fly- than is really necessary. back time depends largely upon the stray capacities C4, C5 and C6. APRIL 701, »38. WIp@IlS2@ 'rq GIoIld Television Topics- Several inaccurate statements occur. On valve ; its effective value may easily be page 31, in referring to IF intervalve coup- 6o 1,,F. or more. Fortunately the asso- lings with coupled pairs of tuned circuits, it ciated resistance is comparatively low, is stated that " the presence of a short grid 111M cArTi-iYIII lead or even a fairly long one is a matter of being R6 in parallel with the series com- little consequence. The lead need not even the Chaaaie Speetate:a& bination of R5 and the AC resistance of V2. be of low capacitance or have low losses, be- The fly -back time is largely governed cause it is simply in shunt with a resonant by the time constants in these circuits, the circuit having high losses." Actually, of time-constant being the product of the course, shunt capacity is very important in- effective capacity and resistance. The re- deed, and for a given band -width and valve sistance component is usually composed mutual conductance the stage gain is limited chiefly of the valve resistance, because it only by capacity, the gain being inversely proportional to capacity. The importance is lower the coupling resistance, than of low capacity in the tuned circuits gener- being often only one -tenth the value of ally does not seem to be appreciated by the the latter. Now the valve resistance is author. not a constant but varies with the anode In dealing with the question of feeding the voltage, increasing as the voltage falls. CR tube directly from the detector, the only Because of this we always use a high disadvantages of this course are given as the load resistance in a triode voltage ampli- extra high IF gain needed as compared with fier, for the variations in AC resistance the case when a VF stage is used. Actually, are then small compared with the load the greatest difficulty lies in obtaining suffi- occurs. cient output from the last IF valve. He resistance and little distortion goes on to say that with a VF stage it is From the point of view of the time - necessary to use a direct connection between constant, however, the valve resistance the detector and VF valve and between this and load resistance must be considered as valve and the tube in order to preserve the in parallel, and variations in valve resist- DC component. In the circuits shown, how- ance have an appreciable effect. When ever, there is some discriminatory action the valves are being driven hard, as they against the DC component, in spite of the "ONE of the direct results of unbridled com- usually are in a time -base, the variations direct connection. The important question petition between set manufacturers, into a to important. of DC restoration is barely mentioned. which has developed race are Some excellent photographs of defective produce the cheapest sets rather than the best, At the start of the fly -back the grid television images are included and some in- has been an increasing tendency to take un- voltage of V2 is at its most positive point is of of defects, warranted risks in the matter of the choice of dication given the nature the World," March 24. and the anode voltage is consequently at very little as to remedies to components."-" Wireless but the proper It is precisely for this reason that it is not its most negative. The anode voltage of apply. W. T. C. possible to offer McCarthy Chassis at a price V3 is at its most positive potential. At comparable with the cheapest ; but it. is the instant of fly -back, therefore, the AC possible for McCarthy engineers to specify of V2 is at its highest and that materials and components of fine quality, resistance FERRANTI ELECTROLYTIC affording an adequate margin of safety. of V3 is at its lowest. Stray capacities CONDENSERS As an example of these sound principles in are consequently more important in the ELECTROLYTIC condensers are not design and construction, we offer the McCarthy output circuit of V2 than in the case of common for higher voltage ratings than V3, and to obtain a rapid fly -back it, is 50o volts or so, but Ferranti, Ltd., of important to reduce them to the lowest Moston, Manchester, ro, have introduced a -WAVE possible figure. type rated for 65o volts working and 9 -VALVE 4 capable of withstanding surges of 72o volts. The condensers are available in 8-mfd. SUPERHETERODYNE blocks in the cardboard -case type or in Television Reception Technique. By Paul priced at 14 guineas including valves Published by square or cylindrical cans. Special models D. Tyers. Pp. 144+x. can be supplied for tropical use, and in The Circuit in Brief.-The pre -selector Sir Isaac Pitman and Sons, Ltd., Pit- is coupled to high -gain radio frequency Kingsway, these no metal but aluminium is used inside circuit man House, Parker Street, the cases. The overall dimensions of the amplifier operating on all 4 wave -bands, which London, W.C.2. Price r2s. 6d. is transformer-coupled to latest type triode- cardboard -case type are 4in. x x in. x IN the first chapter of this book the basic hexode frequency -changer. There are 2 band- principles of television are very briefly pass transformer -coupled I.F. amplifiers (inter- the resonant mediate frequency 465 K.C.'s). The double described, and in the second diode second detector provides automatic aerial and its feeder are discussed. The main volume control applied to 4 preceding valves, section of the book is then begun with a and first stage L.F. amplification. The triode chapter on amplification, RF, IF and VF. phase-changer is capacity -coupled to push-pull Chapters on cathode-ray tube practice, time - output pentodes (or Harries-tetrodes) delivering base and synchronising circuits follow, and g watts. then the vision receiver as a whole is dealt Principal Features.-Waveband coverage - with. The book concludes with a chapter 12.8 -33, 29-80, x90-550, 800-2,000 metres. on vision receiver faults and an appendix. Controls-sensitivity control (varying bias on In his preface the author addresses him- R/F stage) : 5 -position wave -change and to those who may become en- gramophone switch : combined volume control self primarily and on/off switch and progressive variable tone gaged in the design of a television receiver, control (both operative on radio and gramo- and it is, consequently, upon its value to phone). must be judged. such engineers that the book The McCarthy Portable. 6 gns. Unusually Although a fairly wide gtound is covered, fine performance obtained from special reflex the book is to a large extent merely descrip- circuit. Weight only r6¡lbs. Compact. Ex- tive in character and the details are very ceptionally low consumption. Attractive finish In very few instances are values of and choice of three colours. sketchy. Ferranti high - components mentioned; while this may be a voltage conden- legitimate omission in a book intended for EASY TERMS ON APPLICATION ser in cardboard Send 3d. In stamps for complete illustrated catalogue designers, it detracts from its value when case. with technical data and circuit diagrams of other coupled with an absence of any intimation interesting McCarthy chassis of all types, for A.C., as to how they may be calculated. It is true Battery, or A.C. D.C. Abridged list free of charge. that it is always possible to derive the neces- With their high voltage rating 'the con- sary equations for oneself from basic circuit densers are suitable for use as reservoir con- Mt,CARTI1 V RADIO. LTD theory, but this is a lengthy business and densers in HT supply systems with trans- 44, Westbourne Grove, London, W.2 few people can spare the time. former windings up to 45o volts RMS. Telephone : Bayswater 3201/2. 320 The Wireless World, April 7th, 1938

Random Radiations By "DIALLIST" Sunday Television liteners, or, say, 3,500,000. As it is, the time to convince them that it doesn't cost total output from B.B.C. stations represents much THIS week B.B.C. to produce a sensitive set that will the inaugurated its roughly one -tenth of a watt per licence, and bring in heaps of foreign it Sunday television programmes from the stations, though that of the more - Alexandra Italian stations than four costs a lot to make a receiver that will please Palace, and these should help to tenths. a musician's ear when dealing with a trans- give television another big push in the right mission from direction. With an outside broadcast in the Queen's Hall. Short of actual demonstration, it is often still harder the afternoon and a play in the evening, Housing the Television Receiver to make them believe for owners of television sets had splendid fare that anything like TELEVISION has introduced new fidelity you must have a big set housed ìn on the first Sunday, and it is expected that, a large cabinet. during the lighter part of the year at any problems to the designer, apart from rate, some such arrangement is likely to those of an electrical nature. When the ap- be continued. Another excellent innova- paratus is not in use, the blank end of the The Only Way tion is the transmission of a news bulletin CR tube is apt to spoil the appearance of At this point your seeker after good on the ultra -short waves after the week -day the cabinet, looking at it as a piece of furni- counsel may confound you by saying that he evening programme. As the evening trans- ture. To overcome this it has been proposed (or more probably she) has heard in some- mission begins at 9 o'clock, those who were that the tube and speaker be masked by a body else's house a midget, almost given looking in previously missed the National grille or fret which is arranged to fold so as away by its vendors, whose reproduction bulletin. It is the recording of this that is to expose the end of the tube only when the was as near perfect as makes no matter. now sent out for the benefit of viewers. apparatus is in use. You then realise that the enquirer has never As the equipment is used in a generally heard-and what proportion of those who darkened room, some illumination of the listen to wireless programmes have In the Right Direction controls is often desirable. The suggestion heard? has been made that the control panel should -a first-rate receiving set at work. Their That 41.5 -megacycle news bulletin I wel- wireless education is, in fact, little therefore be made of transparent moulded more ad- come, too, for another reason : it gives vanced, so far as is material and illuminated from the edge. the ear concerned, than those who have wireless receivers that tune yours was the best part of ten years ago. down to the neighbourhood of 7 metres real The use of a plastic material has the great If your own set happens advantage of simplicity in manufacture. to be in working encouragement to use their sets for local order at the time (though that belonging ultra -short-wave reception. It is true that to the real enthusiast is generally out of they can't yet sample to the full the quality action for alterations just at such moments) of reproduction, that is obtainable on the The Simple Little Set you can stage a demonstration that will be ultra -short waves except on Sundays, for on YOU, I expect, are like me in having a real revelation by inviting both your sup- other days this news bulletin is a recording. pliant and the owner of the midget set to I hope, though, the bulletin may be the friends who appoint you their mentor and guide in matters wireless. If so, you are spend the following evening, the latter thin end of a wedge that many of us would being asked to bring his little marvel with like to see driven home. The Wireless familiar with those who desire " only the They want, him. By installing a simple aerial and earth - World has long urged that the whole of one simplest little set." they de- clare, something quite small ; it needn't switching system, so that you can work one or other of the London programmes should set against the other, you will soon convince be radiated on the ultra -short waves, and it bring in more than just two or three foreign stations, and really they could manage quite all concerned that there is something not ob- is understood -that the B.B.C.'s preparations tainable for a five -pound note or with a tiny for doing so are complete to the last turn of well if it brought in none at all. But as they are musically inclined and like to hear receiver in this quality business. The alter- wire. If only the oppositieen to them were native is to take the believer in five -pound removed a wonderful field would be opened the big concerts perfectly reproduced, what they do insist upon is high quality from the high -quality reproduction to some big wire- for the development of the genuine high- less shop, where the respective merits of the fidelity receiving set for local use only. You loud speaker. They conclude by saying that since they don't want lots of foreign stations simple little set and the highly complicated have only to hear the " sound " portion of big set can be demonstrated. the present television programmes repro- quite a cheap little set will obviously do all duced by such an instrument to realise what that they want, so what can you recommend ti ti ti an appeal there would be to those who want at about five pounds? Observing, perhaps, the very best in radio reproduction and are a slightly pained expression on your coun- Foreign Broadcasts tenance, they hasten to add that, of course, prepared to pay for it. I mentioned that our Arabic if it was really necessary they wouldn't RECENTLY ti g ti mind going to six pounds, or perhaps even broadcasts were not going down too to seven. They then stress the point that it well with listeners in some parts of the Near Surprising Italian Figures is only a little set that they want-a port- East, Palestine in particular. Further in- able, in fact, might do quite well. formation from people on the spot adds JWAS astonished to hear the other night confirmation. There appear to be two chief in the news bulletin that the official troubles. One is, as I suggested, that they figure for licensed listeners in the whole of Hard to Convince don't like the European music that we give Italy was only 840,000. This means that Whenever that sort of enquiry comes my them for their entertainment ; the other though Italy's population is only one -and- way I am reminded of a jest that appeared that the Arabic spoken by the B.B.C. a -quarter millions less than ours her licensed in Punch many years ago. The illustration announcers and talkers is too highbrow to listeners number less than one -tenth of those showed a perfectly brainless youngster in be readily understandable by many of the in the United Kingdom. With us, approxi- converse with a hard-boiled old horse coper. Arab inhabitants of Palestine. Readers mately one in five of the entire population Every horse in the stables has been trotted may remember that when this business of holds a receiving licence ; for Italy the figure out for inspection and found not quite the short-wave broadcasting in foreign lan- is one in fifty-one. Yet the Italian broad- thing. " I thinks I knows exactly what you guages was first mooted I ventured to doubt casting service is a particularly good one. wants, sir," says the dealer. " Well-bred whether it would be a success if undertaken Not reckoning short-wave transmitters, the 'oss up to a good deal of weight, sound as a direct from this country owing to the diffi- country possesses i8 stations, of which ten bell and with perfect mouth and manners. culties up by the existence of so many are rated at to kilowatts or more, and only Good shoulders, the right sort of 'ocks, well languages and dialects. I suggested then one at less than r kilowatt. Italy has thus ribbed up, short in the back and deep in the that it might be better, so far as the Empire one more station than Britain, though there chest. Jump hanything. Price about and mandated countries were concerned, to is considerable difference in the total out- twenty pound. I can tell you just where make greater use of local broadcasting ser- put rating. Taken together, the ratings of to find 'im." " Whdre? " " In 'Eaven." vices. And that I still think is the best British stations work out at 86i.3 kilowatts, It's awfplly hard to explain to the uniniti- possible solution of the problem. Palestine, whilst the Italian figure is 363.2. On a kilo- ated that such a simple little set at such a for example, has a pretty good broadcast- watt basis Italy should have rather more simple little price is not to be found on ing service of its own, and the 20 -kilowatt than two -fifths of our number of licensed this earth of ours. It takes you all your Jerusalem station must be well heard not APRIL 7th, í938. WfiTsD@og 2r WcuIlcl only in its own country but also over a con- The valve is the Type zzo IPT, and is siderable part of the world where Arabic is rated for 15o volts and 8o volts for anode spoken. Is it not worth while at any rate and screen respectively. As a detector re- to try the experiment of subsidising first- sistance coupling should be used with a o. r rate programmes for Arabs from that Ma coupling resistance, while the screen same material should be fed from positive HT through a station, providing at the time [DNDEN5ER SPECIALI5T5 for the news bulletins and leaving it to the 1 Mº resistance and decoupled with a local speakers to use the kind of Arabic 1 mfd. condenser. The mutual conductance FOR AVER THIRTY YEARS that is most readily understood by their is i mA /v at 15o volts, 6o volts, and o hearers? volts for anode, screen and grid. The valve is fitted with a 7 -pin base and the anode is the top connection. Many Happy Returns Although similar to an RF pentode, the READERS, I'm sure, were delighted to valve is not recommended as an RF ampli- hear the " Roosters " again when they fier, for its grid -anode capacity is too high gave their twenty-first birthday party the for the maintenance of stability. The valve other evening. Theirs is a record to be is designed to operate as a detector. proud of, as you must have realised if you heard that show. The " Roosters" were born as a concert party at Salonika in 1917, and took their name from Captain Roose, Television Programmes who was commanding the company to which they belonged. They did noble work at THURSDAY, APRIL 7th. Salonika in cheering up troops dispirited by 3, Powder and Pipe-clay-a revue of old Army a long period of doing absolutely nothing. songs. 3.30, British Movietonews. 3.40, From Salonika they went to Palestine, 135th Edition of Picture Page. where they were officially appointed as 9, 136th Edition of Picture Page. 9.30, O.B. Divisional Concert Party. And a pretty from the Harringay Arena of the I.ight- hard time they must have had of it, trek- Heavyweight Championship of Great Britain- McAvoy v. Harvey. 10, News Bulletin. king miles every day by lorry from unit to .dey,. unit. Before the Armistice they were at FRIDAY, APRIL 8th. Alexandria, and they continued the good 3, Marcel Boulestin gives a cooking demonstra- II work there until they were " demobbed " in tion. 3.15, Gaumont -British News. 3.25-4.25e 1919. Their first broadcast was in 1923-I " Will Shakespeare "-a special version of remember it 'since then they have Clemente Dane's great biographical play, with well-and Henry Oscar in the name part. provided some of the most welcome of And he will. Such is the depend- variety.. was good 9, Repetition of 3 p.m. programme. 9.15 radio's It to hear when ability of the service he uses. It's the the roll was called that only one of the British Movietonews. 9.25, " The Seventh Man -a play by Michael Redgrave, based on the same with T.C.C. original Roosters had fallen by the way. story by " Q." 9.55, Preview. 10.5, News Long may the rest live and often may they Bulletin. If T.C.C. make a claim for a condenser, entertain us ! SATURDAY, APRIL 9th. or for a particular service, you may rest 2.50, O.B. from the Wembley Stadium of the assured that that claim will be met. For International Association Football -Match- over 32 years T.C.C. have been giving Three -Valve Straight Set England y. Scotland. 4.40-4.50, Gardening IT is regretted that an error occurred in the talk by R. Findlay-Spring Flowers. a service second-to-none in the in- in design, practical wiring diagram of this receiver ; 9, " Going Places "-a trivial travelogue. dustry. Pioneers technical the diagram appeared on page 284 of The 9.20, Gaumont-British News. 9.30, " Wren of pioneers in the policy of giving just Wireless World for March 31st, 1938. In St. Paul's " written for television by Christine that little more, T.C.C. have earned the the drawing pin No. 1 of the valveholder for Hablo. 10.10, " Clock Summer in with Horrabin summertime feature. 10.20, confidence of all who use and specify the APP4E valve was shown unconnected ; "-a actually, of course, it should be joined to News Bulletin. condensers. T.C.C. Condensers. and cathode, Pin No. 6. SUNDAY, APRIL loth. Condenser Service are 8.50, News Bulletin. 9.5, " The Blue Madonna" danced by Wendy Toye to the music of the DEPE NDABLE NEW COSSOR BATTERY VALVE Air on the G String (Bach). 9.10, Clothes Line. of most unusual has been 9.25, Gaumont -British News. 9.35-10.15, AVALVE type " Wien," a Viennese entertainment, including introduced by A. C. Cossor, Ltd., of Lisa Minghetti, Irene Prador and Marcella Cossor House, Highbury Grove, London, Salzer. N.5. It is an indirectly heated pentode for MONDAY, APRIL uth. battery operation ! 3, " Going Places," repetition of Saturday's Detector valve 9 p.m. programme. 3.25, Gaumont -British for portable News. 3.35, " The Seventh Man," repetition of sets. Friday's 9.25 p.m. programme. 9, Starlight. 9.10, British Movietonews. 9.20, Cabaret Cruise, compered by Commander A. B. Campbell. 10, News Bulletin. TUESDAY, APRIL 12th. 3, Fashions for Cruising. 3.15, British Movie- tonews. 3.25, Cabaret Cruise, repetition of Monday's 9.2o p.m. programme. 9, Spring Fashions. 9.15, Gaumont -British News. 9.25, " The Gay Lord Quex "-a play by Arthur Pinero. 10.20, News Bulletin. U WEDNESDAY, APRIL i3th. T. 3, " The End of the Beginning," a comedy in ALL -BRITISH one act by Sean O'Casev. 3.25, Gaumont - The heater takes 0.2 ampere at 2 volts, British News. 3.35-4.35, " Everyman "-a and the valve is fitted with an indirectly masque by Pepler. CONDENSERS micro - heated cathode in order to reduce 9, Ambrose and his Orchestra, with Evelyn phony. It is intended primarily for use as Dall, the Three Admirals, and Max Bacon. in portable receivers, in which a detector 9.30, British Movietonews. 9.40, " The Maker THE TELEGRAPH CONDENSER CO.LTD. trouble is sometimes experienced from of Dreams," a Fantasy by Oliphent Down- microphony when filament -type valves are cast includes Dinah Sheridan and Quinton WALES FARM RD. NORTH ACTON,W.3. nsed. McPherson. 4443 The Wireless A,38ril 71 PRINCIPAL BROADCASTING STATIONS OF¡. nEUROPE Arranged in Order of Frequency and Wavelength (Stations with an Aerial Power of 50 kW. and above in heavy type) Tuning Station. his. Positions. Metres. kW. Tuning Station. kas. Positions. Metres. kW. Ankara (Turkey) ...... 152 1973.5 5 Leipzig (Germany) 785 382.2 120 Kaunas (Lithuania) ...... 153 1961 7 Barcelona, EAJI (Spain) ...... 795 377.4 7.5 Radio Romania (Brasov) Romania.. .. 160 1875 150 Lwow (Poland) ...... 795 377.4 50 Hilversum, No. 1 (Holland) (10 kW. till 1640) 160 1875 150 Welsh Regional (Penmon) (Anglesey) 804 Lahti (Finland) ...... 166 373.1 5 1807 150 Welsh Regional (Washford) ...... 804 373.1 Moscow, No. 1 (Komintern) (U.S.S.R.) ... 172 1744 70 500 Milan, No. 1 (Italy) ... 814 368.6 50 Paris (Radio Paris) (France) .,, ... 182 1648 80 Bucharest (Romania) ...... 823 364.5 Istanbul (Turkey) ...... 185 1622 12 5 Agen (France) ... 832 360.6 Irkutsk (U.S.S.R.) ...... 187.5 1600 1.5 20 Kiev, No. 2 (U.S.S.R.) ... .,, ... 832 360.6 40 Deutschlandsender (Germany) ...... 191 1571 60 Berlin (Germany) 841 356.7 100 National (Droitwich) ...... 200 1500 140 Sofia (Bulgaria) 850 352.9 100 Minsk (U.S.S.R.) ...... 208 1442 35 Norwegian RelayStations Reykjavik (Iceland) ...... 208 - 1442 16 Valencia (Spain) 850 352.9 3 Motala (Sweden) ...... 216 1389 150 Simferopol (U.S.S.R.) ...... Novosibirsk (U.S.S.R.) .,, 859 349.2 10 .:. 217.5 1379 100 Strasbourg (France) ... 859 349.2 100 Warsaw, No. 1 (Poland) ...... 224 1339 120 Poznan (Poland) Luxembourg ... 868 345.6 16 ...... 232 1293 150 London Regional (Brookmans Park) 877 Moscow, No. 2 (U.S.S.R.) ...... 232 342.1 70 1293 100 Linz (Austria) ... 886 338.6 Kalundborg (Denmark) ...... 240 1250 15 60 Graz (Austria) 338.6 15 Vienna, No. 2 (Austria) ...... 240 1250 ...... 888 0.5 Helsinki (Finland) 895 335.2 10 Kiev, No. 1 (U.S.S.R.) ...... 248 1209.6 100 Limoges, P.T.T. (France) -., ...... 895 335.2 1.5 Tashkent (U.S.S.R.) ...... 256.4.... 117G 25 Hamburg (Germany) ... Oslo (Norway)...... 904 331.9 100 ...... 260 1153.8 60 Dniepropetrovsk (U.S.S.R.) ... .., 913 Vigra (Aalesund) (Norway) ...... 260 328.6 10 1153.8 10 Toulouse (Radio Toulouse) (France) 913 328.6 Leningrad, No. 1 (U.S.S.R.) ...... 271 1107 60 100 Brno (Czechoslovakia) ...... 922 325.4 32 Tromsö (Norway) ...... 282 1065 10 Brussels, No. 2 (Belgium) ...... 932 321.9 15 Tiflis (U.S.S.R.) ...... 283 1060 35 Algiers (Algeria)...... 941 Moscow, No. 3 (U.S.S.R..) ...... 300 318.8 12 1000 100 Göteborg (Sweden) 941 318.8 10 Saratov (U.S.S.R.) ...... 340 882.3 20 Breslau (Germany) ...... , 950 315.8 100 Finmark (Norway) ...... 347 864 10 Paris (Poste Parisien) (France) 959. 312.8 60 Archangel (U.S.S.R.) ...... 350 857.1 10 Bordeaux-Sud-Ouest (France) Rostov -on -Don (U.S.S.R.) 988 309.9 30 ...... 355 845.1 20 Odessa (U.S.S.R.) 968 Budapest, No. 2 (Hungary) ...... 359.5 309.9 10 834.5 18 Northern Ireland Regional (Lisnagarvey) ... 977 307.1 Sverdlovsk (U.S.S.R.) 37.5 100 800 40 Bologna (Radio Marconi) (Italy) ...... 986 304.3 50 Voroneje (U.S.S.R.) ...... 390 769 10 Torun (Poland) (Sweden) 986 304.3 24 Boden ...... 392 765 0.6 Hilversum No. 2 (Holland) (15 Banska-Bystrica (Czechoslovakia) kW. till 1810) 995 301.5 80 (15 kW. 392 765 30 Bratislava (Czechoslovakia) ... 1004 after 1700) ...... 298.8 13.5 Chernigov (U.S.S.R.) ...... 1013 296.2 Geneva (Switzerland) ...... 401 748 4 1.3 Midland Regional (Droitwich) 1013 296.2 70 Ostersund (Sweden) ...... 413.5 726 0.6 Barcelona, EAJ15 (Spain) Oulu (Finland)...... 1022 293.5 3 ...... 431 696 10 Cracow (Poland) 1022 Tartu (Estonia) ...... 512 293.5 2 586 0.5 Oviedo (Spain)...... 1022 293.5 Hamar (Norway) ...... 519 0.7 578 0.7 Königsberg, No. i (Heilsberg) (Germany) ... 1031 291 100 Innsbruck (Austria) ...... 519 578 1 Parede (Portugal) Ljubljana (Yugoslavia) 1031 291 5 ...... 527 569.3 6.3 Leningrad, No. 2, RW 70 (U.S.S.R.) 1040 Viipuri (Finland) ...... 527 288.5 10 569.3 10 Rennes-Bretagne (France) ... ..- ... 1040 288.5 120 Bolzano (Italy) ...... 536 559.7 10 West of England Regional (Washford) Wilno (Poland) ... 1050 285.7 50 ...... 536 559.7 50 Bari No. 1 (Italy) 1059 No, 1 283.3 20 Budapest, (Hungary) 549.5 - 120 ...... 546 Paris (Radio Cité) (France) ...... - 1068 280.9 2 Beromünster (Switzerland) ...... 556 539.6 100 Tiraspol, RW57 (U.S.S.R.) ... Radio Eireann (Athlone) . 1068 280.9 10 (Ireland) ...... 565 531 100 Bordeaux -Lafayette (France) ...... 1077 278.6 35 Klaipeda (Lithuania) ...... 565 531 15 Falun (Sweden) Palermo (Italy) ... 1086 276.2 2 ...... 565 531 3 Zagreb (Yugoslavia) ... 1086 Stuttgart (Germany) ...... 574 276.2 0.7 522.6 100 Madrid, EAJ7 (Spain) -,...... 1095 274 5 Alpes -Grenoble, P.T.T. (France) ...... 583 514.6 20 Vinnitsa (U.S.S.R.) ... Madona (Latvia) 1095 274 - 10 ...... 583 514.6 50 Kuldiga (Latvia) 1104 271.7 Vienna, No. 1 (Austria) 10 ...... 592 506.8 100 Naples No. 1 (Italy) ...... Athens (Greece) ...... 1104 271.7 10 ...... 601 499.2 15 Morayska-Ostrava (Czechoslovakia) 1113 Rabat (Morocco) ...... 601 289.5 11.2 .... 499.2 25 ; Alexandria, No. 1 (Egypt) -.. ... 1122 267.4 Sundsvall (Sweden) ... .., ...... 601 0.5 499.2 10 North-East Regional (Stagshaw) .,. ... 11.22 267.4 60 Florence, No. 1 (Italy) ... .,. ... 610 491.8 20 Nyiregyhaza (Hungary) ...... 1122 267.4 Brussels, No. 1 (Belgium) 6.25 ...... 620 483.9 15 Hörby (Sweden) 1131 Cairo, No. 1 265.3 100 (Egypt) ...... 620 483.9 20 Turin, No. 1 (Italy) -:. Christiansand (Norway) ...... 1140 263.2 7 ...... 629 476.9 20 Genoa, No. 1 (Italy) ... Lisbon (Portugal) ... 1140 263.2 10 ...... 629 476.9 15 Trieste (Italy) ...... 1140 Tröndelag (Norway) ...... 629 263.2 10 476.9 20 London National (Brookmans Park) 1149 261.1 20 Prague, No. 1 (Czechoslovakia) ... 638 470.2 120 North National (Slaithwaite) Lyons, P.T.T. (France) 1149 261.1 20 ...... 648 483 100 Scottish National (Westerglen) ...... 1149 Petrozavodsk (U.S.S.R.) ...... 648 261.1 50 463 10 Kosice (Czechoslovakia) -...... 1158 259.1 Cologne (Germany) ...... 658 455.9 10 100 Monte Ceneri (Switzerland) ...... 1167 257.1 15 Jerusalem (Palestine) ...... 668 449.1 20 Copenhagen (Denmark) .-. 1176 North Regional (Slaithwaite) ...... 668 255.1 10 449.1 70 Nice -Celte d'Azur (France) 1185 253.2 60 Sottens (Switzerland) ...... 677 443.1 100 Frankfurt (and Relays) (Germany) ...... 1195 Belgrade (Yugoslavia) ...... 251 25 686 437.3 20 i Prague, No. 2 (Czechoslovakia) -.. ... 1204 Paris, P.T.T. (France) ...... 695 249.2 5 ... 431.7 120 I Lille, P.T.T. (France) ...... 1213 247.3 Stockholm (Sweden) 60 ...... 704 426.1 55 Rome, No. 2 (Italy) ... 1222 245.5 Rome, No. 1 (Italy) ...... 60 ... 713 420.8 100 Gleiwitz (Germany) ... 1231 243.7 Hilversum, No. 3 (Holland) .., 5 722 ¡ 415.4 17 Cork (Ireland) ... 1235 242.9 1 Kharkov, No. 1 (U.S.S.R.) ...... 722 415.4 10 Saarbrücken (Germany) ...... 12.49 Fredrikstad (Norway) ...... 240.2 17 ... 722 415.4 1 Bilbao, EAJ8 (Spain) ...... 1258 238.5 Madrid, EAJ2 (Spain) ...... 731 1 410.4 3 Riga (Latvia) ... 1258 238.5 15 Seville (Spain) ...... 731 410.4 5.5 Florence, No. 2 (Italy) ... 1258 Tallinn (Estonia) ...... 238.5 1 ...... 731 410.4 20 Nürnberg (Germany) ...... ,. 1267 236.8 Munich (Germany) ...... 740 2 ... 405.4 100 Radio Mediterranée (Juan-les-Pins) (France) 1276 235.1 27 Marseilles, P.T.T. (France) ...... 749 400.5 100 Aberdeen 1285 Pori (Finland) ...... 233.5 1 ... 749 400.5 1 Dresden (Germany) ... 1285. 233.5 0.25 Katowice (Poland) ...... 758 ... 395.8 12 Klagenfurt (Austria) ... 1294. 231.8 5 Scottish Regional (Burgheac') ... 767 ... 391.1 60 VorarlbergAustria(Austria) ... :.. 1294 231.8 5 Scottish Regional (Westerglen) ...... 767 391.1 70 Danzig ..: 1303 Stalino .., ...... 230.2 0.5 (U.S.S.R.) ... 776 386.6 10 Swedish Relay Stations 1312 228.7 Toulouse, ...... 776 P.T.T. (France) ... 386.6 120 Magyarovar (Hungary) ...... 1321 227.1 1.25 APRIL 7th, 1938. weremg '323 W©m

Tuning Tuning Station. kc/s. Positions. Metres. kW. Station. Ws. Positions. Metres. kW. German Relay Stations ...... 1330 225.6 - Alexandria, No. 2 (Egypt) ...... 1429 209.9 0.5 Lodz (Poland) ...... 1339 224 2 Turku (Finland) ... 1429 209.9 0.5 Montpellier, Y.T.T. (France) ...... 1339 224 1.5 Miskolc (Hungary) 1438 208.6 1.25 Dublin (Ireland) ...... 1348 222.6 0.5 Paris (Eiffel Tower) (France) 1456 206 7 Königsberg, No. 2 (Germany) ...... 1348 222.6 2 Pecs (Hungary) 1465 204.8 1.25 Rjukan (Norway) ...... 1348 222.6 0.15 Belgian Relay Stations ... 1465 204.8 0.1 Salzburg (Austria) ...... 1348 222.6 2 Bournemouth ...... 1474 203.5 1 Tampere (Finland) ...... 1348 222.6 0.7 Plymouth 1474 203.5 0.3 Nottoden (Norway) ...... 1357 221.1 0.3 Binche (Belgium) ... 1487 201.7 0.1 Italian Relay Stations ...... 1357 221.1 - Belgian Relay Stations ... 1492 201.1 0.1 L'Ile de France (France) ...... 1366 219.6 2 Nimes (Franco) 1492 201.1 0.7 Basle (Switzerland) ...... 1375 218.2 0.5 Albacete (Spain) ...... 1492 201.1 0.2 Berne (Switzerland) ...... 1375 218.2 0.5 Santiago(Spain)Sain ...... 1492 201.1 0.5 Warsaw, No. 2 (Poland) ...... 1384 216.8 7 Belgian Relay Stations ... 1500 200 0.1 Lyons (Radio Lyons) (France) ...... 1393 215.4 25 Pietarsaari (Finland) ...... 1500 - 200 0.25 Stara -Zagora (Bulgaria) ...... 1402 214 2 Radio Alealá (Spain) ...... 1500 200 0.2 Radio Normandie (Fécamp) (France) ... 1411 212.6 15 Karlskrona (Sweden) ... 1530 196 0.2 Vaasa (Finland) ...... 1420 211.3 10 Liepàja (Latvia) 1734 173 0.1 SHORT-WAVE STATIONS OF THE WORLD

Call - Tuning Call Tuning Station. Sign. kc/s. Positions. Metres. kW. Station. Sign. kola. Positions. Metres. kW.

Bombay (India) ...... VUB 3,300 90.80 4.5 Capetown (South Africa) ... ZRK 9,600 31.23 5 Bandoeng (Java) ...... PMY 5,150 58.30 1 Sourabaya (Java) ... YDB 9,610 31.20 1 Caracas (Venezuela) ...... YV 5RC 5,800 51.72 1 Rome Italv ...... 12R03 9,635 31.13 25 Vatican City (Vatican State) ... HVJ 5,970 50.26 15 Lisbon (Portugal) ...... CS2WA 9,655 31.09 2

...(Italy) - Moscow (U.S.S.R.) ...... VZSPS 6,000 50.00 20 Buenos Aires (Argentina) ... LRX. 9,660 31.06 10

Mexico City (Mexico) ...... XEBT 6,000. 50.00 1 Madrid (Spain) ...... EAQ1 9,860 30.52 10 Montreal (Canada) ...... CFCX 6,000 50.00 0.1 Lisbon (Portugal) ...... CSW3 9,940 30.18 5 Pretoria (South Africa) ...... ZRH 6,000 50.00 5 Ruysselede (Belgium) ORK 10,330 29.04 9 Havana (Cuba) ...... COCO 6,010 49.92 2.5 Buenos Aires (Argentina) ...... LSX 10,350 28.99 12 Prague (Podebrady) (Czechoslovakia) OLR2A 6,010 49.92 30 Teneriffe (Canary Isles) ...... EAJ43 10,360 28.94 4 Zeesen (Germany) ...... DJC 6,020 49.83 5-40 Lisbon (Portugal) ...... CSW2 11,040 27.17 5 Boston (U.S.A.) ...... W1XAL 6,040 49.67 20 Prangins (Radio -Nations) (Switz'l'd) HBO 11,400 26.31 20 Miami (U.S.A.) ...... W4XB 6,040 49.67 5 Warsaw (Poland) ... SPD 11,530... 26.01 20 Daventry (Gt. Britain) ...... GSA 6,050 49.59 10-50 Winnipeg (Canada) ...... CJRX 11,720 25.60 2 Cincinnati (U.S.A.) ...... W8XAL 6,060 49.50 10 Paris (Radio -Colonial) (France) ... TPA4 11,720 25.60 12 Philadelphia (U.S.A.) ...... W3XAU 6,060 49.50 10 Huizen (Holland) ... PHI 11,730 25.5 25 Motata (Sweden) ...... SBO 6,060 49.50 0.75 Daventry (Gt. Britain) ...... GSD 11,750 25.53 10-50 Vienna (Austria) ...... OER2 6,080 49.41 1.5 Zeesen (Germany) ... DJD 11,770 25.49 5-40 Lima (Peru) ...... OAX4Z 6,080 49.41 15 Boston (U.S.A.) ...... W1XAL 11,790 25.45 20 Chicago (U.S.A.) ...... W9XAA 6,080 49.41 0.5 Tokio (Japan) ...... JZJ 11,800 25.42 50 Nairobi (Kenya) ...... VQ7L0 6,080 49.41 0.5 Vienna (Austria) ... OER3 11,800 25.42 1.5 Delhi (India) ...... VUD 6,080 49.41 - Rome (Italy) ... 12R04 11,810 25.40 25 Toronto (Bowmanville) (Canada) ... CFRX 6,090 49.26 0.5 Daventry (Gt. Britain) GSN 11,820 25.38 10-50 Hong Kong (China) ...... ZBW2 6,090 49.26 2.5 Lisbon(Portugal) ... CWS4 11,840 25.34 5 Capetown (South Africa) ...... ZRK 6,100 49.20 5 Zeesen (Germany) ...... DJP 11,850 25.31 5.40 Johannesburg (South Africa) ... ZRJ 6,100 49.20 0.2 Daventry (Gt. Britain) GSE 11,860 25.29 10-50 Bound Brook (U.S.A.) ...... W3XAL 6,100 49.18 15-35 Pittsburgh (U.S.A.) ...... W8XK 11,870 25.27 24 Chicago (U.S.A.) ...... W9XF 6,100 49.18 10 Paris (Radio Colonial) (France) ... TPA3 11,890 35.24 12 Belgrade (Yugoslavia) ... YUA 6,100 49.18 1 Moscow (U.S.S.R.) ... VZSPS 12,000 25.00 20 Daventry (Gt. Britain) ...... GSL 6,110 49.10 10-50 Reykjavik (Iceland)...... TFJ 12,235 24.52 7.5 Calcutta (India) ...... VUC 6,110 49.10 0.5 Warsaw (Poland) ... SPW 13,635 22.00 2 Wayne (U.S.A.) ...... W2XE 6,120 49.02 10 Amateurs 14,000 21.42 0.01 Pittsburg (U.S.A.) ...... W8XK 6,140 48.83 30 to to Winnipeg (Canada) ...... CJRO 6,150 48.78 2 14,400 20.84 San Jose (Costa Rica) ...... TIPG 6,410 46.80 1 Sofia (Bulgaria) ... LZA 14,970 20.04 1.5 Amateurs ... 7,000 42.86 0.01 Zeesen (Germany) ...... DJL 15,111 19.85 5.40 to to Vatican City (Vatican State) ... HVJ 15,123 19.84 25 7,300 41.10 Daventry (Gt. Britain) ...... GSF 15,140 19.82 10-50 Tokio (Japan) ...... JVP 7,510 39.95 50 Bandoeng (Java) ...... YDC 15,160 19.80 1.5 Moscow (U.S.S.R.) ...... RKI 7,540 39.79 25 Daventry (Gt. Britain) ... GSO 15,180 19.76 10-50 Prangins (Radio-Nations) (Switz'l'd) HBP 7,800 38.48 20 Hongkong (China) ...... ZBW4 15,190 19.75 2.6 Budapest (Hungary)...... HAT4 9,125 32 .88 6 Zeesen (Germany) DdB 15,200 19.74 5-40 Prangins (Radio Nations) (Switz'l'd) HBL 9,340 32.10 20 Pittsburgh (U.S.A.) ...... W8XK 15,210 19.72 20 Havana (Cuba) ...... COCH 9,430 31.80 10 Huizen (Holland) ... PCJ 15,220 19.71 60 Madrid (Spain) ...... EAR 9,480 31.65 10 Prague (Podebrady) (Czechoslovakia) OLR5A 15,230 19.70 30 Rio de Janeiro (Brazil) ...... PRF5 9,500 31.58 12 Paris (Radio -Colonial) (France) ... TPA2 15,243 19.68 12 Melbourne (Australia) ...... VK3ME 9,510 31.55 2 Boston (U.S.A.) ... W1XAL 15,250 19.67 10 Bangkok (Siam) ...... HS8PJ 9,510 31.55 5 Daventry (Gt. Britain) ...... GSI 15,260 19.66 10-50 Daventry (Gtr Britain) ...... GSB 9,510 31.55 10-50 Wayne (U.S.A.) ... W2XE 15,270 19.65 10 Skamlebaek (Denmark) ...... OZF 9,520 31.49 6 Zeesen (Germany) ...... DdQ 15,280 19.63 5-40 Pretoria (South Africa) ...... ZRH 9,520 31.49 5 Buenos Aires (Argentina) ...... LRU 15,290 19.62 7 Hongkong (China) ...... ZBW3 9,520 31.49 2.6 Daveetry (Gt. Britain) GSP 15,310 19.60 10-50 Jelöy (Norway) ...... LKC 9,520 31.40 1 Prague(Podebrady)(Czechoslovakia) OL115B 15,320 19.58 30 'Schenectady (U.S.A.) ...... W2XAF 9,530 31.48 25 Schenectady (U.S.A.) W2XAD 15,330 19.57 18 Suva (Fiji) ...... VPD2 9,540 31.45 0.4 Zeesen (Germany) ...... DJR 15,340 19.56 5-40 Tokio (Japan)...... JZI 9,540 31.45 50 Budapest (Szekesfehervar) (Hungary) HAS3 15,370 19.52 6 Prague (Podebrady) (Czechoslovakia) OLR3A 9,550 31.41 30 Zeesen (Germany) ...... DJE 17,760 16.89 5-40 Zeesen (Germany) ...... DJA 9,560 31.38 5-40 Wayne (U.S.A.) ... \V2XE 17,760 16.89 10 Lima (Peru) ...... OAX4T 9,560 31.38 10 Huizen (Holland) ...... PHI 17,770 16.88 25 Millis (U.S.A.) ...... W1XK 9,57o 31.35 10 Bound Brook (U.S.A.) W3XAL 17,780 16.87 15-35 Manila (Philippine Isles) ...... KZRM 9,570 31.35 1 Daventry (Gt. Britain) GSG 17,790 16.86 10-50 Daventry (Gt. Britain) ...... GSC 9,580 31.32 10-50 Bangkok (Siam) ... HS8PJ 19,020 15.77 5 Lyndhurst (Australia) ...... VLR 9,580 31.32 1 Zeesen (Germany) ... DJS 21,450 13.99 5-40 Philadelphia (U.S.A.) ...... W3XAU 9,590 31.28 10 Daventry (Gt. Britain) GSH 21,470 13.97 10-50 Sydney .(Australia) ...... VK2ME 9,590 31.28 20 Wayne (U.S.A.) 5W2 XE 21,520 13.94 10 Perth (Australia) ...... VK6ME 9,590 31.28 2 Daventry (Gt. Britain) ...... GSJ 21,530 13.93 10-50 Huizen (Holland) .. .. . PCJ 9,590 31.28 60 Pittsburgh (U.S.A.) ...... W8XK 21,540 13.93 6 Prangins (Radio -Nations) (Switz'l'd) HBI. 9,595 31.27 20 Daventry (Gt. Britain) ...... GST 21,550. 13.92 10-50 Moscow (U.S.S.R.) ...... RW96 9,600 31.25 20 32-1 The Wireless World, April 7th, 1938

mined by a sinusoidal curve ini- tially graphed -out for each in- dividual craft, in much the same way as magnetic error is compen- Recent sated for in a ship's compass. Inventions In the drawing (a) shows a voltage. from the scheme for applying the correction Brief descriptions of the more interesting radio vertical or non - automatically. A " quadrantal directional aerial is . applied in error curve " C is devices and improvements issued as patents parallel. The output from the drawn out on a rectifiers cylinder P, so that it takes the will be included in this section feeds a centre-zero indi- place of the usual index pointer. cating device, so that any devia- tion to As shown in (b), the cylinder is port -or starboard of the driven by a gear wheel W TELEVISION SYSTEMS tion. Then comes a train P of craft carrying the equipment is at from WHEN a ray of light falls signals, the shaft S which carries the frame on picture corresponding to once registered. aerial. to the photo - sensitive one single scanning line, whilst the In order to The intersection of the preserve the phase - curve C on " mosaic" of a cathode-ray tube part F corresponds to the framing relation between the directive the graduated scale the resulting emission of electrons gives the correct reading. creates a charge proportional to Marconï s Wireless Telegraphic the incident light on each mosaic Co., Ltd. and R. J. Kemp. Appli- cell. This in turn produces an cation date, June 25th, 1936. No. 477346. electrostatic field, which is dissi- o o o 0 pated, or varied, by the action of the electron stream used for scan- THE field and search coils of a ning the mosaic surface. radio - goniometer are both Similarly, when a ray of light fitted with powdered-iron cores, falls on to a fluorescent surface a for the sake of compactness, whilst polarisation of the atoms, or of the search coil is wound in two the fluorescent crystals, is said to parts, which are relatively adjust- occur, and to set up an electric able in order to compensate for field, which is also discharged or octantal error. Shunt coils, also varied by the action of the elec- fitted with powdered-iron cores, tron stream used for scanning. Train of television signals described in Patent No. 476935. are arranged to compensate for one The result, therefore, of scan- type of quadrantal error, whilst ning either a fluorescent or photo- impulse, which, in practice, ex- and non-directive voltages re- magnetic shunts eliminate a second sensitive screen is to produce tends for an interval corresponding quired to give the well- variant of the same type of error. variations in the electrical field to ten picture lines. known heart -shaped response, in An auxiliary winding, coupled to surrounding the screen. Accord- The various signals are separated spite of accidental variations in one of the field coils, allows any ing to the invention the changes out in the receiving set, and the the values of the amplifiers and initial lack of symmetry between in field -strength induce currents signal impulses G, after being recti- tuning impedances, the inventor the coils to *be corrected. (proportional to the original light fied, are used to control the sensi- now provides an adjustable phase - C. Lorenz Akt. Convention intensity) in a " collecting elec- tivity, of one or more of the am- shifting device in the lead to the dates- (Germany), January 24th, trode " situated outside the plifying stages. common circuit in which the two and September 24th, 1936. No. A. D. Blumlein. Application sets of signals are first combined. 478395. date, May 15th, 1936. No. 476935. F. J. Hooven. Application date o o o o 0 0 0 0 March 3rd, 1936. No. 476721. (Addition to 472111.) CATIIODE.RAY TUBES PHOTO=SENSITIVE 0 0 0 0 ATRIPLE set of electrodes is " MOSAICS " arranged inside a cathode-ray TN well-known WHEN taking wireless bearings tube to enable three separate a method of tele - from 1 vision, the picture is first a moving body such as streams of electrons to be indepen- focused a ship or an aeroplane, it is neces- dently controlled, at least so far as upon a photo -sensitive sary make screen, or cathode, made up of a to allowance for an in- their vertical traverse over the mosaic of small cells, which emit herent discrepancy between the screen is concerned. One pair of electrons under the action of the true ,direction and that shown on deflecting plates controls all three Scanning systems fo- a tele- the indicator. This is due to the streams simultaneously during the vision transmitter. incident light and so become charged electrically. The scanning reflection of the incoming waves lateral scanning movement over stream of electrons from the metal parts of the vehicle, the screen. The deflectingplates cathode-ray tube, and these are releases the and since cell charges, one by one, and so the effect differs with the are operated in push-pull, about used to produce signalling cur- direction of the incoming signal, the anode voltage rents. produces signalling currents. as zero, in order As shown, for example, in the It is, however, pointed out, that figure, a picture P is focused by of the total electrons emitted, only a lens L on to a photo -sensitive a fraction is utilised, namely, those screen S, which is scanned in the which are radiated during the ordinary way by the stream short period of the scanning opera- passing from the cathode C of the tion. The object of the invention C-R tube through the usual de- is to make good this loss by stor- flecting plates D. The resulting ing-up the light energy from each variations in the electric field cell during the interval between from the screen induce currents in successive scannings on a " Len- an external " collector " K, ard phosphor " screen. The latter which, after amplification at V, is then scanned by a beam of infra- are radiated from the aerial T. red light, which is synchronised V. Zeitline, A. Zeitline and V. with the ordinary electron scan- Kliatchko (Assignees of Cie pour ning beam. This releases the la Fabrications des Compteurs, whole of the stored -up energy so etc., à Gaz). Convention date that it can be utilised for signal- (France) May gth, 1935. No. ling. 476865. The British Thomson -Houston o o o o Co., Ltd. Convention date (Ger- WHEN transmitting television many), July 25th, 1935. No. Method of compensating in DF equipment for quadrantal error." signals to or from a moving 4772r6. vehicle, such as an aeroplane or o o o o in a cyclic manner, it is known to prevent undesirable interaction motor car, it is essential to provide DIRECTION FINDING as " quadrantal error." In prac- between the separate streams. an automatic and rapid method of tice it is corrected by adding to, Radio -Akt. D. S. Loewe. Con- gain -control, so as to offset the THE signal received on a frame or subtracting from the apparent vention date (Germany), June variation in signal strength with aerial is combined with that readings, a fraction which is deter - loth, 1935. distance. from a vertical aerial in a common No 477043. The Figure shows a typical train circuit, after each signal has been of signal impulses in which line - subjected to a common hetero- The British abstracts published here are prepared with the permission synchronising impulses L in the dyne frequency and passed of the Controller of H.M. Stationery Office, from Specifications blacker-than -black direction are through separate amplifiers. The obtainable at the Patent Office, 25, Southampton Buildings, London, followed by gain-control impulses directional voltage from the frame W.C.2, price 1'- each. A selection or patents issued in U.S.A. is G of reversed polarity, i.e., extend- aerial is then applied in push-pull also included. ing in the whiter-than -white direc- to a pair of rectifiers, to which the No. 972. THURSDAY, APRIL 14TH, 1938. VOL. XLII. No. 15.

Proprietors : ILIFFE & SONS LTD. EDITORIAL COMMENT

Editor : HUGH S. POCOCK. Noise in Receivers they have been experiencing, are to be Why Wait for Legislation ? brought back, as it were, into the fold, Editorial, and have their interest in wireless Advertising and Publishing Offices : WHILST we are continually renewed, the service man should be DORSET HOUSE, STAMFORD STREET, LONDON, S.E.I. being promised that the ready to remind them of the Post Government Bill destined to Office interference complaint forms Telephone: Waterloo 3333 (5o lines). Telegrams: "Ethaworld, Sedist, London. give the Postmaster -General and .help them in filling them up and, authority to control electrical inter- in fact, do everything in his power to COVENTRY : Hertford Street. Telegrams: Telephone: ference with wireless reception is just assist in giving the listener the best «Autocar, Coventry." 52ro Coventry. round the corner, time drags on and reception possible free from troubles BIRMINGHAM: still we wait. of electrical interference. Guildhall Buildings, Navigation Street, 2. The preparation for the Bill has pro- Telegrams : Telephone : "Autopress, Birmingham." 2971 Midland (4 lines). gressed so far that we are entitled to look forward with confidence and a Post Office Help MANCHESTER : 260, Deansgate, 3. reasonable amount of certainty that Telegrams: Telephone: ' Iliffe, Manchester." Blackfriars 4412 (4 lines). legislation on this subject will ulti- Whilst discussing this subject we mately come and so help to relieve the would like to pay a special tribute to GLASGOW : 26B, Renueld Street. C.2. Telegrams: "Iliffe, Glasgow." Telephone: Central 4857. interference problem for the future. the Post Office for the work which not nearly they are doing in the interests of the PUBLISHED WEEKLY. ENTERED AS SECOND In our opinion, however, CLASS MATTER AT NEW YORK, N.Y. enough is done at present by way of listening public. Not only are their trying to improve reception conditions energies directed towards eliminating Subscription Rates : by methods which can be applied at the these troubles wherever possible, but, Home, LI Is. 8d. ; Canada, LI is. 8d. ; other countries, Li 3s. xod. per annum. receiving end. We know that this is a in addition, the technical staff is comparatively expensive method when making a close study of every aspect As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before perhaps a hundred or so receivers have of interference so as to be able to give making use of them, to satisfy themselves that they would not be infringing patents. got to be dealt with individually, whilst advice. the remedy for the interference, if A paper read recently before the tackled at the source, would in many Wireless Section of the Institution of cases involve no greater expenditure Electrical Engineers, by Mr. A. J. than the cost of tackling the interfer- Gill and Dr. S. Whitehead, briefly CONTENTS ence at one of the hundred points of referred to elsewhere in this issue, is Page reception. Nevertheless, we think it is an excellent example of the thorough- unfortunate that service men are not ness of Post Office methods. The paper Editorial Comment 325 more alive to the fact that all over the is a comprehensive summary of the Sunset and Fading .. 326 country there are those who have present state of knowledge on the Phase -Shift Measurement 329 abandoned listening to wireless and subject of electrical interference and Television Topics 331 will no longer entertain the idea of its elimination in very many branches. News of the Week .. 332 either a new set or an overhaul of the Even when legislation goes through, old one, simply because they have been nobody can expect that electrical inter- New Time Base .. .. 334 disgusted with the continual interfer- ference will disappear as if by magic. New Apparatus Reviewed 336 ence to which they have been subjected. It will take years to make the legislation Unbiased .. 337 In very many cases, if the service man really effective throughout the country, Eddystone E.R.A.7 Reviewed 338 were active in applying proper remedies and with interference steadily growing Readers' Problems 340 at the receiving end much, and in some as it is at present, it is a poor lookout all, of could be for wireless reception in some Voltage Stabiliser . . 341 cases the interference districts removed. if distributors of sets and service men to the Editor Letters 342 The listener requires from those continue to be indifferent to the On the Short Waves 342 called in to attend to his set more than problem and leavé the listener to think Random Radiations 344 technical service. If listeners, dis- that the noises in his set are an integral Recent Inventions.. 346 gruntled because of the interference part of broadcast reception. I 326 The Wireless World, April 14th, 1938

Sunset and Fading

the end of last year (in The Wire- adjacent channels (776 and 785 kc/s). less More AT World of Dec. 3oth) some Measurements They are free from local -station or shared - results of measuring -the signal channel interference (Leipzig is exclusive, strengths of broadcasting stations were of Signal Strength and Toulouse shares a channel with two published. It was impossible not to take comparatively small and very remote some account of fading, because all ex- By "CATHODE RAY" stations from which nothing could be de- cept the nearest stations are more or less tected). They are both about 55o miles subject to it, and the signal strength from London. Leipzig is almost due east, in measured at one moment may be quite stations which these quantities are the and Toulouse is nearly due south. So one different from that taken an hour, minute same. Of course, it would be no good if is in the line of approaching sunset, and they were exactly the same frequency, but or even a second later. At the time, I was the other is at right angles to it ; the sun concerned with giving typical strengths a difference of one or two per cent. isn't sets nearly an hour sooner at Leipzig, but received by a typical outdoor aerial, and likely to influence the general results very almost simultaneously at Toulouse. profoundly. To make the variations in strength were given only the approach of Actually I had taken quite a lot of read- sunset as different the broadest classification-day and as possible (so as to ings before I realised last concentrate attention that the state- night. But in pointing out that the pub- on it) I looked for ment is true only twice a the a pair in which one year-at lished results are subject to very large station lies due east spring and autumn equinoxes. A and another due south. little variations I promised to deal more par- The best pair playing. about with a globe seemed to be Leipzig terrestrial ticularly with fading later on. and Toulouse. They showed that in mid -January (when the are both rated at 120 kW. They Of course, the subject is even vaguer work on first results were obtained) the edge of the than the length of an unspecified piece of sunset shadow crosses Europe obliquely, string. There are hundreds .of stations, and, moreover, the low angle of the sun and reception from them by any given in relation to that part of the earth makes aerial is constantly changing, and there the transition from day to night very are dozens of conditions-time of day and 1/i° gradual, which might be expected to 7 7 2° 15° year, weather, frequency, distance, posi- obscure the intended observations. So (as tion, etc.-that might have some influence r' an Editorial note announced) the experi- on the results. But, by comparing l ment was postponed until the spring results when all except perhaps one of the / 9 equinox (March 21st). conditions are the same, it may be pos- The method of measurement was de- sible to trace the influence of that one. a scribed in the Signal Strength article, so I We all know that, on the average, the need only say that the signal picked up most marked change in signal strength is LONDON by a typical outdoor aerial by means of that which corresponds to the difference 50° a highly selective receiver was read on a between daylight and darkness. That is --- microammeter in the detector circuit, and why in the previous article I gave separate the whole arrangement was calibrated in day and night figures. A receiver that microvolts in the aerial by a standard brings in half a dozen stations during day- signal generator. It is not claimed that light usually gives scores, at least, after Ir every minor fluctuation in strength was dark. noted, but by taking readings sometimes So it ought to be interesting to study the ° as close as half -minute intervals the extent change -over from daylight to darkness 0 . 71/2 15 and shape of the major fades is shown conditions. Does it coincide with sunset? fairly reliably on the graphs. There was And, if so, is it sunset at the receiving no rapid fading such as is common on end or the transmitting end or somewhere Leipzig and Toulouse, the transmitters on the short waves, in between? which observations were made, lie respec- tively east Some results taken in January are pre- To eliminate questions of distance, fre- and south of the receiving station in London. Relative times of sunset sented here as a matter of interest and quency, and power, I looked for a pair of are shown. certainly do nbt encourage hopes of dis- APRIL 14111, 1933. Wfineeeo 37 WcuollCl

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Strength of signals from Leipzig and Toulouse as received in London at around the time of sunset : L, (light line) Leipzig ; T, (heavy line) Toulouse. 328 APRIL 14th, 1938.

Sunset and Fading- that daytime reception, though weak, was and irregularly all over the place, whereas covering any clearly defined effect of the consistent, while night-time reception was at night the same stations faded down- different approaches of the sunset shadow. strong but subject to fading. Here once wards from some more or less definite On January firth both stations seemed to more it can be seen that reception by day- high level." No need to alter that. have reached practically night strength by light is far more unreliable than at night. Another" thing is that the influence, if the time observations were started, more This day (March 23rd) Leipzig is de- any, of gradual or sudden onset of dark- than an hour before sunset. And instead cidedly worse than Toulouse during the ness over the country between transmitter of a marked difference between the two early afternoon. Note that both signals and receiver is swamped by other influ- signals they both exhibit a gradual up- exceed 3,000 before sunset. During the ences that are not traceable from these ex- ward trend from 30o to 3,000 microvolts hour or so before sunset there is some periments. Some readers may be able to (µV) during the 3-k hours around sunset. slight trace of what was hopefully ob- suggest something, but personally I can Yet even this conclusion cannot be served on March 18th. But any faith in think of nothing that is adequate to generalised, for only the day after next this that has not already been destroyed account for the fact that at ten to six p.m. the results are quite different. During a by the March 22nd results is completely on March 22nd, 1938, no measurable period of about an hour shortly before extinguished by March 28th, where it is signal could be detected from either Tou- sunset, when, on January 11th, a fairly quite impossible to detect any tendency for louse or Leipzig, whereas at the same time steady 30o µV had been shown, now, on the growth of the Toulouse signal to in- the very next day, with no visible change January i3th, Toulouse is practically nil crease more suddenly and nearer sunset in the weather or anything else, both and Leipzig is wildly irregular. Both than the Leipzig signal. signals were coming in at over 1,000 micro- stations show an upward tendency just Can we draw any conclusions other than volts. Local station reception was iden- before sunset (when the observations had that there are no conclusions? One thing tical each day, showing that nothing funny to be given up for the day), but it would that seems to be consistent, especially if had happened to the receiver or aerial. be unwise to base any conclusion on this. the earlier results on other stations are Another conclusion is that to make sure Now for glorious spring, when the ap- included, is that daylight reception is not of this sort of experiment one would have proach of sunset can be traced without only weaker than at night, but is usually to do it every day for several years, and headaches due to having to struggle more irregular. Quoting from my pre- even this might not arrive at positive against the astronomical problem with vious article, " Daylight fading generally results. Nevertheless, negative results are spherical trigonometry. At the equinox consisted in the strength fluctuating widely not to be despised. the sun sets everywhere at six o'clock (local time), and darkness takes nearly an hour to traverse the Leipzig -London line, but swallows up the Toulouse-London line almost instantaneously. Does the growth of received signal show any correspond- ing difference in these two extreme cases? On March i8th there seemed to be some evidence that it does. Toulouse provided a negligible signal until 5.3o, when it sprang up in a matter of minutes to a 30o µV level and remained thereabouts (except for occasional deep fades) until the test was shut down at 9 o'clock. It never came near 3,000 µV as it did on January 11th. Leipzig, on the other hand, gave a strongish signal before 5, and in- creased more gradually, just as might have been expected.

Inexplicable Fade-out

Alas for hasty conclusions ! A few days later, when readings were taken with the apparatus unaltered, no measurable signal was obtainable from Toulouse at any time from 2 o'clock until lighting-up time, though a faint sound showed that the station was not shut down. Leipzig ap- peared to be smitten by the same evil in- fluence and was nearly as bad, giving only occasional faint bursts of reading before Television at the Ideal Home Exhibition sunset, when the signal suddenly increased TELEVISION section is included in seen undergoing the process of being to what would be considered quite a large A this did not year's Daily Mail Ideal Howe Ex- " made-up " for television preparatory to amount if one look at the upper hibition at Olympia. The main exhibit is their appearance in the studio. graphs. If any violent change in the a replica of a television studio, and it is During the normal hours of television weather had intervened one might have glass -enclosed so that visitors can watch transmission the picture emanating from blamed it for the extraordinary difference artistes being televised without hindering in the Alexandra Palace is reproduced on the in reception. But both days were included any way the activities of the engineers and television receivers. These are situated in in a period of exceptionally settled and studio staff. the entrance to the television exhibit, and tranquil weather. This studio can in no sense be called a are the products of six manufacturers : The very next day the results showed working model ; on the contrary, it is much Baird, Cossor, G.E.C., H.M.V., Marconi - a complete change -around, -different from more nearly the real thing, and during cer- phone, and Murphy. Outside the normal tain hours visitors can walk any of the foregoing. For a long time round the transmitting times these receivers give a pic- corner to the television receivers and see on ture produced in the adjacent studio. At before sunset reception from both stations their screens the artistes they have just left times, however, this local studio programme was anything up to ioo µV, but very in the studio. Adjacent to this studio is a will be sent to Alexandra Palace by a radio irregular. I mentioned last time how small " make-up " room, of which one side link, and will be radiated as part of the - these tests destroyed the belief I had held is again of glass. Here the artistes can be normal programme. The Wireless World, April rglh, 1938 329 Phase -Shift Measurement

SIMPLE APPARATUS FOR FREQUENCIES By SIGliRD ZIENAU UP TO lo MC/S.

VALVE HE author describes an arrangement of two valves VOLTMETER in push-pull, which, with the addition of a diode voltmeter, may be used for measuring both the gain and phase -shift of an amplifier. o A AMP

THE problem of phase -shift has Fig. 3.-Block dia- greatly increased with the advent gram showing method of measur- of video -frequency amplification. ing stage gain. AMP, a nplifier under test ; For the distortion -free reproduc- A, attenuator ; O, oscillator. In our equations for the phase angle we tion of television signals it is absolutely have assumed the input voltage to the necessary that the phase -shift in the amplifier under test to be equal to its out- apparatus be a linear function of fre- voltage to the amplifier, VI its output put voltage. This assumption sounds quency. Actually a flat phase -shift curve voltage. The voltmeter in the output rather absurd when it is remembered that is also of more importance than one is apt circuit will, of course, measure the ampli- the purpose of amplifiers is to amplify to think in ordinary IF and RF amplifiers. fied result of the two inputs, V. Thc. signals in some wav or other. A little Phase modulation or a twist in the modu- thought will show, lation envelope can occur when the phase - 0+ H T however, that the shift varies with frequency. condition men- By now, however, these problems have tioned can be been realised and many research workers brought about by have paid attention to the subject. It is the interposition et quite feasible to calculate the phase -shift an attenuator be- in an amplifier, and, on the basis of this tween test signals calculation, to design the amplifier in such and amplifier. If a way that both gain and phase character- the loss in db. of istics are flat pver the desired frequency this attenuator is range. However, it . is always very con- such that the input venient to be able to measure the actual to it will equal the phase -shift in amplifying gear. Many output of the circuits have been evolved for this pur- amplifier, then the pose and have been fully analysed else- gain of the latter in where. It is the intention of the writer db. is equal to the to give an outline description of one of loss in the at- the simpler types of apparatus, suitable tenuator. Fig. 3 for this purpose, which incidentally will shows the hook-up also serve as . a stage -gain measuring for these measure- device up to frequencies of the order of ments. For the io Mc/s. purpose of our The basic problem is to arrange a circuit phase -shift that will vectorially add up the input volt- Fig. 2.-Circuit of practical measuring equipment, comprising the measurement the push-pull valves of Fig. z, plus a diode voltmeter valve. Component age and the output voltage of the amplifier values as in standard practice. attenuator has, of under test. A push-pull circuit with the course, to be de- anodes in parallel and the output con- phase angle 0 is then given by the signed and constructed in such a way as to a voltage measuring device will V'-(V2'+VZ') not to introduce any phase -shift of its nected expression cos b = do this trick extremely well. The outline 2 (V2 x VI) own. There is not much difficulty in circuit will, therefore, look as shown in In the case that Vi equals V2, this, and the real problem lies in the fre- Fi,. r. In this figure, V2 is the input quency range which the equipment is then 2 cos ¿ 0= VI required to cover. In actual practice +HT a diode voltmeter re- places the voltmeter V. Also pentodes are Effect of Valve Capacities mostly used instead of triodes, for it is easy by means of screen potential adjust- With regard to frequency range, it will ments to balance them out. The circuit of be realised that, as the valve anodes are a practical valve voltmeter would look in parallel, the valve input capacities are somewhat like Fig. 2. In some cases it also virtually in parallel, thereby adding would be advisable to use grid stoppers to up. The sensitivity will, therefore, begin reduce any tendency to oscillate. By to drop in the vicinity of one or two Mc / s. shorting out one section it is possible to As, however, both valves fall off in sensi- use the apparatus as a straightforward tivity at the same rate, the accuracy of valve voltmeter. As an attenuator is measurement will not be impaired. If a needed in any case, the voltmeter can be higher frequency than io Mc/s is wanted, used to measure the gain of the amplifier a more sensitive meter will have to be Fig. z.-Simplified circuit of an arrangement at the same time, as will be described used in the diode circuit, and the value for measuring phase -shift and stage gain. below. of the diode load resistance becomes MpdGoo APRIL 14th, 1938. 330 eoppd Phase -Shift Measurement- for best results. A value between one and (which can be a o-r mA meter) is then critical. So much for the valve voltmeter. five megohms is suitable. calibrated in decibel gain. Once the meter Returning to the matter of the attenuator, As for the attenuator, a resistance type has been Calibrated in db. it is easy, with

it can safely be said that a resistance ele- for use up to 2 Mc/ s is quite _ easy to con- ment filter will do its job up to about struct. Readers are reminded that good 1! 2 Mc / s. Above that the self-capacity and screening is necessary and the different C1 self-inductance of the resistances becomes stages ought to have exactly the same lay- 'TERMINATING annoying. An inverted L type of re- out. Carbon resistances will do C2 V2 CAPACITY " " when very TC3 sistance filter can be used and about six great accuracy is of no importance. They sections totalling sixty db. will suffice for have the advantage that their ohmic value i almost anything (Fig. 4). The question of can be adjusted by filing them. A capa- characteristic impedance is of importance. city attenuator represents a considerably more difficult problem. The single sec- Fig. 5.-Capacitative " inverted L" filter sec- tions should be well screened from each tion. Calculation : other, while switches with good insulation Vi_k should be used. All leads should be as V2 TERMINATING RESISTANCE short as possible and mica condensers are CI R3 essential. Even though great care has = I kk been taken and good components have Cz= C3 (i-k) been used, the results may be disappoint- ing. This may be due to several reasons : the help of the formula, to take phase - Fig. 4.-An " inverted L" resistance filter defective screening, excessive stray capa- shift measurements. It is difficult to pre- section for the attenuator. Calculation : cities, excessive capacity between the dict what results can be expected vl from =k (attenuation) earthed aluminium box and components, this type of apparatus. A great deal will V2 and, last but not least, badly insulated depend on how much care has been taken RI=R3 (I-k) switches which allow leakage currents. in the construction and how well the push- These defects are not easy R2=k to get over, and pull stage is balanced. Provided these k only readers who are accustomed to high - points have been observed, the accuracy frequency work are advised to attempt the obtainable, so far as gain measurements The input resistance of amplifiers varies construction of this unit. are concerned, ought to be good enough for appreciably, and for flexibility and fre- any ordinary requirements. Up to about quency range a compromise has to be Decibel Readings 2 Mc / s, the same goes for the phase -shift made. Without going into further details, measurements. Above that, results will it may be stated that zoo to 200 ohms will For the calibration, an existing cali- vary with individual apparatus, but most serve quite well. The attenuator has, of brated attenuator and an amplifier are of them should give reasonably accurate course, to be terminated with this resist- necessary. The diode current meter readings up to ro Mc/s. ance. Above 2 Mc/s an attenuator con- sisting of capacity branches must be used. Such a unit can again be of the " inverted L " type, and . its calculation is surpris- ALL CONTINENTS ON TEN WATTS ingly simple, as the example shows (Fig. 5). In the interest of stability it is better to use ,this attenuator between the ampli- fier and the valve voltmeter ; for the filter can then work intó the constant input capacity of the first valve (which becomes the terminating capacity).

Construction and Calibration While the writer does not propose to give constructional details of a complete unit, some points which have to be ob- served in the construction and calibration of the valve voltmeter and associated gear might be of interest to readers. There should be no difficulty in making the valve voltmeter work, at least up to fre- quencies of about 2 Mc/s. For a higher frequency range symmetry in the layout of the push-pull stage is very desirable. It must not be forgotten that equal stray capa- cities in both arms are essential for accurate measurements of gain or phase - shift at the lower wavelengths. For very accurate determination of phase-shift, it is also better to use battery bias instead of cathode bias. Any pentode should work in the circuit ; but a high mutual conduc- tance valve is most probably best, and the valves ought to be identical in character- istics as far as possible. The final balanc- ing can be done by means of the screen WORKMANLIKE AMATEUR STATION.-GSRL, at St. Ives, Hunts, owned by Mr. B. K. Rowell, potentiometer. A triode can be used as has been operating since 1934 on the 20-, 40-, 8o- and 16o -metre bands ; apparatus for the 5 -and lo -metre bands is in course of construction. With a Io -watt input and a diode rectifier and some experimenting " straight " two -valve receiver, the station has " worked all continents " and " worked with the load resistance RI is advisable the British Empire." The Wireless World, April 14th, 1938 331 Television Topics ROBABLY the most widely used tooth oscillator is shown in Fig. i ; RI, SAW -TOOTH generator of the saw -tooth wave- R2, and CI are used merely to provide forms needed for scanning is the grid bias and can be ignored for the OSCILLATORS gas -filled triode. At one time this moment. Starting with the valve in the valve had the reputation of being erratic in non-conductive condition, the condenser C operation, and consequently unsuitable for charges through R from the HT supply. use in the line time -base. This criticism is The voltage across C, and hence the anode the ideal form of (a). It is also obvious no longer applic- voltage of the that it increases the portion of the time of able, however, and v al v e, therefore, the cycle of oscillation which must be there are now many rises. At a certain allowed for the fly -back. Furthermore, it gas -triodes which critical voltage the sets an upper limit to the frequency at have been specially valve strikes, and which a gas triode will operate. developed for tele- as its resistance is For present television the line time -base vision and which then very low com- must work at io,125 c/s, and suitable gas - give very reliable pared with the triodes will readily operate at this fre- operation. In value of R, the con- quency and give an adequate fly -back general, the mer- denser discharges time. Indeed, it is not difficult to find cury -filled type is through -the valve types which will operate at considerably unsuitable for time - very much more higher frequencies. base work, and rapidly than it was Some years ago it was actually difficult helium, argon, and charged through R. to obtain gas -triodes which would func- sometimes neon As the condenser tion reliably at the frequencies necessary fillings are used. discharges the volt- for television line scanning. Conse- The great point age across it falls quently, circuits using ordinary hard about a gas -triode is Fig. 1.-The basic circuit of a saw -tooth and the discharge valves were often adopted, and in the that it is essen- oscillator using a gas -triode. ceases when the minds of many people are still considered tially non - conduc- voltage has fallen more reliable. In the writer's experience, tive until the anode voltage exceeds a cer- to the lower critical value of the valve. however, the gas -triode is entirely satis- tain figure. When this happens, the gas One period of saw -tooth oscillation is factory for television and has been for a ionises: and the valve has an exceedingly made up of one charge and one discharge year or two now. low internal resistance. It remains con- of the condenser ; that is, of one scanning The chief disadvantage of the gas - ductive, moreover, until the anode voltage stroke and one flyback. The relative triode is its high price in comparison with falls below another and lower critical times occupied by these two portions of a hard valve, and for this reason the voltage, usually some 10-20 volts. the cycle depend primarily upon the rela- latter is often adopted in spite of its requir- These critical voltages depend primarily tive values of the charging resistance R ing a more complicated circuit. There are upon the construction of the valve and the and the internal very many ways of gas pressure, but the higher critical volt- resistance of t h e using hard valves as age, or striking voltage as it is usually valve when con- saw - tooth oscilla- called, depends also upon the grid poten- ducting. For tele- tors, and in some tial. With a certain negative grid vision line scanning arrangements very potential the valve will strike, i.e., become the discharge time high operating fre- conductive, at a certain anode voltage. If must not be greater quencies can be ob- the grid is made more negative, a higher than 15 per cent, of tained, far beyond anode voltage is needed to make the valve the total period of anything possible TIME AA, conduct, and conversely with a less nega- oscillation. with the gas -triode. tive grid it will strike at a lower anode The internal re- (a) (b) They are, therefore, voltage. sistance of a gas - of considerable im- Now if we have on the anode a certain triode is so low that Fig. 2. -The ideal saw -tooth waveform is portance, apart voltage which is less than the striking there is no difficulty shown at (a) and at (b) a more practical from television, for form. voltagA and change the grid potential to in meeting this use in cathode - make it more negative, nothing will hap- primary condition. r a y oscillography. pen in the anode circuit. If we make the At high operating frequencies, however, The problem is, in general, to use one grid potential less negative in sufficient another effect comes into play. The or more hard valves in such a way that degree, however, the valve will strike. action of the valve depends on the alter- they simulate the action of the gas -triode, Changing the grid potential in a positive nate ionisation and de -ionisation of the and it is hoped to describe some of the direction, therefore, will initiate the dis- gas and the accomplishment of this more important arrangements in further charge. requires time. When the voltage on the articles. On the other hand, if the valve is con- anode rises to the striking value, the gas ducting the grid will not exercise any does not ionise immediately, but requires control. Although quite a small change a small time interval. There is conse- B.T.H, Sound Amplifying Equipment of grid potential may suffice to initiate quently a delay in the beginning of the IN the latest sound reinforcing equipment for discharge, once it has started it cannot discharge of the condenser. Similarly large halls, developed by the British Thom- be stopped by any variation in the grid at the end, when the voltage has reached son -Houston Co., Ltd., Rugby, volume expan- sion or volume contraction circuits may be voltage ; it can only be stopped by bring- the lower critical value there is a delay switched in at will in the amplifiers. ing the anode voltage below the lower criti- before the condenser . -begins to charge The reproducing equipment comprises an cal figure. When the discharge has again, because a small time is needed for assembly of thin. cone loud speakers for low - ceased, the grid regains control and is de-ionisation of the gas. frequency response and metal diaphragm high - capable of starting a further The result of this is to make the saw - frequency units working into multi -cellular again horns. The microphones used for PA work with discharge. tooth wave tend more to the form shown this new installation are of the directional The basic ci=:uit for a gas -triode saw - with great exaggeration in Fig. 2 (b) than straight-line characteristic ribbon type. 332 The Wireless World, April 4th, 1938

INTERFERENCE : A Comprehensive Survey Its Nature, Propagation and Suppression AN important paper entitled dividual outdoor aerials are im- "Electrical Interference possible, the best solution ap- with Radio Reception," by Mr. pears to lie in the provision of NEWS OF A. J. Gill and Dr. S. Whitehead, a single efficient aerial at the top both of the G.P.O., was read last of the building associated with week before the Institution of a wide -band amplifier, to the NEW BROADCAST WAVELENGTHS Electrical Engineers. The output of which a feeder is con- nature, propagation, assessment, nected which is brought into Recommendations from Cairo and measurement of every flat. interfer- THERE is to be a " little bottom end to below 200 metres, ence, as well as the suppression The use of filters at the point all Cairo " as there was a i.e., 1,56o kilocycles. of the serious kinds, were dealt of entry of supply mains is a " little Madrid," for the out- On with in a most comprehensive valuable aid towards the preven- as the short waves the pro- come of Cairo Telecommuni- posed allocations will be : manner, especially from the tion of interference from plant the - cations Conference a European 6,000-6,200 kc /s additional 50 kc/s building. 7,200-7,900 100 , technical point of view, to which outside the wavelength conference begin aspect the subsequent discussion is to 9,500-9,700 100 the Discussion on February 1st, 1939, for the 11,700.11,900' unchanged was mainly confined. Points from 15,100-15,950 Manufacturers of e 1 e c t r o - purpose of revising the Lucerne 17,750-17,850 additional 50 kC/s Plan and redistributing wave- 21,450.21,750 , 200 Points from the Paper medical HF apparatus might . This band' will have " to be shared At the present time . . . a standardise on a frequency of lengths. It is to be held in with amateurs. member of the general public about 5o Mc is in order to re- Switzerland, and the U.I.R. For use in tropical countries who finds his radio reception strict interference to that band. have been commissioned with three entirely new bands have interfered with or possibly spoilt Interference from ignition the formidable task of preparing been suggested, namely, 2,30o - has no redress, apart, possibly, systems falls off very rapidly as a suggested new waveplan to be 2,50o kc/s, 3,300-3,500 kc/s, from applying in the High Court wavelength is reduced below the put before the Conference. and 4,700-4,965 kc/s. for abatement of nuisance. lower limit at present in general This re -allocation of wave- All these changes are to be Interference arising from the use. lengths is necessitated by the discussed at Ouchy in June as operation of a trolley -bus is Listeners should be educated addition of some fifty extra a preliminary to the February, mainly radiated from the over- to the use of better aerials, and channels on the short -waves and 1939, meeting. The first of a head contact wires, along which landlords should not have the about six on the medium -wave series of conferences convoked the disturbances are propagated. power to force them to use in- bande The list of additional by the U.I.R. for the discussion Domestic appliances : the nor- efficient ones. channels has not yet been pub- by specialists of tendencies and mal path of interference is from It would cost about L2,000,000 lished, but according to our practices in special departments the offending item via the supply to suppress the ignition systems Cairo correspondent those on of programme activity will also mains to the vicinity of the re- of motor cars in this country. the medium -wave band will be be held at Ouchy at the same ceiving aerial whence it is radi- The L.P.T.B. is to be con- brought about by lowering the time. gratulated on the small amount of interference radiated by Lon- don's new trolley -buses. DEFECTS TO ORDER gow, is probably the largest of its kind to be used in Great Have You Heard the " Faults Box " ? Britain, its output being over A" FAULTS BOX " is the r,000 watts. The equipment, latest creation of the B.B.C. which incorpórates 16o loud Research Department at Balham, speakers and twenty micro- London, S.W. Into a box no phone points, is being supplied larger than a petrol can has been by the G.E.C. Part of this inserted a collection of apparatus equipment, involving thirty which duplicates every one of loud speakers and five micro- the long train of defects in the phone points, has already been early days of broadcasting, the installed in the adjoining Ibrox FOR INVESTIGATING IGNITION INTERFERENCE. This new idea being to introduce these Stadium, and is completely self- short-wave interference measuring set, made to the design of the into dramatic and other pro- contained. Electrical Research Association by Belling and Lee, covers a wave - grammes in which the radio 13o loud in range of from 6 The speakers the to 25 metres. Two single -turn diamond shaped must not be " too good:" For Exhibition grounds will be con- frame aerials are used, and double screening is employed. The instance, a set working in a instrument was exhibited at last week's I.E.E. meeting. nected up on five circuits, which Highland crofter's hut of ten can be used independently or a ated from unscreened portions years ago should not be ex- combination employed. pected to give the quality ob- of the wiring and picked up by NOTTINGHAM'S NEW Microphone pre -amplifiers re- the aerial -earth circuit of the re- tainable from a modern radio- motely controlled from the main ceiver. STUDIO-A SCHOOL HALL gram. The " faults box " re- panel, which is housed in a creates the deficiencies of the Ignition interference : the effi- NOTTINGHAM had a relay building at the base of the 3ooft. ciency [of suppressor resistances] station in 1924, but was old microphones, amplifiers, observation tower, will be in- can be very considerably in- deprived of that facility eight lines, transmitters and early stalled in the concert hall, where creased by covering a short years later. A virile agitation horn loud speakers. there will be ten microphones, length of the lead at the plug has been constantly fanned by The device also creates some and in each of the two band- end by a screen of metal foil Nottingham listeners, and interesting aural illusions. It stands, where there will be two so as to form a small con- B.B.C. spokesmen have fre- can vary the harmonic content microphones. denser of about 20 m-mfd., the quently been earmarked to go of a voice to give the effect of foil being bonded to the cylinder down and tell them why Nott- conversation through a speak- block. ingham's ambition to have a ing tube, and can produce such HOW MUCH WILL THE Wherever possible an outside studio could not be gratified. queer echoes as those heard in B.B.C. GET ? aerial should be used, as this not Now the battle has been parti- " The Piper " broadcast of ten THE B.B.C.'s effective share only possesses a lower coupling ally won. The B.B.C. has made days ago. of each ten -shilling licence with the supply mains but at the arrangements with the Park Hill fee during the financial year same time can have a much Congregational Church, Derby P.A. AT THE ending March 3rst, 1939, will he greater effective height than the Road, Nottingham, whereby the 7s. 9d. under the terms of the indoor aerial..'.. Frame aerials Corporation has the use of the EMPIRE EXHIBITION Broadcasting Estimate. The of the small type . . are in- school hall and other rooms Ope Hundred and Seventy Acres Post Office will take told., the efficient compared with the out- connected with it for a mini- to be Covered Treasury rid., and the Corpora- side aerial .. . their directional mum of twenty-five occasions THE installation of PA tion 8s. 21d. But income tax proportions are rarely effective in each year for broadcasting. equipment in the main will amount to roughly 51d. of against interference. The arrangement is for three grounds of the Empire Exhibi- each licence fee, leaving a net In the case of flats where in - years from March 25th last. tion at Bellahouston Park, Glas- share for the B.B.C. of 7s. 9d. The Wireless World, April 14th, 1933 333 DERBY TO BE TELEVISED FROM ALL S a result of consultations between officials of the QU4RTERS B.B.C. and the Epsom Grand Television at I.E.E. Stand Association, the latter has Ar the ordinary meeting of the lifted the ban which it imposed Institution of Electrical Engineers SHE on television, WEEK and the Derby to be held at Savoy Place, Lon- will now be seen by viewers. don, W.C.2, on Thursday next, Sunday Monday. Three cameras will be used, the April 21st, at 6 p.m., two papers WORK IN HAND and The on television will scheduled programmes were re- one in the Grand Stand being be read. One B.B.C.'s New Stations fitted with a six-inch lens. is on " The London Television PROGRESS corded to enable them to be Service " by T. C. Macnamara A report on the used when required. We state of new work in hand un- and D. C. Birkenshaw, M.A., and derstand, however, no in- 111E CANADIAN the other on " The Marconi-E.M.I. by the B.B.C. is interesting that MARCONI CO. dication was given as to MR. EDWARD WILSHAW, Television System " by A. D. and opportune. Here is the Blumlein, whether the items were original Chairman of C. O. Brown, N. E. latest information on this Cable and Davis and E. Green, M.Sc. or recordings. Most radio Wireless, Limited, to whom was matter :- plays Eiffel Tower Television Start Point.-The foundations are now given from re- referred the announcement made cords in Berlin as it has been by Mr. Sarnoff, President of THE Eiffel Tower television for the transmitter building transmitter, which has radiat- have found easier thereby to obtain R.C.A., at the annual meeting, been been laid and the contrac- the services ing regular experimental transmis- tors have begun on of first-class artistes. corrects the impression conveyed the steel- Here, again, no indication sions on reduced power since Sep- work. is in Mr. Sarnoff's announcement. tember, 1937, was officially in- given that the plays are He points out that the R.C.A. augurated by the Minister of Queen Margaret College, Glas- recorded. Posts gow.-Work is progressing satis- were not direct owners of shares and Telegraphs last Friday. It is factorily and the studios should shortly to utilise its maximum come into operation in May output of 3o kilowatts. Confiscated Radio Station with the exception of the large GERMANY'S LIP studio, which will not be RADIO ALDERNEY, LTD., and its finished until the autumn. MICROPHONE, like managing director, were found Aberdeen its English equiva- guilty by the Guernsey Royal Transmitter.-The Court in the action mast has been completed and lent, cuts out all ex- brought against traneous noises, them by the P.M.G. for illegally the installation of plant has but operating a broadcast station. The begun. It. is hoped to bring is highly sensitive to company was fined £Io and costs, the transmitter into operation words spoken at very its plant ordered to be confiscated during this summer. close range. It is and handed over to the P.M.G. and managing Aberdeen Studios, Beechgrove used extensively for the director was fined a. House.-Reconditioning of the relays from political Radio Intermediary of interior the building is in meetings and sports EACH of America's privately hand and work has begun on owned wireless stations has to the extension, which will include contests. renew its licence through the the main studio. Federal Communications Commis- sion every 'six months. ' The Clevedon.-The contract for National the building has _been placed. Association of Broad- BROADCASTING IN in the Canadian Marconi Com- casters, which consists of officials IRELAND pany, but held 11,500 " B" of -425 stations, has appointed a public relations councillor to act NEW HOLLYWOOD IT has been announced by the (non -voting) shares in Canmar Investment as a temporary intermediary, who BROADCASTING HOUSE Irish Minister for Posts and Company, and it is would endeavour to these which have now been pur- smooth out THE master control room in Telegraphs that the wavelength any difficulties which rpight lie in to be used by the experimental chased by Cable and Wireless, the way of licence renewal. the recently completed Limited, from the R.C.A. Columbia Square. building of the 1.5 kW short-wave transmitter, American Radio Comes to Scotland which is being installed at In addition to this holding of Columbia Broadcasting System at B " THE President of the American Athlone, will be fixed at the " stock in Canmar Invest- station, WHB, has organised Hollywood is visible to the public ment Company, Cable and Wire- a through shadowless double glass Cairo Telecommunications Con- trip, to Europe for station direc- ference. The station should be less have recently acquired tors. The- trip, which will begin windows. Sound waves eman- 2,50o " A " (voting) shares of on -July 15th, includes ating from the studios are shown operating by the end of the year. a visit to The that company previously held by the Empire Exhibition at Glasgow, to visitors on oscillographs, and number of wireless where licences in force in Ireland at the Messrs. Lazard Brothers and an official -reception will be electric signs indicate the sec- their associates, thereby obtain- given by B.B.C. representatives. tions of the network to which end of February was 139,534, an increase of 36,214 over the ing the voting control of the Australian War Memorial Broadcast the programme. is being sent. Canadian Marconi Company. Each of the studios in the previous year. The annual AUSTRALIA is arranging for a revenue from licences amounts The control of the Canadian nation-wide relay of the unveiling new building is entirely inde- Marconi Company has always ceremony by the King of the Aus- pendent in equipment, power to approximately £70,000, and tralian advertising yields about £35,000. been in British hands; the War Memorial at Villers and lighting. Each has a series transaction recently entered into Bretonneux in June. The B.B.C. of microphone pre-amplifiers and consolidates that control in the will relay the broadcast to Lon- monitor amplifiers which are UNCLE MAC INJURED hands of the British Communi- don, and also transmit recordings strong enough to send the from Daventry on varying wave- ALTHOUGH Mr. Derek Mc- cations Company. lengths throughout the day. signals directly through to the Culloch has been associated transmitter instead of being with the Children's Hour since TELEVISED NEWSREELS Television at 110 Miles passed through the master con- he joined the B.B.C. over twelve TELEVISION from Alexandra COMPLAINTS by members of Palace is trol amplifiers. It is under- years ago, he is very well being well received in the Cinema Exhibitors' King's Lynn, Norfolk, by Mr. C. J. stood, however, that the primary known to listeners of ail ages, Association concerning the purpose of this high-level trans- Baynes, a radio engineer. Mr. and it must have been with re- granting of television rights in C. J. Gardner, of West South- mission is the elimination of gret that it was learned of his newsreels to the B.B.C. were re- bourne, Bournemouth, is receiving noises due low-level to lines. injuries received in a motor - cently put before the chiefs of excellent pictures on an experi- coach accident last Friday, newsreel companies. mental receiver, built by himself. BROADCASTING AND THE which has resulted in the ampu- According to The Cinema Miscellaneous Advertisements PLEBISCITE tation of his left foot. It was there was general agreement that and April 21st issue only a day or two before that the showing of televised news- ADVERTISERS are reminded that DURING last week-end the he had been appointed Direc- reels in public-houses, etc., was owing to Easter and the slight programmes from the Ger- tor of the Children's Hour. He inimical to the interests of the alteration in our printing arrange- man stations were subject to has had many years of suffer- trade, and that the same con- ments for April 21st issue, it was last-minute changes because of ing since the Great War, in dition might be placed necessary to close the misceI- upon tele- laneous advertisement pages for the Plebiscite. The stations which he served in the R.F.C., vision newsreels as is placed broadcast uninterruptedly for press earlier than usual. No more being severely wounded and upon the broadcasting of news copy can now be accepted for that over thirty-six hours during losing the sight of his right eye. by the B.B.C. number. The Wireless World, 14th, 1938 .7J4 April New Time Base A HARD -VALVE CIRCUIT WITH LINEAR the very lowest up to two or three mega- cycles per second, when C is merely the CHARACTERISTICS By D. G. REID, B.Sc., A.l:.(:.I. inter -electrode and stray capacities asso- ciated with Vr. In the new arrangement to be described THE generation of voltages or ing function-in this case charging the the fundamental circuit is modified to that currents having " saw -tooth " condenser. Its operation can probably shown in Fig. 2, in which the condenser waveforms for the electrostatic best be understood by comparison with C is in series with the cathode lead of the or electromagnetic deflection of that of its logical prototype, the so-called valve V, so that the anode current, rather the beam in a cathode-ray tube has always " squegging " oscillator. This circuit, than the grid current, causes the blocking been a subject of interest in oscillographic shown in Fig. r, was developed by of the grid. This is an advantage, since work, and its importance has increased of Watson - Watt, grid current is very late with the wide application of the tube Appleton, and Herd DESCRIBING a modification dependent on the to television purposes. for the Radio Re- of the original " squegging" material and tem- The chief requirements of generators for search Board, and perature of t h e oscillator which is applicable this purpose may be summarised as fol- was one of the to grid, due to the television receivers and cathode-ray lows : earliest time - base effects of secon- Linearity over the whole of the " for- circuits. Here the oscillographe, etc. dary emission. ward " stroke. triode valve V is T h e discharge Rapidity of " return " stroke. connected as an ordinary oscillator, the device shown here is the usual pentode Positive synchronisation with relatively circuit constants being such as to produce arranged to operate beyond the " knee " small input voltages, preferably with- a very high frequency of oscillation in of its characteristic, although, as will be out the consumption of power from comparison with that of the saw-toothed seen later, this can advantageously be re- this source. output voltage required. The grid con- placed by a high resistance. Economy in supply voltages and the denser C, instead of being shunted by the The operation of this circuit may be number of valves used. conventional leak resistance, has in described as follows : Assume the con - A large number of different forms of parallel with it a tungsten -filament diode such generators, or " time -base " circuits, Vr, the filament of which is sufficiently have been devised, most of which em- under -run to ensure that its total emission ploy the principle of charging (or discharg- current is considerably less than the nor- ing) a condenser at a constant rate through mal grid current of the triode V when i high resistance or a saturated valve, the latter is in the oscillating condition. and periodically discharging (or charging) The battery connected in series with Vi it by means of a gas -filled discharge tube maintains the current through this valve or a combination of one or more hard continuously at the saturation value. valves so connected as -to be equivalent When the valve 'V commences to oscil- thereto. late, the excess grid current which cannot In spite of the acknowledged simplicity flow through Vr flows into C, causing an of the gas -discharge tube type of circuit, increase in the mean negative bias of V there are certain advantages in the use of until oscillation can no longer be- main- hard valves to tained, and t h e perform what may flow of grid current be called the abruptly ceases. C switching function, n o w discharges i.e., the periodic through VI at a Fig. 2.-The new circuit in its fundamental charging or d i s - constant rate until form. charging. Time-lag a point is reached effects due to the w h e r e oscillation denser C to be initially charged to such finite de -ionisation starts again a'nd the a voltage that the grid of V is sufficiently t i m e are absent, cycle is repeated. negative to prevent the passage of anode and the circuit is It is seen that current. The discharge valve Vi draws n.o t sensitive to t h e operation of a constant current from the condenser, temperature fl u c- t his circuit de- the voltage of which falls accordingly. This tuations due to pends on " back- causes a fall in the negative grid bias, draughts, etc., as lash " in the oscil- accompanied by a rise in the potential of is a gas discharge lator, i.e., on the anode with respect to the cathode of tube. Also, t h e oscillation b e i n g V, since the voltage across the condenser average life of a maintained with a is in opposition to the high-tension supply hard tube is gener- Fig. 1.-The original " squegging oscillator " larger negative voltage. Eventually the cut-off point is ally greater than circuit. grid bias than will reached when current starts to flow that of a gas -filled allow its inception. through the charging valve. This current, one, due to the absence of positive ion This condition can readily be obtained by flowing through the condenser in the bombardment of the cathode. the use of sufficiently tight coupling, but opposite direction to that taken by the The circuit described below, which was the extent of the backlash is small in com- discharge valve, tends to increase the developed in the Communications Labora- parison with the anode supply voltage, so negative potential of the grid of V, but tories of the City and Guilds Engineering that the circuit is not very efficient from this tendency is opposed and temporarily College, differs from previous hard -valve the point of view of output voltage, which overcome (if the coupling between Li and circuits only in the manner in which a is taken from the condenser C. The range L2 is in the right sense and of sufficient single valve is made to perform the switch - of frequencies obtainable extends from magnitude) by the voltage which the in- APRIL' z¢th, 1938: Wpg®20 335 WaOpid New Time Base- inductance being sufficient (with a suit- condenser, and between the cathode and creasing current in Li induces in L2. able valve, such as a VMP4G) to induce heater circuit of the charging valve, in Eventually, however, due to the anode the requisite voltages in the grid circuit. the event of the high voltage supply to current reaching the saturation value, or A distinct improvement in the speed of the cathode-ray tube being switched on to the condenser voltage becoming so high the flyback is obtained by this means, before the valves in the time base have that there is no longer sufficient anode -to - and in addition the suppressor grid of had time to heat up, or if the heater volt- cathode voltage available, irrespective of such a pentode provides a convenient age fails for any reason. Such neon tubes are available at a cost of a few shillings, and withstand a voltage of approximately SYNC. i6o before striking. As the normal range A of voltage across C is considerably less +1,500 V 1 than this, the presence of the neon tube r has no effect on the normal operation of the circuit. CONTROL Coil Windings +200 The values of the inductance coils Li T and L2 are not at all critical, -although for the fastest flyback they should be J_ kept as small as possible. Ordinary L2 honeycomb-type coils, tightly coupled, have been found to give good results, the values of the anode and grid circuit coils being about 120 and 200 microhenries respectively. These inductance values are substantially independent of the operating frequency, and are suitable for the whole ) 3,000V range of frequencies over which the cir- FINE FREQUENCY CONROL cuit will work, namely, from a few cycles up to about two hundred kilocycles per Fig. 3.-Modification of the new circuit, with pentode oscillator and discharging resistance. second. The value of the condenser C directly the induced positive grid potential, to point for the injection of the synchronis- controls the operating frequency, and allow further increase in anode current ing voltage. since it is in parallel with the cathode -to - the current in Li becomes stationary. The high rate of change of current in heater capacity of the charging valve, Immediately this happens the induced Li may be made use of to extinguish the and with the grid-to -cathode capacity of voltage in L2 disappears, and the grid beam during the return stroke, by induc- the first amplifier, it is these latter which potential reverts to that of the terminal tively coupling Li to a small coil con- set an upper limit to the operating fre- of the condenser remote from the cathode, nected in series with the control grid of quency. i.e., it becomes very negative thereto. the cathode-ray tube. The anode current through Li now The mere substitution of a resistance starts to decrease, thereby inducing a for the discharge valve in Fig. 2 gives voltage in L2 driving the grid still more rise to exponential distortion of the wave- negative. The current through the charg- form during the forward stroke, unless a ing valve is thus cut off with extreme very high voltage supply is connected in rapidity, limited only by the self -capacity series with the resistance. This is be- of the inductance coils and the inter - cause the percentage variation in the for- electrode capacity of the valve. The con- ward velocity is the same as the percent- denser is thus left with a large accumu- age variation of the voltage across the re- lated charge, since the current passed by sistance. It so happens, however, that the charging valve during its brief con- in most cases where the circuit will be ducting period is many times greater than used such a high voltage source is avail- that drawn by the discharge valve. This able, namely, the supply voltage to the charge now drains away through the dis- " gun " or filament end of the cathode- charge valve, until the potential across ray tube. Especially in cases where sub- the condenser again reaches the cut-off sequent amplification is used, as for ob- point, when the cycle starts again. taining a balanced push-pull output, the sweep of voltage across the condenser Increasing Flyback Speed need only be of the order of 5o volts, so that with 3,000 volts on the " gun " the Fig. 4.-Waveform obtained from the circuit Although the cutting -off action of this linearity is within 2 per cent. A complete of Fig. 3 (frequency 3,300 c/s). circuit is extremely rapid, the fact that circuit diagram embodying this arrange- the whole of the charging current has to ment, together with the fast flyback pen- For satisfactory synchronisation the flow through the inductance Li limits the tode circuit, is shown in Fig. 3, and Fig. 4 " natural " or unsynchronised frequency rapidity of the charging action and thus shows the output waveform obtainable. should be approximately that of the syn- slows down the flyback. This objection It will be seen in Fig. 3 that the ampli- chronising voltage. It is theoretically best is overcome by replacing the triode with fier is directly coupled to the time -base to adjust this frequency entirely by varia- a pentode as a charging valve, the screen circuit, the usual coupling condenser and tion of C, but as this is inconvenient, or auxiliary electrode being taken direct leak being omitted, as the latter would especially at low frequencies, when C is to the positive terminal of the high-tension have to have an impracticably high value large, fine adjustment of frequency is supply. A fairly large fraction of the to avoid exponential distortion. made by variation of the discharge re- charging current then flows straight A small neon discharge tube N is shown sistance over a relatively small range. through the auxiliary electrode circuit to connected across the condenser C. The say, from two to three megohms. the cathode, the remainder flowing object of this is to prevent a dangerously For the framing frequency (5o cycles) through the main anode circuit via the high voltage being developed across the C should be about 0.5 mfd., and for the G Wpshoo APRIL 14th, 1938. Would New Time Base- ment, to obtain the right order of swing Fuses are included for protection, and the line frequency (ro kilocycles) about on the amplifier valves, is effected by ad- whole apparatus is in a black Jeatherette case weighing Ir' lb. 12 oz. Its dimensions 0.002 mfd. These values are applicable justing the high-tension . voltage supply to where the gun voltage is 3,000, the dis- the charging valve (i.e., the zoo -volt are 15lin. by 131 -in. by i5in. It is priced at II guineas. charge resistance 3 megohms, and the supply shown in Fig. 3), while the out- voltage swing on the grid of the first am- put amplitude is controlled by a potentio- plifier valve is 40. For values other than meter in the anode circuit of the first these C would have to be modified pro- valve in the paraphase amplifier. It is portionately. found that, provided .the settings of the Amplitude control is best carried out coupling coils are left unchanged, control Club News in the amplifier circuit, so - as to avoid of frequency by either C or the discharge Eastbourne and District Radio Society alteration of the mean grid potential of resistance has practically no effect on the Headquarters: The Science Room, Cavendish Senior School, Eastbourne. the first amplifier valve. Coarse adjust- amplitude of the output voltage. Hon. Sec.: Mr. J. P. Glickman, " Bersal," Brodrick Road, Hampden Park, Eastbourne. At the last meeting of thé Society two members brought transmitting apparatus and demonstrated how oscillation could be indi- cated by means of a turn of wire and a fuse New Apparatus Reviewed bulb. On April 25th a lecture will be given by a Belling -Lee representative. Recent Products Chadwell Heath and District Amateur Radio Society of the Manufacturers Headquarters: Ralph's Café, Trolley Bus Terminus. Hon. Sec.: Mr. R. C. E. Beardow, 3, Geneva Gardens, Chadwell Heath, Essex. - At the meeting on March 29th morse practice was held from 8.3o p.m. to 9.15 p.m. After WEARITE IF TRANSFORMERS a short interval G8PL gave a talk entitled, RANGE of IF transformers has been in- " Weather Conditions as Affecting Radio." A Weaire, troduced by Wright and Ltd., under the same conditions London Transmitting Society 74o, High Road, Tottenham, London, as the IF94 the of curve shown was obtained. The stage gain Headquarters: io, Raeburn Road, Edgware. N.17. The types with iron -cored coils can Meetings: Thursdays at 8 p.m. is 99, and the band -width for a 3 db. Hon. Sec.: Mr. G. Yale, 40, be obtained for an intermediate frequency drop Raeburn Road, Edgware. is 4 kc /s. A monthly bulletin entitled L.T.S. has been of z Io kc /s (IF96) or 465 kc /s (IF94), and started by the society. It is circulated privately they are priced at 6s. ßd. each. The coils to members. are included with their trimming condensers TUNGSRAM RECTIFIER use in an aluminium ' can for bolting . to the NEW rectifier, designed for in car Wirral Amateur Transmitting and chassis. The four connections are normally radio sets, is announced by Tungsram. Short-wave Club soldering tags at the bottom of the can, but It is a full -wave, indirectly heated type tak- Headquarters: Beechcroft Settlement, \\ het -.t uie Lane, ing 0.65 Birkenhead. tike transformers can be obtained with the amp. at 6.3 volts. The HT rating Meetings: Last Wednesday in the month al 7.30 p.m. grid or anode lead brought out at the top for is 400-o-400 volts at zoo mA. When used Hon. Sec.: Mr. J. R. Williamson, 13, Barrow Grove, with a vibrator it is Bromborough, Birkenhead. 3d. extra. recommended that a The annual meeting was held on March 30th, Tested with a W42 valve a gain of 104 25o -ohm resistance be inserted in the lead to when the chairman announced that there had times was secured with the transformer the transformer centre-tap. been an increase of thirteen in the member- loaded by the, valve voltmeter only. Under The valve is fitted with' a standard British ship during the year, bringing the total to 34. these conditions the circuits are slightly 5 -pin base, the centre -pin of which is used for The club has now .a dozen fully licensed trans- the cathode. mitters and six members with artificial aerial over -coupled, giving the double -humped licences. resonance curve shown. The peak separa - It was decided to continue with the monthly E.T.L. .VALVE TESTER meetings and to have a field day during the AVALVE tester designed for operation summer. from AC mains has been submitted for Croydon Radio test by the Electrical 'Test Laboratories, Society Headquarters: St. Peter's Rail, Ledbury Road, South Ltd., 189, Regent Street, London, W.I. Croydon. The valve under test has its grids and meetings: Tuesdays at 8 p.m. Hon. Pub. Sec.: Mr. E. L. Cumbers, 14, Campden Road, I F 99 anodes strapped together. An alternating south Croydon. A.99 100,000 voltage is applied between these electrodes At the recent annual general meeting it was and the cathode, and the resulting rectified reported that since Christmas the average current is read on a milliammeter. This attendance had reached a figure never attained before. Discussing future programmes, it was carries two coloured sections marked decided that Good " and " Bad." those dealing with quality repro- ó duction should be increased to 75 per cent. of > The reading of the meter depends on the 0 the whole. In the ten-minute talks one mem- cc IF94 of o condition the valve and upon the setting ber showed a home-made cinematograph film, A-104 of a calibrated variable resistance. In use and another demonstrated his two -stage am- the setting of this resistance for the particu- plifier. lar valve under test is looked up in the chart provided and on pressing a safety switch the meter indicates the condi- tion of the valve. On test the instru- The E.T.L. ment gave a clear indication between valve tester. good and bad valves. Twenty valve - 1,0000 0 e v v holders are provided for British and Ameri- á can valves, and two blank holes are pro- FREQUENCY IN KILOCYCLES PER SECOND vided for the addition of new valve -holders should these be necessary in the future. Resonance curves of the Wearite IF94 and Sockets are provided for the connection of IF99 transformers. phones; so that a noisy valve can be picked out. tion is 5 kc/s, and the useful band-width A neon tube is included for testing for 14 kc/s for a drop in response of 3 db. at short circuits between electrodes, including the edges of the pass -band. heater and cathode, and the meter can be The Type IF99 transformers are supplied used for external voltage measurements with without a screening can, and have air -cored ranges of Io, 250 and 500 volts at I,000 coils; they are priced at 4s., and tested ohms per volt. The Wireless World, April 14th, 1938 337

has been giving a series of Television Teas at which there is usually foregathered as motley a collection of females as it has ever been my fortune to see in a somewhat long and varied career. UNBIASED Now I have no rooted objection to the opposite sex ; taken in small doses they picked up when with the police in my can be very agreeable indeed, like arsenic, High - pressure younger days, and I soon found one or for instance. But, as in the case of the Salesmanship two valuable clues. Eventually I dis- mineral substance mentioned, they become covered that this cycle of affairs had been quite intolerable in the mass. I would, ALTHOUGH I always endeavour to take repeated in a large number of districts, however, in my eagerness to see the a kindly view of the shortcomings of and in each case it had been marked by B.B.C.'s television programmes, have put my fellow -men, there are times, I fear, the significant fact that the salesman and up even with these Television Teas, but when my faith in human nature seems on for one very grave disadvantage, namely, the point of failing. No doubt some of the obvious ,necessity of restricting my you have felt the same sort of thing at sun-bathing activities. Since the " club " some time in your lives. I well recollect By type of television receiver appeared, there- an Australian friend of mine telling me c,f fore, I have been repairing every after- the romantic ideas he used to entertain noon to my club in Pall Mall to enjoy my concerning the rural beauty of England, daily dose of sunshine in comfort and about which he had been told by relatives security. in the Old Country whose imagination was FREE GRID Unfortunately, however, in spite of all apt to run away with their sense of this, the degree of sunburn on my person veracity. Eventually the time came when has been steadily decreasing, and I should he was invited to make a prolonged stay an assistant had both taken rooms in the still be at a loss to account for it had not with his relations in Manchester, and he district a few days before the interference a well-known physicist who had been told me that he would never forget his broke out. dozing all the winter before the fire in the bitter disappointment as he sailed up the After this discovery I was not long in Club suddenly woken up one afternoon Manchester Ship Canal one dreary Novem- running my quarry to earth and exacting ber afternoon, and his thoughts imme- a full confession. It appears that they diately flew back to the sunny warmth of had been working an old dodge known as Sydney's aquatic glory, to be followed " creating a demand." This is quite shortly afterwards by himself. common in America, but is happily rare in I am moved to these melancholy reflec- this country. While the salesman went tions by some revelations which a friend on his rounds his assistant was busy recently brought to my attention concern- manufacturing interference in their lodg- ing certain features of American high- ings by means of simple electro -therapeutic pressure salesmanship which had come his apparatus of the so-called violet -ray type. way, and in connection with which he Unfortunately there is no question of re- sought my aid. It appears that quite porting them to the police, as in the recently he and his neighbours were present state of the law over here their A complaint to the Secretary. startled by some truly devastating elec- action is perfectly legal. trical interference which made the recep- and noticed my collarless state. He imme- tion of broadcasting almost impossible. diately summoned an attendant and made A few days later my friend received a a formal complaint to the Secretary, who call from a high-pressure American sales- A Sun-bathing Dilemma explained the position to him, upon which man who practically forced his way into -that most of you are aware he was fortunately able to diagnose the ISUPPOSEthat special television receivers are now cause of my trouble. available for clubs and such -like places The small cathode-ray tube, it appears, where a large number of people wish to emits its full quota of ultra-violet rays, but look in at the same time. For this pur- owing to the fact that a mirror is em- pose the image from a small cathode-ray ployed to reflect the picture on to the So this is tube is passed through an optical magni- screen, this radiation becomes very greatly England. fying system and projected -on to a ground- attenuated. It looks very much, there- glass screen. As in the case of a photo- fore, as if I am faced with the alternative graphic enlargement, the picture has to be of giving up my synthetic sun-bathing viewed from a little distance away if it is altogether or throwing down the gauntlet to compare in quality with that of the to the assembled mob at one of Mrs. Free domestic model, and for this reason is not Grid's Television Teas, a prospect which the house and insisted on demonstrating likely to oust the latter from its position I do not at all relish. an anti -static aerial and a mains filter, in the home. both of transatlantic origin. I must confess that I viewed the coming A.R.R. To give the devil his due, my friend of this projection model with extreme admitted that these gadgets were remark- favour because of certain urgent private THANKS to the many readers who ably efficient in getting rid of the trouble, reasons. As I told you some time ago, have written to tell me that I can and the salesman had no difficulty in the screen of the cathode-ray tube used in obtain a Government grant towards the disposing of the whole stock in the neigh- certain domestic receivers is extremely rich building of the underground loud speaker bourhood. He would not have thought in ultra-violet radiation, and for this pur- which I recently described, as it can be much about this, however, had he not pose I had hoped to use the B.B.C. tele- used as a communal air raid shelter. heard of a similar chain of circumstances vision programmes all through the past Several correspondents tell me that they occurring in a neighbouring district. winter as much for sun-bathing purposes intend to combine business with pleasure His suspicions were aroused, and even- as for the entertainment they give. Unfor- by building one of these loud speakers, tually he consulted me upon the matter. tunately, viewing the B.B.C.'s television and have written to the Government for Fortunately I have quite a considerable programmes became very popular with the necessary subsidy before they com- knowledge of detective technique which I Mrs. Free Grid and her friends, and she mence operations. 338 The Wireless World, April 1.fi11; 1938 Eddystc

9 FEATURES. Waveranges. -(1) 12.95-34.9 metres. (2) 31.98-85 metres. (3) 205-550 metres (4) 900-2,000 metres. Circuit.-Pentode RF amplifier -hexode mixer pentode oscil- lator - pentode IF amplifier (465 kc/s)-double diode triode second detector pentode output valve. Full -wave valve AN EFFICIENT ALL -WAVE RECEIVER OF rectifier. Controls.- (1) Tuning. (2) Volume. (3) Tone. (4) Waverange. (5) RUGGED CONSTRUCTION On -off Switch. Price.-(Chassis, valves and loud speaker) 21 guineas. Makers.-Stratton THE experience of this firm in cater- cedes this stage and is controlled with the & Co., Ltd., Bromsgrove Street, Birmingham, 5. ing for tropical markets is ,of. Iong IF amplifier by AVC, in which the con- standing and their preference for ditions of operation have been chosen pri- solid cast chassis and coil screens is well marily to suit the short-wave ranges. known. From the point of view of dura- That this claim is not without good of a normal all -wave broadcast set. Many bility the advantages of this form of con- foundation was proved when the set was sets of outstanding performance from the struction are obvious, but in temperate inadvertently operated on the lowest wave- point of view of overall magnification seem climes the justification for the additional band with only the short connecting lead to show an avidity for any and every type cost must be sought in the improvements projecting from the side of the chassis as of impulse picked by the aerial, but the which it confers on the overall per- an aerial. Incidentally, twin leads are E.R.A.7's best response is undoubtedly formance. provided here for a doublet aerial, one of reserved for carriers and other CW trans- Stability is the keynote of the whole de- these being joined to the earth terminal missions. - sign; frequency stability contributed to by at the back when a single wire aerial is Second channel interference is neglig- the rigidity of coil mountings, and stability used. When the outdoor aerial was con- ible, and under the conditions of test, from the point of view of uniform amplifi- nected the signal strength of an American with the loud speaker mounted on a sepa- cation resulting from the elimination of station which had been tuned in without rate baffle, microphony was entirely absent unwanted feed back by the efficiency of any difficulty on the short aerial lead rose even at full magnification on the strongest screening. by only a few db. A more remarkable carriers. Air dielectric trimmers are used in the feature of this unrehearsed incident was Sensitivity is well maintained down to three -circuit IF band pass filters and a that the signal-to-noise ratio gave no clue 13 metres, and an unusually good per- separate oscillator is used on a circuit de- to the fact that the aerial was off, neither formance was given on the 13.8 -metre signed to give the minimum of frequency was sensitivity obviously deficient by the broadcast band relative t o the 16 - drift. The frequency changer is a triode- standard of performance which is expected and 19 -metre groups. The scale is pro - hexode in which the hexode portion alone is used for mixing. An RF amplifier Complete circuit diagram. The use of the hexode portion of a triode hexode valve as mixer in tuned on each of the four wavebands pre- conjunction with a separate oscillator is the principal deviation from standard practice.

o

0O a0

h+' N i MIXER

d 6

I The Wireless World, April 14th, 1938 339.

bands as it is of the short waves, and have affected adversely the quality of re- the signal-to-noise ratio is very much production. There is no apparent defi- better than usual below 250 metres. Not ciency of top and the treble response is a single self-generated whistle could be quite free from harshness. This is not E.R.A.7 traced anywhere, and the selectivity on one of those sets where the tone control is medium waves was sufficient to give a an essential element in the ultimate v i d e d with subsidiary graduations on all broad- cast and amateur bands to VALVE RECTIFIER VALVE facilitate logging of sta- 2nd DETECTOR 1W41350 D H 4 2 tions, and the slow motion OUTPUT VALVE PEN. 8 4 obtained when the direc- IF AMPLIFIER VALVE tion of rotation of the AC V P2 tuning knob is reversed conveniently covers each MIXER VALVE of these bands. X 4 1 Calibrations are in megacycles and metres on the two short-wave ranges, and in metres and station OSCILLATOR TUNING names on medium and VALVE CONTROL long waves. Each scale is S P 4 B to inches long and is VOLUME brought into view auto- CONTROL matically by a rack and pinion mechanism coupled to the waverange control. RF TONE CONTROL Mechanically the arrange- AMPLIFIER ment works smoothly and VALVE AC V P2 the change over from one WAVE -RANGE SWITCH waveband to another is

MAINS ON-OFF SWITCH Aluminium alloy castings AERIAL AND EARTH are used for the IF and LEADS The Wireless World signal frequency tuned cir- COPYRIGHT cuits as well as for the main chassis. The rotary tuning scale drum is actuated through a from modulation of London achievement of good balance, and its rack and pinion mechanism by the wave - clearance the range control. Regional well within one channel on function is confined to the mitigation of either side of its normal setting at a dis- background noise under poor conditions of tance of 15 miles. On long waves the reception on short waves. electrically silent-an important point in Deutschlandsender is easily received clear The energised loud speaker supplied a receiver with high overall magnification. of its neighbours and at excellent pro- with the set is of massive construction and Uniformity of sensitivity is as much a gramme strength. makes use of a 12 -inch curved sided dia- quality of the ordinary broadcast wave - The high selectivity does not appear to phragm. The speech coil diameter is above the average, and in spite of a fairly tight surround there is no lack of bass response. Frequency doubling is not ob- vious, and judging from the output power the rating of the final stage (5 watts) is not merely a catalogue figure. ó Sound Construction 7' aóQ t` Workmanship underneath the chassis is in keeping with the clean exterior. Ceramic valve bases are employed, and porcelain is also used for wiring anchor- a CT ages at many points. This is an instrument which cannot fail to catch the eye of the experienced wire- less enthusiast. He will find the perform- ance no less attractive, for the makers have mopped up all the minor troubles which often accompany high magnifica- tion r rid selectivity in a superheterodyne circuit. Furthermore, the quality of VOLUME reproduction makes it an excellent CONTROL mon receiwx for the general use of the house- FICR UV hold. Cabinet work is more or less left to the MAMA purchaser, but a solidly built and attrac- tive -looking console is obtainable to order through the manufacturers. ;1n The Wireless World, April 14th, 1939

planation for it and how it can be sup- pressed. By changing to transformer coupling giving probably a voltage step-up of one to Readers' Problems four- the AF ga-in is proportionally, greater and any residual hum will, of cöurse, be A Selection of Queries dealt with by the Information Bureau, and chosen increased, or at least, that portion that for their more general interest, is published on this page. originates in the earlier stages of the set. We doubt, however, if this would account Location of Reaction Condenser size of a baffle, as a loud speaker let into for a very marked increase in the hum level. READER wishes to know which is the the partition wall between two rooms would It can be tested for by disconnecting the A correct position for a reaction con- probably give the best results in the circum- primary and joining across it .a resistance of denser; between the detector valve anode stances. the same order as the AC resistance of the and the coil, or at the " earthy " end of As this plan is not always convenient, the preceding valve. If the hum still persists next best it is almost the coil, as he has seen this condenser some - would be a baffle of irregular certain to be due to direct induc- shape and not less than 6ft. by 4ft. over- tion into the transformer from either the all, and with the loud speaker mounted mains transformer or smoothing chokes, slightly off centre. but most likely by the former. This conclusion was reached after tests The AF transformer should be removed had been made with baffles of different size from the baseboard, and flex leads of suffi- and shape, the loud speaker response being cient length to enable it to be turned in all illustrated by curves taken at the time. directions connected in place of the existing These were published in The Wireless World secondary leads, the primary still being kept of May 22nd, 1936, in the article, " Loud shunted by its resistance. Speaker Baffles." By rotating the transformer, tipping it up on end, etc., it should be possible to find Power Output a position where the hum is a minimum. The actual position may be very critical. THE reason why it is so often stated in It can then be fixed in this position and the The Wireless World that an output of primary connection remade. four to six watts is necessary in order to obtain the highest standard of reproduction has been the question asked in more than Battery Connections one letter recently. The writers point out IT is required to replace the HT battery that even one watt can be intolerably loud in a small set and to use separate bat- in a room of quite normal size. teries for HT and grid bias in place of a In a broadcast set reaction is usually better This, of course, is quite true, but for ordi- single unit used hitherto. Some difficulty is is joined under control when the condenser nary domestic requirements the receiver or being experienced in identifying the various . at X instead of as shown here. amplifier, as the case may be, is never oper- leads shown in the drawing reproduced in the figure. One is obviously the HT nega- times in the one and sometimes in the other ated at maximum volume. The large out- put stage is necessary in order to take care tive and one the grid bias -negative, but our position. querist has not yet succeeded in finding Theoretically the correct place in the cir- of momentary peaks without introducing how distortion. to connect the grid bias positive of the cuit for this condenser is at the " earthy " separate battery. end of the reaction winding, so that its To achieve this the average level of out- and put will have to be comparatively low, and Of the four leads shown, that with the moving vanes can be earthed thereby black wander plug is avoid the disturbing effects of hand possibly not more than one to one and a half the HT negative and watts. A four -watt amplifier is, therefore, the yellow the grid bias negative, nine volts capacity. grid bias being used. Unfortunately, this is not always satis- not unduly large for high-fidelity repro- duction. If separate batteries are employed, factory in the case of ordinary broadcast another lead sets, as even with the reaction condenser at with a wander plug at one end Nomenclature will have to be connected to the cable lead minimum, or even disconnected entirely, terminating the detector circuit cannot be prevented in the black wander plug. The WHEN the superheterodyne was first added one will be inserted in the positive from oscillating, and it can only be stopped evolved, two valves were used for the by disconnecting the reaction winding from end of a 9 -volt grid battery, and the yellow purpose of frequency -changing ; one was plug to negative the anode of the valve. the of this battery. described as the local oscillator and the The original black plug then goes This state of affairs is brought about by other as to the the first detector. The detector negative of the new HT battery, and .the the existence of a capacity shown dotted qualification was adopted, as there was in the figure between the reaction and the another detector after the IF amplifier, this tuned windings. As this capacity is in being designated the second detector. parallel with RC it will, if large enough, Even when a single multiple -electrode maintain the circuit in oscillation even with valve replaced the earlier two -valve arrange- RC at minimum, RC not then taking full ment the original designations were often control. retained, but it is now the customary prac- If, now, RC is changed over to the point tice to describe this stage simply as the X, the inter -coil capacity is no longer in frequency -changer, whether one or two parallel with it, and the amount of regenera- valves are employed. tion feed-back will then be determined The expression " second detector " is now solely by the capacity of RC. rarely used, this valve being referred to as As both moving and fixed vanes of the the detector without further qualifications. reaction condenser will be " live " to RF, This clarification may be of interest, as it it will have to be removed from the front appears that a little confusion still exists in panel and controlled by an insulated exten- the minds of some readers not fully ac- sion rod. quainted with the current practice of identi- In short-wave sets RC can usually be fying the various stages in a modern super- joined in the " earthy " end of the reaction heterodyne. circuit, since the inter -coil capacity is too small to be troublesome in this respect. Mains Hum The HT battery and cable connection which modified a mains set and fitted a reader requires identifying. Size of Loud Speaker Baffle HAVINGan intervalve transformer where hither- ADVICE is required regarding the correct to resistance -capacity coupling was used, a others to the sockets corresponding to those size of baffle for a loud speaker having reader is troubled by a very pronounced in the old battery. an 8in. diameter diaphragm in order to hum. Actually, the set was not perfectly Green is probably the detector HT supply obtain the best possible reproduction. silent before, but the hum was only just and red the positive HT for other valves in Actually, there is no definite limit to the audible. We are asked if there is any ex- the set. The Wireless World, April /4t1t, /938 '341

Voltage Stabiliser D, r.," PREVENTING FLUCTUATIONS

IN HT SUPPLY + 1 5 1.0 DESCRIPTION of a valve -operated regulator for 0.5 interposition in the HT supply circuit of certain o measuring and testing instruments where a high degree of 05 constancy is required. The system might also be applicable 10 for minimising tuning drift in short-wave receivers, - 1.5 -40 3o 70 10 0 10 20 30 +40 especially in cases where the mains supply is subject to. severe voltage fluctuations. PERCENTAGE CHANGE IN INPUT VOLTAGE Fig. 2.-Showing that wide variations need for an anode supply, of a low -resistance triode, is connected in in input voltage produce comparatively TIEwhich the voltage will remain series with the supply, its grid being at small changes in output. constant despite variations of the same potential as the anode of the load current and mains voltage, control valve. Suppose an increase in once between this fixed bias and the has long been felt. Such a supply is output voltage occurs, the anode of the potential of the point X of the potentio- essential for frequency meters, ther- control valve becomes less positive, caus- meter. It is desirable that the voltage of mionic voltmeters, constant frequency ing the grid potential of the regulator this battery shall havea fairly large value valve to move in a so that the potential of the point X may negative direction. be fairly large. If the point were ro volts The anode -cathode positive a variation of output voltage of resistance of the io per cent. would cause the control grid regulator valve in- potential to vary by one volt,- whereas if creases, causing an it were at a potential of 5o volts a similar increased voltage variation would, cause a change of five drop and so pulls on the grid. To get effective control it is the output down to thus necessary to use relatively large its original value. values of fixed bias so that percentage In the case of a changes in output voltage shall cause fall in output volts large variations in control grid potential ; the reverse action it is advised in the interests of good regu- occurs, making the lation that the battery bias shall be at grid of the regu- least 10-15 per cent. of the output voltage. lator valve move in a positive direction, and Performance the effective resist- Limitations ance of this valve As this type of regulator cannot Fig. i.-Circuit diagram of the voltage regulator, which is inserted falls, allowing the " boost " up the voltage if the input volt- between the source of H.T. supply and the load. output voltage to age should fall too low it is necessary to rise. have a sufficient voltage drop across the oscillators and other precision apparatus, It will be noticed that a battery is shown valve V2 to enable control to be effected and to obtain it batteries are frequently in the cathode circuit of the control valve for all reasonable variations and in prac- used even though AC mains may be supplying a constant negative bias, the tice the output voltage cannot exceed available. grid voltage of the valve being .the differ - about 75 per cent. of the normal input Voltage regulating circuits have been developed in America by the R.C.A. and AC - Bell Laboratories which enable +0 33093 operated power supplies to fulfil these re- - quirements, and to compare with batteries 10,0000 in regard to voltage stability. The prin- 0.5M0 ciple used closely resembles the . AVC action in a receiver. 2.3,0000 A- regulator which will maintain a con- stant output voltage within narrow limits 8 mlda 350-0-350V P is shown in Fig. r. The control valve VI, 10,0000 R1 6J 7 2A3 T8 mida which is a high -magnification screen -grid MAINS or pentode type, is connected in series with a high resistance-Ri--across the input 5,0000 to the unit. The control grid of this valve is connected to a point on a potentiometer network across the output of the unit, so that a change of output voltage will vary the grid bias and so the anode current of the valve. This in turn changes the volt- age drop in the anode resistance RI and so the potential of the control valve anode will vary in sympathy with any variations Fig. 3.-A complete voltage -stabilised H.T. unit. N is a Soo -volt, /-watt neon lamp of output volts. The regulator valve V2, with base resistance removed. 342 APRIL 14th, 1938. Wai Ill Voltage Stabiliser- visual indication that the output voltage despatch of goods was also always carried volts. Some idea of the performance of is under control. The output voltage will out with the least possible delay. the regulator may be gained from the remain constant at 350 volts for any cur- In conclusion, may we suggest that the persons who made the allegations curve shown in Fig. 2. It will be seen rent between zero -and 40 milliamperes or probably that a variation of input dealt with firms of questionable reputation volts between at 200 volts for load currents not exceed- and consequent slovenly methods. 25 per cent. and 3o per cent. is necessary ing ioo milliamperes. It is stated that at Abbassia, Cairo. A. BATY. to cause a change of i per cent. in out- 200 volts output the voltage will remain P. A. SALE. put voltage. Further, by the use of the constant despite primary voltage varia- regulator unit the voltage regulation of. an tions between ioo and 140 volts. A con- South Coast Regionals AC power supply was improved from trol of output voltage is obtained by the IHAVE recently moved to a part of this roughly 3o per cent. to 0.5 per cent. potentiometer RI. With this type of country far distant from London, and In Fig. 3 is shown a complete voltage - power supply unit the hum level is low, in one of the first things I missed was, and is, regulated AC power supply unit, designed spite of the simple filter unit used, as the a reliable alternative station to Droitwich by Grammer, suitable for working re- regulator tends to " iron " out ripple in National. In fact, if it weren't for ceivers, amplifiers and testing apparatus. the output as well as power variations. A England's one and only long -wave trans- mitter I really don't know It will be seen that the biasing battery further advantage is that the effective im- where many thousands of listeners would go for their has been eliminated by the use of a one - pedance is very low and it may be used watt entertainment, except abroad. neon lamp in the cathode circuit of with high -gain amplifiers with a minimum The part of the world in which I now the control valve ; this lamp also acts as a of feed-back. dwell is, as -I have just mentioned, a very great distance from London and other Regionals, and as it does not possess a station serving its own area the choice of home broadcasting is often limited to one. My receiver was new this year and cost 15 guineas, so my trouble in this respect is Letters to the Editor not due-to inefficient apparatus ; also, owners of the biggest and most powerful and " Hum in AC Receivers " The Editor does not hold himself responsible sensitive of sets experience the same diffi- for the opinions of his correspondents culty. The proprietor of the largest radio IWAS extremely interested in Mr. R. E. shop hereabouts told me recently that he is Darnton's query and in the answer confined to Droitwich National for reliable by Mr. D. Halliday which you have pub- quality gramophone records, I should be glad to know if any reader demonstration of his wares. lished recently. has had ex- This state of affairs has perience of fibre needles with suitable tone existed ever since This reminds me of a very interesting broadcasting began, so it is more than high experience which I had a few years ago and correction. time it was remedied ; and I now hear that of similar experiences since then. Those of This is a point of some importance, as the life of records is greatly this is being done. A transmitter is being my acquaintances who are technical experts prolonged when fibre erected at a point needles are used, but, owing to the higher distant a few miles from in radio or power transmission are far from this benighted spot, just a few miles; so unanimous in their explanations, so that compliance of fibre over steel, I feel that very soon all should be well at... . perhaps the problem would interest your transients must suffer even when the loss in the higher frequencies St. Leonards-on-Sea. readers. has been com- T. J. E. WARBURTON. A particular AC receiver was factory pensated for. Some years ago I took an tested in the works by myself on standard output measurement at various frequencies, mains. The hum level was quite normal. using steel and fibre needles, and, as far as CAR RADIO This set was installed fairly near to the I can remember, there was a drop of about A PENTODE signal -frequency amplifier, works in a district that was only partly r2 db at 5,000 cycles when using fibre and heptode frequency -changer and tetrode changed over from DC to AC. The set was as compared with the steel. output valve are features of the Ferranti then found to hum excessively. I had at Hornchurch. F. H. WALKER. car set, illustrated on this page. Arrange- the time no means of checking the, supply ments have recently been concluded voltage, but using the 25o instead of 23o The British Radio Manufacturer whereby matters appertaining to this tapping on the mains transformer only WE have read, with great surprise, in receiver in London and S.E. England are reduced the hum very slightly. On return- your columns during the past few dealt with by Car and General Radio, Ltd., ing it to the works it was again tested and months letters in which instances are of 38, Hugh Street; Eccleston Square, found O.K. It was returned to the cus- given of alleged procrastination and a London, S.W.r, and in other districts by tomer and was left working with the general lack of businesslike methods adopted Ferranti, Moston, Lanes. excessive hum, as it was believed that this by certain, British radio firms when dealing would disappear when the remainder of the with customers abroad. street was changed over to AC. This In fairness to British firms in general, who, ON THEIE proved to be the case, and the hum level having been attaeked as a whole, naturally was restored to normal. cannot reply singly, we think that it is time I believe that the street cable was out something was said in their defence. We SHORT -WAVES of but balance, a power engineer tells me have for some time now been carrying out HE following extracts from the latest that this will not distort the wave -form. It work which has necessitated much corre- General Electric should, perhaps, bulletin should in- he added that there were spondence with British firms and, without terest most readers of this column three streets in the form of :- letter "H." exception, our enquiries have been met with " The General Electric Company oper- At the time hum was experienced one the utmost courtesy and promptness, many ates W2XAD and WzXAF on a non-profit vertical limb and half the horizontal were of the firms supplying us with quantities of basis, without charges on for services rendered, DC and the other half on AC. I have valuable literature for which we had not for the purpose of improving the inter- also been told that supply companies vary asked. In one instance we actually received national broadcast field, furnishing listeners in their methods of balancing cables, some a quotation ßy return air mail ! The in other countries with programmes " as they go " and others not necessarily which until the scheme is more nearly complete. Will Mr. Halliday or some other kind reader again oblige, please? Manchester. R. D. DUCKWORTH. THE FERRANTI CAR RADIO SET is in three -unit form, designed essentially for easy installation in the Fibre Needles typical British type HAVING read with considerable interest of car. the recent correspondence in The Wireless World regarding the use of tone control and volume expansion with high - APRIL 14th, 1938. Whekeg Worel 343 would not otherwise be received and the These new Marconi -Osram AC/DC steep- building of international goodwill." slope, ro mA /V, output tetrodes should have The bulletin goes on to state that : " The a considerable application in small trans- carrier power output on W2XAD or mitters or even in the earlier stages of M CAIiI-1YIu W2XAF is from 20 to 25 kilowatts. The larger transmitters, especially as the grid ill effective carrier power when Alexanderson connection is brought out to the top cap, panel directive antennas are used is from giving a low input capacity. 200 to 25o kilowatts. The heaters are brought out to three pins " Class B low-level modulation is used and therefore have the alternative ratings on all transmitters." of 13 volts o.6 amps. or 26 volts o.3 amps., Finally, a note is added as follows : " On and can therefore be readily used on AC or after June 1st, 1938, a radio -frequency mains when a heater transformer delivering power amplifier having a carrier power out- 13 volts is available. The equivalent 4 and put of roo kilowatts will be available for 6.3 -volt types do not possess the advantage any of the assigned frequencies, i.e., 21.5, of the top grid cap. 15.33, 9.55 or 9.53 Mc/s. Owing to the mechanical construction, Only W2XAD on 15.33 Mc/s (19.56 m.) these valves may be plate modulated to 'a now uses a beam on this country, and, apart very high percentage without noticeable dis- from the omnidirectional transmission on tortion, although, if desired, the screen may W2XAF between 8 and 10 p.m. G.M.T., also be tied into the modulation circuit. all the other transmissions, W2XAD When used as an amplifier on z8 Mc / s, 21.5 Mc/s, W2XAD 9.55 Mc/s, and some degree of neutralisation is desirable, WzXAF 9.53 Mc/s from 10 p.m. onwards, and for preference limiting resistances of are directional on South America. about r,000 ohms should be used in the Gene Darlington's special weekly broad- anode and screen circuits. cast on Tuesdays is still to be heard over Their slope or conductance of ro mA /V both W2XAD and W2XAF at 11.35 p.m. compares more than favourably with the G.M.T, and after April 24th at 10.35 p.m. 6L6 or KT66-6.3 mA/V, and the standard G.M.T. (or 11.35 p.m. B.S.T.). U.S. pentode the 6F6-2.65 mA /V. For the greater part of the year W2XAD Finally, short-wave conditions still remain is probably the most " tuned -to " short- good and all the regular transmitters are wave station in this country ; it is certainly giving a good service. IN modern radio practice, nothing is final; no so in the evenings, although the afternoon Newcomers are Helsinki (Helsingfors, Fin- receiver is so good that it is incapable of performance of W2XE on 21.52 Mc/s is land) on 9.5o Mc/s, a good signal in the development in some detail. a close second. early evenings, and Paris JPB2 on 17.78 Constant attention to improvement in small One hopes that during the coming summer Mc / s-the latter causing a bad heterodyne matters keeps McCarthy chassis in the forefront W2XAD or WzXAF will be able to use the on W3XAL between r and 3 p.m. most after- of modern chassis design and construction. 21 Mc/s channel, too, for early evening noons. Bombay is now working near 6o broadcasts to Europe, since the 15.33 Mc/s metres, 5 Mc/s, in the afternoon, according channel does not become really strong in to our time. The receiver illustrated midsummer until quite late in the evening. ETHACOMBER. The programme material radiated by is the well-known McCarthy these Schenectady stations, too, is gener- ally of a very good standard, and they rarely THE WIRELESS INDUSTRY leave themselves open to the following type 9 -VALVE 4 -WAVE of criticism, which appeared in an Ameri- REDUCTIONS in the prices of the Exide " Hycap " range of LT accumulator cells can radio monthly recently. have do other than been made; as an example, type OCG3 SUPERHETERODYNE "If we had anything to now costs 8s. 6d. The Exide in this radiodor business-we'd charge indicator judging is now being fitted in cells of the CZG range priced at 14 guineas including valves nominate first as reek-of-the-month-any without increase in price. month out of the year-those domestic 0 0 0 0 The Circuit in Briet.-The pre -selector short-wave stations carrying excessive com- National Radio and Television Service Com- circuit is coupled to high -gain radio frequency mercials.. The worst offender of all is pany, 155 and 157, Great Portland Street, Lon- amplifier operating on all 4 wave -bands, which W9XJL on 26.1 Mc/s (incidentalty W9XJL don, W.1, is undertaking the manufacture of is transformer -coupled to latest type triode- is well heard over here and uses GSK's heavy-duty amplifiers for use as permanent hexode frequency -changer. There are 2 band- channel), which station endeavours to sell installations in theatres, arenas, etc. The pass transformer -coupled I.F. amplifiers (inter- same firm also undertakes the construction of mediate frequency 465 K.C.'s). The double double-decker beds to the Eskimos, fur high -quality amplifiers and receivers and to to clients' diode second detector provides automatic coats to South Sea Islanders, Turns specifications. volume control applied to 4 preceding valves, the African cannibals-providing they come 0 0 0 0 and first stage L.F. amplification. The triode to Superior, Wisconsin or Duluth to buy A leaflet describing the E.T.L. Valve Tester phase -changer is capacity -coupled to push -pul them. Because a few sponsors and com- (which includes a noise test) has just been output pentodes (or Harries-tetrodes) delivering mercial departments may consider us a issued by The Electrical Test Laboratories, 9 watts. nation of morons, they should not be per- Ltd., Triumph House, 189, Regent Street, London, W.I. Principal Features.-Waveband coverage- mitted to encourage a similar opinion on 0 0 0 0 12.8 -33, 29-8o, 190-550, 80o-2,000 metres. the part of the rest of the world." A leaflet and booklet dealing with the Edi- 'Controls-sensitivity control (varying bias on Evidently the American conscience' is at swan Loud -Speakerphone are available from R/F stage) : 5 -position wave-change and last stirring to the necessity of restraining The Edison Swan Electric Co., Ltd., 155, Char- gramophone switch . combined volume control purely commercial announcements to ing Cross Road, London, W.C.z. and on/off switch and progressive variable tone reasonable limits. o o o 0 control (both operative on radio and gramo- Very often the sponsor's " blurb " The Solon electric soldering iron is being de- phone). amounts to nothing more than sheer bathos. monstrated on Henley's stand (No. 223 Main TERMS Hall Gallery) at the Ideal Home Exhibition. -DEFERRED Note, the material quoted above was 0 0 0 0 29i- with order and 14 monthly payments of 14¡-. written by an able American short-wave A new catalogue of Pifco productions has On application, or through our City agents, journalist, Zeh Bouck. been issued by Provincial Incandescent Fittings During the past week I have been rebuild- LONDON RADIO SUPPLY CO., Co., Ltd., Pifco House, 58, City Road, London, 11, OAT LANE, LONDON, E.C.2. ing my 14-28-56 Mc/s transmitter, and have E.C. r. converted the Xtal osc. and first two o 0 o o Send 3d. in stamps for compete illustrated catalogue doubler stages to work entirely from D.C. Philips receivers Model 785AX have been with technical data and circuit diagrams of other mains. chosen for installation in a number of schools Interesting McCarthy chassis of all types for A.C.. in the Isle of Man. Battery. or A.C.!D.C. Abridged list free of charge. The valve arrangement is now as follows : and 2nd o o o o 7 Mc/s Xtal osc., 6D6, 1st doublers The servicing of Manes receivers will in M CARTI1y RADI") 1. -no KT31, the heaters being arranged in series, future be undertaken by Bingley Radio Ser- the 6D6 at the earthy end. The 0.3 -amp. vices, Church Street, Bingley. The stall of this 44, Westbourne Grove, London, W.2 heater current is obtained via a Marconi 302 firm is thoroughly conversant with the design Tei hone Baum/ate. 3201/ ifflimtim barretter. of the receivers. The Wireless World, April r4th, 1938

only. The reason is that he lives in a road along which there is a great deal of motor RANDOM RADIATIONS traffic during the daytime, which means that interference with both sound and vision is terribly bad. Unfortunately, he can't Not Always Behind By " DIALLIST " erect an aerial high enough to be completely clear of the field of interference, and that now I have been amazed to must BEFOREcome across something which we have apply to many would-be owners of ceivers sold only one year ago are now obso- televisors. Don't you think it's about time long regarded as a commonplace in radio lete." He concludes hailed with the surprising that we took this business of car -ignition by American papers as the most com- statement, " Television is coming, but it is plete novelty. we've interference on the ultra -short waves seri- I suppose got so much not ' just round the corner."' That's just ously? into the habit of thinking that most new There is no question that it is one the kind of thing that might have been of the factors which prevents television from developments in, at any rate, the reception of written in a British paper about three years broadcast wireless come from the States going ahead more rapidly, and unless steps that ago ; but we should laugh at anyone who we imagine our own doings are taken it is likely to grow- much worse, that in that field made such out-of-date remarks in any paper for can contain little that is new to them. But the motor traffic on our roads is increas- of ours to -day. ing every day. A clause dealing with this we aren't always behind ; in fact, we are kind often a good long way in front, though we of interference might very well form don't always realise it. We had, for part of the Bill dealing with interference example, apparatus for receiving still pic- Plenty of Choice generally which has been so long awaited. many firms would you guess are now tures or facsimiles of letterpress with an . '. ea. ordinary set long before such a thing was HOWmaking television receivers in this coun- believe heard of in the U.S.A. And what about the try? I that -the number is eighteen, When's That Bill Coming ? screen grid valve? and there are certainly sixteen with televisors Or the HT battery that When are we going to have the legislation already on the market. - can be recharged from a 6-volt accumulator? Excluding big dealing with interference By way, screen instruments and taking only those that was fore- the I recently came across a British shadowed a long, long firm, now taking an interest which show images from 6 x Ain. to '34 x time ago, after the in the export Committee enquiring into the subject had market, which was toying with the idea of min., there are more than forty models to choose from, ranging in price from 3o guineas presented its report? One can see no reason using American air -cells that can't be re- now to 170 guineas. The former price is whatever for delay. Exactly what con- charged, and didn't know that air-cells that for the stitutes interference can had been manufactured for many years G.E.C. apparatus for vision reception only, has been laid down and in this country. sound being reproduced by the ordinary the ways of preventing it are well known. It was said some time ago that the various wireless set by means of a ; converter the Wireless Telegraphy Television, Too luxury instrument is the R.G.D., which in- Acts were to be re- cludes an " all-wave " auto -radiogram. There drafted into a single comprehensive Bill and There is no question either we are interference that is, therefore, plenty of choice in the matter of that would be dealt with by this. streets ahead of America in the matter of television receivers, and But there are no signs of that Bill and inter- television, and that our accomplishments there are not a few in which can be bought for no more than the ference is growing worse. A recent letter in that field are comparatively little known to cost of a high-grade The Wireless World showed that one large Americans. In Radio News for radio receiver. There April, 1938, are actually ten models which cost firm at any rate is still selling vacuum I find, for example, Commander E. F. less than ¿5o apiece and two at under £4.0. cleaners that interfere badly, and plenty of McDonald, president of the Zenith Radio other apparatus that offends is being sold. C6rporation, answering the question, " Is The Government could have stopped this Television Here? " with a decided No. He long ago by issuing a warning that their Bill says, " Even with the finest laboratory Cars and Television would prohibit the use of such apparatus or equipment experts have been unable to pro- neighbour of mine who is a tele- make it compulsory for the owner to have it ject clear pictures more than 27 miles." He ANEARvision enthusiast, if ever there was one, " silenced " at his own expense. They did goes on to remark that " changes in tele- has installed a first-rate television receiver, nothing of the kind, and when the Bill does vision transmitting apparatus have been so but finds that, as a rule, he can obtain satis- come it will now probably have to allow rapid and so continuous that television re - factory reception of the evening programmes interfering apparatus to remain in use for

THURSDAY, APRIL 14th. Nat., 6.40, What Makes a Play Successful ?-a discussion. 8, Broadcast Programmes " Rhythm Express," with Benny Frankel and his Orchestra. 8.45, Reading from American humorous FEATURES OF THE WEEK literature (from America). SATURDAY, APRIL 16th. Abroad. Reg., 6.40, " From the London Reg., 6.35, " The Seven Words from Nat., 8, Palace of Varieties, including Berlin, 8, " The Merry Widow Theatre," Raymond Massey and the Cross "-Heinrich Schutz. 9, "- George Robey and Florence Old- operetta (Lehár). Tamara Geva in extracts from " Gallery Goddess romantic "-a ham. 9.20, American Commentary. Kalundborg. 8. Bach Society " The Idiot's Delight." 8.10, comedy of the theatre. 9.35, Years Concert relayed from the Cathedral, Commentary on Abroad. Fifty of League Foot- Ladies' Darts ball-the History the Copenhagen. Championship. Budapest, 7.10, " of Game's The St. Matthew Organisation. Abroad. Passion " (Bach). MONDAY, APRIL 18th. Reg., 6.30, Billy Cotton and his Nat., 7, Paris, PIT, 8.30, " The St. John Milan, I, 9, " Requiem Mass " Monday at Seven. 9.20, Band. 7.30, Easter Passion " (Bach). (Verdi), from La Scala. Carols and World Affairs. 9.35, Television at Hymns. 9. " Vivanti," a play Work-a commentary by John Turin, 9, " Aida,' opera (Verdi). about the villainous character Snagge on the demonstration FRIDAY, APRIL 15th. of air WEDNESDAY, APRIL 20th. created by Sydney Hor!er. defence at Alexandra Palace. Nat., 7.20, " Hail Variety " II, with , Nat., 6.30, Church of England service Reg., 8. Abroad. Spain-both sides of the line. Ella Retford, commère. 8 from St. Sepulchre's, Holborn. 8.20, and Milan, I, 2.45, " Silvano," opera Geraldo and his Concert 9.20. Sir Adrian Boult conducts 8 and 9, " The Dream of Geron- (Mascagni). Orchestra, with Anne Ziegler and tius " by Elgar. The B.B.C. the B.B.C. Symphony Orchestra Rome, I, " Cleopatra," opera (La Eve Becke, 9.20, Excerpt from at Plymouth. Symphony Orchestra and the " Wild Oats." Rosa Parodi). Reg., 6.30, " Swift Serenade." 7.30, B.B.C. Choral Society conducted Abroad. " The World Goes By." 8, ' by Sir Henry Wood. SUNDAY, APRIL 17th. Deutschlandsender, 8, " A Night in Reg., " Band Waggon." 9, " A Rural 7.30, Mazurkas by Chopin and Nat., 7.15, " The St. Lawrence Venice," operetta (Johann Strauss). Szymanowski, "- Ride Renewed." S. P. B. Mais played by Jan Smet- feature programme from Canada. Stuttgart, 10.30, " Martha," opera. erlin, pianoforte. and M. McLaren follow in Cob- 8.45, An Enquiry 9.5, " Tales of Vienna "-light TUESDAY, into the Existence of Mermaids. APRIL 19th. bett s footsteps 9.30, After Dinner music from Vienna. Nat., 7, Gounod's opera " Faust "- Cabaret. Abroad. Reg., 5.30, Easter Music-organ and the B.B.C. Chorus (C) and the Abroad. Prague, I, 8.5, " Stabat Mater " choral from Lithuania. 6, Round Theatre Orchestra, conducted by Cologne, 8, Beethoven Festival. (Dvorák). the Courts. 9.5, Sunday Orchestral Stanford Robinson. Narration Rome, 9, " Die Frau ohne Schatten " Hilversum, I, 9.10, " The Passion of Concert conducted by Sir Adrian spoken and written by Wilfrid opera (Richard Strauss), Our from the Lord," by the Schola Cantorum. Boult-Easter Oratorio. Rooke-Ley. 9.20, America Speaks. Royal Opera. APRIL r4lh, "938. Wpe®20 345 WOpIld some little time to prevent the cry of hard- ship from those who have recently bought it. Television Programmes Vision A Reminder 45 Mcjs. Sound 41.5 Mc,s. Speaking of interference reminds me that THURSDAY, APRIL r4th. I come across an extraordinary number of 3, A Relay from the Television Studio at the [ONOENSER SPECIALISTS Ideal Home Exhibition, Olympia. 11.11.111MMI people who don't know what to do when 3.10, FOR OVER THIRTY YEARS is " Weather or No "-light entertainment, in- their reception of the wireless programmes cluding Walter Gore and William Stephens. spoilt by nasty noises of man-made origin. 3.30, British Movietonews. 3.40, 137th edition Readers can do both their friends and the of Picture Page. Post Office a good turn by letting it be known 9, As at 3 p.m. 9.10, As at 3.10 p.m. 9.30, that bad interference should be reported on Gaumont -British News. 9.40, i38th edition the form that can be obtained over the coun- of Picture Page. 10.10, News Bulletin. ter at any post office. The G.P.O. engineers FRIDAY, APRIL 15th. concerned with radio interference deal with 3, David Seth -Smith presents " Friends from many thousands of cases each year, and, the Zoo." 3.15, Gaumont -British News. though they cannot compel offenders to do 3.25, From Bach and Handel, song, dance and anything, their tactful handling of the matter instrumental music, with Sidonie Goossens, very often leads to a great improvement, if Margot Fonteyn and Richard Watson. not a complete cure. Where they can't in- 9, British Movietonews. 9.10, " Everyman," duce those who cause the interference to end a masque by Pepler, with Alexander Knox it they give the listener valuable advice in the name part. 10.5, News Bulletin. about ways of obtaining better reception by SATURDAY, APRIL 16th. means of anti -interference aerials, disturb- 3, From the Ideal Home Exhibition. 3.15, ance suppressors and so on. Cartoon Film. 3.20, Cartoons by H. S. Foxwell. ". ti 3.30, British Movietonews. 3.40, Variety, Unreasonable including Albert Whelan and Joe Young. Where AGOOD 9, From the Ideal Home Exhibition. 9.15, many people are pretty unreason- Ballroom Dancing. 9.30, Gaumont -British able in what they expect of their wire- News. 9.40, Variety, as at 3.40 p.m.-in less sets. Only the other day a man I know addition, Horace Kenny and Co. in " The GUESSWORK asked me the old, old question, " Why can't Frontiersman." 10, News Bulletin. wireless sets be as reliable as motor cars?" SUNDAY, APRIL r7th. means His trouble, I found, was that after using a 8.50, News. 9.5, Pianoforte Recital. 9.15, set of good make for eighteen months he had Cartoon Film. 9.25, " The Marvellous History had to spend 12s. 6d. on having a new volume of St. Bernard," a play adapted by Henri TROUBLE control fitted. That was the only repair of Gheon, from a manuscript of the 15th century. any sort or kind that had been necessary. MONDAY, APRIL 18th. I pointed out to him that whereas motor cars 3, From the Ideal Home Exhibition. 3.10, require and get pretty constant attention in YOU can't afford to take chances Starlight. 3.20, British Movietonews. 3.30, with condensers. With a dozen such matters as keeping the tyres at the right The Anti -Aircraft Defence of London. A or more special duties to perform pressure, filling up the radiator and the display by the First Anti -Aircraft Division each and every condenser must sump, topping -up the battery and so on, the (T.A.). Commentary by Leslie Mitchell. work according to specification. average wireless set is left to fend for itself 9, From the Ideal Home Exhibition. 9.10, Deviation from an alloted course can until it breaks down. And motorists don't Starlight. 9.20, Gaumont -British News. 9.30, spell disaster to the whole receiver. grumble when they have to have engines As at 3.3o p.m. 10, News. Make sure of utter dependability by decarbonised and the valves ground in after using and specifying only those TUESDAY, APRIL r9th. condensers made by condenser doing some thousands of miles. The volume 3, From the Ideal Home Exhibition. 3.10, specialists-And remember T.C.C. control gets a great deal of work in some Stanelli's Bachelor Party. 3.30, Gaumont- have made condensers-and noth- wireless sets. Of course, it shouldn't break British News. 3.40, " The Maker of Dreams," ing but condensers for more than down after eighteen months' use; but I don't a fantasy by Oliphant Down. three decades. think that anyone whose total repairs, ad- 9, From the Ideal Home Exhibition. 9.10, justments and renewals bill for that period Starlight, 9.20, Judo, the art of self-defence. come to Izs. 6d. has very much to grouse 9.35, British Movietonews. 9.45, " Oroastus," about. a Greek tragedy by S. Leacock, and " Hamlet, the Worker," % ti % a burlesque by Wilfrid Walter. 10.25, News. - A Matey Affair WEDNESDAY, APRIL zoth. I MUST say that I thoroughly enjoyed the 3, From the Ideal Home Exhibition. 3.10, Spelling Bees that we have had, especially Starlight-Irene Prador. 3.20, British Movie- the one in which the men were so soundly tonews. 3.30-4.15, " Ahything May whacked by the alleged gentler sex. This Happen." A Ruritanian Operetta to end all one in particular got rid of any of the Ruritanian Operettas. Cast includes Richard starchiness that is apt to characterise many Murdock, Jean Colin and Charles Wade. studio items and produced a refreshingly 9, From the Ideal Home Exhibition. 9.10, intimate atmosphere. Mr. Freddy Grise - Spontaneous Swing Music. 9.30, " All Eyes wood was ;n excellent form and struck just on Everest," talk by Michael Spender. 9.45, Cartoon film. 9.50, Starlight. 10, News. the right note, as did the members of the FOR DEPENDABILITY teams under his sway. Most readers, I ex- pect, are looking forward to the B.B.C. versus Listeners' match billed for Sunday, COSSOR MODEL May 1st. The B.B.C. mustn't, of course, 393 work Spelling Bees to death, and 'I think A New " Melody Maker " that they are wise in having an interval of a THIS is the eleventh of a series of battery sets month between these two. But the Spelling .C. which have established a reputation for Bee may beget other ideas for informal and efficiency of performance from circuits of simple ALL-BRITISH intimate programmes in which listeners design. Three pentode valves are used in a themselves can take part. I have already straight circuit which is housed with an Bin. suggested "Do You Know? " competitions, moving coil loud speaker in a neat walnut CONDENSERS and there are heaps of other possibilities cabinet measuring r7k by 14k by Join. on these lines. Mental arithmetic with a The two waveranges cover 200-560 and 826- 2,000 metres and the glass -covered tuning scale THE TELEGRAPH CONDENSER CO.LTD. very short time limit for answers might be is calibrated in wavelengths and carries 38 sta- useful. Geography is another possibility, tion names. There is provision for an extension WALES FARM RD. NORTH ACTON,W.3 and many more subjects will come into your speaker and gramophone pick-up, and the price (( 4564 head if you start thinking about them. without batteries is 5 guineas. Tr) The Wireless World, April 14th, 1938

The British abstracts published here are prepared with [h? permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Patent Office, 23, Southampton Buildings, London, W.C.2, price 11- each. Recent Inventions A selection of patents issued in U.S.A. is also included.

SELECTIVITY CONTROL Brief descriptions of the more interesting radio The combined effect of the two IT has already been proposed to aerials is a cardioid curve. But vary the selectivity of one or devices and improvements issued on patents the " minimum " point on this more of the tuned circuits of a set will be included in this section. curve is displaced by 90 deg. from by using a triode valve as a vari- the true bearing direction, so that able shunt or damping resistance. it is usual to provide an auxiliary The objection to this arrangement bination with the condenser C4 required. Alternatively, two pointer on the indicator scale set is that the damping valve is liable and the inter -electrode capacity of auxiliary windings may be ar- at 90 deg. to the main pointer. to introduce distortion, particu- the valve D, to tune to a frequency ranged at each end of the main The object of the invention is larly when it is biased down near which lies towards the lower limit winding for the same purpose. to arrange matters so that the the cut-off point. of the short waverange. A pre- Fernseh Akt. Convention date " minimum " point on the cardioid By way of remedy the triode is set condenser C3 then resonates (Germany), July 23rd, 1935. No. curve is automatically aligned valve, which with the coil L towards the upper 478666. of the dis- replaced by a pentode and o 0 0 0 with the true direction is used as a shunt either across limit of the same waverange tant transmitter so that the the tuned input or one of the in- provides stabilised feed-back. AUTOMATIC TUNING usual 90 deg. correction becomes circuits of a On the medium -wave contact 2 CONTROL This is accomplished termediate -frequency S1, the necessary. superhet set. This provides a of the two switches S, ANY initial error in tuning is by winding the search -coil of the choke Kr comes into action and automatically corrected in two more effective regulation of selec-' end of that by radio-goniometer parts tivity over a wider range of wave- resonates at the lower utilising two control voltages, both which are set at right angles to any waverange, the condenser C2 then lengths, without introducing providing. the required feed-back.. appreciable distortion. A switch reaction on is so the biasing Similarly, Ci provides provided that the long -wave setting. Owing to voltage applied to the grid of the of the conden- may be derived the different values auxiliary pentode sers, and to the fact that they are either from the AVC line for ad- other, each automatically, in shunt with each justing selectivity exercises a substantially indepen- or by manual control from a vari- each waveband. on dent control on able tapping a potentiometer. E. K. Cole and H. A. Brooke. Marconi's Wireless Telegraph Application date October 3rd, Co., Ltd. Convention date No. 078 054.0 (U.S.A.) May 3ist, 1935. No. 1936.

476486. o o 0 0 FOCUSING THE ELECTRON STREAM ALL=WAVE SETS INa cathode-ray tube, of the IT has been found difficult in which an electron re- type in practice to apply stabilised stream of large cross-section is action throughout the whole range its length by of a multi -wave set. The figure focused throughout the magnetic field from an external Circuit details of automatic tuning corrector. shows a circuit designed to over- for come this difficulty. A switch S, winding, there is a tendency which is ganged with the wave - the edges of the picture to become derived from the incoming signal, each other. One or other of these change switch, is moved to the blurred owing to the falling -off in one having a fixed phase -relation is then switched into circuit simul- upper contact r on the short-wave field -strength towards each end of to it, whilst the other varies in taneously with the sense -determin- setting, so as to bring a coil L the magnetic coil. phase according to whether, and to ing aerial. into the output circuit of the As it is not practicable to ex- what extent, the receiver circuits Panstowe Zaklady Teleradjo- radio -frequency dr intermediate - tend the length of the coil beyond are tuned above or below the cor- techniczne, Warszawie. Conven- frequency amplifier V. the neck of the tube, the windings rect signal frequency. If, for in- tion date (Poland) July loth, 1935. Simultaneously a second switch are, according to the invention, stance, a circuit carrying the sig- No. 477963. nal energy is loosely coupled to a o o o o tuned circuit of the receiver, the voltage induced in the latter will SHORT=WAVE AERIALS be in quadrature with the signal FOR transmitting television sig- voltage if both circuits are in tune, nals it is common practice to but otherwise it will vary in phase use a half -wave aerial fed at one according to the sense and degree end by a concentric feed -line. The to which the second circuit is out average impedance of such an of tune. aerial is about 2,000 ohms, whilst As shown in the Figure, the tuned that of the feed -line is of the order anode circuit A, say, of an inter- of loo ohms. It is therefore mediate -frequency amplifier V is necessary to find some way of loosely coupled with a secondary matching the two impedances in tuned circuit L, C, the inductance order to ensure an efficient trans- of which is centre -tapped and fer of energy to the aerial. coupled through condensers Cr, C2 One possible solution is to use to a resistance R. Both the in- a transformer coupling having a ductance and resistance are suitable step-up ratio. This branched across the two anodes of would, however, introduce a con- a diode rectifier D. The cathode siderable amount of selectivity, circuit of the latter is also loosely which is not desirable, since a tele- coupled at Li to the primary cir- vision aerial should be capable of cuit A. The in -phase tuning-cor- handling a very wide band of sig- rection voltage is derived across nal frequencies without discrimina- the resistance R, one end of which tion. is earthed, whilst the other goes to According to the invention, the the biasing line B. problem is solved by replacing the Murphy Radio, Ltd. and H. D. ordinary wire or rod dipole by an Ellis. Application date, June 17th, aerial having a large surface area, 1936. No. 478356. such as an open tube of metal or o o o o wire -gauze, or a group of parallel DIRECTION FINDERS Method of obtaining constant reaction over a wide band of wires arranged in the form of a radio frequencies. WHEN taking bearings on a cylinder. For a wavelength of 6.5 distant transmitter by a metres a tubular aerial having a frame aerial it is customary to diameter of approximately one foot Sr is also moved to its upper con- " stepped " in cross-section so that switch -in the pick-up from a ver- gives a reasonable impedance tact to complete the input circuit the effective number of turns is tical aerial in order to show the match. to the detector valve D. In this greater at each end of the coil correct " sense " of the bearings, E. C. Cork and J. L. Pawsey. position a choke K in the anode than in the middle, thus reinforc- and so remove the usual 18o deg. Application date July loth, 1936. circuit of D is designed., in com- ing the field strength where it is ambiguity. No. 477914. - The THE PRACTICAL RADIO JOURNAL 28e Year of Publication

No. 973. THURSDAY, APRIL 21sT, 1938. VOL. XLII. No. 16.

Proprietors : ILIFFE & SONS LTD.

Editor : EDITORIAL COMMENT HUGH S. POCOCK. Editorial, Export Wireless facturers work in water -tight compart- Advertising and Publishing Offices : ments, each following his own scheme, DORSET HOUSE, STAMFORD STREET, Necessity for Standardisation they must be well beaten by an organ- LONDON, S.E.t. ised industry such as the Americans Telephone: Waterloo 3333 (50 lines). ON several occasions in the past have arranged." Telegrams: "Ethaworld, Sedist, London." we have urged that the over- Once more we commend these views CovENTRY : Hertford Street. seas market for British re- to the British wireless industry. Telegrams: Telephone: ceivers is in such "Autocar, Coventry." 33 to Coventry. an unsatis- factory state that only drastic and some- BIRMINGHAM: what revolutionary action will suffice to Guildhall Buildings, Navigation Street, 2. set Telegrams: Telephone: it on its feet. We recommended that Television Propaganda «Autopress, Birmingham." 2g7t Midland (4 lines). British set manufacturers should get together and agree upon a standard How the B.B.G. Can MANCHESTER : 260, Deansgate, 3. Help Telegrams: _ Telephone: design for export which all manu- F, as we should "Iliffe, Manchester." Blackfriars 4412 (q lines). facturers would follow with the object assume, the B.B.C. is anxious to make television GLASGOW : 26a, Renfield Street, C.2. of avoiding competition between them- broadcasts a success Telegrams: "Ilitfe, Glasgow." Telephone: Central 4857. selves. This would result in a receiver and to stimu- late interest amongst listeners to ac- PUBLISHED WEEKLY. ENTERED AS SECOND at a competitive price, and, even more quire television CLASS MATTER AT NEW YORK, N.Y. important, by means of standardisation receivers, we think more should be done by the B.B.C. : only a minimum of spare parts would Subscription Rates in the way of propaganda. Home, Lt is. 8d. ; Canada, LI Is. 8d. ; other have to be stocked by overseas distri- In connection with countries, LI 3s. tod. per annum. butors. Servicing problems would be the recent Boat Race commentary, the announcer As many of tae c,rarcts and apparatus described in these reduced to a minimum. pages are covered by patents, readers are advised. before mentioned that those who had tele- waking use of them, to satisfy themselves that they would vision sets would not be infringing patents. have an opportunity Confirmation of Our Views of seeing the finish of the race. This is just one example of what the B.B.C. We have lately had the opportunity might do far more frequently in order CONTENTS of seeing a letter addressed from a firm to make listeners television -conscious. of export merchants in South Africa to We recognise that the B.B.C. does Page their head office in .London. This now make occasional references to letter is a strong endorsement of Editorial Comment 347 the television on the normal sound pro- views which we have held for so long. grammes, but it would take up little The Home Laboratory --I .. 348 The letter states that British radio time, and should be most effective in Are High -Slope Valves Wanted ? 352 manufacturers " have allowed the Am- results, if the television programmes Television Topics .. 354 erican manufacturers to capture this were announced daily, say, after the market, .and it is important to note first news Germany's " World that or some other appropriate Sender " 355 until the British radio manufacturers time. The Ultra -High Frequencies . 356 get together as a complete industry Such announcements could not be H.M.V. Model 653 Reviewed 358 and imitate the methods of their regarded as in the nature of adver- News .of the Week 360 American rivals, they are unlikely to do tising, since they would be general in anything important on the overseas character and would not, of course, Unbiased .. 362 markets. . . . The Americans have refer to any make of television receiver Why Maths? . . 363 standardised their components and in particular. Readers' Problems 364 circuits, thereby not only decreasing These references should, for the their production costs, but at the same present, Random Radiations .. 366 we feel, be confined to London - time making the servicing of American area programmes, to avoid tantalising Broadcast Programmes 366 radios a comparatively simple matter. those outside the service area of Recent Inventions.. .. 368 " So long as the British radio manu- Alexandra Palace with such reminders. The Wireless World, April 21st, 1938 348 The orne Laboratory

Part I- By M. G. SCROGGIE, B.Sc., A.M.I.E.E. VALVE to have a calibrated voltmeter, available as heating and power) it is the effective at all frequencies, including the ultra -high, voltage regardless of waveform. A peak, VOLTMETERS and which disturbs the circuit less than or mean, or any other sort of voltmeter can any other type, even if its volt readings be fitted with a scale of RMS values are not always relied upon. And by suit- which will be correct for sine waves, but able design it is possible to ensure that at when used to measure AC of other wave- NE very important instrument- least the larger readings are as reliable forms it will be inaccurate. Unfortunately or, perhaps, rather class of In- and permanent as those of any other sort a true RMS voltmeter must be of a type struments-that was treated ex- of voltmeter. giving a deflection proportional to the tremely sketchily in the first In essence the valve voltmeter is simply square of the voltage. It is possible with 0 " series of Home Laboratory " articles' is a valve operated at a curved portion cf a little care to get a close approximation the valve voltmeter. Although it was felt its characteristic so as to rectify the alter- to a square law by working a suitable that information in plenty about valve nating voltage and give an indication on a valve as an anode bend detector near the voltmeters was already available, the type meter, usually in the anode circuit. The foot of its characteristic, but only over a recently designed by the writer as the result detector valve in any receiver can be con - limited range of voltage. Moreover, a of about fourteen ;verted into a valve square law scale is crowded near thelnini- years' experience voltmeter for meas - mum, so does not enable good readings to with them may be AYEAR or two ago a short series uring its own cir- be taken over nearly such a wide range cuit, by the addi- of voltages as a linear (i.e., uniformly sufficiently unusual of articles appeared under the tion of a meter ; divided) scale such as that of a moving - to be interesting. In Although t h e title of " The Home Laboratory." and often this is coil DC meter. A sensitive indicating in- valve voltmeter is response to requests for more of this actually quite a strument is needed in the anode circuit. such a valuable tool, nature, and particularly for informa- sensible thing to do, Another disadvantage is that the readings because the dis- are particularly liable to be affected by and for some pur- instruments, here is poses has no serious tion about actual turbing effects of valve -operating voltages and characteris- rival, enthusiasm the first of a similar series which introducing meas- tics. Therefore, it is probably necessary must not be allowed also foreshadows the appearance of uring apparatus in- to provide means for checking these volt- one to its to the signal circuit ages. So, although a RMS valve volt- to blind a book in which the whole subject disadvantages. It are completely meter is very desirable, it lacks the virtues is less simple and of radio laboratory work-amateur avoided. of wide range, simplicity, cheapness, reli- convenient t h an and professional- will be treated Before going ability, easy use and permanence Of cali- much further it is a straightforward in detail. bration. meter, so would important to ask If the one advantage of freedom from not be used in what sort of volts waveform error is sacrificed it is possible preference to it where both are applicable. one wants to measure. A valve voltmeter to produce a much more practical type of For example, the owner of a metal recti- can be arranged to approximate to peak, apparatus. fier meter would not use a valve volt- mean, or RMS values. So long as one meter to measure or indicate the output of is measuring pure sine waves it does not For Low Readings a receiver. The metal rectifier is more greatly matter which, because the values robust, simpler, and more convenient. are related by fixed ratios and are readily The most sensitive is the unbiased grid - The fewer accessories there are, such as interchangeable (i peak volt = 1.404 leak type, and if one is interested chiefly batteries, the more reliable an instrument RMS volts= 1.57 mean volts) ; but these in voltages less than i it must be con- is likely to be. Generally the accuracy of proportions alter when the wave is dis- sidered ; but its range of measurement is a valve voltmeter, especially for readings torted or mixed with others, as illustrated very limited, and it is one of the worst for less than about one volt, depends on a in Fig. i. The RMS value is the one that input losses and variability of calibration. variety of things, such as filament, grid is generally assumed, unless the contrary Perhaps the most popular is the auto - and anode voltages, and valve charac- is stated, because for most purposes (such bias type, for it can easily be adapted to teristics. If a lot of trouble has been taken to obtain a very accurate calibra- tion it is not enough to do it once and thereafter rely on it for ever.

As a general principle, therefore, it is PEAK 1 34 preferable where possible to use such in- RMS PEAK 1.0 RMS 1.0 struments as indicators rather than meters, MEAN MEAN 0.57 J and particularly to avoid having to take readings over a wide range of voltage in one experiment. It is usually better to make the result of a measurement depend on adjusting two voltages to be equal, voltage readings. rather than on actual (a) (b) (c) The accuracy of calibration, or even cali- bration at all, is then of no importance. Nevertheless, it certainly is very useful Fig. I.-Showing how the proportions between peak, mean and RMS values of alternating current or voltage vary with the waveform. Different types of meters are therefore liable to give different 1 The Wireless World, 1936. July -17th, 24th readings unless the waveform is pure, (a). Diagram (b) shows 50 per cent. third harmonic with and 31st, and August 7th and 14th. the peaks in phase; and (c) is the extreme case of a flat-topped wave. APRIL 21st, 1938. Wille®20 Would 349 The Home Laboratory- peak volts (which for radio purposes is in adjustment has been made very quick and different ranges by switching various bias itself sometimes a very useful feature) and easy, and the other difficulties have been resistors into circuit. The auto -bias, be- it is possible to design it to be : - overcome. Chief among these difficulties ing of the nature of a negative feed-back i. Practically unaffected by supply is that the bias corresponding to " zero " voltages and valve anode current may be anything within a characteristics. volt or two, according to the sensitivity 2. At least as of the anode -current meter. What looks near infinite input like zero on one instrument might be full- impedance as any scale reading on another. The sensitivity other type. of adjustment is at its very worst where 3. Sensitive to the anode -current curve merges imper- o.1 volt input with- ceptibly into the base line. So it is out any microam- necessary to adjust to some definite anode meter or other sen- current. In actually deciding on the sitive indicator. amount one runs into a dilemma. For 4. Incapable cf one thing, if a large " zero " is adopted being damaged by the meter by which it is indicated is not careless use. sensitive to small changes, and the 5. Extended to adjustment cannot be made to close read voltages of accuracy. Again, if the " zero " is not very any magnitude. small the valve is an imperfect rectifier- 6. Available as the change in anode current due to a a currentless DC signal is the net result of a downward as voltmeter. well as an upward swing-and the bias 7. Extremely voltage needed to counteract a small sensitive for com- signal voltage is smaller still. The slide - paring voltages. back voltage is therefore not truly equal to signal peak voltage, and the beautiful Fig. 2.-Basic cir- simplicity of the idea is spoilt. Very cuits of some differ- weak signals are not measurable at all. ent types of valve voltmeter: (a) anode - With so small a " zero " as 0.5 micro - bend; (b) the same amp. the curvature is seriously noticeable with indirect input; below 0.5 volt signal, and about 0.2 volt (c) grid detection; is the smallest measurable. (d) auto -bias or re- flex, and (e) slide - back. Usually (a) Zero tends to respond to The Point the RMS value of voltage, (c) and (d) to There is another form of error that the mean value, and affects all readings, however large. It is (e) to the peak. found that the ratio of peak voltage to slide-back voltage, instead of being i, is system, tends to stabilise the indications,. The broad principle is to adjust the grid larger by an amount that increases rendering them less dependent on valve bias of a valve until the anode current is noticeably if the " zero " is greater than characteristics and supply voltages ; but, just reduced to zero in the absence of a fraction of a microamp. To see why of course, at some sacrifice of sensitivity. signal. When the signal is applied, an this is so, look at Fig. 3. The selected Both of the two last types tend to read additional grid bias is needed to reduce point on the characteristic curve is marked mean values over most of their ranges. In the current again to zero, and this bias o, giving an anode current of, say, this respect they resemble the familiar voltage is equal to metal rectifier instruments. the peak signal voltage, and is a o Basic Circuit Arrangements measure of it. ÿ Theoretically, the Fig. 2 illustrates the distinctive ANODE prin- valve characteris- CURRENT ciples of the valve voltmeters so far tics do not affect INITIAL described-(a) is the anode -bend type, BIAS the result at all, VOLTAGE preferably operated to give as nearly as ,,_SLIDE -BACK and the problem re- VO-TAGE possible RMS readings ; (b) is the same solves itself into modified for use where the the circuit to be simple one of meas- tested would alter the grid bias or cut it uring a DC voltage. GRID `'ZERO off altogether, as when VOLTAGE CURRENT there is DC or a In practice it condenser. This modification is available for any type, but increases the input losses somewhat ; (c) is the " grid " type, and Fig. 3.-Explaining II.+ SIGNAL I (d) is the auto -bias type. the working of the VOL TAPEGEAK One of the chief disadvantages of most slide -back voltmeter. valve voltmeters is that not only is a more or less sensitive (and, therefore, ex- pensive) moving -coil indicator required, does not work out so simply, and the i microamp. During the greater part of but it is very liable to be damaged by unpopularity of the slide -back voltmeter the signal cycle the current is reduced accidental excessive current, due, for is probably due first to the need for pro- actually to zero. Therefore, for the example, to the grid bias being inter- viding the slide -back voltage and adjust- meter to read i microamp., the average rupted. ing it to equal the signal, and secondly must be maintained by the peak -anode For all purposes where a square law to certain difficulties and errors resulting current being very much greater ; and for voltmeter is not essential, the writer from the deceptiveness of its apparent this the signal peak voltage must be favours the somewhat neglected species ri:nplicity. materially in excess of the slide -back known as the " slide -back ". It measures In the design to be described the initial voltage. As the proportion of the cycle 35a Wpe®20 'APRIL 21st, 1938. G`'Iopild The Home Laboratory- As the " zero " current is so small the To bring the whole instrument right up during which current flows diminishes as usual characteristics of the voltmeter to the test point might be impossible or the signal voltage increases, this excess is valve do not matter very much, and it is liable to cause more trouble than it cured, approximately a constant proportion of selected chiefly for a very high input so it is becoming usual to connect the the whole signal voltage wave. impedance at all frequencies. It is an valve as a " probe " at the end of a length Even though we may be willing to obvious advantage for low input capacity of flex carrying low -frequency currents accept this discrepancy and allow for it in and losses if the grid connection is taken only.

Some of the equipment to be described in this series is seen in this view of the author's laboratory. the calibration, the diagram shows that to a top cap on the glass rather than to While this is a great help in examining unless one is careful the voltage that can a pin on the base. This is now becoming very high-frequency circuits, what can be be measured without danger of grid cur- general practice for mains -driven pen- done to reduce the influence of the valve rent flowing is limited. Suppose the todes, but a triode is slightly preferable voltmeter is finally limited by the time initial grid bias is 2 volts and the signal because it has fewer electrodes to feed and taken by electrons to cross the space inside peak is even as little as r per cent. greater to complicate matters. There is a choice of the valve. The effect, so far as the ex- than the slide -back voltage. Then if grid several DC triodes with top grids, and ternal circuit is concerned, is equivalent current starts at r volt it is obvious that they can be used if the greatest allowable signal is roo volts. the power trans- If a suitably low " zero " is adopted former is provided it appears that a very delicate and expen- with a heater wind- sive indicator is required. Incidentally, ing of appropriate if, in the attempt to prevent any risk of voltage ; but as it is its being driven hard off the scale, the convenient to run 130 VO LTS emission of the valve is severely restricted, the heater fro m it may be found that there is not enough the same 4 -volt to allow for the relatively very high cur- winding as the rent peak shown in Fig. 3 ; and above a TV4, a Tungsram certain signal voltage the error starts to HL4g valve is increase rapidly. chosen. Alterna- tively, one could 30 VOLTS Inexpensive Cathode -Ray Indicator use an American indicator Fortunately, there is a way out of tuning these -grid triode troubles. A very sensitive, cheap, and top 6.3 ZERO -SETTING and undamageable with -volt BIAS portable substitute for heaters. a delicate microammeter is available in To minimise still the cathode-ray tuning indicators -in now further the capacity popular use. The Mullard TV4, in par- 0 -250 VO LTS thrown into a radio - ticular, is visually sensitive to a change of about o.1 volt, and if the resistance across its input is the voltmeter valve anode resistance of i megohm, this volt- Fig. 4.-Schematic diagram of the slide - age corresponds to o. r microamp. back valve voltmeter d'scussed. The grid ; to a shunt resistance which decreases in- input condenser may have a value versely as the square of the frequency. 2 To òbtain the maximum sensitivity it ofi is necessary for the control grid of the o.o1 mid. At 6o Mc/s (5 metres) it may be as low TV4 to have a small negative bias ; but as 5,000 ohms. one does not have to do anything about frequency circuit when the voltmeter For some purposes this may not dis - this because the grid current flowing is connected, the connecting leads 2 Grid Loss at Ultra -High Frequencies. The through the megohm applies a bias. should be eliminated as far as possible. Wireless World, October 23rd, 1936. APRIL 21st, 1938. Wepell@gß 352 WopIlcol The Home Laboratory- should be possible over the whole range. If a very heavy current were taken at qualify the instrument entirely ; a valve of An instrument on the lines suggested is 420 volts it would raise problems of heat ordinary construction such as the HL4g potentially able to discriminate between dissipation ; on the other hand, if the cur-

mentioned is capable of useful work at an 250 volts and 250.1, - so a jerky con- rent does not greatly exceed the maxi- even higher frequency ; but to retain trol is exasperating. For approximate mum of 5 mA. required by the DC volt- satisfactory accuracy and high input im- measurements it would be quite feasible meter, the operation of the slide -back pedance the "acorn " type of valve is to read the voltage off calibrated poten- control is liable to alter the voltages to much to be preferred. Owing to the tial divider scales without any meter at the valves beyond even the fairly con- microscopic clearances between the elec- all ; and, where greater accuracy is re- siderable limits that are tolerable with trodes it is not advisable to use an quired, to check the slide -back voltage by this type of apparatus. To stabilise the "acorn" to measure very high voltages. A means of an externally connected DC voltage an ordinary neon lamp of the peak voltage of ioo on top of an equal voltmeter, applying a correction, if neces- " beehive " type is very effective (and slide -back voltage involves a negative grid sary, for the difference between this and cheap). peak of zoo, which is probably quite the peak signal voltage towards the lower In the next instalment details will be enough. readings. The luxury of a built-in direct- given of the construction of the valve reading instrument scale is not unduly voltmeter outlined above. Input Circuits costly, however, because a specially low current movement is not required ; the one It is often necessary to adopt the alter- used in the apparatus to be described later native 'input arrangement of Fig. 2 (b). is, in fact, a 5-milliamp. instrument. NEWS FROM THE The input impedance is inevitably reduced Even such a robust and inexpensive CLUBS ' thereby, so the resistance should be high. meter is not definitely improved by apply- If very high, much care is needed to pro- ing the full 25o volts when it is switched London Transmitting Society tect ; the valve from small leakages and to the 2.5 -volt range, but the vigilance Headquarters: 40, Raeburn Road, Edgware. stray fields, and it is liable to- be tem- of the operator in this regard can be Meetings: 'Thursdays, at 8 p.m. porarily paralysed by a surge. A suit- Hon. Sec.: Mr. G. Yak, 40, Raeburn Road, Edgware. rendered unnecessary by ganging the It has been decided to accept the invitation able ,compromise is about 4 megohms. range switch and voltage control. of the Golders Green Society to co-operate with The capacity of the grid condenser Sometimes a need arises for measuring them in their 40 -metre field day on May ist. depends on the lowest working frequency. Further progress has been made with the a DC voltage without any current.3 The building of the new It is likely to be required to work at least transmitter, and the con- slide -back voltmeter is ideal for the pur- struction of a communication receiver has been as low as 56 c/ s, and probably to be cali- pose, provided, of course, that connection commenced. brated at that frequency. At 5o c/s is made direct to the grid. It is also Exeter and District there is 1 per cent. error if RC is 0.023. often very convenient to have in the Wireless Society R is 4 megohms, C would then be about Headquarters: 3, Liz's Field, Exeter. It laboratory such a variable voltage source Meetings: Mondays 'at 8 p.m. Hon. o.006 mfd. ; a choice of o.or mfd. causes as the slide -back arrangement comprises. Sac.: Mr. W. J. Ching, 9, Sivell Place, Heavitree, object of not Exeter. rather less error. The Omitting details, Fig. 4 shows the On April 4th Mr. by using, H. Ridge gave 'an interest- making sure of negligible error general arrangement of what has so far ing lantern lecture entitled ' Telegraphs, Wire say, 1 mfd. is, first, that the apparatus been described, and it can be seen that and Wireless." would be very sluggish in action, and indicator valve, - detector valve and slide Dollis Hill Radio Communication Society secondly, that it is essential for the insu- back voltages are all in series. The TV4 Headquarters: Braincroft Schools, Warren Road, Lon- lation resistance of this condenser to be is rated at 25o volts, but can be cut down don, N.W.2. exceptionally high, such as is likely to be Meetings: Alternate Tuesdays at 8 p.m. quite successfully to 130 3o volts is quite Hon. Sec.: Mr. E. Eldridge, 79, Oxgatc Gardens, Lon- N.W.2. obtained only with good quality mica ; enough for the detector valve ; and about don, and mica condensers over 0.01 mfd. are 26o is needed for the slide -back, to At the general meeting on April 5th, a new expensive. Suppose the leakage resist- committee was elected with Mr. E. Eldridge measure 250 and have something in hand. as hon. secretary. The next meeting will be ance is 4,000 megohms (exceptionally The total is 42o. Most of the rectifiers for held on April 26th. A 5 -metre section has now good for a paper condenser) and the this voltage are full -Wave affairs of high been formed and several members can be heard is used to measure a small on the air each night after 8 p.m. Reports will instrument current rating. To simplify matters be welcomed. alternating voltage superimposed on 25o somewhat the Dario SW1 half -wave valve volts DC. Then C and R, acting as a can be used, for there seems to be no Croydon Radio Society potential divider, puts a DC bias of 0.25 reason why its voltage rating of 400 should Headquarters: St. Peter's Hall, Ledbury Road, South valve, which would cause a Croydon. volt on the not be slightly exceeded. Meetings: Tuesdays at 8 p.m. large error. Hon. Pub. Sec.: \Ír. E. L. Cumbers, 14, Campdeu Road, 3 This South Croydon. come to the provision of the absurdly contradictory statement is Now we the penalty that must be endured by readers for The Technical Adviser, on April 5th, Loud slide -back voltage. So long as this con- refusing to accept the suggested " ZF " in place Speaker Night, gave a description of the sists in finding a battery and a suitable of "DC." Society's new baffle which he had invented ; it potential divider to control it the process can accommodate two to loud speakers, either of is too troublesome and unsatisfactory which can be cut out by be popular. Presumably, for conveni- a flap. ence, the rest of the instrument is to be An interesting evening mains -driven, so, obviously, the slide - was spent comparing loud-speaker outputs on back should be also. The voltage to be actual musical reproduc- provided is a matter of individual require- tion and bÿ,ß means of a ment. Many other sorts of valve volt- frequency oscillator. This to a few volts. Seeing was the last evening of meters are limited the session. The society that the slide -back type is limited in this will resume its activities direction only by what the valve will on the first Tuesday in stand, and assuming the HL4g or other October. valve of conventional construction to be used, it is quite safe and sometimes useful to go up to 25o volts peak. It is not a ARMY MOBILE difficult matter, if special occasions re- WIRELESS UNIT extend this from an external brought into use to quire it, to relay the results source. during a recent mili- It is most important that precise and tary competition in steady control of the slide -back voltage India. The Wireless World, April 21st, 1938 Are HîghSlope Valves Wanted importance it is perhaps, not unnatural OPTIMUM MUTUAL CONDUCTANCE that any other possible effect resulting from the presence of this admittedly high DEPENDS ON CIRCUIT CONSTANTS resistance has not hitherto been con- sidered. In Fig. i we show a generator e corre- By W. E. BENHAM sponding to some radio frequency voltage picked up by the coil L, a resistance rr, which represents losses in the coil and THE evolution of radio technique Now although the above facts concern- associated eddy current and dielectric has proceeded, on the whole, more ing triodes and pentodes are fully appreci- losses appertaining to the input circuit rapidly than has our ability to ated in a qualitative sense by the majority excluding valve, a capacity Co in parallel explain mathematically, or on oc- of radio experimenters, considerable with (e, L, ri) and a resistance Ro. The casion even qualitatively, the many and mystery as to the exact mechanism at capacity Co includes the capacity between complex phenomena which characterise the work still exists. For example, it is grid and cathode + screen (N.B. screen is art. The thermionic valve itself possesses popularly supposed that the phenomenon connected to cathode via a large condenser, circuit properties no less involved than of electron damping is important at very as shown). The resistance Ro includes the those of the associated circuits. When high frequencies loss due to electron in addition it is realised that these circuit only. It is, how- damping and that are of importance both to the ever, important at , properties THE author suggests that early due to 'dielectric internal functioning of the valve and to even the lowest and other losses'in- the design of the external circuit, it will radio frequencies- misconceptions of valve action side the valve. To hardly seem surprising that it is usually not in its damping have not yet been entirely dispelled summarise, the gen- easier to design circuits round valves than effect on the input erator e, inductance valves round circuits. signal, but in an- and goes on to explain how the L and resistance rt It is true, of course, that in many cases other connection optimum valve slope for any par- are external to the are designed to meet circuit require- altogether. valve, Co is valves ticular circuit depends intimately partly ments, and successfully so. But it must In order to under- external and partly not be forgotten in this èonnection that the stand where pre- on the constants of that circuit internal, R,, is en- circuit engineer, in attempting to design a vious theories went tirely internal to circuit round a given valve, and finding astray it is neces- the valve. In order the valve has certain limitations, may say sary to recall the out-of-date but still very to make this as clear as possible the to the valve manufacturer, " Can't you do prevalent remark to the effect that the electrodes of the valve are shown in thin this or that?" and so help the valve manu- valve consumes no power from the input line. The by-pass condenser between facturer to achieve optimum design. This circuit and thus acts as an amplifier of screen and cathode is also shown in thin line. is more particularly true in the case of a voltage, and not of power. This notion Let us now divide the current i from the valve which serves a double function, was first dispelled by the discovery that, generator into two parts : a current io such as a triode-hexode. at medium and high frequencies, the effect passing through Ro and a current (i - ia) As is well known, the limitations of of the anode cirçuit impedance made passing through Co. Then if vo denote triodes as amplifiers at radio frequencies itself apparent across the input terminals the voltage across Ro we have three are due, first, to of the valve to an expressions for ve corresponding to the Miller effect, which extent depending on three parallel branches. Now if in the causes a large cap- the grid/anode cap- circuit of Fig. i the resistance Ro and the acity to be thrown acity and the degree capacity Co were independent of the across the grid/ of amplification frequency, it is easy to see that the voltage cathode terminals of taking place. The across Ro would become less and less as the valve, and introduction of the Ro is reduced from infinity downwards, secondly to the fact screen grid removed whether the circuit be tuned to resonance that the effective the great majority or not. resistance across of such feedback, In reality, however, the resistance Ro is these terminals may and the old notion dependent on the frequency and also on be negative, de- was revived. In the mutual conductance g,,, of the valve, pending on the other words, the while Co includes the capacity CC9 between anode impedance Fig. z.-Equivalent valve input circuit. screen grid and pen- cathode and grid of the valve, which in and on the fre- tode valves were turn changes if we make changes in the quency. In a formula which will be given supposed to consume no power from the mutual conductance of the valve. later the optimum slope of a triode under input circuit. With the appearance of certain conditions is found to be consider- papers on transit time theory a modifica- Interdependence ably below. that which can be obtained in tion in this view took place, but only for practice. The same formula when applied high -frequency applications was it con- We thus see that, in studying the effect to a tetrode or pentode gives an optimum sidered necessary to include across the of changing Ro we are studying also the slope which in a typical case is twice that grid/cathode terminals a resistance, the effect of varying Co and g,,,, and it will be of the triode. These conclusions are of value of which varied inversely as the appreciated that the theory becomes the kind that we also firyi experimentally, product of the square of the frequency and complicated. and it may therefore be said that the use the mutual conductance. The value of A solution has, however, been obtained for high -slope triodes would seem to be this " electron loading loss " resistance in the case where changes in g. are severely limited and that the question of works out so high at medium -wave made by simultaneous changes in grid/ our title can be answered in the affirmative frequencies that its damping effect on cathode spacing and grid pitch in such a only in the case of valves in wh'.-h the the input circuit is quite negligible, and way as to keep the anode current constant. control grid is well screened from the anode. as this point is of major practical In other words, we will suppose that we APRIL erst, 1938. Mp@hog WopIlcl 353 Are High -Slope Valves Wanted P- Co circuit. It we were smallest value of which could arise in seeking the transfer have commissioned a valve maker to of maximum power rather than maximum supply a range of valves of different mutual 1 practice would be about 3 voltage across the resistance R,, the conductances, but all having the same with no tuning condenser and 4 with a tuning condenser matching would have to be perfect, that anode current, and that the changes in is to say the dynamic resistance set at minimum. Taking Co = 5C, as of the mutual conductance from valve to valve tuned circuit must be equal to R°. We were effected by means of changes in grid/ typical, g, = (mA/V), i.e., just double are, however, more interested ih maximum cathode spacing and grid pitch only, the voltage since we can measure this more position of the figure obtained for screen and/or anode remaining triodes. readily. - unchanged. One result which emerges from the In conclusion, we may say that analysis We now plug these valves in one after theory is that for low -loss coils, particu- shows that the optimum valve slope, or the other, and tune the circuit to resonance larly small -size low -loss coils, the optimum mutual conductance, for use with any each time, observing with a valve volt- g,, is higher than for .high-loss coils. The particular circuit depends intimately on meter the voltage developed across the physical significance of this result is, the constants of the circuit. The theory grid/cathode terminals of the valve as a roughly speaking, as follows. The ap- is too complex to enable general rules to result of a constant injected RF voltage parent resistance of the valve must to be laid down, but I have tried to give at e in Fig. i. Theory shows that the some extent " match " that of the input some indication of the main results. valve which possesses the slope given by C 3 1 1,000 MA/V...... (1) g,0 = 20C° Tr,X will have maximum voltage developed Paris across its input. The value of gm thus Television Transmitter determined will be referred to as the SOME TECHNICAL DETAILS at i Mc/s, 6.6 db at 3 Mc/s, and 12.6 db optimum mutual conductance. It is only at 8 Mc /s. intended to apply on the basis of a given E new television transmitter at the Due to the fact that amplifiers covering anode current consumption, as explained Eiffel Tower, which was, inaugurated wide bands beginning at very low frequen- above, moreover by the Minister of French P.T.T. on cies are difficult to manufacture with satis- special valves with April 8th, is auxiliary (secondary soon to be one of the most, if factory characteristics, the o to 2,5oo,000 emission) cathodes not the most, powerful television stations c/s vision are excluded from this argument. These signal is impressed on a high - in the world. The transmitter, which has frequency carrier for transmission over the have much less damping (i.e., higher R°) been regularly operating since September, cable. For transmission of the image band for a given gm, as the current taken from 1937, with reduced power, has recently been a carrier frequency of 5.5 Mc /s is employed, the cathode can be much lower, the anode transmitting with a power of 15 kW, and this giving a total transmitted band of current being made up largely of secondary will shortly be broadcasting with its peak 3 Mc/s to 8 Mc/s. electrons. It may, indeed, be that the output of 30 kW. The transmitter is designed to operate on The aerial is secondary emission valve will eventually supported by the Eiffel a frequency between 40 and 5o Mc is (at the displace ordinary valves, Tower, .and is fed by a cable having a total moment 46 Mc/s is being used), and has a but at the length of 38o metres. present time the cost Two new studios peak continuous power output of 3o kW. of manufacture is with the most up-to-date equipment are The the limiting factor. An illuminating frequency is maintained constant within situated at distances oT 5 and 2.5 kilometres narrow limits by a quartz crystal oscillator, article by two members of the Philips from the transmitter, to which they are con- which is followed Research by two doubler stages Laboratory appears in the March nected by co -axial cables. These have a which raise the frequency to the final carrier issue of The Wireless Engineer, in which characteristic impedance of 71 ohms and a value. These doublers are followed by a a mutual conductance of 9 mA/V is maximum attenuation of 4.8 db per mile single valve amplifier, two air-cooled push- quoted as a practical possibility. pull amplifiers, and three water-cooled push- We will now seek the optimum mutual pull amplifiers, the output of the final stage conductance of triodes and tetrodes on the being coupled through the 56 -ohm transmis- basis of our formula (i). sion line to the aerial. Due (a) Triode. Here Co will include to difficulties which are normally con- present siderable grid/anode capacity due to in DC direct -coupled amplifiers, fre- quencies of o to 5 c/s are Miller effect. Taking Co roC,, we impressed on a = have carrier of 3 Mc /s. This modulated carrier gm= 5 (mA/V). The resistance r, may is then amplified in five push-pull air- r,, cooled stages to a level of 2 kW, which is vary between, say, r ohm for a very rectified in a symmetrical diode circuit. The small low -loss coil to several hundred ohms load resistance of the rectifier is connected for a pancake coil. Highest value of gm through a low-pass filter in series with the grids of is seen to be 15 mA/V, lowest considerably the last RF amplifier. The recti- fied carrier voltage below r mA/V. It should here be men- supplies the fixed grid bias for the RF amplifier, and the modu- tioned that the optimum value of gm as lation frequencies modulate the RF ampli- defined in this article is definitely pessi- fier grids. The modulation amplifier em- mistic, since the anode current change due ploys a large reverse feed-back, which keeps to a signal v° is a maximum, not when v0 the linear distortion at a low level. is a maximum but when (gmvo) is a The modulating amplifier for frequencies maximum. Theory gives, however, no from 25 to 2,500,000 c/s receives an input maximum for (gmvo) i.e., as gm is increased of 3 volts peak in 70 ohms from the co- (whether at constant anode current or axial cable terminating equipment, and am- plifies no) gmvo increases indefinitely, it to a peak value of about 2,5oo volts until, that for modulation of is, the valve has become incapable the grid of the final radio - of frequency amplifier. The amplifier consists handling the voltage a°, as it will do if of four air-cooled stages followed by two we go on closing up the grid winding in water-cooled stages, and a modified form of order to keep the anode current constant. resistance-capacity coupling is used through- For this reason we have chosen to define out. Due to the extreme limits of the band our optimum gm in the way we have. to be transmitted with small amplitude and (b) For a tetrode or pentode, the grid/ phase distortion, care is taken to keep the screen capacity can be at least as small The entrance to the new Paris television capacity to earth of the active elements at as the grid/cathode capacity. Allowing station designed and installed by Le Matériel a minimum. In spite of this, it is essential Téléphonique, French licensee of the Inter- to operate the valves into a load circuit of for strays equal to C, itself (which, it will national Standard Electric low remembered, Corporation of impedance in order to minimise the loss be excludes strays), the New York. at the higher end of the amplified band. The Wireless World, April 21st, i938

Topics HARD -VALVE Televísion TIME -BASES AST week the action of the gas -triode Under these conditions Vi has a low re- was dealt with and it was said sistance and C is rapidly discharged ate valves can, of course, be used. VI is that it is possible to simulate the through it and the resistance RI. The operated as an amplifier and for the best I Vi then returns to- results its anode circuit must be decoupled action of such a valve by one or cathode potential of more evacuated types, such as those wards the potential of the HT line and to the cathode by C2 as shown. Both generally used in receivers. Such circuits the current falls. This results in a valves have the same negative bias pro- are of considerable importance in tele- positive pulse being applied through CI duced by the anode current of VI flowing vision, and one is R2 to the grid of through R3. shown in Fig. i V2 and this pulse When C is uncharged there is no anode which is also of par- renders V2 con- voltage on V2 and this valve passes no ticular value for ductive again with current. The condenser charges through oscillography when the result that the R and the anode voltage of V2 rises. When a time -base is re- grid of Vi is driven it reaches a certain figure, which, depends quired to operate at negative and this on the valve characteristics and the grid a higher frequency valve is made non- bias applied from R3, anode current flows than is possible with conductive in readi- and increases the total current through R3 a gas -triode. ness for the next and hence the voltage drop across it. This This circuit has cycle. means that the grid potential of Vr be- been described in The action is ex- comes more negative and its anode detail by Puckle' ceedingly rapid and potential more positive. This change is and two hard gives a quick fly- communicated to the grid of V2 by means valves are used to back, and when of Ci and R2 and drives the grid positive act as a gas -triode ; properly designed making V2 of low resistance and accelerat- the condenser C the circuit will ing the discharge of C. R Fig. r.-A hard -valve time -base which operate at very When the discharge is nearly complete and resistance functions extremely well is shown here; form the charging VI is the discharge valve. high frequencies. the current falls off and the grid potential circuit. In many Its main disad- of Vi returns to its normal value and the applications, of course, R is replaced by vantage is that it needs two valves instead change of anode current provides a nega- an RF pentode so that linear charging can of one, but this is not as great as it seems tive pulse on V2 which cuts off the anode be accomplished to voltages approaching since hard valves are cheaper than gas - current and allows C to charge, up again. that of the HT supply. This is not essen- triodes. A minor disadvantage is the In the writer's experience this circuit tial to the operation of the circuit, how- necessity for the cathode of Vi being at a does not function well for very small ever, and a resistance can be used with potential considerably above earth and at amplitudes of saw -tooth voltage across reasonably linearity if the saw -tooth a fluctuating potential. In general, a the condenser but works well for ampli- amplitude is kept to about 7 per cent. of separate heater winding must be provided tudes of some 40 volts p -p or more. It is the HT voltage, as with other time -bases. for this valve, and if high frequency opera- not very suitable for low voltage HT sup- Starting with no charge on C, it is easy tion is desired this winding must have a plies, therefore, but should be used with at to see that Vi has zero anode volts. The low capacity to earth and the heater least 70o volts HT when a linear sweep is grid potential of V2 is substantially zero wiring must be screened to prevent radia- 'needed. and this valve passes anode current con- tion. Capacity between the cathode and sequently there is a voltage drop along R3 earth is effectively in parallel with C and and the anode is considerably negative consequently limits the maximum operat- with respect to positive HT. The grid of ing frequency. Technical Instruction V= is joined to the anode of V2 and is Another circuit which is similar in its consequently also negative with respect to general operation is shown in Fig. 2. The have recently examined the prospec- its cathode. Vi is consequently non- writer has used this with an American WE tus of a correspondence course issued conductive. The condenser C then double -triode of the 6A6 type, but separ- by The British Radio Engineering College. charges through R and its lower plate and The course is primarily planned for students with it the cathode of VI movës negative proposing to enter the servicing and main- with respect to positive HT. tenance branches of the industry. Those responsible for its preparation have aimed at producing something to bridge the gala The Discharge Valve that exists between popular expositions of radio principles and advanced technical Eventually the cathode potential of VI books of a mathematical nature. approaches the grid potential. Anode It has been urged that the training of current then --lows in Vi and through RI, the majority of those employed in the vari- causing the anode to become more nega- ous technical branches of the industry tive than positive HT. This change of tends too much towards the superficial or anode potential is communicated to the practical " aspect, and that few have grid of V2 as a pulse through the coupling mastered the fundamentals. There can be CI R2. This reduces the anode current of no doubt that such reproaches have some with foundation, and it is good to read that the V2 and its anode potential rises and B. R. E.C. course, though non -mathemati- it the grid potential of VI. This in turn cal, pays due attention to basic principles, increases the current through Vi, and V2 and the earlier lessons aim at imparting a is rapidly driven to anode current cut-off proper foundation on which knowledge of and the grid of Vi to a highly positive practical applications can best be based. can be obtained potential. Fig. z.-Another two -valve arrangement, Copies of the prospectus for which a double -triode can be used, is from the College at 179, Clapham Road, London, S.W.9. 1 Journal of the Television Society, June, 1936. given in this diagram. The Wireless World, April 21st, 1938 355 Germany's World -Sender By Our Berlin Correspondent

This listener uses a seven -valve all -wave AC set and would like a pen -friend. Winnipeg, Canada, listens -in to DJE and DJQ, and also gets DJA and DJC from 5.3o-10.45 p.m. E.S.T. Perhaps the most amusing report comes from a dingo trapper in Central Australia, 280 miles from anywhere. He only sees other white men when he goes once a year CELEBRATES ITS to sell his goods (scalps, he calls them). ZEESEN FIFTH BIRTHDAY Why should such a man take the trouble to write to Zeesen? The answer is a simple HAT the Deutschlandsender is was recently given an opportunity to go one : he passed a happy time on the Rhine to listeners in Germany, the through some of these and have received just after the war ; and the old link has German short-wave station is permission to reproduce some of the been revived by the short-wave station. to Germans overseas. Official remarks. statistics claim that there are about 18 A listener from British Guiana reports Technical Troubles millions of them, to say nothing of those good reception of DJQ and DJB between scattered in various parts of Europe, out- 6 a.m. and 7.30 a.m. E.S.T. He says From Mossel Bay, in South Africa, side the a borders of the recently extended that reception is even better when it is cold listener sends personal greetings to Fatherland. Both one of stations attained their but also remarks that ninety is the usual the announcers. A shift -worker in Belolo, fifth anniversaries last month. temperature in the shade. New Guinea, has a no -volt supply and is It is the aim of the German short-wave Another correspondent in Sandakan, worried about his set. From Ottawa station to uphold and the strengthen the Ger- North Borneo, is delighted with Zeesen user of a Victor 5 -tube 1934 model reports man feelings of those living abroad and midday concerts, which come rolling in on good reception of DJB. to keep them informed of events in the DJB and DJE and also on DJR. Suva, The time seems past when home country. purely tech- Germany also decided to Fiji, reports " Berlin comes in regularly." nical information was given by listeners. extend the programmes to foreign listeners Somebody in Post Moresby, British New Even the careful questionnaire and therefore introduced which the foreign lan- Guinea, reports R9 reception on 19 and short-wave station sends out to technical guages. The main purpose of these pro- 16 metres ; " reception second to none." listeners is very often grammes returned without is to keep the world at large in- He specially enjoys the Hamburg early details as to aerial used, etc. formed as to events in Germany and the morning harbour concert. One very amusing letter from a German point of view, DJA, German and also to attract DJN and DIQ, notably the latter, wireless officer on board ,a tramp asks visitors and aid the tourist are very if trade. loud in Akaroa, New Zealand. he has to pay a licence fee for listening to Projecting German Ideas It has been said of the Zeesen station that it broadcasts propaganda. This is correct. It boosts Germany and German ideas and German reactions, but it does not interfere directly with affairs of other countries and only hits back when struck. For instance, on the day of the Jewish boycott in Berlin, on April Ist, 1933, the day of the short-wave station's first regu- lar programme to America, a well-known German radio writer (Hans W. Priwin) spoke to the U.S.A. as a representative of German Jewry from the Zeesen station. This broadcast was intended to counteract the effects of various statements in the foreign Press. The short space at my disposal does not permit of describing all the varied activi- ties of the station. Listener service is an important factor, and already 65,000 over- seas listeners get a free programme booklet from Zeesen every month and thousands of overseas papers reproduce the pro- grammes and photos illustrating them. In 1933 only 3,000 letters were received. In the Berlin studio generally This number reached 5o,000 in 1937. used for broadcasts to North America. Through the sound - I roof window facing the announcer is the control room. Wpgi32g 'APRIL erst, 1938. 356 Would Germany's " World -Sender "- (The ionisation density and consequent the Zeesen transmissions, even though he The Wireless Industry upper frequency limit of the layers varies only touches Germany every year or so. range of Cossor HT batteries and considerably from day to day and also He also wants to know whether he ought ANEWL.T. accumulators is announced. Prices ivith the time of year. Whereas the E to ask the captain about it and get special of 12o -volt batteries vary from Gs. to 15s. 6d. layer shows maximum ionisation in mid- permission. One doesn't know if he is 0 0 ó summer and minimum in mid -winter, the pulling our legs or if he seriously thinks The directors of W. T. Henley's Telegraph F layer ionisation is at its greatest at the that he ought to pay a contribution to Works Co., Ltd., have decided to recommend, end of February and again in late Octo- He reports subject to audit, a final dividend on the ber, dropping very much in mid -summer Zeesen for the programmes. income tax, of ordinary stock of ro per cent., less and to a less extent in mid -winter. On reception of DJB, P and L in regions making, with the interim dividend of 5 per the Pacific where neither the U.S.A. nor cent. paid on October Ist, 1937, 15 per cent. some summer days the E layer bends the East Asia beam from Zeesen are for the year ended December 31st, 1937. They signals of all usual frequencies. Under also recommend a cash bonus of ,5 per cent., such conditions long-distance signals are audible. less income tax, for the year. Other listeners are delighted with poorly received, since they are returned Zeesen's " ever ready to please " system, n P to earth at short distances before reach- ing the F layer. It would at first appear and only the other day an American Since our review of the Ambassador Model family coming over to Berlin seized the 6778 AC went to press, we have been informed that due to the increased solar radiation opportunity of addressing their friends in by the makers that the price of the console in summer the F layer ionisation would the U.S.A. by short wave from Europe. model has been increased to 15 guineas. increase from mid -winter to mid -summer. The station has a daily " Greetings to To some extent it does this from Decem- but then, instead of con- Listeners " feature in each programme The series of Tempovox Radio Receivers, ber to.February, zone, and Aunt Maria's long-Iost daughter which include a built-in clock, has been ex- tinuing to increase, begins to drop off. to the mike to send greetings, and tended by the addition of two new models de- This is the result of some other counter- comes from British sometimes one hears the tearful voice of a scribed in leaflets available acting effect of the sun on the outer layer Tempovox, Ltd., Tempovox Works, Holly which is not yet fully explained. fond mother wishing her only son a happy Road, Hampton Hill, Middlesex. One of the birthday away across the water. sets is an upright " grandmother " model. In order to obtain more information as to the highest frequency on which long- distance contacts were possible, during 1937 the writer daily observed the highest receivable frequency. The results were plotted, and are shown in the accompany- The Ultra High ing graph. Since the ionisation density is proportional to the frequency of the refracted signals a record of this is also A REVIEW OF obtained from the graph. At first only signals from over 1,20o CONDITIONS IN 1937 Frequencies miles were recorded, but from May Ist the signals were divided into,tw groups, By D. W. HEIGHTMAN first, those from distances of over 1,200 miles, which are bent in the F layer and riEFORE describing some of the shown by a dotted line ; secondly, those observations carried out at the from distances of up to 800 miles, bent writer's station, G6DH, Clacton, ARECORD of daily observations in the E layer and shown by the con- Essex, it may be as well to briefly throughout the past year on the tinuous line. The graph shows very summarise accepted theories of the pro- highest receivable signal frequency clearly the F layer peaks of February - pagation of high -frequency signals over (and hence a measure of the prevail- March and October-November, when long distances. ing ionisation density of the E and F long-distance conditions were best. It is Under the influence of solar radiation layers of the upper atmosphere) is interesting to note that 56-Mc /s transmis- sions from G6DH were heard in U.S.A. the outer rarefied air of the earth's atmos- given in the graph which accompanies is, mole- during both these periods, also American phere becomes ionised, that the this article. cules are split into ions or charged ultra -high -frequency stations were well re- particles. The ions in the atmosphere, ceived here, W2XHG on 41 Mc,'s being in general, increase in number at the particularly good on several days. higher altitudes, where the air is so rarified down in the layer and then reversed in With the approach of the summer that relatively few collisions of ions take direction without reaching that height, months it will be seen that the F layer place to re-form molecules. Such an but for convenience the layer is con- limit dropped to a minimum while the E atmosphere of ions has the property of sidered as a mirror with a reflecting sur- layer reached its peak ionisation. On bending radio waves. When a signal is face situated at the " virtual height." several days at that time of the year the transmitted vertically upwards, an echo is Although the presence of many layers intense E layer ionisation was sufficient to received a fraction of a second after- has been detected, the two which affect refract signals of at least 5o Mc/s, and wards, making it possible to calculate the the transmission of radio waves to the had there been amateur activity on the distance it has travelled, assuming the greatest extent are known as the E and F 56 Mc / s band at suitable distances, no speed. As the frequency of the trans- layers. The E layer is situated at an doubt many contacts would have resulted. mitted signal is increased, say, from one average height of 15o km. and the F at This fact is borne out by the good results megacycle upward, the distance travelled least twice that height. Obviously, obtained by American amateurs last sum- (i.e., the height) also increases somewhat therefore, a signal bent by the F layer mer, when many long-distance contacts up to a certain limit, when suddenly the covers a much greater distance. During took place over ranges of between 500 and height from which the signal is returned daylight and particularly during the 1,000 miles. Such contacts are generally is found to be greatly increased, giving summer the F layer splits into two separ- fairly localised geographically, and as the rise to the statement that the ionosphere is ate layers, the outer one being termed the signals are bent in the E layer the distances formed in separate layers. F2 layer. Usually the E layer, having covered are not much more than i,000 It should not be overlooked that a less ionisation density, reflects signals of miles. On July 18th signals were heard layer .may be 200 km. deep. The virtual fairly low frequency and allows signals of up to 61 Mc/s, the highest frequency re- height of a layer is the height measured higher frequency to pass through it, only ceived during the year. by the method previously mentioned. to be bent back to earth in the outer F It should not be overlooked that the graphs show the upper frequency limit on The . wave, of course, is probably slowed layer. APRIL 21st, 1938. 1 pehoo opIl 3.57

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Daily upper frequency limits of reception for 1937. The dotted line relates to reception at distances the F layer, while the full line refers to short of over 1,200 miles of signals bent by -distance reception of signals affected by the E layer. Periods during which no observations were made are indicated by question marks. any particular day and for all directions. The shower of particles is apparently bent by the arrival of charged particles on the The practical working limits would, of by the earth's magnetic field and arrives aerial. course, be somewhat less than the values chiefly at the Polar regions, consequently It is interesting to note that shown. On days when fade-outs occur the observations the circuits most affected are those north this year so far' indicate a considerable F layer limit may be high for, say, signals of east or west, such as, for instance, to drop in the upper frequency limit ; from easterly directions, yet low for west- appar- U.S.A. or Canada. At such times the ently, therefore, the winter period of 19361 erly directions. During abnormal activity writer has often observed the reception of - 37 was the peak one for the ultra -high fre- there is an emission of particles from the a peculiar radiation, mostly on frequencies quencies. sun which has the effect of neutralising the over zo Mc/s, which on a receiver takes outer F layer ionisation so that the upper the form of a smooth though loud " hiss- ' This was written at the beginning of frequency limit falls much below normal. ing " sound. This is presumably caused March.-ED. The Wireless World, April 21st, 1938 ' 358

H.m.v. MODEL 653 God Quality of Reproduction from an Inexpensive Table Model

secondary windings of the mains trans- FEATURES. Waveranges-(1) former. This refinement, togethèr with 13.5-50 metres. (2) 195-580 metres. the precautions which have been taken (3) 1,000-2,000 metres. Circuit- to screen completely the radio frequency Heptode frequency changer-tetrode tuned circuits as a separate unit, accounts noise IF amplifier double - diode - triode for the low level of background - of second detector-tetrode output valve. which is a characteristic the per- Full -wave valve rectifier. Controls - formance. (1) Tuning. (2) Volume and on -off This is a comfortable set from the oper- switch. (3) Waverange. (4) Tone. ator's point of view. Tuning, volume, light smooth, Price 10,1 guineas. Makers The and tone controls are and - - is positive, the Gramophone Co., Ltd., 98-108, Clerkenwell the waverangé switch and PRODUCED specifically to meet the Road, London, E.C.1. control knob has a well -shaped finger grip demand for an AC all -wave receiver L giving ample leverage. Above all, the dial at a somewhat lower price than the can be read at a glance from any position. cheapest of the Olympia show It is remarkable what an improvement models, the Model 653 is, nevertheless, a stations. Iron -cored transformers are used the few degrees of projection makes over characteristic H.M.V. product and one in the band-pass filters associated with the the conventional vertical end recessed which will ably represent the firm's work IF stage, which n* kes use of an RF dial. in the markets for which it is intended. tetrode valve. A doúble-diode-triode There are three wavebands, and it is second detector is arranged as usual for Tuning Control worthy of note that there is no curtail- AVC rectification and first -stage AF am- ment of the short-wave range, which goes plification. A pick-up may be connected The desirability of giving the short-wave down to approximately 13 metres. The in the grid circuit of the triode, and the range the longest possible scale has bc2n superheterodyne circuit comprises four volume control operates on both radio and appreciated, and, as a result, the recognised valves, the first of which, a heptode fre- gramophone. When the pick-up plug is broadcast bands, which are each marked quency changer, is preceded by a single inserted a capacity is _aeltomatically con- with arbitrary graduations; are not too tuned aerial circuit on all three wave- nected across the grid circuit of the 1F cramped. A subsidiary vernier scale con- bands. The coupling is inductive, , and amplifier to suppress radio interference. centric with the main tuning pointer iron -cored coils are used on medium and The output valve, which is a beam rotates nine times for, a full traverse of long waves. On short waves the coupling tetrode, is resistance -coupled to the pre- the dial, and not only provides a means to the aerial is capacitative. ceding stage. The power supply circuits of accurately logging stations, but is a Part of the aerial primary circuit is used follow conventional practice, and it is in- valuable visual aid to final adjustments. on long waves as a low-pass filter to pre- teresting to note in a receiver of this price The single -ratio reduction gear is natur- vent break -through of interference from, that an electrostatic screen has been in- ally a compromise between the require- and whistles generated by, medium -wave corporated between the primary and ments of the three wavebands, but the

Complete circuit diagram. Tetrode valves are used in the IF and output stages and the tone control is arranged to give some measure of negative feed back. APRIL 21st, 1938. We@Il@go WopIlA 359 bias is, if anything, towards short waves, takes in the tympani and double basses and it is not unduly critical on this range. of the orchestra without investing speech Television - Programmes The signal-to-noise ratio is very good with hollowness unless the volume is indeed, An hour's special film transmission in- and microphony has been kept turned up to an unnatural level. Occa- tended well for the Industry only, will be given under control so that the receiver can - sionally there is evidence of excessive top, from 11 a.m. to 12 noon, each weekday. be worked always at maximum efficiency. but as fully three-quarters of the tone con- Vision Magnification is uniformly high from trol is Sound 45 used up before the top cut is at all 45 Mc/s. 41.5 Mc/s down to the bottom end of the scale, and drastic, the balance can in all circum- tails off only slightly towards 5o metres. stances be adjusted with nicety. THURSDAY, APRIL 21st. 3, Relay from the On medium waves the sensitivity is ex- The reproduction from this set will Television Studio at the ceptionally well maintained at Ideal Home Exhibition. 3.10, Starlight. 3.20, the extreme prove a thorn in the side of those who hold Gaumont -British News. 3.30, 139th edition ends of the range, and a crisp and clear- that a large -diameter speaker is necessary of Picture Page. cut performance is obtained alike on local for good quality. The effective diameter 9, From the, Ideal Home Exhibition. 9.10, and distant stations. Fécamp on its new of the cone is little more than 5 inches, Starlight. 9.20, British Movietonews. 9.30, i4oth edition of Picture Page. 10, News Bulletin. FRIDAY, APRIL 22nd. 3, " The Gay Lord Quex," play by Arthur W. Pinero. Cast includes Arthur Wontner and D. A. Clarke -Smith. 3.50, British Movieto- news. 4, Preview. 9, Eve Becke. 9.10, Zeebrugge. Vice -Admiral Carpenter gives an account of the Zeebrugge OUTPUT Landing. 9.20, Gaumont -British News. 9.30, 2nd VALVE " Anything May Happen "-a Ruritanian DETECTOR K T 6 3 Operetta to end Ruritanian Operettas, words VALVE and music by MacDougall and MacKinnon. DH63 Cast includes Jean Colin and Richard Murdoch. 10.5, Cartoon Film. 10.10, Preview. 10.20, IF RECTIFIER News Bulletin. IÌ IIÌI131 -AMPLIFIER im VALVE

HH upmm SATURDAY, APRIL 23rd. VALVE IIIIIIIIIII, °ll° ni U 5 0 KTW63 ;. IIII IIIINIIIIIIIflÌi lll 3, Judo, the art of self-defence. 3.15, Cartoon Film. 3.20, In Our Garden, C. H. Middleton. 1-=x..`it:: 3.30, " Oroastus," a Greek tragedy by S. FREQUENCY MAINS Leacock and " Hamlet the Worker," by Wilfrii Walter. CHANGER VOLTAGE VALVE ADJUSTMENT 9, Cabaret, including Ken Harvey, banjoist, and X63 Scott Sanders, comedian. 9.25, Zeebrugge, -a reconstruction in miniature on the Alexandra Palace lake of the night attack on Zeebrugge. 9.45, British Movietonews. 9.55, Betty Humby, pianoforte. 10.5, News Bulletin. SUNDAY, APRIL 24th. AERIAL 8.50, News Bulletin. 9.5; Repetition of Satur- day's 9.25 programme. 9.30, " Acis and Galatea," an operetta EARTH (Wireless°'° World by G. F. Handel. COPYRIGHT PICK-UP SOCKETS MONDAY, APRIL 25th. - 3, David Seth -Smith presents Friends from the Zoo. 3.15, Gaumont ,British News. 3.25, " The Shadowy Waters," a play by W. B. The perforated back panel is fitted with leather hinges and folds over on top of the Yeats. cabinet. Note the size of field magnet in relation to the loud speaker cone diameter. 9, Friends from the Zoo. 9.15, British Movieto- news. 9.25, The Vic -Wells Ballet in " The Wedding low wavelength requires the volume con- -but it Bouquet." Music by Lord Berners, was observed that the periphery of words by Gertrude Stein. 10, News Bulletin. trol to prevent overloading. The selec- the seamless paper cone was thinned con- tivity, too, is clean and gives a decisive siderably to reduce the restoring force and TUESDAY, APRIL 26th. cut-off outside one channel on either side lower 3, Catch -as -Catch -Can Wrestling. 3.20, the natural period. Doubtless the British of London Regional at 15 miles. acoustic Movietonews. 3.30, " Marshal your properties of the cabinet have Facts," with Edward Cooper, Wendy Toye and The long -wave selectivity does not quite been taken into account in deciding on the Charles Heslop. fulfil the expectation raised by the shape of the response curve, but, what- 9, Starlight. 9.10, " The Smell of the Library,' medium -wave performance, and the éver the means, the result gives no clue from the story by Michael Arlen. 9.40, Cartoon Deutschlandsender carries a background to the size of the moving-coil Film. 9.45, Talk on the Budget, by Sir Josiah unit. Stamp. 10, News Bulletin. of sideband interference from both Droit - The sub -baffle upon which the loud wich and Radio Paris. There is no fault speaker is mounted is inclined, and the WEDNESDAY, APRIL 27th. to find, however, with the sensitivity on front is protected by a woven metal grille. 3, Light Entertainment. 3.15, Gaumont - this range, and the only self -generated There are ho external loud speaker British News. 3.25, As on Monday at 9.25 p.m. whistle in the set, which appears just sockets, but soldered connection 9, Starlight. 9.10, British Movietonews. 9.20, may be " There's below 1,400 metres, is merely incipient made to the speech coil tags for an exten- Always Juliet," a comedy by John would pass unnoticed van Druten. Cast includes Leonora Corbett and nine times out sion speaker if desired. The impedance and Michael Shepley. 10.15, News Bulletin. of ten. should be of the order of 3.5 or 4 ohms. The chassis is of cadmium -plated steel An Efficient Speaker and is cross -braced at the ends to give Books Received rigidity. Similarly the walnut cabinet is La Télévision. By Marc Chauvièrre. Pp. 267. Good as is the radio performance of this designed to afford the maximum stiffness 244 diagrams. Dunod, 92, Rue Bonaparte, set, it is the quality of reproduction which without wasting material. Paris, 6. Price 78 francs, paper cover; 95 do most to francs, board cover.-A book which combines will establish its reputation. In conclusion, a word in praise of the a complete theoretical treatment of television Crisp transient response and exceptional leather strap hinges for the back panel, with a good deal of practical information. clarity on all types of transmission are its arranged so that it may be turned over o:1 How to Overcome Competition. By Herbert chief characteristics. The bass response to the top of the cabinet while replacing N. Carson. Pp. r59. The Efficiency Magazine, has been skilfully managed, for Kent House, 87, Regent Street, London, W.1. it easily valves or making adjustments. Price 5s. 360 The Wireless World, April 21st, 1938

B.B.C. SEEKS ARAB CANADIAN BROAD- CASTING INVESTIGATION REACTIONS IT was learned during the Listener Research recent biennial Canadian THE B.B.C. is disappointed Parliamentary investigation into broadcasting that the Govern- S because there has been no NE OF constructive criticism of the ment, through the Canadian Arabic transmissions from Daven- Broadcasting Corporation, places television as a secondary subject CHURCH BROADCASTS: try. The fear is rife at Broad- TECHNICAL CRITICISM casting House that only the in- to facsimile transmission, and IT is alleged that the average articulate Arabs are listening to that the right to transmit the to latter will be retained by the Variety programme broad- them, and if these wished the B.B.C. receives far communicate with the B.B.C. C.B.C. Members of Parliament cast by to hire the ser- also learned that private broad- more attention in the matter of they would have presentation than do most vices of the scribe in the local casting stations are to be more is now being sug- heavily taxed than their annual broadcast religious services. bazaar. It The main points of criticism gested that small blank record- $50 licence ; that the C.B.C. will only continue commercial broad- are (a) that too little attention ing discs should be sent to the B.B.C. listening leaders, casting until it completes the is paid to vocal balance, community engineers having no say in the who would persuade their flock erection of at least three more so -kW stations, two of which positioning of the choir ; (b) to utter their true opinions re- to before are to be erected this year in the that the microphone tends garding the programmes coast) pro- emphasise singing out of tune, a recording microphone, the Maritime (Atlantic Canada; a prevalent fault with choirs ; completed discs being shipped vinces and .Western that eventually private broad- (c) that organs are misused, the to England. to swamp In the meantime, the Cor- casting stations, of which there tendency being making contact with are at present seventy-two, will singers. poration is only be allowed to function with The ideal arrangement would Moslem leaders, British resi- of z kilowatt ; and be for the Balance and Control dents and newspaper editors a power limit to obtaining some that $3,2ó0,00o will be required Engineer to go into close con- with a view for the year ending March 3zst, sultation with the organist and kind of listener reaction. builders are 1939, of which $ 2,700,000 will choirmaster before a church The programme licences as far as regards its come from listeners' and broadcast to ensure that, also in the dark and the remainder from commer- as possible, the musical side of Spanish and Portuguese lis- this justify cial programmes. the service shall be worthy of teners. But does the broadcasting medium. the transmission, on Easter BERLIN A. R. P. SHELTER morning, to Arab, Spanish and which is loft. high and contains Portuguese listeners, of the POLICE RADIO IN a spiral gallery with accommo- service from St. dation for 30o people, is fitted Protestant AUSTRALIA with loud speakers for the Paul's Cathedral? NEW SOUTH WALES now diffusion of music from gramo- possesses a polite radio phone records, altheugh there system of which it can be justly is no technical reason why B.B.C. ADVISES proud. The main transmitter wireless should not have been NEWFOUNDLAND is situated at Sydney, while a used. New Station for St. John's" subsidiary station is located at after alterations which _ are HOUSE is Newcastle, about zoo miles BROADCASTING north of Sydney. Both stations scheduled for this year. still the hub of broadcasting The equipment of the Cape - The operate on the same wavelength. throughout the Empire. The Sydney transmitter's power town Castle, which will also be engineering department has similar in each of the other and technical is rated at Zoo watts unmodu- just sent plans lated carrier for telephony and vessels, consists of a 2 -kilowatt advice to the Government of CW / ICW medium- and long - the erection 70o watts for CW telegraphy, Newfoundland for and that at Newcastle has a wave transmitter, a 14 -kW a dual-purpose station at St. and a of power rating of zoo watts un - short-wave transmitter, John's, which will not only pro- 1 -kW quencheed spark gap emer- its own for modulated carrier for telephony. vide programmes of To overcome the difficulty gency set together with receivers the scattered population, but covering the whole of the com- from of electrical interference with relay the programmes reception, a receiving site in a mercial wavelengths. A direc- Daventry. quiet residential area about tion -finder with double loop Work is about to begin on the fixed frame for navigational to be 7 miles from the main trans- station, which is expected mitter in Sydney has been purposes is being fitted, and ready early in 1939. chosen. It is equipped with transmitters and receivers are to superhets, and the signal from be installed in two lifeboats. AMERICAN METHODS FOR any receiver is fed through a BRITISH BROADCASTING ? switchboard to the main station GARDENING TALKS : by means of direct land line. PARTIAL Americanising of A PROBLEM Fourteen patrol cars and two from the B.B.C. programme launches are fitted with wireless LETTERS to the B.B.C. methods, with a speeding up of equipment, and the patrol radius listeners in the North have presentation, may follow the is 6o miles and pointed out that Mr. Middle - from Sydney talks re- present visit of Mr. R. E. L. from Newcastle 40 miles. ton's weekly gardening Wellington, Assistant Pro- late only to gardening condi- gramme Controller, to New tions in the South of England, LANCASHIRE MOUNTED RADIO EQUIPMENT IN LINERS York. Mr. Wellington' is spend- POLICEMAN using one of where nature's processes are ing three months in an intensive the transmitter -receivers with THE contract for the supply sometimes at least a fortnight in of com- Novocastrians who study of broadcasting at Radio which . the section is now and maintenance advance. City. equipped. The transmitter has plete wireless equipment for" the follow Mr. Middleton's advice Meanwhile, Mr. Val Gielgud, a power of about 4 watts and new Union Castle liner, Cape - and plant out tender seedlings the Drama Director, is still on a range of two miles. The town Castle, has been given to find, too late, that the icy blasts complete apparatus, which the Marconi Company. Three of winter wastes the work of tour in America, and will com- weighs approximately 55 lbs. plete a " busman's holiday other vessels of the same com- months. It is now suggested and is constructed in the be re- by producing G. K. Chesterton's Lancashire Constabulary's own pany, the Winchester Castle, that the talks should " Lepanto " at Radio City, New workshops, operates on a wave- Carnarvon Castle, and Warwick corded for broadcasting to Scot- York, on April 27th length of 5 metres. Castle, are also to be refitted land and the North. The Wireless World, April 21st, 1938 36r -

Radio Beacons Polyglotic Italy ACCORDING to the Lighthouse IT was recently announced by Service Bulletin the total number the Minister of Popular Culture in of marine radio beacons in use in the Italian Chamber of Deputies the world at the beginning of that there were now transmissions 1938 was approximately 42I, an in nineteen languages from the 'HE WEEK increase of 41 during the year. Italian stations. Licence Figures "Radio Wein " INDUCTION ON THE Radio National. Similar trans- THE approximate total number THE official Austrian pro- TELEPHONE missions are radiated on the of licences in force at the end of gramme paper, Radio II' ien, . DURING the last few days 25 -metre waveband during the March, 1938, was 8,590,950, as ceased publication at the end of telephone subscribers in evenings. compared with 8,127,630 at the March. Worthing have been entertained Russian listeners have also end of March, 1937. Si Parla Italiano by snatches from the B.B.C. been subjected to anti -Govern- German Radio Exhibition THE Hungarian Broadcasting National programme when they ment transmissions from an Company has ordered that their have been " holding on " for unknown station transmitting "BROADCASTING the voice Of announcers should not only be long-distance calls. The Post on 29.9 metres. This station the nations " is the slogan for the able to understand Italian, but be German Radio Exhibition, which able to speak it fluently. Office states that the trouble is identifies itself with the words, opens on August 5th and lasts " The Union of caused by induction from a new Liberators." until August 21st. Vacancies for Wireless Operators line put up by the local Radio It is reported that forty-six Relay Company running parallel arrests have been made in con- Ministerial Changes BIG shipping companies are ex- THE French Minister of \Vireless periencing a severe shortage of to one of their own. The matter nection with the German clan- wireless operators. There are no could be easily rectified if sub- destine transmitter, whose activi- in M. Daladier's Cabinet is M. Jules Julien. strict age limits imposed upon scribers were to complain. ties were described in these applicants, whose period of train- pages on March 3rd. Wireless Appeal ing is about twelve months. GERMAN TELEVISION ALTHOUGH Christopher Stone's Short-Wave Train Communication broadcast appeal on behalf of the THE 441 -line equipment in FROM ALL British \Vireless for the Blind was AFTER several months' trial the the new Berlin Television QUARTERS made as long ago as Christmas Norwegian State Railways have studios is undergoing its test Day, occasional gifts continue to equipped goods trains plying be- arrive. Donations have reached tween Trondjem and the Swedish period, but it is understood that Radio on Belgian Trains will not work- the total of £23,041. Mr. Stone frontier with short-wave wireless the transmitter be " RADIO -TOURIST " trains are to ing regularly until June or July. is to appeal on behalf of St. apparatus which enables the he introduced on the Belgian State George's Hospital, London, on brakeman to establish communi- Meanwhile Intendant Nirentz, Railways this summer. Broadcast Sunday. cation with the engine -driver. Programme Director, who is a programmes will be picked up, and will well-known poet and former film travellers also hear gramo- Iatesfss ace in the U.S.A. Encouragement for Radio producer in the Propaganda phone recordings relayed from the Playwrights brake van and descriptions of the ELECTRICAL interference ill Ministry, continues with spot- America is not merely trouble- THE French Minister of Posts light scanning. He has even country through which they are and Telegraphs has fixed a scale passing. Each coach will be some to the short-wave listener produced a ballet of six dancers but to the police radio- systems, of fees for original works and fitted with one or more loud adaptations for broadcasting. This performing in the dark studio in speakers. most of which operate on the light. 9 -metre waveband. the recently is intended to be an encourage- front of the scanning ment for radio playwriters. The State Museum in People's Receiver in Austria formed National Association for Prevention of Radio Interference Munich will open a special tele- THE Austrian radio industry has Lifeboat Wireless undertaken to produce a People's is doing good work in exposing vision show on May ist. This perpetrators of this Offence. IT was recently revealed by the will remain open to the public Receiver, with the promise that 6o,000 of these will be accepted Secretary of the Royal National until the of October. Lifeboat Institution out of beginning for sale in Germany, whilst - E.IB.A that, the the which could be German radio industry undertakes AT the annual Iuncheon of the 53 boats fitted sell Industries Benevolent with wireless, 27 had installations, LINGUA FRANCA not to their own People's Re- Electrical INDIAN ceiver in Austria before the end Association the President, ;Mr., and before the end of the year it hoped 23 A T the Calcutta Conference of of 1939. At the next German Radio E. E. Sharp, 'said that he wanted was that another would , Indian station directors Exhibition the Austrian radio to raise the Association's invested be similarly equipped. held recently, much time was industry will have the opportunity funds to £250,000, and this meant. New Turkish Transmitter spent in discussing the.question of conducting propaganda for the that £190,000 had to he raised sale of these sets. this year. TURKEY IS to construct a new of the diversity of Indian lan- medium -wave transmitter of guages. That this question is 12o k\V and a short-wave trans- a very serious one will be realised mitter of 20 kW. from the fact that in Bombay there are three languages, be- Broadcast Advertising sides English, which are widely A " CHAMBRE Syndicale de la namely, Maiathi, Gujarati Publicité Radiophonique " has used, just been founded in France. It and Hindustani. will deal with all matters relating It is pointed out in The Indian to broadcast advertising. Listener that it is almost impos- sible to incorporate a number Verboten of languages in one programme, THE erection of poles for aerials and there is no doubt that on the new housing estates is for- ultimately a mixture of Hindi bidden by the Peniston (Hudders- and Urdu will be the lingua field) Urban Council, the opinion of India, but in the mean- of the Council being that indoor franca aerials time a committee will be set up are quite satisfactory. to consider a vocabulary for use South America is Interested in broadcasting. A SUDDEN increase in the sales of short-wave sets in South America is attributed to the in- CLANDESTINE TRANSMITTERS terest taken in the recently in- ARE POPULAR augurated B.B.C. Spanish Ser- FRENCH listeners have been vice. a startled by mystery station Radio Bicycles which for some days past has AN ANNOUNCER'S DESK at the Zeesen short-wave headquarters in on Adolf Hitler Platz, Berlin. To obviate mistakes the microphone bears ACTING on the suggestion of been transmitting anti -Govern- a list of the wavelengths and calf signs used. Note the control Haut-Parleur wireless manufac- ment propaganda from 1.15-1.3o buttons in the foreground ; one closes the time signal circuit, the turers in France are contemplating p.m. each day. The station, second is for communicating with the control room, the third for the the large scale production of light- which works on a wavelength of interval signal and the fourth for warning those responsible for the weight wireless receivers, designed 250 metres, announces itself as next item that the announcer is about to finish. (See article on p. 355.) to work on bicycles. The Wireless World, April 21st, 1938

programmes, more especially plays, are, made up of film transmissions instead of flesh -and-blood performances. As for an alternative word which is easily remembered and comes readily to UNBIASED the tongue, what could be better than the word ? capacity insulators of the proper in- " televisor " Is it too late to drag Cheeseparing Economy type this stead of trying to save a few miserable valuable word from its association at the Palace pence by sending the boy round to the IN spite of my frequent criticisms of the local sixpenny stores, which is obviously BY B.B.C.'s pettifogging pigheadedness what they have done in this case. and irritating irrationalism in many It is not only the glaring technical un- matters, I have hitherto held them in very soundness of this method which is worry- FREE GRID high esteem for their technical ability, ing me, however, as there is a far more but I am sorry to say that as a result of serious aspect of the matter, and that is with the receiving end of the business? A certain happenings last week I have been the danger to the public if the insulators televisor is surely a thing that televises, compelled, pending an explanation by break under the mechanical strain im- and this exactly describes the function of the B.B.C., to modify my opinion. posed on them during a gale. With the the so-called television camera. Failing It so happened that I made a special proper method of connection this possi- the adoption of this word, one could journey up the hill to the Alexandra bility is duly taken care of but, as things borrow from the world of sound broad- Palace the other day armed with a pair of are, in the event of a breakdown in a high casting and use the word which is so ob- binoculars, the object of my visit being wind innocent citizens are likely to be vious a companion -in -arms to the word to make a close inspection of the television struck by flying fragments of aerial wire. " microphone," namely, " microvisor." aerials with a view to carrying out cer- I sincerely trust that some responsible tain improvements in the one I use at person at the Alexandra Palace will take home. When I focused my glasses .on the necessary steps to remedy this state of the top of the aerial mast I could scarcely affairs without delay. Old Friends Are Best believe my eyes at the frightening vision IMUST ask you to excuse me if these which met my gaze. When I had investi- rough notes of mine do not seem quite gated a little further, however, I found up to their normal technical standard this that I had been looking at a greatly en- week, but as a matter of fact I have larged vision of an insect which had received a very severe shock and I am somehow or other got between the lenses. still feeling somewhat weak and ill in con- Having duly removed the offending sequence. My feelings must, I suppose, insect I again levelled my glasses at the be somewhat akin to those experienced by mast but received another rude shock the great and learned savants of the world and naturally at once suspected my when Galileo first announced that the glasses again and proceeded to dissect earth was round, thus destroying at a them. Unfortunately, I carried the latter single blow the very foundations upon process a little too' far and it has cost me which all their scientific work hàd been a pretty penny to have them reassembled built up. by an optician for which, in view of what In my case it is not a question of the I am about to relate, I think the B.B.C. world's roundness but something fully as ought in common justice to pay. When important, namely, Ohm's Law, which I I had received the glasses back and made have hitherto believed was as strong and a fresh journey to the Palace I was immovable as the proverbial laws of the amazed to find that the sight which had "My worst suspicions were confirmed." Medes and Persians were supposed to be. caused me to dissect the binoculars on the It is very hard to give up one's cherished previous occasion was still in evidence. illusions, and I must confess that when I For a moment I was completely non- Camera or Televisor ? read in The Wireless World recently that plussed. I did not like to blame my Ohm's Law "crumbles into loose sand binoculars again, although I could IWONDER if it is possible before it is where rectifiers are concerned " I was scarcely credit that that which I saw was too late to . register a strong protest sorely tempted to sit down and write a there in actual fact. Suddenly, however, against the use of the word " camera " in strongly worded letter to the Editor de- I recollected the famous words of wisdom connection with television. Recently I manding the public renunciation of this uttered by Mr. Gladstone in 1878 to the raised the question personally with some heresy. effect that the camera cannot lie and I of the bigwigs of television only to receive Saner counsels prevailed, however, and hurried home in a fast car to collect my the rather lame excuse that it is a highly I realised that I should probably get my- camera and a good telephoto lens. The convenient word. Convenient or not, I self involved in .intricate_ mathematical result is that, as you see by the photo- know from my own experience that it is formule which would ill befit my some: graph I took and which I reproduce here- having a very baneful effect from the point what humble position in the technical with, my worst suspicions were con- of view of encouraging Mr. and Mrs. world. My irrational self, however, firmed. Everyman to become really television - cannot help feeling a sneaking regard for It will be at once painfully obvious to minded. that stalwart friend of my youth, Old you fellows that the B.B.C. Technical Hearing the word so often in connection Man Ohm, and although I have, needless Bigwigs do not even know the correct with television, ordinary citizens are prone to say, now thrown him overboard, I feel. method of connecting up simple egg insu- to come to the conclusion that there is not that I cannot calmly watch him drown- lators. Of course, I am fully aware of much in television after all, as it is merely ing without making some attempt to save the fact that they will save their face by some sort of glorified cinema film transmis- him. I" am, therefore, thinking of form- replying that this method of using the sion. Probably they are assisted in this ing an Ohm's Law Protection Society," insulators was adopted for a very im- wrong attitude of mind by some hazy re- and I shall be very glad to hear from any portant technical reason, namely, to collection of hearing at some time or of you who would like to join me, more obtain low capacity. Surely, however, a another of the old " delayed -film " system. especially the more technically -minded of mighty corporation like the B.B.C. can Even quite knowledgeable people are, you whowould be prepared to enter the design and get made for them special low - however, apt to think that all the television technical jousts in an old friend's fayour The Wireless World, April eist, 1938 363

hy' Maths 7 By "CATHODE RAY"

T school we had a geometry master completely and utterly beyond the ordin- Apart from a, if the meanings of the who, when he asked a boy to ary reader, that is not to say that every- letters are not given, one has to decide prove that certain triangles were thing remotely resembling it is to be what they are likely to mean in that par- similar (or whatever rot he hap- shunned like the plague. By steer - ticular connection. If the subject is pened to be teaching at the time) , would in clear of every trace of x and y valves (the wireless sort, not steam engine draw them on the board as shown on this and B and 7, one is actually making things or bicycle tyre) it can be assumed that ¡I page-, if the boy's name happened to be more difficult for oneself. These letters stands for amplification factor: But if Watson. When it came to my turn, of and other symbols are just a quick, easy iron cores for transformers are being dis- course, the triangles were C.A.T., H.O.D. way of saying things, and can be made cussed, µ should be read as permeability. Apart from adding a welcome touch of use of by anybody who can do elementary Or if it comes before a big F (farad) it is pleasantry to the schoolroom, this practice arithmetic. an abbreviation for micro-meaning one helped to emphasise that the truth of a One of the simplest and most helpful millionth. Talking about a millionth, one mathematical statement does not depend uses of letters in place of numbers is the often comes across it written as 10-6. It on the letters or symbols used to express formula. This is just an abbreviated is easier to see that 2 x io -6 is two mil- it. Some people are frightened of algebra method of telling one what to do in order lionths than if it were written 0.000002. and trig., and things like that because the to work out a result from particulars given. The small number above the io indicates idea of " doing sums " with letters seems the number of places the decimal point is In involve brain -work of an almost occult to be shifted, - indicating a movement order. Actually, the letters and things to the left, and + (or nothing) meaning are there to make the work easier. I am X and a movement to the right. For example, sometimes amused by the long-winded and y 3.72 x 1012 is 3,720,000,000,000 ; and clumsy ways in which things are 'some- 23.94 x 10-9 is 0.00000002394. That is times explained by non -mathematical Sometimes Make quite sensible, surely, for saving time and persons, when they could be given clearly making things clearer? In radio one so and concisely in a simple formula. Even Things Easier often comes across very small or very large ordinary language would sometimes be numbers, that this sort of shorthand is very clearer if some of the conventions of useful. mathematics were used. They would make To find the number of square yards of lino It is true that there is occasionally some quite plain the differences between " a to cover a rectangular floor it is necessary risk of confusion through using letters, shall red (deer hunter)," "a small (red to,multiply the number of yards in the and they ought to be chosen and used with deer) hunter," and " a (small red deer) length of the floor by the number of yards care, but for common purposes in radio hunter " by showing which words qualify in' the: breadth. This is usually stated as there are comparatively few to learn. which. " multiply. the length by the breadth," What is, perhaps, liable to be muddling The person who shudders and hurriedly but, of course, that is nonsense unless 'it -though it doesn't seem to be so in prac- closes any book or paper in which mathe- is understood to be an abbreviated form tice-is that letters are used in different matical symbols appear is in this state of of the previous statement. It could be ways. The way I havé been discussing is shyness probably because unwise methods abbreviated still more by adopting a semi- as a substitute or abbreviation for some of school teaching gave him the impres- mathematica: appearance : number that is filled in when it is known sion that maths was beyond him. When area = length x breadth. (as in the lino measurements). There is page after page is covered with symbols, Having got so far, one might as well V or y or E or e for a voltage (the E is there are two explanations : either they write it still more quickly :- derived from electromotive force), and C are necessary, in which case the matter a=l x b, or a=lb, for capacity, and L for inductance, and is beyond the ordinary reader ; or they are which is the stage at which some readers so on. Unless anything is said to the con - not necessary, in which case it is fit for begin to take fright. The only reason why nobody. The latter class of work, pre- the letters a, l and b were selected is that sumably written to gain a reputation for they remind one of the things they stand learning, not only obscures the subject for. Apart from that there is no reason treated, but gains mathematics a bad why the same truth should not be written reputation. as:- x=yx, Mathematicians-and Others or even :- a=ßY, I suppose there are people who can read so long as one knows what these symbols through pages of mathematical work as mean. As there are only 26 letters in our easily and naturally as they do ordinary alphabet, and fewer still in the Greek, it writing, but as I am not one of them there is not feasible to allocate any one of them need be no fear of my introducing that permanently, be it a or x or a, to mean One way of selecting letters for diagrams. sort of thing here, necessary though it may the number of square yards of lino re- be in its place. If a writer cannot put quired to cover a floor. One letter that trary, these quantities must be understood what he is getting at into plain words, the does seem to have a fixed meaning is to be in volts, farads, henrys, etc., respec- chances are that he is not at all clear about representing the ratio of circumference to. tively. I=R is a familiar statement it himself. Faraday was perhaps the diameter of a circle. This is a particularly greatest of electrical scientists, and his good example of abbreviation, because to (Ohm's law) ; when one has a current writing is practically non -mathematical. write down the number represented by r passing through a resistance there is a On thé other hand, we wouldn't have got it would be necessary to keep on literally voltage across the resistance, and if any far in radio if it hadn't been for mathe- for ever. It is 3.1415926535. . . . etc., two of these are known numerically, the maticians like Clark Maxwell. etc. The first three or four decimal places above formula explains how 'to find the But because some mathematical work is are near enough for most purposes. third. It holds good for amperes, ohms 364 Miltd APRIL 21st, 1938.

Why Maths P- simple thought is part of the dreaded dif- page do not have to do work like this ; but and volts ; but if it is to apply for milli - ferential calculus. even in everyday life it is helpful to tackle amps it is necessary to alter it to But it illustrates yet another use for problems in a mathematical spirit instead I- i,000E letters. The 8 is not a quantity, like f or of groping vaguely. R ' C, nor does it point out something on a Of course, there are always some people Another use of letters is as an abbrevia- diagram. It is more of an instruction to who carry things too far, whether it be tion, not for a number, as above, but for do something ; in this example, to increase non-stop dancing or flag days or broadcast the name of something. Thus, while I (or decrease, if there is a minus sign) f or listening, and the mathematicians are no represents a number of amperes, A stands C by a very small amount. It is, there- exception. One can start off with sym- for " ampere." If in a particular case a fore, like other instructions, such as = bols representing definite things, and resistance of 5o ohms is applied to the 200 - or+or1/. juggle with them so much that a stage is volt mains, by substituting these numbers Mathematical symbols are useful for reached where the result conveys no use- (or values) in the above equation, I works saving time in writing things down, but ful meaning, if any meaning at all. This out to 4 amperes, which can be written that in itself is hardly mathematics. If may be all right as a harmless and amus- briefly as I=4A. This is not a formula, one had to find the capacity of a cylindri- ing pastime, but if one is attempting to or equation, stating that the current is cal tank non -mathematically 'it would be investigate a problem, say, in radio, it equal to 4 multiplied by some mysterious necessary to fill it up with liquid labori- seems to me that one should never lose quantity A. ously measured out in a quart pot, or touch with what the symbols mean. Other- If the resistance had been 50,000 ohms, other standard container. And, having wise it is quite possible for a discovery to the current would have been 4 -thousandth done so, one would be no further on to- be unearthed and yet not to be recognised of an amp, or o.004A ; but here m as an wards measuring other cylindrical tanks ; and turned to good account. One reason abbreviation for " thousandth " becomes they would all have to be done in the same why I am so slow in reading through a useful, and this small current is prefer- tedious way. But without moving from lot of mathematical working is that I am ably written as 4 mA, read as " 4 milli - his desk the mathematician can say, " let unhappy unless I can see at each stage amps." The only occasions when people l be the length of any cylindrical tank (in what the symbols signify. It is not enough show a curious reluctance to save them- any agreed units, such as feet or centi- to agree that mathematically the working selves the trouble of saying or writing a metres), and d the diameter, in the same is correct. That is why, in my opinion, lot of- preliminary noughts is when small units. Then the volume, in cubic units a writer should be obliged to state in capacities are mentioned. Personally, I of the same sort, of any cylindrical tank words, every so often, what he has dis- find " 5b µµF " much easier than x42 covered. And then people where ir is what we said it was. may or may " 0.00005 µF." is not be interested in the mathematical Give him longer time, and he can work out stages by which he has arrived at those Reference Letters the actual value of it to any required conclusions. It depends on how much accuracy. All one has to do to find the faith the reader has in him ! Still another use for letters, and one that capacity of a particular tank is to fill in In any case, if the maths were has even less right to be considered deleted the two easily measured dimensions and entirely it would probably not be clear " mathematical," is simply as a label, for employ simple arithmetic. what are the conditions example, when referring to the resistor under which his The value of this is enormous. When a conclusions are true. Even the famous R2 in a diagram. The litfle 2 has no radio transmitter is ordered it is not neces- Ohm's law formula mathematical significance (such as it already looked at is sary to keep on making transmitters until not universally true. The would have if it were written R2), but as. conditions under the right one is arrived at (if it ever is) ; the which it applies are usually resistors in a dia- considered to be so there are several engineer sits down and works out the sizes well known that they are gram it is necessary to number them. R hardly ever men- of things from the requirements specified, tioned ; but in newer work it is very im- is an obvious choice for resistor, but in- and if the mathematician has been clever portant to avoid applying results . stead of making a coil C (because that is to con- enough there should be at most only minor ditions that lie outside the assumptions. already booked by condensers or capaci- alterations needed when an actual trans- It was just letter that sort of thing that made ties) it is customary to borrow the mitter has been built. experts wrongly judge to for value short waves to be used in formulæ stand the of Now the majority of those who read this no use for long distances. inductance, L. This letter, therefore, may refer to a coil in a circuit diagram, or the number of henrys inductance of that coil, or both. One reason why there is less confusion in the use of letters than might be expected Readers' Problems is because even apart from those letters that have definite meanings attached to A Selection of Queries dealt with by the Information Bureau, and chosen them, there is general agreement, for for their more general interest, is published on this page. example, that x and y and z shall be re- served chiefly for variable quantities, and Screen Grid Voltage Supply The potentiometer would pass 5 mA AREADER has a receiver in which a only, but as these early sets did not have a, b and c for fixed quantities ; and, as an- variable other example, if any letter such as f repre- tapped resistance is used as a potential -mu valves good regulation of the divider to screen voltage is not a quantity, a very small increase or supply the screen grid in the RF essential. sents valve, and this resistance has broken down. decrease in that quantity is written 8f (or Owing to the age of the set and the absence Measuring Instruments Af). Both these Greek sometimes letters of markings on the resistance it is impos- WE are asked to explain the difference are " delta," one being the small letter and sible to determine its original value and we between a voltmeter and a milliam- the other the capital, and they mean are asked to indicate a suitable value of meter as the " works " of the two instru- " difference." The letter f may stand for resistance and tapping point for a replace- ments appear to be identical. the frequency of an oscillator tuned by a ment. Actually there is no difference in the capacity C, and if the capacity is shifted Zhe set is AC operated and in view of its mechanism of the two instruments, for very slightly by an amount 8C the fre- age most likely includes an HT supply unit whether it is marked a voltmeter or a giving quency alters by a small amount 8f. Al- about zoo volts at the working load. milliammeter the meter itself only responds A potentiometer of 40,000 ohms total seems to current. though it is not true to say that C 2f, if = to us a reasonable value in this case, and if The difference lies in are so small as to infinitesi- the method of appli- 8C and if be a centre -tapped resistance is used, or two cation. For instance, if voltage measure- it is true to say 8C = 28 f, or in other 20,000 ohm resistances joined in series, the ments are required a resistance is joined in maliwords, the frequency changes half as fast centre point will provide about the right series with the meter, its value being such as the capacity. Oddly enough, this voltage for the screen grid in the valve. that when the combination is connected APRIL 21st, 1938. Wpell@ez 363 WopDi across a supply of say, 50o volts, sufficient testing is not likely to locate the trouble, current only is allowed to pass through the and an orderly stage -by -stage test is indi- instrument to move its pointer over to the cated. M end of the scale. Though the instrument If a gramophone pick-up is available, the' ill cÀIIFYIiI used may be o to r milliammeter, this point two audio stages, which, though not shown on the scale can be marked 50o volts. If in the accompanying circuit, follow the the instrument is now connected across a detector, can quite easily be tested by con- 250 -volt supply only 0.5 mA will flow corre- necting it in the grid circuit of the first AF sponding to about half-scale deflections. amplifier. It can be judged from the results A full-scale deflection can be obtained obtained whether or not this portion of the for any desired voltage merely by joining set is functioning correctly. a suitable" value of resistance in series with Assuming this aid is not available, then the meter. the alternative course is to join the aerial For the measurement of currents larger to the primary of the RF transformer and than that for which the meter is designed to include a small condenser C of o.000i mfd or pass resistances of suitable value are joined less as shown. The RF valve should be re- in parallel, or shunt, with the meter. Thus moved for this test ; tuning is now carried part only of the total circuit passes through out on Cr, and although the selectivity will the meter, the remainder flows through the be poor, quite good signals ought to be ob- shunt resistance. tained. If not, the detector and AF circuits It is this common ground of operation that should be examined for any error in the enables a multi-range instrument to be pro- wiring or faulty component. During this duced that by the turn of a switch becomes test the opportunity might be taken to cure either a voltmeter or a milliammeter (or an the reaction defects. ammeter). All that the switching does is to A condenser of about o.000r mfd joined connect appropriate resistances either in in the position C2 will help to ` tame " the series or is shunt with the current measuring reaction on the medium waveband, while instrument. if a resistance of about Soo ohms is in- For this explanation it is assumed that the serted at RI it should overcome the long - voltages and currents are of the direct cur- wave trouble. rent kind, but it applies also to the universal What apparently is taking place is that type of meter that deals with AC as well as the raction circuit is oscillating at a dif- N modem radio practice, nothing is final; no DC, as for the former a rectifier is used to ferent frequency to that to which the grid receiver is so good that it is incapable of convert it to DC before it reaches the meter. circuit is tuned. We would expect, how- development in some detail. There is a difference between the two kinds ever, its strange effects to be noticed also Constant attention to improvement in small of instruments, but this is incidental, not on the medium waveband. However, the matters keeps McCarthy chassis in the forefront fundamental, to their operation. A volt- same difficulty has in the past been en- of modem chassis design and construction. meter invariably has a very high internal countered in sets having a single reaction resistance, whilst a current measuring meter coil, and it has always responded to this is of low resistance. treatment. The receiver illustrated Actually, it would be better to move the condenser to the other side of the reaction is the well-known McCarthy Stage -by -Stage Tests winding, but it will have to be removed HAVING constructed a three -valve bat- from the panel and operated by an insulated tery set, a reader is dissatisfied with its extension" spindle. 9 -VALVE 4 -WAVE performance. Sensitivity is poor and reaction Having corrected any faults, in the detec- is behaving in a very peculiar manner. It tor -AF portion of the set, the RF valve SUPERHETERODYNE 14 guineas including valves +120 V priced at +60V The Circuit in Brief.-The pre -selector circuit is coupled to high -gain radio frequency amplifier operating on all 4 wave -bands, which TO AF STAGES is transformer -coupled to latest type triode- hexode frequency -changer. There are z band- pass transformer -coupled I.F. amplifiers (inter- mediate frequency 465 K.C.'s). The double diode second detector provides automatic volume control applied to 4 preceding valves, and first stage L.F. amplification. The triode phase -changer is capacity -coupled to push-pull output pentodes (or Harries-tetrodes) delivering 9 watts. Principal Features.-Waveband coverage - 12.8 -33, 29-80, 190-550, 800-2,000 metres. Controls-sensitivity control (varying bias on R/F stage) : 5 -position wave -change and gramophone switch : combined volume control and on/off switch and progressive variable tone control (both operative on radio and gramo- phone). DEFERRED TERMS 29/- with order and 14 monthly payments of 14/-. ) -LT On application, or through our City agents, LONDON RADIO SUPPLY CO., 11, OAT LANE, LONDON, E.C.2.

RF and detector circuits of the set for which a stage -by -stage test is described. Send 3d. in stamps for compiete illustrated catalogue with technical data and circuit diagrams of other interesting McCarthy chassis of all types for A.C., is reasonably satisfactory, though somewhat can be replaced and the aerial returned to Battery, or A.C./D.C. Abridged list free of charge. fierce in operation on the medium wave- its proper terminal. If the RF stage is be- band, but on the long waves it has no ap- having correctly a very marked increase in iNc CARTHy RAD1 O 1.71) parent effect on signal strength, yet the signal strength should follow. If this is not 44, Westbourne Grove, London, W.2 detector valve can be made to oscillate. the case, then there is either a wrong con- Telchoae- BapnoaNr 32011) mzumnsw This seems to be a case where haphazard nection or a faulty component. The Wireless World, April 21st, 1938

you are actually on the spot than you do if you stay at home and hear the running RANDOM RADIATIONS commentary from your loudspeaker. At Aintree, even from the best place. on the Grand Stand, you see only part of the race Something for Nothing ? By " DIALLIST " in any detail and know very little of what THERE still be those who fondly hope is going on when the horses are " out in the to get something for nothing, or next country "-especially if it's at all misty. At about it. Even if you worried the thing the Boat door to it, in the way of wireless gear, even out and Race all that most of the throng built the set it would not be worth see is the crews flashing past though in their heart of hearts they know using." I don't think that he'll be caught just one point well enough that it can't be done. Here's in the four -mile course. The broadcast again-though I wouldn't be too sure about commentary enables you a case in point. A man I know asked it if his happens to follow either eye to light on an adver- race clearly from finish. rather sheepishly when I was at his house tisement offering some start to The astounding bargain Magician is just behind crews the other day if I'd give him a hand at for less than half what it would be worth, the the whole sorting out a kit of parts that he'd bought way in the Boat Race, and the "National " were it genuine. It takes all sorts to make commentators some time previously. Enquiries elicited a world. are stationed at various that he had responded to an advertisement vantage points. If sound broadcasting can do in a lay paper, which seemed to offer amaz- ti ti all this, how marvellous it will be when ing value. It was very loosely worded, but Great Work such events are televised in their entirety, it gave the impression for, a mere as no doubt they will be before very long.' that NO one thirty shillings you could obtain the latest who watched the England versus The " in -looker " will indeed see most of Scotland soccer match, as televised ! thing in American AC / DC - " all -wave " the game receivers, complete with tubes. He parted from Wembley, could begrudge the .B.B.C. with his thirty shillings and received in return the self-administered pats on the back that for it not a made-up set, box formed part of the news bulletins that Not So New but a contain- evening. ing an alleged kit of parts " with com- It was a really first-rate show. By the way, the B.B.C.'s plan for tele- plete instructions for building the receiver." and the B.B.C. was not far wrong in saying vising the Boat Race by showing model That the parts' were mainly junk one could that it was the best piece of work that the boats moved along a map of the course as see at a glance-no makers' names on any O.B. staff of the Alexandra Palace has telephoned or radio -ed information came of the condensers or resistances. The done yet. The light was exactly right for through wasn't quite such a novel idea as " complete instructions " consisted clear, contrasting images, and the emitrons many thought it would be. wonder if of a rose I any cyclostyled circuit diagram of the most nobly to the occasion. But it wasn't readers " saw " the Boat Race of 1906 (ot only engineering people elementary kind of straight 3 -valve set. the who excelled. was it 1907?) at the Union at Cambridge?., Those in charge of the cameras manifested If any did they may remember real that a vast showmanship by keeping the centre òf map of the course was hung on a wall of So Clear ! play on screen. the I'm sure that no one the room in which the debates are held. A This had apparently been drawn by the who saw the match by means of a televisor trunk telephone line to London had been office boy from memory ! Where he wasn't missed very much of the game. Everyone secured for the duration of the race, and quite sure where one lead crossed another I've met who " looked in " was loud in his over this observers stationed many praises. This at or was connected to it he had made a blur transmission should go a long points 'phoned information about the posi- that might have represented either. Again, way towards giving television the boost tions of the crews. As each message came not one single value was shown. Nor, that it needs, for many thousands of people through cardboard boats, must one light blue,' apart from this weird diagram, was there have seen it, not only in private one dark, were fixed in the proper places on any kind of help for the would-be set houses, but in wireless shops and at centres the map by drawing pins. And so, fifteen builder. " Better write for full instruc- such as the Ideal Home Exhibition. tions," years or more before broadcasting, let alone I suggested. " I've written three 1 1 L television, was in being, an audience of times already," said the victim ruefully, about a hundred people was able to follow " and not one of my letters has been A Look Ahead the race through all its stages. It's true answered." I gave him the only advice that IF you've ever been to the Grand National nowadays seemed that the commentary or the to fit the case. " Throw the whole or the Boat Race you'll agree that you images come through with no time-lag. But' outfit into the dustbin," I said, " and forget know much less about what's going on when those who watched the Boat Race at the r

THURSDAY, APRIL FEATURES 21st. Broadcast OF THE Abroad. Nat., 7.30, Joe Kaye and his Or- Programmes WEEK Berlin, 8, " Tannhäuser," opera chestra. 8, W. H. Berry in (Wagner). " Whose Hooper? " a musical way. 9.30, Variety from More- from Munich. 9.5, World Theatre Brussels I and Radio Paris, 8.30, play founded on Sir Arthur Pineró s cambe. -VII, " Rosmersholm," by Ibsen. Franco-Belgian Exchange Concert. farce. 9.25, " Handel in Rome," Abroad. Reg., 6, Bird music played Songs from the Forestry TUESDAY, APRIL 26th. by a section of the Berlin II, International Contempor- Commission Boyd Ned Orchestra. Land near Bury St. ary Music, including Bax's Sixth Edmund's. 9.5, Songs from Nat., 8, Scrapbook for 1928. 9.15, Reg.. 6, Charles Heslop Requests the The Symphony. opera " Fallen Fairies," music by Budget-Sir John Simon. The Pleasure of Your Company," Edward 9.30, America Speaks. 9.50, Re- variety German, words by W. S. from Eastbourne. 8.30, SATURDAY, APRIL 23rd. Gilbert. cital by Laffitte, pianoforte. The Birmingham 9.50, Kneale Kelley con- Philharmonic Nat., 8, Music Hall, including ducts Reg., 6.30, Music from Czecho- String Orchestra. Albert the Eastbourne Municipal 9.15, Cabaret Sandler and Charles Hayes. 9.20, Orchestra. slovakia. 7.30, Peter Yorke and his from Bournemouth, including Jane American Commentary. 9.35, Tele- Abroad. Orchestra. 9, Old Time Music Hall. Carr and Douglas Byng. vision at Work, a Stuttgart, Abroad. Abroad. commentary by 7.15, " Aida,r' opera Thomas Woodrooffe on the attack (Verdi). Brussels II, 7, " Siegfried," opera Brussels II, 8, " The Rhinegold," on Zeebrugge, reconstructed at (Wagner). opera (Wagner). Alexandra Palace. MONDAY, APRIL 25th. Stuttgart, 9, Handel Evening. Milan Group, 9.0, " Don Carlos," Reg., 6, W. H. Berry in " Whose opera (Verdi), from Nat., 2, Speeches from the British WEDNESDAY, APRIL 27th. Venice. Hooper ? " 8, " My Eightieth Sportsmen's Club Lunch for Aus- Nat., 5.20, Henry Hall and his Birthday," by Dame Ethel Smyth. tralian Cricketers. 7, " Monday at Orchestra. 9.20, The Budget. FRIDAY, APRIL 22nd. 8.15, Sir Adrian Boult conducts Seven." 8.20, Fraser Darling Talk by Mr. Attlee. 9.30, The Nat., 7.30, " Lines on the Map B.B.C. "- Orchestra (B). 9, Victor Talks on " Wild Life Around Us." Melody is There. IV, Communications by Air. 8, As Silvester and his Orchestra. 9.20, World Affairs. 9.35, Jack Reg., 7.30, Band Waggon. on Thursday at 6 p.m.. (Reg.). 8.30, 9.35, Abroad. Hylton and his Band. " Norway," tracing Norse influence Robert Donat as the Man in " The Radio Eireann, 7.15, " When Handel Reg., 8.15, Hoffmann Concert from on the North of England, with Dark Lady of the Sonnets," by a Came to Dublin "-a play. the Queen's Hall, B.B.C. Orchestra special relay from Oslo. Bernard Shaw, the play preceded conducted by Sir Adrian Boult. Abroad. by a prologue SUNDAY, APRIL 24th. written and spoken 9.25, From Manchester Centenary by the author. Leipzig, 830, Bruckner's Eighth Nat., 10.45 a.m., Fred Hartley and Dinner, speeches by Earl of Derby, Symphony. Reg., 7.30, Dance Music from France. his Sextet. 11.30 a.m., Tollefsen, Lord Hewart, Mr. Lloyd George Warsaw, 9, Chopin Recital 8.30, European Concert by J. from Nor - accordion. 630, Bavarian Songs and the Mayor of Manchester. Smidowicz. APRIL 21St, 1938. WheIlc 67 WopIlcal Cambridge Union all those years ago got out what they were saying. It's only a their news only a matter of seconds late, one -valve set, however, with head -phones." which was pretty red hot for those days. Only a few weeks ago he again visited Mr. . .. X and there was the same " one -lung " set with a cat's cradle of wires running to the Atmospherics and the Short -waves accumulator and HTB on the floor and the [ONDEN5ER 5PECIAl,I5T5 Some time ago I reported that the short- same pair of head -phones resting on the FOR OVER THIRTY YEARS wave stations at Bombay and Delhi had arm of his chair. I have come across some had to raise their wavelengths to 90.77 and pretty ancient sets still in use, but I think 60.06 metres respectively for their evening that this veteran, which is probably about transmissions, which take place between fourteen years old, must hold the record 5.3o and II p.m., local time, or noon for long and continuous service. Until re- and 5.30 p.m. B.S.T. The change was cently I possessed a portable about eight made, if you remember, because the skip years - old which was employed for distance was found to be so enormous after occasional jobs and was very useful at dark when wavelengths in the 31 -metre times in the sickroom. This set, though, band were used. It will be interesting to had so frequently been brought up to date see whether the longer wavelengths are suc- that very few of its original bits and pieces cessful during the hot weather, which is were still within it. now under way. Atmospherics are poison- ously bad during this season in most parts Portables of Yesteryear of India, and it remains to be seen whether Talking of portables, do you remember they will not make it impossible to continue some of the early models ? Some of them using a wavelength so long as 90 metres. weighed 3o or 40 pounds and if you were Some valuable data concerning atmo- rash enough to take one to a picnic you spherics have been obtained by Mr. S. P. began to wonder after half a mile or so Chakravarti, of the University of Calcutta. across country whether portable was really He has recently set up cathode-ray direc- the correct epithet. One early portable of tion -finding equipment for the recording of which I have recollections made things a. atmospherics, and his present investigations bit easier since it was housed in two cases into the wavelengths below loo metres which could be carried separately. The which are chiefly affected by them should most ancient portables of all did not con- Two roads-twin roads-for one-way form an important contribution to our tain built-in frame aerials. You carried traffic-for SAFETY. knowledge. with you a coil of flex, a ball of string and .. . possibly a catapult. Your first business For precisely the same reason all wise was to hurl or shoot a stone with a string Radio Manufacturers (and all knowledge- Still Going Strong tied to it over a convenient branch. You able amateurs) use T.C.C. Condensers- AREADER sends me an account of then tied on the wire and hauled up. In for safety. T.C.C. reliability safeguards what must be one of the oldest receiv- 1927 Pye was making a 5 -valve portable reputations-T.C.C. performance is safe- ing sets still in service. He saw it first in with built-in frame guaranteed to receive guarded by 32 years of research - 1926 at the home of a friend to whom it Daventry anywhere in the British Isles-I 32 years of making and improving belonged, though it wasn't by any means wonder if they tried it in Cornwall ?-for condensers - and nothing but con- new then. His diary contains a note modest sum of £30 12s. 6d. The - to the Peto densers. After 32 years all T.C.C. the effect that in the hope of hearing the Scott " Sociable Five " was cheaper at users expect reliability. They get it. news on one of the early days of the X29 ros., but then it did not claim to General Strike he visited Mr. X and listened receive Daventry beyond 120 miles. By to it on his wireless set. " Couldn't make 1929 prices had come down. The " Sym- .. for the same reason that phony," whose reproduction was stated to approach very nearly to complete realism, wise setmakers and shrewd cost a mere £17 6s., complete with Lido - amateurs always use Blue stormproof cover! ti S ti A Finicky Job THE other day it fell to my lot to have to do one of those fiddling little jobs that sometimes come T.C.C. the way of those who make their own apparatus or keep it in repair. A ALL-BRITISH " dis." was found to have taken place in a tiny coil wound with No. 42 silk -covered wire. Inspection showed a break in the CONDENSERS wire, which was, luckily, at one of the ends of the windings rather more than a quarter of an inch from the tag which formed the fixed contact. There wasn't enough of the loose end to reach the tag, but it could just be made, without stretching it, to overlap for about a 32nd of an inch with a little piece of wire left attached to the tag. With a very fine bit it was just possible to solder the two together. I don't know whether you know the tip for making a soldering bit suitable for fine work of this kind. File off the point of an old soldering iron and drill in it a hole which is a push fit for No. 16 swg. copper wire. Cut off about an inch of this wire, insert one end into the hole and fix it firmly A PUBLIC ADDRESS van, used by the by hammering the bit. Shape off the pro- Stuttgart Municipality, carries two 15o watt truding amplifiers which provide enough power for end of the wire neatly. You now twenty of the city's permanently installed have a soldering iron which will do finicky jobs well. Owing its loud speakers. The van's equipment also to size, the original bit THE TELEGRAPH CONDENSER CO.LTD. includes two microphones and suitable points retains the heat, and the fine point, care- WALES FARM RD. NORTH ACTON,W.3 for another six ; two mixing desks, a double fully tinned, which protrudes from it, makes gramophone desk and a wireless receiver. miniature soldering jobs comparatively easy. 1M 4607 368 The Wireless World, April 21st, 1938

to the use of a high -frequency oscillator for converting the DC into AC, chiefly on account of its disturbing effect on the receiving set and timing circuits. Recent Inventions According to the invention the problem is solved by using an Brief descriptions of the more interesting radio plane of a" beam of wireless waves oscillator valve which generates used to " search " the sky. oscillations of the order of 2,000 devices and improvements issued as patents As soon as the search beam cycles 'a second. These are will be included in this section sweeps across the hidden machine stepped -up to the required voltage the downwardly reflected waves across a tuned transformer with a are picked up by a ground station laminated iron core, and then recti- " STATIC SUPPRESSORS" winding W on to a " composite " and are fed to two cathode-ray fied. The arrangement has the S.rATIC " disturbance from a screen, which consists of a fluores- tubes. These are so arranged that added advantage of enabling the " J dynamo or motor likely to cent material F backed by a electrons are only liberated when voltage supplied to the set to be interfere with broadcast reception photo -sensitive material S. The the rotating frame aerial points regulated simply by detuning the is suppressed by the arrangement electrons from C produce a fluores- towards the source of the reflected secondary of the step-up trans- shown in the Figure. A condenser cent light on the near side F of wave. Two luminous traces. are former. C is shunted across the mains sup - the composite screen, and this, in thus formed, one on each of the E. Michaelis. Application date, fluorescent screens, and are July, 11th, 1936. No. 47830o. turn, gives rise to a further emis- then o o o o Sion of electrons from the far or combined on an external screen in photo -sensitive side S of the such a way that their point of DIRECTIONAL AERIALS screen. A similar action takes intersection indicates the position THE Adcock system of direction - place at other intermediate screens of the hidden aeroplane. finding depends upon the use such as Sr, S2. The picture which E. Montu. Convention date of four vertical dipoles, which are is produced on the last fluorescent (Italy) January 3ist, 1936. No. erected at the corners of a square screen Fr is stated to be intensi- 478456. and are coupled in pairs through fied in brightness and is finally O 0 0 0 horizontal transmission lines to a projected by a lens Li on to an PIEZO.ELECTRIC OSCILLATORS central receiver. In the ordinary external viewing screen. - APIEZO-ELECTRIC crystal, way the arrangement is free from V. Zeitline, A. Zeitline and V. suitable for high -frequency the so-called " night error " caused Kliatchko (assignees of Cie pour control purposes, is cut with its by waves reflected down from the la Fabrication des Compteurs, etc., length parallel to the optical axis, Heaviside layer. d Gaz). Convention date (France) its width parallel to the Y-axis, It has been found, however, that May 18th, 1935. No. 478641. and its thickness parallel to the X - a certain amount of field distor- tion occurs at each dipole when the surrounding earth is not homo- geneous, owing to the creation of lines of force which are inclined at an angle to the earth instead of be- Filter for suppressing interfer- S2 ing perpendicular. This in turn ence from an electric motor. tends to vitiate the accuracy of the bearings taken. ply leads MS, one terminal of the a To overcome this difficulty each condenser being four dipole connected to the L1 of the aerials, such as earthed framework through parallel A, is mounted in a tripod stand T condensers Cr, C2 in series with in such a way as to allow of its inductances Li, L2. The series being set, by means of an adjust - combination is designed to act as a band-pass filter for frequencies A liable to create artificial interfer- ence and, in effect, by-passes them to the frame and so to earth. Since condensers arranged in this way can be made of lower value than those normally used for the same Details of photo -emissive electron multiplier. purpose, the risk of shock to the user of the machine or appliance TELEVISION RECEIVERS axis. The dimensions are so chosen is reduced. TH E fluorescent screen of a that the crystal possesses only a The British Electrical and Allied cathode-ray tube is not a single fundamental frequency along Industries Research Association plane surface, since it follows the the X-axis and another along the and L. H. Daniel. Application curvature of the end of the glass Y-axis, one of these frequencies date July 18th, 1936. No. 478646. bulb. Accordingly, when an opti- being a multiple of the other. o o o o cal system is used to project a Such a crystal can be used to HIGH -FREQUENCY magnified image of the picture on stabilize two different circuits at AMPLIFIERS to an internal viewing -screen, it widely different frequencies, say, at WHEN amplifying a wide band becomes necessary to correct for 200 kc. and z,000 kc., or at loo kc. of signals, as for instance the initial curvature in order to and 90o kc. respectively. It can, in television, a limit is set to the prevent distortion. - therefore, be used, for instance, to faithful reproduction of the higher According to the invention the align and calibrate the tuning -dial frequencies by the inter -electrode cathode-ray tube is mounted in the scale of a wireless receiver. .capacities of the valves, even receiving cabinet below the level Marconi's Wireless Telegraph when screen -grid valves are used. of the viewing -screen so that it is Co., Ltd. (assignees of C. F. Bald- To overcome this difficulty, a out of sight of the observer, and win and S. A. Bokovoy). Conven- screen-grid " buffer " ' valve is an ordinary magnifying -lens is tion date (U.S.A.), June 29th, arranged between two successive used to project the picture up- 1935. No. 476889. amplifying stages. Although this wards. The viewing -screen, how- o o o o Method of mounting Adcock di- does not add to the effective am- ever, is made slightly convex in pole so that the aerial can be plification, it serves to minimise the direction of the observer, and MAINSSUPPLY UNITS tilted. the capacitative load of one ampli- this serves to offset the inherent RELATES to means for obtain- fier on the other, and so prevents distortion due to the curvature of ing sufficiently high voltages ing screw S, at a slight angle to any falling -off in the proportion of the fluorescent screen. from direct -current mains to the vertical, as shown in dotted high frequencies to low in the E. Michaelis. Convention date operate a television set. The known lines. final output stage. (Germany) June 12th, 1936. No. type of vibrating -contact rectifier C. Lorenz Akt. Convention date P. W. Willans; A. J. Brown; 477814. is said to be inefficient and un- (Germany), July 18th, 1936. No. and Baird Television, Limited. o o o o stable. Objections are also taken 479330. Application date July 7th, 1936. DETECTING AEROPLANES BY No. 477815. RADIO o o o o T11E, presence of an aeroplane The British abstracts published here are prepared with the permission " IMAGE INTENSIFIERS" hidden by fog or cloud is of the Controller of H.M. Stationery Office, from Specifications APICTURE P is projected by a detected, and its position deter- obtainable at the Patent Office, 25, Southampton Buildings, London, lens L on to a photo -sensitive mined, by a method of direction - W.C.2 price 1 - each. A selection of patents issued in U.S.A. is cathode C, where the emitted elec- finding which depends upon the also included. trons are focused by an external reflection from the invisible aero - The THE PRACTICAL RADIO JOURNAL 28 th Year of Publication rcrldF-4-4,tg.Zoa +/// /1l l

No. 974. THURSDAY, APRIL 28TH, 1938. VOL. XLII. No. 17.

Proprietors : ILIFFE & SONS LTD. Editor : EDITORIAL COMMENT HUGH S. POCOCK. Editorial, Advertising and Publishing Offices : we should feel some misgivings as to DORSET HOUSE, STAMFORD STREET, Interference Suppression whether Post Office enthusiasm over the LONDON, S.E.i. matter of electrical interference suppres- Telephone: Waterloo 3333 (So lines). Post Office Enthusiasm in sion is as great as it formerly was. In a "Ethaworld, Telegrams: Sedist, London." Jeopardy recent issue we remarked that the Post COVENTRY : Hertford Street. Office was becoming commercially minded Telegrams: Telephone: to an extraordinary degree. Post Office "Autocar, Coventry." 52ro Coventry. THE Postmaster -General, as the authority for trading profits, we said, break fresh wireless licensing records every year, BIRMINGHAM : has shouldered and these achieve- this country, ments Guildhall Buildings, Navigation Street, 2. responsibility for taking whatever call forth unstinted admiration on Telegrams : Telephone: all sides. We expressed the view that so "Autopress, Birmingham." 297e Midland (4 lines). steps are possible to reduce electrical inter- long as the Post Office confine ference which so seriously spoils the enjoy- continued to its activities to the development of those MANCHESTER: 260, Deansgate, 3. ment of broadcást listening. It is some Telegrams: Telephone: sections of its services in which it has an "IIiee, Manchester." Blackfriars 44x2 (4 lines). years now since this journal, recognising exclusive field, it was unlikely its the menace of electrical interference to the that suc- : 26R, cesses would be hailed with Gummy Renfield Street, C.2. future of broadcast reception and appre- anything but Telegrams: "Iliffe, Glasgow." Telephone: Central 4857. satisfaction. ciating that as the use of electrical appli- PUBLISHED WEEKLY. ENTERED AS SECOND ances increased so the matter was becom- CLASS MArrER AT NEW YORK, N.Y. ing more and more urgent, recommended Circumstances Have Changed Subscription Rates : that the only satisfactory way of tackling Home, LI Is. 8d. ; Canada, £r is. 8d. ; other the problem would be by the introduction Recently, however, and long since com- countries, LI 3s. rod. per annum. of legislation. Under the terms of such mitting itself to the task of eradicating legislation the Postmaster -General would electrical interference, the Post Office has As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before be given the necessary authority to oblige shown determination to develop relay making use of them, to satisfy themselves that they mould not be infringing patents. those responsible for causing unnecessary broadcast services throughout the country interference, whether users or manufac- on a big scale. In conformity with the turers of electrical apparatus, to take practice in their other enterprises these reasonable preventive measures. relay services would undoubtedly be con- ducted on a commercial basis with a view CONTENTS to profits on the undertaking. There is The First Steps no disguising the fact that, in a very large Page measure, the success of a relay under- Editorial Comment 369 There seemed at the time to be so much taking would be in proportion to the uncertainty about how the matter should decline in the business done by inde- Balance and Control at Home.-I 370 be tackled that we put forward the sug- pendent wireless receiver manufacturers. The Home Laboratory.-II. Valve gestion that the Institution of Electrical Now it is well known that relay services Voltmeter Construction 372 Engineers, as representing practically all thrive in districts where electrical inter- the interests concerned, should appoint a ference is severe, and that where reception Electrostatic Deflection .. 375 Committee to go into the question in detail by means of a broadcast receiver can be Unbiased .. 377 and pave the way for legislation. This obtained without local disturbance there Decca PT/AC Set Reviewed .. 378 suggestion was acted upon and the Institu- is little room for a relay service to suc- tion formed a Committee of a widely ceed. How, we may ask, is the Post " . Not as Other Men" .. 380 representative character. This Committee Office to be expected to exert every effort Television Topics.. 381 deliberated for a long while, and ultimately to suppress electrical interference for the reported in favour of legislation. We now benefit of users of broadcast receivers of the Week .. News 382 await the presentation to Parliament of a when such success must adversely affect Random Radiations 384 Bill, having this object in view, which will the progress of their commercial enterprise On the Short Waves 385 be sponsored by the Postmaster -General. in connection with relays? And the There is so much delay in pushing on situation is not simplified when we remem- Valve Nomenclature .. .. 386 with this matter that it is perhaps not ber that the same department of the Post Recent Inventions.. .. 388 unnatural if, in the light of recent events, Office deals with both these matters. 370 The IFireless World, April 28th, 1938 Balance and Contro THE resonance and echo character- Part I.-INFLUENCE istics of the listening room may OF ROOM CONDITIONS have a profound effect on quality of ON RESPONSE reproduction ; means of making the best of local conditions are discussed . instance, the buyer can detect no differ- the set ; usually the former will be more in this . article, while a succeeding ence in quality between two amplifiers of marked in small rooms and the latter in instalment will discuss questions of different performance, it is both logically large ones. For many types of programme audio frequency output- and speaker and practically wrong for him to choose a certain amount of these two is very efficiency. the dearer, simply because he is informed helpful, such items as the organ and large that it has a better response. instrumental combinations being rather As an instance of how mere figures can improved by it, but for speech it is unde- VERYONE who has a wireless set mislead, take the case of two listeners in sirable in any large amount, reducing the wishes to obtain reproduction as a concert hall, one near the front and the intelligibility and lending an unnatural nearly perfect as possible, yet other at the back. These two receive the coloration to scenes supposed to take place it seems that seal perfection will music at very different levels, and it might in the open air. It is lucky that the aver- never be attained in the home, even if appear that they would hear diverse inter- age room, conventionally furnished with it were desirable, since it would demand pretations ; actually, if they are used to carpet, curtains and upholstered chairs, concert -going their ears will , make due has a reverberation time well the re-creation of all the . conditions, suited to the allowance for the position, and they could majority of ' visual, audible and mechanical, present items broadcast-perhaps it at the original performance. For instance, discuss the interpretation the conductor would be fairer to the B.B.C. to say perfect realism of an organ finale could had given without difficulty. not be attained without re-creating the Passing . to the detailed . characteristics of the hall. However, ex- conditions of .recIption, we ENE ceptionally fine quality can be achieved find that a scientific analy- R-xs within a small room, if suitable steps are sis of, the acoustic constants taken to use the set to the best advan- of . one room would cost more than the set, so it tage, this being possible owing to the that 70 is not possible to indicate R -s.000 n ' .I ability of the ear to compensate for con- positively the response re- R . 250 siderable discrepancies. 15 R -on It is a common fallacy to suppose that quired for each case, but the " straight-line " response in set and am- general principles can be given, and the reader will be plifier would necessarily give perfect re- s e s e e production. As with all fallacies, there is able to select the treatment required in his particular a kernel of truth in this one ; but the con- FREQUENCY IN CYCLES PER SECOND ditions obtaining in the listening room instance. affect matters greatly, and balance is The first point to con- often improved by deliberate departure sider is the position of the Fig. 2.-Amount of top cut introduced by a o.of mfd. con- from linearity, in particular by lilting the speaker ; if this is in the set denser, in series with the various resistances shown, across an impedance of response curve to correct for the deficien- it must naturally be handy 3,000 ohms. cies of the speaker and the " liveliness" to aerial and earth connec- of the room. tions, and convenient for tuning, which " natural " rather than " lucky," since Since the action of the ear is as much somewhat limits the choice, but a separate this is largely due to their efforts. The physiological as mechanical, there can be speaker is more flexible : and may be author well remembers the difference no absolute standard of perfection, apart mounted anywhere desired. Experience observed in a room where the floor, which from the listener himself, and the ear must shows that, in general, an artificial effect had been hitherto covered with linoleum, always be the final arbiter. If, for is caused if the sound comes from above was carpeted over more than half the area, or behind the listener, for our ears are for average items the conditions were directional in their response, especially at greatly improved, but the amplifier the higher frequencies. If two speakers characteristics had to be considerably are used they should be as near together altered before a large orchestra sounded as possible, having regard to the minimum natural, and even then the effect was not distance needed to prevent interaction, "so realistic. since a very distressing effect is produced Microphone curves of response taken in on many people if two sound beams inter- a room should be accepted with some sect near them. A separation of eight to reserve since the setting up of standing twelve inches is enough. waves may cause variations not matched by the ear, due to the fact that both ears Mounting the Loud Speaker are in use ; also there are not many occa- sions when a note low in pitch is sustained The ideal position in most homes would for long periods. be in the chimney-breast ; this is .difficult Most readers will be familiar with the to arrange in the usual circumstances and spurious resonances caused by' such ob- a recess at the side will be a good substi- jects as vases, which are sharply tuned tute. Speakers directed downwards from and re -radiate a certain note in their imme- the ceiling seem to be lacking in natural- diate neighbourhood. There is another ness, however good their response. Fig. 1.-Method of introducing top cut by manifestation of the same nature which connecting a resistance -capacity filter across Every enclosed space has to some extent may cause coloration of the programme the primary of the output transformer. the . properties of resonance and echo, if a high level is used ; a piano can cause Ci, 0.1 mfd. ; R1, 0-25,000 ohms, variable. which will modify the normal quality of a large number of resonances when it is The Wireless World, April 28th, 5938 371 tt Home By R. H. WALLACE

near a speaker giving a high acoustic output. Although the strings are damped, when not struck, by pads of felt they can still vibrate in such manner as would leave a node at the point of damping. This point varies, but in the case of the lower notes is such that harmonics of the order of the fifteenth can sound. These harmonics of the lower half of the key- board all lie well within the audible range, although they are weak compared with the strength of the fundamentals. When a piano is in the room, and a large volume is used, it should therefore be as far from the hearer and loud speaker as possible. Since the local factors are so variable it is impossible to design the set precisely to suit them, and it is essential, for the best results, to adjust the response in the room in which it will be used. Here is the designer's justification for a normally level output, since a set with such charac- teristics will not sound really bad, and gives us a good starting point from which to begin our modifications. In the final Photo by cours^sy Boumlans stages of this job the help of a friend with The modern " made to measure " furniture lends itself well to the incorporation of a radio set and in some cases adds considerably to the effectiveness of the baffle. a good musical ear is invaluable, since one is apt to imagine the result one knows should follow a given -alteration, while an increase the proportion of top by means in the coupling constants of the amplifier. independent observer is not so handi- of a tweeter speaker, fed through a con- In a concluding instalment the author capped. denser of 0.25 to o.01 mfd. capacity ; the will discuss the amount of AF output re- value will give a measure of the amount quired for good reproduction under Methods of Compensation of top introduced. The condenser should various conditions. be connected across the In the absence of real tone controls in primary of the output trans- the set the following are some of former. The same effect u the 0.2mId methods useful in specific cases, or a tone can be achieved, if the exist- control unit, such as was described in ing speaker has a good top 5 .02 ne The Wireless World, can be constructed response, by reducing the and the best combination value of a coupling con- found by trial. 10 0.1 mfd Suppose the room is too " dead " and denser in the amplifier sec- eproduction lacks brilliance, then we can tion so that the lower notes 15 ' will be cut in proportion to the higher ones. On the other hand, if s there is too much top in the s i i $§ R R 1 k reproduction the balance can be corrected by a re- sistance -capacity filter across the primary of the speaker Fig. 4.-Amount of bass cut introduced by the circuit of transformer, or, more ele- Fig. 3, when the values of coupling capacity shown are used. gantly, by boosting the lower frequencies in the amplifier itself. There are strong reasons for suggest- ALL -WAVE MODULATED ing that the tone controls, if fitted, should TEST OSCILLATOR be regarded rather as preset than panel controls, and if the set is suitably In next week's issue full con- balanced they should rarely need altering structional details will be given for radio reception ; a better control for of a modulated test oscillator varying conditions being afforded by covering some ioo kc; s to 30 Mc; s manuipulation of a variable -selectivity (3,000 -ro metres) in six bands. device in the RF circuits. Dry battery operation is adopted,

The alterations suggested in this and . the two valves are used in such a way that the output con- Fig. article cannot be made without some 3.-A resistance -capacity AF stage ; trol has no effect on the os_illator reduction of Cr from the normal value will trouble but are well worth while, and will give a controllable bass cut. Ri, 30,000 provide a good insight into the effects frequency. ohms ; R2, 5 megohm ; Ci, 0.o5-o.z mfd. caused by small experimental alterations -1 -37' The Wireless World, April 28th, 1938 The Home Laboratory Part II-Constructional Details By M. G. SCROGGIE. of a Novel Slide -back Valve B.Sc., A.M.I.E.E. Voltmeter

L THOUGH the circuit diagram (seee EXTERNAL MICA BUSH VOLTMETER Fig. i) of the slide -back voltmeter GRID to be described may look alarm- SWITCH ,INDICATOR WINDOW , ingly complicated, that is only EXTERNAL SHORTING BUTTON because a highly developed form is shown, VOLTMETER including such things as provision for the 'EARTHY" use of either of the two types of valve RANGE BIAS ADJUSTMENT recommended. If preferred, a much SWITCH EARTH simpler version can be made by omitting such optional features as the duplicate valves and the DC voltmeter with its range switching. The outstanding advantages of this instrument are : - TN the preceding The front of (i) The calibration is practically un-: article the the affected by supply vglfa,es and valve valve voltmeter, author discussed showing functions characteristics. . the various kinds of valve of the various voltmeter, reaching the COARSE FINE (2) Nearly infinite input impedance. ON- OFF controls., conclusion that the slide - SLIDE -BACK (3) Measures from o.s to 25o volts peak. back type of instrument has much (4) Can be extended Upwards to read in its favour, and that most of any voltage in reason. its weaknesses can be overcome by suitable Incidentally, the above figures are for the _(5) No design. The construction of a slide -back meter microammeter needed, and even valve hot ; if it is switched off which employs - an inexpensive cathode-ray they alter DC voltmeter - optional. indicator is fully described in this instalment. very slightly towards a lower impedance.. (6) Meter, if incorporated, cannot be If for economy the acorn is omitted, overrun. provision should be made for improving (7) Measures at any frequency up to the HL4g for high -frequency use by zoo Mc / s or more and down to zero (DC). able to . enjoy the best of both worlds ; cutting out the indirect connection, and ';For use at very -high frequencies, especi- where minimisation of losses is important perhaps by using the . " probe " mounting ally those over 30 Mc / s, and across very the acorn is used at the end of a cable shown here for the acorn. If both valves low -loss circuits, the " acorn " valve offers plugged into the panel, so that it can be are fitted, whichever is not in use ought substantially higher input impedance than brought right to the work instead of hav- to be withdrawn. those of conventional construction, partly ing to be connected by high -frequency because of its low grid -to -other -electrodes leads. The input resistance of the instru- The DC Voltmeter capacity (2-4 mmfd., compared with 7-16 ment, measured at i Mc / s, is nearly The slide -back voltage controls are mmfd.), and partly because of its reduced io megohms, and the capacity mmfd. is 4 calculated for use in conjunction with a electron transit -time effect (typical input Connection is direct to the grid, of course, voltmeter taking 5 mA at full deflection ; resistance at 6o Mc / s is 45,000 ohms, for it is used chiefly across closed tuned and alternative schemes are to use an circuits. For low fre- external DC voltmeter, with quencies a calibration or high voltages, curve for the lower voltages, or omit or where an indirect to the connec- voltmeter entirely and use a simpler form tion is necessitated by a of potential-divider calibrated superimposed in volts. voltage or This device then really earns its common the absence of a closed cir- title of "potentiometer." The cuit, and last generally where method is not highly accurate, of the use course, of leads and a some - but for many purposes it is not really essential to have a calibration at all. The Reliance Manufacturing Company By using a flexible can supply a set of potentiometers ; a " probe " the grid single one of 500 ohms for initially adjust- of the voltmeter ing the bias to " zero," a double gang of valve may be Zoo ohms each for covering the lowest placed "on the job," thus avoiding range and for fine adjustment on the other long live leads. ranges, and a triple gang of 2,000, io,000 and 50,000 ohms for these three ranges. A Ferranti instrument switch controls the range of the meter and simultaneously connects the appropriate potentiometer. compared with 5,000 ohms). On the other what lower impedance are not objection- The last switch positio-i is vacant and hand, it is a more expensive and delicate able, the internal HL4g is more con- permits an external source of volts and/or valve, and it should not be used for venient. Its input resistance, including voltmeter to be connected. ' The photo- measuring voltages over about ioo. the associated circuit, also at i Mc /s, is graph shows a switch for changing from With the instrument illustrated one is 1.9 megohms and capacity ii mmfd. internal to external voltmeter or both in APRIL 28th, 1938 Unzishoo 373 Woptd. - The Home Laboratory- current flows which, with the r megohm valve; comparatively large capacities are parallel, but it has been omitted from the in circuit, biases the grid slightly, the illu- fitted in the body of the instrument in diagrams as being superfluous. minated area when there is no other bias order to cope with low frequencies, but to Another object of the " External Volt-. than this being somewhat as shown in by-pass the flexible cable for very high meter " terminals is to render the o -250 - Fig. 2. Although this corresponds to frequencies condensers of 0.0005 or 0.001 volt supply available externally for other zero anode current in the valve, for rea- mfd. are connected in the " probe " in uses. sons already given it is not advisable to such a way as to give the most direct The general working of the apparatus try to adjust to this condition, but rather paths.

20H 20 rn A

0.01 ild 0-1) n ON 3 OFF SWITCH mtd INPUT NEON tI LAMP B mlds 525 Y Z0, A MAINS

pO

500 0 BIAS ADJUSTMENT

200 Sf MAX. 0-SmA ----60,0000 2w 12,00000.5W RANGE Fig. 0 025° r.-Complete circuit diagram of valve 25,00 (! 2,400 Sf voltmeter illustrated. The lower r5,000 -ohm EXTERNAL 8 resistor should be rated at 5 watts. VOLTMETER FINE 50 9400 S? 2.5 250 COARSE

8 LIA 2000 and use of the " magic eye " as a sensitise to some such current as a third of a micro - The larger condensers serve additional indicator for setting the anode current of amp. This can be judged by reducing purposes ; the one from " earthy " ter- the valve to a fraction of a microamp. the valve bias slowly until the start of minal to cathode (across the slide-back), was described in the previous article. current is clearly seen by an appreciable in co-operation with the 25,00o -ohm resist- The TV4 differs from most other increase in illuminated areas, the bound- ance, removes any ripple left over from cathode-ray indicators by displaying a aries of which can be marked on the glass the smoothing filter. The anode -cathode pattern resembling a Maltese cross, the condenser 'prevents any AC component effect of greater negative bias being to from blurring .the outline on the TV4 widen the illuminated sectors and narrow Fig. 2.-Type of visual screen: An excessive capacity here makes the arms of the cross. For instrumental indication given by the the indicator sluggish. It is vital for the TV4 tube. The slide - purposes this form of indication is not back is adjusted until condensers to be free from appreciable quite so suitable as the single sector of the boundaries of the leakage, . and the valves should be free other makes of tube, but, unfortunately, pattern coincide with from " backlash " (i.e., negative grid they have a much larger grid bias and the marks. The dotted current). If one cares. to take the trouble circle indicates the correspondingly lower sensitivity. It is position of the viewing to test for such leakage currents it can be best to concentrate on one of the four arms window in the panel. done with a TV4 in much the same way of the cross, viewing it through a small as the small anode current is detected. window as shown by the dotted circle in The supply voltages to valve and indi- Fig. 2. at the end of the tube in Indian ink or cator are stabilised by the " beehive " If the grid of the TV4 is short-circuited other convenient manner. neon lamp, which must be ordered to cathode the illuminated sectors narrow By-pass condensers are used to form without internal resistance and connected almost to lines. A certain amount of grid short high -frequency paths around the so that the wire spiral is illuminated. If WfipeIl®22 APRIL 2811t, 1938. 374 WczIld The Home Laboratory- there are suitable low -loss switches, but Assuming a " zero " current of about the disc glows the lamp should be the one shown was extemporised and half a microamp, a is not greater than reversed. arranged, after considerable thought, in 1 by wpm than about i per cent. ; b de- As the peak voltage across the first such a way as to introduce a minimum pends on the valve, but is normally power filter condenser normally exceeds of extra capacity and loss. When pushed about 0.5 to 0.7. So for voltages 500 volts slightly it should be rated to in it stays in and keeps the input shorted above the region of 20 there is not work at 525 or preferably higher. till it is released by depressing slightly more than about i per cent. error in (Fig. 3) . The grid terminal is mounted taking V, = Vs, and only a DC volt- on a piece of selected mica. meter is needed for calibration, which may The voltmeter is scaled to read peak quite well be more accurate than a calibra- volts directly, the maxima for the ranges tion on AC. In fact, from 2 volts upwards MCA being 2.5, Io, 5o and 250 volts. It could, the accuracy is still quite useful. The 0'07 mfd MICA GRID CONDENSER of course, be scaled to volts TERMINAL read RMS lowest range, however, definitely requires by dividing the readings by 1.404, but AC calibration, which can be done by SHORTING they would be liable to error when dividing off the 5o c / s supply by means BUTTON 4MG measuring distorted wave-forms. of known resistances, or in any other way The initial adjustment before using that may be available. The scale shown EARTHY the apparatus is to have the slide - was calibrated with a HL4g valve, and was TERMINAL back controls at zero and set the bias found to hold good for such a different control until the indicator registers with valve as the Osram HAI acorn by adding INSULATING BUSHES the " zero " marks. This adjustment o. i volt to all readings. A signal of 0.1 PANEL usually needs to be done only at the start, preferably Fig. 3.-Showing how the short-circuiting after about five switch is arranged to minimise input minutes' warming - capacity and losses. up, but differs ac- Sometimes one wants to apply a valve cording to which voltmeter to pöints that are live to earth valve is in. use. (e.g., acctoss a 'coupling in an anode cir- When a voltage to cuit) and the " works " are therefore be measured is ap- insulated from the metal case, but can plied the illumina- optionally be earthed to case by joining tion advances, and the " earth " and " earthy " terminals. If it is considered ' orth while using a Fig. 4.-Panel drill- 6 -pin socket, the cable screen and metal ing diagram. Sizes : casing of the " probe " can be treated A, 2a in. ; B, in. ; C, á in. ; D, *in., likewise ; with a 5 -pin socket the next best Belling -Lee ter- " for thing is to common it with the " earthy minals ; E, I in. ; F, lead. The transformer screen and valve fixing holes; G, j in:; metalising are joined to cathode. H, rin. ; J, 2$ in. The probe is built up of part of a suspension lamp fitting, the ZEGTIFIER flange of a bat- - ten holder, a shade ring, and a strip of copper sheet soldered

volt produces a deflection on the lowest POWER NEON LAMP range, but the scale is very cramped as TRANSFORMER far as 0.5 volt. SMOOTHING Although there is a good deal of lati- CHOKE tude in the choice of some of the com- ponents used, the following list of the more important items may be helpful *f -TV4 INDICATOR :- Bias control Reliance type TW, so0 ohms ELECTROLYTIC Fine slide.back control CONDENSERS HL4g VALVE (200200 ohms (double -gang) Reliance type TW ohms Coarse slide.back control (triple -gang) 50,000 ohms around to form the Reliance type TW ro,000 ohms portion. l2.000 ohms cylindrical Interior view of Meter Ferranti o-5 mA It is useful to be the meter. Range switch Ferranti Type 6 able to short-circuit Case Eddystone 1033 the input to the Power transformer N. Partridge Special is brought back by 4 Volt i A, 4 volt r A, 380 volt 20 mA valve, especially Smoothing condensers Dubilier 0288 with the indirect adjustment of the S=way cable plug Bulgin P36 connection, for it slide -back controls. Resistance, 15,000 ohms Bulgin. PRI2 can then be done without risk of shorting For large voltages the relationship Detector valves between signal peak voltage - Tungsram HL4g, Osram HAI any DC supply included in the circuit V, and slide Rectifier valve Dario SWl being tested, and a button is provided on back voltage V, is given approximately by Tuning indicator Mullard TV4 the panel for this purpose. Possibly VB=aV,=b. Neon lamp Osglim 59 The Wireless World, Agil 28th, 1938 375 electrostatic Deflection WITH PARTICULAR REFERENCE TO HIGH -VACUUM TUBES

ATfirst sight the problems connected stant depending on the geometry of the with the electrostatic deflection tube, and V is the potential through of a beam of cathode rays would which the electrons have fallen. Thus. appear to be capable of solution in order to determine the sensitivity of by means of very simple circuits. That the pair of plates further from the screen, these problems are, in fact, not easily a factor dependent upon the instantaneous solved has become increasingly apparent effective potential on the live deflector as the cathode-ray tube has been nearest to the screen must he added to the developed. voltage off the final anode in order to As is often the case, the elimination of obtain the correct value for V. one fault in the cathode-ray tube has The foregoing remarks will be more brought to light others easily appreciated if it which were previously is N explanation of the causes borne in mind that masked by still greater the electrons forming faults. The change of image area; distortion and astigmatism in cathode-ray the beam are controlled from gas - focused to tubes, with by the electric fields high -vacuum tubes and suggestions for over-' through coming' these defects. which the y the gradual develop- pass, and these fields ment of the latter has control t h e velocity By O. S. PUCKLE, A.M.I.E.E. made it obvious that the application of of the beam in the plane of the field con- an asymmetric deflection . potential, cerned. Hence, the beam of electrons When two pairs of deflectors are con- whether AC, DC or a mixture of both, is attains various velocities in different parts nected asymmetrically, as shown in unsatisfactory in the majority of cases, of the tube. Electron velocity is usually Fig. i, and fed with two DC potentials e.g., where the amplitude of deflection is expressed in " equivalent volts," the which may be separately varied, the re- more than about ro per cent. of the screen appropriate voltage at any point in the sultant area of the image will be 'like a diameter. path of the beam being that through which quarter of a trapezium. Fig. 2 will make The circuit arrangement adopted for the electron has fallen on its passage this clear. Assume that the potentials asymmetric application of the deflecting from the cathode. Thus, if there is -a on the two deflectors X and Y may be potentials is shown in Fig. r. When two difference of potential of 5,000 volts be- varied from o to roo volts positive with deflecting systems are arranged so that they tween the final anode and the cathode, respect to the potential of the anode to lie mutually at right angles to one another the electron velocity at the anode is ex- which the other two deflectors are con- pressed as being 5,000 volts. . The elec- nected. Let (b) denote the position of trostatic deflectional sensitivity is 'in- the spot when deflector Y is at a potential versely proportional to the square of the of zoo volts and X at zero potential. If electron velocity at the point at which the Y remains at roo volte positive and the deflecting field is applied, it being, of same potential is applied to X the spot course, crnderstood that the deflecting will move to position (c). Note that the field appe_ars at right angles to the direc- distance (cd) is less than the distance (ab), tion of motion of the beam. because the, sensitivity of the Y deflector has been reduced due to the potential on Influence of Various Fields X. If, now, the potential on Y be re- duced to zero, leaving that on X at roo The velocity of the beam at any one volts positive, the spot will move to posi- point along its length is tion (d). Upon removing Fig. z. Asymmetrical connection _of two actually a com- the voltage pairs of deflector plates. pound one, due to the original radial from the X deflector the spot returns to velocity acquired by the electrons when position (a). and in such a manner that one pair of emitted from the cathode, the sum of the If the circuit is arranged so that the deflectors is nearer to the fluorescent longitudinal velocities due to the various screen than the other, a change of mean accelerating fields existing between the potential of the pair nearer to the screen focusing electrodes and the transverse modulates the sensitivity of the other fields produced by the potentials applied pair. The arrangement behaves as to the deflectors. .though the velocity of the electrons in There are also several minor; fields the beam between the plates nearer to the which still further complicate the force anode was modulated by the variation of acting on the beam ; the more or less mean potential of the other pair. A longitudinal decelerating field due to the change of mean potential necessarily charge acquired by the fluorescent screen occurs in an asymmetric system since one by electron bombardment, the fields plate of a pair is constantly varying in produced by charges on the surface of the potential, the voltage on the other plate glass together with that due to the remaining fixed. The deflectional-sensi- presence of secondary electrons emitted tivity of a pair of deflectors in a cathode- from the screen, and, finally, the radial ray tube is equal to where K is a con- field due -to mutual repulsion of the elec- Fig. 2. Deflection of the beam by the V trons forming the beam. arrangement of Fig. 1. wpeggg APRIL 28th, 1938. 376 wollte Electrostatic Deflection- mean potentials between each pair of Details connected with the manufacture plates are fed with AC potentials (the deflectors and the anode are not only con- of the tube :- potential on Y being at a higher fre- stant, but that they remain fixed at (a) The beam must be circular in cross-section. quency than that on X), thus causing the specific values. (b) All the electrons in the beam must pass a given point with the same longitudinal X and Y deflectors each to become Astigmatism has the same meaning in velocity. alternately positive and negative to a electron -optics as in light -optics, i.e., it (c) All the. fields through which the beam passes peak potenial of, say, -Too volts, then the denotes the condition existing when one must he homogenous. " area covered by the image is as shown in obtains good focus in one direction and (d) The electrode structure should be in per- of in direction at right angles fect alignment. Fig. 3, i.e., a 'complete trapezium. It lack focus a (e) The electrode apertures must be perfectly should be noted that the long edge of the to the first. Astigmatism may be intro- circular. trapezium lies adjacent to that X plate duced by certain transverse fields, and Details connected with the use of the which is connected to the final anode of especially by any misalignment of the tube:- the tube. electrodes forming the electron lens (f.) Except for very small deflections the two The use of these simple asymmetric system. Furthermore, asymmetry -of deflecting potentials must be symmetri- deflecting systems also introduces, at position of, the deflectors with respect to cally applied; and, finally, (g) The mean potentials of the two pairs of least theoretically, two ,forms of distor- the hole in the final anode is a serious deflectors should be constant and should tion of the spot on the screen ; an enlarge- cause of defocusing of the spot. bear definite but unspecified relationships ment, of the spot and astigmatism, or The amount of error in electrode to the potential of the final anode. drawing out of the spot into a line in the alignment which can produce astig- direction of the deflection. matism in a cathode-ray spot is so small that the majority of tubes supplied by any Television Programmes factory show some signs of this defect. For this reason it is advantageous to be Vision Sound able to correct astigmatism in the circuits 45 Mc/s. 41.5 Mc/s. external to the tube. To this effect, it is THURSDAY, APRIL 28th. necessary to arrange that the mean 3, Intimate Cabaret. 3.25, British Movie- only tonews: 3.35, 141st edition of Picture Page. potential between each pair of deflector 9, " Marshal your Facts," with Arthur Marshall, plates and the final anode may be Wendy Toye and Charles Heslop. 9.30, separately adjusted. By this means, we Gaumont -British News. 9.40, 142nd edition of introduce two variable cylindrical lenses Picture Page. 10.15, News Bulletin. at right angles to one another which can FRIDAY, APRIL 29th. be adjusted so as to neutralise the effec- 3, " Ah! Wilderness," a comedy by Eugene tive cylindrical lens action introduced by O'Neill ; cast includes Percy Parson, Kitty De Legh and Joan Miller. 3.50, Gaumont -British small displacements of the electrode News. true alignment. system from 9, Herbert Sutcliffe, the cricketer, shows " How The_ necessity for adjustment of the It's Done." 9.5, Intimate Cabaret. 9.20, mean potential of each pair of deflectors British Movietonews. 9.30, Russell Thorndyke to a fixed value with respect to that of the in his play ' The Tragedy of 'Mr. Punch." 10, News Bulletin. Fig. 3.-Shape of the area covered by the final anode is unfortunate since it adds image with alternating deflecting potentials. to the complexity of the associated circuit, SATURDAY, APRIL 3oth. deflections are required, 2.27, O.B. from Wembley Stadium of the but, where large F.A. Cup Final between Preston North End and It should be clear from the foregoing the resulting improvement in focus is Huddersfield Town. -4.40-4.55, " The Three remarks that trapezium distortion is due to generally appreciable. The potential Bears," a short ballet to music by Eric Coates the fact that the mean potential between required for this purpose varies with and choreography by Joy Newton. the deflectors is not constant with respect different tubes even though they are made 9, Intimate 'Cabaret. 9.30, Gaumont -British to the ,final anode of News. 9.40, Commentary on Darts Match between a B.B.C. Four and a Team from the the electron lens Press.Clúb. 9.55, Cartoon Film. 10, Repetition system. of 4.4o p.m. programme. 10.15, News Bulletin. The mean potential SUNDAY, MAY 1st. can obviously be kept 8.50, News Bulletin. 9.5, David Seth -Smith constant by applying ti presents " Friends from the Zoo." 9.20-10.30, the deflection in a Tobias and the Angel," a play by James Bridie ; cast includes Tyrone Guthrie, Jean symmetrical manner Cadell and Frank Bennett as Tobias. to both plates of each MONDAY, MAY 2nd. pair, but the word X Y Y ti 3, " There's always Juliet," a comedy by John I " symmetrical" re- Van Druten ; cast includes Leonora Perrycoste, quire to be accepted T Leonard Corbett and Michael Shepley. 3.50, ' INAL ANODE British Movietonews. . F in its literal sense. -FOCUS ELECTRODE This meals that the - EIFIRST ANODE 9, Starlight. 9.10, Talk on Fashions. 9.35, \ tr EGR ID Gaumont -British News. 9.45, Harriet Cohen two potentials must be -7.21.E.---CATHODE with the Television Orchestra. 10.10, News equal at every Bulletin. ASTIGMATISM TUESDAY, MAY 3rd. CONTROL S 3-4, " Acis and Galatea," a pastoral with music Fig. 4.-Method of by G. F. Handel performed as a masque ; cast correcting for astig- includes Parry Jones and\Isobel Baillie. matism. 9, Starlight. 9.10, " In your Garden "- C. H. Middleton. 9.20, British Movietonews. 9.30, Repetition of Friday's 3 p.m. programme. 10.30, News Bulletin. or, alternatively, that their algebraic sum to the same design. Fig. 4 shows one WEDNESDAY; MAY 4th. must be constant. method of arranging the circuit to provide 3, Forecast of Fashion. 3.15, British Movie- Unfortunately, however, the above means of adjustment. tonews. 3.25, Jack Jackson and his Band considerations, while sufficient to avoid In conclusion, the following details 3.55, Cartoon Film. trapezium distortion, are not enough to must receive meticulous attention if the 9, Repetition of 3 p.m. programme. 9.15, ensure the best results, as astigmatism cathode-ray tube is to provide good focus Starlight. 9.25, Gaumont -British News. 9.35, Cathleen Nesbitt and Mall MacGinnis in "' if The must also be avoided. It is, therefore, all over the screen and trapezium dis- Shadowy Waters " ; a verse play by W. B. Yeats. further necessary to arrange that the tortion is to be avoided. 10.15, News Bulletin. The Wireless World, April 281h, r938 377

discovered why such a high percentage of their sets have reached customers in a non -working condition. It is not a case of sets merely putting up a poor overall performance or being instable such as UNBI SE would be the case if the resistance values in anode and screening grid circuits were Misguided Ingenuity incorrect. Something far more serious has been occurring as sets have been re- AS a result of my recent note concern- By fusing to function altogether and have ing the regrettable traits of character been received exhibited back into the Service De- by the modern boy, I have re- partment with -out valves due ceived burnt to an intensely interesting letter from HT connections being made to heaters and an examiner whose duty it is to make suchlike things. periodical investigations into the degree of FREE GRID In many cases this has led to perfectly knowledge or ignorance displayed by the innocent rising generation. members of the public being A year or two ago, he accused of invalidating the manufacturer's tells me, he and his colleagues were low -powered U.S.W. trans -receiver, the guarantee tampering greatly heartened by with the set, and by the tremendous im- morse key being in the youth's trouser the result has been that ill -feeling has been provement in the standard of knowledge pocket. The ear -piece was under the exhibited created all round. The trouble is that in by modern youth. The answers lapel of his coat and this, of course, ex- many sets the various connections are also to examination questions appeared to ex- plains the apparent short-sightedness, as hibit colour -coded in order to enable factory not only intelligence but also very the close application of the eyes to the operatives to identify them quickly. precise knowledge. It There was only one fly paper on the desk brought the candidate's does not need a great deal of imagination in the ointment and that was the appalling ear close up to the lapel of his coat. to-envisage the chaos that would ensue if state of ignorance betrayed in connection only one or two of the factory staff, such with questions involving rather compli- and testers, were cated mathematical as wirers -up partially formule. I is ex- The colour-blind. This, understand, great discrepancy between the actly what has been happening. ignorance betrayed in certain branches of mathematics The result is that certain firms are now and the very precise know- making special for ledge hastily arrangements exhibited in other matters eventually their staff be tested for colour-blind- aroused all to suspicion. As a precautionary ness, while this test is to be very rigidly measure candidates for the next examina- newcomers tion were enforced in the case of all to widely separated and a strict the ranks. Needless to say, I am exceed- watch kept but no attempts at communi- cation ingly gratified to have been able to be of with each other were detected nor some small service to the radio industry were candidates seen to produce note- in drawing attention to this very grave books from their pockets. Eventually source of trouble. a very curious fact was ob- Colour-blindness is a very serious thing served and that was that all the highly on one occasion very nearly precipi- successful and candidates appeared to be tated a war. As students of history will no afflicted with short-sightedness, as when Caught in the act. doubt remember, during a certain Soulh writing their answers they all kept their the flag of a non- heads American revolution glued closely to the examination The villain of the piece who was supply- combatant was fired upon owing to the un- papers. This caused several theories to be ing the answers to the questions wirelessed colour-blindness of a responsible forward suspected put to the effect that the answers to him in morse, was the man who looked executive officer on one of the belligerent to the questions were written in invisible after the central -heating apparatus. He battleships, who mistook it for that of the ink on the examination papers; and the was discovered in the stokehole with a enemy which it somewhat closely re unfortunate printers immediately fell similar trans -receiver and surrounded by sembled in pattern. under suspicion. a plethora of text -books. The reason why The most careful chemical tests failed the ruse was not successful in certain parts to reveal this, however, and the authori- of the mathematical paper was soon ties were at their wits' end when suddenly solved for after all it is difficult to send in the whole mystery was solved owing to morse a mathematical formula such as : -

vm 0v 3 dv[sin s 6dB-J t'sin a 8d8 -I ( 1dz- fsin BdB-(aex ( ldz1. . o o t, otex p\ .ocosB/ J t 9 t / o p\AocosB/ J the fact that one of the examiners was an ardent reader of this journal, and had The Radio Industry Saved constructed the Ultra -Short -Wave receiver I HEAR from reliable sources that my Consternation described some time ago. Happening to recent revelations concerning colour- among set be whiling away an idle hour in an ante- blindness has caused consternation among manufacturers. room while waiting to take his turn of set manufacturers. It may be remembered' duty, he was astonished to pick up morse that after endless trouble with a .home- code transmissions of the questions in the made set I suddenly discovered that it was If there are any of you who have built paper then being taken. all due to the fact that I had unknowingly receivers " exactly to authors' specifica- Quickly entering the examination room become colour-blind with the result that I tions" and have unjustly blamed the he found nothing unusual in progress, and was putting totally wrong values of resist- designer for a failure to achieve the anti- the mystery would probably never have ances into the set owing to my inability to cipated results, I should strongly advise been solved had he not risked an action read correctly the colour coding by means you to get your eyesight tested. It is for assault and battery by suddenly seizing of which the values are designated. more than probable that colour blindness the nearest, short-sighted candidate and Faom information which has reached is at the root of the whole trouble, and tearing his outer garments from him. On me I learn that as the result of my dis- it is the ordinary doctor rather than the the suspect was found a cleverly concealed covery certain manufacturers have at last radio doctor who should be consulted. 378 The Wireless World, April 23tú, 1938 Decca PT/AC

Press - Button Instead of the conventional compres- sion trimmers with mica dielectric, rotary Selection of trimmers with semi -circular electrodes are employed. Both the base and the Seven Pre -tuned rotating disc are of ceramic material (" Tempa ") having a high dielectric Circuits constant and exceptional freedom from temperature changes, warping or moisture absorption. The electrodes are of silver, and the two halves of the condenser are FEATURES. Type.-Table- held - in contact. by a spring washer, thus model superheterodyne with manual preventing all relative movement except tuning or automatic selection of rotation in a plane parallel to the elec- seven pre -tuned stations. Wave- trodes. The capacity of the trimmers is ranges.-(1) 19-49 metres. (2) quite small, and the tuning capacity is 200-550. metres. (3) 1000-2000 made up where necessary by fixed metres. Circuit.-Triode-hexode frequency ceramic or silvered mica condensers. changer-var-Mu pentode IF amplifier- Pairs of circuits for aerial and oscillator double diode second detectorpentode output are provided for each of the stations valve. Full -wave valve rectifier. Controls. , selected by the seven press buttons. The -(1) Manual or press -button tuning. multiple selector switch is of the trigger - THIS was one of the first of the (2) Volume and on -Off switch. (3) Wave bar type in which movement of any of the recent spate of sets with auto- range. (1) Tone. Price. 14t guineas. i switch buttons -lifts the bar and releases matic tuning to reach the stage Makers.-The Decca Gramophone Co., , all other switches in the line. At the of quantity production. Both Ltd., 1-3, Brixton Road, London, S.W.7. right-hand end is a double -pole switch mechanically and electrically it is of button for changing from automatic to simple and robust design, and the vital manual operation. question of tuning stability is answered circuit is an IF filter and a 261 -metre re- Strictly speaking, of course, this test by a new design of trimmer in the pre - jector to avoid whistles generated by report should extend over six months tuned station circuits. oscillator harmonics on long waves. with periodical bulletins of the way in ' The basic circuit is,.a straightforward There is little point in taking special which the pre-set circuits .are holding superheterodyne consisting of a triode- precautions over the stability of tuning their tune ; but it is reasonable to assume hexode frequency changer, variable -mu in the frequency changer stage if the IF that such a test has already been made in pentode IF amplifier working at 465 kc / s, amplifier is allowed to 'drift. Accord- developing the . chas'sis. At all events double diode second detector providing ingly the ceramic 'trimmers are of the every circuit was in perfect 'alignment AVC to the preceding valves on all three same stable type as those used in the RF when tested, and some considerable time wavebands and a pentode output stage. circuits, and the iron -dust cores of the had obviously elapsed since the' set came Associated with the single -tuned aerial transformers are sealed in position. off the makers' assembly line, for the

Complete circuit diagram showing individual tuned circuits and switching of " Prestomatic " station selector. APRIL 28th, 1438. Wpehoo Would 379 Radio Paris, but with a gap hardly wide enough to let through the Deutschland- sender as a station of programme value. The cabinet is of unconventional de- sign,' and its tapering depth from back to front effectively suppresses all trace of box resonance. The wooden slats bridging .the loud speaker opening slant TONE CONTROL downwards and prevent useless radiation of high frequencies upwards without affecting the forward response. There is no fault to find with the general repro- OUTPUT duction on all types of transmission, and VALVE the lack of the customary table -model FREQUENCY AC 5 PEN. CHANGER bass is not necessarily a disadvantage. VALVE The maximum acceptable volume was ACTH1 estimated at the equivalent of 2i to 3 watts. IF RECTIFIER VALVE. The "Prestomatic " trimmers are AMPLIFIER readily accessible by removing a VALVE R2 panel in the base of the cabinet, but it V P 4 B is unlikely that they will require expert attention 2nd except for alterations in station wave- DETECTOR lengths. ' These trimmers certainly look VALVE MAINS the part, and their performance seems to 2D4A VOLTAGE amply justify the makers' ADJUSTMENT choice. CLUB NEWS Exeter and District W.S,. Headquarters : 3. Dix's Field, Exeter. Meetings: Mondays. at. 8 p.m. "Wireless World Hon. Sec.: Mr. W. J. Ching, 9. Siren Place,. íieaai- COPYRIGHT tree, Ex_ter. At the last meeting a lecture entitled " AIe1- suring Instruments " was given by Mr. Rich, of the Mullard Co.. The lecturer gave practical demonstrations on several The automatic tuning device adds nothing to the size of the chassis and the cabinet is in fact instruments, includ- shallower than that of the average table -model. ing a cathode-ray oscillograph, a frequency modulator and a measuring bridge. Surrey Radio Contact Club Radio Normandie circuit and the dial the set shows itself to be a lively per- Headquarters : The Alhambra, Wellesley Rond, Croy- marking were on the old wavelength. former on all three wavebands. Self - don. Meetings : First Tuesday in the month. When the set was first switched on the generated whistles are absent on the Hon. Sec.: Mr. A. R. Wilshire, 14, Lytton Carden, various B.B.C. regional stations occupying medium waveband, Wallington. but a few of no great At the April 5th meeting Mr. Pickard, the first four buttons were all taking strength of the were to be found on long waves Webbs Radio, gave a lecture followed 'by a *de- same programme, and it was most in- and near the bottom of the short-wave monstration of modern 'American communica- structive to change from one to another range. They in no way interfere tion receivers. The receivers demonstrated with new of in rapid succession and to compare the the usefulness of the receiver for long- were the model the Sky Challenger. II with the London and the RME boLSI, both of which were fitted results Regional station distance reception - on short waves. with crystal gates. The Harvey UXHto trans - tuned -in accurately with the manual con- trol. In the first place there were no differences in quality which might indicate the creeping of one or other of the cir- cuits towards the fringe of sidebands, and, secondly, the test paid striking tribute to the efficiency of the AVC cir- cuits for there was hardly any change of volume. Except for slight differences in the character of the background noise, they might all have been the same station. Droitwich and Luxemburg were the long -wave stations on the " Prestomatic " control, and here again no difference could be detected from the best results obtained with manual tuning. It is neces- sary to move the waverange switch before the latter stations can be received, but this is no great hardship-at any rate it is less trouble than tuning manually. It should be emphasised that the stations mentioned are not the only ones that may be included View of ceramic trimmers and selector switch as seen through inspection aperture in base in the automatic control. Each trimmer of cabinet. has a range of adjustment that overlaps its neighbours, and the service man can Selectivity on medium waves is equiva- mitter and the New McElroy Straight key were easily provide an alternative choice of lent to the loss of two channels on either also demonstrated. stations or readjust to changes of wave- side of the London Regional station at a On May 3rd there will be a sale of surplus length at any time. distance of gear. The programme for the summer includes 15 miles, and on long waves a television demonstration, a talk by a well- Used as a normal broadcast receiver gives easy separation of Droitwich and known VQ4 amateur and a social outing. jRo The Wireless World, April 28th, 1938 fi Not as Other Men!" Government. So I must expressly make By "CATHODE RAY" TRIALS OF THE clear that it is nothing of the kind. The QUALITY ENTHUSIAST fact is that I, and probably most of my Great Public (if any), have found the last few efforts since the start of 1938 rather D VERTISEMENTS are very enter - tough going ; and this is by way of being hope of being able to improve the stand- tainingg these days. I have been a little relaxation to restore the worn ard of sound reproduction. amused by the young lady who tissues of the brain by indulging in some Why is it bad now? Apart from those hás cancelled all her invitations to gentle exaggeration of the possible results who lay the chief blame on the spon- stay with friends because her home is now of pursuing too relentlessly_ the ideal of sored programmes, some say because the so well warmed that she can no longer perfect reproduction. manufacturers would like to make high - tolerate any other. No doubt, the adver- quality sets, but have to supply what the tising managers of radio businesses are Missionary Work public demands. Others say that the kicking themselves for riot having thought public demands just what the manufac- of this first. For when you come to think To prove the absurdity of drawing turers educate it by their advertisements of it there is nothing to which it applies the conclusion that I am discouraging to demand. Probably the real reason is better than to radio. efforts to reach a high standard of quality, made of all these and some others, such If you are a quality enthusiast, have it is only necessary to appeal once more as sidebands and wage cuts and feminine you not found yourself developing an ,to the advertisement that supplied the in- intolerance of baffle area, and so forth. anti -social tendency? The nearer per- spiration for these reflections. Would a Still, after all allowances are duly fection you get with your own equipment, firm advertise with the object of discour- allowed, how many of your friends living the more painful -it is to endure your aging the use of its products? in baronial halls, rolling in wealth and friends' radio. What they chat or knit or No presumably the idea is that the lolling in idleness, enjoying the fine things play bridge to, presumably with pleasure charm of the young lady's presence will of life, looking down their aristocratic and satisfaction, is to you like the wailing be so missed among the circle of her noses on every daily paper at exclusive of midnight cats a.nd the squealing of oil - acquaintance that they will begin to make brands of whisky and champagne, and less machinery. If you allow your tactful enquiries about the cause of her telling you they are not really fussy, have natural instincts staying at home ; in the corner of the room a wretched little 'full "play with re- and if she is as box of radio, the cheapest " Manufac- gard to this, you charmingly Ire e turer's surplus " line ever imported into gain a reputation %/ from dissimulation the country? Instead of, gritting your for being unplea- as most modern teeth and putting on a hypocritical smile santly superior and young ladies she of assent when they turn it on and say critical, at least ; or will reply, " Be- " Not bad, eh? " take a deep breath and at worst, for being cause your house is tell them exactly what you think of it, a dangerous and so cold! " and why. And explain that if they do destructive maniac Whereupon the y not wish to lose you, their oldest fellow - If you curb these will all enquire cad, they must do something about it instincts you will about the heating before they ask you over again. be considered system used by her morose and taci- and install same. Beyond Reproach ? turn. While if, Similarly, you, either as a result of the connoisseur of I have been taking for granted that the foregoing or in quality, ought to you, the expert, can clinch the argument an effort to escape bring your friends by demonstrating real quality There is, from aural tor- to a realisation of however, a proverb about shoemakers' ments, you refuse the depths of de- children. And I have a guilty recollec- 'all social visits, pravity to which tion of having admitted lately "To your friends' radio." that I listen attend no football endure their senses of with an eight-year -old receiver. But just matches, s p e e d - hearing have sunk as it is a strain on the health, comfort ways, political meetings, or other places by being drugged to bad quality, as Sir and temper of an American to emerge where doubtful amplifiers may be used, Noel Ashbridge popularly put it. There from his central heating to visit Britain, and even cut out the local cinema, then is no doubt that the general standard of so it would be running serious risks to you will be described as a hermit. sound reproduction is bad. For evi- accustom myself to ultra -perfect double- The alternative is to give up the search dence, one has only to think of the popu- superfine extra -high-fidelity sound repro- for high fidelity and be content with an larity of Continental sponsored pro- duction. For, you see, it falls to my lot " ordinary " standard of reproduction grammes. Of course, if these programmes from time to time to test and report on yourself. But I must not call this article are considered by the people to be so in- mass-production receivers prior to manu- ` The Flight from Quality," and give the herently desirable as to be worth any facture. I mean to say, a reader em- impression that I really mean it, because amount of distortion, the case seems hope- ployed by the' publisher of the Bloodstain then its passage to the Editor's WPB less, for it would be a sinful z,vaste of Library of Long Complete Thrilling would be swift and uncompromising. For money tò listen to them on a high -quality Romances would soon get himself into although I am, so to speak, only the set. And over -modulation has commer- trouble if he accepted nothing of a lower cousin of the deputy semi -permanent cial advantages as regards service area. literary standard than that of _Shake- Under -Secretary's typist in the Ministry But assuming that these stations will speare. But you, who are free from sor- of Fisheries and Agriculture (known in be compelled to broadcast only in their did commercial trammels, can assure some circles as Fish and Chips) I must own languages, or that the B.B.C. starts your friends that it is not they whom you never forget that my lightest word in a patent medicine sideline to pay for the have ceased to love, but their radio ; and these columns is liable to be mistaken for television service, or that the ears of the perhaps give them some effective advice an official statement of the Policy of the masses are educable, there is some faint on what to do about it. The Wireless World, April 281h, 1938 Television Topics. THEN a hard -valve is used :for This action is only obtained with careful As before, start with the condenser dis- dischgi ng th in design of the transformer, for it can work charged. The cathode is then at the saw-tooth oscilleatorcondenserit is necesa in a somewhat different manner. It can potential of positive HT, which is also the sary for its grid potential to be be seen that the circuit is similar to that anode potential. The grid is very con- changed in a positive direction as soon as of 'an ordinary oscillator if we remember siderably negative, being returned to the the discharge commences. It is also neces- that both primary and secondary have a slider on RI, consequently the valve sary for the grid to be driven negatively certain self -capacity and have the valve as soon as the condenser is discharged. capacities in shunt with them. With Unless this is done the system is incapable certain circuit values it will actually of maintaining oscillations. operate as an ordinary oscillator and give With the hard-valve circuits recently an approximation to a sine wave output. discussed this action was achieved with the With other values it will generate a saw- aid of an additional valve. This is not tooth waveform, but instead of- operating essential, however, and it is often possible as described above the valve will oscillate to replace it by a transformer. The circuit at a frequency determined by the trans- then takes the form shown in Fig. i. The former during the condenser discharge valve has a certain negative grid bias due period. - to the average anode current flowing Starting as before with C discharged, through RI ; the anode current is actually this condenser charges until the anode pulsatory, but the use of a large capacity voltage is sufficient to start the anode condenser Cr across RI enables an almost current, The valve then oscillates at a steady voltage .to be high frequency until maintained across this the condenser is dis- Fig. 2.-A modification of Fig. 1 which is often less convenient but resistance. charged to such a which sometimes SINGLE -VALVE leads t) a better performance is shown in Starting with C dis- degree that the anode this diagram. charged, it charges voltage is .insufficient through R, and the OSCILLATORS to maintain oscillation. passes no current. As the condenser anode voltage of the This is quite possible, charges the cathode steadily moves nega- valve rises. All this for it is well known tively with respect to positive HT ; con- time the valve passes no current, but at that the conditions for the starting and sequently it becomes more negative than length the voltage rises sufficiently to start stopping of oscillation are not always the the anode and comes nearer to the grid anode current, and this current flows same-if they were there would be no potential. In effect, the anode voltage overlap through the primary of the transformer, " " in a reacting detectór. rises with respect to the cathode and the thus causing a voltage to be induced in The success of this saw-tooth oscillator grid potential moves nearer to that of the the secondary. If this secondary is con- depends chiefly upon the design of the' cathode. nected correctly the induced EMF changes transformer. For the frame frequency the When the potentials are such that anode the grid potential in a positive direction, writer has used ._a cheap AF transformer current flows the action is the same as thus increasing the anode current and fur- and for the line a super -regenerator quench before. In fact, the only difference at any ther increasing the grid potential. coil with reasonably good results. It is, time is that the grid potential changes with The anode current is supplied by the however, eery important that the trans- the anode potential, reckoning_ both with condenser and its voltage consequently former be properly damped. In general, respect to the cathode. This does, how- falls. Therefore it at length becomes too a resistance should be connected across ever, make for a more positive action. low to maintain the current and the anode the primary, and the lower its value the With either of these circuits synchronis- current commences to fall. The falling better is the performance of . the circuit. ing can be effected by arranging for the If it is too low, however, the circuit fails sync' pulses to drive the valve grid posi- to work at all. The optimum value must tive just before its own discharge action be found experimentally for the particular would commence. One way of injecting valve and transformer used ; it is gener- the pulses is by means of a third winding ally in the neighbourhood of 5,000 ohms on the transformer or a resistance of a few at frame frequency, however. hundred ohms can be included in series It is quite easy to get the circuit to work with the earthy end of the secondary and at frame frequency, but it is more difficult the pulses applied through a condenser to at line frequency. The coils are more the junction of the transformer and resist- critical and the damping must be just so. ance. If a damping resistance is used on Sometimes a resistance shunt to the the secondary the pulses may be fed into secondary is better than one on the pri- a tapping on this resistance. ' mary, but sometimes both are needed. Rather better operation is secured by arranging the circuit in the modified form THE WIRELESS INDUSTRY Fig. r.-One of the simplest single -valve of Fig. 2, but this has the disadvantage of saw -tooth oscillators is shown here. THE Iieates-Hacker Co., Ltd., 91-93, requiring a special heater winding for the Bishopsgate, London, E:C.2, have pro- anode current through the transformer valve unless the heater -cathode insulation duced an attractive catalogue containing, in primary induces an EMF in the secondary is good enough to withstand the high peak addition to a technical specification of their latest 19 -valve chassis, a series of photographs in such phase that the valve grid is driven voltage. The difference in this circuit is illustrating typical cabinet designs in relation negative, thus making the anode current that it is the cathode potential which is to furnishing schemes of diverse character. still smaller until the valve ceases to pass varied rather than the anode potential, 0 o c o current. The condenser C then com- and as a consequence the anode and grid The Jewel Pen Company, of 21-22, Great Sutton Street. London, E C. r, wishes to draw mences to charge again and the cycle is potentials are varied simultaneously with attention to the fact that the " Red Diamond " repeated. respect to the cathode. crystal detector is still teing manufactured. 382 The Wireless World, April 28th, 1933 B.B.C. HIGH FIDELITY TRANSMISSIONS Toscanini Concerts on Ultra -short Waves.? OWNERS of ultra -short wave phony Orchestra is in the front NEWS OF sets in the service area of rank. A concert by such an the Londón Televisión station orchestra under such a conduc- may soon have their first oppor- tor, reproduced on ultra:short WIRELESSMAN'S BADGE each of ten types of variety tunity of receiving high fidelity waves, with the wide band of Proficiency of Boy Scouts broadcasts. . The results, which transmissions of the National frequencies which they make THE Boy Scouts Association provide useful comparisons be- programme. If arrangements, available, would, provide a the condi- tween the popularity of different 1 has remodelled types of variety programmes, now in hand, fructify, a series of musical treat and a'splendid op- tions for obtaining the Wireless - are as follows :- - -of -porfunity for the connoisseur of relays on 7.23 metres the man's proficiency badge. These Percentage who Toscanini concerts in the Lon- high -quality reproduction. conditions may interest reader's, -would -would -are will If the experiment is tried, like like satis- don Music Festival be trans- and their comments will be wel- Types of Programme. more. less. fled. mitted. Excerpts from the first there can be little doubt comed by the Boy Scouts Asso- Straight Variety 70 1 29 of six concerts about its success, and it is Reginald Foort at the part of each the ciation. B.B.C. Theatre Organ 55 5 40 are planned, beginning at 8.15 probable that a regular series To obtain this badge a boy Comedy Shows 54 5 41 until appröxi- of seven -metre relays may Concert Parties 44 8 48 and continuing must: (r) have an. elementary " Interest " Features 41 7 52 mately 9 p.m., when the normal be inaugurated, creating a knowledge of how a thermionic Cinema Organs 41 8 50' Serials 31 12 - 56' _ new market - for high-fidelity re- television programme begins. valve works as an HF amplifier, Musical Comedy 29 19 52 No more auspicious start ceivers. The quality ` of the detector and LF amplifier, and Dance Music 17 28 54* sound in 'tëlevision American and Foreign could be chosen for this -long-. the transmis- how a Westector works; (2) Relays 8 57 34* awaited experiment the heed sions has already evoked wide- know the functions of condenser, Average 39 15 46 been spread " praise from musicians, for which has frequently resistance, inductance, reaction (' 1 per cent. did not reply.) stressed by The Wireless World. many music' critics of the p1`o- and mains rectifier transformer ; Arturo Toscanini is recognised grammes from .Alexandra Palace (3) know how to cure hum or as the world's foremost conduc- having been tempted to ignore how to 'build a cheap mains GLASGOW CHANGE -OVER tor, and the Maestro- häshimself the visual side in their eulogies eliminator ; (4) know how ' to ÁCHAPTER in Scottish stated that the B.B.G. Sym- of the sound. locate and cure a simple fault broadcasting history will be in a receiver ; (5) show a work- closed on May 14th with the -coil SCOTTISH NATIONAL . The first step will be to effect ing knowledge of moving final transmission from the old POWER INCREASE? aerial adjustments with the pos- loud speakers ; (6) draw a simple Glasgow studios in Blytheswood sible introduction of reflectors f diagram shówing how to connect Square. The first programme The Result of a Deputation if this is still unsatisfactory the up a resistance capacity coupled from the new studios in the SIR NOEL ASHBRIDGE has Scottish National transmitter stage and an LF transformer, Botanic Gardens is scheduled cheered the hearts 'of six power may la, increased. and show a knowledge of the for Sunday, May r5th. Dundee listeners by his thousand principles involved ; (7) read a The original Glasgow studio, promise, at long last, to increase technical diagram and interpret which was in a comparatively the field strength of the Scottish SWEDISH WIRED WIRELESS the symbols ; (8) have assembled squalid apartment in Cross National transmitter in Fife- a simple receiver and know all Street, was inaugurated with the shire. The Chief Engipeer of DESPITE the construction of the distress signals ; and (9). opening of 5SC on March 6th, the B.B.C. gave this undertak- several high -power trans- know the methods of charging a depu- mitters in Sweden, the quality 1923, on the top floor of the Cor- ing on April rith, when and looking after accumulators. poration power station at Port tation of local radio traders, ac- of reception is still poor in many Swedish localities, chiefly owing Dundas. The move to Blythes - companied by Major Peter, Square was in Chairman of the R.M.A., and to the mountainous nature of VOTES FOR VARIETY wood made several Members of Parliament, the country. With a view to MIDWAY through the November, 1934. -visited Broadcasting House. combating this difficulty a wired B.B.C.'s twelve -week sur- The main burden of complaint, wireless system installed by the vey of the Variety Listening TELEVISION AT THE I.E.E. which was voiced by a local Government has been tried out Barometer, the 2,000 log -keepers TWO important papers were trader, Mr. E. J. Allan, was that in Karlshamn, with great suc- in all parts of the country read at the Institution -of the Westerglen transmitter cess. It is now proposed to answered a special questionnaire Electrical Engineers last Thurs- fades badly after dark and is - introduce the relay system fin which asked them to indicate day, April 21st. One, by Messrs. also subject to local interference. Stockholm. their views on the quantity of T. C. Macnamara and D. C. Birkinshaw, described the Lon- don Television Service, and the other, by Messrs. Blumlein, Browne, Davis and Green, dealt with the Marconi-E.M.I. Tele- vision System. Probably the most interesting section of the latter was that dealing with the reason for the choice of the particular trans- mitted waveform. The type of scanning, duration and ampli- tude of sync pulses, the advan- tages of positive and negative modulation were all discussed. In other sections the genera- tion of the various scanning and pulse frequencies was treated as well as the " bend " and " tilt " signals needed for camera cor- rection. The transmitter itself was considered with particular reference to the special problems of television which necessitated for their solution the use of AT THE I.E.E. meeting held last Thursday while A. D. Blumlein was reading his section of the paper on the " cathode - followers " in - the Marconi-E.M.I. Television System. The papers, which were delivered to a large gathering, were a most valu- coupling stages and the extensive able record of present progress and the E.M.I. engineers deserve the highest praise for their work in pre- adoption of constant impedance paring them. networks. The Wireless World, April 2811, 1938

THE MIXING of two ribbon microphones on the stage and one in the orchestra 'pit at Covent Garden, will be effected this 'HE WEEK year, for the first time, from one of the Grand Tier Boxes. NEW HOLLYWOOD BROAD- AS OTHERS SEE US This will enable the CASTING HOUSE ONON his return to the States " mixing " expert to CIVIC, State, and _ national from a recent European tour follow the movement dignitaries from all over the Mr. E. K. Cohan, the Director of the singers ; he United States will be present on of General Engineering for the will also follow a April 3oth at the opening cere- Columbia Broadcasting System, complete score of the mony of the Columbia Square reports that he was somewhat Headquarters of the Columbia disappointed in /the public re- Broadcasting System in Holly- sponse to television in England, wood. the country which, as he says, is Transmissions, which will be- admittedly in advance of other gin at 3 p.m. B.S.T._ are to be nations in that field. While the radiated by the .entire network B.B.C. engineers are making and should be well received in highly satisfactory advances, he England from the C.B.S. inter- feels that the public seems to le national short-wave station just curious rather than evincing W2XE. a real programme interest in The entertainment side of the teldvision. dedicatory programmes will be supplied by famous radio and SHORT WAVES IN INDIA film artistes, and the atmosphere AS the result of the introduc- of the occasion is to be musically tion of short-wave transmis- Interpreted in a new work, sions in India, large numbers of "' Slidin' Down a Kilocycle to medium -wave wireless receivers Columbia Square." have. been rendered obsolete. opera. During rehearsals, experiments will be made with uni -directional TELEVISION Suitable converters which enable VISUAL CHECK ON old sets to receive these trans- microphones. The pictures show the control point,' which last year FREE GRID, on a cele- was installed under the stage. The controls at the bottom of the panel missions have been placed On the are for orchestral and stage microphones and those at the top are for brated occasion, drew market, and new all -wave re- attention to a discrepancy be- echos ; in the centre is the programme meter. The first relay takes ceivers are" in great demand by place on Monday evening. tween an alleged O.B. from a an enthusiastic if somewhat dis- country church belfry that he gruntled public. had picked up on a portable re- FROM ALL of the Glamorgan County Council ceiver, and the actual sounds A.R.P. Committee. It is interest- which came tó his ears from the EMPIRE BROADCASTING QUARTERS ing to note that the amateurs of church itself, only a short dis-_ THE history and technical this country have several times tance away. development of Empire The Empire Exhibition dffered their services to the Home THE KING be heard A similar test, with vision in- Broadcasting, the foundations of H.M. will Office as a corps of emergency which were laid in 1927 with the from all B.B.C. transmitters, operator, but no definite official stead of'sound, revealed no such except London and North plan has so far emerged. discrepancy when a Dulwich establishing of G5SW by the Nationals, on Tuesday next, May (South London) televiewer tuned Marconi Company at Chelms- 3rd, when he opens the British ford, are interestingly reviewed Pitcairn Calling in the " air raid " which was Empire Exhibition at Bella- SIGNALS from the new station televised from Alexandra Palace in a new B.B.C. publication, houston Park, Glasgow. on Pitcairn Island, of "Mutiny on Easter Monday. From a "The Empire Short-wave Sta- B.B.C. News Bulletins on the Bounty " fame, are being tion, A window fourteen miles from the Daventry." detailed REFERENCE was made in our regularly received by Mr. George scene of action he was able to technical description of the issue of March 3rd to the pend- Brown, a radio ' pioneer at Bir- watch the searchlight beams present station, giving, among ing agreement between the B.B.C. mingham. The signals are heard obeying which he many interesting features, a plan and the Newspaper Proprietors' between 6 a.m. and g a.m. on a the orders frequency of 14.343 Mc/s. could see being carried out on of the aerial arrays; is also in- Association. This has now been the television screen at his cluded in this well -illustrated 'signed and, as previously stated, main change is that the Cor- Whitehall Wireless elbow. is believed to be little booklet. the This poration will now be free to ob- IT is reported in the Daily Tele- the first occasion on which a tain news from sources other than graph that although the British viewer has been able to apply GERMAN DIALECT MEMORIAL the four agencies as heretofore. Consul in Valencia is no longer a direct visual check to the pic- HERR HITLER was, some able to communicate overland ture on the television screen. time ago, presented with a "The Luxembourg Listener" through Barcelona and France, he collection of gramophone records Tins is the name given to is keeping in touch with White- R.A.F. RADIO SOCIETY of about three hundred German the plane which has inaugurated hall by means of a private wireless a regular air service from England transmitter. THE objects of the recently dialects by the Association of to the Duchy of Luxembourg formed R.A.F. Amateur German Civil Servants. This by Wireless Publicity, sole started . Football Club Transmitter Radio Society are to encourage collection is housed in a special British Empire agents for Radio facilitating the A SPECIAL USW transmitter hais and assist members in private cabinet in the Führer's house at Luxembourg, thus -been installed in the stadium of experimental work with high- Berchtesgaden. A second cabi- shipping of programme materials station. the Kobenhavns Boldklub, a frequency apparatus. Serving net is kept by the Propaganda and artistes to that Copenhagen football club. It will and past members of the R.A.F. Ministry at Berlin. Radio Research radiate running commentaries on connected with the now re- all Major sporting events, trans- and civilians The Association has AT the next meeting of the Service may become associate quested Telefunken to add Aus- Wireless Section of the I.E.E., to missions being picked up by the members. trian dialects to the collection, Place, Landon, official broadcasting authorities le' held at Savoy and re -radiated -over the ordinary has sprung special ' car -on Wei e'sday, This organisation and the recording \V.('.2, at 6 p.m. networks. from the Cranwell Amateur used for the first series will May 4th, Dr. Ralph Bown will Radio Transmitting Society shortly start on a tour through lecture on " Researches in' Radio Telephony." Ship -to -Shore Telephony 'CARTS), which was formed by Austria. , THE problem of providing ship - several amateur transmitters The official title of the col- Amateurs and A.R.P. to -shore- telephony at Glasgow pur- meeting fortuitously at the Elec- lection, which Cannot be A SUGGESTION to enrol Great Docks was referred to three mem- trical and Wireless School at chased by the public, is " The Britain's 2,000 amateur trans- bers of -the Glasgow Chamber of Cranwell. The " CARTS " Memorial in Sound of German mitters to give the nation warn- Commerce. They have approached transmitter, G8FC, is well Dialects at the Time of Adolf ing of impending air raids was the Clyde Trust on the subject, but known throughout the Empire. Hitler." .made by Major Morgan, a member as yet without result. The Wireless World, April 28th, 1938

RADIATIONS F"WRITING of`a" radio in India reminds me RANDOM °xthat e new Lucknow transmitter was opened by the Government of the Receiving " Long -Short By " DIALUST " United Provinces on April 2nd. Lucknow Wavelengths has a 5 -kilowatt plant and operates with the call -sign VUW on 1,022 kc / s, or 293.5 AN ingenious method of improvising of flex and a crocodile clip. So long as the means metres. At present it is giving an evening for receiving short-wave stations IF of the set lies between 450 and 470 kc /s, programme only, on a superhet not designed for " all -wave " from 6.3o to II p.m. as nearly all IFs do nowadays, Bombay is Indian Standard Time, which is fout and reception has been described by " Trouble found with the set apparently tuned to the a half hours Shooter" in recent issues of The Indian fast of British Summer Time. neighbourhood of 212 metres. From our point of view, Listener. M readers may recall, n large therefore, Lucknow is on the from 2 part of India relies for its evening pro- air p.m. to 6.3o p.m. Whether any of grammes on the short-wave transmissions Even Third Harmonics our dyed-in-the-wool D- Xers will succeed in logging VUW I don't of Bombay and Delhi. The former gives The method was also worked out 'for know, its evening programme 3,305 though I doubt it. Lucknow's call - on kilocycles Delhi, which was then operating on a neigh- sign, by the metres). The adoption of this wave- way, is the first to break the (9o.77 bouring channel. But no sooner had that rule that those of All -India Radio length -revealed two weaknesses in receiving been done than Delhi stations most disobligingly consist of the letters VU followed by the sets. Many covered either the medium changed its frequency to 4,905 kc/s (6o.1 initial of the town-VUB, Bombay ; VUC, waves and the long waves or the medium metres). Undismayed, " Trouble Shooter " Calcutta ; and so on. Lucknow had no waves only, whilst most of those of the " all - girded up his loins once more and found option since VUL had already been appro- wave would 90 r_= " type not tune up to otres that in places not over -far from Delhi the priated by Lahore. on their short-wave range. Naturally, there 6o.1 -metre transmission could be received was considerable grousing, for it seemed by means of the third harmonic of the cscil- 'that the great majority of the sets in use in lator with the set tuned to about 227 metres. places outside the medium -wave service The third harmonic is, however, usually Fun With the Wireless Set area of the station were automatically ren- rather feeble and reception by its aid will WHEN I first heard about motor -tuned dered obsolete -by the adoption of this long - probably seldom be found to be of great receivers which brought in the station short wavelength. But the gallant practical value. It occurs to me that that you wanted for the mere pressing of a " Trouble Shooter " stepped into the readers might find it interesting to experi- button, I was rather disposed to place them breach, describing a way of receiving Born - ment with the second -harmonic method, in the category of stunts likely to appeal bay on a two -band superhet by making use choosing times in the small hours when the chiefly to those who don't take wireless very of the second harmonic of the oscillator. medium -wave band is pretty quiet. Jt seriously. For the last day or two, how- may, for instance, be possible to bridge in ever. I have been using one of them, and Interesting Figures this way the gap between zoo and Zoo I must really admit that this kind of tuning Here is the way in which he set to work. metres that exists in most receivers. Sup- is a distinct addition to the broadcast Most, if not all, sets are so arranged that pose, for example, that we tune the set to receiver's good points. You can, cf course, -the oscillator is working at a higher fre- the normal setting for Radio-Mediterranée use manual tuning whenever you want to quency than that of the incoming signal. on 1,276 kc/s, we should be able to get on the medium waves and the long waves, If the intermediate frequency is 456 kc/s down to approximately zoo metres. When and you have to do so to tune in short-wave the oscillator frequency is thus -1,880.5 L-c/s the signal frequency is 1,276 that of the stations. Hence you can tune the set in when the tuning indicator points to 1,424.5 oscillator, assuming an IF of 456, is 1,732 the good old-fashioned way when you are kc /s, or approximately 212 metres. The kc/s. The second harmonic of this is 3,464, seeking for those smaller and more distant second harmonic of the oscillator is 3,761 which beats with 3,008 kc /s to produce the stations that are the joy of the long-dis- kc /s, which beats with Bombay's 3,305 kc /s intermediate frequency of 456. Or, again, tance man's heart. But it's great ftin to to produce the IF of 456. It is, of course, by making use of this second -harmonic be able to tune in any one of a useful selec- necessary to by -pis' any signal -frequency principle on the short-wave range of an tion of strongly received stations by just stage, and this, is' done by connecting the all -wave " set it may be possible'to tune, touching the appropriate button. Not the aerial to the trimmer of the frequency - after a fashion, up to frequencies far beyond least fascinating part of the business is changer grid -tuning condenser with the aid its normal scope. watching the pointer travelling round all

THURSDAY, APRIL 28th. FEATURES TUESDAY, MAY 3rd. t 7.20, Tha Band of H.M. Royal m m OF Nat., 10.45 a.m., H.M. the King opens Nat., Broackast Programmes1 I ogrammes Rifle Corps. 8 Variety from the WEEKE the Empire Exhibition at Bella- Holborn Empire. 8.40, " Trans- houston. 8, " Forty -Second Street," port "-1, Talk by Basil Marsden - Abroad. Reg., 6, Round the Courts. 6.40, an adaptation of the film success. Smedley. 9.20, Talk on the Budget Vienna, 7.30, " Turandot "-opera Old Bannerman "-play. A 9.20, America Speaks. by Sir Archibald Sinclair, (Puccini). Voyage in the West Indies sixty Reg., 7.30, Fred Hartley and his Reg., 6, " Scrapbook for 1928." 8, Hamburg, 8,10, " The Bird Fancier years ago. 9.50, Spelling Bee. Swing Strings. 8.20, Midland_ A Sound Impression of the Empire -operetta (Zeller). Parliament-" Industrial Welfare." Exhibition in the Abroad. Making. 8.40, SATURDAY, APRIL 30th. 9.10, " Night Out "-Tour of the Rhythm Express. Berlin, 8, May Day Gala Programme. Nat., 1.10 and 4.45, Cricket Com- Empire Exhibition at Night. Rome, 9, Berlin Philharmonic, from mentary ; the Australians P. Wor- Abroad. Abroad. Teatro Vittorio Emanuele, Flor- cestershire. 2.30, Commentary on Brussels I, 8, Russian Concert with Leipzig, 7.30, " Othello ence; conducted by Furtwangler. "-opera the F.A. Cup Final, Preston North the Russian Choir of Brussels. (Verdi). End e. Huddersfield Town. 9.20, Eiffel Tower, 8.30;Concert of Music Bucharest, 7.35, " The Valkyrie."- MONDAY, MAY 2nd. American Commentary. 9.45, Mr. by modern European Composers. opera (Wagner). Winston Churchill will propose the Nat., 1.15 and 5.45, Cricket Com- WEDNESDAY, MAY toast at the Royal Academy Banquet. mentary ; the Australians P. Wor- 4th. FRIDAY, APRIL 29th. Reg., 3.55, Ralph Reader Revue. 8, cester. 7, Monday at Seven. Nat., 7.40, Act 1 of " Der Rosen- Backstage at Bellahouston. 9, 9.20, World Affairs. kavalier " from Covent Garden. Nat., 7.30, Ralph Reader Revue No. 3. B.B.C. Ballroom. Reg., 6.30, Swift Serenade. 7.55, 920, The Trial of Katharine Nairn 8.15 " Banging the Big Drum " ; Covent Garden Opening Night ; -Edinburgh, August, 1765. the story -of publicity ancient and Abroad. " Magic Flute," Act 1. 9.15, Eddie Reg., 3,10, Commentary on the modern. 9.20, Talk on the Budge' Bucharest, 7.35, " Siegfreid "-opera (Wagner). Carroll and his Orchestra. Chester Cup. 6.40, From the by Mr. J. Colville, M.P. London Theatre. 7.30, The World Abroad. Reg., 7.30, Frank Mannheimer, piano- SUNDAY, MAY 1st. Goes By. 8, Band Waggon. forte. 8, " Madam Butterfly," Nat., 9.30 a.m., Emilio Colombo Lille PTT, 8.30, Concert of French Abroad. Act 1 of Puccini's opera from Octet. 10 a.m., Military Service Music from Valenciennes, Con- Leipzig, 8, Concert of German Folk Sadlei s Wells. 9.30, Duke from York Minster. 7, Songs of the servatoire. Dances. Ellington and his Orchestra, relayed British Isles. 9.50, Josef Hofmann, Milan, 9, Berlin Philharmonic, from Paris PTT, 8.30, Concert from the from New York. pianoforte. Florence. Troyes Conservatoire. Wpdge@ APRIL 28th, 1938. opIll 385 by itself and .coming to rest at the right revolver or bulleted ammunition, and that.. e spot. This particular set has AFC, and so system has been found quite satisfactory. long as the stations selected are normally I am glad to see that in Caiiada a scheme M` H strongly received and not subject to inter- of this kind has been adopted by the CART ference from their neighbours its operation Government. In that country, though, the is perfectly satisfactory. It's remarkably licensing regulations are not quite the same quick, too, the time taken to pass from as ours : a Canadian must have a licence Radio Normandie near the bottom of the for each and every receiver, though with us medium -wave band to Athlone near the top one licence covers as many non -portable being only a matter of a second or two. receivers as we like (provided that they all Another distinct advantage about. this belong to the licensee or to members of his method of changing automatically from one household and are used under his roof), and station to another is that as soon as a one portable set as well. Even so, I can't button is touched the set is silenced until see that any great difficulty would arise if the desired station is reached. There are the licence had to be shown before wireless thus none of those highly unpleasant noises goods could be bought. that may occur when the change is made manually, unless one remembers (as usually one doesn't) to turn the volume control right back during the process. On the Future Refinements Though the system described is undoubt- edly good, and the set which incorporates Short Waves it excellent value for money, we shall, 1 expect, see a good many refinements intro- Notes from a Listener's Log duced when large and expensive auto -tuned receiver§ make their appearance. And the Asmost readers are probably aware, the opportunity for refinements is almost un- Easter week-end was a very active limited. Here's one that I should like to one from the solar point of view. of With the 'appearance of two' large sunspot see. As things are, touching the button no a station does not switch on the set if it groups it became obvious that considerable IN modern radio practice, nothing is final; changes might occur, and this certainly receiver is so good that it is incapable of was switched off beforehand. It would be development in some detail. an additional pleasure to be able to walk proved to be the case. Two days after the up to a silent receiver, touch one button meridian passage of the largest of the two Constant attention to improvement in small and hear the selected station come in as groups the most severe magnetic storm in matters keeps McCarthy chassis in the forefront at - soon as the valves had warmed up. Then, living memory was recorded. It stated of modern chassis design and construction a button marked " Search " be 05.48 G.M.T. and lasted until 16.30 G.M.T. would not of rather jolly? My idea is that this should on April 16th, the horizontal component The receiver illustrated operate on all wavelengths. When the the earth's magnetic field being most affected, button was pressed and held down the set the variations at times amounting to almost is the well-known McCarthy would not be silenced and AFC would be one -eighth of the total force. cut out. The pointer would travel very Prior to the magnetic storm, however, it Greenwich that the lead- slowly over the scale, stopping as soon as had been noted by -WAVE one released the pressure on the button. ing group was very active spectroscopically 9-VALVE 4 were noted This one would do when a desirable trans- and bright hydrogen eruptions as ; AFC would then follows:- mission had been found Magnitude SUPERHETERODYNE come into play to pull the set into perfect April 12th 11.02-11.40 G.M.T. 2 valves resonance. It seems quite possible, again, April 12th 14.50-15.07 G.M.T. 2 minus priced at 14 guineas including that we may have sets intended for reception April 12th 15.03-15.10 G.M.T. 2 local The Circuit in Brief.-The pre -selector of the highest possible quality of the April 13th 09.45-11.52 G.M.T. 3 max. radio frequency or two at 09.49 circuit is coupled to high -gain stations, and perhaps just one others, amplifier operating on all 4 wave -bands, which without any dials at all. Besides a small April 13th 10.54-11.30 G.M.T. 2 -coupled to latest type triode- 14th G.M.T. 2 is transformer array of buttons the only controls needed April 10.12-10.39 hexode frequency -changer. There are 2 band- would be for volume and for bass and treble Magnitude 3 means that the eruption was pass transformer -coupled I.F. amplifiers (inter- accentuation. But these, once adjusted to a very extensive one, and most likely to mediate frequency 465 K.C.'s). The double the owner's liking, would seldom need to be produce the so-called Dellinger fade-out on diode second detector provides automatic be volume control applied to 4 preceding valves, touched again, and they could quite well the illuminated half of the earth. The triode small door in the very interesting to hear if and first stage L.F. amplification. hidden' away behind a It would be phase -changer is capacity-coupled to push-pull cabinet. The auto -tuned set seems to have readers observed such fade-outs at the times output pentodes (or Harries-tetrodes) delivering great possibilities, and I expect that enter- and dates given above. 9 watts. be slew to of activity, and on prising manufacturers will not On the basis this coverage make the most of them. statistical evidence which shows that spots Principal Features.-Waveband - the 12.8 -33, 29-8o, 190-550, 800-2,000 metres. having areas over 1,50o millionths of Controls-sensitivity control (varying bias on ti ti '1. sun's hemisphere are liable to produce mag- R/F stage) : 5 -position wave-change and netic storms on the second day after their gramophone switch : combined volume control. A Good Way With Pirates meridian passage, the Royal Observatory and on/off switch and progressive variable tone HOW many folk there are nowadays who warned the G.P.O. that disturbances with control (both opgrative on radio and gramo - diddle the G.P.O, the B.B.C. and their the telephone and telegraph circuits might ,phone). fellow listeners by using unlicensed receiv- be experienced. A prediction which very EIEFERRED TERMS is to be correct. ing sets, no one knows. The figure often quickly proved 29/- with order and 14 monthly payments of 14/-. point of view the dis- put at about half a million, though I doubt From the short-wave On application, or through our City agents, whether it is quite so high as that. Still, location ,of the North -American and Cana- successful prosecutions for the dian services occurred even earlier than the LONDON RADIO SUPPLY CO., the fact that LONDON, E.C.2. use of unlicensed sets are always being magnetic storm proper. This is, of course, 11, OAT LANE, undertaken shows that there must be a good quite natural since a magnetic storm is of Send 3d. in stamps tor complete illustrated catalogue few pirates about. Long ago I suggested almost certainly an earthly manifestation with technical data and circuit diagrams of other one should be able to purchase a very disturbed conditions in the ionised interesting McCarthy chassis of all types tor A.C., that no list free of charge. radio receiver, or the parts from which to layers. Actually, both W3XAL and Battery, or A.C./D.C. Abridged make one, without producing his receiving W2XAD became inaudible at about 16.0o RADII) Ihro licence. There shouldn't be any great diffi- G.M.T. on Friday, April 15th, the magnetic CARTHY culty about enforcing such a regulation. storm, as stated above, starting early on 44, Westbourne Grove, London, W.2 After all, you have to show your fire -arms Saturday morning. bra Telephone : Bayswater 320112. certificate if you want to buy a rifle, In spite of the disappearance of W3XAL . 386 The Wireless, World, April 28th, rn38

On the Short Waves- and W2XAD, however, some 28 Mc/s sig- nals from W4's made their appearance later and on Saturday, W4EPX in particular being in evidence. Valve Nomenclatur Whether this is due to some peculiar vir- tue of z8 Mc/s under these conditions or to the very southerly location of Florida is THE present system of By R. M. V. ESTON not known. designating valves is A friend one which leaves much to writing from Bogota, Colombia, be desired, tells me that on the night of the auroral for the type numbers tion on the useful characteristics of a display in January (January 25th) he often convey little or no useful informa- valve in its type number is unfortunately noticed nothing abnormal in the perform- tion. They serve merely as distinguishing foredoomed to failure, for it leads to an ance of Daventry's short-wave service, even marks and do not indicate the electrical appallingly complicated array of letters although, this and other stations on all fre- characteristics. and numbers. The matter is much quencies were completely inaudible in Any attempt to convey precise informa - simpler, however, if the attempt is made Canada and the. U.S. on that occasion. By the late afternoon of Easter Monday conditions seemed to have been restored to SUGGESTED METHOD OF VALVE NOMENCLATURE, normal, and WzXE on 21.52 Mc/s was excellent around 4 and 5 p.m. Electrodes. Type. Symbol. Meaning. Example. For those readers who are interested in picking up India is here the latest schedule DIODES ... .., HT power rectifiers ... ,.. ... R Rectifier of the A.I.R. : short-wave stations - Do. do. for 250 v. ... add 2 R2 B.S.T. Do. do. 350 v. ... ' 3 R3 VUD2 Delhi ro kW. Do. do. 500 v. 5 R5 2.3o -4.3o a.m. RF rectifiers for detection, 9.59 Mc/s... AVC, etc. D Diode 17.30-9.30 ,. Gas -filled HT power rectifiers ...... G Gaseous 4.995 Mc/s. ... 1.30-6.30 p.m. VUB2 Bombay so kW. DOUBLE DIODES Any of above types ...... prefix 2 2113, 2D, ete. 9.55 Mc/s. . - 7.00-9.30 a.m. 3.305 M/cs./ 1.00-6.30 p.m. TRIODES ... Output triodes ...... T Triode Almost [Also general symbol for the word certainly the strongest reception triode when used with an additional will be from VUD2 on 9.59 Mc / s between word as in Triode-Hexode, Double 4.3o 2.3o and a.m., apart from the possi- diode -triode, etc.] TX, 2DT bility. of interference from W3XAU at this High resistance triodes (over 7,000 n) time, and PCJ if working. add H High TH Gas -filled triodes or relays .. add R Relay TR Double Ultra -short Wave Portables triodes for " Class B " operation B Class -13 TETRODES ... Screen grid tetrodes ...... S Screen For the past week or so I have had the Do. do. with variable mutual use of a Peto -Scott 5 -lo metre portable, a conductance add V Variable SV review of which recently appeared in this Output or " kinkless " tetrodes ...... K Einkless- journal. This little portable, which you can buy PENTODES Output pentodes ...... P Pentode practically over the counter, gives a very [also general symbol for the word good account of itself pentode when used with an additional on the Alexandra word as in Palace sound at Epsom, in valley, Triode -pentode, etc.] TP the using High frequency pentodes .. add H HF p11- only 5ft. of wire as an aerial with the re- Do., with variable mutual conduc- ceiver on the -ground. The signals are defi- tance--. ... .-. ... add Variable PV nitely of the " phones on the table " Double pentodes for " Quiescent " opera- variety and would comfortably work a small tion Q Quiescent loud speaker. Excellent CW reception of crystal controlled 56 Mc /s signals was ob- HEXODES X Hexode HE PTO DES H Heptode tained, hand capacity being negligible. The OCTODES new X23 battery triode-hexode is used as O Ostode Triode -Pentode TP the mixer, - followed by an IF stage on 2 Triode-Hexode Mc/s approx., with reacting detector and TX output tetrode, the total current consump- CATHODES and If cathode is filamentary F Filament tion being about 9 mA. One should . add, HEATERS. Filament voltage ... ..- ... 2, 6, etc. F2, F6 too, that the above results were obtained With I.H.C., heater not 4 y. 1 A. or when the 120 volt HT battery was only 4 v. 2 A., heater voltage ... 4, 200, etc. showing 90 volts on load ! 41 It is a good thing that moderately priced 42 British receivers of this type are becoming Do. 6.3 v., current not 0.2, 0.3, 0.4 or available for amateurs in this country, 0.6 A...... A Automobile (American) Do. 6.3 v. 0.2 A. .., A2 Do. 0.2 A. especially at a time when competition be- Do. 6.3 v. 0.3 A. tween ourselves and our American A3 Do. 0.3 A. cousins Do. 6.3 v. 0.4 A. A4 Do. 0.4 A. is getting very keen. Do. 6.3 v. 0.6 A. A6 Do. 0.6 A. The latest development here is, perhaps, Do. 13 v. 0.2 A. C2 Car 0.2 A. (English) the production finally by R.C.A. of a steep - Do. 13 v. 0.3 A. ... C3 Do. 0.3 A. slope RF -pentode, the 1,581, for television Do. 13 v..0.4 A. ... C4 Do: 0.4 A. receivers, it now being admitted openly that Do. 13 v. 0.6 A. -C6 Do. 0.6 A. the normal types, the 6C6, 6D6 and their Do. Universal AC/DC, current not 0.2, 0.3, 0.4 or 0.6 A. U Universal octal equivalents, the 6J7 and ,6K7, are Do. do. 0.2 A. entirely unsuitable for ...... U2 - Do. 0.2 A. ultra -short wave work. Do. do. 0.3 A. U3 Do. 0.3 A. What is more, the R.C.A. television trans- Do. do. 0.4 A. U4 Do. 0.4 A. mitter on top of the Empire State building Do. do. 0.6 A. 136 Do. 0.6 A. is now to be modified to bring it, more in line with current B.B.C. practice at Alex- Note. -Should two or more types of valve (made by the same manufacturer) have the same symbol under this system and andra Palace. In future, one understands, A Mazda TPF2A DC be dissimilar in some respects, distinguishing symbols should the component will be radiated, as has be added to indicate B TPF2B been the case with own such differences. The differentiating our television trans- symbols may be the letters A, B, C, etc., as now occasionally C, etc. Mullard 2D4A mitter since its inception. teed and would have no strict meaning. They would only 2D4B ETHACO M BER. indicate dissimilarity between types. The Wireless World, April 28th, 1938 J'SÌ

New Scheme for Simplifying Identification

to indicate only the general type of a This is, however, a state of affairs by no valve together with its filament or heater means unknown to -day, so that con- EONDENSER SPECIALISTS voltage and current. ditions could be no worse.. FOR OVER THIRTY YEARS A new scheme of this nature has been To obtain the full value of this scheme worked out and is given here together it would have to be generally adopted by with a number of examples. It may be valve makers, and if close co=operation

said that if this %uggestion were adopted between them could . be achieved it might indiscriminately it would lead to con- be possible to obtain that desirable con- fusion since different valves by different dition where a valve type XYZ is the same 'bakers might bear the same type number. no matter by whom it is made.

EXAMPLES.

Present Suggested Valve. Maker. Type No. Symbol. Interpretation.

FREQUENCY- Cossor ... 41MPG H41 Ileptode I.H.C. 4 v. 1 A. CHANGERS Osram ... X2.2 HF2 Heptode filament, 2 v. Mazda ... TP23 TPF2 Triode-pentode filament, 2 v. Mazda ... ACTH' TX4 Triode-hexode I.H.C. 4 v. not 1 A. or 2 A. Mullard... FCI3c OC2 (Mode I.H.C. Car -type 13 v. 0.2 A.

SCREEN -GRID Osram ... MS4 S41 Screen -grid tetrode,, I.H.C.; 4 v. 1 A. TETRODES Mullard ... 1'M12 SF2 Screen -grid tetrode, filament, 2 v. 4 taíl -14mp American 36 SA3 Screen -grid tetrode, Auto -type, 6.3 v.,0,3 A. H.F. PENTODES ... Mullard... SP 1:3C l'H C2 Pentode, H.F., I.H.C., Car -type, 13 v. 0.2 A. in daylight 7 American 6.17 PHA3 Pentode, H.F., I.H.C., Auto -type, 6.3 v. 0.3 A. American 6B7 2DPVA3 Double -diode, H.F. variable -mu, I.H.C., Auto -type, 6.3 v. 0.3 A. Why do all trains-goods and passenger -carry a tail lamp-even in daylight? DIODES ...... Cosser ... D134 2D4 Double -diode, R.F., I.H.C., 4 v (not 1.0 A. For safety-for signalmen to check that or 2.0 A.). the train is complete-that no vehicles TRIODES ...... Osram ... MH43 TH41 Triode, Ra> 7,00052, I.H.C., 4 v. 1 A. have broken away. Mullard ... 31 Z05-60 TF6 Triode, Ra<7,000.12, filament, 6 v. American 76 THA3 Triode, Ra>7,000d2, I.H.C., Auto -type, Wise set -makers and discreet amateurs e.3 v. 0.3 A. fit T.C.C. Condensers for the same reason-for safety. Because they know OUTPUT TETRODES Brimar ... 71)6 PU2 Output pentode, I.H.C., Universal, 0.2 A. that backing each condenser is 32 years and PENTODES Osram ... KT42 K42 Output tétrode, I.H.C., 4 v. 2 A. L research American 38 PA3 Output pentode, T.H.C.,Auto-type, 6.3 v 0.3 A, of specialised -32 years devoted to building condensers and nothing but DOUBLE OUTPUT Osram ... B21 BF2 Class B double -triode, filament, 2 v. condensers. Because they know they're VALVES Osram ... QP21 QF2 Double -pentode, filament, 2 v. safe with T.C.Ç. RECTIFIERS ... Brimar ... 1D5 R2U2 11.T. Rectifier: 250 v., Universal, I.H.C., 0.2 A. American 80 2R4F5 Double H.T. rectifier, 400 v. filament, 5 v. .. for the same reason that wise setmakers and shrewd

CLIX VALVE HOLDER top -cap connector. It consists of a split ring amateurs always use fitted with a insulating ANEW valve holder for American Octal - terminal of black base valves has been produced by material. It is priced at i d. British Mechanical Productions, Md., of The well-known Clix All -In Terminal is 99a, Rochester Row, London, S.W.'. The now available in brown, with markings for holder is of the chassis -mounting type and Aerial, Earth, Input or Output. It is listed ät 6d. N ALL- BRITISH E.T.L. VALVE TESTER IN the review of the Electrical Test CONDENSERS Laboratories' Valve Tester which ap- peared in The Wireless World for April '4th, 1938, it was not perhaps made suffi- ciently clear that this equipment enables For valves with the valves of all types to be checked. Not only American can all standard types of British, American Octal -base. and Continental valves be tested, but also the Ostar -Ganz types. The meter included is also available for external use as a three -range voltmeter. the spring contacts are floating, making for easy insertion of the valve and giving an anti-microphonic action. There is a line pres- sure between the contacts and the valve L'Encyclopédie de la Radioélectricité, A -G.- Etienne Chiron, 4o, Rue de Seine, Paris - pins, and they are self-cleaning. Unusually Vie. low losses are also claimed, as the metal parts only contact with the solid dielectric The first volume of an encyclopedia cover- ing electrical and wireless matters has been re- which are widely separated. THE TELEGRAPH . CONDENSER CO.LTD. at the rivets, ceived. It is in French, but at the end of the This new product is at present available explanatory paragraphs the English and Ger- WALES FARM RD. NORTH ACTON.W.3 only. to manufacturers man equivalents of the word or phrase are M 656 This firm is also producing an Octal-valve given. The Wireless World, April 28th, 1938

cell is arranged to receive light direct from the lamp, the result- ing currents from that cell being supplied to amplifiers, arranged in parallel with the main signal am- Recent plifiers, and including - Inventions a phase changing circuit and a telephone. Brief descriptions of the more interesting radio are arranged immediately after The telephone is coupled to a devices and improvements issued as patents the anode, the adjacent ends microphone in the output circuit being of opposite polarity. They of the main amplifier. The result will be included in this section are also biased with an increasing is that the " undesirable " current positive voltage to provide an fluctuations in the parallel circuit electrostatic focusing component. are fed back in phase-opposition " DIELECTRIC GUIDES " the amplifier V. Then if a non- Zeiss Ikon Akt. Convention with those in the main amplifier IN order to amplify or relay very linear resistance, such as a tung- date (Germany) May 28th, 1936._ so that the two cancel out. sten -filament lamp filament, No. 478410. high -frequency currents along -is o o o o Standard Telephones and a transmission line of the so- 'used, say, as the resistance R3, its Cables, Ltd. (assignees of A. W. called " dielectric -guide " type, a resistance will increase with the TELEVISION TRANSMITTERS Horton, Junr.). Convention date special triode valve is used having output voltage, and this in turn, THE figure shows a television (U.S.A.), July 23rd, 1936. No. a control grid in the form of a will decrease the negative feed- transmitter of the Iconoscope 480483. perforated wall or " septum," back across Rs. In other words, which divides the valve into two the Overall gain of the amplifier separate chambers. The transmis- will increase with signal strength, sion line is broken at the relay thus giving the effect of volume point, and its two ends are made expansion. to overlap along the grid or If, on the other hand, the re- septum " of the valve, which is sistance Rr is replaced by the thus made common to both parts tungsten -filament, the amount of of the line. negative feed-back will increase This prevents undesirable with the output voltage, and this capacity coupling between the will give the effect of volume con- valve electrodes, and confines the traction. Alternatively, a non- energy transfer to the electrons linear resistance having a negative passing through the meshwork of temperature coefficient, such as a the grid. The two overlapping carbon filament, can be used to parts of the guide -Erie mayl also give similar but opposite effects. be provided with " iris ' dia- G. W. Johnson' (communicated phragms, which are spaced a by Pliilco Radio and Television quarter wavelength away from the Corporation). Application date, coupling -grid, so as to form end - August 4th, 5936. No. 479485. sections tuned to the working 0 o o o wavelength. Standard Telephones and Cables, CATHODE=RAY TUBES Ltd. (communicated' by Western IN focusing the electron stream of a cathode-ray Electric Inc.). Application date, tube on to Iconoscope tube embodying electron multiplier for television March ist, 1937.. No. 478462. the fluorescent screen, it is pos- transmission 00 o o sible to use either the magnetic field from a winding located out- type NEGATIVE FEED=BACK side the glass tube, or the electric in which means are provided TELEVISING FROM AN AERO- TILE figure shows a low -fre- field from electrodes carrying high to intensify signal currents by PLANE quency amplifier in which a voltages inside the tube. The secondary emission. The picture IN war time the pilot of an aero- negative feed-back circuit compris- to be televised is first projected on plane may require to transmit latter arrangement is generally to ing resistances Rs, R2, R3 is preferred, because there are cer- a photo -sensitive screen S of the from his machine, whilst in flight, branched across the secondary of tain disadvantages attaching to mosaic -cell type (shown foreshort- pictures of an enemy terrain, such ened) which is then scanned by the as a gun the output transformer T. High - the use of external windings. - emplacement or other frequency signals may be applied electron stream from the gun G of position of military interest. If According to the invention, the the at S, rectified at D, and applied electron stream is focused by a tube. Instead of using the re- high-speed scanning is used, the through a potentiometer P to the combination of electric and mag- sulting discharges from the back of movement of the machine will not amplifier V. Or the pick-up from netic fields, both the screen for signalling in the nor- make much difference to the trans- of which are pro- mal way, a gramophone may be applied di - duced inside the tube. The advantage is taken of the mitted picture, but practical con- fact that as the electron stream siderations appear to rule out any passes over the screen S secondary but the simplest type of transmit- , electrons are emitted in proportion. ting apparatus. HT+ to t the light intensity of each pic- This naturally implies a low - ture point. speed of scanning in which case the These are attracted into the rapid movement of the machine " leg " L of an electron -multiplier would lead to distortion. M by the high biasing -voltage The invention discloses means on an accelerating electrode A, and for producing, at the transmitter, are made to impact first against an additional movement in the one target electrode T and then direction of line -scanning, and at D against a second electrode Tr. the frequency of frame scanning, so Secondary emission takes place as to compensate for the motion at each impact, so that a greatly of the transmitter when in opera- amplified signal current -becomes tion. The correction is derived available at the output electrode O. from the time -base circuits, in the Marconi's Wireless Telegraph case of a cathode-ray tube, or by Co., Ltd. Convention date imparting an additional swing tc (U.S.A.), July 261/7,.1935. No, a vibrating -mirror scanner. G - 478967 Baird Television, Ltd., T. M. C. 0000 Lance; and B. B. Austin. Appli WHEN televising, say, from a cation date, August 6th, 1936. No, studio, where the scene is 479458. R3 artificially illuminated, the re- flected light supplied through the scanning device to the photo- The British abstracts published electric cell may contain, in ad- here are prepared with the per- Negative feed-back amplifier, mission of the Controller of which may also include volume dition to the ordinary light -and - expansion or contraction. 11.Á1. Stationery Office, from 'shade effects, a fluctuating coin- spaciflcations obtainable at the ponent from the flood -light lamp, Patent Office, 25, Southampton rectly across P. One advantage focusing electrodes are cylindrical particularly if the latter iy of the arrangement is that any form, Buildings, London, W.C.2, price in and are made of some energised from alternating mains. 17- each. A selection of patents distortion components present will permanently magnetised metal, In order to remove this unde- issue.' in U.S.A. is also in- be reduced by the negative feed- say steel or a " Hensler alloy." sirable component from the signal cluded back from Ri on to the grid of Preferably two such electrodes currents, a second photo -electric