EDITORIAL COMMENT Editor : HUGH S

THE PRACTICAL RADIO JOURNAL 27 t12 Year of Publication wo

No. 923. FRIDAY, MAY 7TH, 1937.

Proprietors : ILIFFE & SONS LTD. EDITORIAL COMMENT Editor : HUGH S. POCOCK. television station will extend the range The Coronation of sight as well as sound, with the Editorial, arrangements to televise the procession and Publishing Offices : Broadcasts Advertising World-Wide from Hyde Park Corner. DORSET HOUSE, STAMFORD STREET, DENSE as will be the crowds LONDON, S.E.s. Some details of all these Coronation lining the route of the arrangements are given elsewhere in Telephone: Waterloo 3333 (50 lines). Telegrams: "Ethaworld, Sedist, London.' Coronation procession and this issue. - participating directly in this In addition to broadcasting and tele- COVENTRY : Hertford Street. are small Telegrams: Telephone: great occasion, the numbers vision programmes-mention should 'be "Autocar, Coventry." 5210 Coventry. by comparison with the vast corn - made of the elaborate planning of will be brought into BIRMINGHAM : munities who loud speakers and amplifiers along the Guildhall Buildings, Navigation Street, 2. touch with all that is happening in processional route, as well as in centres Telegrams : Telephone: London through the medium of broad- will be Autopress, Birmingham." 2971 Midland (4 lines). throughout the country, which casting in this country, Empire trans- primarily used to reproduce the Abbey MANCHESTER : 260, Deansgate, 3. missions to the Dominions and ceremony to those outside. The whole Telegrams : Telephone: .Iliffe, Manchester." Blackfriars 4412 (4 lines). Colonies, and commentaries arranged organisation is one which commands by foreign countries which will be put admiration and we believe that the GLASGOW : 26B, Renfield Street, C.2. networks of their own LIegrams: "Iliffe,Glasgow." Telephone: Central 4857. out over the success of these arrangements will broadcasting services. prove a full reward to all those who PUBLISHED WEEKLY. ENTERED AS SECOND in complet- CLASS MATTER AT NEW YORK, N.Y. Months have been spent have been associated with them. ing the organisation and for weeks Subscription Rates : past Post Office and B.B.C. engineers Home, LI Is. 8d. ; Canada, Lz is. 8d. ;. other of countries, £c 3s. zod. per annum. have been engaged on the task installing the necessary microphones Short Waves As many of the circuits and appa.atus describea in these and linking them up to the control pages are covered by pa ants, readers are advised, before Remarkable Vicissitudes making use of them, to satisfy Ihernsetvec that they would points and amplifiers required. It is be infringing patents. not stated that a total of no fewer than N account is given in this issue fifty -eight microphones will be used of the recent extraordinary during the clay, thirty -two for the behaviour of long- distance actual ceremony within the Abbey and short -wave transmissions. The most CONTENTS the remainder for commentaries on the surprising and prolonged interruptions progress of the procession and for of short -wave communication between Page obtaining " effects " along the route. East and West which have yet been of Editorial Comment . . . . 437 Every precaution has been taken to encountered in the history these will stand wavelengths have occurred during the 5 to 15 Metre Reception -A Three - ensure that the preparations requirements past week or so. In our report some valve Battery Set . . . . 438 up to the most exacting of the occasion. explanations are given as to why these The Royal Week -A Guide to the The responsibility which rests upon conditions have developed, but the Principal Broadcasting Events 442 those entrusted with the task of explanations tend to increase rather Why the Triode - Hexode ? I 446 broadcasting the Coronation is great than diminish the scientific interest these peculiar happenings arouse. Broadcast Brevities 419 because it can be said that the whole which world will be listening, and the event One cannot help contemplating what Current Topics . . 450 will be one to be remembered in millions an extraordinary upheaval in our New Apparatus Reviewed 451 of homes and to go down in history as modern civilisation might be caused if the first occasion when, through the physical changes of this nature affecting Principal Broadcasting Stations . . 452 medium of broadcasting, so vast an short waves were not confined to these Anti-Interference Filters. I 454 audience could participate in a cere- bands ; but it must be left to a Jules or H. G. Wells to tell the story Random Radiations 456 mony, local geographically, but which, Verne nevertheless, is world -wide in signi- of what might happen if the ether Letters to the Editor 458 ficance. suddenly failed us as a medium for

Recent Inventions. . 460 To a restricted audience the B.B.C. radio transmission.

www.americanradiohistory.com 438 Wireless World, May 7th, 1937. 5 -15 Metre

THREE - VALVE BATTERY SET FOR THE EXPERIMENTER

By D. W. HEIGHTMAN

negligible on lower amateur bands) could substitute 15 mmfds. frequencies, a r e in place of the larger condensers. certainly not so on As the grid connection of the SG valve these frequencies. is brought out on top, the tuned grid In fact, the design circuit of this valve can be sufficiently of such a receiver isolated from the detector tuned circuit, merely involves adapting a conventional without screening, to prevent self oscilla- circuit for ultra high frequencies and find- tion in the RF stage, thus simplifying con- THE ultra high frequencies are ing daily providing a suitable layout and the choice of the struction. more of interest right components. for listeners and for The aerial is coupled by Li and either the outlay It was decided to use of a modest a tuned grid cir- the ordinary inverted L or a twin feeder sum it is possible to cuit for the RF stage, build a receiver which as the aperiodic RF type may be used. In the former case one will give many choke, commonly used in hours of extra radio this position, end of Li is connected to the chassis and enjoyment. With this often causes false fact in view the signals. Since the tuning in the latter one feeder is connected to set has been designed of such a stage is comparatively to provide an inexpensive, broad the either end of Li. An earth will not simple yet tuning- condenser can satisfactorily be generally be found efficient receiver, primarily for frequencies necessary. ganged to the detector stage condenser. The RF stage is coupled between 20 and 6o Mc / s suitable to the detector and for The tuning condensers have a capacity by means of the condenser 'phone or C.W. reception. At the C3, a 3o mmfd. same of mmfd. In view of the wide fre- mica trimmer with a time, with suitable coils, 40 ceramic base, and the it gives an ex- quency band to be covered, this value was choke cellent performance on frequencies Ch.i, which should be of a good down decided upon as being the most section wound type. to 5 Mc / s and suitable, Besides acting as a is extremely easy to handle. since smaller condensers necessitate coupling Being battery operated so condenser C3 is useful for match- and compact, the many coil changes to completely cover ing up the RF and detector set can be used for portable work. a tuned circuits, range of 20 -6o Mc / s. If a good slow- Provided it is properly designed and motion dial is fitted no difficulty is expe- handled, the " straight two " type of rienced in tuning with the mmfd. con- receiver is capable of giving excellent 40 densers, even at the highest frequency of results, but suffers from the great disad- the tuning range. Those requiring vantage that the aerial has a most undesir- only a limited frequency range (for able effect on the detector stage of causing example, the 56 and 28 Mc /s instability of the received signals (unless the aeriál is rock- steady), and poor reaction-i.e., dead spots on certain sections of the tuning range. It was therefore decided that a radio frequency stage, prior to the detector, would be essential. The next question was to find a valve suitable for this stage, as most SG valves, far from amplifying, produce a considerable loss in signal strength on frequencies above 25 Mc /s. Obviously, the acorn type of valve was the best for this position, but its use was ruled out on a question of cost ! Fortunately, the special Hivac SG22oSW was found to be suitable for the purpose. This valve has the grid connection on top, is fitted with a ceramic base, and, as will be seen later, allows an excellent layout to be obtained, also no noticeable loss in signal strength is pro - di ced up to 6o Mc /s, while some gain is obtained lower than about 35 Mc /s. Inspection of the circuit in Fig. r will show it to be quite conventional. As in all ultra high -frequency receivers, the orthodox circuits work well, provided extreme care is The RF valve is mounted above the tuning exercised in the layout of condensers and both grid and anode leads components, and it is remembered that are thus made as short as possible. small capacities, leads, etc., while being

www.americanradiohistory.com 439 Wireless World, May 7th, 1937.

THE ultra -short wave receiver described in this article will provide a new interest for the amateur experimenter since it covers a waveband below that of the average short wave set. It is well suited also for the more experienced ultra -short Reception wave worker, for every care has been taken to make the set as efficient as possible.

This view shows the of method A zo mmfds. reaction condenser is as varying the supporting the RF coil and . . . . fitted, as provided a good section wound capacity of this RF choke is used in the detector stage condenser alters this condenser is found to have sufficient the amount of capacity, and, being small in value, stray capacity gives a control of reaction which is not across the detec- too critical. The detector is resistance - tor circuit. transformer- coupled to the output stage As the signals as this method of coupling is found to to be received be less likely to cause " threshold howl" usually have low (i.e., howling on the edge of reaction) values of than the direct transformer method. strength, reac- The condenser C7 and resistance Rz tion has been re- shown in the circuit diagram are actu- lied upon as the ally contained in the Transcoupler unit. o n 1 y volume The output circuit requires no com- control neces- ment, as it is quite straightforward and sary, but, if de- any low consumption high gain pen- sired, other tode is suitable for this stage. It should forms of control be mentioned, however, that the small could, of course, RF chokes in the output leads are neces- be fitted. sary in order to prevent body capacity The Hivac effects, particularly when using head- DzioSW 11 a s phones. been chosen as It is recommended the detector that all the makes of valve as this components specified type has been for the RF and detec- found to oscillate tor stages be adhered more readily at to, as a change in the UHF than most type of a component battery triodes, is liable to have a and the fact that the grid con- considerable effect on nection is on top also simplifies the performance of and improves the layout of the the receiver. The set. Grid leak and condenser layout depicted in values for the detector have been best the drawings and chosen, after test, as giving the photographs should and also smooth reaction rectification be carefully followed. should be noted that the the detector also control. It valve which is seen The coils for various frequencies are leak is taken to the positive side grid behind the Trans - shown in the illustrations, and they can of the filament circuit. coupler unit.

+H T +H T 75V 120V

1 CHOKE 3 00009, --0+ ECHOKE OUTPUT Ti CHOKE 2 r- 1 62115.613%-o- ::,f CHOKE 4 'bob6b.` LOW C3 2 'TIM.; R2

C7 GRID Al ANODE p,

L1 EARTHO QG B L

q---L..T A2 S1 T

Fig. s.- Theoretical circuit diagram of the ultra-short wave receiver.

www.americanradiohistory.com Vfp ®@o, '440 MAY 7th, `joreIlc1 1937 5 -15 Metre Reception - or brass. It is cut to the size given be obtained in these condensers the detector coil base is from Messrs. Denco, , 59, the drawings, and the brackets for sup- Burrs Road, supported by means of 14 gauge thick Clacton, Essex. These porting the detector -valve holder and RF wire connections, coils were designed specially as will be seen in the for this re- tuning condenser are made from the same photograph, thus the ceiver as the few types at present connecting leads are on the material. The base of the set is _prefer- reduced to a minimum length. market are difficult to adapt for an ably made of aluminium- covered plywood The Eddystone Frequentite valve - efficient layout. By being mounted close gin. thick, known as Plymax, and the holders should now ; to the condensers they allow be mounted that for a minimum panel is fixed to it by means of small the detector being supported Iength of connecting leads to be used both by a brackets. At the rear of the base the bracket held in position by the panel on the formers and in the receiver. ebonite strip is 2.?sn held by two brackets, bracket bolts. After the RF tuning con-

7 -(-13/8" 3Y;

SG 220 SW t 17/16 LAYOUT OF COMPONENTS and the 5/1"6 PRACTICAL WIRING PLAN

D210 SW 8

35/16

BASEBOARD

4 CHOKE 2

ANODE-LOW -HIGH !tamer. 8

GRID -G B -EARTH 0 0 0 0 0 23/8" CONTROL GRID

L1 & L2

p 2 4 OUTPUT a-2 + 3i A2 VI A2 OUTPUT- CONNECTIONS FOR COIL BASE

-4-11/4" 212" c 1

It is essential that everything be made which can be made by bending up small denser rigid and vibrationless and coil base have been mounted otherwise trouble pieces of the aluminium used for the the rest of the construction will be experienced with and wiring " wobble " on panel. This strip carries two aerial ter- can be carried out in any the received signals. For this order the con- reason the minals and two 'phone terminals. The structor prefers. It is advisable panel should be at least r /16th inch first, thick tuning and reaction condensers should however, to put the GB battery and it can be made of aluminium, and the copper first be put in position on the panel. On HT reservoir condenser C8 in their posi-

www.americanradiohistory.com s 41r MAY 7th, 1937 Wfi s WopIlcl 5 -15 Metre Reception - tions under the baseboard so that sufficient space is left for them when wiring. Most of the wiring can be done under the base, thus adding to the neatness of the set, and the battery leads are brought out through a hole in the rear terminal strip. The on -off switch breaks the LT negative lead, one side being taken direct to the panel. All baseline connections are taken to the nearest point on the chassis ; for instance, the negative filament terminals on the valveholders are taken to the bolts securing the holders. When connecting up the Bulgin transcoupler the HT positive is taken to the low resistance terminal. It should not be overlooked that the HT positive SG connection is taken to what is usually the grid pin on the SG22oSW valve. When fixing the slow motion dial the maker's instructions should be carefully followed. On completion no difficulty should be experienced in getting the set to operate as there are practically no initial adjust - ments. An HT voltage of about 120 volts gives best results with i5 volts on the SG of the RF valve, but the set will work satisfactorily with HT batteries as The grid battery, telephone RF chokes, quite HT wiring approach of the sum- C3 is set with its screw condenser C8, filament and especially with the low as 75 volts. are all accommodated below the base- those within 8o half undone. If the layout and mer months. However, about board. or so (in most directions) of shown in the drawings have been miles wiring Alexandra Palace will be able to test on adhered to the ganging of the two tuning when con- should be correct without the television transmissions condensers longer distances are poor. further adjustment, but in order to check has to be increased for peak tuning C3 ditions for whether this is so or not the following pro- should, of course, be decreased in value. cedure should be carried out. After The following ranges and dial readings The Radio Industry various coils. having tuned in a fairly strong signal with are those covered by the According to the official organ of the Indus- the dial at about 90 degrees, preferably For the highest frequency range the two - trial Dcvìloprncut Association of'Wolverhamp- coils are used and the coverage is ton, the local firm of Reproducers and Ampli- with the lower-frequency coils in position, turn New 62 to 42 Mc /s. The fiers, Ltd., has secured contracts in loosen the grub screw on the flexible approximately of heavy com- about Zealand and Estonia in the face coupler so that the spindle of the RF 56 Mc,'s amateur band is centred petition from America and Germany respec- tuning condenser CI can be rotated in- 5o degrees on the scale. The next range, tively. dependently of the detector tuning con- three -turn coils in this case, covers 48 to 41.5 Mc /s television A system of controlling traffic by loud denser C2. CI is then varied so as to bring 32 Mc 's and the be the first of its kind in at about 70 on speakers -believed to the signal up to a maximum. If it is sound transmissions tune -is being installed by the G.E.C. at the capacity is required on CI the scale. For the lowest range four - newly opened Kincardine-on -Forth Bridge, found that less cabin on the RF circuit into tune C3 should turn coils are employed, and these give a The controller will be stationed in a to bring in the crown of the bridge; a projection speaker slightly increased. This will mean coverage of 34 to 21 Mc /s and bring be on is mounted at each end. that C2 has to be reduced to receive the the 28 Mc /s amateurs round about 70 retuned this con- the scale. Two hundred a nd twentyy Philco receivers signal, and after having authori- above procedure is repeated In conclusion it may be as well to re- have been supplied to the education denser the ties of Uruguay'for use in the State schools of the signal is received with the mov- mind those new to ultra -high frequency until no sig- that country. ing plates of both tuning condensers in listening not to be disappointed if the same position. If it is found that CI nals are heard on any particular day, The new editi on (price Gd.) of a booklet issued by the V.G. Manufacturing Co., Ltd., Royal, London, N.W.ro, LIST OF PARTS. Gorst Road, Park describes at length the Simplat system of home Certain components of other makes but of similar characteristics may be used recording. as alternatives to those given in the following list. -- of test 1 Switch, QMB on /off, S1 Bulgin S80 Recent additions to the range Condensers: Bulgin LF10 by 1\Iarconi -Ekco Instru- Variable 1 Transcoupler, TI apparatus produced 4 Ltd., comprise an ultra- short-wave 2 40 rnin fds., Cl, C2 2 Valve holders, -pin ments, Eddystone " Frequentite " 949 signal genera tor, a valve inter- electrode Eddystone "Microdenser" 900/40 and a 1 Valve holder, 5 -pin W.B. Rigid Type capacity tester (0.000r to 1.0 mmfd.) 120 nrmfds., C5 describing these Microdenser " 900/20 I Battery cable, 5 -way Bulgin BC3 resonance test set. Leaflets Eddystone " Eelex are available. Address: Electra I .o inmfds. mica, C3 Eddystone 1023 4 Terminals instruments 5 Wander plugs Eelex House, Victoria Embankment, London, W.C.2. Fixed et- mica, C4 Hunt's 1121 2 Spade ends Eelex I c.0011)05 mid. 1175 Co., Ltd., have issued a 10.or mfd. non -inductive, tubular, C6 2 Plug =top valve connectors Belling.Lee A. l3arson and I Grid Bias battery, 9 volts leaflet describing a universal saw set; the saws Dubilier 4421/E as well 1 Knob for reaction condenser Bulgin K44 should be useful to wireless constructors r 2 mfds. 700 volts test, C8 Wego Plymax base, 7 x 8 x jjin. Peto.Scott as for general purposes. Messrs. Barson's new Road, 1 Dial, slow motion Aluminium panel 7 x 8 x ; bin. and 2 brackets for address is: Levsian Buildings, ill, City Utility " Micro =dial " W 181 RF condenser and detector valve holder London, E.C.i. Bulgin E1112 1 Flexible coupler Peto.Scott Miscellaneous : Reid megohms, ¿ watt, R1 Dubilier wire, screws, nuts, bolts, The price of Z3 r95. 6d. for the 1 Resistance. 5 Small quantity " receiver, quoted last week, Chl, Ch2 Denco ebonite strip 7 x rl x -,'iin., two small panel " Pocketphone 2 Section wound SW chokes, case ; leather and canvas Denco brackets, etc. sloes not include the 2 Small RF 'phone chokes, Ch3, Ch4 cases cost respectively 12s. Gd. and 5s. Gd. Valves : Hivac 1 Set of 6 coils (3 ranges) and 2 bases Denco s SG22oSR', I DzloSW, i Y22o. extra.

www.americanradiohistory.com -442 Wireless World, May 7M, 1937.

from St. Margaret's Church, Westminster. At the conclusion of the service Howard Marshall and Michael Stand- ing will co- operate in describing the final scenes in the Abbey and its annexe.

The Return Journey : A Sound Picture Their Majesties' drive in state to Buckingham Palace is expected to begin at approximately 1.4o. George Blake will depict the scene as the cheering crowds, pealing bells, and barking guns proclaim the newly . crowned King and Queen of England. On the return journey, instead of observers, four " atmosphere " microphones will tell the story by reproducing THE focal point of the Copyright, "The Times" the sounds as HIS the procession week's broadcast pro- MAJESTY at his desk in Buckingham Palace whence he will passes. These grammes is, of course, speak to his people at 8 o'clock on Coronation Day. will be placed at approxi- the ceremony of the mately eight-minute intervals Coronation of Their Majesties here John Snagge will describe Harold Abrahams will then be -the first at the Victoria Em- King George VI and Queen the scenes as the procession heard from his observation bankment end of Horse Elizabeth on Wednesday next, starts down the Mall. Then post outside the Ministry of Guards Avenue, the second in May 12th. This great George Blake, from one of the Labour in Whitehall, where Trafalgar Square, close to the national event will be out- observation boxes above Mid- he will describe the scene as statue of King Charles I, the standing in many respects, not dlesex Guildhall facing West- the State coach approaches third on the roof of St. the least of these being the minster Abbey, will portray and passes the Cenotaph and James's Palace, and the enormous part broadcasting the arrival at the Abbey of the goes on to Parliament Square. fourth on the balcony of a will play in this, the first peers, commoners, and Domin- George Blake will then resume building in Piccadilly Circus. coronation of an English ion delegates. his story from Middlesex The sounds thus picked up monarch since its inception. At Buckingham Palace Guildhall in time to picture will be interpreted by S. J. de Much has the arrival of Their Majesties Lotbinière, the Outside already been From the inner courtyard of Broad- written both in The Wireless at II o'clock. casts Director, as each micro- Buckingham Palace, Harman phone World and in the daily Press Grisewood The Coronation is brought into circuit. will describe the Ceremony As the on what will be broadcast first appearance procession nears Con- during in public of As they move into the stitution Hill, Thomas Coronation Week, Their Majesties on Coronation Abbey Wood - which heralds what annexe, Michael Stand- rooffe, from his observation promises Day, when at 10.34 they leave ing will to be the most brilliant season tell of the marshalling post by the Quadriga -the the Palace. From his position of the Great Proceeding and in the last quarter of a cen- Harman four -horse statue surmounting Grisewood will have of the memorable scene as the Wellington Arch tury. From all this it is obvi- an unimpeded view -will have a ous that of them procession moves slowly up wide view of the approaching the B.B.C. Pro- entering the ancient gilded. the gramme Planning Depart- carpeted aisle. Some cavalcade. He will, as it State coach, and will be able thirty -eight microphones in ment has gone ` passes beneath him, be the " all -out " to to depict the scene as the Royal the provide listeners with the best Abbey will convey to only commentator to have the procession forms and moves listeners the service. Occa- opportunity possible entertainments and away. of describing the have By means of Micro- sionally the. B.B.C. Director two -mile-long procession ensured that the solem- phones placed over from nity of the arch of Religion, the Rev. F. A. beginning to end. the occasion is fittingly of the palace doorway, sounds portrayed by services, Iremonger, Chaplain to the John Snagge, from his corn - will be superimposed on his King, stationed alongside mentaries, and talks. narrative, post, will picture the scene thereby enhancing, Howard Marshall, will read as Their Majesties, o - > the realism at approxi- of his story. and, where necessary, explain mately 3.10, arrive at REX IMPERATOR As the the State coach begins its the rubrics. The only part of Palace and, as is expected, ON the all- important day all journey down the Mall, John the service which B.B.C. will not be appear on the balcony. transmitters will be Snagge will again take up the broadcast is that from the end " on the air " at 9.30, when, story. Whilst the procession of the Sanctus (the Ascription A Masterpiece of Organisation until 10.15, they will give the is journeying towards the " Holy, holy, holy, Lord To ensure usual morning weather fore- the smooth run- Abbey, Howard Marshall, God of hosts, ") to the beginning of such a complicated cast, etc., followed by a and sum- from the triforium, will pic- ning of the Lord's Prayer. intricately timed O.B., mary of Coronation news. At ture an the scene inside the This includes the administra- elaborate series of cue sen- 10.15 they will be switched Abbey as everybody awaits the tion of the Sacrament to the tences has been arranged so over to an observation post arrival of the King and Queen, King and Queen. During this some Soft. high erected that each observer will be above Michael Standing, from the break in the broadcast the able to indicate the stands in the Green that his de- Park Abbey annexe, will continue hymn "Let all mortal flesh scription is finished, thus en- overlooking the forecourt of this pre -view of the scene keep silence " will be broad- abling Buckingham Palace. the next commentator From which awaits Their Majesties. cast by the B.B.C. Singers to continue without a break.

www.americanradiohistory.com Wireless World, May 7th, 1937 443 oyaI \'Veek ---A Guide to the Principal Broadcasting Events Each observation point will be of Burma, Dr. Da Maw. BY THE AUDITOR fed with the whole broadcast Next will be heard the Viceroy programme so as to maintain of India, Lord Linlithgow, IN PREPARATION Scotland, Wales, Ireland, and continuity. speaking from India. The THERE have been a number London, will be assembled. At the conclusion of such a Prime Ministers of Southern of programmes arranged For this broadcast the B.B.C. masterpiece of organisation I Rhodesia, Dr. G. M. Huggins, which bear either on the his- is issuing a special souvenir am sure we will one and all and of S. Africa, General toric or spiritual aspect of the order of service. be thankful that we have been J. B. M. Hertzog, will next Coronation, not the least im- enabled to take part in the be heard from London. portant of these being the SYMBOLISM service and celebrations via The programme will also service in preparation for the ALL regular features and the ether whether having embody some of the features Coronation, which will be talks series have been sus- heard the broadcast along the which have become part of the broadcast from the Concert pended for this week, special or in our own homes. Christmas Day broadcasts. Hall, Broadcasting House, at programmes having been route to For, in addition to the official 7.55 on Sunday. His Grace arranged to help listeners GREETINGS greetings, representative citi- the Lord Archbishop of Can- realise the true significance KING GEORGE V was, in a zens will be heard speaking terbury will give the address; and solemnity of the centuries - special way, endeared to the from Canada, New Zealand, the Thanksgiving will be said old ceremony of the Crowning hearts of his people. This was Australia, and S. Africa, as by the Rev. M. E. Aubrey, of a King. undoubtedly largely due to his well as spokesmen of the M.A., Moderator of the On Sunday, in the National regular Christmas Day broad- people in the British Federal Council of Evan- programme, at 5, comes a talk King's by casts to the peoples of the Isles. gelical Free Churches; and the entitled " What Mean Ye British Empire, through which The greetings will be prayers by the Rt. Rev. Pro- this Service? " which is to be Tanner. he seemed to have a personal brought to a fitting conclusion fessor Daniel Lamont, D.D., given by Laurence E. link with his subjects. His. by the Prime Minister of the Moderator of the Church of In it he will emphasise the re- Majesty King George VI will United Kingdom, Mr. Stanley Scotland. The final hymn, the ligious significance of the speak to his Empire from a Baldwin, speaking from his National Anthem, and a Coronation. Mr. Tanner, who room in Buckingham Palace at residence in Downing Street. solemn fanfare will be broad- is Keeper of the Muniments at West- 8 o'clock on the day of his Fanfares to introduce the cast from under the Dome of and sub- librarian Coronation. It will be a Dominion greetings have been St. Paul's Cathedral, where minster Abbey, has also unique and historic occasion by Arthur Bliss and members of the Coronation written a history of the - composed will the first on which a King, will be played by the B.B.C. Choir, together with delegate Coronation Chair. This through the medium of broad- Military Band. singers from the Dominions, be broadcast at 4.3o (Reg.) casting, has spoken to his subjects throughout the world within a few hours of his Coronation. Preceding His Majesty's talk will come, for forty minutes from 7.2o, " The Empire's Homage." Listeners will be taken_ westward round the world as they hear a chain of greetings from the peoples of the Empire to their newly crowned King. From Ber- muda the Governor, Lt. -Gen. Sir Reginald Hildyard, will be heard. The Vice -Chairman of the Newfoundland Commis- sion of Government, Mr. W. R. Howley, will speak from London, as will also the Prime Ministers of Canada, Mr. W. L. Mackenzie King ; of New Zealand, Mr. M. J. Savage; of Australia, Mr. J. A. Lyons; and the Chief Minister

THE STATE COACH bearing Their Majesties King Edward VII and Queen Alexandra in the Coron- ation Procession on August 9th, 1902. The celebrations of this year will be recalled in " Scrap- book for 1902."

www.americanradiohistory.com 4-14 WIp4soo I1.4Y 7111, 1937 Word,c1 chestra will be in attendance. National programme on Sun- The party, which is due to day at 9.20 and Regionally begin at 8.15 (Nat.), will run on Monday at 7.3o, so that it for 75 minutes. will be thoroughly coherent in -> -> -> its radio version, although GALA REVUE bereft of its spectacular stage THE Coronation Gala Radio pageantry. Revue, which is to be broad- Mere narration would de- cast twice during this week, on stroy the i6th-century atmo- Tuesday at 8 (Nat.) and on sphere, and in place of a Thursday at 7.3o (Reg.), will narrator three imaginary i6th- be produced by Harry S. century players have been Pepper and John Watt. The substituted. These are Walter book has been specially writ- Wilkins, who is supposed to ten by Douglas Furber, his have written the piece ; Jill first work for the B.B.C. He Purtley, who is cast for a is, however, well known to leading rôle ; and Silas Sim- theatre -goers as the author and kins, a second -rate comedian part- author of many success- who wants to play all the male OBSERVATION BOXES erected above the stands at the Middlesex ful West End shows, number- parts. In the conversation Guildhall. From these the commentators of many countries will ing more than fifty. His and wrangling between the see... songs, ranging from " The three of them, the story of on Sunday, headed " The was to be expected in a Coro- Bells of St. Mary's " to " Lime - King's Chair." In it he will nation Year, was full of ac- house Blues," have sold in trace the history of the chair tivity, and this will be suitably thousands. from its installation in the portrayed. George Robey will take the Abbey by King Edward I to part of a waiter, Wilson Hal- the present time. Although CORONATION PARTY lett will be an exceptionally intended for the children, this A TOPICAL counterpart of the unpleasant child and Mabel broadcast will doubtless prove now well -established Christ- Constanduros will be mother. interesting to adult listeners mas Radio Party will represent The cast also includes Sir also. radio's contribution to the Frank Lawton, Cecily Court- Later on Sunday, at 9.2o jollifications of Coronation neidge, Lcslie Hutchinson (Reg.) , Felix Felton will pro- Day. Charles Brewer, who is (" Hutch "), Wynne Ajello duce a feature programme in charge, has invited the fol- and the Western Brothers. which he has compiled, en- lowing well -known artistes, Reginald Foort will be at the titled " The King's Anoint- who have all intimated their Theatre Organ, Harry Pepper ing." It will trace the con- intention of being present : and Doris Arnold at two tinuity of Kingship and the Elsie and Doris Waters, pianos, and pipers will be story of the Coronation Jeanne de Casalis, Clapham under the direction of Pipe - through the centuries. An and Dwyer, the Two Leslies, Major McIntosh. The Variety adaptation of this programme Leonard Henry, Davy Bur- Orchestra and a chorus of N.B.C. Phorograpi will be broadcast for naby and Michael 16 voices will be FROM AMERICA. Rudy Valee, children North. conducted by the well -known American band on Coronation Day at 5.15 Bryan Lawrence, Jan van der Mark H. Lubbock. leader and crooner, who will be (Reg.) . Gucht, Raymond Newell and heard with guest artistes in the National programme Stuart Robertson, four vocal- ".' MERRIE ENGLAND " on Saturday at 8. THIRTY -FIVE YEARS AGO ists well known to listeners, SPECIAL arrangements have ADDED interest will be given will, as a quartet, sing humor- been made for the production " Merrie England " will be to the broadcast of the ous part- songs. The Revue of Sir Edward German's told, whilst the music will be next Scrapbook, compiled by Chorus and the Theatre Or- " Merrie England " in the rendered by singers, the Charles Brewer and Leslie B.B.C. Revue Chorus, and Baily, which will be broadcast Theatre Orchestra. Stanford to -night (Friday) at 8 (Nat.) Robinson is returning from and on Saturday at 6 (Reg.), Italy to conduct this produc- since it covers the year 1902, tion, which will be heard in which included the Coronation St. George's Hall. of King Edward VII. The similarities and differences be- VISITORS TO LONDON tween the two periods of fes- FIVE continents will be tivity will be brought out by represented by interesting per- the collaborators in this pro- sonalities who will come to the gramme. It is hoped that microphone during the week's personalities in various walks broadcasts of " In Town To- of life who have memories of night." The producer, A. W. the ceremonies of 1902 will Hanson, will choose from the recall their impressions of the multitude of visitors to the events. Among these will be metropolis representatives of Captain W. A. Featherstone, Europe, Africa, Asia, America who was one of the State and Oceana, thus bringing to trumpeters at the Coronation. listeners a unique picture of Another important happen- life in all parts of the world. ing of the year was the end of Who they will be, however, the Boer War. Cecil Rhodes must remain a secret until they did not live to know of this, THE ABBEY ANNEXE as the people arrive. This view was taken by broadcast. ' ` In Town To- for he died on March 26th. a Wireless World photographer from one of the boxes before the hoarding around the annexe had been removed. The night " will be heard in the The entertainment world, as scaffolding on the left is for the stands. National programme at 7.4o

www.americanradiohistory.com ., WAT@Il2m - MAY 7th, 1937 445 WopDd1

' ` from Monday to Saturday of Britain Dances " will be trans- English, for the U.S.A., the Opera House by Bucharest at Coronation Week with the mitted. In this, dance bands following languages will be 7.35, and something less five -act exception of Wednesday. from all over the country will used : -Czech, Danish, Dutch, familiar, Mussorgsky's co- operate in a chain of Finnish, Flemish, French, Ger- "Khovanstchina," from Buda- BRITAIN DANCES fifteen - minute programmes man, Hungarian, Japanese, pest No. I at 8.15. Mussorgsky's THE dance music highlight linked together by and alter- Norwegian, Spanish (for the colourful music drama is some- of the week will occur on nating with the B.B.C. Dance Argentine) Swedish and Yugo- thing as intensely and touch- Coronation night, when, from Orchestra. The bands have slavian. ingly national as any Russian 10.15 until I the following been chosen as representative Many stations will be relay- music we know. The scene morning, a programme entitled of the areas from which they ing the address of His Majesty opens with dawn on the river will be broadcasting, and they in the evening. Moskva, and as the sun rises will thus furnish a sound pic- In compliment to England, the gathering light reveals the HIGHLIGHTS OF THE WEEK ture of Britain celebrating in a number of European stations FRIDAY, MAY 7th. dance the crowning of the are incorporating English Nat., 6.25. Sullivan programme : King. music in their programmes for B.B.C. Orchestra (E). 8, Scrap- Wednesday. Kalundborg at book for 1902. PROCESSION ROUTE IN MUSIC 8.5 gives a Henry Purcell Reg., 7.30, The King's Health - A DESCRIPTION 111 music of History of health drinking and orchestral concert, and at 10.25 toasting. 9.5, " Aidai the Royal Procession route to a programme of light English Abroad. and from Westminster Abbey music. The same station, at 9, Gomez festival programme Rome, will be broadcast by the 9.35, will radiate a speech by from La Scala, Milan. Variety Orchestra in the the Danish Foreign Minister, SATURDAY, MAY 8th. National programme on Sun- M. P. Munch, expressing his Nat., 3.45. Rugby League Cup day afternoon. Composers have country's congratulations to Final. 8, Rudy Vallee. written many popular works Reg., 6, Scrapbook for 1902. 8.15, our King and his people. Debate: "This Planning Busi- on the sights of London, From Radio Luxembourg on ness." and most of the important Tuesday at 6.3o the Rt. Hon. Abroad. thoroughfares have been por- Winston Churchill will give a Kalundborg, 8, Act 1 of " The Count trayed in music. The pro- in of Luxembourg." (Léhar). talk on the Coronation gramme will include a Corona- French and English. SUNDAY, MAY 9th. tion march, " Royal Caval- c o relayed o Nat., 3.30, Viennese Music cade," specially written by OPERA from Vienna. 7.55, Service in Royal COMMENTATOR for the N.B.C. preparation for the Coronation. Albert Ketelbv. Two relays from the Coronation broadcasts. Blevins 9.20, " Merrie England." _ Opera House grace the pro- Davis, Yale University authority Reg., 5, Stiles Allen (soprano) and THE CORONATION ABROAD grammes again this week. on British history, studying the B.B.C. Military Band. 9.20, THE great day will be duly The first is to -night (Friday) at imitations of the Crown Jewels. " The King's Anointing." 10, celebrated abroad in the broad- Purcell's " Sound the Trumpet." 9.5 (Reg.), when the second all Rus- cast programmes of the five Holy of Holies to Abroad. act of Verdi's " Aida," with sians Red Square in " Tosca." The B.B.C. has -the Stuttgart, 7.30, Verdi's continents. Martinelli as Radames and takes provided ten observation boxes Moscow. The action MONDAY, MAY 10th. Gina Cigna in the name part, of the at the Middlesex Guildhall and place in the time Peter Nat., 8, Sir James Barrié s " Dear with a mainly Italian cast. Great. The opera, on which Brutus." The action takes place at the composer worked for many Reg.. 7.30, " Merrie England." and Thebes in the 8.35, Ystalyfera and District Memphis years yet left only in a pro - Choral Society and the Band of time of the Pharaohs. The visional rough draft at his H.M. Welsh Guards. second is on premature death at the age of Abroad. Tuesday, when 9.25, Concert version forty -two, was overhauled and Kalundborg, Act 2 of Bizet's . of " The Mikado." finished by his friend, Rimsky- " Carmen " will Korsakov. TUESDAY, MAY 1 I th. be heard at 9.10 Nat., 8, Gala Radio Revue. 9,50, On Saturday at 9, Milan Memories of the Coronation of (Reg.). Sir gives " II deserto tentato," King George V. Thomas Beechani the work of a contemporary Reg., 6.45, Talk " Playing for Eng- will be conduct- Italian composer of first rank, land," by Patsy Hendren. 7.30, ing and there will " Dear Brutus. 9.10," Carmen." Casella, as well as the seldom - Abroad. heard comic opera by Rossini, PETER DAWSON, Paris PTT, 8.30. Reynaldo Hahn " Il Signor Bruschino." Both his music. the world -famous conducting a concert of Australian singer, of these will be relayed WEDNESDAY, MAY 12th. with Miss Vera Buck, from the Teatro Comunale, Nat., 10.15 -3.30, Coronation Broad- an Australian com- Florence. These two operas poser. He will be cast. 7.20, The Empire's Horn - will also be heard from Rome age. 8, His Majesty the King. singing one of her 8.15, Coronation Party. songs, " Reminis- on Wednesday at 9. Sulli- Reg., 10.15 -3.30 and 7.20 -8.15 cence," in his broad- van's immortal " Mikado " National programme. 8.45, cast recital on comes from Munich on Satur- at 6.45 " King's Post." Letters from Wednesday day at 8.10 and from Kalund- kings and queens. 10.15, Britain (Reg.). Dances. borg on Monday at 9.25. Abroad. four in Green Park near Buck- be a new Carmen in the person " Tosca," with a particularly Radio Paris, 8.30, Famous lovers in Palace for commenta- of Renée Gilly, who is the fine cast, comes from Stuttgart and operetta. ingham opera tors to broadcast descriptions daughter of the well -known on Sunday at 7.30. On that THURSDAY, MAY 13th. of the scenes to their respective baritone, Dinh Gilly, while evening also " Tiefland," the Nat., 6.30, Band of H. M. Cold- It has been neces- Don José will be sung by the masterpiece of that dynamic stream Guards. 8, Choral and countries. to make soundproof famous French tenor, Georges Glasgow -born genius, Eugen Orchestral concert. 1 0.25, sary these Albert Hall Costume Ball. in order to ensure there is no Thiel. d'Albert, comes from Frank- Reg., 7.30. Gala Radio Revue. 9, interference from adjacent The week is also rich in furt at 8. Thursday brings us " Gradely Folk," programme on commentaries. The effects, opera from abroad. To -night the three -act comic opera, rural areas of the North. therefore, are being provided (Friday) we have that peren- ' ` Die drei Pintos," by the I Abroad. Lyons PTT, 8.30, Operetta music. by outside microphones. In nial delight, " Figaro," re- king of German romantic com- addition to the commentaries in layed from Romania's Royal posers, Weber.

www.americanradiohistory.com 44.6 Wireless World, May 7th, 1937. Why the Triode-Hexode? PART I.- DEVELOPMENT OF THE 1ST -DE- TECTOR TYPE OF FREQUENCY CHANGER

By J. A. SZABADI this introductory (Technical Department, Tungsram Electric Lamp IN article the Works). author traces the development of the superheterodyne frequency changer, valve had to be a detector, and provides graphical explanations and hence it was called the first detector. The actual of the di,faculties encountered with demodulator which turned the radio fre- early frequency changers and the quency into audio frequency, and which reasons for the development and present popularity of the triode- lzexode.

_11-1'11l Fig. 3. -The starting potential in ii`r - :r 111 early valves was generally in the positive region of grid potentials. VER since the invention of the ji superheterodyne method of recep- 2nd HAR MON fO y'' EG f s essential or axiomatic, and was I F RESULTANT OF F tion in 1917, frequency changing l á only a consequence of the type F. has . EG f osc. been the ever-present problem. (a) of mixing used in those early Every development, though hailed as the days, and, in fact, it will be final solution, has been found to bring new f S .1>n. shown that rectification in the difficulties in its train. ",\ mixer in modern valves is actu- In the Ab early days, two valves were in- 1t Ala ally to be avoided at all costs, variably required for changing frequency, 1 as its presence is responsible for one valve functioning as an oscillator while nearly all the troubles which in the other the mixing of the desired ' caused the superheterodyne set to be shunned by many of the (b) early enthusiasts. The Levy- Armstrong mixet circuit (Fig. 1) was a pure addi- Fig. 2.- Diagram (a) shows additive mixer, i.e., tive mixing the amplitudes in grid- rectifying ist of the input signal detector ; no beat -frequency is and the produced by additive mixing when oscillator wave were added to- rectification is absent as in gether arithmetically. If we diagram (b). examine Fig. 2b; it will be seen that the resultant IF ampli- was situated after tude of pure addition is zero, and it is the IF amplifier, only when rectification is present, as in naturally became Fig. 2a, that a resultant IF amplitude is the second detector. produced. It will be readily appreciated We now know that that it does not matter which frequency is this early rectifica- rectified, whether the signal frequency or tion is by no means the oscillator frequency, or both, for in

Fig. 1.-The classical frequency- changing circuit. Fig. 4. - " Ultra- signal frequency with that of the oscillator dyne " circuit in took place, and so was produced a third which Vi is not a frequency, the so- called intermediate grid detector, but fre- virtually an RF am- quency, to which the anode circuit of the plifier with anode mixer was tuned. As it was found that, rectification of the in those early mixers, a larger IF output oscillator voltage, was obtained when the incoming which is applied in signal place of the usual was rectified, it was assumed that this steady HT voltage.

www.americanradiohistory.com MAY 7th, 1937 VellmIlmooIll 447 In Why the Triode- Hexode ? - bias, the valve passed no grid current, and was different, being mainly additive. either case beat notes are produced. Levy thus acted quite well as an RF amplifier this arrangement the oscillator frequency and Armstrong both used this method, and of very small signals. Fig. 5 shows the is rectified by space- charge grid action, hence they introduced the term first actual sequence in time. (As this type of the first grid having a slight positive poten- detector. mixing very closely resembles a strobo- tial. The second grid -the modulator in this case -does not directly ° Even the early electrode and acts experimenters r e - affect the cathode space charge, ; it should cognised the serious EA(fosc.) only as an amplifier control grid limitation of this IF RESULTANT method ; the sensitivity of the whole -E H T }HT tHT receiver was limited by the threshold value of the grid leak rectifier. Prac- tically all valves in Fig. 5.- Showing additive mixing in ' ` Ultra - those days had dyne " circuit. their grid current starting potential in the positive region, scopic action it which meant that unless the grid bias was was later called very critically adjusted the detector would " Strobodyne " in only respond to a signal larger than this America. ) limiting value (Fig. 3). 'In modern ter- At about the minology, the receiver squelched all signals same time an en- below a certain value. This was very in- tirely new type of convenient because in those days all sta- mixer circuit made tions were very weak, and such a limita- its appearance on tion was looked upon as a very serious the Continent. Only handicap. o n e double - grid In the early twenties a great advance valve was required

+H T

Fig. S.-Cathode- coupled circuit with triode -pentode valve.

to perform the be slightly negative with respect to the combined functions grid current starting potential. of oscillating and The mixer action in this case is also mixing (Fig. 6). mainly additive, and very similar to that Although this cir- shown in Fig. 2a. The more assymetric- cuit closely re- cally the valve oscillates, due to the posi- sembles that used tive space- charge grid, the greater is the with more recent IF output. multi grid con- About 1929 the Americans produced verters, its action their first mains- operated screen -grid valve, Type 24. They no doubt tried to use this four -electrode valve in a circuit similar Fig. 6.- (Above) . The first single -valve mixer circuit, as widely used on the Continent. to Fig. 6, but could Fig. 7.- (Right). Cathode injection mixer, not have been very made practicable by the introduction of the successful, due to indirectly- heated SG valve. the entirely different construction of "` Ultra - was made when, in the so- called valve, and rectification in the first this dyne " circuit, grid very soon a special was dropped in favour of detector stage circuit suited par- (not anode -bend) of the anode rectification ticularly to t his amplitude oscillator frequency while large- type of valve was letting in the minute signals from the weak stations in an uninterrupted un- evolved (Fig. 7). distant This was generally rectified condition. seen from Fig. 4 that from the called the cathode It will be mixer cir- view of the incoming signal, the injection point of in it the mixer valve is really an RF amplifier, cuit, and voltage is varying continu- input signal is recti- whose anode anode -bend ously, it being supplied by the oscillator fied by and not by an HT battery. The slightly detection. one - valve positive starting potential of early valves This actually favoured this circuit, as, with zero frequency changer,

www.americanradiohistory.com 448 Wgpg.®00 MAY 7th, 1937 Wopkl Why the Triode- Hesode ?- the " storm " is due to another smaller the Indian broadcasting authorities have though very efficient, had all the disad- region which appeared over the east limb come to the conclusion that the lower vantages of the additive method, which near the time of the start of the short-wave medium wavelengths are going to give the were mainly whistles and cross- modula- disturbance. The larger spots do not always best results in most places. I have not yet tion. These troubles appear to be the most active. Finally, one heard the reason officially given for this, but were even more remarkable pronounced, because overall sensitivities feature is that during the very it may be because reception on such wave -, poor conditions on Saturday z8 Mc /s signals lengths is found to were now much greater. An additional suffer less from atmo suddenly came in in fine fettle from India! spheric interference. Atmospherics can be shortcoming was a considerable variation Was this E region bending? poisonous in many parts of India. in sensitivity over the tuning range, due Be that as it may, seven out of nine of to the difficulty of designing a suitable the wavelengths now announced are below stable oscillator system which would not 300 metres. The remaining two are Delhi, " squeg." 340 metres, and Trichinopoly, 397. In 1933 attempts were made in this Distant Reception Notes The first of the new transmitters is ex- country to use the same circuit, but with pected to be at work in August, and the AS I write, the Conference summoned at remainder should an output pentode in place of the screened all be in action within less the instance of Holland is still dis- than a year from then. D. EXER. tetrode. This arrangement was super- cussing the state of the long wave seded in 1934 by the Mazda cathode - band and endeavouring to find some means coupled triode -pentode (Fig. 8). of cleaning things up a little. Hilversum This circuit was a considerable improve- No. i teems at last to have realised that ment on previous types, and can be said it cannot go on holding on to the wave- Television Programmes to have been the best of all the additive length of 1,875 metres, which was allotted Brasov. In Transmissions are from 3 -4 and 9 -10 mixer systems. Cross -modulation was under the Lucerne Plan to daily June, 1933, when the plan was drawn up, (except May 12th). greatly reduced, but due to the cathode : the Romanian transmitter was rated at only Vision Sound : coupling there were still inherent faults, I kilowatt. Huizen, as Holland's long 45 Mc /s. 41.5 Mc;s. namely, a tendency towards cross-modu- wave was known, refused wave- then the FIIUIDAY, lation on strong signals and pulling or length of 1,345 metres offered to it and, MAY 7th. feeling sure that it could down the 3, Starlight : Dances by Vera Zorina, star of interlocking on weak stations or on shout " On Your Toes " at feeble Brasov, grabbed the 1,875 -metre the Coliseum. 3.15, shorter wavelengths ; also, the possibility Friends from the Zoo. 3.30, Gaumont -British channel on plea it had established of modulation hum, particularly in AC/ the .that News. 3.40, Theatre Parade ; Flora Robson DC sets, was increased, due to the floating a right to it by long use. in Act II of " Anna Christie " as produced at Since Brasov, now known as Radio the Westminster Theatre. cathode. Roumania, went up to 15o kilowatts the 9, Clifford Stanton in impressions. 9.10, Dutch station's transmissions have been Repetition of 3.15 programme. 9.25, British badly interfered with even in Holland. It Movietonews. 9.35, " Vauxhall " : a masque of Vauxhall Abnormal Short -Wave is interesting to note that of late Hilversum Gardens. No. i has been heard testing after pro- SATURDAY, MAY 8th. Conditions gramme hours on 1,186 metres. Under the 3, For the Children -Paul Leyssac reading two Lucerne Plan this wavelength belongs to of Hans Andersen's stories. 3.10, Bruce Bairns - Complete Interruption at Times Norway, and it is actually used by Vigra, father, creator of " Old Bill " Cartoons. 3.20, British Movietonews. DURING or Aalesund, to give it its better -known 3.30, Cabaret with the past fortnight there has name. Hildergarde, Rudi Grasl and the Metaxa Girls. taken place one of the most exten- Norway, however, is entitled to only one 9, Wynne Ajello (songs). 9.10, " The 'ole in sive failures of. ; short -wave communi- long wave channel, the Road " sketch by Seamark. 9.25, cation to Canada and fhe U.S.A, on record. though at present it has Gaumont- British News. 9.35, Scenes from The disturbance started abruptly at Oslo working on 1,153.8' metres (a channel John Drinkwater's play, " Abraham Lincoln." that does not appear in the original Lucerne 21.00 G.M.T. on Saturday, April 24th, as Plan), far as short-wave communication was con- as well as Aalesund on 1,186. The MONDAY, MAY loth.. latter is only a io- kilowatt station and Nor- 3, Starlight : Jane. Carr. 3.10, The World of cerned, but the magnetic traces at Abinger way might first began to show be induced to give up the wave- Women (III)- Anything New ? 3.25, British signs of disturbance at length, synchronising Aalesund with one or Movietonews. 3.35, Cabaret Parade. Irmo G.M.T. on the sane day. . It was not more of her other stations. 9, Starlight : Phyllis Robins (songs). 9.10, ' surprising, therefore, to see reported in the Would Hilversum find the 1,186 metre Repetition of 3.io programme. 9.25, Gaumont - correspondence columns of The Times for channel acceptable? The corresponding British News. 9.35, Repetition of 3.35 pro- April 27th a .bright . gramme. that auroral display had frequency is. 253 The door been witnessed during the early morning kcs. next of neighbours in Europe ate Kiev on 248 kcs. April 25th from the Chilterns between Tring TUESDAY, MAY 11th. and Oslo on z6o ; there is thus a frequency and Dunstable. The auroral -arch was 3, The Markova -Dolìn ballet. 3.15, Gaumont - separation of 5 kilocycles on one side and British News. 3.20, Arrangements for bluish -green in colour with three nearly televising 7 on the other. This makes rather a tight the Cbronation Procession explained by the equidistant shafts of shimmering reddish fit, but it should be a good deal better than Director of Television. 3.30, Fifty -third Picture light which extended high into the heavens. having a station right on your wavelength. Page. 3.55, Gaumont -British News. 9, Irene Scharrer (piano). Halifax, Nova Scotia, in a more northerly There is also Tashkent, only 3.4 kilocycles 9.15, Repetition of latitude, reported that on the night of 3.20 programme. 9,25; British Movietonews. away ; but Tashkent, rated at 25 kilowatts, 9.35, Fifty- fourth Picture Page. April 27th the aurora was so brilliant as is in distant Turkestan and would probably almost to floodlight the town! cause no trouble. WEDNESDAY, MAY r 2th. Whilst writing these notes one learns that The Inter -American Conference, which Transmission start's at 2. I short-wave communication with Canada is Part providing meets towards the end of the year, will have views of the park and the crowds and Part 1I still disrupted, whilst in the case of the some knotty problems to deal with. Canada the 'complete procession. Transmission ends U.S.A. conditions are very erratic and re- approximately at 3. and the United States arrived years ago at . ception alternates from 21 -17 -15 or 9 Mc /s. a modus vivendi, both countries agreeing to 9, The Poet Laureate will read his Coronation Reception from the south and south -west organise their on kilocycle Ode. 9.5, Music Hall Cavalcade. 9.50, distributions a'ro- Gaumont -British News. has, however, been relatively unaffected, basis and each recognising the other's ex- but conditions to the west have at times clusive right to certain channels. All went been quite poor, though' not disturbed to THURSDAY, MAY 13th. well until broadcasting began to grow by 3, Screen Scene. 3.10, Masks through the the extent of wholesale dislocation. leaps and bounds in Central and South cable Ages -IV (conclusion). 3.25, Gaumont- British Even the circuits have had unwork- America. News. 3.35, Harry Roy and his hand with his able periods due to earth currents. You don't realise how many separate wife, Princess Pearl. The cause of all this trouble has probably countries there are in that part of the world 9, Starlight : Clapham and Dwyer. 9.10, been an active sunspot group, comprising till you examine an atlas -over twenty of Coronation cartoons : Nicholas Bentley will three major spots of area 1,75o, 900, 700 them are to take in the Autumn Con- draw what he saw in the Coronation crowds. part British Movietonews. millionths of the sun's hemisphere respec- ference: No wonder the problem of inter- 9.25, 9.35, Some Visitors to London : Personalities in London for the tively. ference between stations in different coun- Coronation. 9.45, " Rhythm in the Dawn " ; This group is at the moment disappearing tries has become serious. first performance of a modern rhapsody by over the west limb, but it is possible that After a good deal of experimental work, Ord Hamilton.

www.americanradiohistory.com Wireless World, IIay 7111, 1937. 449

NEWS FROM Broadcast Brevities PORTLAND PLACE No " Royal " Microphone been recurring quite a lot in the is attended by a B.B.C. sleuth will take listeners out to sea on of the last few -who, by the way, pays for his an eel- fishing expedition. micro- programmes ALTHOUGH special Nevertheless, t h e seat -and if the haul is not will be used months. phone cases answer is no. always a large one, that is not In the Shadow when the King gives the Royal the fault of these striving " near and yet so far " sums Message to the Empire on the New Talent officials. SO evening of Coronation Day, it In recent weeks more ',Ilan up a tragedy of Corona- B.B.C. sleuths can usually be principal should be emphasised that the twenty artists new to broad- recognised square jaws tion Day in which the by their are Leslie Woodgate, the microphone itself will, as casting have been booked for and air of disillusionment. actors be from stock. among t hem popular B.B.C. conductor, and always, taken radio drama,

www.americanradiohistory.com Wireless World, May 7171, 1937 Current Topfes EVENTS OF THE WEEK IN BRIEF REVIEW A Newspaper Substitute LOUD speakers have been A Bigger Exhibition tors who will be stationed out- established side the Abbey. The same com- at fifteen differ- THE wireless section of the ent places in Addis Ababa, Foire de Paris, which will mentators will describe the de- and parture after the service, which at noon every clay they are be held from May 15th to the used to disseminate news in the 31st, occupies double the space will also be broadcast to French listeners. Another local dialect. Most of the citi- it did last year. French com- zens are mentator will be stationed out- illiterate. Programmes from Greece side Buckingham Palace to describe the return from the Sounding the Stratosphere IT is reported that at last a Abbey. start has been made with the IN. RADIO- EQUIPPED bal- building of a transmitter at A Stunt Programme 1 j loon recently sent up by Athens. It will have a power the French National Meteoro- AN unusual programme was logical Office reached a height of 15 kW but will be capable recently broadcast New of easy conversion to too kW. in of 25,500 metres. The balloon York. In the script 50,000 was fitted with an automatic Balkan Plans words were used in which the radio transmitter to signal to letter E, the most used in the the ground its height and the THE official building pro- English language, did not occur reading of the self- registering gramme of the Yugoslavian IN THE MALL. Film Indus- once. meteorological apparatus which tries speakers installed on a broadcasting authorities pro- it contained. These balloons lamp standard. vides for the erection of a too - Standardisation of which are sent up from time to kW station in Belgrade, a 20- Components time are equipped with a para- valves which have some slight kW station in Zagreb, and THE Radio Component Manu- chute which stations brings the appara- mechanical defect. In this smaller in Split, facturers Federation has tus safely to earth. Twenty- Skoplje, and Sarajevo. manner it has been possible to now issued further supplements five francs is paid to the finder reduce very considerably the io its Standardisation Report. of the apparatus. Another High -Power daily number of rejects. One of The present supplement . deals the most important Station with mechanical companies and electrical A Pirate has, however, recently adopted THE new Czechoslovakian details of potentiometers, vari- Transmitter HE authorities in Italy are the policy of destroying all de- transmitter now being able resistances and fixed resist- fective valves, no matter how erected at Melnik will, it is ances. Copies are obtainable said to be greatly troubled by a secret wireless station slight the fault. This has actu- hoped, be completed by the end for is. 6d. from the Secretary, ally had the effect of reducing of the year. Official details 83, Cannon Street, London, which is frequently to be heard between midnight and a.m. the number of duds, since it has concerning its power are not yet E.C.4. 7 inspired factory operatives to available, but it will probably Its chief broadcasts consist of anti -Government propaganda. exercise greater care owing to be between 6o and too kW. Broadcasting in the fact wages It works on 21 and metres as that vary accord- Esperanto 42 ing to the number of rejects. well as on the medium wave - Moscow's Broadcasting THE number of items broad- hand. House cast more or less regularly Indian Activities WHAT is claimed will be the in Esperanto is showing a AN interesting paper steady increase. from Television entitled finest broadcas ing ,head- Apart Exhibition " The Propagation of Radio (Wafters in the world is to be the transmissions of Prague and MEMBERS of the Wireless Waves Through Brno, well -known the Iono- çommenced in Moscow during the Hilver- Section of the I.E.E. are sphere," was submitted by Dr. sum station is to continue pro- the present month. The main to have a private view of the Saha and Mr. R. N. Rai, of studio will be approximately viding programmes in that lan- Television Exhibition which is Allahabad guage. University, at the 3o feet high and have an area of to be opened by Lord Selsdon last meeting of the National In- 600 square yards. It will Some Interesting Figures at the Science Museum, South stitute of Sciences (India). accommodate an orchestra of Kensington, on June loth. The 25o performers, together with DURING the period from private view will be held from PA Assists 1932 Strikers an audience of 35o. to the end of 1936 the 5 p.m. to 8 p.m. on the opening proportion of musical items in IN the recent sit -down strike at day. This exhibition, to which several large automobile Prison for a Pirate German broadcasting rose from the public will be admitted free 64 per cent. to 74 per cent., and manufacturing works in the AN inmate of a Berlin prison of charge, will be open on Mon- U.S.A. the men's leaders made (luring the saine period talks fell days, Tuesdays and Wednes- situated a few yards front 32 use of PA vans to communicate from per cent. to 19 per cent. days, from 10 a.m. fi one of the broadcasting trans- to p.m. instructions to the trikers. has received an The closing time will be two Since the sit -down strikers were mitters just Anti- Interference hours later on Thursdays, extra month on his sentence for Campaigns Fri- inside the factory and the operating a wireless set without days and Saturdays, and on leaders outside, this was the only OTHER countries apart from Sundays it will be a licence. An earphone and a open from method of letting them know our own are carrying on an 2.30 p.m. to 6 p.m. It will what crystal smuggled into the prison active campaign against electri- was going on in the out- gave him excellent signals when last for approximately three side world. cal interference. During the months. - connected to the ironwork of Specimens of single past year 355 complaints were core co -axial cable, as laid he- his bed. investigated by the Polish Miscellaneous tween Broadcasting House and Advertisements for French Coronation authorities and a cure was Alexandra Palace, and the 4- effected in 79 of them-. The core cable laid between London May 21st Issue Broadcasting authorities in Romania have and Birmingham will be on view. WITH the approach of the VERY complete arrangements now decided to begin an official Whitsun Bank Holiday are being made in France campaign against interference. slight alterations are necessary for the broadcasting of the Although monthly reports are Dud American Valves in our printing arrangements. Coronation ceremony. The no longer published in France, HITHERTO valve makers in Miscellaneous advertisements broadcast will commence with concerning the work of the offi the U.S.A. have en- intended for the issue of May the description of the arrival of cial static hunters, steady pro- deavoured to reduce manufactur- 21st must be received not later the main procession by two gress is believed to be the order ing costs by maintaining a than first post on Friday, well -known French commenta- of the day. special department to deal with May 14th.

www.americanradiohistory.com Wireless World, May 761, 1937. 451

New Apparatus Reviewed Recent Products of the Manufacturers "AVO" VALVE TESTER It obviates a lengthy explanation of mutual conductance and what it signifies, Itf is generally agreed that unless facilities for making a comprehen- and if the pointer comes to rest on that part are available is very sive test on a valve, the one measurement of the scale marked " Replace," it reveals more than any other the state convincing proof that the valve is faulty. arc approximately half this thickness. The that is used with a of the valve is that of mutual conductance. Filament volts from 2 to 4o can he usual accumulator acid " Valve Tester provides selected, and provision is made for screen specific gravity of 1,250 when fully charged. The new " Avo in this information in a simple and straight- voltages of 6o to 250 in suitable steps, while A moulded bakelite case is used, and This is a forward manner, at least so far as its actual anode voltages of from 8o to 250 are pro- one end is a small glass window. and handling are concerned. vided. most useful feature, as with most batteries operation it is necessary to remove In addition to giving a figure for mutual This very useful valve tester forms a with opaque cases tetrodes valuable addition to the range of test equip- the filler plug to examine the acid level. conductance of triodes, pentodes, acid sections of multi -type ment made by the Automatic Coil Winder In the case of the Simplak battery the and the individual level can be seen through the window. In addition to the positive and negative terminals being of different colours, they are also fitted with a different size of shank, so are thus non -interchangeable. The price of this battery is its. 6d.

BELLING -LEE FLAT -PIN PLUGS obvious reasons it is most desirable that no confusion should arise between loud speaker extension points and electric supply mains lighting or power points, since both are often mounted on the skirting - board in a room. Dissimilar types of fittings for the two New "Avo " Valve Tester and the two valve panels now available. services are most essential for relay systems, hospitals, and all public buildings valves, provision is made for heater -cathode and Electrical Equipment Co., Ltd., Winder equipped with radio, and particularly is this insulation tests, while for all rectifier valves, House, Douglas Street, London, S.W.r, and necessary when headphones are employed. including RF diodes and the diodes in its price, including one valve panel, is Belling and Lee, Ltd., Cambridge Arterial multi- electrode valves, an emission test is err ris. The extra valve panel costs L2 2s. Road, Enfield, Middlesex, have now intro- made. duced special flat -pin plugs and sockets for The test set comprises two units, the SIMPLAK ACCUMULATOR all radio extension points. They are made main tester contains the meter, switching in two- and three -pin types, and the socket and all WELL -MADE 2 -volt accumulator fittings can be supplied for flush or surface for the various' electrode voltages of features of supply unit. The A that combines some the controls, also the power type, but is quite power, is taken from the very slow- discharge operating incidentally, of delivering one ampere on con- AC mains and no batteries are used in capable the tinuous discharge, is made by Simplak Bat- the instrument. teries, British Industries House, is valve -holder panel, Ltd., The other unit a Marble Arch, London, W.I. Known as the and this can be supplied fitted and wired Type M5, it measures 44 x 31- x 6tin. total for either British or American valves. It unit by a height, and is fitted with a permanently is connected to the main test handle. nine -pin plug. With the two attached carrying cable and The is given as 70 hours at valveholder panels the instrument provides capacity 1 discharge almost every valve now amp. and 3o hours at amp. facilities for testing rates respectively. Two positive and three in general use. negative plates are used with a compara- is not proposed to give a detailed It tively wide spacing between them, which description of the method of operating the tester since this is very fully explained in the instructional leaflet. It will suffice to say its operation is extremely simple that New Belling -Lee flat -pin fittings for radio for what is a comparatively complicated extension points. measurement, and one that, as a rule, only laboratory -type apparatus provides. All that need be done is to refer to the mounting, the flush type being fitted with a valve charts supplied, transfer to the switch- bakelite plate measuring Sin. square. ing the voltage values given, and on press- These fittings are designed for radio ing a lever to the left, the actual mutual speech circuits up to 5o watts with a conductance value is read off direct from nominal maximum current handling the meter's scale. Nothing could be capacity of 5 amps. RMS. simpler. These fittings can be used for any radio Actually there are three scales on the purpose other than the mains supply, and meter, one calibrated directly in mutual they would accordingly come in useful for conductance in mA /V, another for heater- microphone extension points, etc. Both cathode resistance measured in megohms, two- and three -pin types are non -reversible and one other divided into three differentls' and they cost 25. 4d. for a two -pin plug and coloured sections, marked " Replace " and socket and 25. 8d. for a three -pin variety. " Good," with an intervening space indi- Flush or surface mounting patterns in each cating poor or indifferent. style cost the same. The last scale is really for the benefit of Simplak two -volt accumulator Type M. There are no exposed metal parts in any non -technical users, and also to enable of the fittings, and the whole is well pro- dealers and servicemen to show their cus- space is occupied solely by electrolyte, as tected by bakelite mouldings. The stan- tomers in a way easy to comprehend the spacers are not employed. The positive and dard patterns are in brown Bakelite but actual state of any valve submitted to them one of the negative plates are each tin. cream bakelite fittings are available, and for test, thick, while the two outside negative ones these cost rod. more in each case.

www.americanradiohistory.com Wireless World, May 7/h, 1937 PRINCIPAL BROADCASTING STATIONS OF EUROPE Arranged in Order of Frequency and Wavelength (This list is included in the first issue of each month. Stations with an Aerial Power of 50 kW. and above in heavy type)

Station. Ong Tuning kc's. Positions. Metres. kW. Station. kc /s. Positions. Metres. kW. Ankara (Turkey) ...... 152 1973.5 5 Leipzig (Germany) ...... 785 Kaunas (Lithuania) 382.2 120 ...... 153 1961 7 Barcelona, EAJ1 (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 1840) 160 1875 150 North Welsh Regional (Penmon) . 804 Lahti (Finland) 373.1 5 ...... 166 1807 150 West Regional (Washford Cross) 804 373.1 70 Moscow, No. 1, RW1 (Komintern) (U.S.S.R.) 172 1744 500 Milan, No. i (Italy) .. 814 368.6 50 Paris (Radio Paris) (France) .. .. 182 1648 80 Bucharest (Romania) Istanbul (Turkey) 823 364.5 12 ...... 185 1622 5 Kiev No. 2, RW9 (U.S.S.R.) 832 360.6 35 Irkutsk (U.S.S.R.) ...... 187.5 1600 20 Agen (France) .. .. 832 Deutschlandsender ...... 360.6 0.5 (Germany) .. .. 191 1571 60 Berlin (Germany) .. .. 841 356.7 100 Droitwich ...... 200 1500 150 Sofia (Bulgaria) .. 847.5 Minsk, RW10 ...... 354 0.75 (U.S.S.R.) ...... 208 1442 35 Norwegian Relay Stations 850 352.9 Reykjavik (Iceland) .. .. . 208 1442 16 Valencia (Spain) ...... 850 Motala (Sweden) 352.9 3 ...... 216 1389 150 Simferopol, RW52 (U.S.S.R.) 859 349.2 10 Novosibirsk, RW76 (U.S.S.R.) 217.5 .. .. 1379 100 Strasbourg (France) .. .. 859 349.2 100 Warsaw, No. 1 (Poland) 224 ...... 1339 120 Poznan (Poland) . . . . 868 345.6 16 Luxembourg ...... 232 1293 150 London Regional (Brookmans Park) .. 877 342.1 70 Leningrad, No. 1 RW53 (Kolpino) (U.S.S.R..) 232 1293 100 Linz (Austria) ...... 886 338.6 15 Kalundborg (Denmark) .. .. 240 .. 1250 60 Graz (Austria) ...... 886 338.6 15 Vienna, No. 2 (Austria) ...... 240 1250 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 Vigra (Aalesund) (Norway) ...... 253 1186 10 Hamburg (Germany) ...... 904 Tashkent, RW11 .. 331.9 100 (U.S.S.R.) ...... 256.4 1170 25 Dniepropetrovsk (U.S.S.R.) .. 913 328.6 Oslo (Norway) .. 10 ...... 260 1153.8 60 1bulouse (Radio Toulouse) (France) .. 913 328.6 60 Moscow, No. 2, RW49 (Stchelkovo) (U.S.S.R.) 271 1107 100 Brno (Czechoslovakia) .. .. 922 Tromsö (Norway) 325.4 32 ...... 282 1065 10 Brussels, No. 2 (Belgium) ...... 932 321.9 15 Tiflis, RW7 (U.S.S.R.) ...... 283 1060 35 Algiers (Algeria) ...... 941 Saratov (U.S.S.R.) 318.8 12 ...... 340 882.3 20 Göteborg (Sweden) ...... 941 318.8 10 Finmark (Norway) ...... 347 864 10 Breslau (Germany) ...... 950 Archangel (U.S.S.R.) 315.8 100 ...... 350 857.1 10 Paris (Poste Parisien) (France) 959 312.8 60 Rostov -on -Don, RW12 (U.S.S.R.) .. 355 .. 845.1 20 Bordeaux- Sud -Ouest (France) .. 968 309.9 30 Budapest, No. 2 (Hungary) ...... 359.5 834.5 18 Odessa (U.S.S.R.) .. 968 309.9 10 Sverdlovsk, RW5 (U.S.S.R.) .. .. 375 800 40 Northern Ireland Regional (Lisburn) 977 Voroneje, RW25 (U.S.S.R.) 307.1 100' ...... 390 769 10 Genoa (Italy) ...... 986 304.3 10 Boden (Sweden) ...... 392 765 0.6 Torun (Poland) .. .. 986 Banska -Bystrica .. .. 304.3 24 (Czechoslovakia) (15 kW. 392 765 30 Hilversum No. 2 (Holland). (15 kW. till 1840) 995 301.5 after 1700) 60 Bratislava (Czechoslovakia) ...... 1004 298.8 13.5 Geneva (Switzerland) .. 401 .. .. 748 1.3 Midland Regional (Droitwich) .. .. 1013 296.2 70 Moscow, No. 3 (RCZ) ( U.S.S.R.) .. .. 413.5 726 100 Chernigov (U.S.S.R.) ...... ]013 296.2 Ostersund (Sweden) .. 413.5 4 ...... 726 0.6 Barcelona, EAJ15 (Spain) ...... 1022 293.5 3 Oulu (Finland)...... 431 696 10 Cracow (Poland) ...... 1022 Tartu (Estonia) .. 293.5 2 511 587.1 0.5 Oviedo (Spain)...... 1022 293.5 0.7 Hamar (Norway) 519 ...... ,. 578 0.7 Königsberg No. 1 (Heilsberg) (Germany) .. 1031 291 100 Innsbruck (Austria) 519 ...... 578 1 Parede (Portugal) ...... 1031 291 5 Ljubljana (Yugoslavia) ...... 527 569.3 6.3 Leningrad, No. 2, RW70 (U.S.S.R.) .. 1040 Viipuri (Finland) 288.5 10 ...... 527 569.3 10 Rennes-Bretagne (France) ...... 1040 288.5 120 Bolzano (Italy) 536 ...... 559.7 10 Scottish National (Falkirk) ...... 1050 285.7 50 Wilno (Poland) .. 536 ...... 559.7 50 Bari No. 1 (Italy) ...... 1059 283.3 20 Budapest, No. 1 (Hungary) ...... 546 549.5 120 Paris (Radio Cité) (France) ...... 1068 280.9 Beromünster (Switzerland) 556 0.8 ...... 539.6 100 Tiraspol, RW57 (U.S.S.R.) ...... 1068 280.9 10 Athlone (Irish Free State) ...... 565 531 100 Bordeaux -Lafayette (France) .. .. 1077 Klaipeda (Lithuania) 278.6 12 ...... 565 531 10 Zagreb (Yugoslavia) ...... 1086 276.2 0.7 Palermo (Italy) .. 565 ...... 531 3 Falun (Sweden) ...... 1086 276.2 2 Stuttgart (Germany) ...... 574 522.6 100 Madrid, EAJ7 (Spain) .. 1095 Alpes- .. .. 274 5 Grenoble, P.T.T. (France) .. .. 583 514.6 15 Vinnitsa (U.S.S.R.) ...... 1095 Madona 274 10 (Latvia) ...... 583 514.6 50 Kuldiga (Latvia) ...... 1104 271.7 Vienna No. (Austria) 592 50 i ...... 506.8 100 Naples (Italy) ...... 1104 271.7 1.5 Rabat (Morocco) .. - ...... 601 499.2 25 Morayska- Ostrava (Czechoslovakia) 1113 Sundsvall (Sweden) 269.5 11.2 ...... 601 499.2 10 Radio Normandie (Fécamp) (France) .. 1113 269.5 Florence (Italy) 610 10 ...... 491.8 20 Alexandria, No. 1 (Egypt) ...... 1122 267.4 0.25 Cairo, No. 1 (Egypt) ...... 620 483.9 20 Newcastle .. 1122 267.4 1 Brussels, No. 1 (Belgium) .. 620 .. .. 483.9 15 Nyiregyhaza (Hungary) ...... 1122 267.4 6.25 Lisbon (Portugal) ...... 629 476.9 15 Hörby (Sweden) ...... 1131 Tröndelag (Norway) 265.3 10 ...... 629 476.9 20 Turin, No. 1 (Italy) ...... 1140 Christiansand (Norway) 263.2 7 ...... 629 476.9 20 Trieste (Italy) .. .. 1140 263.2 10 Prague, No. 1 (Czechoslovakia) .. .. 638 470.2 120 London National (Brookmans Park) .. 1149 261.1 20 Lyons, P.T.T. (France) ...... 648 463 100 North National (Slaithwaite) .. .. 1149 Petrozavodsk (U.S.S.R.) 261.1 20 ...... 648 463 10 West National (Washford Cross) .. .. 1149 261.1 20 Cologne (Germany) .. . 658 .. .. 455.9 100 Kosice (Czechoslovakia) ...... 1158 259.1 10 North Regional (Slaithwaite) .. .. 668 449.1 70 Monte Ceneri (Switzerland) ...... 1167 Jerusalem (Palestine).. 257.1 15 ...... 668 449.1 20 Copenhagen (Denmark) ...... 1176 255.1 10 Softens (Switzerland) ...... 677 443.1 100 Nice-Corse (France) ...... 1185 Belgrade (Yugoslavia) 253.2 60 ...... 686 437.3 2.5 Frankfurt (and Relays) (Germany) .. .. 1195 251 25 Paris, P.T.T. (France) ...... 695 431.7 120 Prague, No. 2 (Czechoslovakia) .. .. 1204 249.2 Stockholm (Sweden) 5 ...... 704 426.1 55 Lille, P.T.T. (France) ...... 1213 247.3 60 Rome, No. 1 (Italy) ...... 713 420.8 50 Bologna (Radio Marconi) (Italy) .. .. 1222 245.5 50 Kharkov, No. 1, RW20 722 (U.S.S.R.) .. .. 415.4 10 Gleiwitz (Germany) ...... 1231 24.3.7 5 Fredrikstad (Norway) 722 ...... 415.4 1 Cork (Irish Free State) ...... 1235 242.9 1 Tallinn (Estonia) ...... 731 410.4 20 Saarbrücken (Germany) ...... 1249 240.2 Madrid, EAJ2 (Spain) 17 ...... 731 410.4 3 Riga (Latvia) ...... ] 258 238.5 10 Seville (Spain) ...... 731 410.4 5.5 Rome, No. 3 (Italy) , ...... 1258 238.5 1 Munich (Germany) .. .. 740 .. .. 405.4 100 Bilbao, EAJ8 (Spain) ...... 1258 238.5 1 Marseilles, P.T.T. (France) ...... 749 400.5 120 Nürnberg (Germany) ...... 1267 236.8 2 Pori (Finland) ...... 749 400.5 1 Radio Mediterranée (Juan -les -Pins) (France) 1276 235.1 27 Katowice (Poland) ...... 758 395.8 12 Dresden (Germany) ...... 1285 233.5 0.25 Scottish Regional (Falkirk) ...... 767 391.1 70 Aberdeen ...... 1285 233.5 1 North Scottish Regional (Burghead) .. 767 391.1 60 Klagenfurt (Austria) ...... 1294 231.8 5 Stalino (U.S.S.R.) ...... 776 386.6 10 Vorarlberg (Austria) ...... 1294 231.8 5 Toulouse P.T.T. (France) ...... 776 386.6 120 Danzig .. 1303 230.2 0.5

www.americanradiohistory.com MAY 7th, 1937 453 WOOiillq!

Tuning Tuning Station. kc/s. Positions. Metres. kW. Station. kc /s. Positions. Metres. kW. Swedish Relay Stations ...... 1312 228.7 - Vaasa -Vasa (Finland) ...... 1420 211.3 0.5 Magyarovar (Hungary) ...... 13131 227.1 1.25 Alexandria, No. 2 (Egypt) ...... 1429 209.9 0.5 German Relay Stations . .. .. 1330 225.6 - Turku (Finland) ...... 1429 209.9 0.5 Montpellier, P.T.T. (France) .. .. 1339 224 1.2 Miskolc (Hungary) 1438 208.6 1.25 Lodz (Poland) ...... 1339 224 2 Paris (Eiffel Tower) (France) 1456 206 5 Dublin (Irish Free State) ...... 1348 222.6 0.5 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 Cairo No. 2 (Egypt) ...... 1348 222.6 0.5 Binche (Belgium) ...... 1487 201.7 0.1 Königsberg (Germany) ...... 1348 222.6 2 Belgian Relay Stations ...... 1492 201.1 0.1 Nottoden (Norway) ...... 1357 221.1 0.15 Nimes (France) ...... 1492 201.1 0.7 Italian Relay Stations ...... 1357 221.1 - Albacete (Spain) ...... 1492 201.1 0.2 L'l1e de France (France) ...... 1366 219.6 0.7 Santiago (Spain) .. 1492 201.1 0.5 Basle (Switzerland) ...... 1375 218.2 0.5 Belgian Relay Stations ...... 1500 200 0.1 Berne (Switzerland) ...... 1375 218.2 0.5 Pietarsaari (Finland) ...... 1500 200 0.25 Warsaw, No. 2 (Poland) . .. .. 1384 216.8 7 Radio Alcalá (Spain) ...... 1500 200 0.2 Lyons (Radio Lyons) (France) .. .. 1393 215.4 25 Karlskrona (Sweden) .. .. ,. .. 1530 196 0.2 Stara -Zagora (Bulgaria) . .. .. 1402 214 2 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. kc /s. Positions. Metres. kW.

Batavia (Java) .. .. YDA 3.040 98.68 10 Lisbon (Portugal) .. .. CT1AA 9,655 31.09 2 Kharbarovsk (Russia) .. .. RV15 4,273 70.20 20 Buenos Aires (Argentina) .. .. LRX 9,660 31.06 5 Caracas (Venezuela) ...... YV5RH 5,800 51.72 1 Lisbon (Portugal) ...... GT1CT 9,680 31.00 0.5 San Jose (Costa Rica) .. TIGPH 5,S20 51.52 0.5 Madrid (Spain) ...... EAQ 9,860 30.43 20 Vatican City (Vatican State) .. HVJ 5,970 50.26 10 Lisbon (Portugal) , . , , . , CSW 9,940 30.18 5 Mexico City (Mexico) .. .. XEBT 6,000 50.00 1 Bandoeng (Java) .. .. PMN 10,260 29.24 3 Moscow (Russia) ...... RW59 6,000 50.00 20 Ruvsselede (Belgium) .. .. ORK 10,330 29.04 9 Montreal (Canada) ...... CFCX 6,005 49.96 - Buenos Aires (Argentina) .. .. LSX 10,350 28.99 12 Havana (Cuba) COCO 6,010 49.92 0.5 Teneriffe (Canary Isles) .. .. EAJ43 10,360 29.94 4 Prague (Podebrady) (Czechoslovakia) OLR 6,010 49.92 30 Tokio (Japan) , . .. .. ,1 VM 10,740 27.93 20 Bogota (Colombia) ...... HJ3ABH 6,018 49.90 1 Bandoeng (Java) ...... PLP 11;010 27.25 3 Zeesen (Germany) ...... DJC 6,020 49.83 50 Lisbon (Portugal) ...... CSW 11,040 27.17 5 Boston (U.S.A.) ...... WIXAL 6,040 49.67 10 Motala (Sweden) ...... SBG 11,700 25.63 1 Miami (U.S.A.) .. .. W4XB 6,040 49.67 2.5 Winnipeg (Canada) .. .. CJRX 11,720 25.60 2 Daventry (Gt. Britain) .. .. GSA 6,050 49.59 15 Paris (Radio-Colonial) (France) . , TPA4 11,720 25.60 12 Cincinnati (U.S.A.) .. .. W8XAL 6,060 99.50 10 Daventry (Gt. Britain) .. ., GSD 11,750 25.53 15 Philadelphia (U.S.A.) .. .. W3XAU 6,060 49.50 10 Zeesen (Germany) ...... DJD 11,770 25.49 50 Skamlebaek (Denmark) .. .. OXY 6,060 49.50 0.5 Boston (U.S.A.) ...... W1XAL 11,790 25.45 10 Motala (Sweden) ...... SBG 6,060 49.50 1 Tokio (Japan) . -. .. .. JZJ 11,800 25.42 20 Chicago (U.S.A.) ...... W9XAA 6,080 49.34 0.5 Vienna (Austria) ...... OER2 11,800 25.42 1.5 Nairobi (Kenya) .. .. VQ7L0 6,083 49.31 0.5 Rome (Italy) , . .. .. I2R0 11,810 25.40 25 Bowmanville (Canada) .. .. CRCX 6,090 49.26 0.5 Daventry (Gt. Britain) .. .. GSN 11,820 25.38 15 Hong Kong (China) .. .. ZBW2 6,090 49.26 2 Wayne (U.S.A.) ...... W2XE 11,830 25.36 10 Johannesburg (South Africa) .. ZTJ 6,100 49.20 5 Lisbon (Portugal) .. .. , . CT1AA 11,830 25.36 2 Bound Brook (U.S.A.) .. .. W3XAL 6,100 49.18 35 Zeesen (Germany) DJP 11,850 25.31 50 Chicago (U.S.A.) .. .. W9XF 6,100 49.18 10 Prague (Podebrady)(Czechoslovakia) OLR 11,840 25.34 30 Belgrade (Yugoslavia) .. .. 6,100 49.18 1 Daventry (Gt. Britain) .. .. GSE 11,860 25.29 15 Manizales (Colombia) .. .. HJ4ABB 6,105 49.12 1 Pittsburgh (U.S.A.) . , .. W8XK 11,870 25.27 40 Daventry (Gt. Britain) .. .. GSL 6,110 49.10 15 Paris (Radio -Colonial) (France) .. TPA3 11,880 25.23 12 Calcutta (India) ...... VUC 6,110 49.10 0.5 Moscow (Russia) ...... RNE 12,000 25.00 20 Wayne (U.S.A.) ...... W2XE 6,120 49.02 10 Lisbon (Portugal) .. .. CTICT 12,082 24.83 0.5 Havana (Cuba) ...... COCD 6,120 48.95 0.25 Reykjavik (Iceland) ...... TFJ 12,235 24.52 7.5 Pittsburgh (U.S.A.) ...... W8XK 6,140 48.86 40 Parede (Portugal) ...... CT1GO 12,400 24.20 0.35 Winnipeg (Canada) ...... CJRO 6,150 48.78 2 Warsaw (Poland) ...... SPW 13,635 22.00 10 Lisbon (Portugal) . .. .. CSL 6,150 48.78 0.50 Amateurs ,. .. ,. 14,000 21.42 0.01 Caracas (Venezuela) ...... YV5RD 6,150 48.78 1 to to Parede (Portugal) .. .. CT1G0 6,200 48.40 5 14,400 20.84 San Jose (Costa Rica) .. .. TIPG 6,410 46.80 0.5 Sofia (Bulgaria) ...... LZA 14,970 20.04 1.5 Barranquilla (Colombia) .. .. HJ1ABB 6,450 46.52 1 Zeesen (Germany) , . DJL 15,111 19.85 50 Valencia (Colombia) ...... YV4RV 6,520 46.00 0.5 Vatican City (Vatican State) . , HVJ 15,123 19.84 10 Riobamba (Ecuador) .. .. PRADO 6,620 45.31 2 Daventry (Gt. Britain) .. . , GSF 15,140 19.82 10 Amateurs ...... 7,000 42.86 0.01 Bandoeng (Java) .. .. YDC 15,160 19.80 3 to to Daventry( Gt. Britain) .. .. GSO 15,180 19.76 10 7,300 41.10 Hongkong (China) ...... ZBW4 15,190 19.75 2 Moscow (U.S.S.R.) RV96 7,520 38.89 25 Zeesen (Germany) ...... DJB 15,200 19.74 50 Prangins (Radio -Nations) (Switz'l'd) HBP 7,780 38.48 20 Pittsburgh (U.S.A.) ...... W8XK 15,210 19.72 40 Suva (Fiji) ...... VPD2 8,720 31.40 3 Huizen (Holland) PCJ 15,220 19.71 20 Budapest (Hungary)...... HAT4 9,125 32.88 5 Prague (Podehrady)(Czechoslovakia) OLR 15,230 19.70 30 Bangkok (Siam) ...... HS8PJ 9,351) 32.09 20 Paris (Radio -Colonial) (France) .. TPA2 15,243 19.68 12 Madrid (Spain) .. .. EAQ2 9.480 31.65 20 Daventry (Gt. Britain) .. , , GSI 15,260 19.66 10 Rio de Janeiro (Brazil) .. .. PRF5 9,5(10 31.58 5 Wayne (U.S.A.) ...... W2XE 15,270 19.65 10 Daventry (Gt. Britain) .. .. GSB 9,510 31.55 15 Zeesen (Germany) .. .. DJQ 15,280 19.63 50 Melbourne (Australia) .. .. VK3ME 9,510 31.55 1.5 Buenos Aires (Argentina) .. .. LRU 15,290 19.62 5 Hongkong (China) ...... ZBW3 9,520 31.49 2 Daventry (Gt. Britain) .. .. GSP 15,310 19.60 10 Jelöy (Norway) .. .. LKJI 9,520 31.49 1.5 Schenectady (U.S.A.) .. .. W2XAD 15,330 19.57 18 Schenectady (U.S.A.) .. .. W2XAF 9,530 31.48 30 Zeesen (Germany) DJR 15,340 19.55 50 Zeesea (Germany) DJN 9,540 31.45 50 Budanest(Szekesfehervar) (Hungary) HAS3 15,370 19.52 20 I' rague (Podebrady)(Czechoslovakia) 01.R 9,550 31.41 30 Hongkong (China) ...... ZBWS 17,750 16.90 2 Zeesen (Germany) ...... DJA 9,560 31.38 50 Zeesen (Germany) ...... DJE 17,760 16.89 50 Bombay (India) ...... VUB 9,565 31.36 4.5 Wayne (U.S.A.) ,. .. .. W2XE 17,760 16.89 10 Millis (U.S.A.) .. . . WIXK 9,570 31.35 10 Huizen (Flollan8)1 .. .. PHI 17.770 16.88 23 Daventry (Gt. Britain) .. .. GSC 9,580 31.32 15, Bound Brook (U.S.A.) .. ., W3XAL 17,780 16.87 35 Lyndhurst (Australia) .. .. VK3LR 9,580 31.32 1 Daventry (Gt. Brita.n) .. .. GSG 17,790 16.86 10 Philadelphia (U.S.A.) .. .. W3XAU 9,590 31.28 10 Bandoeng (Java) ...... PLE 18,830 15.93 60 Sydney (Australia) ...... VK2ME 9,590 31.28 20 Bangkok (Siam) ...... 11SSP 19,020 15.77 20 Huizen (Holland) . .. . PCJ 9,'590 31.28 20 Bandoeng (Java) .. .. PMA 19,350 15.50 60 Frangins (Radio -Nations) ( Switz'l'd) HBL 9,595 31.27 20 Daventry (Gt. Britain) .. .. GSH 21,470 13.97 10 Moscow (Russia) ...... RAN 9,600 31.25 20 Wayne (U.S.A.) ...... W2XE 21,520 13.94 10 Rome (Italy) ...... I2R0 9,635 31.13 25 Daventry (Gt. Britain) .. .. GSJ 21,530 13.93 10 A 1 grnirahava (.Taval _ _ ...... - VT)R Q 1 aA - - - - . _ . - 21 AQ 1 135E-1,,,.,,6 !TT C WQYSC 91 KM 1`-t 02 do

www.americanradiohistory.com Wireless World, May 7111, 1937. Anti- Interference Filters BY way of introduction to his By F. R. W. STRAFFORD subject, the author explains in

: and Lee, Ltd.) (Research Dept. Belling this instalment how an apparently simple electro- mechanical operation, electrical interference must be ONE of the many annoying forms frequency such as the recurrent interruption of in which electrical interference fully understood before a real knowledge with broadcast reception mani- of suppression may be attained, and it a DC circuit, may produce impulses elu- fests itself is associated with the is proposed to devote a little time in capable of causing interference to the house wiring. cidating the fundamental theory. main electric supply over a wide band of frequencies. Electrical disturbances due to impulses Consider Fig. r (a), which depicts a a of current from some commutating or in- simple DC circuit in which is inserted termittent circuit such as a motor or flash - rotating contact which rhythmically makes ing sign, perhaps several hundred yards and breaks the current flow through R. distant, may travel along the mains supply When the switch is closed a current and be picked up by the flows and a voltage E ap- produce the original square -topped wave receiver. pears across R. When shown in Fig. I (a). Such forms of interfer- PART I -THE the switch is opened the The foregoing discussion shows (it is ence are characterised by RE voltage instantly falls to hoped) that any rhythmic impulses of the harsh crackling noises NATU OF zero. current or voltage may be considered as which they produce in INTERF ERENCE If the switch is rhyth- composed of a vast ,number of individual the loud speaker, and mically opened a n d sinusoidal components of differing fre- generally by their untun- closed by means of a quencies and magnitudes which, when able nature. They may be picked up in motor, the curve of voltage across R with acting together, result in the original shape two ways: first, the interfering current respect to time T is clearly shown in Fig. of the impulse. Thus, our ten- cycle -per- superimposed upon the mains supply may z (b). second impulses of square- topped form enter the receiver via its mains connecting This indicates a square -topped wave may have sinusoidal frequency compon- lead. Secondly, the interfering currents form and is a typical example of the wave ents at r,000,000, r,000,010, I,000,020 may produce an appreciable radiated form, of current which may be expected cycles per second, etc., extending right magnetic field in the close vicinity of the when an electric flashing sign is operated over the tuning range of a broadcast aerial lead -in where it joins the receiver, on DC mains. Why (in terms of this receiver. and in such a case the interference is in- square -topped wave occurring at a rate of It may also be assumed that a sharply jected through the aerial circuit. possibly ten times per second) should this defined wave having very steep sides, as It is obvious in the latter case that the produce a harsh untunable crackle in a in Fig. I (b), will extend over a much wider means for suppressing the interference broadcast receiver? frequency range and with much greater should be located at a point at least a few The answer is very clear to mathema- uniformity of amplitude. In other words, feet from the receiver itself so that the ticians and invariably hopelessly compli- it will be quite untunable over a very wide mains lead carrying the supply voltage to cated to laymen. Without going into any wave range on the receiver. But if the the receiver should be free from the dis- details of the famous Fourier trigonometri- interfering wave is rather rounded, as for turbance where it runs close to the lead -in cal series, Fig. I (b) may be replaced by example in Fig. 2 (c), less sinusoidal corn- to the receiver itself. Fig. 2 (a), in which the wave is replaced ponents will be required to build up this by a number of sinusoidal waves. shape, and thus the interference may fall How Interference is Generated By suitably selecting the amplitude and off quite rapidly at the higher frequencies. phases of each of the sinusoidal waves it In this case greater interference would ap- One is apt to talk a little glibly about should not be difficult for the veriest lay- pear at long waves, less at medium, and electrical interference without_ a funda- man to imagine that the addition of all possibly little or nothing on the short mental understanding as to its production waves. and propagation along the mains .supply In the extreme case when the interfer- wires. Electrical interference is normally ing currents become a pure sinusoid, the characterised by the presence of myriads interference will only be produced at one of individual components covering a very frequency, and may or may not be tun- wide band of frequencies which extends able by the receiver. from the audio- into the radio -frequency spectrum. Thus a certain type of electrical Wide Frequency Range a j may cause annoyance to the ( interference now know something of the a sensitive AF amplifier, while a We should user of electrical interference, for we neighbouring broadcast receiver may be mechanism of E sudden electrical im- practically immune. In this instance the have seen that every of the interfering pulse must be regarded as a vast number frequency components ->T whose located at audio - of individual frequency components spectrum are mainly (b` by the The reverse may occur, when lowest frequency is determined frequencies. of the disturbance itself, the amplifier is immune but the broad- rhythmic period Artificially generated interference : have mag- is badly affected. In this Fig. 1.- and whose higher frequencies cast receiver operation of the rotary switch in diagram upon the steepness of of the interfering frequencies are wave form nitudes dependent case most (a) produces a square- topped the impulse with respect to located in the radio -frequency spectrum. represented by curve (b). the curve of of time. . the frequency distribution Finally, it does not matter whether the the electrical interference may cover such these components would make up a wave Actually is is rhythmic or not. The mere a vide range as to adversely affect both as depicted now in Fig. 2 (b), which impulse audio amplifier at the very similar to that shown in Fig. i (b). process of closing an electric light switch radio receivers and variation in the current time. If sufficient sinusoidal waves are taken produces a sudden same through the mains circuit, and The reason for these variations in the it should then be possible exactly to re- distribution

www.americanradiohistory.com MAY 7th, 1937 Wll® 4.55 WcpIlc1 Anti -Interference Filters- Exeter and District Wireless Society' this one impulse contains myriads of Headquarters: Y.W.C.A., 3, 1)ix's Field, Southernhay, Exeter. alternating frequency components cover- Meetings: Mondays at 8 p.m. Hon. Sec.: Mr. W. J. Ching. 9, Sivell Place, Ileavitree, ing a vast spectrum, and accounts for the Exeter. clicks heard from most loud speakers when At a recent meeting an interesting lecture a neighbouring light is switched on or off. was given by Mr. Mays on electrical interfer- The mathematical analysis in this case is ence and methods of curing it. A selection of even more profound. gramophone records, on which were recorded almost every type of electrical interference, was played. McCA IQ1f It-1 Bideford and District Short -Wave Society 6 -valve all -wave Superhet Headquarters: lligmtette Walk, Bideford. Hon. Sec.: Mr. E. K. Jensen, 5, Furzebeam Terrace, Bideford. with Radio Frequency Stage In view of the interest shown in 8 stages. amateur 8 tuned circuits. transmissions it has recently been decided that - alternate meetings, which are held fortnightly, 3 wavebands. should be devoted to this subject. The club ra¡ subscription has been fixed at is. per fortnight. The Society now possesses its own short-wave receiving apparatus. A large attendance of members witnessed the first transmitting demonstration by the chairman when contact was macle with four amateur stations on the 1.7 megacycle band. (b) Golders Green and Hendon Radio Scientific Society Headquarters and Hon. Sec.: CO, Pattisou Road, Hamp- n n n stead, N.\F:2. Interest in the Society's recent visit to the (c) Marconiphone television demonstration theatre was so great that several people had to be dis- PRICE appointed. Preceding the demonstration Mr. (Complete with Fig. 2. From the point of view. of inter- A. S. Radford gave an explanatory talle on the V.A. valves) £8.17.6 ference, the simple square- topped wave form system of transmission employed and a brief Performance (made possible by use of multi -electrode valves) of I (b) may be replaced by Fig. the complex description of the Marconiphone television re- equal to that of many receivers employing 8 valves or more curves of diagrams (a) and (b). The rounded ceivers. The Society has prepared the follow- Brief specification includes : Large " Airplane " dia], With wave form of diagram (c) would cause inter- different coloured lights automatically switched on for each ing activities for the summer wave 2 ference full details of -range. Micro-vemier -speed drive. 4 -point wave - mainly with long -wave reception. which may be obtained from the Hon. Sec.: change and gramophone switch. Volume control and variable tone control on gramophone_ May 23rd. -Coronation direction -finding com- also operative Reinforced petition heavy -gauge steel chassis. Covers 19 -2,1)00 metres. The next instalment will deal with the on 8o metres near St. Albans, Herts. Circuit comprises : Preselector circuit, radio frequency amplifier Tea at 4.3o p.m., followed by conference. (operative on all 3 wavebands), triode -hexode frequency manner in which electrical interfering im- June znd, July changer, double band -pass I.F.T. coupled I.F. amplifier, 11th and September 12th. - double diode -triode detector and L.F. amplifier. D.A.V.C. pulses are propagated along the mains 5 -metre field -day competition. applied to 3 preceding valves. 3 -watt pentode output. wiring, and it will be shown how their Special effect upon a broadcast receiver may be Radio Society of Northern Ireland materially reduced. Headquarters: Y.M.C.A. Radio Club, Wellington Place, 6-VALVE BAND-PASS Belfast. Meetings: The first Wednesday of each month. SUPERHETERODYNE Hon. Sec.: Mr. F. A. Robb, 4G, Victoria Avenue, Sy-den- ham, Belfast, N.1, The Morse practice class which is held every News from the Wednesday is very well attended, and the Club now possesses twelve operators for its transmitter (; 6YM. The transmitting members Clubs hold a QSO party at midnight every Saturday on the 14- megacycle waveband. The contest Croydon Radio Society for the R.S.N.I. Leonard Trophy, full details Headquarters: St. Peter's 1kí11, Ledhury Road, South of which appeared in the April 30th issue of Croydon. The Wireless World, is taking place during Meetings: Tuesdays at S p.m. the week -ends of May. Hon. Pub. Sec.: Air. E. L. Cumbers, 14, Campden Road, South Croydon. The final meeting of the session was devoted to a musical programme derived from gramophone records. Mr. L. F. Marshall was elected to the position of Secretary in place of Mr. K.B. MODEL 630 Complete with H. C. Salter. B.V.A. Valves.) A New All -Wave AC Mains Thames Valley Amateur Radio and Specially designed and built for high quality radio gram work. Television Society Superheterodyne SPECIAL FEATURES : Reinforced stout steel chassis. High class components by well -known makers of acknowledged Headquarters : The Albany Hotel, Station Yard, Twickenham, 1l iddlesex. reputation used throughout. Fitted with attractive and Meetings: Wednesday, at 5.15 p.m. AN unusual feature of the circuit of this specially large full- vision dial, glass fronted, and supplied complete with escutcheon and fittings. Separate illumination Hon. Sec.: llr. J. N. Roe, 19a. The Barons, St. Mar - receiver, just released garets- ou- Thames, Middlesex. by Kolster automatically switched in for radio/gramophone. Brandes, Ltd., is CIRCUIT DETAILS : The annual subscription that two IF stages are Inductively coupled band -pass to the Society is employed. They follow filter, triode -hexode frequency changer, band -pass I.F.T. 3s. 6d. per year. All those interested in ama- a triode -hexode coupled I.F. amplifier, I.F.T. coupled to diode detector. teur short -wave work will be \velcomed. The frequency- changer, which is the first valve D.A.V.C. applied to preceding valves. L.F. amplifier capacity in the set, and automatic volume coupled to output pentode 3 -3i watts undistorted. Variable Society has prepared the following activities for control is tone control and volume control operate on both radio and the summer, lull details of which can be applied to all three stages. AVC is derived gramophone. obtained from the Hon. Sec.: from a double -diode ALTERNATIVE TRIODE OUTPUT second detector and the All McCarthy receivers supplied complete with May 9th. -lo-metre field -day competition. output stage is a pentode. valves, knobs, pilot lamps, leads, mains cable and May 26th.- Lecture and demonstraton of plug. 12 months' guarantee. There are three waveranges as follows : short -wave components Deferred terms on application, or through London and apparatus by Mr. 16.5 to 52 metres, 195 to 565 metres, 97o to Radio Supply Co., 11, Oat Lane, 2.0.2. E. Cholot, of Lissen, Ltd. 2,300 metres. Cash with order on 7 days' approval. Also write June 5th and 6th. Society Station names on the for illustrated catalogue of complete range of all -The will operate " Alphadex " dial McCarthy receivers an 8o -metre portable station for District 15 in are grouped alphabetic- the R.S.G.13. National Field -day Competition. ally, and the tuning is effected through a McCAF?1TI1Y UÀID III IC Il . June 30th.- Lecture ou r0 -metre work by two -speed drive with ratios of 8 : 1 and 48 : 1. Mr. H. Wilkins, (;6 \VN. Provision is made for gramophone repro- 44a, Westbourne Grove, London, W.2 July .4th. -2o -metre Field -day Competition. duction, and the price is 12 guineas. Telephone: Bayswater 320112.

www.americanradiohistory.com Wireless World, Diqy 7th, 1937

By Random Radiations "DIALLIST " B.B.C.'s general equipment. A and his The Short -wave Range cables ; sound, over ordinary telephone the lines. Given the fine day for which we are fellows have, in fact, built up the B.B.C.'s I1I glad to see considerable improvements now run to nearly four million of some all praying, television will make history on assets that in the short-wave departments look in " pounds. B, on the other hand, has not paid One of these is to divide Wednesday. I shan't be able to " of the new sets. my will be more or less glued a penny towards all this, though he comes the short -wave bands covered into at least because ear to the loud speaker of my own medium - in on the same ten -shilling basis. But B two ranges instead of trying to go from ; will henceforth have to shell out year by of the wave set but I hope to be able to tell you about 15 to 6o metres in one sweep so B.B.C. of ranges how my neighbour receives the television year, long as the spends part condenser vanes. With two or more revenue on similar things, for the benefit wavebands can broadcast. its tuning is far easier, and the of C, who buys his first licence in 1947. be provided with metre or megacycle scales A Suggestion that aren't nearly so hard on the eyes. last engenders an idea Not a Club worthy of all That sentence Then I observed a tendency, which I pass on to the B.B.C. with my praise, to take in the 13 -metre band, which If we take this reader's view, the purchase blessing. There will be numbers of owners of one's first wireless licence is rather like was omitted in many of the older models. who won't want to miss steadily of television sets joining a club. The new member finds the The optimum wavelength is growing anything of either the commentaries or the shorter and shorter, and is likely to go on club -house with all its furniture and other " televiews." Why not relay the whole of amenities ready waiting for him, and the doing so for the best part of the next two the spoken commentary from inside and years from now. The B.B.C. now makes entrance fee that he pays is his contribu- no regular transmissions at all from the tion towards their cost. That is very right Empire Station on wavelengths above 31.55 and proper. But broadcasting isn't on the metres (GSB), and recommends that all re- same footing. It has already been pointed ceivers intended for Empire use should be out in The Wireless World that your receiv- capable of tuning down at least to 13.93 ing licence merely entitles you to use a radio metres, the wavelength of GSJ. Don't grab receiver, just as a game licence makes you pen and paper to tell me that GSA is still free to shoot game. It is not an under- shown in the short-wave lists with a wave- taking to provide you with broadcasting to 'listen to any more than the game licence is length of 49.59 metres. I know it is ; but if you examine the details of the six regular an undertaking to provide you with game Empire transmissions you'll find that GSA to shoot. Broadcasting is run by means of is not now shown for any of them. I Government grants, and in practice these believe, though, that it is occasionally used are worked out in proportion to the amount under certain exceptional conditions. received from licence fees. Posterity The Best of Luce: ! " We do a lot for posterity," sighs my THE B.B.C. deserves to have every suc- correspondent, " but what has posterity cess with next Wednesday's Coronation done for us? " Well, I suppose one might broadcast, for so far as is humanly possible say that it's only because we have one eye nothing has been left to chance. An im- on the future that we keep on bringing mense amount of preliminary work has been things up to date. If it weren't for pos- done in all kinds of directions. It was terity we might not have nearly such a good necessary, for instance, to find by surveys broadcasting system as we now have -ana of the Abbey and of the route taken by the we probably shouldn't be so keen on de- procession and by experiment the most suit- veloping television, to come back to the able positions for each of the 58 micro- KEEPING IN TOUCH. Signallers of the main theme of the argument. I am all in phones that will be in use. The best places Life Guards will maintain one of a number favour of borrowing when borrowing is for rooms had to be found, and of portable wireless stations for the trans- necessary, but my reason for hoping that the'control mission of official messages from different once this was done the G.P.O. co- operated television expenditure during the next few points on the Processional route on years will be met by a bigger Government with the B.B.C. in carrying out the 472 Coronation day. miles of wiring required. An imposing grant rather than by raising the wind is array of special apparatus was built for the outside the Abbey on the ultra -short sound this. The B.B.C. is already faced by a control rooms to enable them to handle the wavelength, just breaking it during the time huge programme of new building and re- incoming transmissions from 32 points when the television images with their special . building in its " sound " broadcasting within the Abbey, from " effects " micro- commentary are being sent out? It should sphere, and so far as one can see this kind phones along the route and from the com- be simple enough to do that, and if it can of broadcasting is going to be the main fare mentators' boxes, and to pass these on to be managed I'm sure that it will be greatly of the great mass of wireless users for some Broadcasting House for home and Empire appreciated by those who have television little time. By its charter the B.B.C. can services, or to the International Trunk Ex- receivers. Otherwise, they'll have to keep borrow only a certain limited amount. change for relaying to foreign countries: a medium -wave receiver going, or to switch This may well be needed for the proper over from the ultra- shorts to the medium development of " sound " broadcasting ; waves if the television set has an " all - wouldn't it, therefore, be as well to avoid Television, Too ! wave " sound department. borrowing for television purposes if it is at A stupendous piece of organisation! all possible to do so? I can't help feeling Every listener will, one hopes, realise the that it would. hard work that has been put into the pre- Should the B.B.C. Borrow ? parations and will wish the O.B. depart- FROM a Birmingham reader I have a neat ment the best of luck when Wednesday sees criticism of my suggestion that the Televising the them carrying out the biggest job that they B.B.C. should, if possible, avoid borrowing have yet undertaken. to meet the cost of television development. Procession Success, too, to the television engineers, He puts it something like this. A is an old Coronation who will be undertaking their first genuine stager who has held a receiving licence since UNNDOUBTEDLY the televising of the O.B. - outside the Alexandra Palace 1922. B is a newcomer who took out his Coronation Procession will give an grounds, that is. A co -axial cable has been first licence this year. Out of each ten shil- added fillip to television. It is an laid from Broadcasting House (already con- lings that A has paid a proportion -say two ambitious undertaking and the first big nected by one to A.P.) to Apsley Gate, shillings -has been spent on building O.B. attempted. From the results of the Hyde Park. Here there will be three studios, plant, cilices and so on. as well as rehearsal which the engineers had last Fmitron cameras, with a mobile control van. in buying furniture, musical instruments Monday, it is certain to be a milestone Vision will be transmitted over the co -axial and goodness knows what else that make up in the history of television. In Broadcast

www.americanradiohistory.com MAY 7th, 1937 My'silma WopIld 457 Brevities it has already been stated that a wavelength of about 3 metres from a three cameras will be used. On another directional aerial. These signals will be page in this issue will be found photographs picked up at Alexandra Palace on an aerial C O N F U C i U S of Apsley Gate, Hyde Park Corner, giving mounted at the top of the main transmitting 551-478 B.C. the positions of these cameras. mast. The third motor contains the power ir. It is necessary to provide control room plant which will generate the sync pulses apparatus at the scene of the television and the scanning voltages for the cameras. broadcast, and to enable this to be carried 'The engineers will use the recently laid co- out the B.B.C. will be using the three -unit axial cable to transmit the vision fre- mobile transmitter, recently purchased. The quencies to Alexandra Palace. They will control room is installed in one of these probably use at the same time the ultra - vehicles, which is about the size of a Green short -wave transmitting van, so that the Line motor coach, the apparatus being engineers at the Alexandra Palace can take mounted on two rows of racks along the their choice and use the better of the two sides of the vehicle. The operators are able transmissions. ,, j`V to see the televised picture on a tube fitted At z o'clock the transmission will begin AS into the compartment over the driver's by giving crowd scenes around Hyde Park head. In addition, it is equipped as a small Comer, then a camera, trained on East . 1/4k sound control room with all the necessary Carriage Drive, will give views of the faders and amplifiers to deal with the four approaching cavalcade. The camera on the microphones which , will pick up the voice of pavement, which will be within about six T1 the commentator and the sound effects. feet of the passing Procession, will give f This motor will be parked behind the park - close -up views of the Royal Coach and other 5 keeper's lodge on the west side of 5 I the gate, important parts of the Procession as it three multiple cables connecting the cameras passes through the gate. The third camera, will run from it to the top of the gate, across which will face Wellington Arch, will inter- which they will pass to the plinth erected for sperse views of the disappearing pageant. the Emitron cameras. The cables are about Thus, until the last horseman passes the SO asked Confucius r# inches in diameter and contain twenty - gate, viewers two will, it is hoped, receive a thousand years ago. A far cry seven insulated cables, two of which are of complete picture of the Procession. from ancient low China to modern capacity to carry the VF signals. Frederick H. Grisewood, the announcer who radio but to -day, as of old, that The second vehicle, the ultra- short -wave was recently appointed Staff Reporter, sta- which "bringeth surcease from transmitter, will be parked alongside the tioned alongside the cameras, will give a care " is no less a jewel. And other and will radiate the vision signals on continuous commentary. it need; not the philosophy of Confuc:us to appreciate its value. Setmakers, Designers and Con- structors too, have found in T.C.C. Wet Electrolytics a The Norwegian Folkemottager real remedy for trouble in A.C. Receivers. IAIPRESSED by the success attended by three valves instead of two pentodes plus The momentary building up the marketing of Germany's famous rectifier, as in the case of the mains set. of HIGH SURGE VOLTS " Volksempfänger," many other coun- This receiver is when switching on is the most sold for little over l4, prolific cause tries of Europe are now attempting to fol- there being a vast gap between this and of breakdown. low her lead in this respect. The latest Maybe just a condenser, may- the ordinary mains set, which sells for from be valves or even a transformer lr2 to lis -. The set proved burnt out. Free yourself of this popular immediately it was ever present possibility - Fit marketed, and it was not T.C.C. 'Wets,' and condensers long before the first and components are safe batch against made- r6;000 sets -was sold damage. No lc ad' out. The surges cannot develop -nor- preliminary batch mal working conditions are was produced by two well - constantly maintained. known Oslo manufacturers, special arrangements being made with patent holders for reduced payments in respect FIT T.C.C. 'WETS' AND END of these sets. It is expected that before very long the other CONDENSER WORRIES

FOUR TYPICAL TYPES The mains model is de- Type Capacity Continuous Working Volts signed to operate from 802 16 mfds. 440 volts Peak two pentode valves. 602 8 mfds. 440 volts Peak 805 8 mfds. 500 volts Peak 809 32 mfds. 320 volts Peak Special types are available to meet the stringent conditions found country to do so is Nor- in A.C./D.C. Receivers. Write for full details. way. T h e Norwegian ' ` Folkemottager," o r " People's Receiver," is available in two models, for mains and battery operation. In both cases tuning arrangements are similar, VOLTAGE REGULATING but whereas the mains set uses an RF pentode WET ELECTROLYTICS vahve as a leaky grid detector, the battery Scandinavian countries will follow the lead set employs a triode. In both cases the de- of Norway and market special receivers of is tector followed by a resistance coupling. this type. No definite announcement THE TELEGRAPH CONDENSER CO., LTD., Triodes has are used in the battery set through- yet been made, but there would seem little WALES FARM ROAD, NORTH ACTON, W.3. out, and consequently there is a total of need to depart from the Norwegian design. (G.1 I,-I;

www.americanradiohistory.com Wireless World, May 711m, 1937

The Editor does not hold himself to the responsible for the opinions EditOr of correspondents Letters his conditions is that expansion of the F layer, Sunspots and Short Waves due to heating, causes less nett inonisation REFERRING to the article " Sunspots density during the summer. It would seem and the Short -wave Listener " in your something is lacking in this theory, that his calcula- issue of April 23rd, and particularly the because on frequencies above zo Mc /s long - becoming too unwieldy. For remarks regarding sudden fade -outs, I note distance communication over the Equator tions for the baffle speaker Mr. Voigt actually that it is stated that these fade -outs are (i.e., north -south) is consistent throughout uses a frequency of 5o c /s as a basis, and caused by sudden excessive rise in ionisa- the year, while parallel to the Equator, in compares the results with those for .a horn tion resulting in complete attenuation of the northern or southern hemisphere, it is speaker working within its frequency range high- frequency signals, and am wondering only consistent during the winter months, of efficient loading. if this fact has been definitely proved. My becoming erratic in spring and nil during It is an interesting fact that the principal experience on frequencies above zo Mc /s the summer. For example, on the 28 Mc /s manufacturers of sound film reproducing would go to show that the opposite is the amateur band South Africa can be con- equipment, both in this country and the case and that the fade -outs are caused by tacted very consistently throughout the U.S.A., use a large baffle speaker for repro- decreased ionisation. year, while U.S.A. on one side and Russia duction of the lower register. I believe I am Some time ago, in a letter to you, I on the other can only be contacted correct in stating that the reason is the enor- pointed out the reception from time to time erratically in spring and autumn and con- mous difficulty of building a horn that would of a peculiar " hiss " occurring during day- sistently during winter. In the southern be capable of efficient working at low fre- light hours on frequencies between io and hemisphere the same thing applies, i.e., quencies, as compared with a comparatively 4o Mc /s and generally peaking about Africans can contact us throughout the year, simple but efficient large- diaphragm baffle 25 Mc /s. It has since been noted that on but can only work Australia and South speaker. the days when this hiss has been heard fade- America consistently during their winter Dealing once more with the question of outs have often been reported, so also have (i.e., summer here, of course). If the ex- air loading, if Mr. Voigt will refer to his magnetic storms, and there appears to be pansion theory were true we should expect original advertisement he will find that he some connection with the aurora borealis. the nett ionisation over the Equator to be uses the words " with a baffle, the loading The nature of the agent causing the hiss less than elsewhere and, therefore, trans- is a maximum for wavelengths so small is is not clear, but it is suggested that it Equator contacts on ultra -high frequencies " and not " with baffle speakers. . . . a shower of particles shot off from the sun, not possible or erratic. The difference is subtle but very important. particularly during high sun -spot activity. D. W. HEIGHTMAN. Mr. Voigt's statement, to be correct, would Apparently the particles are attracted by Gt. Clacton, Essex. necessitate the removal of the speaker from the earth's magnetic poles and tend to follow its baffle. Surely, then, it ceases to be a its magnetic field. If this shower possesses baffle speaker? The same argument might the power of neutralising the ionisation (due Horn - Loaded M.C. Speakers be raised for a horn unit, and would not be to ultra- violet light) it will be seen that here THIS is someone else's private fight, and any more irrelevant. of the fade -outs, we have an explanation I ought not really to butt in ; but I Finally, may I take this opportunity of as obviously the neutralising effect would cannot let Mr. Todd's letter pass. He expressing my appreciation of Mr. Voigt's be greatest on the outer layers. to transient response, which is good, efforts towards the development of better lately, and refers The hiss has been very active for that is a most important point. But he loud speakers, while maintaining that on April 25th the writer and others had a implies that it is more or less independent friendly discussions of this nature react for co- particularly good example of the relation of frequency response. the good of the industry in general? of it and fade -outs. In the early morning He cites " Fourier's Analysis " as hav- For Goodmans Industries, Ltd., of this day the hiss was observed to be no bearing on transients. Presumably G. A. BARDEN. unusually continuous and loud, and on ing at he means " Fourier's Theorem." But has Wembley, reaching the G.P.O. receiving station he not overlooked " Fourier's Integral Middlesex. Baldock we found that they had had a com- ? cover transients, etc., circuits for Theorem " This does plete fade -out on U.S.A., and indicates that, other things being equal, about three hours and were just getting frequency response im- through again at rr.30. every increase in Reflections on " Random Radiations " only from observa- proves fidelity on transients. AT the risk of taking up your space, I will Although I can speak as no generally accepted and on above 20 Mc / s, it has There is yet comment briefly upon a few of the tions frequencies of the problem in always been found that fade -outs occur first rigorous analysis transient points raised by " Diallist " in the issue loud speakers ; but experience indicates that on circuits north of east or west, while dated April 2nd. Thus : in southerly directions are the last the two main desiderata are : Besides the intermittent circuits frequency response. Playing Up.- to go out-if they go at all. This supports (i) Wide fault in a set, what about the tip- and -run the neutralising agent is (2) Absence of sharp resonances. You complain about the fact that in design, the question kind of interference? the poles, as obviously its effects Given equal brains of an American gangster attracted to does not seem to a noise like that would be greatest on the layers over the of horn loading or baffle words, a sound like a machine this film -in other polar regions and nil, or practically nil, on affect point. gun -and in due course (perhaps overdue is over the equator. P. K. TURNER, Office engineers arrive those Hartley -Turner Radio, Ltd. the better word) Post Going one step farther, it seems to me on their motor bikes (in my case they arrived that in the above there may possibly be an Isleworth. during a thunderstorm!). You switch on the explanation of the fact that communication set and-provided there's no thunderstorm over long distances east and west (and, of IWAS interested to read that Mr. Voigt, -not a sound is to be heard except the sweet course, north of both) is not possible during of March 26th, agrees with music of somebody's quintet. No machine- ultra -high fre- in his letter summer months on the a horn type of loud speaker capable guns at all. Nothing but harmony. The is assumed that there is me that quencies. If it of reproduction down to frequencies of 4o c / s engineers' pleasant manner perceptibly always, to some extent, an emission of this freezes, and soon they depart, obviously sun, then is impracticable for average domestic use. neutralising shower from the has gone to a considerable thinking hard to themselves that you're not summer months, since the North Mr. Voigt during the of trouble to show why a horn -loaded quite all there. Immediately they have left, is nearer the sun, we should expect amount Pole speaker " down to its cut -off frequency " is the offender starts up his drill again, and the greater part of the shower to be you switch off, feeling incapable of summon- the neutralising superior to a baffle speaker. As I pointed attracted to this pole and I am entirely in ing the busy fellows again in case the same on the layers in the northern out in my original letter, effect thing happens as before ! Why don't local be much greater than agreement with this. My query was, is there hemisphere would in a horn speaker, post offices have their own listening depart- during the winter months. Therefore, any relative advantage operating below its cut -off frequency, ments? although the effect of the ultra -violet agree thoroughly with " Dial - the effect over a baffle speaker, bearing in mind Piracy. -I radiation is greater in summer, has an addi- list's " remarks thereon. Very often the is still greater and the nett the fact that the baffle speaker of the shower ca .n be arranged people who cheat the B.B.C. and their less. tional advantage in that it ionisation lower cut -off without listeners are people who can well afford the The present explanation of poor summer to have a considerably

www.americanradiohistory.com MAY 7th, 1937 4.59 W0711 d. los. licence. I know of someone myself who steals his entertainment, but all the same Coronation PA Contracts I'm not going to send one of those anonymous A11IPL1FIERS giving an undistorted output postcards exposing him ! There are probably of 48o watts with thirty projector speakers many more pirates than is generally realised. are being installed on sta ak in \Vhitchall by And, as " Diallist " points out, piracy could B.T. -H. Other important installations are easily be eradicated. being carried out at Blackpool anal Bath. Chain Listening. -That's where we battery folk gain. The possessor of a set working Grampian PA equipment is being installed off expensive HTB's simply cannot, unless at about thirty sites on the Coronation route, A radio input via land lines is being taken he's a millionaire, keep it on all day. Be- from a central receiving station outside the sides, even the best HTB would rebel against central London area. such treatment. So, therefore, to avoid expensive and frequent replacements one Marcuniphone apparatus is being installed in chooses items one really wants to hear, and the Nlall, on all the stands round the Houses of that, whatever the items may be, is " good Parliament, St. Margaret's stand adjoining Westminster Abbey, all the stands roumi St. listening " ! T. J. E. WARB URTON. George's Hospital, and at many other impor- East Molesey, tant Surrey. points. se 0 Trix Sound Equipment is to be installed for official use inside the new annexe at West- minster Abbey; three complete installations with sixteen speakers will be used. tither Trix P.A. Along Coronation Route equipment is being fitted on the official stands at the Horse Guards, Treasury and Admiralty WITH reference to your Editorial on the buildings. use of P.A. equipment along the Coro- 4> c nation route, we should like to point out Many dealers have been supplied with Vor- that a precedent was set during the passing texiou 20 -watt amplifiers for use during of King George V's funeral. We were then Coronation celebrations. officially advised to fade out when the pro- o -,> cession into view, in case some It is anticipated that the permanent Voigt came our installation at the Royal Empire, Society build- threequarter -mile away. The sane stipula- ing will be temporarily extended for the Corona- A 9%" ' DIAMETER tion has been made for the Coronation pro- tion. cession. SPEAKER WITH We strongly agree with your suggestions 12" PERFORMANCE for a rehearsal, as in some instances the " Cellophane " procession will come into view only a It is no exaggeration to say hundred yards or so away from loud- IN a letter from Mr. W. A. Richardson on that the new Rola F742 -PM speaker positions, and it will be noted that the subject of recording, published in The has a performance equal to the nearly all the speakers are necessarily of Wireless World of April 23rd, the use of majority of 12" speakers. It the directional -horn type, capable of carry- " Cellophane " was recommended. isn't as good as the giant Rola ing considerable distances. Furthermore, " Cellophane " is the registered trade G.12 -P.M., of course, but the many have been erected pointing towards mark of British Cellophane, Ltd., applied flux density is the same and it procession. their products, and the name, gives you super- sensitivity at the oncoming to therefore, a very much lower price. A N. J. LEAK. should not be used in reference to trans- new magnet material " Al- London, W.6. For H. J. Leak and Co. parent cellulose sheeting generally. nico " is used with this model, and another special feature is the new metal and compound s hie 1 d e d universal transformer, not only dust -proof but moisture -proof, a further instance of Rola technicians' PHILCO PHONE care. For battery sets or for that weak short -wave station, New Intercommunication System as Extension Speakers or under any conditions where extreme for Private Installations sensitivity is a requisite, the Rola F742 -PM is the ideal THE Philco speaker to specify. Phone, a new Write to -day for leaflet AB. system of instant, private, two - way communication, is to be introduced into England in the near future by Philco Radio. The instrument has been developed in the United States, where it has The master control unit together with a remote unit. been installed in pri- WITHOUT TRANSFORMER 42 - vate homes, business houses, restaurants, doctors' offices, amuse- The equipment is built of all Philco stan- OVER': 8 MILLION- IN USE ti ment places and many other buildings. dard components, and it can be used on Philco Phone provides two -way com- either AC or DC supplies. It can be installed munication between a master control unit anywhere within a few minutes. and one, two, three or four remote units. The master control unit is encased in a The system can be used between distant compact, attractive walnut cabinet. Com- points in homes, offices, stores, hotels, fac- bination speaker -microphone permits in- tories, theatres, garages, hospitals or simi- stant conversation with one or all remote t7ie Wert,r'd rroirce44 lar places. It is an inexpensive but effi- points at will. A turn of the volume knob ?ilia( Re cient communication system. The price sends the voice to the remote units in all as loud THE BRITISH ROLA CO., LTD. will, probability, be of the order of or as low as desired. A red signal light on zo with one remote MINERVA ROAD. PARK ROYAL,N.W.10. unit, additional remote the master unit shows when the system is units costing about ¡2 each. in operation. PHONE : WILLESDEN -4322- 3- 4 -5 -6.

www.americanradiohistory.com World, May 7th, 1937. 460 Wireless

Brief descriptions of the more interesting radio Recent Inventíbns improve- INTERLACED SCANNING " SECREI " SIGNALLING devices and AFREQUENCY "wobble" is WIIEN the rate of picture - ments issued as patents the imparted to the carrier wave, repetition is lower than to impart a measure of will be included in this frequency of the mains supply- ill order cycles secrecy, by using a piezo- electric section. which in America is 6o -it crystal as the master control, and is difficult to keep the AC compo- natural fre- Its pres- so mounting it that its nent out of the picture. quency constantly varies. As Assembly of the two cylinders ence is manifested by what is in in a television scanning system. or shown, the crystal Q is circular AUTOMATIC SELECTIVITY_ kneiwn as " flag waving," shape, and is mounted to roll CONTROL periodic changes of light and contained cylinder C are both THE selectivity of a wireless re- shade, which greatly increase the rotated about the longitudinal ceiver can be automatically apparent flicker. axis of the latter. The result, it controlled so that it is highest for If, however, the rate of picture - is stated, is to throw, not a true weak or distant signals and low- repetition is made equal to the image of the object on the screen est for strong signals. According fundamental AC frequency, these V, " but persistence of vision in to the invention, the control is difficulties at once disappear. Ac- the eye of the observer causes the secured by causing the incoming cording to the invention, a suffi- continually changing groups of signals to vary the effective link- ciently high repetition -rate is used luminous lines actually projected age between the primary and in combination with a system of on the screen to appear as a pic- secondary windings of a band -pass interlaced scanning, in which the ture of the obj'.'et presented to the coupling. ordinary saw- toothed oscillations slot S." As shown, the primary winding are combined with a series of The arrangement is also used to P and the secondary winding S square -topped waves; on two series record on a cinema film a series form part of a band -pass coupling of saw- toothed waves may be used, of markings, which, although not between the two radio frequency provided the " line " and " frame " recognisable at sight as the pic- or intermediate -frequency ampli- oscillators are interlocked. ture scanned, will reproduce the fiers V and Vr. Associated with Farnsworth Television Inc. Con- the windings P and S are auxiliary vention date (11.5.. -1.) November windings PI and Si, which are 5111. 1934. No. 459400. wound in such a way that they 0 0 0 0 tend to oppose the effective coupling between the coils P and S. " DETECTIVE " VALVES The winding P and S are origin- APAIR of valves are recipro- ally over -coupled so as to give a cally coupled so as to form wide band -pass effect, but so long a multi- vibrator circuit in which as only a weak signal is being re- the period of oscillation is ceived the link circuit Pr, Sr determined by the values of the serves to neutralise the original coupling resistances and capacities. Method of mounting a piezo- electric crystal to " wobble " the frequency of a master The outside cylinder has a slot oscillator stage. at one end and a viewing screen at the other. freely in a recess in the face of a rotating electrode E. original picture when projected A second electrode Er is set at on to a viewing screen through a slight angle to the first, so that apparatus similar to that already the effective spacing between the described. crystal and its pair of electrodes is H. l'ierl. Convention dates constantly changing. This causes (Germany) .parch 2711i and Octo- in ber 1rt1r, 1934. No. 459042. the carrier frequency generated 0 0 0 0 the circuit I., C to vary in a cyclic fashion. In addition the speech SUPER.REGENERATIVE currents are " inverted," so that AMPLIFIERS the high frequencies are trans- order to get the best results formed into low, and vice versa, I from a super -regenerative am- before they are applied to the plifier the quenching oscillations modulator valve. should be adjusted until the valve Marconi's Il'ireless Telegraph is very close to the threshold of Co., Ltd., and T. D. Parkin. Ap- self -oscillation. In practice it is plication date July 51h, 1935. No. difficult to secure a sufficiently over quenching, 459303. elastic control the o 0 0 0 so that the valve is often worked TELEVISION SYSTEMS considerably below the optimum THE object is scanned by the coupling. Circuit arrangement for automatic selectivity control. apparatus shown in Fig. 1 According to the invention a fine which consists of a tube T (shown control over the quenching is ob- setting and to produce only a The combination is then utilised more clearly in Fig. 2) containing tained by using a capacitative im- narrow band -pass or highly selec- to detect the approach of a body a slotted cylinder C mounted on a pedance to vary the amount of tive coupling. However, when or perso0 towards a protected transverse axis. The tube T is feed -back from plate to grid. a strong signal comes in, the AVC area. The capacity of the intrud- formed with a slot S at one end, Actually a variable condenser is to the grid of the ing body is added to that of the and has a ground -glass viewing - arranged in series between the voltage applied induct- valve V1 reduces the output cur- circuits, and the resulting change screen V at the other end. The usual back -coupled grid rent from that valve, so that the in the period of oscillation is used cylinder C is pierced by a series of ance and the anode. .11. M. and point Y falls below the potential to operate a rclav or to sound an slots K set in a spiral, and it con- L. Merdler, Scott of the point X. Current then flows alarm. tains a photo -electric cell con- Baird Television, Ltd. Applica- through the Thyrite elements Zr, The device may be used, say, to nected to brush contacts, B, Br. tion date July 511í, 1935. No. Z2, and reduces their resistance, guard the approach to a strong- In operation the tube T and the 45930o. so that Zr short -circuits the wind- room or safe, or to open or close ing Pr, whilst Z2 damps the wind- a door automatically, or to record ing S. This cancels the effect of the passage of vehicles over a The British Abstracts published here are prepared with the permission the reverse coupling -liuk Pr, Sr bridge or through a tunnel, or to of the Controller of H.M. Stationery Office, from Specifications and restores the original wide light up a particular object on the obtainable at the Patent Office, 25, Southampton Buildings, London, band -pass effect. approach of a customer, or for W.C.2, price l,- each. A selection of patents issued in U.S.A. is E. K. Cole, Ltd.; G. Bradfield; advertising purposes generally. also included. and F. A. Inskir. Application A. C. A1e.randra. Application dale July 1st, 1935. No. 459209. date July 25th 1935. No. 460297. r_

www.americanradiohistory.com Th e rele-s THE ,;=¡.^ PRACTICAL RADIO yry:.:`1,_ JOURNAL 27 th Year of Publication Wc \\:`///// ) I

No. 924. FRIDAY, MAY 14TH, 1937. VOL. XL.

Proprietors : ILIFFE & SONS LTD. EDITORIAL COMMENT Editor : HUGH S. POCOCK. The result in Europe, unless designers were Editorial, Superhet entirely satisfied that the superhetero- Advertising and Publishing Offices : dyne would remain the last word in DORSET HOUSE, STAMFORD STREET, Finality in Receiver Design ? receivers. To succeed in getting a LONDON, S.E.i. clear channel in Europe for the benefit ECEI T'ERS employing the Telephone: Waterloo 3333 (5o lines). of the superheterodyne receiver, only Telegrams: "Ethaworld, Sedist, superheterodyne London.' principle have to find that the pendulum had by then grown in popularity through- COVENTRY : Hertford Street. swung back in favour of straight sets, R out the world to such Telegrams: Telephone: an would be farcical. Autocar, Coventry." 5210 Coventry. extent that we are inclined to ignore We believe that it would be extremely claims of any other receiver principle BIRMINGHAM: useful to have the views of readers of Guildhall Buildings, Navigation Street, 2. to a point where anything which is not The Wireless World, both in this Telegrams : Telephone: a superhet is looked upon as obsoles- . Autopress, Birmingham." 2971 Midland (4 lines). country and Abroad, on cent. The the question of American Radio Manu- whether the superheterodyne principle MANCHESTER : 260, Deansgate, 3. facturers' Association last year, in Telegrams : Telephone: should now be accepted so widely, "Rifla, Manchester." Blackfriars 4412 lines). recommendations to (4 the Federal Corn- or whether the neglected straight set munication Commission, pointed out GLASGOW : 26e, Renfield Street, C.2. still has advantages over the super- that the present popularity of the Telegrams: "llifle, Glasgow." Telephone: Central 4857. heterodyne which justify its retention superheterodyne was likely to continue PUBLISHED WEEKLY. ENTERED AS SECOND and development, because technically and especially in the CLASS MATTER AT NEW YORK, N.Y. economically it light of recent progress. offered big advantages over the straight Subscription Rates : Although we have only touched on set, but that it still had the dis- Home, is. 8d. ; Canada, Si is. 8d. ; other the subject, we feel that enough has LI advantage that it was liable to inter- countries, I 3s. iod. per annum. been said to stimulate correspondence ference when transmitters worked on a from readers whose technical know- As many of the circuits and apya.alus describes in these frequency close to the intermediate pages are covered by patents, readers are advised, be /ore ledge or practical experience puts them making use of them, to satisfy themselves that they would frequency chosen for the superhetero- not be infringing patents. in the position of being dyne. The Association able to con- suggested that tribute usefully to a discussion. if a value should be standardised by designers for the intermediate frequency of sets, then this frequency Reliability CONTENTS might be kept clear by the Federal Communication Commission by de- Care In Set Manufacture Page clining to allot this frequency to IN the scramble to obtain the ,Editorial Comment .. 461 transmitters. utmost performance from their A year or two ago such a proposal receivers there has been in Building Sets to Las! 462 the as this would not have found favour past a tendency on the part of manu- Resistance- Coupled AF Oscillator 465 because designers, even in America, facturers to pay insufficient attention were not prepared to concede then to the matter of reliability. Broadcast Brevities 467 that the superheterodyne represented Breakdowns and service troubles, Anti -Interference Filters. 11 .. 468 finality, or that its advantages were so however, taught their lesson, and to -day great as to eclipse the prospects of a the most stringent precautions are Listeners' Guide for the Week, .. 470 return to favour of the straight set. taken to avoid breakdowns due to IWhy the Triode - Hexode ? 472 If now the superheterodyne is to faults in the manufacture of the better become the universally standardised types of receiver. The Television Receiver. IX .. 47,5 receiver, then it would be well to con- An interesting account is given in 'Unbiased .. 478 sider whether in Europe, too, it might this issue of how some of these tests of be possible to adopt one intermediate reliability of component parts and the Current Topics 480 frequency and keep this frequency assembled sets are conducted. This clear of transmitting stations. Letters to the Editor .. .. 481 But information should do much to increase there would be no purpose in starting confidence in the dependability of 1ecent Inventions .. . 482 an elaborate campaign to achieve this modern receivers.

www.americanradiohistory.com 102 Wireless World, May i4th, 1939. Building Sets POINTS WHICH MAKE FOR RELIABILITY

Underside of chassis It is instructive to make a tour of a in course of wiring, works like that of Murphy Radio, Ltd., showing liberal use where reliability has for many years been of sub -assembly established as a creed, and to see the panels. Note paper washers under hundred- and -one details and operations soldered joints on which are concerned, either directly or valveholders near indirectly, with ensuring the permanence top edge of chassis. of the sets. Much has already been done by sheer THE very essence of any public For instance, a manufacturer who brings forethought before the plans have left the service is reliability. In the out sets which, from a technical point of drawing office. Take the case of the sphere of broadcasting the review, are in advance of current designs, waverange switch fitted to some of the sponsibility for the maintenance must expect those sets to be kept in ser- two -waveband models. A rigid frame of an uninterrupted service is shared by vice for a longer period than the products ensures that strains shall not permit move- the B.B.C. and by the manufacturers who of firms hunting in the rear of the pack. ments which might introduce noises, supply the public with receivers. In- Fortunately, there are many ways in while a very small diameter cam, formed evitably the receiving end will be more which reliability can be achieved without by a flat surface milled in the switch vulnerable than the transmitter, for few adding a penny to the cost of a set. It spindle itself, reduces the torque required people can afford to duplicate their equip- takes just as long to make a bad -soldered to produce the necessary contact pressure. ment or pay for the large margins of joint as a good one, and in the case of The cam does not rub on the springs safety which are the rule at the transmit- components it often happens that a less themselves, but works in a trough of ting end. On the other hand, nn one is costly design turns out in the long run stainless steel, which has good wearing going to buy a set which will be liable to be the more reliable. There are, of properties and is, of course, above sus- to expire with the termination of the maker's guarantee period, for although in a _ rapidly developing art a new set every year would be a good principle, in practice most of us stick to the sets in which we have invested our hard- earned cash until they are conspicuously inefficient by comparison with current models. Common ground is reached by both maker and user when the question of cost is considered. Reliability is an essential factor of " value for money," which in (Above) A bank of waverange switches the long run is the manufacturer's best being " run in " by a special machine. weapon in a competitive market, and . is (Right) Checking contact pressure with the all- embracing figure of merit by calibrated spring tongs. Contact, which must be maintained against the opening which the wise purchaser arrives at a force of the test tongs, is indicated by the final choice. But there is an economic meter in the background . limit to the money which can be spent in providing reliability, and the decision as course, vital points where the best to how far this object can be pursued materials regardless of cost must be used, must vary according to circumstances. but for the most part the reliability of a receiver will depend upon the skill and picion from the point of view of corrosion. CONTACTS ST,INLESS STEEL experience of its Stainless steel is also used for the roller in POLLt' designer and the the locating device, and is kept in contact MANGANESE BRONZE GAM SPINDLE vigilance and pro- with the indents by a steel spring dipped per organisation of in a special rust -proofing solution. The the works' testing main bearing of the switch is quite free department. from any side thrust due to this spring, as the tension is applied between the roller and the spindle, and is independent of the frame of the .switch. Mechanical a n d is a powerful ally of reliability Simplification electrical reliability. For instance, by designing an STAINLESS STEEL are of equal im- CHANNEL portance in the aerial filter circuit with magnetic coupling, waverange switch, a both primary and secondary coils can be component which, wound on a single former, and separate like the volume con- STRAIGHT SPRING SL A DE trol and on - off screening cans, coupling condensers, and RUST- PROOFED switch, is subjected numerous additidnal connections are CONTROL SPRING to hard wear. eliminated. Much can be done by the

www.americanradiohistory.com Wireless World, May 14th, 1937, 4íj to Last

HIGH performance in a receiver is of little value unless it is maintained. The factors contributing to reliability are discussed and illustrated by points observed in a tour q¡ the works of Murphy Radio Ltd.

use of sub -assemblies for decoupling resistances, by -pass condensers, etc. Test- ing and inspection in the early stages A corner of the Reject Analysis Department where cases of faulty construction are investigated. narrows the search for faults which may be detected in the final assembly, and, a good deal of searching inquiry, and the All test apparatus is checked daily as most of the soldering is done while the fluid used is made up to the works' own against sub -standards, and the sensitivity parts are accessible, it is increasingly specification. But good flux may give rise in most cases is at least ten times that of difficult for an operative to make a bad to nearly as much trouble because of its the tolerance allowed in the component. join t. insulating properties as bad flux does from Special attention is paid to the output In passing through the component corrosion, so valve -holders are fitted with from all mains transformer windings, since assembly section it was observed that a absorbent paper discs to prevent excess the life of valve cathodes and other com- wire covered with both enamel and silk flux from flowing into the sockets. The ponents is directly affected. was being used for the primary and high- paper is, of course, removed after the soldering has been completed. The testing department, which super- ficially might be regarded as being concerned only with the production at the end of the assembly lines of a receiver uniform in performance and up to the required standard, proved on closer enquiry to be one of the most important lllll:dllRilítili guarantors of permanence. Gang con- tllillilllllllllllllllii densers, for instance, are aligned in two ilillill Breakdowns in output transformers are stages, the first being a close approxima- reduced to a minimum by the use of sleeving tion, after which they are aged to allow ill ill ll made from a transparent plastic substance time for strains and fatigue in the metal for leading out the inner end of the primary to settle down before the accurate adjust- winding . ment to the final limits is made. This voltage windings of mains transformers - question of permanence of alignment is an a vital component where only the best important one, for although an abrupt materials are good enough. It was also failure of the set may give rise to acute interesting to learn that random winding annoyance, a steady deterioration is the in output transformers has proved more more serious, as it may well escape reliable than layer windings interleaved detection by anyone accustomed to listen- with paper, which has shown a tendency ing to the set from day to day. It goes to absorb acids from the air. The de- without saying that the accuracy and per- signers are fully alive to the possibilities manence of the modulated oscillators used of new chemical products, and sleeving of for the final adjustment of the completed a transparent plastic material has proved receiver will be reflected in the uniformity ideal for leading out the inner wire of of the product, which is yet another inter- output transformer primaries. pretation of the term " reliability." Each Soldering flux has naturally come in for of the fourteen separate transmitters Testing an experimental layout in one of the latest console cabinets for heat distribution. supplying different The thermometers indicate the temperature checking points on in the vicinity of the oscillator coils, the the medium and gang condenser, the electrolytic smoothing long wavebands is condensers and the mains transformer. crystal - controlled, A very complete system of records is and has AVC on kept by the test department. Every part both output and bears a code number by which the name modulation depth. of the employee responsible for a . given operation can be traced at any future Life tests of volume date. Apart from the use of such records controls and on -off in supplying information for future de- switches are carried value out with this re- signs, their moral in the interests of ciprocating mech- conscientious workmanship can hardly be anism. The ma- overestimated. There is also a section chine runs day and whose sole function is the analysis of night and a counter first with the at the top records the reject parts, object of number of move- identifying and reducing the causes of ments made. excessive waste, and again with indirect

www.americanradiohistory.com 464 WAp@R®go MAY 14th, 1937 WoNlid Building Sets to Last - dealer, for it is realised that by so doing Nairobi, VQG ; Canada, Drummondville, bearing on future reliability, for the he is helping to improve the breed. The PQ, CGA ; and in S. America, at Hurling- smaller the percentage of failures arriving information revealed by the analysis of ham, LSL, and Monte Grande, LSY, both near Buenos Aires. given less chance these records, which go back to the very at any test point, the The Bermuda service is routed via New there will be of parts with incipient faults first sets produced by the company, pro- York. filtering through into the final product. vides the answer to countless minor Conditions during the past few weeks,have Periodically, a component is pounced problems of design, and is drawn upon by been very poor, especially during the last upon at random by the Engineering De- all sections of the organisation. week in April, and this particular period partment and subjected to the same type Thus we see that the initial reliability was dealt with in a special note in last of destructive test as was devised origin- of a firm's products will depend primarily week's issue, since it was thought that ally to prove its suitability for inclusion. on the experience and imagination of the readers Would appreciate early information on the very bad conditions which prevailed. Here a staff of scientific torturers devises designers. Thereafter it becomes an instruments to compress into a few weeks organic growth to which all branches of a lifetime's wear of volume controls, the firm make their own special contri- Failure of Canadian Signals There seems to be little doubt that charged particles ejected by the sun were responsible for this particularly continuous failure of the signals from and to the north -west, the Canadian services having been even more affected than the American ones. These particles are gathered up by the earth's magnetic field and concentrated at the poles, so that the maximum disturbance is to be expected on those circuits, such as the Canadian ones, whose great circle paths traverse the polar regions. This type of disturbance should not be confused with those due to bright hydrogen eruptions and the abnormal emission of ultra -violet light by the sun, which are much more transitory in character. In fact, the rapidity with which conditions return to normal after this type of fade- out suggests (according to Prof. Appleton) that the region affected is probably the D and not the E region. Only at the lower height of the D region is the gas pressure sufficient to bring about the rapid recombination of electrons and ions which will fit the observed rate of restoration of normality after the fade -out. In fact, the general tendency now seems Records play an important part in the progression towards complete reliability. The case to be to attribute to the D and C layers history of every set is filed and statistics are prepared for the information of all sections the attenuating properties which were pre- of the works. viously thought to be the main property of the E region as far as the short waves are waverange switches, and other mechanical bution. Above everything else, pride in, concerned. details. Electrolytic condensers are given and enthusiasm for, the good name of the long -period standing voltage and recurring firm and the keeping of proper records are Reception Reports surge tests, and even pilot lights are inves- indispensable. Owing to the poor conditions which life have tigated to find their effective at various prevailed there is not a great deal of worth- degrees of brilliance. The amount of heat while reception to report. that tuning scales will withstand without Good reception of W9XAZ on 26.4 Mc /s distortion is known, and all other com- was, nevertheless, experienced for a short likely be affected by the tem- while at 9.3o p.m. on Friday, April 23rd, ponents to t- peratures met with, say, in DC/AC sets On h e and W2XE on 15.27 Mc /s and W3XAL on are investigated. When a new cabinet 17.78 Mc /s were both quite good during the evening. design is evolved, the interior layout is A mystery morse transmission, GWW adjusted until a satisfactory temperature de Short-wave GTZ, was also heard on 33 Mc /s about distribution is obtained, and the cabinet 6.40 p.m. at good strength. Conditions this itself is observed for signs of distortion or evening were quite good. deterioration of finish. Other long- period NOTES FROM A From Saturday, April 24th, to Thursday, researches undertaken in this department LISTENER'S LOG April 29th, conditions from the U.S.A. were include the comparison of various types of very poor indeed. plating and enamels for chassis plates After Thursday conditions improved, but must start these notes by apologis- tested in all weathers out of doors. they have not yet reached excellent again. ing for an error in phrasing which Some interesting signals have been OXY, Enough has been given to show that QNEcrept into my last notes. Skamlebäk, on 9.52 Mc /s between GSB and everything possible " by taking thought " In dealing with the B.B.C.'s short -wave LKJx, and the second harmonic of Rabat, has been done to add to the potential life broadcasts which carne via the G.P.O. CNR, on 25.66 Mc /s (11.7 m.) at 7.35 p.m. of a new receiver before the first model radio -telephone services I implied, acci- on Friday, April 3oth. is sold to the public. It is the service dentally, that relays from Australia and Conditions were definitely good, however, department who will pass final judgment India were transmitted via New York. on May 1st, with W2XE (new transmitter ?), on efficacy or otherwise of the measures This is not the case of course, since the W2XAD and W3XAL all performing well. which have been taken. Full records are transmitting terminal for Australia is In general, the higher frequencies seem Sydney, VLK, and for India, Kirkee, V \VY to behave well on some days and the lower kept of every service job ; not only those (near Poona) ; all are received, however, at ones on others -but an especially consistent undertaken at the works, but minor Baldock. signal, although of no programme value, has repairs and adjustments carried out by The other transmitting terminals of the been PMC, the Javanese multiplex trans- dealers. Reports on special forms are G.P.O. circuits are situated as follows : mitter, on 18.135 Mc /s. regularly sent to head office by the Africa, Klipheuvel, Capetown, ZSS ; Kenya, ETHACOMBER.

www.americanradiohistory.com Wireless World, May 1937. i4th, 465 Resista ceCoup1ed AF

A MODIFIED " MULTI = VIBRATOR" CIRCUIT By T. A. LEDWARD, Assoc.I.E.E. Oscillator

DESCRIBING a simple and inexpensive audio- frequency oscillator primarily designed to cover a range from 15o to jo,000 cycles per second.

UDIO- FREQUENCY oscillators of manner. Violent the beat -frequency type, while oscillations are pro- having the advantage of being duced in such a cir- continuously adjustable over a cuit, and the output wick band of frequencies by means of a at terminals Tx, T2 single control, are somewhat in the nature is fairly consider- of a luxury for the average amateur, and able, but the wave are not very easy to construct in a simple form is such that it and reliable form. The oscillator circuit is useless for any to be described, while not possessing the test purposes until single control feature of a good beat -fre- it has passed quencv instrument, has the merit of sim- through filters. It is

Fig. 2. A multi -vibrator circuit giving an output of better wave form.

extremely rich in renders it not so useful to the average harmonics, and a wireless amateur. large number of test If we can arrange that the output at the frequencies m a y , terminals shall have a good wave form, therefore, be ob- then filters will be unnecessary. Variation tained from the out- of frequency may then be made by vary- put terminals by ing one or other of the coupling compo- interposing suitable nents. The circuit shown in Fig. 2 indi- filters. This makes cates one way of attaining this result. it a valuable ar- Here it will be seen that the output from rangement for cer- valve B is fed back to A through a poten- tain laboratory tiometer R. The feed -back is thus con- tests, but the com- trollable, and by suitably limiting the feed- plication of filters back an excellent wave form may be

Fig. 1. - The simple " multi- vibrator " gene- otH T 120V rator. 10,000 plicity. Also the resulting wave form is very good, r r- and an appreciable output -0 is obtained. OUTPUT r fd C1M 1 The oscillator proper re- 2M 0'1MO 50,000 C. O quires only two ordinary i-0 nifdl triode valves, and the L other components are simply fixed and variable VOLTMETER 1'5M 0 0'05 mfd 0'05 mod -fl resistances and condensers. 50,000 The principle of operation will be best understood by 2 referring first of all to Fig. I, which shows the circuit 5,000 of what is known as a L3tLT 2V " multi-vibrator." It will MOM IILT be seen that in this arrangement the first valve ¢-o--H T 11`` A is coupled to the second QtGB valve B by means of a normal form of resistance - G 61'5V capacity coupling, while the second valve B is coupled back to the first Fig. 3.- Circuit of a practical oscillator ; the extra valve provides isolation between the output terminals valve A in a similar and the oscillator proper.

www.americanradiohistory.com 466 WAp®Ilgoo MAY 14th, 1937 WOpflcl Resistance- coupled A.F. Oscillator- conjunction with the fixed condensers. The wave form is assured and the output obtained. The frequency may now be following table indicates approximate potentiometer may be calibrated in volts. altered by changing the condenser C. values of condenser C for different fre- It is of interest to note that the circuit In order to obtain satisfactory results quencies. may be used for providing audio -fre- is quency reaction over a wide band of frequencies it im- Cis 150 1 400 750 1,000 5,000 10,000 without oscillation, but portant that suitable values of coupling Mfds 1 0.5 0.03 10.008 0.005 `0.00015 0.00005 the effect will be to boost up particular components should be used. Also, the It will be seen that for frequencies above frequencies depending upon the values of resistance R is preferably divided into two 40o the capacity is approximately propor- the components used. variable parts, giving coarse and fine ad- tional to the inverse square of the fre- justments, and a third valve is added, quency. At the lower end of the frequency principally for the purpose of isolating the scale this relationship is not maintained, Television Programmes output terminals from the oscillator circuit and any increase of C above o.5 mfd. has Transmissions are from 3 -4 and 9 -10 and thus avoiding trouble due to capaci- comparatively little effect on the fre- daily. ties of connecting leads, etc. At the same quency. Vision : Sound : acts, as an time, of course, this valve If it is desired to extend the frequency 45 Mc /s. 45.5 Mc /s. amplifier and increases the output. A range below 15o cycles, this may be done FRIDAY, MAY 14th. further requirement is that each stage by adding condenser Cr, connected as 3, Jack Hylton and his band. 3.35, British should be enclosed in an earthed screen. shown. For instance, with C= 0.5 mfd. Movietonews. 3.45, Theatre Parade : Leslie A practical circuit, which has been found and Cr = o. i mfd., the frequency will be Henson with Fred Emney and Richard Hearne in scenes from " Swing Along." to give very satisfactory results from about about 5o cycles. If CI is increased to 0.56 25 to about io,000 cycles, is shown in Fig. mfd. the frequency will be 25 cycles. 9, Albert Sammons (violin). 9.10, Artists and and R2 give very their work : talk by Frank Salisbury, LL.D. 3. The resistances RI The wave form at these lower frequen- 9.20, Gaumont -British News. 9.30, Theatre control of the amplitude of oscilla- smooth cies, although quite good, is somewhat in- Parade : Tyrone Guthrie's Globe Theatre tion. RI is arranged as a potentiometer ferior to that obtained at the higher fre- production of " Love, and how to cure it." and gives a comparatively coarse adjust- Fig. 4 indicates the wave forms quencies. SATURDAY, MAY 15th. ment, while R2, which is a variable resist- as shown on a cathode -ray oscillograph at fine adjustment. In operat- 3 -4, Tour of the London Television Station, ance, gives a (a) 15o, (b) 50, and (c) 25 cycles. At all with Leslie Mitchell as guide and George Robey ing the oscillator, R2 should first be set to frequencies above 15o the wave form is as the visitor. Viewers will see Gaumont -British the short- circuited position and RI ad- equal to Fig. 4 (a). News, and meet C. H. Middleton and Clapham justed until oscilla- The valves used in the test circuit were and Dwyer. tion commences. RI three small power valves. The values of 9 -10, Repetition of the tour. Viewers will see should then be re- British Movietonews and a variety from the anode resistance and grid leak in the the Empire, including Flotsam and Jetsam adjusted until oscil- first stage are, of course, totally unsuitable (Australia), Rosette (New Zealand), Oliver lation just ceases for an ordinary RC amplifier, but they Wakefield (S. Africa), and The Seven Hindustans and R2 can then be were found to give the most satisfactory (India). used to start oscilla- control in this circuit. MONDAY, MAY 17th. tion and will give It will be noted that the output ter- smooth and easy 3, Alexandra Park on Bank Holiday. 3.10 minals are shown connected to a potentio- Ernest Mills (cartoons). 3.20, Gaumont - control of ampli- meter in the anode circuit of the last valve, British News. 3.30, The White Còons Concert tude. With all the while voltmeter terminals are provided Party. other components and are so connected that the full voltage 9, Captain C. R. W. Knight introduces his of fixed values the output is always applied to these terminals African eagle and will show extracts from his frequency is deter- film " African Adventure." 9.20, British irrespective of the potentiometer setting. Movietonews. 9.30, Repetition of 3.30 mined by the value These features are not essentials, but they programme. (e) of the condenser C, are useful refinements. The voltmeter and is not appreci- should be a high- resistance rectifier type. TUESDAY, MAY 18th. ably affected by If the oscillation amplitude is always ad- 3, Starlight : Steve Geray and Magda Nun. Fig. 4. -The wave quite large varia- 3.10, Cart Horse Parade : some competitors form of the oscil- justed to give the same reading on the from the Whit- Monday Parade held in. Regents lator at frequencies tions of battery voltmeter, and this reading is such that Park. 3.25, " The Beggar's Opera." 3.55, above 15o c is as voltage or by ad- the valves are not overloaded, then a good British Movietonews. good as indicated by justment of the 9, The Future of Television : the third per- diagram a. amplitude controls. sonality to give their views. ' 9.10, Dog Show : For the range of exhibits from show to be held at Olympia on the 19th. 9.25, Repetition of 3.25 pro- frequencies from 15o to Io,000 cycles, a gramme. 9.55, Gaumont -British News. number of fixed condensers ranging from o.00r mfd: to o.5 mfd. are required, and WEDNESDAY, MAY loth. a variable o.00i mfd. condenser is desir- 3, Captain Knight and his African Eagle. able for frequencies requiring lower con- 3.20, Fifty -fifth Picture Page. 3.50, Gaumont- denser values, and for fine adjustments in British News.

9, Play Parade : scenes from " The School of Scandal." 9.20, British Movietonews. 9.30, Fifty-sixth Picture Page. THURSDAY, May loth. 3, Fashion Parade : London -Paris-New York. 3.15, Architecture -IV. 3.35, British Movie - tonews. 3.45, Students' Songs : impressions of a German beer garden. 9, Repetition of 3.45 programme. 9.15, Repetition of 3.15 programme. 9.35, Gaumont- British News. 9.45, Repetition of 3 programme.

SYMBOLICAL AERIAL. -A Ford car fitted with an aerial taking the form of the familiar " V8 " device. The external aerial, more effective and conducive to a better signal -to -noise ratio than the concealed type, is gradually coming into use on cars fitted with broadcast receivers.

www.americanradiohistory.com Wireless World, May r4th, 1937. 467 Broadcast Brevities NEWS FROM PORTLAND PLACE

Television Cable HIS MAJESTY before the microphone which he used when TELEVISION is full of sur- addressing his people last prises, and one of them has Wednesday. The case between been the disclosure by the the two microphones contains B.B.C. engineers that short -dis- the cue light. ance " O.B." work in the Lon- don area can be satisfactorily out with a twin -wire broadcast in the Concert Hall at carried Broadcasting House would be balanced cable, of an inch :n French, which contains only announced in German diameter, and Italian. has been stated two internal leads and is pro- It lead that this multi -lingual innova- tected by an external tion would be introduced for the sheathing. sake of the Continental delegates One of the fundamental differ- in the Hall, who represented the ences between the operation of International Asscciation for this cable and " co -axial " is that Testing Materials. ' " modu- co axial works with a Happily, or unhappily, the lated carrier wave ; twin -wire B.B.C. remembered, at the last does not. moment, a three -year -old agreement with the International Co -axial for Long Distances Broadcasting Union. The new cable is being used Welsh Independence Day the Regional chair ; in fact, to link the mobile unit with The Occasional Exception JULY 4th is America's Inde- Percy Edgar is already in coni- London's television " belt," also Under this agreement the Cor- pendence Day, but from 1937 maud in Bristol, and is now composed of twin -wire cable, poration undertakes not to an- onwards it may also be known combining his West of England which pursues a nounce foreign languages. as Welsh Independence Day, for duties with his work as Midland tortuous route in Regional Director. down Regent Street, through Thus, in these days of radio from that date the Welsh Region will be finally from the Piccadilly Circus to Whitehall, propaganda, the B.B.C. adheres severed Pioneer Westminster and Victoria, re- strictly to the principle of isola- Nest of England Region. turning to Broadcasting House tion, while a dozen Continen- The existing National trans- Mr. Edgar is the doyen of via Hyde Park Corner, Park tal stations appear to use any mitter at Washford will then Regional Directors, for he was Lane, Marble Arch and Oxford language but their own. take over the Scottish National appointed Director of the old wavelength of 285.7 metres and Birmingham station in 1922 and will radiate an exclusively West has been the most prominent of England programme, while figure in Midland broadcasting the Washford Regional trans- ever since. He is immensely mitter, on 373 metres, will go popular. When it was rumoured " All -Welsh " some years ago that he might be Scottish National will be syn- transferred to London there was chronised with the London and a local outcry. North Naticnals on 261.r metres. It was Percy Edgar who in 1922 inaugurated the "Radio Circle " -the first " Children's Hour."

Surprise for B.B.C. Man FAN mail " on the grand " scale, so everybody thinks, exists only in America, where radio and film stars are bom- barded with the most trivial communications from people they have never seen and hope never to see. Felix Greene, the B.B.C. IN THE NEWS. -The e two cuttings from last North American representative, week's Pathé Gazette news reel show the television had a surprise the other day control van and one of the three cameras that when he dropped in at the Com- were used on Wednesday last at Apsley Gate, Hyde inodore Hotel in New York and Park Corner. The side of the van is in six sections, found Tommy Dorsey, the two of which are shown open, to allow easy access dance to the backs of the various control panels. band leader, with a tableful of letters from English fans who had heard his broadcast relay from America. Street. Between Portland Place Occasionally the B.B.C. re- Percy Edgar and the West and Alexandra Palace both co- laxes its attitude, but pro- It is an honour for the West The Fan Germ axial and twin -wire cable are gramme producers have strict of England Region to have Mr. The correspondence showed installed. orders not to depart from Eng- Percy Edgar as temporary that the English listener, if the It is expected that for the lish without first consulting the Regional Director, pending th' fan germ really gets him, can long- distance relays of the future Programme Controller. And choice of Mr, E. R. Appleton's beat the Americans at their own co -axial cable will be used. permission to do so is given only successor. Mr. Appleton's game. Among the letters were in emergencies, as in the case of period of service with the Cor- three proposals of marriage ad- No Foreign Announcements S O S messages or when a foreign poration does not expire dressed to Mr. Dorsey's vocalist, DISAPPOINTMENT awaited language is desirable from the officially until June ; but he is Edythe Wright, who was on the European listeners who ex- artistic or programme point of now enjoying two months' holi- air for not more than two and a pected that Jack Payne's recent view. day, and will not again occupy half minutes.

www.americanradiohistory.com g68 Wireless World, May 14/h, 1937 Anti -Interference Filters IN this instalment the author PART II. -MAINS -BORNE IMPULSES describes the two main divisions AND THEIR SUPPRESSION into which mains -borne interference may be classified, and discusses N the first part of this article it was duce interference into the aerial or other the appropriate types of preventive shown that any sudden fluctuation in adjacent wiring. filters with particular reference to the normal supply current from the On the other hand, since the two. wires the value of condensers used on electric mains may be separated into comprising the electric mains carry the supplies a vast number of individual sinusoidal asymmetrical component in one direction AC components covering an infinitely wide only (the return path being via earth), frequency spectrum. It was also shown electric fields will be created, and the inter- that the relative amplitudes of these com- ference will be radiated in all directions. By F. R. W. STRAFFORD ponents is a function of the shape of the In general it must be obvious that the initial impulse. asymmetrical components of interference (Research Dept., Belling and Lee, Ltd.) Consideration must now be given to the are the worst offenders, since their sup- propagation of these interference currents pression at the mains input to the receiver Now the reactance of a o.i mfd. con- cannot possibly affect the radiated corn - denser at 15o kc / s (2,000 metres) is only ponents which may reach part or whole io.6 ohms, while at 1,50o kc /s (200 of the aerial system and thus be trans- metres) it is i.o6 ohms, both values of ferred to the receiver. which are quite small compared with the mains impedance of 15o 'ohms. Hence the Mains as a Transmission Line suppression of the symmetrical component of interference can be effected by the use The suppression of the symmetrical of a capacity of o.i mfd. across the mains component (go and return through mains) input to the receiver, shown in Fig. 3. is a relatively simple matter, as it is only Similarly the suppression may be necessary to connect a condenser of ap- effected at the source by connecting the proximately o.i mfd. across the mains in- 0.1 mfd. condensers across the outgoing put to the receiver in order to reduce the pair of wires from the dynamo. Fig. 1. -The passage of interfering impulses interfering voltage to a negligible value. In actual practice the addition of series along supply leads. At first sight one would think that the capacity between the pair of wires con- along the electric mains, and how the be- stituting the electric mains would be so to high large as to make the effect of an additional MAINS RECEIVER haviour of the mains frequencies r o'1 mfd MAINS OR DC) is vastly different from its normal function- o.' mfd. quite negligible. (AO INPUT ing conditions to DC or 5o -cycle AC. It must be remembered, however, that In Fig. Z a dynamo is supplying current one is now dealing with broadcast fre- 4o a broadcast receiver by means of a pair quencies, and at these frequencies the Fig. 3.- Simple suppressor circuit for the of wires (i.e., the electric mains). Inter- effective capacity of the mains, as viewed elimination of symmetrical component of fering impulses will be created by the corn - at the wall socket of lampholder, is by no mains -borne interference. mutation of the dynamo, and will appear means the same as the capacity at, say, as random sinusoidal frequencies covering 5o cycles. chokes in the mains leads is often neces- a vast frequency range. These may be This, of course, is because the electric sary, as the suppression afforded by a propagated along the electric mains via mains is behaving as a high- frequency o.i mfd. condenser is sometimes insuffi- two distinct paths, and it is necessary to transmission line, in which it must be re- cient in cases of acute interference. The distinguish very carefully between these membered that not only has the mains a same effect would have been obtained, two paths. distributed capacity over its length, but in however, by increasing the capacity of the First, the interference may be propa- addition a distributed series inductance parallel condensers. For DC supplies this gated along a path shown by the small is the more econo- arrowheads. The components of inter- mical proposition, ference thus conveyed to the receiver are since no current termed the " symmetrical components." 6 1 1 1 .u11ItIKIL SW11 passes through the On the other hand, the interfering currents condensers, but, on may use the pair of supply wires as one etc. e tc. AC, condensers of path, the return path being through the large capacity may earth back to the generator. These are possibly operate shown by the large arrowheads, and the f l e e wwl9I1I11T 11114 the wattmeter at components thus conveyed are termed the the supply intake. " asymmetrical components." Fig. 2. -So far as their behaviour to radio -frequency currents is con- Although the con- Two highly important points immedi- cerned, a pair of mains leads may be represented as in this diagram. denser current is ately become evident. In the case of sym- theoretically watt - metrical interference, the go and return and resistance. In fact, the circuit of the less, it must be remembered that a poor paths of the interfering currents are very two -wire electric mains is as depicted in power factor for the condenser, or a fairly close (i.e., the electric supply wires are Fig. 2. high wiring circuit resistance, will dissipate adjacent). Because of this there can be no Statistical evidence obtained by many energy as the result of any additional radiation of electric force from the mains, measurements indicates that the average wattless current flowing round the circuit. so that the symmetrical component is only impedance of the electric mains between Large capacities of the order of i mfd. or capable of bringing the interference the two wires of any outlet is of the order more have been known to cause indica- directly into the receiver, and cannot in- of 15o ohms at broadcast frequencies. tions on AC wattmeters. The use of chokes

www.americanradiohistory.com MAY 1tth, 1937 WIp®hoo WopIlcl 469 Anti- Interference Filters - low -impedence path must be provided of the earth from the consumer's earth is, therefore, advised when a condenser between the metal casing and one side point to the power station or sub- station not greater mfd. than 0.25 is not suffi- of the supply. Such a path is provided may average roo ohms, so that the watt- ciently effective for the suppression of the by the condenser C in Fig. 4. less current flowing through the condenser symmetrical component of interference. Now it is an even chance whether the may produce sufficient power dissipation Actually, the chokes may ultimately he plug is inserted in such a manner that the in the resistance of the earth path to record necessary in any case, because of their on the intake wattmeter. Although the ability to suppress asymmetrical inter- amount recorded may be quite small, it is ference, so that they do assist in suppres- cumulative, particularly if the switching sing the two forms at the same time. on the receiver is ELECTRIC arranged to follow in- It is thus necessary to consider now the MAINS stead of precede the suppression filter, general questions of the suppression of which is the normal practice. asymmetrical interference (go via mains, If such a filter is embodied in a receiver return via earth). the centre -tapped condenser may be in- Since the interfering voltage now Fig. 5.- Another method of suppressing creased, since the switching is then per- appears between the pair of mains wires interference from a device of which the formed from the intake, but it must be metallic as one common connection, and earth as casing (dotted lines) is unearthed. remembered that the fitting of suppressors the other, a condenser from one side of inside the receiver cabinet does not materi- condenser C is connected to the neutral the mains to earth provides a reduction ally reduce the asymmetrical component line. It is an even chance, therefore, similar to that effected by the mains that of interference, because the radiating the condenser is connected to the live parallel condenser in the case of sym- mains wire is brought right to the receiver metrical interference. mains, and the metallic case thus takes chassis, up the mains potential and may easily couple to the Unfortunately, the size of this condenser with respect to aerial input circuit. ground. The voltage which would appear from mains to earth is important from a The correct position for such a sup- between the case arid ground when com- safety viewpoint, as will now be explained. pressor is at least Oft. from pleted by a resistive circuit the receiver, such as the in which case the cord from human body depends first upon the receiver the size to the suppressor is now free from radia- of the condenser C, and secondly upon the tion, and far better suppression thereby circuit resistance to ground. Statistical results. evidence shows that a condenser of greater value than o.or mfd. may give an unpleasant shock to the average person BOOK REVIEW wearing leather soles and standing upon a The Decibel Notation. By Alfred Morris, plain stone floor or damp boards. A.R.C.Sc., D.I.C., M.I.E.E. Pp. 57. Fig. 4.-Explaining the need for caution in In Fig. 5 an alternative method of con- Published by Dorling and Co. (Epsom), fitting a suppressor to a non -earthed electrical appliance. nection is depicted, in which a pair of Ltd., Station Road, Epsom, Surrey. 0.005 condensers are centre -tapped to the Price 2s. 6d. casing. INTENDED primarily for students of com- In practically every AC or DC electrical From a suppression viewpoint the effec- munication engineering, this little hand- supply undertaking in this country one book should do much to remove the tive capacity is still o.or mfd. (0.005 many pole of the supply mains is earthed. In + misconceptions which, by general usage, are o.005), but the effective voltage to ground the case of DC supplies, the earthing is in danger of becoming permanently asso- is now halved, and less shock is effected at the supply station only, the use thus ex- ciated with " the decibel." Its identity is perienced. In this it is of additional earths being deprecated on case; however, clearly established as a conventional nota- possible to obtain a shock not the grounds of electrolysis and hum effects. no matter which tion and as a unit. Strictly speaking, way the plug is Most AC systems are three -phase, in which connected, while the neutral is earthed at the supply and in at each sub- station. the case of Fig. 4 - J 60áaa this is only pos- If a voltmeter is connected between the 0'005 mfd sible in one posi- ELECTRIC neutral lead of the electric mains 0-1 mfd1 RECEIVER and a tion. MAINS local " earth," a very small voltage will A further restric- 0'005 m fdI be measured. This is due to the small tion to the size of ohmic resistance of the neutral lead and ''-\9Q4(29)-1- the conden- the total current passing through it, the earth ser (apart from the combined effect producing a small PD to earth. question of shock) must now be con- Fig. 6. -A choke - condenser filter applicable to general use. Protection from Shock sidered in terms of Fig. 6), which depicts a popular type therefore, reference to " the decibel " or " a Unfortunately, however, there is no hard - of mains filter which is applicable to AC decibel " is inadmissible. and -fast rule regarding the disposition of or DC working. The text is singularly free from "padding" the neutral lead when connected to any From a DC viewpoint, the size of the and the author plunges directly into the theory of indices socket or lampholder outlet, and the con- condensers incorporated in this unit may and logarithms. Although sumer does not know which is the live or the treatment is concentrated, the student's be increased without restriction, since no task is lightened by a liberal use worked neutral lead. It is thus an even chance of - current can flow through them. On AC, out examples, and through these he is given whether he obtains a severe shock or not however, the input condenser is restricted facility in expressing in the decibel notation when touching one of the two supply leads to o.r mfd., since it is possible for larger the power relationships which are commonly and earth at the same time. values to work the wattmeter at the met with in practice. In dealing with volt- Consider an appliance such as an elec- supply intake for reasons already age ratios the author places no special em- tric hair dryer. Electrically, this consists discussed. phasis on the necessity for equal resistances of a small motor encased in a metallic Since the centre- tapped condensers are for input and output loads though, as most of frame but insulated therefrom. Suppres- definitely earthed by a low- resistance path, the examples deal with telephone engineering practice, this condition is tacitly assumed. sion of the symmetrical component of it might be argued that the absence of the interference may be readily achieved by There is a good leavening of examples possibilities of electrical shock would per- taken from allied subjects, and the book connecting a o. r mfd. condenser across the mit these to be increased to at least should prove of value to the junior staffs of input leads as already described. In order o. r mfd. sound -recording studios, control rooms and to reduce the asymmetrical component, a This is not so, because the resistance telephone repeater stations. F. L. D.

www.americanradiohistory.com 470 Wireless World, May 14th, 1937.

-- Listeners' ciuí Florence Desmond, Elsie Car- in the National programme on lisle and Billy Caryll and Hilda Monday at 3.3o. Major G. Munday are also billed. Phipps -Hornby will comment Nearly two hundred Boy upon the last five chukkas of Scouts, the biggest cast ever to the match.

EMPIRE'S YOUTH A SPECIAL Empire service of youth to be held in Westmin- ster Abbey on Wednesday afternoon will be relayed in the National programme at 4. To this service will come youth representing all parts of the Empire, including a contingent of some three hundred students from Canada. The address REVIEWING THE FLEET. The Victoria and will be given by the Arch- Albert passing between the lines during the bishop of Canterbury. 1935 Jubilee review. B.B.C. commentaries on On the previous evening, Thursday's review will be broadcast Nationally. An impression of the sight as the rockets are Tuesday, an Empire rally of fired from the ships' decks can be gained youth will be held at the Albert from the picture on the right. Will the com- Hall, and the speeches by the mentator be able to describe this scene ? Prime Minister and Mr. Alfred Noyes will be broadcast in the CORONATION festivi- the Fleet's ait arm National programme at 8.10. ties continue to grace will be broadcast o the broadcast pro- at 5.35. For these grammes again this broadcasts two observers will take part in a single act in HOCKEY ON ROLLER SKATES week. The highlight of the be on the Nelson, Lt. -Com. St. George's Hall, will con- IN his new capacity of radio reporter, Freddie ' Grisewood week is His Majesty's review of Woodrooffe in the foretop and - dude the programme. They the Fleet at Spithead. No Corn. D. A. Stride in the fore- are all members of " The Gang will be heard in the Regional fewer than five times the castle, whilst the observer on Show," which is produced by programme on Tuesday at a running com- microphone will break -in on the jetty- will be Lt. =Com. Ralph Reader. 9.40 giving the scene and convey to lis- G. V. Knight. mentary with Charles Whit - and sound The commentaries from the SPORTS croft on the second half of the teners impressions Rink Hockey shots of the proceedings. The Nelson will be transmitted on ON Saturday afternoon International Match between England and review is to be held on Thurs- ultra -shorts and picked up at cricket and athletics will pro- will be day, and the first impression a B.B.C. receiving station at vide commentaries for National Germany. This played T. at the Pier Pavilion, Herne will be conveyed to listeners at Southsea Castle whence they listeners. From Lord's, on Bay. It is the first of its kind 8.45 on Wednesday, will be sent by land line to Woodrooffe will comment (Nat.) Sussex to be and should when Lt.Com. T. Woodrooffe Broadcasting House. the Middlesex versus broadcast, A. E. prove a novelty O.B. will describe the scene as at The last flash from Spithead match, after which sunset His Majesty's ships will describe for listeners the Lawton, from Old haul down the ensign. He will inspiring sight of the Fleet Trafford, will de- be stationed on H.M.S. Nelson illuminated and the sky scribe the match and, in the ten minutes allotted stabbed by hundreds of search- between Lancashire him, will endeavour to portray lights. Woodrooffe will again and Yorkshire. The sunset from the Fleet, whilst be in position in the foretop on Universities Ath- " effects " microphones pick- H.M.S. Nelson and will thus letic Union Cham- up the bugle sounding " Atten- have an unimpeded view of pionships at the the panorama of the illumin- White City Stadium tion " and "Sunset." by On the actual day of the re- ated ships. will be described observer stationed on > H. M. Abrahams. view an match the South railway jetty will at CORONATION MUSIC HALL The polo scenes at the THE last variety production between Australia 2.5o describe the at jetty and the departure of His of Coronation Week which will and the Army, Majesty's yacht Victoria and be broadcast on Saturday at 8 Hurlingham, will Albert from Portsmouth Dock- (Nat.) will last for ninety min- provide a 45- yard. Listeners will then hear utes. John Sharman, pro - minute commentary the Royal Salute of 21 guns dricer, has booked notable from the Fleet as the Royal artistes for this great occasion. THEIR MAJESTIES yacht approaches the head of Matheson Lang, Irene Van - the King and Queen the lines. At 4.50, as the brugh and Victoria Hopper of Denmark and lines, will be heard in Iceland. Their Silver yacht returns down the and Company Jubilee Thanksgiving Lt. -Com. Woodrooffe will de- an excerpt from " Drake," Service will be scribe the scenes and..listeners specially arranged for broad -. broadcast Nationally will hear the cheers of the casting. Flanagan and Allen, on Saturday. ship's ratings. The fly past of Will Fyffe, Bertha Willmott,

www.americanradiohistory.com Wireless World, May i4th, 1937. Outstanding Broadcasts ic for the at Home and Abroad HIGHLIGHTS OF THE WEEK BLACKPOOL BY NIGHT Christiansborg Palace, their brings two rather unfamiliar A TOUR of Blackpool's songs from the forecourt, and operas. The first, from Buda- FRIDAY, MAY 14th. palaces of entertainment will His Majesty's talk to the pest No. I at 7.3o, is " The Nat., 6.20, Talk by Hugh Walpole, Families in Fiction." 7.40, be conducted by "Our Albert" - students from the Palace bal- Queen of Sheba," by Gold " In Town To- night." 8, Danc- for Regional listeners at 8 on cony. mark, a Hungarian Jewish ng Through. 9, Pianoforte Monday. During the tour the composer who died in 1915. recital : Myra Hess. Tower ballroom will be visited, NORWEGIAN FESTIVITIES This opera, which is a brilliant Reg., 6.40, Recital : Isobel Baillie where Reginald Dixon will be THE week under review will, and colourful piece of work, (soprano). 8.15, The River Clyde : feature programme. 9, heard at the organ, also Nor- in addition to the Jubilee in was first produced at the Court A J. Alan man Newman and the Tower Denmark, include another Opera in Vienna, in 1875. The Abroad. Band. At the Palace Theatre Scandinavian National festival, other, at 8.55 from Hilversum Rome, 9, Uhar's The Count of Luxembourg." Charlie Kunz will be at the namely Norway's celebration No. 1, is " Doktor and Apoth- piano, and from the South Pier of its Independence Day on eker," a lively, soundly con- SATURDAY, MAY 15th. listeners will be given an ex- Monday. Some of the more structed, but rather Nat.. 10.25 a.m., Silver Jubilee of rough Their Majesties the King and cerpt from the Arcadian Queen of Denmark. 3, Sports Follies. commentaries, 7.30, " In Town 4 To- night." 8, Gala Variety. DANCING THROUGH 10.30, A. J. Alan. GEnAI -Do's popular series, Reg., 7.30, Recital Maggie Teyte. is corn- 9, Coronation Concert from the " Dancing Through," Town Hall, Birmingham. ing to National listeners on Abroad. Friday at 8 in a special Kalundborg, Special programmes edition to celebrate the Corona- throughout the day for Silver Jubilee tion. It will be a one -hour's celebrations non -stop pot -pourri of dance SUNDAY, MAY 16th. music and light music covering Nat., 4.55, British Legion Memorial Service at the Cenotaph. the period 1901 -1937, present- Reg., 5.20, B.B.C. Orchestra (D) ing a cavalcade of music of two and Harry Wendon (tenor). 9.5, reigns. In fact, every tune will Scenes from Shakespeare s " A an episode during that Midsummer Night's Dream " recall Abroad. period. It is expected that the Vienna, 8.35, Elisabeth Schumann record of 162 tunes featured in singing Scottish and Sacred songs. will be ex- the last edition MONDAY, MAY 17th. ceeded in this present one. Nat 3.30, Polo commentary. 6.40, From the London Theatre : DANISH SILVER JUBILEE excerpt from Henry V. 7, THE outstanding broadcast Monday at Seven." abroad is undoubtedly Den- Reg., 7.30, Whit Week Customs. mark's programmes on Satur- 8, Entertainment Tour of Black- pool. 9, Mark Hambourg. day to celebrate the completion Abroad. of twenty -five years' reign of Leipzig, 7, " Aida " with Margarete Their Majesties King Christian Teschemascher 'n the name part. X and Queen Alexandrine. TUESDAY, MAY 18th.

National listeners at 10.25 a.m. Nat., 6.30, Musical Comedy : A will hear the Thanksgiving Twelvemonth and a Day." 8.10, RALPH READER and some of the Scouts in the film " The Gang Show " in Copenhagen's Albert Hall Rally of Empire Service by Herbert Wilcox Productions Two hundred members of the cast Youth. Cathedral, Vor Frue Kirke. will be heard on Saturday evening in the gala variety. Reg., 6.30, Recital : W H. Squire Prior to and after the service ('cello). 9.40, Hockey on roller a B.B.C. commentator will interesting events for British comic opera by the 18th cen- skates. describe the animated scenes listeners are a concert by the tury Viennese composer, Karl Abroad. Radio Paris, 8.30, Pau, Dukas outside the Cathedral. . Students' Choir from the Aula von Dittersdorf. commemoration concert. The Danish programmes of the Oslo University at 12 bfonday brings a choice of WEDNESDAY, throughout the day are of a noon and a gala programme at two Verdi operas, " Aida " MAY 19th. nature consisting Nat., 7.50, Gracie Fields from jubilant 7.3o. from Leipzig at 7, and Rochdale. 8.45, Sunset from the mostly of Outside Broadcasts. " Rigoletto " from Berlin at 8. Fleet : relay from Spithead. At 7.5o a.m., the Royal OPERA Wednesday is certainly a 9.20, Discussion : Should Blood Sports be Prohibited ? " . Guards parade on Amalienborg WE are to have another re- Haydn day. Hamburg at 9 Reg., 8.25, Glyndebourne opening Castle Square will be broad- lay from the Royal Opera gives a performance of his " La night. I I Song of the nightingale. cast. Then at 9, from the House this week. It comes to Canterina " a comic opera Abroad. same square, comes a " Singers' National listeners at 10.15 on rarely heard nowadays. At 9.45 Vienna. 9.45 Music to " King Homage " to His Majesty. Monday and will consist of Vienna gives a rare treat -in- Lear." In the evening, at about Act III of Wagner's " Die cidental music to Shake- THURSDAY, MAY 20th. 6.15, King Christian will ad- Walküre." The opening night speare's " King Lear." This Nat., 2.50, 4.50 and 5.35, Relays dress his people. of the from Spithead. 7.40, Palace of season at the Opera was recently discovered at Varieties. At 9 a gala concert will be House, Glyndebourne, Sussex, Esterhazy Castle near the Reg., 8, Danish European Concert. relayed from the Tivoli Concert will provide another opera little town of Eisenstadt, where A Twelvemonth and a Day." Hall, Copenhagen. At 9.45. broadcast. This will be on Haydn lived as Kappelmeister 10.25, Illuminations of the Fleet : the concert will be switched out Wednesday, when at 8.25 for many years. This pro- relay from Spithead. a Abroad. for short time to relay a listeners will hear Act II of gramme will also be given by Deutschlandsender, 8.10, Romantic running commentary on the Mozart's " Don Giovanni." a number of other stations. opera music. Students' Torch Procession to From abroad Friday evening THE AUDITOR.

www.americanradiohistory.com 472 Wireless World, May l;tb, 1937. Why the Triode#Hexode ? PART II.- DEVELOPMENT OF THE ELECTRON- COUPLED MIXER

AFTER having described the development of the classical if' it liad its own cathode, with the excep- rectifying frequency changer in an earlier instalment, the tion that this virtual cathode is not a con- author goes on to explain the modern electron- coupled stant source of electrons and has no inertia. system, with multiplicative mixing. The quantity of electrons in this space charge is not constant but instantaneously

NEW mixer technique was being By J. A. SZABADI evolved independently in EG4 Is America and on the Continent (Technical Department, Tungsram T>, during 1932 and 1933. Efforts Electric Lamp Works) were being directed towards the elimina- ' . tion of the serious disadvantages asso- hI5i / ciated with additive mixing and with the need for rectification in the mixer. This Fig. z I.- Showing IF resultant new frequency- changing technique, known by produced multiplicative mix- i A 1-7IF V"-TA" EG1( Josc.) as electron coupled or multiplicative mixing without recourse to rectifi- RESULTANT ing, solved most of the problems that up cation. to now had been troubling the superhet. It can be considered as the most important (b) Valves in which the first grid is the varying. As the anode current depends

step in making the superheterodyne the signal input grid : . Hexodes (Fig. 9d). on the mutual conductance of the second most popular circuit in the world, and one (These did not attain great popularity as, control grid to anode system, which, which enabled designers to obtain good due to the oscillator section deriving its deriving its electrons from the virtual quality and stable reception with great electrons from the virtual cathode, AVC cathode, is itself a function of the first case and simplicity of design. could not be applied as the oscillator control grid voltage, it follows that In America RCA developed the pentagrid, while Telefunken in Germany, working on different lines, developed the hexode. These were followed somewhat Fig. zo.- General heptodes (basically the EG3+sI characteristics of later by numerous VELOGRID-OGTODE mixers in group a ; same as pentagrids) in this country and note the higher IA OR HEPTODE i on the Continent, which were very soon ENTAGRID anode impedance of the octodes. by -octodes developed by OCTODE superseded SUPPRESSOR GRID Philips in Holland and Tungsram in Hun- I- gary. The former had a negative sixth so grid (providing suppressor action), the z EG4- CONST. latter, a positive sixth grid termed the EG1 =OPTIM. HET. velogrid (providing accelerator action). O VOLTS the anode current J The Two Basic Types î must be propor- ó tional to both, All these multiplicative mixers can be z i.e., to the mul- divided into two groups : (a) Valves in EA tiple of the input which the oscillator grid is the one nearest and oscillator sig- the cathode : pentagrid ( heptodes) and nal amplitudes :- both kinds of octodes (Fig. 9, a, b, and c would stop oscillating.) Both groups IaIF = ¡a,Eg, Cos ((,1, t11,) t respectively). (Fig. 10 shows the differ- have the common feature of having a where a, = amplitude on g, ences between these three types, the second space charge in which (or close to EG, = modulator grid volts octodes causing the least IF shunt -loss, as which) a second control grid operates. U11 = 2;7f osc their impedance is highest.) The second control grid operates just as U), - 274 MOD

OUTPUT + ++ OUTPUT + ++ OUTPUT + ++ OUTPUT + ++ OUTPUT + +4 osc ANODE ANODE ANODE ANODE ANODE ANODE ++

OSC ANODE SCREEN INPUT SCREEN INPUT SCREEN ++ GRID GRID + GRID t -OSC. GRID SCREEN USC. ANODE OSC ANODE OSC. ANODE OSC. ++ ++ ++ SCREEN GRID USC. GRID OSC GRID OSE. GRID 1P1PUT INPUT GRID GRID

(a) (b) (c) (I ) (e)

areas Fig. 9.- Showing relative potentials and functions of pentagrids (heptodes), suppressor grid octodes, velogrid octodes and hexodes. Shaded the cathode, while the area between the first positive screening indicate space charges ; the normal cathode space charge occupies the area nearest grid and the second negative control grid comprises the virtual cathode space charge.

www.americanradiohistory.com MAY 14th, 1937 Wilpgwo OpIld '473 Why the Triode -Hexode ?- tween the two control grids, which I shall charge and the rubbed glass rod brought Thus it will be seen that in order to pro- endeavour to elucidate. Fig. 13 shows near an electroscope. The electroscope duce an IF beat note rectification will not a diagrammatic representation of a heptode will indicate a charge when the rod is ap- be required, as the resultant is produced as well as a representation of a section proached, which will disappear again by pure multiplication as shown graphic- through its structure (Fig. 14) with shad- when the rod is taken away. ally in Fig. Ir. If we do the same thing to a long con- As these various ductive rod an instantaneous current will TX4 TRIODE-HEXODE multiplicative mixers 1,000 flow in it until equilibrium is established, do not require recti- and the current will flow in the reverse fication it is obvious 800 114LF NEUTRALISING direction when the influence is withdrawn. w that the tendency to O VO4 OCTODE CONDENSER Exactly the same thing happens in an cross -modulation will E 600 \`\\ electronic mixer valve of Group (a) be- MH 4105 HEPTODE -- \ tween the oscillating space charge and the 0 400 \16RF N O input grid G4, an influence current Fig. 12.- Variation of CO \ flowing in and out of this grid. This is called conversion conduct- 200 the ance with frequency, space- charge coupling effect. showing beneficial effect It is clear that, due to the input cir- of neutralising con- 0.01 01 ro 10 100 denser between points cuit impedance, an oscillator frequency X and Y (see Fig. t3). M c/s , voltage will be built up on the input grid G4. The oscillator frequency voltage on G4 will be greatest difference be substantially reduced. the density when the If the Ia /EG4 ing to illustrate instantaneous between the oscillator frequency and the curve is a perfect exponential curve (so- of electrons. The accompanying table resonant frequency of the input circuit is called anti -cross curve) this trouble can be gives an explanation of the function of even further reduced. With the progress the electrodes as well as their potentials of valve- making technique generally, even relative to cathode. the relative inefficiency of the early multi- The characteristic in Fig. 15 shows the plicative mixers could have been over- quantity of electrons in the virtual cathode come, and it really appeared that one or space charge as a function of the voltage on the first grid. As the voltage on a + GI approaches zero so the quantity of electrons increases and takes up a larger space, the centre of gravity of this space being near to G4. K = CENTRE When Gr becomes Ksc = BETWEEN K AND G1 H = INSIDE K Fig. r3.- Show :ng the virtual cathode space charge between first Fig. 14.- Representation of a section positive screen and through a heptode. second control grid. The oscillator frequency small. Furthermore, this voltage on G4 Is transferred to G4 by will be in phase with GI if the input cir- virtue of influence. cuit is inductive with respect to Fosc, and will be 180° out of phase if the input other of the octodes would become the more negative, on the other hand, circuit is capacitive. final mixer valve. However, there was the quantity of electrons decreases and If the oscillator frequency is greater one further serious trouble, and this only the centre of gravity- recedes nearer to than the resonant frequency of the input really came into prominence in 1935-36, G3. It is due to this shifting of virtual circuit, the influence voltage will be i8o" when short -wave reception was being cathode that the slope of the mixer por- out of phase and the conversion conduct- asked for in receiving sets ; this trouble, as tion of the valve changes from a maxi- ance will decrease, while in the opposite shown in Fig. 12, is due to a falling -off mum to a minimum, and produces the IF case it will increase. in conversion conductance towards the by the normal multiplicative mixing, as In most commercial superhets. the fre- shorter wavelengths. was shown in Fig. 11. quency of the oscillator is greater than This falling -off is due to an inherent So far we have regarded the negatively that of the signal, and we find, as shown factor, namely, space- charge coupling be- biased input grid (G4) and its attached in Fig. 12, that the conversion gain drops circuit as entirely independent Symbol. Description. Potential Remarks. of the flow of electronic Heater H Indirectly heated. discharge passing IC Cathode ... 0 through it. Unfor- Iíso Cathode space Slightly negative -0 Sustantially constant. charge. tunately, this as- GI Oscillator grid ... From about -50 V. Oscillate:. sumption is not to +1 V. or so. justified. If we G, Oscillator anode... From about +250 V. Oscillates. remember the to +20 V. classical demon- G3 First screen grid... +100 V...... Constant. Vfisc Virtual cathode Slightly negative -0 Space charge quan- stration of " influ- space charge. tity varies. ence " from our G, Modulator grid ... Input signal ...... Also -3 to -50 V. schooldays we shall vari -mu control. readily e Gs 2nd screen grid ... +100 V...... Constant. see t h similarity between A Anode ...... From about +150 to Signal output oscilla- Fig. i5.- Distribution of electrons in the +350 V. tion. this approaching virtual cathode space charge as a function of and receding space the voltage on the first grid.

www.americanradiohistory.com E@ll® MAY r41h, 1937 'Vega Why the Triode -Hexode ?- curve in Fig. 12 shows the relative to the hexode does not alter the triode off below 5 Mc, s, though the drop is immunity of the triode- hexode from this anode current at all. not really appreciable until we get down space- charge coupling trouble ; it is thus Fig. 16 shows a typical modern five - to about Io Mc /s. One can partially the frequency changer par -excellence for waveband frequency-changer stage using neutralise space -charge coupling by in- all -wave superhets., with practically linear a triode -hexode with AVC applied. In this serting a small condenser between points response to all frequencies. circuit, in order to obtain absolutely linear marked X and Y in Fig. 13. The con- A further advantage of the triode - response within each tuning range, a denser value in most practical cases will hexode over all other mixer valves, and Colpitts oscillator ircuit is adopted for be approximately i µµF. As is shown one which is again of particular interest the triode section. Due to decrease of in Fig. 12, quite an appreciable extension on short waves, is the considerably L/C ratio in the input circuits towards the of the useful part of the conversion con- reduced tendency. to frequency -pulling lower frequency end of each tuning range, ductance curve is possible by this means. with AVC. there would be a drop in response, and However, it is equally clear that The pentagrids, heptodes, and both the increased reaction coupling given by neutralising the space -charge coupling is kinds of octodes suffer considerably from this Colpitts circuit at the lower fre- only a partial remedy. The main diffi- pulling on short waves. This is due to the quencies results in an increase of the

20,000 a

T (

0-0001 m f d 0 0001 mfd

0005 mfd (MICA) (MICA) (MICA)

0'1 mfd 01Mí1

Fig. i6. -A modern frequency -changing circuit for a five -waveband receiver. The non -inductive properties of the mica condensers as shown are important on the shorter wavebands.

Cully is, of course, that the amplitude of fact that as the AVC voltage applied to heterodyne voltage to compensate for the oscillations transferred to the input grid the input grid G4 becomes more negative decreased response of the input circuits. via influence is very large compared with so the virtual cathode space charge is It is therefore advisable to design this the amplitude of most short -wave signals. partially forced back through the meshes oscillator circuit so that when the tuning If only one could reverse matters all of the first positive screen (G3) and causes condensers are at maximum capacity the would be well. This is exactly what takes the oscillator anode current (IG2) to in- heterodyne voltage is optimum ; as the place in the hexode and triode -hexode. crease. As this increase is not produced tuning capacity decreases the heterodyne We make the first grid the signal input by an increase in oscillator anode voltage voltage drops while the L/C ratio of the grid, while the oscillator frequency is (EG2), it means that 'the anode conduct- input circuits improves, thus keeping the applied to G3. ance of the triode oscillator has increased, response substantially linear. Though space- charge coupling does but, as this altered conductance, or its What of the future ; is the triode -hexode still occur its effect is negligible, as the reciprocal resistance, is coupled to the the last word ? It would, of course, be voltage being transferred from the input oscillator tuned circuit via the reaction absurd to answer this question in the un- grid to the oscillating grid is negligible. coil, it follows that as this changes so does qualified affirmative, but it can be said Furthermore, in the triode -hexode the the oscillator frequency. This serious with some confidence that, unless broad- injector grid is linked to a powerful triode trouble is not encountered in the triode - cast reception descends below 3 metres, oscillator, and thus the minute influence hexode as the oscillator triode is a totally the triode -hexode has come to stay, voltages lose all importance. The top independent unit, and the AVC applied though it may be improved in detail.

www.americanradiohistory.com Wireless World, May í46h, 1937. 475 The Television Receiver SYNC SEPARATION WITH t

VF AMPLIFICATION wzF- Ow 0 c ácr By W. T. COCKING D U

use vision frequency amplification leads 1 HE of - I ói + in synchronising. The GRID VOLTS to some further problems I reason for these is explained in this article, and their solution is given. Fig. 20. -When sync separation is carried T has been shown in earlier articles flat top of the curve, out at VF as in Fig. in this series that the real objection so that it is only 18 the action is as to the use of vision- frequency ampli- the sync pulses depicted here. fication is that it increases the diffi- which cause a culty of synchronising. Types of ampli- change in the tude filter suitable for sync separation anode current of were dealt with in a previous article in the valve. The Wireless World,' and it was shown Now this same that the most suitable of the types sync separator can described is an RF pentode operating also be used with a VF input, and sent. The presence of the resistance R2, with an RF or IF input. The valve is when the CR tube is fed directly from which may have a value of some 50,00o operated with about 6 volts HT only, a diode detector we can adopt the system ohms, is essential. some 40 volts screen potential, and about of Fig. 19, which shows both detector and It will be seen that over the range of -3 volts grid bias, with the result that sync separator. The detector output picture signal voltages the sync separator a characteristic similar to that of Fig. i8 which is developed across Ri is applied operates with a positive grid, with the to the grid of result that grid current flows and this the sync separator valve has a low input impedance. If it through R2, with were connected directly across RI it t the result that the would largely short- circuit the diode load wz operating conditions resistance and prevent the proper volt- ow SYNC. O PULSES n] are as pictured in ages being developed across it. The zce 1

I GRID VOLTS valve characteristic making it no longer necessary for the is not really neces- valve to have a flat -topped characteristic sary, but its pre- over a wide range of positive voltages. sence does no harm Actually, on the picture signal R2 and PICTURE SIGNAL MODULATION and is of some the input resistance of V2 form a poten- advantage when tiometer across Ri so that only a small interference is pre- proportion of the voltage across RI is applied to the SYNC SIGNAL MODULATION valve. On the sync +H T pulses, however, the grid of V2 is negative and grid 1.4- 30 ó ---+ current no longer I. 100 "b flows. SYNC The valve OUTPUT then has a very Fig. 18.- -The operation of an amplitude high input re- filter operating on the modulated carrier is sistance, and R2 shown here, and it is readily seen how only causes a negligible can affect the output. the sync pulses drop of voltage. This effect is so is obtained. In this illustration the marked that it is manner in which the RF input is applied is also shown, and it can be seen that the negative carrier voltage changes all CR fall beyond the point of anode current TUBE Fig. 19. -Sync sep- -off and so do not affect the output. aration can be cut carried out on the Furthermore, the positive portion of the VF signal across the picture signal modulation falls upon the diode load resistance RI ; the separator valve is Vz. ' The Wireless World, January 22nd, 1937.

www.americanradiohistory.com 476 NVAp®Il®@0 MAY 14th, 1937 WopIld The Television Receiver - ditions to obtain moderate stability of signals tend to settle down across the zero quite possible to obtain good sync separa- synchronising, but it is never very good. line in such manner that the contour lines tion by it alone, and V2 can be a diode ; Experience shows that the best results are enclose an equal area on either side. It is R2 must then be increased to 0.5 megohm, obtained with a capacity of o.i /LF. for clear from this illustration that we cannot however, and as the phase of the output C, a resistance of is wrong some form of phase reversal 50,000 ohms for must follow. R2, and io,000 Now although this circuit enables prac- ohms for R3 ; the tically perfect synchronising to be ob- grid bias should be tained, it is by no means easy to use it zero or slightly posi- following a VF amplifier, even if we retain tive. the DC component. Theoretically, it The difficulty is would be possible to use the circuit of brought about by Fig. 21, in which Vi is the output valve the absence of the and V2 the amplitude filter. The values DC component in of resistances in the voltage divider are so the signals applied chosen that in the absence of a signal the to V2. When the cathode of V2 is about 3 volts positive DC component is with respect to the anode of Vi, and the present the wave- screen and anode of V2 are about 40 v. form of the output and 6 v. positive with respect to its own of the receiver is of cathode. the form shown in There is no doubt that the system would Fig. 23 (a), where be entirely satisfactory if it were possible the signals corre- to maintain these potentials. In practice, sponding to a nor-

Fig. 22. -This circuit is the same as that of Fig. 21 save for the insertion of the condenser C. This removes the trouble of inconsistent operation, but proper synchronisation cannot be obtained because the condenser removes the DC component of the signal. mal picture line, a separate any series of pulses of constant black line, and a amplitude from signals of this nature, for white line, are it is not possible to draw across these shown all resting on signals a pair of parallel lines, representing the same base line. the upper and lower bends in the valve V2, It is also clear that which will cut through identical signals in we can draw a line every case. (dotted) through What are we to do then? We cannot these signals such retain the DC component and yet we that below it the cannot do without it. At first sight it sync pulses are all appears as though we cannot use VF identical ; if the amplification. Fortunately, there is a way signals above this out of the difficulty. If we apply the line are cut off by waveform of Fig. 23 (b) to a rectifier which the sync separator is adjusted to pass current on the negative we are left with a peaks of the sync pulses, we can obtain a uniform series of voltage which is nearly equal to the Fig. 21.-This circuit operates in a similar manner to that of Fig. r8, sync ulses which amount by which the signal extends below but is impracticable because small voltage variations in the HT supply are Nu i t e inde- the base line. If this voltage is then upset the operation. pendent of the applied to the sync separator in series with magnitude and form the signal, it acts in such a way that it however, it is not. For correct operation of the picture signal modulation. pushes the signals upwards so that they all the grid potential of V2 must be kept con- Now when the DC component is re- rest on the same base line just as if the stant within about o.5 volt ; the anode moved the signals tend to the form shown DC component had been 'retained. potential of VI, however, may vary by as at (b). The changes of voltage are repro- This sounds very complicated, but the much as 20 volts in some cases through duced practically perfectly, but the circuit is actually very simple indeed. It mains voltage fluctuations and through bottoms of the sync pulses no longer stand is sown in Fig. 24, and the diode V2 poor regulation of the mains equipment on the same base line. Instead, the performs the magic function of restoring when the gain control is varied. As the grid of V2 is joined to the anode of VI through a resistance, its potential will suffer similar variations. Now if we adopt resistance -capacity coupling in the obvious manner shown in Fig. 22, we shall find it exceedingly difficult to secure any reasonable approach to good synchronising. This circuit is essentially the same as that of Fig. 21 save for the inclusion of the coupling condenser C and the grid -leak R3, but its performance Fig. 23. -Three typical signals are shown at (a), the first corresponding to a normal line, the is very different. It is possible by very second to a black line, and the third to a white line. The same signals are shown at (b) with careful adjustment of the operating con- the DC component removed.

www.americanradiohistory.com MAY 14112, 1937 Wfiadsoo 477 WOpIlc1 The Television Receiver - load resistance in the manner of Fig. 19. the DC component. When the voltage The circuit is in no way critical and func- across R3 swings so that the anode of V2 tions admirably. is positive with respect to the cathode, as Not only does this restoration of DC it does on each sync pulse, the diode con- enable the sync separator to function, but ducts and charges the condenser C posi- it restores it also as far as the CR tube is tively with respect to earth. The con- concerned, and it is no longer necessary to denser can charge quickly through the low retain it throughout the amplifier. This n1cCAilRlf If-1 resistance of the diode, but during the permits us to connect the tube at the point following line signal it can only discharge shown in Fig. 24, and so avoid applying slowly through the high resistance R3, so the HT of the receiver to it. We are also 6 -valve all -wave Superhet with Radio Frequency Stage }HT 8 stages. 8 tuned circuits. 3 wavebands.

R2 r--- V3

C R PRICE TUBE (Complete with on B.V.A. valves) nv l7.ó R Performance (made possible by use of multi -electrode valves) equal to that of many receivers employing 8 valves or more. Brief specification includes : Large "Airplane" dial, with different coloured lights automatically switched on for each wave -range. Micro- vernier 2 -speed drive. 4 -point wave - change and gramophone switch. Volume control and variable tone control also operative on gramophone. Reinforced heavy -gauge steel chassis. Covers 19 -2,000 metres. Circuit comprises : Preselector circuit, radio frequency amplifier (operative on all 3 wavebands), triode -hexode frequency changer, double band -pass I.F.T. coupled T.F. amplifier, double diode -triode detector and L.F. amplifier. D.A.V.C. valves. 3 -watt pentode output. Fig. 24. -In this circuit the DC component is lost because of the condenser C, but is restored applied to 3 preceding artificially by the diode Vz. This arrangement is quite practicable and gives very good synchronising. Special 6 -VALVE BAND -PASS that the line signal is added to the con- no longer restricted to the use of a single denser voltage. VF stage, for we can use normal LF -type SUPERHETERODYNE In practice R3 can be o.r megohm and couplings and ignore the DC component, R2 500,000 ohms, with C = o. z µF. , and since ve are able to restore it in the output the difficulties of synchronising are corn- circuit. pletely removed. The performance of the Lest it be thought that this restoration following amplitude filter V3 is just as of the DC component is liable to cause dis- good as if it were connected to the diode tortion, it should be remembered that the DC component in the transmitted signal is actually produced in this way. In the transmitter circuits a very large amount of VF amplification is employed, and it is out of the question to employ DC amplifiers. Consequently, no attempt is made to retain the DC component, and it is re- (Complete with inserted at a suitable late stage in a man- B.V.A. Valves.) ner similar to that just described. Specially designed and built for high quality radiogram work, SPECIAL FEATURES : Reinforced stout steel chassis. High class components by well-known makers of acknowledged reputation used throughout. Fitted with attractive and vision glass fronted, TRULY PORTABLE RECEIVERS : A NEW specially large full- dial, and supplied complete with escutcheon and fittings. Separate illumination IDEA.- Shaped like a golf bag, but about automatically switched in for radio/gramophone. half its size, this American Crosley set oper- CIRCUIT DETAILS : Inductively coupled band -pass ates on a short trailing aerial. Both filter, triode- hexode frequency changer, band -pass I.F.T. HT and LT are obtained from dry coupled I.F. amplifier, I.F.T. coupled to diode detector. D.A.V.C. applied to preceding valves. L.F. amplifier capacity batteries, and the total weight is given coupled to output pentode 3 -31, watts undistorted. Variable as 18 lb. The circuit tone control and volume control operate on both radio and employs five valves, gramophone. plus a barretter which ALTERNATIVE TRIODE OUTPUT All McCarthy receivers supplied complete with presumably provides valves, knobs, pilot lamps, leads, mains cable and automatic regula- plug. 12 months' guarantee. tion Deferred terms on application, or through London of filament Radio Supply Co., 11, Oat Lane, E.C.2. current in spite of Cash with order on 7 days' approval. Also write voltage variations. for illustrated catalogue of complete range of all McCarthy receivers. MICICAIRIf[FI IFAUIC STD,, 44a, Westbourne Grove, London, W.2 Telephone : Bayswater 3201!2.

www.americanradiohistory.com Mir

Wireless World, May rgth, 1937 UN sE Seeing Double at the By FREE GRID Coronation _.,.._ OW that the shouting and the so my HT supply cost me tumult ' has died, and the nothing. Accumulators were ar- Captains and the Kings are ranged to take care of the LT. taking their departure from supply, in the ordinary manner. London, we can take stock of the casual- When I had finally completed ties sustained by those of use who were the building of my HT battery, foolish enough to try to fight our way to and the installation of the set on the front of the crowd on Coronation Day. the tea -waggon, I commenced my For my part I was extremely lucky, and preliminary tests and speedily got off very lightly. Apart from having came across one very important my hat knocked over my eyes, my coat omission which prevented me torn off my back and nearly losing my from seeing anything at all : I trousers in the scrum, I sustained no great had neglected to provide an damage. If it had not been for the great aerial. Unfortunately, this placed Emptied the contents of blessing of television and ordinary broad- me in a very awkward predica- -their accumulators . . casting, I should neither have seen nor ment, since it would be im- heard anything, whereas, as it was, I did possible for me to erect any form of tele- stages of this they are fed out again, with- quite a lot of both and finished off the day scopic aerial which could be reared above out any rectification or other nonsense, to as His Majesty's guest. the tops of the houses until it had an un- the second aerial, which re- radiates them Like yourselves, of course, nearly all interrupted line of sight to the Alexandra in greatly magnified form. Owing to the my spare cash goes in buying hats for Palace. I did for a time toy with the idea small dimensions of the aerial used for Mrs. Free Grid, and so I hadn't any hope of hiring a telescopic fire escape from the ultra- short -wave work, it is a perfectly of being able to pay the extortionate price local fire brigade, but eventually aban- simple matter to screen them from each that was being demanded for seats in the doned it, for I came to the conclusion that other so that they do not interact and stands ; not that I would have paid the the police would raise silly objections. produce a sort of self -oscillation effect. price even if I had possessed the money, Unfortunately, aerial -less reception of tele- The thing is, in fact, analogous to the as it is against my principles to pay for vision in London streets is practically G.P.O. valve repeaters on their so- called anything unnecessarily. At first I was impossible owing to the screening effect of wired- wireless circuit, and I expect that in some doubt as to whether I should see steel- framed buildings. the B.R.C. originally cribbed it from the Coronation at all, as I well remember Had it not been for a fatuous remark them. the fierce fight I had to get to the front of made by Mrs. Free Grid, who suggested It did not take long to enter into nego- the crowd in 1902 and again in 1911. The a periscope on the roof top to divert the tiations with the owners of the shop in only alternative is to take up your stand Regent Street near which I hoped on the kerbside the previous night, but, . .. on the crowd below. to take up my stand. I managed unfortunately, I am no longer as young to hire a bit of roof space very and active as I was at the time of former cheaply owing to the fact that coronations. It was absolutely essential, r lrs. Free Grid spends the greater therefore, to bring science to my aid. part of my income there, and naturally the proprietors did not H.T. from the Bank wish to risk losing her custom. The negotiations for the site corn - I quickly made up my mind that I pleted, I soon had my installation would get as near to the front of the multi- rigged up and arranged for it to tude as I could and take my television be in the charge of a couple of the set with me by the simple expedient of little Grid Leaks, cutting short mounting it on the chassis of a tea -waggon their objections that they and trundling it in front of me. When wouldn't be able to see the pro- I had completed my preparations there cession themselves by pointing were one or two small snags, one of which out that as they were very young was the question of HT supply. The they stood a good chance of see- maximum voltage requirements of a tele- ing future coronations long after vision set are 6,000 volts, but fortunately I had found a final resting place the current demands are only i / loth of a in the Abbey. milliampere, and so there was no need to On the great day in question I set go to the expense of connecting up a whole forth early with my impedimenta, the re- string of HT batteries in series. I made television rays downwards, I should have laying party having gone the previous up a very simple HT battery by building been compelled to abandon the whole night. I eventually fought my way to a a straightforward Voltaic pile consisting idea. Although, of course, Mrs: Free fairly favourable position near an impos- of a large number of pennies and half - Grid was obviously talking through her ing- looking grandstand. I attracted con- crowns and electrolyte- soaked cloth discs, new Coronation hat, I determined to adopt siderable attention, not only from those each having a hole bored through the an idea for which I am indirectly indebted in my immediate vicinity but also from centre and threaded on a string in the to the B.B.C. This is to use two aerials several plutocrats in neighbouring stands. proper sequential order, and finally hung on a neighbouring roof ; the first is em- Some of the latter, whom I realised by round my neck like a mayoral chain. ployed to feed the incoming signals from the look on their faces must be readers of My local bank manager, of course, lent the Alexandra Palace straight to the grid The Wireless World, were so keen that me the necessary coinage for the occasion, circuit of an HF valve. After one or two they went so far as to surrender their seats

www.americanradiohistory.com MAY 14th, 1937 Wflp@lleogopIll 479 'Unbiased- could wish for, and the crowd around me to others, saying that they would rather cheered vociferously, and at others it do this than miss such an opportunity of resembled nothing so much as a scene from improving their technical knowledge. Dante's Inferno and the crowd reacted Ilhdho, All would have gone well had I not accordingly. Needless to say, those who overlooked the fact in my calculations had given up their seats in the stand in r--w_ -.. - that the B.B.C. would probably use an the hope of having a first -class television ,;; ultra -short wave link as well as a co- view began to get a little restless. . -- . At first I the little Grid - ''i axial cable between Hyde Park Corner thought that I ^ and Alexandra Palace. At any rate, I Leaks had got the sound and vision wave- can explain subsequent happenings on no lengths mixed up, and it was only after other basis, and I am not shaken in my a lot of feverish semaphoring to them that opinion by any foolish denials on the part the bitter truth dawned on me. By this of the B.B.C., which bitter experience has time, however, the crowd was getting long since taught me to discount. thoroughly out of hand, and there were Although you would scarcely think that open murmurings by certain malcontents the B.B.C. would be so foolish as to use concerning what they alleged were my the same wavelength for the wireless link subversive political activities, and some as for the main transmitter at the Alex- even went so far as to say that I was andra Palace, yet they must at any rate probably in the pay of some foreign have at least employed a harmonic of it, power. It only needed a spark to set into as otherwise the regrettable events which open conflagration the undercurrent of occurred would never have taken place. hysteria and lynch -lust which is for ever iiiiji:.11íiidd It will be obvious to you that the little latent in the minds of crowds on these Grid Leaks in their roof-top eyrie and occasions, and the suave voice of the myself in the street below were about B.B.C. announcer telling us what a won- half a mile from the B.B.C. at Hyde Park derful television broadcast it had been Corner and some ten times that distance provided it. from the Alexandra Palace. A simple Had it not been for the prompt action VISION arithmetical calculation will enable you to on the part of the little Grid Leaks up aloft, realise that this unfortunate circumstance who emptied the contents of their accu- meant that the direct signals from Hyde mulators on the crowd, I hesitate to say Park were reaching me a tiny fraction of what would have happened. Even as it a second earlier than the main ones from was, I spent the night as one of the many Alexandra Palace, with the result that I guests which His Majesty entertained at got pictures of the same event from two Vine Street and elsewhere on that memor- different sources, but -and here was the able occasion. snag-owing to the difference in the dis- My friends in the suburbs are of the tances from which the two pictures were opinion that the contretemps was due VION has always coming, one was just about half a line solely to technical incompetence on my been a highly prized tell me the results on behind the- other. part,' as they that asset. Over 28 years This resulted, of course, in certain parts their television receivers were all that ago T.C.C., gifted of the picture showing white where they could be desired. It is quite obvious, should have been black and vice versa. however, that in their case they were well with their facility to although in many instances all was well outside the range of the comparatively visualise the needs of tomorrow, planned momentarily as, for example, when two feeble emanations of the B.B.C.'s Hyde and built for the future. the picture separated from each Park transmitter, whereas I was not only parts of far policy, ever insistent on the a happened for a frac- within a mile of it, but was getting its A -sighted other by half line highest tion of a second to be of more or less the signals together with those of the Alex- use of the finest materials, the same tone. Thus at times the picture was andra Palace boosted up by a directional skilled labour and the best brains available perfectly recognisable and as good as one relaying system. has justified the extra care, trouble and expense it involved ... today T.C.C. are dominant in the field of condenser design and practice. Dominant because every TUNING worthwhile condenser development has emanated from T.C.C.... dominant be- AID cause Setmaker, Designer, and Construc- tor alike has learned to trust T.C.C... . FOR THE the "condenser that never lets you down." BLIND

STATION names are grouped on geographical basis in the tuning scale of the German " Sie- e n s - T.C.C. in Standard." There are also two ALL-BRITISH additional scales with raised dots for the use of the blind. CONDENSERS These are situated on the lower edge of the initial letters of the principal German stations The Telegraph Condenser Co. Ltd., Wales Farm Road, frame surrounding the dial and a projecting and the lower line a selection of foreign N. Acton, W.3. pointer indicates the setting of the tuning stations. In all, there is a choice of 22 alter- condenser. The top line of type carries the native transmissions. M1813

www.americanradiohistory.com TT'ireless T1'orld, May 1.011, 1937. CURRENT ToPics Paris Exhibition Postponed Amateurs Celebrate THE opening of the Foire de THE World Friendship Society Paris has been postponed of Radio Amateurs has just until May 22nd. It will remain celebrated its second anniver- open until June 7th. Its period sary. It held a birthday pat-t;- of opening will thus coincide on the ether in which all its with the first two weeks of the transmitting members took part. Paris International Exhibition, which opens on May 24th. The Station Closes Down availability of the special cheap THE broadcasting station travel tickets from this country which the Government of has been altered to coincide Irak opened some months ago at with the new date of opening. Baghdad has closed down owing to the difficulty of obtaining New Commercial Stations artistes. THE Norwegian Post Office is to erect a to-kilowatt coast Preparing for 1940 station near Ostre Hauge (Lista) JAPAN has already commenced to replace the existing Flekkeroy to make preparations for the station, which is out of date. At Olympic Gaines, which will be the same time, the Swedish P.O. held in Tokio in 194o. Sixteen is building a new commercial short -wave telephonic transmit- receiving station at Enkoping to ters are to be built at a cost of replace the present one at Kungs- approximately 1 million sterling TELEVISION NERVE CENTRE. The interior of the control van backa. The cost will be 645,000 in order that the commentaries which was used for the television broadcast of the Coronation Procession. Swedish Kroner. will be really world -wide. At the far end of the van can be seen the two monitoring tubes on which the control engineer sees the picture as transmitted. Each tube is connected to a separate camera. A Wireless Strike ? An Historic PA Undertaking DANISH radio operators, who ALTHOUGH the public ad- A Record ? growths in the human body intended to come out on dress system installed in THE most radio -minded family which are quite invisible with strike on May 7th, following a Wcstutinster Abbey for the in the world is said to X -rays. At the same time, Dr. breakdown in the negotiations Coronation was not exception- live at Brisbane. Paterfamilias Kornet, a member of the Aus- for better conditions, have ally large as installations go Mackenzie is the owner of trian Biophysical Society, has agreed to remain at their posts noWadays, the undertaking is station VK4GK, his daughter, been experimenting with the pending an investigation of their sorely the most important ever Madeleine, operates her own application of short waves to claim by the Public Conciliator. carried out in this country. station, VK4YL, at the same ad- cheese, and is stated to have had Apart from questions of salary According to engineers of dress, while a third transmitter, remarkable results in the matter increases, one of the chief points Standard Telephones and VK4HJ, is the property of the of improving its vitamin content. in the dispute is in regard to Cables, the firm which under- eldest son. Two younger sons, automatic call devices on ship,. took the work, acoustic condi- aged nine and ten respectively, Historic Building Changes These devices, according to the tions in the Abbey are not un- are both fully qualified Mors Hands operators, are unreliable. favourable -in fact, they are experts. The daughter obtained HOUSE, distinctly bet t e r her transmitting licence when she MARCONI which than those usually was only twelve years old. 11 was the headquarters of obtaining in similar Marconi's Wireless Telegraph buildings. Five am- Beverage Aerial and Co., Ltd., and its associated plifiers of 30 watts Interference companies from 1912 to 1933, were used, with 12.E OWING to severe interference has been taken over by the Air cabinet loud v from Moscow, the Uleaborg Ministry and renamed Ariel speakers fitted with station in the East of Finland House. This building, which small auxiliary dia- has been compelled to abandon was built in 1903, was originally phragms for high - for the time being the use of a the Gaiety Hotel. It will prob- note reproduction wireless link in relaying the ably be best remembered as the and a phasing ar- Lahti transmissions. At the original home of both trans- rangement for bass moment a cable connection, mitter and studios of 2L0, reinforcement. which is said to be very costly, which commenced regular broad- is being employed, but the casting on November 14th, 1922. engineers at Uleaborg are ex- The studios were moved to THE perimenting with a Beverage Savoy Hill on May 1st, 1923, but LINK. the transmitter was used until A network of special aerial over a mile long. They are said to have high hopes of February, 1925, when it was twin wire cable for roof of Self- television purposes, this device solving the problem. transferred to the linking up Broad- ridges in Oxford Street. casting House and New Ray Discoveries Alexandra Palace FREUD is stated with several promi- PROFESSORto have made important 5 -15 Metre Reception nent points in the an West End of London, communication to the Vienna In the circuit diagram of this has recently been Society of Medicine, in which he receiver, which was described laid by the Post alleges the discovery of a ray last week, the Hivac Y22o out- Office. The cable similar to X -rays, but occupying put valve should not have been was made by a different part of the spectrum. indicated as a pentode but as a Siemens. The new ray is said to reveal tetrode.

www.americanradiohistory.com Wireless World, May r4th, 1937 Letters to the Editor The Editor does not hold himself ktiOlf L3112 " Distortionless " Driver responsible for the opinions your issue of April 3oth, Mr. W. N. of his correspondents IN Weeden describes a method fpr reducing I driver distortion in Class AB circuits by the introduction of negative feedback round the Recently, the writer, dissatisfied with the of the .MAN driver stage itself. He also points out the performance of the AVC system of his re- advantages of degeneration in the output ceiver (a commercial superhet 7), which stage if pentodes are used, but complains produced only 3.95 volts bias on the three ROLA F 742-PM that this increases the demand on'the driver. variable-mu valves even when tuned to This difficulty can be avoided if the nega- Droitwich, decided that conversion to am- tive feedback connection is taken from the plified AVC was easily practicable. The output load of the amplifier to the input alteration was therefore effected, and an circuit of the driver ; and, although some immense improvement was immediately care must be taken to prevent the occur- noticeable both in background noise and rence of positive feedback conditions at very diminution of fading. The bias had jumped high frequencies, this arrangement transfers up to 18.8 volts on Droitwich, and I feel the demand for increased signal voltage to that every ounce is not now being squeezed the pre- driver stage, where it may be met out of the valves to provide sufficient bias. without any difficulty. Moreover, the fre- It immediately became apparent, how- quency and phase characteristics of the am- ever, that a symptom I now know as plifier as a whole will be more nearly perfect, "flutter" had made its appearance. As due to the inclusion of the coupling between my experiences. in this connection are at the driver and output stage in the feedback variance with those of your previous corre- scheme. spondents, I give them hereunder :- The accompanying oscillograms, obtained (I) Flutter can be provoked on any fairly with a pair of 6L6 valves driven by a para - powerful carrier whether it is being modu- phase combination, show results obtained lated or not. AN IDEAL under conditions of uniform output (a) with- (2) Flutter occurs only at minimum set- out degeneration and (b) when degeneration ting of the volume control. UNIT FOR is added in the manner described above. A (3) Flutter occurs at frequency of one per test signal was applied direct to the X plates second at zero volume (observed by watch- BATTERY SET USE of the oscillograph and also through an ing neon tuning indicator), and increases as in- Only a very sensitive speaker attenuator to the will get the best results from put of the amplifier. a battery set. But very sen- The output voltage sitive speakers are frequently was applied to the very high in price. Here at Y plates and ad- last is a new 9ö" PM unit justed by means of with a flux density equal to t h e attenuator to the big Rola G.12 -PM selling at only 49/6. I t is an excellent give a figure at 45 speaker for use with any degrees to the X and receiver, but for a battery set, Y axes. It is evi- as an Extension speaker, or dent that in the under any operating conditions where extreme sensitivity is required, it is abso- Cathode -ray figures lutely ideal. The new Rola obtained from ampli- F742 -PM makes use of the fier. (a) Without new magnet material " Al- degeneration, (b) with nico " and is equipped with a newly designed metal and N: degeneration. (a) ( b) compound shielded universal transformer, impervious to moisture -just another Rola absence of amplitude and phase distortion VC is advanced, and finally disappears at refinement. this figure will be a straight line, while any ordinary listening volume. Write to -day for leaflet AB. other figure may be analysed graphically to (4) Flutter occurs at above 9 Mc /s, since determine the amount of phase shift and either Schenectady or Zeesen on 19 Mc /s harmonic content. In this way we have will start it on my receiver. measured the percentage of second and third (5) It has been completely eradicated by harmonic in the two cases illustrated. For (a) reducing delay ; (b) reducing resistance the amplifier with negative feedback they in triode -cathode circuit ; (c) increasing are 0.44 per cent. and 3.13 per cent. respec- negative voltage to which diode is con- tively. Without feedback the second har- nected. monic remained at a very low value, but All three, of course, amount to the same the third harmonic rose to 14.7 per cent. thing, and are much cheaper than the other London, S.W.r. R. P. G. DENMAN. methods advocated. WITHOUT TRANSFORMER 42 - E. S. L. BEALE. I trust the above is of sufficient interest to warrant inclusion in your columns. OVER 8 MILLION IN USE % " Flutter " Fareham, Hants. HAROLD STRIPE. T VM interested in the letters now appear - ing in your valuable weekly on the sub- The Radio Industry ject of " Flutter." Whilst your correspondent, Mr. G. H. THE Dubilier factory, which closed down for the Coronation holidays on May 11 th, will Bradbury, appears to have formulated a reopen on Tuesday morning, May r8th. Em- 71rP lrot14 Tu[e4t Re l`llrlil[CQ`G) more convincing theory than that proffered ployees are being paid for the holiday period. by Mr. R. G. Young, I do not feel satisfied o o o o THE BRITISH ROLA CO.. LTD. in my own mind that either of the views Four Grampian C377 amplifiers were used MINERVA ROAD, PARK ROYAL,N.W.10, expressed is the precise interpretation of the for crowd control, etc., for the Cup Final at PHONE WILLESDEN 4322-3-4-5 -6 cause of the phenomenon. Wembley

www.americanradiohistory.com 482 Wireless World, May 14th, 1937-

Brie/Brief descriptions B the more interesting radio Inventions devices and improve- pulses occurring in the intervals magnetising current through the ments issued as patents between two successive trains of powdered -iron core of an induct- will be included in this picture signals -it is possible to ance, and hence the tuning of apply the former at an earlier associated circuits. section. point in the chain of amplification British Thomson-Houston Co., than the latter without any risk Ltd. Convention date (France) of intermodulation. June 7th, 1934. No. 459658.

According to the invention this o O O O is done, the picture signals in a SUPERHET. RECEIVERS INTERVALVE COUPLINGS 40 kW transmitter accounting for ADIODE valve is used as the THE circuit shows a valve coup - 6o per cent. of the modulation and a first detector in a superhet. 1 ling suitable for amplifying the synchronising impulses 40 per set, and at the same time means wide band of signals, such as are cent. The method simplifies the are provided to prevent reradi- used in television, without dis- operation of " mixing " at high ation of the local oscillations from criminating between the high fre- voltage levels, and allows either the aerial. The incoming signals quencies and the low. The anode phase or amplitude distortion in arc applied to a circuit A, whilst to screen -grid capacity of the am- either type of signal to be cor- plifier Vi can be represented by the rected independently. condenser Cr, since the screen -grid A. J. Brown and Baird Tele- is at fixed or " earthy " potential. vision, Ltd. Application date July Similarly the condenser C2 repre- 23rd, 1935. No. 460222. Amplifier for television signals sents the grid- cathode shunt capa- o o 0 0 city of the amplifier Vz. to maintain correct phase re- These are both in series with AUTOMATIC TUNING lation in input and output two inductances, Li, L2, the mid- CONTROL circuits. is effected by hand in point of which is connected TUNING through a resistance to the high - the first instance, and advan- stage is designed so that the out- tension supply. The capacity Cz tage is then taken of a charac- put remains in phase with the in- should be greater than twice, or teristic change which occurs in a put. As shown, the input voltage less than half, the value of the " working current " of there- is applied at I across the control capacity Cr. A mathematical ceiver, on the approach of grid and the cathode. The screen analysis of the frequency -charac- resonance, to set the circuits auto- grid is connected to HT through a resistance R, and to the cathode through a large capacity C in series with resistances Rs, R2. This causes its voltage to swing in Non-radiating first detector phase -opposition to that of the stage for a superheterodyne control grid. The anode voltage, receiver in turn, is in phase opposition to that of the screen grid, which brings it into line local oscillations are fed to a cir- with the control cuit B, the resulting intermediate grid. The output is taken from frequency the terminals marked O. being collected in the T. H. Bridgewater. circuit C. A circuit D, comprising Application a resistance date September 261h, 1935. No. shunted by a con- 460673. denser, is inserted in series with o the anode and cathode of the diode o o o as shown. FLUORESCENT SCREENS Because of the series arrange- AFLUORESCENT screen giv- ment only a small proportion of ing a brilliant response, the voltage existing in the lccal- closely approximating to pure oscillator circuit B will appear white, is made by mixing zinc across the input circuit A, so that borate -which requires a slight there is practically no radiation content of an activating substance from the aerial. such as manganese dioxide -with N. V. Philips Gloeilcaupcn- chemically pure zinc sulphide. A fabrieken. Convention date (Ger- water- suspension is first made of many) August 19th, 1935. No. the mixture, and after this has 460408. been dried out the fine powder is 0 0 0 0 sprayed over the inside surface VALVE AMPLIFIERS of the bulb -end of a cathode -ray IN most amplifiers, particularly if tube. resistance -capacity coupled, The subsequent processing of the Circuit for amplifier with wide -band frequency response er- h stage introduces a phase - tube must be carried out at a tem- change of 180 deg., so that an perature not exceeding 300 -400 deg. C., so as to matically to the exact tuning even number of stages nntst be avoid any chemi- teristics of the circuit is given in used if the phase of the output is cal reaction between the pure sul- the specification, together with the point. A " working current " is phide to include any current to agree with that of the signal and the dioxide used as an electrical values of the various cir- defined input. In the case of a television activating agent for the borate. cuit components. flowing through one of the chain Although the of amplifiers, but excludes any receiver it is important that this light response of the J. Hardwick and E. L. C. White. phase mixture is a more ' current which is a replica, or de- coincidence should be pre- natural " Application dale July 9th, 1935. served, since otherwise signals colour than either of the two in- No. 459581. rivative of the signal oscillation. The use of auxiliary control de- corresponding to a positive pic- gredients, taken separately, the 0 0 0 0 vices operated directly by the ture appear as a negative image time -lag effect is no greater than TELEVISION SIGNALS on the screen. Accordingly, one that normally exhibited by zinc signal currents is also excluded. forced IN transmission, picture signals The invention is applicable to may be 'to use a four -stage borate. are usually applied to modulate " straight " receivers as well as to amplifier, when, in fact, three Farnsworth Television Inc. Con - the outgoing carrier -wave at the superhet. circuits. In one arrange- stages would be sufficient. vention date (U.S.A.) March 13th, same point in the chain of ampli- ment, a triple set of condenser To overcome this difficulty each 1935. No. 460.479. fiers as the synchronising im- plates is operated through a gal- pulses. This means that the latter vanometer, responsive to the The British abstracts published here are prepared, with the permission must be of comparatively large " dip " in anode current, and serves of the Controller of H.M. Stationery Office, from Specifications amplitude. But since the two types to trim three of the tuned circuits obtainable at the Patent Office, 25, Southampton Buildings, London, of signals are not present at the to bring them into resonance. In W.C.2, price 1!- each. A selection of patents issued in U.S.A. is I same moment of time in the radi- another arrangement, a change in also included. ated wave -the synchronising im- anode current is used to vary the

www.americanradiohistory.com THE PRACTICAL RADIO JOURNAL 27 th Year of Publication

N o. 925. FRIDAY, MAY 21sT, 1937. VOL. XL. No. 21.

Proprietors : ILIFFE & SONS LTD.

Editor : HUGH S. POCOCK. EDITORIAL COMMENT Editorial, Advertising and Publishing Offices : DORSET HOUSE, STAMFORD STREET, from the Alexandra Palace studio or LONDON, S.E.I. Television grounds in previous transmissions. Telephone: Waterloo 3333 (5o lines). These results are encouraging to Telegrams: "Ethaworld, Sedist, London." Successful Experiment television and should pave the way COVENTRY : Hertford Street. for the broadcasting of further scenes Telegrams: Telephone: HE arrangements made for "Autocar, Coventry." 5210 Coventry. broadcasting the ceremony and remote from the transmitter itself.

BIRMINGHAM: pageant of the Coronation have called forth universal Guildhall Buildings, Navigation Street, 2. Interference Telegrams : Telephone: admiration. It was the greatest broad- Autopress, Birmingham." 297r Midland (4 lines). cast in history and the Empire range of Screened Aerial Systems MANCHESTER : 260, Deansgate, 3. the transmissions was further extended Telegrams: Telephone: 'Iliffe, Manchester." Blackfriars 4412 (4 lines). through the commentaries put over WHILST we hope that the time the broadcast networks of other nations. when legislation will control in- GLASGOW : 26B, Renfield Street, C2. By contrast, the television trans- terference daily draws Telegrams: "Iliffe, Glasgow." Telephone: Central 4857. nearer, mission was limited in its range to this does not relieve broadcast receiver PUBLISHED WEEKLY. ENTERED AS SECOND the circumscribed area CLASS MATTER AT NEW YORK, N.Y. covered by the users from a responsibility to do what- Alexandra Palace ultra -short wave ever they can at their end to alleviate Subscription Rates : transmitter. We could not put the the trouble. Manufacturers of receivers, Home, £r is. 8d. ; Canada, Xi is. 8d. ; other number of those who countries, £1 3s. rod. per annum. saw the Corona- too, have their part to play and should tion procession through the medium make every reasonable effort to improve As many of the circuits and apparatus described in these of the television screen much higher conditions at the receiving so pages are covered by patents, readers are advised, before end as making use of them, to satisfy themselves that they woa4i than 50,000 and this is a very small to bring about the best possible not be infringing patents proportion indeed of those who partici- reception, clear of electrical disturb- pated in the event, either directly or ances. by means of sound broadcasting. At present much can be done by the These circumstances did not, how- use of screened aerial down - leads CONTENTS ever, detract from the achievement of associated with two transformers, one television. The Page broadcast may be de- at the lower end of the screened lead scribed as having been in the nature of connecting Editorial Comment 483 to the receiver itself. A an experiment, for the reason that there writer in this issue forward Screened Aerial Losses puts the 484 was practically no time or opportunity proposal that this lower transformer The Hartley Circuit .. 486 for proper rehearsals. The television and the transformer on the input side More AVC for Motorists 488 cable laid between the cameras at of receivers, should be replaced by one Recording on Paper Tape 488 Hyde Park Corner and the Alexandra transformer designed to match the Rediffusion of Empire Broadcasts 489 Palace transmitters was an innovation impedance of the aerial " line." Current Topics . . .. 491 in itself, the possibilities of which had A receiver so designed would not be Pye Baby " Q " Portable 492 not been fully tested. In addition to suitable for use with an ordinary type

Unbiased . . .. 494 these difficulties, the engineers were aerial but only with a " line " of New Apparatus Reviewed 495 unfortunately faced with a change in definite impedance. This seems tc weather Listeners' Guide for the Week 496 conditions just as the proces- be the only serious objection to an sion came within range of Magic from the Air .. 498 their cameras arrangement which otherwise must and rain continued to the end of the have Broadcast Brevities .. 500 many advantages. It might transmission. In spite of these adverse mean Practical Hints and that manufacturers would have Tips 501 circumstances, we were delighted with to develop two models, one Random Radiations for use 502 the detail and clarity of the picture, with an ordinary aerial and another Letters to the Editor 503 which compared not unfavourably with for screened aerials, a line of fixed im- Recent Inventions.. 504 anything which has been put over pedance being standardised.

www.americanradiohistory.com 484 Wireless ll rid, May 21s1, 1937. Screened Aerial Losses T is shown that a screened aerial system should ideally be designed IS ONE OF THE TRANSFORMERS REDUNDANT ? to work with a particular type of receiver and that a given equipment, By PAUL D. TI ERS though in itself beyond criticism, may introduce heavy losses when used with more neon signs are employed, while there secondary winding of the aerial trans- a receiver for which it happens to be is an increasing use of domestic apparatus. former and the matched primary winding The other cause is the tremendous in- of the set transformer, together with the The suggestion is made unsuitable. crease in the sensitivity of the broadcast connecting pair, form a low- impedance that the characteristics of the input receiver. A set with a sensitivity of 20 circuit, and accordingly the capacities tuned circuit of the receiver should be microvolts is now quite commónplace and between the leads, and between the leads is sold at a low price. Previously the sen- and the Screen, are not very important. modified to serve as a line-to -valve sitivity of a receiver was of the order Moreover, the equivalent resistance due matching transformer. of hundreds of microvolts. It is not surprising, therefore, that the interference problem has become very real. FLECTRICAL interference can reach It has already been implied that if an a receiver in two ways, It can be aerial is located in a space where there is mains- borne, entering the receiver no interfering field, interference -free recep- through the power supply trans- tion is obtainable. The field of the interfer- former, or else it can be introduced as ence due to electrical apparatus is for the direct radiation picked up by the aerial. most part confined to a low level, and Interference arising via the mains connec- diminishes rapidly with increase in height tion can be effectively cured by the fitting above the ground. of a low pass filter such as the familiar If, therefore, the aerial is raised as high centre- point- earthed condensers, but the as possible, and its down -lead is screened, the chances of obtaining clear reception are Fig. 2.- Aerial input circuit of a typical receiver ; there is no standardisation of the greatly increased. An various constants. ordinary screened lead is useless as a down - to the dielectric losses in the connecting lead because the capa- leads do not have very much effect upon city is far too high. the circuit. It might appear, therefore, The first step was to that the use of such an arrangement is use what is commonly quite efficient. A little examination soon known as the " ele- shows that this is not necessarily io in phant trunk," consist- every case. ing of a very large dia- The input of any radio .receiver com- meter tube with a prises a tuned circuit, resonant to the fre- small centrally- placed quency of reception. This must be associ- Fig. 1.-Basic anti -interference aerial circuit. wire. Even this has ated i;vith the aerial through some coupling had a rather high device, and in any broadcast receiver the treatment of the other kind is not so capacity, and by no means low losses. arrangement adopted is necessarily a com- simple. Accordingly, the transformer system was promise. In the case of a receiver working The function of an aerial is to convey to soon adopted. on medium and long waves, in which the the receiver minute voltages which are pro- This consists of a pair of transformers aerial and down -lead are a fraction of the duced by virtue of the aerial being within connected back to back, the low -ratio wavelength of transmission, there is an an electromagnetic field due to a desired sides being connected by a screened lead, optimum condition for any given wave- transmission. Unfortunately, electrical or more generally a screened pair. The length. Luckily, it is possible to use a apparatus such as small motors, neon signs basic arrangement is shown in Fig. r. The coupling coil or aerial winding which and car ignition apparatus produce fields forms a good com- against which normal receiving apparatus +5 promise for each cannot discriminate, and so interference is employed. 0 waveband produced. we examine the db 11,11111111111 If Various systems have been proposed for IIIMEMEN111111113 basic network in Fig. balancing out the effect of radiated inter- 10 Mill1111111EMMIN I we find we have a ference, but the present standard practice pair of transformers 20 811111111íi111 is to place the aerial in a position free from which are required to interference and connect it to the receiver (a) couple the aerial to through a screened down -lead. Although this system is now so well established it +5 Fig. 3.- Diagram (a) does seem desirable to consider its limita- 0 shows losses introduced by the same tions and its general effect upon receiver db screened aerial performance. s 10 equipment into It is well to realise at the outset that the different broadcast subject of radiated interference has only 20 receivers, while become increasingly important because, in 300 400 500 600 1,000 1,200 1,400 1,600 1,800 2,000 diagram (b) shows WAVELENGTH IN METRES losses introduced by first there has been, within the the place, (b) different screened last ten years, a marked increase in the aerials into the same number of interfering sources. More and receiver.

www.americanradiohistory.com MAY 21st, 79 37 Wipishoo 485 `j orIlcl Screened Aerial Losses. mendous difference to the frequency a staggered amplifier in which circuits are the input of a representative receiver characteristic of the whole network. set off -tune with a view to increasing the equally efficiently over an exceedingly Fig. 3 (a) shows a group of insertion loss band width. wide waveband. If switching is to be curves of one screened aerial equipment, Losses as high as 20 to 3o decibels have avoided this waveband may extend from taken with representative modern broad- been recorded with certain combinations cast receivers. Fig. 3 (b) is another of equipment and sets. The desirability

5 rather interesting set of curves showing of obtaining the highest possible voltage the insertion loss of t vo different equip- on the grid of the first valve with a view to 0 ments when used with the same receiver. eliminating background noises is well known, and it is obvious that, quite db / ...... ss Fig. 4 shows the loss obtained with a apart i transformer network designed to operate from the loss of signal strength, any device 5 / with one particular set, while it also shows which introduces a large insertion loss is i what happens when it is used with a highly undesirable. It would seem that io / -- --. receiver having totally different constants. the less complicated we make the network -- When it becomes obvious that a network the more easy would it be to obtain a lower 75 200 300 400 500 of the type in Fig. r must necessarily be insertion loss over a wide waveband. If, WAVELENGTH IN METRES susceptible to very small inductance and then, the sensitivity of sets is likely to in- capacity changes, one is justified in con- crease, and if there is likely to be no Fig. 4. -The full line shows losses introduced sidering whether some step should not be diminution in the intensity of domestic by a transformer system into the receiver for taken to improve the arrangement. electrical interference of the radiated type, which it was designed ; the dash -dot line represents losses with another set. The greater the number of circuits with the time may come when the screened a high L C ratio the more susceptible down -lead equipment is an integral part zoo to 2,000 metres, with a small gap will the network become to small changes, of the receiver. between the medium and long waves. It whilst each so- called semi -aperiodic coup- Under such conditions we should have, is obvious that if an ordinary aerial coupling device must necessarily introduce a as before, the single unswitched aerial ling coil is only a compromise, then the number of natural resonances over the transformer, but the external set trans- design of the complicated network involv- entire waveband. The low insertion loss former immediately disappears. The mere fact ing two transformers and a length of obtained with the experimental device of of cutting out one transformer in screened line must the system should obviously help to in- be a far more diffi- crease the overall efficiency. The designer can then approach the problem in twc cult compromise . and it cannot, from ways. first principles, be In the first place, he can use some ar- as efficient as a rangement such as that shown in Fig. 5, single aerial coup- in which the screened lead terminates in a ling coil. transformer, the secondary of which is the Screened aerial first tuned circuit, or preselector, of the equipment is pro- set. Actually there are further possibili- duced for general ties. As the external set transformer is use with represen- now eliminated the introduction of switch- tative broadcast re- ing in the input arrangement presents no ceivers, It might be difficulty whatever, because switching can thought that this be ganged with that in the remainder of would be fairly the receiver.. The problem might be simple, as the per- helped even further by the use of quite formance of con- involved and complicated LCR combina- temporary sets is tions which could be switched into circuit very similar. Actu- for different wavebands with a view tc ally, however, the improving the matching or transference constants of the in- loss. In fact, experiments on these lines put circuits of rep- are already showing very promising resentative sets, results, and it does not seem to be difficult such as those in to obtain a reasonably low loss over a very Fig. 2, vary tre- wide waveband. mendously. Many Should receiver design develop on the aerial connections lines suggested, the only additional equip- are made through ment would be the aerial transformer. I1 fixed condensers, is now quite possible to produce a highly while variation in efficient aerial transformer which is very the absolute induct- little bigger than an ordinary shell insu- ance of the aerial lator. It will be more than interesting, coil and the mutual therefore, to see whether some such change inductance between as that anticipated occurs in the imme- the coil and the diate future. tuned circuit is far greater than is generally realised. It CCIR Meeting is a circuit of this A 1\IEETING of the Liternational Tech- Illustrating use of the receiver input in type that is con- Fig. s. the circuit place of nical Consulting Committee, snore nected to the the usual " set transformer " of the normal screened aerial equipment. usually known by its French initials of set transformer. These trans- which a curve is given in Fig. 4, de- CCIR, is now being held in Bucharest. At screened conference the International of the so- called aperiodic type signed for one particular receiver, is due this Amateur formers are Radio Union is represented by an American and comprise tightly coupled coils with a entirely to the fact that the various reson- and a Canadian. The CCIR meets at in- very high L/C ratio. Accordingly, slight ances of the whole system were intention- tervals during the five years which elapse variations in the impedance into which ally controlled. The whole arrangement between the International Telecommunica- the set transformer works will make a tre- is then rather similar to what is known as tions Conferences.

www.americanradiohistory.com Wireless World, May 21st, 1937 The Hartley Circuit

EVOLUTION OF THE `SINGLE- COIL" OSCILLATOR various circuits step by step, in order to make their applicabilities clear. It would be possible to put in the bat- By M. G. SCROGGIE, B.Sc., A.ïI.I.E.E. teries as shown in Fig. 2. Even if the grid battery is omitted, as being generally unnecessary, it is clear that whatever point THE Hartley circuit-sometimes called the Amateur's Fairy Godmother on this circuit is regarded as earthed there is at least one battery " up in the air." -has long been a favourite, as it allows a workable oscillator or Also the oscillating part of the valve receiver to be set up with the fewest and simplest of components. The current has to go through the anode basic circuit and some of its variants are described in this instalment.

DESPITE their differences in ap- rule it out from such applications as a pearance, all valve oscillator gang -tuned superhet. However, in some circuits are really the same in of its forms this difficulty is avoided. principle. To side -track criticism Omitting all accessories, the Hartley it should be added that there are a few circuit appears in its simplest theoretical obvious but relatively unimportant excep- form in Fig. I. Assuming that an oscil- tions to this rule : for example, the mag- lation has somehow been started surging netron and the dynatron. But there is back and forth around the loop line formed variety enough among the main body of by the coil and condenser, the oscillating oscillator or reaction circuits in general. voltage developed across the part of the As the underlying principle is identical, each of these variations has been devised because it works better or is more con- in view. (Below) Fig. 3.- Fig. 5.- -The parallel -fed arrangement. venient for the particular purpose Full HT voltage on Probably the best-known of all oscilla- the grid -clearly an tor circuits is called the Hartley ; and, as inadmissible state of battery. Both of these conditions are, very few people seem to know why, it affairs. more or less, undesirable. The latter can may be of interest to mention that a Mr. be got over by shunting the battery with a R. V. L. Hartley patented it for the large- capacity by -pass condenser, but the Western Electric Company in 1915. The former demands more consideration. Hartley circuit itself appears in several The most usual practice is to earth the ; different forms ; without going into legal cathode therefore, to bring the anode exactitude it may be said that the features battery also to earth potential it must be common to all are a single tapped coil, connected as in Fig. 3. This has the effect with the tuning condenser connected across of putting the full anode battery voltage the whole of it. Actually one can depart on the grid also, which is clearly inadmis- slightly from the strict letter even of this sible. There are several ways out of this basic definition without infringing the difficulty. One is to stop the battery volt- spirit of it. age off from the grid by a condenser, There are several reasons for the popu- which, nevertheless, allows the oscillating potentials to reach the grid. Fig. 4. -The series - To prevent the working voltage of the fed Hartley circuit; grid from being indefinite, the grid is con- this and succeeding (Below) Fig. 1.- nected to cathode or to some other fixed diagrams show or choke of The Hartley oscil- practical working voltage through a resistance lator in its simplest arrangements. such high impedance as not to short - possible form. circuit the oscillations (Fig. 4). This circuit is known as the series -ted Hartley. coil between cathode or filament and grid According to it, either the cathode and its is in the right direction to release across the other part of the coil an amplified voltage that boosts the original oscillation. And so it grows larger and larger until the valve is unable to supply it with enough power to make it grow any more. Fig. z. -The batteries might be con- Of course, strictly it is not the valve it- nected in this self that feeds power into the oscillating manner, but are " in circuits, but batteries under the control of the air." the valve ; and the practical varieties of Hartley circuit differ chiefly in the ways arity of the Hartley; it oscillates very in which the batteries are accommodated. freely ; it is simple ; and it is easy to under- They must be arranged (1) to supply the stand and to calculate. Against these valve with the correct operating voltages, good points there is the disadvantage that and (2) not to mislead the oscillating ordinarily both terminals of the tuning currents. Perhaps the reader will forgive Fig. 6. -The popular parallel -fed Hartley condenser are " live " -a feature that may me if I illustrate the evolution of the circuit in more recognisable form.

www.americanradiohistory.com MAY 21st, 1937 Wflinhoo Wopild 487 The Hartley Circuit - the grid end, and, therefore, 7 is Fig. to Still another oscillator circuit which is . battery or the oscillating circuit must be at be preferred. For example, if it is allow- at least very similar to the Hartley is the a high battery potential with regard to able to have the equivalent of ioo,000 earth. Where this is undesirable, the ex- ohms reactance shunted across the whole pedient adopted for bringing the grid to tuning coil, and the filament is tapped the right voltage is repeated for the anode. one -tenth of the way up, the filament This gives us the parallel -fed Hartley (Fig. 5), which, however, is not usually choke can be as low as or r,000

Fig. io. -The Franklin circuit has a close family resemblance to the Hartley. one named after Franklin, and used quite a lot for short -wave work. The coil is split at or near the centre and the gap is (a) (b) bridged, so far as oscillatory currents are concerned, by a relatively large condenser (Fig. ro). At very short wavelengths, Fig. 7.- Arrangements permitting the grid end of the tuned circuit to be earthed. The filament- circuit coil in diagram (b) must be closely wound with the tuned winding. however, this circuit, for reasons not dis- closed by the diagram, is more closely drawn like that ; Fig. 6 is the same thing ohms. At 1,000 kc /s (30o metres) this allied to the Colpitts circuit. in conventional diagram form. means a choke of about i6o microhenrys. (To be concluded). The stopping condenser between anode At shorter wavelengths the inductance can and tuned circuit, if variable, makes a be correspondingly less, but this influence convenient means of controlling the feed- is usually counteracted by the necessity World Globe Clock back, both above and below the oscillat- for a higher tapping in order to obtain ing The by -pass THERE are two separate features of inter- condition. condenser is ready oscillation. At ultra -short wave- est to long- longer necessary, distance enthusiasts in this no because the oscillat- lengths there is no difficulty in providing instrument -a well- mapped globe in colour - ing currents have a different route pro- enough inductance in a very low resist- and a 24 -hour spring -driven clock giving the vided for them. Also the grid condenser ance choke, even if the tap is half way up time in any part of the world at a glance. and leak are not necessary now for the the coil ; but this circuit is inferior to The drum dial is divided into black and original purpose, but they are often re- white r2 -hour sections and a red pointer tained as an automatic source of negative indicates local time. The corresponding time grid -bias voltage resulting from rectifica- in 75 of the principal cities of the world can tion of the oscillations. be read off from a fixed scale mounted on a Finally, the same dodge can be used bezel round the base. For some places a once again, this time with the filament 1 day must sometimes be added to or sub- tracted from the local date, and this can be battery, making it practicable to earth one checked by reference to the International side of the tuning condenser. Either grid Date Line on the globe. Ì

Fig. 9. -The filament choke may be avoided by using an indirectly heated valve. earlier varieties in one respect, that the total effective stray capacity across the coil is slightly greater ; and every µµF counts below io metres. Fig. 8.- Earthing the anode end of the An alternative to the filament choke ;s tuned circuit. a bifilar winding (Fig. 7b), which compli- cates the coil but gets over the resistance end (Fig. 7) or anode end (Fig. 8) can be difficulty. earthed ; but it is important that the fila- Using a separately heated valve, the ment choke should be so low in resistance filament choke is cut out, but instead there as to cause negligible loss of voltage, and, is a stray capacity between cathode and unless the frequency of oscillation is high, heater that comes across part of the tuning The World is this restriction may make it difficult Globe Clock obtainable in to coil, and is a nuisance at the shorter wave- this country from R. A. Rothermel, Ltd., provide a high enough impedance. lengths. It is represented as a dotted con- Canterbury Road, London, N.W.6, and the Generally the filament tapping is nearer denser in Fig. 9. price is £3 r2S. 6d.

www.americanradiohistory.com Wireless World, May 2tst, 1937.

potentiometer R which is tapped back to a series of contacts C. A switch arm A is More AVC for Motorists pivoted at B under the control of two relay windings W, Wi shunted across the terminals of the dynamo D. In the VOLUME TO SUIT THE SPEED position shown the car is running at full speed, and the control resistance is completely cut out. But if one applies the THIS is not the long- sought -for scheme trifugal governor, mounted or connected brake tale current through the windings of automatic " velocity " control for in any way to the transmission gear, can falls off, the arm A is gradually which so many poor pedestrians be used to move a contact to and fro along W, Wr and over to the left to bring in more and yearn, but an adaptation of ordinary AVC a potentiometer resistance. moved resistance. This automatically as we know it in the household set, applied Alternatively, the ordinary dynamo of more speaker volume rise or fall to solve a problem peculiar to those who the car can be made to serve the same makes the loud in with the running speed of listen -in " on the road." purpose. As shown in the figure, the sympathy In a car radio set the volume of sound input circuit of the AF valve V includes a the car. required to give satisfactory hearing varies with the speed of the car. For, instance, when the car is stationary a far lower level of sound is acceptable than when one is ambling gently through a thirty -mile Recording on Paper Tape limit ; and what might pass muster then may not be loud enough when the car is going " all - out " along the Kingston NEW -TYPE DOMESTIC GRAMOPHONE FORESHADOWED by-pass. The problem is perhaps somewhat OF the many types of recording in bulk and cut it into six strips. They also subtle, but, according to an Ekco Patent apparatus now used for bottling employ their own processing tanks, and are broadcast programmes for future use, thus entirely independent of outside firms. , by linking - (No. 450606) it can be solved machine in the input one of the most interesting is the Seleno- The spools in the recording hold up a variable control resistance 90o feet of film which gives rather more than ten minutes running time, assuming that ordinary talkie speed is used. The variable - The Selenophone area method of recording, by means of which reproducing ap- scratch noises are said to be reduced to a paratus. Note the greater extent than by other methods, is cooling fins on used in the system. the two illumin- The German broadcasting authorities are ating units be- reported to be developing a very similar tween which can own. be seen the photo- system of their The most interesting cell tube. news concerning this system, however, is that it is being used as the basis of a new

circuit of the audio -frequency valve with some part of the driving mechanism that reflects the speed at which the car is moving. For instance, an ordinary cen- The Selenophone recording apparatus seen on the right is that used by the Austrian broadcasting authorities.

phone, used extensively by Ravag, the type of gramophone which its sponsors hope Austrian broadcasting organisation. This will eventually supplant the ordinary particular apparatus, which is an Austrian domestic disc machine. The home instru- invention, employs either film or paper tape ment will be very much smaller than its suitably coated with a light- sensitive emul- commercial prototype, and will use coated sion. A full description of this system was paper tape, the actual recording being done given ill The Wireless World of February 4th, by a combination of photo -chemical and 1931, and the present apparatus was illus- ordinary mechanical printing processes. trated in the issue dated March 29th, 1935. Patent difficulties, which at first threatened The paper tape or film used is about one - to be a severe stumbling block, are now said sixth of the width of ordinary cinema film to have been completely overcome. It is the Ravag people hoped that full details will be available Volume according to the speed : novel and, as a matter of fact, application of AVC to a car radio receiver. actually purchase unperforated cinema film before very long.

www.americanradiohistory.com Wireless World, May erst, 1937. 489.

An impression of the area covered by the B.B.C.'s new Empire Station at Daventry can be gathered from this view taken from over a mile distant.

Re- diffusion of Empire Broadcasts LOCAL SERVICES FOR ISOLATED COMMUNITIES THE rapid development of short- By EDWARD COVERLY tion of the British long- and medium -wave wave broadcasting, together with stations is often out of the question. Geo- the production of short -wave graphical and atmospheric conditions in- receivers as commercial articles vital importance lies in its geographical evitably make the local listener rely on the at a popular price, has, in effect, placed position on the sea -route to India and the stations of Southern Europe and, since world -wide -- reception of programmes East and its consequent use as a base by Italian is spoken by a considerable propor- within reach of anyone. European coun- all our fighting services. Although the tion of the native population, it is but tries with colonies or -other vital interests majority of the natives are of Phoenician natural that Rome and Naples should be in various parts of the globe are thus pro- origin, a section of the upper classes are of the stations to which the Maltese listener vided with an easy means of maintaining mixed Spanish, French and Italian normally turns. touch with their own nationals abroad by descent. At one time and another these The advent of short waves changed the broadcasting news of the home country people have shown an interest in Italian problem, in that satisfactory reception of ideas and culture. Disputes and other ' ` good will " programmes. Such over the use English programmes became possible. At is broadcasting's legitimate sphere ; it has of the Italian language in the Law Courts about the time that the short -wave receiver been recognised in this country and the and in schools has resulted in the with- became a popular commercial article, His B.B.C. has performed a valuable public drawal, by the British Government, of late Majesty King George V first broadcast service by developing its Empire station. to the people of the Empire, on Christmas Nevertheless, the possession of a suitable Day, 1933. The Government realised the receiver is not within the means of more LL-EQUIPPED central importance of enabling the population to than a small percentage of the inhabitants hear receiving station should always the speech. of our dominions and colonies, nor are In the absence of any local broadcasting receiving conditions on the short waves by provide better reception of long - station they turned to the Navy, and that any means always ideal when the question distance broadcasting than the Service hurriedly improvised a transmitter of entertainment value as opposed to mere apparatus available to the average at Rinella suitable for telephony and novelty has to be faced. Hence the estab- coupled it to a short -wave receiver tuned lishment of local broadcasting services in individual listener : schemes for to the Empire programme. Men from the all parts of the Empire is a natural devel- " community " reception and re- ships begged and borrowed receivers and opment. In our larger dominions and diffusion are especially likely to installed them on Christmas Day in the colonies and in India such broadcasting public squares of every village. prove attractive to isolated services are now fully developed ; they are Such a makeshift arrangement might self-supporting, able to provide much of communities. solve an important problem on one occa- their own programme material, but always sion, but it was clear that a more perma- working in co- operation with the B.B.C. nent service was necessary, and to this the and exchanging programmes as requisite. more than one form of constitution. Government turned their attention. The Similar developments in our smaller Malta, unlike the majority of our island was too small to provide more than colonies, such as Gibraltar and Hong - Empire, is within easy range of the ordi- a very occasional programme of its own. Kong, for example, or our many small nary long- and medium -wave broadcasting Furthermore, the revenue which could be islands are, however, a different problem, stations in Europe. Reception conditions, expected from licences was so small that if only because the financial aspect is such on the other hand, are not always good, the utmost economy would have to be a limiting factor. for atmospherics are often troublesome, exercised. The small area of the island As a typical example of a small colony while the high -powered transmitters be- indicated that only a -low- powered trans- we may cite Malta. Here is a small island longing to the Navy and Air Force, not to mitter was required. And lastly, the ques- (or rather group of islands, but only one mention the many ships of the Medi- tion of interference with and from the Ser- is of importance) only seventeen miles terranean Fleet in Valetta harbour, often vice and commercial stations on the islani long and eight miles broad, yet congested cause interference which requires elabor- had to be considered. When all these fac- with a population of about 258,000. Its ate equipment to eliminate. Hence recep- tors were taken into account it was decided

www.americanradiohistory.com 190 Wtaggo MAY 21st, .1937 WoIrIli Re- diffusion of Empire Broadcasts tal stations, programmes by local artistes Except for the fact that atmospherics that rediffusion was the most satisfactory from its own studio, speeches by the have been rather a nuisance at times, the sunspot activity which has been proving so solution. All parts of the Island were Governor or other prominent citizens and devastating On the short waves does not - running commentaries of important within easy reach of an economical land any appear to have had any very adverse effect line system. An elaborate receiving sta- event which may take place in Malta. on medium -wave and long -wave reception. tion, complete with all apparatus neces- It is worth noting, though, that on the first sary to eliminate interference, could be day of this month atmospherics were so con- erected. The B.B.C. Empire programme tinuous and so violent, in my locality at could be satisfactorily relayed to the DISTANT any rate, that they interfered seriously with people while, with the addition of a small reception of the local stations even on a studio at local programmes could RECEPTION portable set using a frame aerial. Valetta, NOTES It's a pity, I think, that so many stations always be transmitted. - seem to find it necessary to change their pARTLthrough my own observations Here, then, surely did re- diffusing names. Certainly it doesn't make things assume its legitimate role as a chal- and enquiries and partly through in- -not formationY kindly supplied by a London any easier either for long- distance folk or lenger to broadcasting but as a useful reader I have been able to clear up once for those who have to make station -name servant. It will only be fitting to conclude and for all the, vexed question of " Radio tuning dials. France's present long -wave this article with a brief account of how the Verdad." " Radio Verdad " does not now station began its career as Radiola ; it is now Government's plan has worked in practice. claim to be a broadcasting station. It is Radio Paris, and soon it will become Radio The decision to adopt rediffusion was the title given to news bulletins in Catalan National. The Deutschlandsender was at and Spanish, broadcast twice each night first Königswusterhausen (light -heartedly, if taken early in 1935, and an English com- incorrectly, translated as King's sausage pany was licensed to install the system and from certain Italian stations. It is sent out from Florence, Rome, Milan houses by some old hands !) ; the Dutch to run it. Unfortunately, before it had at 7.45 p.m. long -wave station was known at first simply r Genoa, at p.m. from commenced operations a new factor arose. No. and and it as PCGG, but it soon turned into Hilver- Florence and Milan. sum, not long. Hilversum The European situation in August, due to When I first heard the " Radio Verdad " though for Italy's intention to invade Abyssinia, became the name of their medium -wave transmissions I was pretty sure that that was station and the long -wave transmitter was resulted in tension between Britain and was happening, though an address what named Huizen. Then a time high - known, intense anti - for Italy, and, as is well (Plaza Bandos Puig, Salamanca) was powered transmissions on the long waves propaganda was broadcast. The several times given out for the benefit of British were labelled Kootwijk ; and now the name position of Malta was vital, and the need intending correspondents. Whilst I was is back again to Hilversum. for countering such I don't so much mind this chopping and propaganda w a s changing so long as the name of the station imperative. indicates the place where the transmitter is Since the re -dif- situated -though even so you may be service was rather sunk unless you are constantly buy- fusion ing up -to -date atlases. My own, for not the ready, example, knows Angora, but not Ankara ; Government once Lemberg, but not Lwow. more called on the The most annoying names are those like Navy. The re- Deutschlandsender or Radio Roumania, or diffusion company lust Radio National, which merely show the willingly co - oper- country of origin. A pity, I think, call - ated, lending the signs of letters and figures have almost dropped out for broadcasting stations on this necessary receiver side of the Atlantic. In the United States which was coupled they continue in regular use, and as they to a Naval trans- are always accompanied by both the town mitter. The Empire and the state you can find any station's location in a matter of moments and can then turn up its particulars in an alpha- betical table just as quickly if you want to do so. D. EXER. Four short -wave receivers at Tatsfield, where the B.B.C. pick up and relay for rediffusion pro- News from the Clubs grammes from abroad. The Donis Hill Radio Communication Society Headquarters: The Rraincroft. Srlmul,s, Warren Road, London. S.W .2. still making enquiries by post I rigged up Hon. Sec.: R. llodgkyns, 102, Chri t Road, Crieklewood, a frame aerial and found that the bearing N.W.2. News bulletin was thus broadcast nightly of the transmission on 368.6 metres was At the opening meeting of the above society 5 -regenerative - -east. This is Milan's a lecture on -metre super trans in the Island and immediately afterwards almost exactly south receivers was given by C. J. Search followed by a translation, in Maltese, was relayed from bearing from me. Next I tried Radio a demonstration. On May 25th at 8.30 p.m. a room in the Governor's Palace. The re- Nacional, the high- powered Franco station a talk on valves will be given by Mr. S. C. which does broadcast from. Salamanca on All interested in wireless matters diffusion company this tern - Ash. those operated 274 metres and found that its bearing was will be welcomed at the meetings of the society porary studio and provided loud -speakers a little west of south. and are invited to communicate with the hon. in the principal public squares. One or two people have asked me lately secretary for full particulars concerning it. On November 11th, 1935, the company how it is that there are two EAJBs in the was able to open its own service, and field at the moment, $ilbao and San Southall Radio Society Sebastian. The call -sign belongs, of course, Headquarters: The Three Titus Hotel, The Green, within a year had obtained more than sou tha11. 2,000 subscribers. Now it is rapidly properly to San Sebastian, but when Meetings: Tuesdays at 8.15 p.m. Southall. spreading its tentacles to all parts of the Franco's troops were advancing on this Hon. Sec.: H. F. Reeve, 26, Green Drive. town the radio transmitter was moved to A DF contest is being held on June zoth. A large receiving station is being provided for annual com- Island from its Bilbao. Thus the original EAJ8 is the one -silver trophy erected a few miles outside Valetta. It petition, and in addition to this the winning which is now at work at Bilbao. But the team of three will he presented with medals. provides its subscribers with two pro- Nationalists rigged up a new plant at San The transmitter, which will be handled by Mr. grammes for, in addition to the Empire Sebastian and, having done so, adopted the Douglas Walters (G5CV), will operate on a fre- transmissions, it relays selected continen- old call -sign for it. quency in the 40-metre band.,

www.americanradiohistory.com Wireless World, May 21s1, 1937 49r Current Topics EVENTS OF Another Newcomer was a great deal of morse jam- THE Finnish Government has ming from the Rugby -Karachi THE WEEK set aside a quarter of a mil- service, but it would seem that lion marks for the erection of a the French engineers were ask- IN BRIEF National S \V broadcasting sta- ing for trouble by attempting to tion. It will be built by the use long instead of short waves. REVIEW P.O. near Lahti. Radio Morue More High Power Coming A- WIRELESS transmitter has Super PA THE Icelandic Broadcasting been installed on the " St. Corporation is Yves," which is a special mis- STOCKHOLM engineer stated to A have awarded a 129,000 contract sionary vessel, known as the named Ekman is reported to the Marconi Co. for re- church boat, attached to the to have devised a new type the of construction of Newfoundland cod -fishing fleet. CORONATION HONOURS LIST loud speaker for special PA the Reykjavik station. Its power is he in- The station is known as Radio included a Knighthood for Louis work. It is said to have a range to creased to too k\V. is hoped Morue (cod). Saul Sterling, managing director of between six lt of and seven miles. to have the reconstructed trans- Electrical and Musical Indus- Car Radio Licences tries, and a director of Marconi - Broadcasting and Art mitter in operation early next E.M.I. Television. year. REPLYING to a question in T HE first International Con- the House recently the gress of will PA in Schools Radio Art be Radio in the Arctic Assistant - Postmaster - General held in Paris from July 8th to once more found it necessary NEW and elaborate receiv- A SPECIAL radio centre has to ing installation has been loth. The agenda is to be been installed repeat that a separate licence divided into seven sections deal- in ,Moscow to acquired by the Dala Municipal communicate with the stations was necessary for a wireless set : School, Goteborg, All class- ing with the following subjects in the fixed in a car. A portable set, The theatre, music, Arctic regions. In spite rooms have been equipped with journalism, of the great distance reception however, used in a vehicle was educational transmissions, tech- covered by the owner's loud speakers which are con- conditions are said to be very ordinary nected to a switchboard in the nical arrangements for transmis- good, there being wireless licence. sion and reception, television remarkable headmaster's room, so that he freedom from severe atmo- and general questions. Radio can supply them with the spherics. The Russian Govern- Telegraphists' special wireless transmissions for Australian SB ment is to erect three ne.v Union schools picked up by the re- stations in the Arctic THE chairman of the Corn- Circle. T HE headquarters of the Wire- ceiver or can address the whole less Operators' International school itself via a -A- monwealth Broadcasting Cor- Tea nical Blunder microphone. poration announces that an all - Union has been moved from Australian network of broad- T is revealed that considerable London to Copenhagen. There Extra Television Hour casting stations has just been annovauce was caused in are about 8,000 members in the predicted in The Wireless formed, modelled on the Ameri- Paris by the wireless interfer- Union, these coming from 18 As World April 23rd, different of the can principle. There are 15 sta- ence at the boat race recently countries, and it is B.B.C. announces an hoped that extra tions in the Australian system, held on the Seine between that their numbers will period of television, lasting ap- shortly be and it is estimated that they eights representing Pa ris and reinforced by 1,50o proximately an hour, will serve 8o per cent. of the inhabi- Oxford and Cambridge. Fol- Japanese operators. The Union shortly be given every weekday lowing the example of the an- is to be represented at the In- tants of the five most populous ternational morning between 12.30 and 1.30 of the Australian states. nual Oxford and Cambridge Telecommunications p.m. A special film, surveying boat race a relay was at- Conference at Cairo next year. the activities of television since tempted from a launch. There Eiffel Tower Television Amateur -Night Up to date the opening of the service about THE television transmitter six months ago, has been pro- ordered by the French THE system of granting audi- duced by the B.B.C. and will P.M.G. will have a power of tions to amateur performers be shown every day in the extra 3o kW. The aerial will he in order to discover possible hour. The B.B.C. wishes to mounted on the flagpole at the hidden talent has always been a emphasise that this transmis- top of the tower and will thus great feature of the Paris broad- sion is not for the entertainment be well over a thousand feet casting station. It is now being of home viewers. above ground level. The trans- adopted by the programme mitter is being supplied by the authorities at Radio Bordeaux Television Holiday French concessionaires of the and Radio Lyons, who are bent IN order that an overhaul and International Telegraph and on tapping what they believe to certain internal adjustments be a great wealth of latent Telephone Corporation of New may be carried out at Alexandra ; York. artistic ability in the southern Palace, arrangements have been half of France. Wavelength Changes macle, with the concurrence of Avalanche Warnings the Television Advisory Corn- THE 26o kc. Oslo station has mittee and the approval of the for some time past been BY an agreement between the postmaster-General, for tele -. troubled by experimental Swiss Ski Federation and vision transmissions to be sus- transmissions which the Finnish the station authorities, the Bero- pended for three weeks, begin- station at Lahti has been carry- münster transmitter will broad- ning on Monday, July 26. ing out on 262 kc /s. Lahti has cast bulletins concerning the now given up the idea of put- state of the snow at 7 p.m. on N.R.E.A. Branch Meeting ting out programmes on this fre- Fridays and 12.25 p.m. on A LECTURE to the Romford quency, and hopes to inter- AUSTRALIAN PIONEER. Saturdays. The report will deal branch of the National . change wavelengths with Mos- Ernest Thomas Fisk, A.M.I.E. specifically with all points Radio Engineers' Association cow. (Ault.) Managing Director of threatened by avalanches. The will be given by Mr. E. W. The SW station at Motala Amalgamated Wireless (A'sia), service is only experimental at Harris, of the Radio Develop- , now be who has played a prominent may heard on both the part in developing the wireless present, but it will be comment Company, at 8.3o p.m. on 25 and 50 -metre wavebands. services of the Commonwealth, pletely organised during the Wednesday, May 26th. The These transmissions are at also received the honour of a summer so that it will be in meeting will be held at the Vic- present. experimental. Knighthood. working order by next winter. toria Hotel, Romford.

www.americanradiohistory.com t92 Wireless World, May 21st, 1937 rye' Baby "Q portable

tien works remarkably well and ensures a FEATURES. Type. - Portable good minimum when using the set near a battery receiver. Circuit. Pentode powerful transmitter. There is a slight RF amplifier- triode grid detector - time lag due to the heat content of the triode first AF amplifier - pentode filament, but the delay is not sufficient to output valve. Controls.- (1) cause serious inconvenience. Mechanically Tuning. (2) Combined volume and the control is so arranged that the RF reaction. (3) Waverange.and on -off valve filament is at full brilliance before switch. Price. -Sgns. Makers. - reaction comes into operation. A-suitable Pye Radio Ltd., Radio Works, grid bias, giving the best compromise be- Cambridge. tween detector efficiency and smooth reaction, is obtained by dual grid leaks forming a potentiometer which gives a voltage somewhere between + and - LT. The detector is followed by a first stage audio frequency triode with resistance A coupling. The output from this valve is COMPACT SELF.CONTAINED RECEIVER then passed to the pentode output valve WITH AN EFFICIENT through a parallel -fed transformer. There FOUR =VALVE CIRCUIT can be little doubt that the generous audio frequency amplification provided is re- LTHOUGH of considerably smaller matie bias has been included in the cir- sponsible for a good deal of the liveliness size than the battery portable re- cuit specification. of the performance. ceivers which were standard a few The first valve in the circuit is a vari- During daylight we were successful in years ago, there is nothing else in able-mu RF pentode with tuned anode receiving programmes of good entertain- this set which justifies a comparison with coupling to the triode detector valve. Re- ment value from ten of the fourteen sta- the so- called midget receivers in which action is applied through the usual tions marked on the medium -wave scale, minimum dimensions have been made the capacity controlled circuit and the con- and after dark nearly forty stations were first consideration. denser is ganged to a filament resistance logged, of which twenty -five were un- A 2o- ampere -hour accumulator and a in the negative lead to the RF amplifier. questionably of usable strength with a 90-volt HT battery of standard capacity This revival of a practice which was com- good margin for any possible fading in are provided, and the reduction in over- mon in the earlier days of wireless recep- the case of stations near the bottom end all dimensions is due entirely to the skill of the designers in compressing all the necessary component parts into a narrow chassis on the top of the cabinet. When 1st A F AMPLIFIER VALVE DETECTOR VALVE it is realised that space has to be found for K 30 K K 30 K a permanent magnet moving-coil loud speaker and receiving valves of standard size, there can be no hesitation in award- ing the designers full AERIAL marks for their in- AND genuity. EARTH The frame aerial winding is actually SOCKETS built into the thickness of the cabinet itself, and some saving in space has been effected OUTPUT by tilting the chassis slightly upwards to VALVE RF AMPLIFIER give a K 70 B sloping dial and tuning panel. The VALVE latter takes the form of a moulding with K 50 M which is incorporated the carrying handle. The dial is transparent and the pointer is mounted underneath. Felt washers are fitted under the tuning knobs, so that the instrument is completely dust- proof. The front of the loud speaker is covered by TELEPHONE fabric which is in turn protected from SOCKETS damage by a strong wire mesh grille. Care has been taken to ensure that both HT and LT batteries are firmly located and to this end a sponge rubber disc is 'Wireless World fitted to the back of the loud speaker COPYRIGHT magnet which presses the battery against angle brackets. One of these can be swivelled to facilitate battery replacement. A compact receiver chassis leaves ample space for batteries of standard capacity. The frame No grid bias battery is'required as auto- aerial windings are incorporated in the sides of the cabinet.

www.americanradiohistory.com WApA®og MAY 21st, 1937 Wald 493 Pye Baby " Q " Portable - tion was 0.54 amp., which at a conversa- of the dial. The small frame aerial was tive estimate should give 3o hours' service Cathode - Ray Tuning perhaps not quite so efficient on long on a single charge from the jelly electro- waves, but Droitwich was received with- lyte LT accumulator. The weight of the Indicator - out calling upon reaction and, if anything, set is 172 lb., and the carrying handle is so required a slight reduction by means of designed that if the set is picked up in The Mazda ACME the volume control. Luxembourg, Radio - the natural way the loud speaker grille Paris and Hilversum provided excellent will be pointing in towards the person, and volume with a degree of reaction which the centre of gravity will cause the set to called for reasonable care but which could tilt slightly outwards to avoid the discom- not be described as critical. fort of having deliberately to hold the set The efficient little moving -coil loud out sideways. In the title picture the set speaker apparently makes excellent use of is being held the wrong way to show the the ioo milliwatts output for which the out- control panel and loud speaker fret. If put valve is rated. Certainly the volume held normally some difficulty would be sounded considerably more than we are experienced in recognising it as a wireless accustomed to expect for this figure. Also, receiver. the reproduction was exceptionally free There is provision for an external aerial from harmonic distortion at moderate and earth, though it is extremely unlikely levels with the volume control turned that the need for this will be felt. Also, ONE of the most popular types of tuning down. for use in exceptionally noisy surroundings indicator is that operating on the cathode-ray principle, and the Mazda ACME is the latest ; ddition to this branch of electronics. Similar in appearance to an ordinary valve, it actually contains the elements of a triode amplifier and a minia- ture cathode -ray tube. A small fluorescent screen is mounted inside the valve and is visible through the upper end of the bulb. When the grid and cathode of the triode are at the saine potential, some 270 degrees of the circular screen fluoresces green. As the triode grid is made negative, the green area expands, so that the initially unlighted segment of go degrees contracts. When the grid is made highly negative, almost the whole of the screen is illuminated. The recommended connections are shown in Fig. s and will be seen to be extremely simple. The input terminals are connected across the diode detector load resistance, the Automatic bias is provided for the output stage and the filament rheostat volume control cathode of the ACME being joined to the detector cathode. With these connections ti is undoubtedly effective in practice. only one-half of the detector voltage is applied to the indicator, and this is about Having regard to the excellent perform- or for the convenience of people hard of right for the average receiver. The indi- ance from the point of view of volume and hearing, telephone sockets have been in- cator will then commence to function for quality it was surprising to find only cluded. These are so arranged that the 7.2 mA. was being drawn from the 'phones may be used with or without the go -volt HT battery. The LT consump- accompaniment of the loud speaker. LAN ANODE O OTGRID E RADIO RESEARCH DURING 1936 CATH °TAR \ODE° HEATER / The National Physical Laboratory Report their effect on wave propagation have a for the Year 1936.-Pp. 144. Published direct connection with direction finding, and by H.M. Stationery Office. Price 2s. 6d., the work of the department, which has postage extra. hitherto been concerned principally with ver- j'TUCH interesting information on recent tical incidence, has now been extended to llll developments in wireless and allied oblique incidence records on a 350 -mile base subjects is to be found in this report, cover- line. The analysis of records taken during ing the whole of the activities of the N.P.L. the Polar Year (1932 -33) has been completed, The sections devoted to the work of the and some interesting facts are given regard- Radio, Electricity, and Physics Departments ing the complexity of echoes obtained at will no doubt be studied first, but the rest of Trömso relative to simultaneous records the publication makes stimulating reading made at Slough. Other activities of the an in Radio Department, of which ample details for anyone with interest technology. Base connections and circuit for using Direction finding, with special reference to are given, include investigations into elec- the ACME indicator. the requirements of aircraft, has occupied a tronic oscillations in valves and oscillators of good deal of the attention of the Radio De- stable frequency. detector inputs exceeding about 0.5 volt, partment, and the results of experiments In the Electricity Department apparatus and will continue to operate until the input using the short-wave Adcock direction finder has been developed with a frequency range exceeds 4o volts. For the clearest results, over distances up to 9,000 miles with ships of 10 to 1o,000 lcc / s for the testing of dielec- however, the detector input should not be and 300 miles with aircraft are given. Work trics employed in television apparatus, and less than 2 volts. On the possibilities of ultra- short-wave (5- in the Physics Department investigations The indicator is indirectly heated, and it to 10- metre) direction finding, and the effects into the measurement of noise have resulted consumes 0.5 ampere at 4.o volts for the of obstacles in the path of transmission, has in an objective meter giving correct indica- heater. The maximum anode potential is already begun, and the influence of cables tions for intermittent and impulsive sounds 250 volts, and the triode anode current does and fences on site errors has been investi- and suitable for the measurement of sound not exceed 0.24 niA., the target current gated. The properties of the ionosphere and levels from motor car exhausts. being nearly constant at 1.5 mA.

www.americanradiohistory.com 494 Wireless Wòria, M 21st, 1937 UNB IASED 1 is not often that I am co-corn- By FREE GRiD "- pelled to call on you for assistance, but I always feel secure in Badge of re- tle' knowledge. that if ever I of his body round to his friends as a warn- cognisation should, through no fault of my ing, or, alternatively, he means that he own, be in desperate straits, you will commit hari -kiri and leave instruc- would be willing to do all in your tions for bits of him to be distributed to which I reproduce herewith, to be worn power to assist me. I am now his acquaintances as souvenirs. Which- in the buttonhole. I am not at all sure compelled to seek your help, but not so ever is the true explanation, I don't relish whether I ought to accept this invitation much on my own behalf as of one of your receiving a parcel containing an odd ear and I am seeking your advice in this mat- fellow readers living in far-off China who or finger, and so perhaps some of you will ter, since the avowed objects of the associa- has made a desperate appeal to me for do your best to avert the tragedy by tion are of distinctly anti -social nature assistance. supplying the information and help which which is, I suppose, only what you would He has sent me a letter written in he needs. expect from a secret society. quaint, but perfectly understandable The information which my correspon- The society's raison d'être is to wage war is English in which he requests " certain dent in search of is whether or not the on users of too-loud loud speakers and honourable information." He has, it characteristics of certain locally made those who take the loud speaker into the appears, just completed the building of valves which he proposes to substitute for garden during the summer, by means of the famous "Every- the British ones are suitable for the re- violet -ray machines and unsilenced elec- man Four " receiver. He sends me a page from the trical apparatus Although radio generally. ceiver, which some local journal containing advertise- noisy loud speaker owners are certainly ments which, he states, give full of you old lags will technical one of the pests of society and a Kt characteristics in form. remember was de- tabular Unfor- menace to the popularity of wireless, I do tunately for him, my knowledge of scribed in this not think I ought to go so far as to journal just over encourage the generation of deliberate ten years ago. I interference, even though the members of dare say that you the proposed association have pledged are quite as familiar themselves to make a nuisance of them- as I am with the selves only in those areas where a nuisance old motto " Slow already exists. but Sure," but, even so, ten years may seem to you Women and Television along time to take in building a THE report which I noticed recently in set. The Wireless World to the effect that The delay has, however, been over 90 per cent. of the many thousands due solely to the length of time of people attending certain television the manufacturers have taken to demonstrations in London are men is a deliver the parts, a phenomenon truly astounding commentary on the which appears to be even more marked out Oriental languages is limited to words de- extraordinary lack of interest which the Far East than it is over here. These scribing the necessities of life, such as beer women seem to have in scientific matters. few years' delay has net hitherto ruffled and tobacco. It is, therefore, in the des- Actually you would, of course, expect the my correspondent's Oriental calm and perate hope that some of you Oriental figures to be reversed and the majority patience, but even this well -known scholars may be able to read the adver- of the people attending these demonstra- characteristic of our Eastern brethren has tisement that I reproduce it herewith. fions to be women, for they have ample its limits, and the non- arrival of the valves It behoves you to act quickly, however, time and leisure to do so. It says much has apparently reached it. since if the worst comes to the worst I for the energy and intellectual superiority In anticipation of having his set corn- shall certainly pass on to you any anato- of men that they have managed to find pleted by June 2nd he sent out some mical specimens which may be sent to time from the hard daily grind of their months ago an invitation to certain high me. lives in the City and elsewhere to slip police officials of his native city to come away -presumably in their lunch hour - and listen -in to the world- famous Derby The Ancient Order of to see the demonstrations, whereas women broadcast at his house. If he disappoints have not had the energy or the gumption his guests he will have committed a social Ether Hogs to rouse themselves from their lotus -eating faux as which in the Orient is looked AT my age secret societies have no lives in the home even for one hour in upon as one of the seven deadly sins, longer the same appeal as they had in order to improve their minds. namely, breach of hospitality. But quite the days of my youth, and, as a matter of I suppose that, as usual, they are wait- apart from this, it appears that the chief fact, I have taken little or no interest in ing for it to be brought to them served up magistrate of the city, who is among the them since the early years of the century on a plate, as it eventually will be when invited guests, suffers severely from liver when I was thrown out of the Camorra their husbands and other male bread- trouble and my correspondent informs for gross clumsiness and lack of profes- winners have saved up enough of their me that if he fails to deliver the goods, sional finesse by using TNT instead of the hard -earned cash to buy a television re- honourable body will be dismembered time -honoured arsenic for removing an ceiver for themselves. This revelation and components distributed to friends." unwanted citizen. ought at any rate to be a valuable guide Now I am not quite sure what the latter I have, however, been asked to accept to the budding C. B. Cochrans at the remark means, but those of you who have the presidency of a proposed society to be Alexandra Palace and enable them to give lived out East twill probably know. Either known as the Ancient Order of Ether us more virile programmes and cease to he means that the Chief Magistrate will Hogs, members of which will be able to put out effeminate milk- and -water items execute him and afterwards send pieces recognise each other by means of a badge for an audience which does ,not exist.

www.americanradiohistory.com Wireless World, May erst, 1937. 495- New Apparatus Recent Products of the Manufacturers Reviewed NEW BULGIN SWITCHES This particular type of base has eight WITCHES that operate only when the pins and a self -locating centre plug. The lever is pressed over by the finger are Benjamin valveholder has semi -floating often extremely useful in the construction sockets, while the soldering tags are of certain types of test apparatus. This arranged in a concentric circle outside the method of changing the internal connec- sockets. Socket and soldering tag is tions is most valuable when the changes stamped out of one piece of metal. These so effected render the meter ultra sensitive, new -style valveholders cost 9d. each. as by automatically returning to the original position it can usually be arranged for the CROMPTON MICROPHONE Wharfedale three -ratio replace- meter, or test set, to be less liable to damage THIS is a transverse current carbon micro- ment output transformer. in the event of an overload. phone of the type now largely used in Switches of this pattern are now obtain. PA work. It is a robust instrument and ing -90 :1 ratio DC able from A. F. Bulgin -without flowing has and Co., Ltd., exhibits good workmanship, while it is also an inductance of 65 henrys, which is reduced Abbey Road, Barking, Essex. They attractive in appearance. A turned and to 15 henrys with 16 mA of DC, and to 9 resemble in appearance the ordinary toggle polished ebonite case is used with a chro- henrys when 4o mA of DC is passing mium- plated front cover and four large through it. screw eyes are provided for suspending it in The resistance of this winding is 600 ohms. a stand. When using the 6o : 1 ratio the resistance No resonances of any consequence could of the primary is 38o ohms and its induc- be traced by aural tests when the micro- tance with no DC is 33 henrys. This value phone is correctly matched to the input of becomes eight henrys with 20 mA of DC the amplifier and provided a good trans- and five henrys with 40 mA of DC. former is used. This transformer can also be supplied The reproduction of speech is very good with a centre -tapped primary for push -pull indeed, and different individuals can easily use at no extra charge. be recognised by their particular character- The transformer is fitted with a " Stal- istics of speech and inflexions, etc. boy " core, and it is intended primarily as This microphone has a very low back- a replacement component. Bulgin Type S172 toggle switch. ground noise, and it operates satisfactorily with between six and nine volts. Its resist- BELLING -LEE FLAT -PIN PLUGS pattern, but the internal mechanism is so ance is approximately 500 ohms. arranged that the contacts are closed or IT should have been stated in our recent opened, according to the type of switch, review of the new Belling -Lee flat -pin only while the " dolly " lever is pressed over plugs and sockets that they are designed by the finger, and on release they imme- to conform to the British Standards Speci- diately return to the original position. fication 666, which applies to plugs and The principal features of these new models sockets for use in radio speech circuits when is that though in effect they are push- button the power does not exceed 5o watts. switches the design is such that they will The purpose of this specification is to carry up to 3 amps. at 25o volts, and the render it impossible to confuse radio exten- make and break is of the quick, or snap - sion and mains power points and also to action, kind. provide a standardised form of connector In the Type Su7r the contacts are nor - so far as its electrical properties and essen- mally open and close with pressure on the tial physical dimensions are concerned. lever, while in the Type S172 the contacts are closed in the normal position. The price of either type is is. 9d. The Radio Industry Crompton transverse current EUGEN FORBAT, agent for -Ganz carbon microphone Ostar BENJAMIN OCTAL VALVEHOLDERS universal high- voltage valves, has transferred his MOUNTING offices to Goschen Buildings, 12 -13, ("HASSIS- valveholders for The makers are G. Crompton, Woodfield Henrietta Street, London, \W.C.z. The associ- the new International valves now avail- House, Woodfield ated company, Universal High Voltage Radio, are fitted Terrace, Bury, Lanes, and able and which with what is the price is £1 19s. 6d. Ltd., has moved to the same address. described as an octal base, can be obtained C -1 v A new catalogue of Trix Sound Equipment WHARFEDALE OUTPUT has just been issued. Address, Trix Electrical TRANSFORMER Co., Ltd., 8 -9, Clerkenwell Green, London, AN output transformer similar in size and E.C.1. appearance to that fitted to their loud speakers can now be obtained from Wharfe- New Times Sales Co., 56, Ludgate Hill, Loailon, E.C.4, has issued a new list of short- dale Wireless Works, 62, Leeds Road, wave sets and components. Bradford, at the price of 6s. It measures approximately Sin. X 2M. x 2in. overall and provides the choice of three ratios, viz., The Cressall Manufacturing Co., Ltd., Eclipse Works, 31 -3z, -Tower Street, Birmingham, 19, 3o, 6o and 90 to 1 respectively. makers Benjamin chassis- octal of resistances, etc., announce a ten per mounting The various ratios are obtained by tap- cent. increase on all existing prices. valveholder. ping the primary winding and employing one or other of the two sections, or the Mr. M. Featherstone, 51, Fourth Street, Ash - from The Benjamin Electric, Ltd., Brant - whole, as the case may be. bury, New wood Works, South Wales, Australia, would like Tariff Road, Tottenham, Some measurements made with this trans- to receive catalogues, etc., from firms exporting London, N.17, former show that the whole primary wind- to Australia.

www.americanradiohistory.com 21st, 1937 .1-96 Wireless World, May Listeners' a Outstanding Broadcasts at Hoff

The races themselves are some- is first -rate. The bill also in- - what grim affairs, the boats eludes the third broadcast of actually bumping each other, Gus Chevalier and his partner. often much too severely. John Snagge will, from the University Boat Club, give a " DOGS OF DEVON " AN abridged general description of the first version of Dogs of division races on Monday at " Devon," or " Foiled 6.1o, which will be followed Again," specially prepared and adapted by Cyril Wood, by a descriptive picture of the will broadcast Isis dressed for the gala. It be on Saturday at 9 (Reg.) . This comic opera is hoped to bring to the microphone celebrated old Oxonians is ideal light entertainment, and essentially English in character. It is, in fact, as attractive to -day as when it WITH so many repre- MARATHON. Members of the English and Australian teams for was first in 1913. on the track at Wandre, near staged sentatives of the the Six Days Cycle Race practising Nearly six years ago " Dogs British Empire in Liége, Belgium. The race, which is being held at the Empire Stadium, Wembley, will provide a short commentary for Regional of Devon " was broadcast in the Home Country listeners on Saturday at 50.5o when the last ten minutes of the its entirety from Cardiff. The at this time is added interest race will be described. cream of the opera, including given to the celebrations of Empire all the favourite numbers, will Day. The broadcast be broadcast in this abridged programmes include three first broadcast last month who will be at the races, many version. special features. The first is before the Children's of them whilst visiting this 11.55 them at 0 0 at a.m. when Nàtional Coronation concert in the Cen- country for the Coronation. listeners will hear the Empire tral Hall, Westminster. The - ROYAL PERFORMANCES Day Service from St. Paul's Empire singers are members AN interesting programme Cathedral. Their Majesties, VARIETY of songs and excerpts from of, and represent, various JOHN SHARMAN is bringing King George VI and Queen Empire choral societies. They plays which have been acted Elizabeth will be present as back to his " Music Hall " on before British royalty has been took part in the Coronation Saturday Alexander and Mose, will also representatives of the Service in Westminster Abbey. prepared for National listeners Dominions. The address will the well -known black -faced on Monday at 9.35 under the Margaret Godley (soprano) pair, whose title hides Billy be given by the Archbishop of will be the soloist. heading " Incidental to a York and the lessons read by Bennett and James Carew. Play." the Canadian Premier; Mr. -> 4. The bill also includes For- Mackenzie -King. TOSCANINI sythe, Seaman and Farrell, a In the evening the annual THIs week brings the first comedy trio, and a new Empire Day programme will of the series of six Toscanini partnership billed as Major be provided by All India concerts from the Queen's and Minor. Another act is Radio. It will give a picture Hall. These constitute the that of the Six Viennese Sing- of the characteristics of the London Music Festival, and ing Sisters who have broadcast eleven Provinces, and there- all six concerts will be con- once before. They are a fore the great differences which ducted by the Maestro himself. vivacious troupe who sing exist among the peoples of Within a few days of the songs of their native land in India. Ceylon will also make issuing of the tickets for these close harmony. Others in the a contribution. Although this concerts, all the seats were cast for Saturday's Music Hall will probably not be so am- sold. For Wednesday's con- to be broadcast at 8 (Nat.) are bitious a programme as those cert which will be broadcast Billy Russell and Stainless provided by Australia, Canada at 8.15 and 9.25 (Nat.) , the Stephen. and S. Africa in the past programme includes Beet- Listeners can rely upon a three years, it will serve as a hoven's overture, Coriolan, good programme of mid -week reminder of the importance of and Brahms' Symphony No. 1 variety on Wednesday at 9 the Indian Empire. This in C Minor. (Reg.) . The cast includes programme will be radiated Aileen Stanley, who scored a at 7.30 (Nat.). OXFORD EIGHTS WEEK great success in the early days Later in the evening, at 9 ADDED interest to the of the Kit Kat Club, and is (Reg.), the special Empire famous Eights Week of Oxford visiting this country again Day Concert will be broad- University is given this year from America. She has an cast. Sir Walford Davies and by the Varsity's win over Cam- excellent microphone voice Clarence Raybould will be bridge in the annual Boat and perfect technique, and her the conductors, and Empire Race. For those listeners un- singing of American numbers singers will comprise the choir. acquainted with Eights Week, The music will include Sir Wal- it may be explained that it is ford's own fantasy, " Big Ben an aquatic garden party to rela- GRACIE FIELDS, who was Looks On," which, dedicated which undergraduates' heard by listeners on Thursday to the two Princesses, Eliza- tives flock to see the college of last week, will be seen by beth and Margaret Rose, was Eights in their annual race. viewers on Saturday evening.

www.americanradiohistory.com Wireless World, May 2151, 1937.

THE MAESTRO. Arturo Toscanini, who will conduct the B.B.C. Symphony Orchestra for each of le for the the sis; concerts of the London Music Festival to Perli (Dora Labbette), with be held in the Queen's Hall. nd Abroad André Gandin as Pelléas. The third comes from the Opera FREEDOM House at Glyndebourne, and HIGHLIGHTS OF THE WEEK THE programme " Louisa will consist of the first act of FRIDAY. MAY 21st. Wants a Bicycle," which was Mozart's " The Magic Flute." Nat., 8, Lauri Wylié s " Wireless broadcast some time ago, will This will be broadcast on Puppets " (6th edition). 9.20, Responsibilities of Empire -V. be revived for Regional 6.45 Thursday at (Nat.). 1 1.30, Eye -witness account of the listeners on Wednesday at Rome gives us a treat at 9 Wightman Cup Matches. 8.15. It deals with the fight to -night (Friday) with the Reg., 7.30, Tommy Matthews and for woman's freedom, and relay from the Teatro his Concert Orchestra. 8.30, Covent Garden relay. among the characters which Comunale, Florence, of Abroad. will be portrayed are Florence Wagner's " Tristan and Hilversum, 8.55, Symphony Concert Nightingale, Anna Jameson, Isolda," performed by a Ger- by the Arnhem Orchestra. Millicent Fawcett, and John man company which includes SATURDAY, MAY 22nd. Stuart Mill. It is difficult for such well -known names as Nat., 6.45, B.B.C. Orchestra (E) and the youth of to -day to imagine Josef von Manowarda, Hans Aubrey Brain (hdrn). 8, Music in Hall. a world without women Reg., 6, " Wireless Puppets." 9, such activities as sports, Comic Opera, " Dogs of Devon." " Sarka," a transmission athletics and politics. And 10.50, Six Days Cycle Race. which is to be relayed by all yet it is but a few years since Abroad. Rague, 7.50, Friml's Operetta, "The Czech stations. This corn- their emancipation even in Vagabond King." poser, a native of North Mora- this England. The various SUNDAY, MAY 23rd. via, is intensely national in his steps in attaining this will be Nat., 6, " I Knew a Man " -Mark compositions; indeed, so portrayed for listeners in the Twain, by Sir Ian MacAllistair. dynamic is his music that one programme on Wednesday. 7.15, Bird Songs from a Surrey might almost describe his work Wood. 9.5, Victorian Melodies. Reg., 5, Relay from Berlin. 7.55, as futuristic. EMPEROR JONES Service from St. Michael's, Corn - Part of a famous Swedish THE character of Brutus hill. 9.5 The Miracle of Lodz. opera is being broadcast to- Jones, the escaped convict who Abroad. night (Friday) at 8.30 from Berlin, 8, Love Scenes from Opera. became Emperor in a savage all Swedish stations, when the land, as portrayed in Eugene MONDAY MAY 24th. latter half of Peterson - O'Neill's play " The Emperor Nat., 1 1.55 a.m., Empire Service at Berger's " Domedagsprofer- is which grips St. Paul's. 7.10. The Music Jones," one the Shop -XVI. 9.35, Incidental to terna " (Day of Judgment hearer from the start to the a play. Prophets) will be rendered in finish of the story. Peter Reg.. 6.10, " Eights Week " : com- the Stockholm studio. Cresswell is to produce this for mentary from the Oxford Univer- Paris PTT, at 8.15 on National listeners on Tuesday sity Boat Club. 8.10, Hero and Heroine : songs and duets from Saturday, gives Moussorgsky's at 6.25 and for Regional famous operettas. 9.10, Empire " Boris Godunov," from the listeners on Thursday at 8.55. Day Concert. Opéra. The part of the Emperor was Abroad. n o played by Paul Robeson in the Lille, PTT, 8.30, National Orches- tra, with Poulenc as solo piano in NORWEGIAN SONGS stage production, and will be FROM GERMANY. Otto his own Concerto. Dobrindt who will conduct the THE National Students Choir taken by Robert Adams for the TUESDAY, MAY 25th. broadcast version. Deutschlandsender orchestra of Norway will broadcast from during a programme of light Nat., 6.25, " The Emperor Jones." all Norwegian stations to- 8, " Gallery Goddess " : a roman- music which will be relayed night (Friday) at 9.10 an in- OPERA from Berlin for Regional tic comedy of the theatre. 7.45 and 8.40, Garden of old THREE listeners on Sunday at 5. Reg., Covent teresting programme broadcasts under relays. this heading come to English Norwegian songs which should Abroad. be well worth listening to. listeners this week. The first Nissen, and Army Konetzni. Radio Paris, 8.30, Colonne Concert is to -night (Friday) at 8.3o Only in recent years has it Society's Symphony Concert. a (Reg.) , when the Second Act become generally known that WEDNESDAY, MAY 26th. NATION SHALL SPEAK Nat., 8.15 and 9.25, London Music of Wagner's " Gotterdäm- this great love - drama of PEACE . Festival Concert from the Queen's ANOTHER " Cabaret Across merung " is relayed from the Wagner's was inspired by Hall. Royal Opera House. The Mathilde Wesendonck, the Reg., 8.15, " Louisa Wants a the Frontier " is to be broad- next, also for Regional lis- woman who came into his life Bicycle." 9, Variety, including cast by all Swedish and Danish teners, comes on Tuesday at at the time when his genius had the Southern Sisters, Issy Bonn stations on Saturday at 8, and Gus Chevalier. consisting of alternate items 7.45, when the first two Acts reached full maturity. This Abroad. of Debussy's " Pelléas et opera is particularly popular Leipzig, 8.10, Dresden State Opera from Denmark and Sweden. Mélisande " will be relayed in the United Kingdom, deal- Woodwind Quartet and soloists In contrast to many other from Covent Garden. Most of ing as it does with the romance in German light classical music. nations who apparently con- the artistes are from the Paris of Isolda, an Irish princess, THURSDAY, MAY 27th. sider broadcasting solely as a Opera and Opéra- Comique. and Mark, King of Cornwall. Nat., 6.45, Relay from Glynde- weapon of propaganda, the bourne. 8.5, Variety -Jeanne de Scandinavian countries are The part of Mélisande, how- It was first heard in London at Casalis and Hildegarde. 10.20, ever, will be sung by Lisa Drury Lane in 1882. Pianoforte recital, Josef Wagner. strong advocates for using Brno, one of the subsidiary Reg., 6.30, " Gallery Goddess." broadcasting as a means to Czech stations, gives us a taste 8.55, " The Emperor Jones." establish peace and goodwill Details of this week's of national opera, albeit a con- Abroad. between the peoples of Scan- Television programmes Leipzig, 7.45, " Fidelio " (Beet- will be found on p. 499 cert version only, in the 8.45 hoven). dinavia. transmission Of Janácek's THE AUDITOR.

www.americanradiohistory.com Wireless World, May 2rst, 1937. Magic from the Air AN OLD ENEMY IN MORE FRIENDLY GUISE

announcement referred to is supplementea by a verbal plea from a concealed loud By speaker. The same may be adopted to confer on the now prominent pedestrian a "CATHODE RAY" wayside lecture on personal hygiene, in the frank but friendly manner familiar to the clientele of Anglo- Continental broadcasting stations. It is particularly interesting to note that the invention is so devised as to cause this talk to continue to its appointed end even if the listener then, is a valve oscillator, arranged Di D you ever have the misfortune thing, finds herself unable to stay so long. to hear certain depressing moans to produce a beat note with another The mirror in this system is used as one issuing from a loud speaker and oscillator (in the " Theremin." the broad- plate of the tuning condenser and is coated controlled by a man jerking his cast station was replaced for this purpose just enough to be opaque and reflecting hand to and from a stick, like a timid by a second oscillator in the instrument) when illuminated only from the front, but as to have an excep- snake charmer ? The injury inflicted on and so bady screened to be semi=transparent when a light is his hearers by this performance was tional amount of " hand capacity effect." placed behind. The presence of a person usually accompanied by the insult of The rod sticking up out of the instrument or other disturbing object alters the capa- being asked to believe that the operator was, in fact, a sort of extension.of one of city, and trips a relay that turns on the was extracting music (sic) from the air. the oscillating circuits, and the presence light behind, which, of course, offers Of course, given certain technical proof a hand within the immediate neigh- many possibilities for display. Alterna- visions for the continued existence of the bourhood constituted part of the tuning tively, or additionally, the relay may be operator, the experiment could be per- capacity ; hence the pitch of the note caused to switch on a talking film. formed equally well in a vacuum ; better, issuing from the loud speaker could be in fact, for the audience would thus be varied by the owner of the hand. Uplift Talks spared from hearing any of it, assuming As a musical instrument the technique the loud speaker to be in the vacuum too. was novel and not very easy to acquire ; The possibilities of this are immense. The promoters of this enterprise were, by and the results, even with the greatest Our own benevolent P.M.G. might be pre- modern advertising standards, no doubt application of skill, were difficult to justify vailed upon to arrange things so that when entitled to the use of a poetic headline apart from novelty ; although improve- we approach the pillar box in the dark phrase, not intended as a scientific defini- ments were later introduced for moving a Golden Voice remarks " You are too tion. But even in an age tolerant of from one note to another without neces- late to post here to- night, but if you go crooners, musical saws, contemporary sarily executing a glissando, and for con- round the corner at the end of the road chamber music, and swing," this was trolling timbre and loudness more satis- you will find the District Office box still one too many, and it has gradually faded factorily. uncollected. Post early." Or safes might from our scientific lecture theatres, concert Anyway, it has failed to obtain a per- be caused to deliver a good moral talk to halls, radio exhibitions, and fairground manent place among musical instruments. the burglar to while away his time till the sideshows (in that order). But it is fairly obvious that the same constable, summoned by the burglar- But, as an old proverb says, if you find principle can be applied to accomplish actuated alarm, comes to collect him from a dead horse on your hands it is more other things than the emission of catcalls the burglar- actuated trap. profitable to enter the catsmeat business from a loud speaker. The hand capacity The burglar alarm, by the way, is an- than to flog it. Apparently Music From effect can be made to bring a tuned cir- other application of the capacity relay. It The Air exponents have adopted this cuit more or less into resonance, thus con- is not a new one, because I remember trolling the current in a valve circuit, policy, in principle at least ; for according reading an exposition of this very method to Electronics (Feb., 1937) the essence of which in turn can be used to work a relay, at least twenty years ago in the fictional the invention, which was due to Professor and hence to ring a bell, explode a bomb, works of Arthur B. Reeve. The capacity Theremin, has been developed along quite electrocute a gangster, launch a ship, or element was extended to embrace an en- different lines. About the ingenuity of cause an advertisement to appear. Appar- tire room, and the variation due to the them, as well as the origin from which ently the last of these acts offers most presence of an intruder was conveyed by they sprang, there is no room for doubt, scope for business, and it is in this direc- wire or wireless to the appropriate however. tion that it has been chiefly applied. interests. There must have been some For example, a mirror has been set up practical difficulties which militated in a prominent place, and a passer -by goes against its general adoption ; " Hand - capacity Effect " Glorified one of these up to it to take advantage of it for some appears to be a tendency for false alarms As there may be some readers who are un- purpose or another. As she comes close to be caused by slow drifts from the familiar with the original Theremin device to it the opaque mirror suddenly becomes original adjustment, due to temperature, I must explain that it depended on a translucent, revealing an invitation to share valve ageing, or other influences. So an principle unconsciously applied by many in the advantages conferred by using a important part of Theremin's system is a of the earlier broadcast listeners, who were certain proprietary cosmetic. The bene- patent for an invention whereby any publicly requested by the B.B.C. to " look ficent donor of the mirror, if he considers changes in capacity or other operating con- to their sets," because of the annoyance that its possibilities have not been ade- ditions, tending to trip the relay, are caused to their neighbours by the exces- quately developed in this way, may go on compensated by a thermal device. As sive use of reaction. The essence of the to arrange things so that the visible this device is incapable of responding

www.americanradiohistory.com MAY 21A. ' 1937 WApISIl®00 499 Wordicl Magic from the Air- Horse Marines or serving in the Swiss rapidly it does not prevent legitimate Navy. There is a synchronised AC mains action due to the relatively rapid change clock for DC mains! The clock works off in capacity with the approach of a person, AC, as usual, and the AC is produced by but it does protect the mechanism against a valve device due to Theremin, which slow drifts. operates from DC. The vital synchronis- The same stabilising system is applicable ing agent is the commutator ripple, which to other types of relay than the capacity - is there anyway, but which may be used McCAiQrH sensitive sort. There is the photo- electric to synchronise clocks if the generators are relay, which has become fairly familiar frequency -controlled as is general for AC nowadays in connection with exceptionally machines. 6 -valve all -wave Superhet valuable exhibits of jewellery, counting of But it is to be hoped that in this country with Radio Frequency Stage newspaper bales, and the more refined the disappearance of DC mains will not be Belisha crossings. The interesting feature so long retarded as to the 8 stages. make establish- 8 tuned e'rcuits of the photo -electric relay as contrived by ment of this system worth while. 3 wavebands Theremin's concern is that instead of being actuated by a break in the ray when an object comes between the source and the photo -electric cell it depends on the reflected light from the object. It can Television Programmes therefore be used where the ordinary sort is inapplicable. For instance, the beam Transmissions are from 3 -4 and 9 -10 can be shot out of a shop window (adver- daily. tising again !) and the reflection of it from Vision : Sound: a person within a certain distance of the 45 Mc /s. 41.5 Mc /s. window affects the cell and causes the whole shop window to be lit up. This un- FRIDAY MAY 21st. expected result not only draws the passer's a, Friends from the Zoo. 3.15, Gaumont - British News. 3.25, Scenes from the London PRICE attention more closely to the window than Coliseum production " On Your Toes." a mere constant illumination, but his ab- (Complete with B.V.A. valves) £ ,17.6 sence saves current which might otherwise 9, Music Makers ; Lubka Kolessa, a Ukranian ó pianist who will play in National costume. Performance (made possible by use of multi -electrode valves) wasted on a 8 be deserted street. 9.10, Friends from the Zoo. 9.25, British equal to that of many receivers employing valves or more. as Brief specification includes : Large "Airplane" dial, with Lastly, an example of this versatile Movietonews. 9.35, Cabaret. different coloured lights automatically switched on for each technique, a problem has been solved wave-range. Micro- vernier 2 -speed drive. 4 -point wave- change and gramophone switch. Volume control and variable akin to that of communicating with the SATURDAY, MAY 22nd. tone control also operative on gramophone. Reinforced 3, Ernest Brisbane's Punch and heavy -gauge steel chassis. Covers 19 -2,000 metres. Judy. 3.8, Circuit comprises : Preselector circuit, radio frequency amplifier Spade work ; C. H. Middleton in the grounds (operative on all 3 wavebands), triode -hexode frequency of Alexandra Palace demonstrating the first changer, double band -pass I.F.T. coupled I.F. amplifier, steps in double diode -triode detector and L.F. amplifier. . D.A.V.C. making a garden. 3.20, British Movie - applied to 3 preceding valves. 3 -watt pentode output. tonews. 3.30, Time to say Goodbye : a review of farewells. Special 9, Television Orchestra. 9.20, Gardening talk 6 -VALVE BAND -PASS by C. H. Middleton. 9.35, Gaumont- British News. 9.45, Starlight ; Gracie Fields. SUPERHETERODYN E MONDAY, MAY 24th.

3, Music Makers ; Emilio Colombo (violin). 3.10, The World of Women -IV. 3.25, Cabaret Cruise. 3.50, British Movietonews.

9, Music Makers : Lisa Minghetti (violin). 9.10 and 9.25, Repetitions of 3.10 and 3.25 programmes. 9.50, Gaumont -British News.

TUESDAY, MAY 25th.

3, Roval Tournament : some of the displays that will be seen at Olympia. 3.20, Gaumont- British News. 3.30, Viennese Honeymoon : a revue for television by Hans Kafka.

9, Starlight : Billie Houston and Nina Devitt. (Complete with 9.10, I.00k at Mars To -night ; an explanation B.V.A. Valves.) with diagrams as to why Mars is so bright this month. 9.20, British Movietonews. 9.30, Specially designed and built for higl quality radio /gram work. " Lionel and Clarissa " : the ballad opera in a SPECIAL FEATURES: Reinforced stout steel chassis. shortened version for television. High class components by well-known makers of acknowledged reputation used throughout. Fitted with attractive and specially large full- vision dial, glass fronted, and supplied

complete with escutcheon and fittings. Separate illumination , WEDNESDAY, MAY 26th. automatically switched in for radio /gramophone. 3, Canvas to cover us : display of camping CIRCUIT DETAILS : Inductively coupled band-pass equipment and practice introduced by Sir Percy filter, triode -hexode frequency changer, band -pass I.F.T. coupled I.F. amplifier, I.F.T. coupled to diode detector. Everett, Deputy Chief Commissioner of the Boy D.A.V.C. applied to preceding valves. L.F. amplifier capacity Scouts Association. 3.20, British Movietonews. coupled to output pentode 3 -3f watts undistorted. Variable 3.50, Fifty -seventh Picture Page. tone control and volume control operate on both radio and gramophone. 9, The Four of Us. 9.20, Gaumont- British ALTERNATIVE TRIODE OUTPUT News. 9.30, Fifty- eighth Picture Page. All McCarthy receivers supplied complete with RADIO FLOOD GAUGE. As a precaution valves, knobs, pilot lamps, leads, mains cable and against avoidable repetition of recent dis- plug. 12 months' guarantee. asters due to floods, the authorities in THURSDAY, MAY 27th. Deferred terms on application, or through London Radio Supply Co., 11, Oat Lane, E.0.2. California have installed automatic wireless 3, Dancing lesson by Alex Moore and Pat Kil- Cash with order on 7 days' approval. Also write transmitters, actuated directly by water for illustrated catalogue of complete range of all patrick. 3.15, Gaumont- British News. 3.25, receivers. gauges which measure river levels, at certain " Lionel and Clarissa." McCarthy of the more remote danger points. Dry batteries are used for both HT and LT, while 9, Hella Kurty (Viennese songs). 9.10, Re- MCC UTI-IY JRÀI®IiC ILTD. the receivers are put into operation at pre - petition of 3 programme. 9.25, British Movie - Grove, London, W.2 determined hours by switches. 44a, Westbourne time- tonews. 9,35, Pasquinade No. 2. Telephone; Bayswater 320112.

www.americanradiohistory.com Wireless World, May erst, T937.

Engineers in Training The B.B.C. men are now learning how to handle the gear Broadcast Bre it Les themselves. Six months' experience with the apparatus at Alex- Attitude of the Dominions andra Palace has helped them NEWS FROM PORTLAND PLACE considerably, but it must be re- His great problem is to dismembered that the mobile gear, transmitters and wavelengths cover any real warmth of feeling besides embodying improvements When Ignorance Was Not towards B.B.C. programmes in Bliss the B.B.C. advised overseas on its prototype at the television listeners to try all wavelengths Dominions whose own broadcast- station, differs in many other FREDDIE GRISEWOOD, in turn for the time being. The ing organisations are providing ways as a result of the designer's who took to television engineers at Broadcasting House effective services without any efforts to incorporate as much as commentating like a duck takes feel that many South African help from outside, thank von, possible in the relatively small to the water (and water was in listeners failed to try the experi- and to whom the sole appeal of space. abundance at Apsley Gate on the Empire service is its patriotic ment. «-, Gez,) 'o, May 12th),. mystified viewers and Imperial background. by his repeated apologies for Stream of Reports " Televising " the Derby New Zealand had excellent Will He Get the Money ? the poorness of the picture. Sc) people who Broadcasting House feels that had been hop- The light, he explained, was reception of the " Homage " ing that the Derby would if any one of its officials is likely be dreadful, and everybody on the programme, which was re- televised will be disappointed. plinth at Apsley Gate was ter- broadcast by all stations. Good to be taken by overseas broad- Technically casting authorities to their hearts the feat should not ribly upset. reports also came from New be impossible, as the ultra short Delhi, Montreal, Ottawa, Mel- Beresford Clark is that man; if Actually, the received picture wave radio link, if not quite gave the impression of a fairly bourne, Cairo, Shanghai, Nai- he is able to obtain any support capable robi, and the Gold for a scheme to induce the corn- of bridging the gap be- bright day, so sensitive were Coast. tween Epsom and Muswell Hill, the cameras, and it was not could have covered the ground until Messrs. Grisewood and as far as, say, Victoria or Hyde Cock returned to the television Park, the signals being trans- vans after the Procession that ferred there to the permanent they learned that the whole television cable. broadcast had been an outstanding success. Pictures from the Past Probably, however, the B.B.C. Cameras Excel the Eye are wise not to risk a fiasco in And even then the Director of these early days. According to Television 'phoned Alexandra present arrangements the race Palace for confirmation of the will be televised in the same fact. " If the light had been manner as the Grand National, really good," said Mr. Cock, the ordinary sound commentary " we should have given a pic- being supplemented by plans of ture which would have amazed the course and pictures of famous even the television staff. As it races of the past. was, the camera has proved how much more sensitive it is than the human eye. The light was so bad that we could hardly see Sidelights of Recording the head of the Procession as it "AltE you an announcer? " reached Stanhope Gate." " I regret I have nothing to broadcast." " We never "Unforgettable Experience" speak to strangers." " Can you Those who saw the Procession tell me where I can find a on the television screen will re- taxi? " " Could you please call that the first horsemen A MOMENTOUS OCCASION. One of the very few pictures taken of tell me what all these people could be seen plainly immedi- a B.B.C. television camera in action on Coronation Day. This event are waiting for? " came into view round will no doubt go down in broadcasting history as one of the outstanding These were some of the ques- ately they achievements of the pioneering days. the bend of the East Carriage tions and statements which Drive. Hong Kong reported fair re- portent parts of the Empire to were put to Lynton Fletcher The first telephoned congratu- ception of the Abbey service share the cost of the B.B.C.'s and his colleagues of the B.B.C. lations reached Alexandra and excellent signals in the Empire service, he will have per- Recorded Programmes Staff Palace from Brighton, and soon evening. Ca pe town's report formed an invaluable service to when they made records at afterwards came a telegram from was in similar terms. the British listener in relieving Admiralty Arch early on an Ipswich viewer who referred The first cables reached him of an ever- growing tax on Coronation morning. to the " unforgettable experi- Broadcasting House at 6.3o on his ten shillings a year, and to ence of seeing and hearing the Coronation evening, and then the broadcasting administration For Scrapbook 1937 Procession perfectly, at home." continued in a steady stream at home in releasing more money The wandering microphone No one doubts now that until the small hours. for the home service. attracted a lot of attention, Coronation Day put Television and the records, which will be " on the map." Hail and Farewell stored in the B.B.C. archives to Six Weeks' Respite commemorate the Coronation WITHWITH a very faint flourish of for future generations, include trumpets and an almost im- OPEN -AIR television from the singing of popular songs World Reception of perceptible wave of farewell - Hyde Park has whetted and cheering the King by thou- Coronation Broadcasts so much in keeping with his viewers' appetites for more, but sands of voices. reception of the innate modesty and characteristic the mobile television unit will not There were also interviews WORLDCoronation broadcasts absence of " side -Mr. J. come into regular use for at least with Rover Scouts putting up proved that the new Daventry Beresford Clark, Director of the six weeks. A good deal of harriers, and with people who transmitters were a success. In B.B.C. Empire Service, left Vic- " rush " work was involved in had come long distances to take no place was complete failure ex- toria last week for Malta on the getting the vans ready for the up their stands in the Mall. perienced, though South Africa first stage of his seven months' Coronation, and it is an open There were eye- witness accounts reported signals as only " poor tour of the Empire to discover for secret that their operation on the also of the scene in Trafalgar to fair." himself to what extent the Em- great day itself was largely en- Square as it appeared at mid- It should be explained- that pire broadcasting service is ful- trusted to the Marconi- E.M.I. night to watchers on the top of on the introduction of the new filling its purpose. engineers. Admiralty Arch.

www.americanradiohistory.com Wireless World, May 21St, 1937.

or two, three or four times in rapid succession. Practical Without suggesting for a moment that a completely satisfactory repair can always be effected by these means, the plan suggested may be worth while trying in cases Hints and Tips where the faulty transformer would otherwise be totally useless. A repair by the Ia portable set the designer may often normal method of rewinding is often out have allowed for a fixed degree of re- of the question. action, upon which sensitivity largely Any source of high DC voltage, and not depends. It therefore sometimes happens only the mains, could, of course, be used when replacing RF and detector valves by for the experiment. new ones that reaction is then overdone, resulting in a wipe -out Can you pick Stray of all stations below, say, London National. ACAUSE of crackling noises, appearing Reaction In a case recently in- at irregular intervals, which is fre- vestigated the relative quently overlooked in the expectation that the WINNER position of two anode leads to valve caps the source is either within the set or a were causing the trouble and the simple machine or sign noise, may be found in expedient of separating them as far apart the screw connections of wiring to tumbler as possible was sufficient to prevent the switches and fuse unwanted reaction. It might, of course, " Crackling boxes. Although these ONE condenser looks be argued that these leads should have may have been very much like another. On appearance Noises been shielded, but here it must be re- tightened hard at one alone it might be a gamble to know membered that the designer probably time, the screws may which will prove the winner. But it's to take place, and work loose, possibly to the intended some reaction due vibration simple to make sure of picking it would not be wise to make alterations of of passing traffic, and although it may be the right this kind unless absolutely' necessary. On in another part of the house the loose con- one ... look for the initials " T.C.C." the other hand, there would be little justi- nection will make itself heard in the loud Without them no condenser can boast fication for replacing a metal- coated valve speaker. a 28 -year pedigree, can claim such fine by an unmetallised specimen, even though Another cause is dependent on the cross- materials both inside and out, or have in other respects it were suitable ; the ing or touching of lead- covered câbles passed through so many tests in the reverse generally applies as well. which have not been bonded and may not hands of so skilled a team of workers. cause trouble when the wiring is new, but Setmakers know this ; they say " T.C.C. in the course of time, when oxidisation has set in, intermittent crackling noises will throughout " and so play for safety .. . ALMOST everyone knows that an It's a tip worth following! audio- frequency transformer that has appear at more and more frequent inter= vals and the only cure. for trouble due to a fault may sometimes be tern - developed been PLAY FOR porarily restored to usefulness by pass- this cause is ,bonding where it has current through the wind- overlooked in the past or has become SAFETY -USE ing a surge of faulty. ing. Such surges may be produced by T.C.C. momentarily interrupt - Kill ing one or other of the THROUGHOUT or receiver power circuits IN operating a battery receiver with OPP ` Cure or even by switching or Class ' B " output, there is often on and off the electric an unexpected wastage of HT current light in the room where the set is arising from the fact that heterodynes of operating. adjacent stations are being reproduced A correspondent claims to have had by the output valve or valves (though not considerable success in repairing defective normally heard in the transformers by momentarily connecting High -Note speaker, or heard only faintly). sound the faulty winding across 230 -volt DC Wastage A of mains ; a lamp is connected in the manner very high pitch can shown in Fig. i to act as a current -limiting cause the current in device. _Voltage is applied, for a second such an amplifier to rise alarmingly, though the sound output from the speaker is apparently quite moderate, particularly LAMP if the conventional o.or -mfd. shunting condenser is used across the speaker. This trouble can be alleviated to a large extent by employing shunting condensers before the output valve -for example, between the anode and earth line of the LF WALL PLUG valve if one is used, or across the secondary of the output transformer. .C. Suitable values can be found by trial, and TRANSFORMER usually round about o.00r mfd. is suitable. ALL-BRITISH By inserting a milliameter in the HT supply to the output stage it should be CONDENSERS possible to tell whether the condensers have the desired effect, for such an in- The Telegraph Condenser Co. Ltd., Wales Farm Rood, Fig. 1.- Desperate ills call for desperate crease of current is continuous, and not remedies ; illustrating a scheme that may N. Acton, W.3. possibly restore, if only temporarily, a varying like that due to speech and defective transformer to usefulness. music. i5

www.americanradiohistory.com Wireless World, May erst, 1937.

be that, owing to the phenomenal sunspot activity, the charge was far greater than RANDOM RADIATIONS usual and that the metal part of the ship was not properly earthed owing to the dry- ness of the ground lines. The Coronation Broadcast III By "DIALLIST" II SI .- THE B.B.C.'s six and a half -hour broad- The Danish Way cast of the processions and of thu reassuring to listen, as I ply the pen, to the service in the Abbey on Coronation Day B.B.C.'s news bulletin, which records that DENMARK manufactures no wireless was, without a doubt, the finest and most reception has been excellent in the New valves, and for the last six years ambitious feat that has yet been accom- World. In South Africa it was only "fair," the country has therefore had to ob- plished in radio. An enormous amount of but it seems to have been good in many tain the whole of its valve supplies from hard work was put into the preparations for other distant countries. European sources. Recently there have it, and right well the labours of these -. -. -. been bitter complaints that the Danish lis- responsible were repaid. I wasn't able Well -named tener was being exploited by European to hear the whole thing from start to finish, valve manufacturers. A petition has now WHO thought out the new name for Mar- since I had been roped in for various duties been made to the Government to allow in connection with local celebrations coni House, which has now been taken American \ alves to come into Denmark the - Ministry, I know, but including the installation of a wireless set over by the Air don't again, and it seems possible that the powers it was quite an inspiration. " Ariel House," that be will lend a sympathetic ear. Iu to provide music whilst 30o schoolchildren not only its were getting outside their Coronation tea. by the happiest of puns, suggests any event, makers on this side of the Her- present purpose but also its long connection ring Pond have become so alarmed at the But I did hear the broadcast from ro.15 development wireless in morning until nearly half -past two, in the past with the of possibility that it is reported that they are the in country. Between 1912, when Mar- and I picked up snatches of it as this about to bring their prices to Denmark thereafter coni moved in with his Wireless Telegraph and when 1 could. During the whole time down in order to stave off possible com- Company, and 1933, when a transfer was petition from the State's. that I was listening these wasn't a single made Em- hitch. Everything ran like clockwork to the present premises on the -and bankment, the history of wireless as we the best -quality clockwork ? at that. know it to -day was written. One of the What Will Happen Here -. .. -. most interesting periods in the history of One wonders whether we shan't see the The Abbey Service Marconi House was that when it contained prices of British valves forced down for a THE relay of,the service in Westminster the entire B.B.C., including its programme rather different reason before so very long. Abbey was the most impressive thing that and engineering staffs, its one studio Our manufacturers are now making valves I have ever heard by wireless. So perfect and the transmiting plant. That was of American type, and I understand that was the placing of the microphone and the in 1922. I don't think, though, that Mar- some set makers are going to use American operation of the control room that every- coni House can claim to have been the valveholders (tube -sockets they call them thing was beautifully heard. The music- birthplace of British broadcasting. That over there) in their new broadcast receivers. glorious music gloriously performed -came honour must go to Writtle, whose Tuesday If so, it is likely that American valve manu- through magnificently, and every word of evening programmes old hands will remem- facturers will +turn their eyes still more the Archbishop of Canterbury and of His ber well. Writtle possessed only a half - longingly towards our valve -replacement Majesty the King was as clear as the kilowatt plant, but it used to be heard all market, in which they are not doing so badly even now. Even after paying import proverbial bell. I don't know for certain over the country. . duty, freight charges and so on, who it was who read the rubrics and ex- -. % -. first -rate plained the service, though I believe it was Once Bitten, Twice Shy American valves come out a good deal own cheaper than our own products, at present the B.B.C.'s chaplain, the Reverend THE other day I was asked by a friend F. A. Iremonger. The task could not have prices. There will undoubtedly be strong whether or not it was advisable to have competition from across the Atlantic, and been carried out better. Everything was an earthing switch for an indoor aerial in one's mind's the only way of meeting it is to market first - made plain and one could see erected in an attic. I told him that I eye all that was happening. It was wonder- class British valves at about the same prices always used one, not with the idea of pre- as American. And it isn't only the home ful to think of the whole Empire listening venting the aerial from being struck by markets which have to be considered ; there to the presentation and joining in spirit in lightning, but to save myself from unpleasant both the acclamation and the homage. are those of the Empire as well. The surprises in the way of shocks. It is quite % % -. Americans and the Dutch are getting too surprising what a charge a well- insulated big a share of these already -and they will Well Commented, Sir and unearthed indoor aerial can collect in into the microphone on so get more if our valve prices aren't cut dras- thundery weather. Before I made a practically. COMMENTINGmoving a spectacle as the Coronation tice of keeping mine earthed when not in procession must be -one of the world's most use I got several muscle -twisting shocks difficult tasks. Some of the commentators - uvhen thoughtlessly picking up the bare end or observers, to give them their official, of the down -lead. I expect others have though not, to my thinking, very happy had similar experiences, though I admit title -were obviously so carried away by that my ohmic resistance appears to be on the wondrous beauty of the sight that it the low side, for I'm very susceptible to was difficult for them to find words where- electric shocks. with to describe it. All did well, but for that part of the broadcast that I heard the Sunspots and the Hindenburg honours must to Blake and go George And Howard Marshall. The former excelled in talking of static charges, it seems more likely the painting of word- pictures as the pro- than that the sunspots which have been playing such pranks with short- cessions arrived and departed ; the latter, wave reception of were respon- never at a loss for a word, helped us to see late mainly in detail the marvellous scenes that unrolled sible for the terrible fate of Germany's air- before his from his vantage ship, the Hindenburg. In this country we themselves eyes across point in the Triforium. don't cone the naturally produced static charge very much, but in hotter and % uis -. drier climates it's a real problem. In the World -wide Reception United States and India, for instance, it is SEVERAL times during the broadcast 1 common practice for private cars and com- switched over to the short waves in the mercial vehicles to use earthing chains to hope óf discovering how listeners in various make contact between the chassis and the parts of the Empire and in the United road. Without these the vehicle is, of States were faring. I found my set, uvhich course, insulated by its rubber tyres. It is is á sensitive one, very lifeless on pretty its quite normal for airships to collect a big- PROGRESS IN TELEVISION is not confined short -wave range and began -to fear that one gish static charge when they are in flight, to this country. A television transmitting of those semi -blackouts with- which we have though this is normally dissipated when the tube is shown being made in the Philco been familiar of late was taking place. It is ground lines are dropped to earth. It may factory in America.

www.americanradiohistory.com Wireless Trerl7, _17ay erst, 1931. 503

Letters to the Editor______-. The Editor does not hold himself responsible for the opinions Interference Reports of his correspondents r IWAS rather surprised to read Mr. T. J. E. Warburton's comments in the May 7th issue. Some day I hope Mr. Voigt's firm will pro- With reference to his remarks regarding vide themselves with moulds and cores so " overdue " visits, the local Post Office en- that they can go to a house and cast the gineers are always ready to call on any Voigt design in solid concrete in the corner special day, if requested to by a complain- of the room and make it part of the house ant, and if the visit was overdue I expect as we have done with our wall baffles. That it was for lack of information on the form will be my day. I will send my wife for a which he is expected to complete. short holiday. . . . It would be interesting to know when he With regard to the trumpet of Mr. Maggs, complained to the Post Office, as he states I think one mistake he has made is to have the engineers arrived on " motor bikes." those curves in the folded horn. I think This is strange in view of the fact that the that, if you must bend' and fold a horn, motor cycles were replaced by the now it is better to have sharp angular bends with familiar " Radio Service " vans some con- internal plane reflecting surfaces correctly siderable time ago. placed in the angles to change the direction Also, the engineers consider themselves of the sound waves. I believe the old lucky if the noise happens to be on when acoustic Columbia graphophone used this the first visit is made ; the usual procedure principle, and so does Mr. Voigt in his is to request the complainant to compile a speaker. log of the times the interference is experi- Caerphilly. W. E. LEAVER. enced, so that further visits can be made. Mr. Warburton should consider himself lucky that he does not suffer from continu- AN EXCELLENT ous interference. The Broadcast Licence MODEL FOR His remarks about local Post Offices having their own listening departments is T MUST object to a view sometimes ap- EXTENSION SPEAKER USE foolish, having regard to the fact that the t proved by The Wireless World, namely, that we pay for a licence to maintain a Where an Extension Speaker majority of interference is " local " to the giving unusually fine repro- ; we for our los. complainant. receiving station what get duction is required, the new I wonder what aerial system he uses to in the way of programmes is merely an act Rola F742 -P.M. is the ideal experience such terrible interference, as it is of grace. unit to use. Although not obvious from his remarks under " Chain That may be legally sound, but common designed primarily as an d sense dictates that it does not represent the Extension Speaker, its super - Listening " that he is using a battery set sensitivity renders it specially and is, therefore, not getting interference true position. Suppose the Government closed down the B.B.C., telling us that in suitable for this purpose and entering the receiver via the mains lead. also for battery set operation. PHILIP W. CROUCH. its place it proposed to give us the speeches The Rola F742 -P.M. makes use Newton Abbot, Devon. from Parliament, etc., or, alternatively, of the new magnet material that we were free to turn to France or Ger- " Alnico." It has the same many or Russia for entertainment. Do you flux density in the gap as the see me paying for a new green slip? giant G12- P.M.- 11,500 lines per square centimetre -and No ; we all know that the licence system Horn - loaded MC Speakers its sensitivity is quite un- provides a convenient mechanism whereby equalled by any speaker in Air AY I be allowed to add this one fur- we can be made to pay for our programmes. class. Fitted Y1 the same price they contribution to the recent corre- Legal quibbling must not be used as an with a new metal and corn- spondence on horn- loaded moving -coil excuse for failing to give us value for our pound shielded universal trans- Ss speakers? money -complete with accountant's certifi- former to match most valve I heard the Voigt Domestic Speaker at cate as to how it is spent. combinations, it is both dust - Olympia some years ago, but have not yet Birmingham. J. ALEXANDER. proof and moisture -proof. heard it under proper working conditions. Like Mr. Cotterell, I have found that the only plane baffle with any sense to it is a solid brick or stone wall. My own Hartley - Output Rating Turner speaker has been so mounted for the I draw your attention to a peculiar last two years. The speaker frame is bolted MAYphenomenon with regard to output to a slab of marble about two feet square valves, namely, that when a certain valve and two inches thick, and the whole is used in one receiver the output is claimed assembly is again bolted solidly to the wall. to he 34 watts, whereas when the same Again like Mr. Cotterell, I thought this valve is used in another receiver the output was the last word, but now begin to doubt is supposed to be only 24 watts. it. I don't pretend to know much about WITHOUT TRANSFORMER 42'- Tinkering in my workroom last evening, radio, but these discrepancies_ are so wide soldering -iron in hand and listening on a and there seems so little justification for OVER 8 MILLION IN USE commercial set to a talk on " Timber " from them, except, of course, from the advertisers' the B.B.C., the speaker, referring to the point of view, that it would appear desirable many uses of timber and wood, said, " My for some body (may one whisper the British voice is in all probability coming to you at Valve Manufacturers' Association) to fix an this moment out of a cabinet made of agreed method of test of output rating for wood." their power valves. I paused in my work, and remarked aloud Of course, one way of dealing with it is to myself, " Too true " ... and some more to do what one manufacturer already has Gl/otltti !leiJt Re itodircetS that I can hardly expect you to print. done, to give his output as " undistorted My grouse about the Voigt speaker is that 24 watts, maximum 34 watts." THE BRITISH ROLA CO.. LTD. it is made of wood, and I cannot bring The views of your readers on this sug- MINERVA ROAD. PARK ROYAL,N.W.10. myself to see that anything about a speaker gestion would be interesting. J. B. PHONE : WILLESDEN 4322-3-4 -5 -b. made of timber is all right. Manchester.

www.americanradiohistory.com Wireless World, May zest, 1937.

The British abstracts published here are prepared with the permission of the Controller of H.NI. Stationery Office, from Specifications obtainable at the Patent Office, 25, Southampton Buildings, London, W.C.2, price il- each. Recent Inventions A selection of patents issued in U.S.A. is also included. SCANNING SYSTEMS Brief descriptions of the more interesting radio play. In other words, it can A A THEN amplifying the saw- devices and improvements issued as patents no longer be regarded as an ' II V toothed oscillations used for " earthed " lead. scanning there is a tendency for will be included in this section. According to the invention, this the straight -line parts t6 " de- difficulty is overcome by housing generate " into curves, as shown but potentiometers are arranged question is one that does not the valve, as a whole, inside a in Fig i. This is due to " curva- to vary the scanning voltages so affect the received picture, tieing metallic casing which can he re- that, when a close -up is to be substantially equal to a multiple garded as " earth." An arc -shaped shown, the electron beam is re- plus one half of the framing fre- strip of metal is arranged close to stricted to cover only a selected quency. the anode -grid coupling -loop, but part of the whole picture. G. W. Walton. Application insulated from the metal casing, The voltages applied to the date August 7th, 1935. Nu. and the tap in the anode -grid cir- electron focusing electrodes are 460721. cuit is made very short and slides also adjusted to sharpen the focus 0 0 0 0 over the insulated strip, which is proportionally to the smaller area. SOUND AND PICTURE connected to the HT supply. Fig 1 Simultaneously, the intensity of RECEIVERS Telefunken Ges fur drahtlose the stream is regulated to the new THE use of AVC in a combined telegraphic nl.b.h. Convention Fig. r.- Tendency exists in area. The net effect of the re- sound and picture receiver date (Germany) June Sth, 1935. adjustments is that the picture is desirable in order to compensate Nu. 459348. scanning oscillators for straight - 0 0 0 0 line parts to degenerate into signals developed produce an for quasi -permanent differences of curves. enlargement of the selected area field- strength within a given re- VOLUME CONTROL at the receiver, since there will be ceiving area. At the same time it SWITCHES tore " in the anode current of the no change in the total area of is not desirable to make it depet - THE Figure shows a circuit amplifiers. suitable for either wireless To compensate for it, a high - reception or gramophone repro- pass filter circuit, such as R, C, duction, the volume control being in Fig. 2, is inserted between the common to each. For receiving gas -filled oscillation-generator T wireless signals, the switch S is and the grid of the amplifying open, and the incoming carrier is valve V. The condenser C favours rectified across the first diode, the the higher frequencies, and so AF components being tapped off compensates for the inherent curva- as shown across the resistance R. ture in the output current from the The incoming carrier is also tube. The same result may also applied to the second diode be obtained by inserting a choke through a condenser C, so as to K, as shown in the grid circuit of provide AVC voltage across the the amplifier, in which case the resistance R2, and delayed AVC filter R, C is omitted. across resistances R r, R3. Radio -Akt. D. S. Loewe. Con- For gramophone reproduction vention date (Germany) March the switch S is closed. Since the pick -up impedance is 29th, 1935. No. 459422. low, it will o o 0 0 short- circuit the first diode and TUBES prevent any carrier frequency CATHODERAY present from being rectified. Also THE electron- focusing system, PU as well as the two pairs of as the pick -up is connected to deflecting- plates, in a cathode -ray earth there will be a negative tube are normally arranged and voltage across R1 sufficient to pre - so the electron stream vent the diode from passing any biased, that Fig. 2.- Frequency compensated amplifier for television scanning current. The gramophone voltage is brought to a focus at a given circuit. point. But this focus is maintained only so long as the point view, nor in either of the fre- dent upon the picture -signal moves over the surface of a quencies applied to the scanning carrier -wave, since this is often de- sphere. electrodes. liberately varied in order to This is not always convenient Marconi's Wireless Telegraph convey DC components corre- in actual practice. For instance, Cu., Ltd. (assignees of H. lams). sponding to changes in the aver- in some of the tubes used for re- Application date (U.S.A.) May age or background brilliance of the ceiving television, the curvature of 26th, 193.1. No. 458750. transmitted picture. the fluorescent screen is not spheri- 0 0 0 0 Accordingly, the AVC voltage is j cal; often the screen is plane. The derived from variations TELEVISION in the result is that a certain amount of field strength of the sound carrier - distortion is produced. Again, in ONE of the problems in tele- wave, and is applied as a bias to vision is keep the Iconoscope type of television to the back- at least one valve in the path of RADIO camera, the photo- sensitive screen ground or overall brightness of the received sound -signals, and to INPUT is flat, and is placed at an angle the received picture -as distinct at least one valve in the path of to the normal path of the scanning from the detailed contrasts of the picture -signals, one of these beam. light and shade -in step with that valves also being part of the first According to the invention the of the transmitted picture. The frequency -changer, i.e., prior to electron- focusing system is ar- difficulty arises because such the intermediate -frequency stage. ranged so as to preserve a true changes of background illumin- The General Electric Co., Ltd., focus for any desired path of ation take place comparatively and D. C. Espley. Application scanning. For this purpose auxili- slowly, and, therefore, involve fre- date November 27th, 19t5. No. PU ary correcting voltages are added quencies which are so low that 460675. to those normally applied to the they cannot be handled by the 0 0 0 0 deflecting- plates as the beam valves used to amplify the signal travels over the fluorescent screen. currents. SHORTWAVE GENERATORS J. E. Keysten; F. H. Nicoll According to the invention, the RELATES to a back -coupled AVC Application valve for generating - and O. Klemperer. problem is solved by energising a ultra VOLTAGE dates March 19th and May 7th, special photo- electric cell at the short waves. The anode is con- 1935. No. 458746. transmitter from a source of light nected by a single loop of wire o 0 0 0 which is controlled by the average through a blocking condenser to Circuit arrangement when a TELEVISION "CLOSE =UPS" or background illumination of the the grid, and the degree of back - volume control common to ATELEVISION camera of the scene that is being transmitted. coupling is controlled by moving a radio and gramophone is used. Iconoscope type is adapted to At the same time the source of sliding contact from the high -ten- transmit either long -range views, light is cut up or interrupted at a sion supply over the wire of the therefore builds up across the or enlarged " close- ups," at will particular frequency, so that it loop. In such an arrangement it volume- control resistance R. and by a simple adjustment. The produces a fluctuating current is fot.t:d that, as the frequency is A. C. Cossor, Ltd., and whole of the picture is focused on capable of being handled by the rai,ed, the inductance of the slid- F. R. W. Strafford. Application the mosaic -cell screen as usual, amplifiers. The frequency in ing tap comes more and more into date July 22nd, 1935. No. 46°214.

www.americanradiohistory.com The THE PRACTICAL RADIO JOURNAL 27 tit Year of Publication

No. 926. FRIDAY, MAY 28TH, 1937. VOL. XL.

Proprietors : ILIFFE & SONS LTD.

Editor : HUGH S. POCOCK. EDITORIAL COMMENT Editorial, Advertising and Publishing Offices : Short broadly or with the interests of the DORSET HOUSE, STAMFORD STREET, Ultra Wave mass of the listening public in mind. LONDON, S.E.I. Broadcasting Under present conditions of recep- Telephone: Waterloo 3333 (5o lines). tion on the normal broadcasting bands, Telegrams: "Ethaworid, Sedist, London." A Growing Demand there seems to be little further scope COVENTRY : Hertford Street. for improvement in quality of repro- Telegrams: Telephone: "Autocar, Coventry." 5210 Coventry. AN article in this issue deals duction, but ultra short wave trans- with some new aspects of the missions would overcome these diffi- BIRMINGHAM: of wave culties and open up great possibilities Cuildhall Buildings, Navigation Street, 2. question ultra short Telegrams: Telephone: broadcasting. We have re- for the manufacturer to develop sets Autopress, Birmingham." 2971 Midland (4 lines). peatedly urged the attractiveness of capable of providing reproduction of

MANCHESTER : 260, Deansgate, 3. an ultra short wave broadcasting ser- outstanding quality. Telegrams: Telephone: vice on principally of Riffe, Manchester." Blackfriars 4412 (4 FRCS). the grounds enhanced quality and comparative CLAscow : 26B, Renfield Street, C.2. immunity from interference. Every- The Straight Set Telegrams: "Iliffe, Glasgow." Telephone: Central 4857. one who listens to the sound accompani- Our Invitation to Readers PUBLISHED WEEKLY. ENTERED AS SECOND ment to television is impressed with CLASS MATTER AT NEW YORK, N.Y. the high quality resulting from trans- T will be remembered that in Subscription Rates missions on a wide frequency band. our Leader in the issue of May Home, £r Is. 8d. ; Canada, LI Is. 8d. ; other The B.B.C. are not achieving popu- 14th we raised the question of countries, LI 35. rod. per annum. larity with the bulk of the listening whether the time had come to endea- .45 many of the circuits and apparatus described in these public when they are obliged to develop vour to follow in Europe recommenda- pages are covered by patents, readers are advised, before making use 0/ then, to satisfy themselves that they would the television by utilising funds which tions which had been put forward in not be infringing patents. it is felt would otherwise be available the States that the superheterodyne to improve the ordinary programme receiver intermediate frequency should service. be standardised, and the authorities Our contributor points out that to asked to avoid allotting this and CONTENTS start an ultra short wave experimental adjacent frequencies to transmitting Page service would be regarded as a develop- stations, with the object of reducing, Editorial Comment 505 ment associated with television. This as far as possible, the present whistles would do much to counteract criticisms associated with superheterodyne re- Aerials 506 Television regarding television expenditure and ception. Broadcasting in Spain 508 the service would appeal to all lovers We invited readers to express their The Hartley Circuit 510 of quality reception and to a vast army views on the matter, which we implied On the Short Waves 512 of listeners who take some interest in could be reduced to a discussion as to Current Topics .. 513 the experimental side. In addition, whether the superheterodyne should be we believe that it would stimulate the considered the universal standard re- The Television Receiver .. 514 sale of new equipment, to the benefit ceiver or whether the straight set Random Radiations .. 517 of the radio industry. had to -day special claims for rein- Listeners' Guide for the Week 51,4 Just why the B.B.C. are marking statement, particularly in view of Ultra Short Wave Broadcasting 520 time instead of launching ultra short recent developments in receiver design The Television Programmes 521 wave transmissions is not clear. It in general. Broadcast Brevities .. 522 seems certain that it is not because of We have already had correspondence any technical difficulties, and there sent us on this subject and publish Television Larger Screens 523 are unfortunate rumours circulating in this issue a letter which contains The " Mag- Nickel " Fuse 523 that the B.B.C. are being influenced a strong claim for the reinstatement of Letters to the Editor 524 by pressure from outside sources which the straight set. Further views would Recent Inventions.. . 526 we feel are not looking at the matter be welcomed.

www.americanradiohistory.com 5oÓ Wireless ¡Porld, May 23íh, 1937

Di -pole aerial with reflector for television reception mounted on the roof of the Science Mus- eum, South Ken- Television sington.

DESCRIPTION OF AND DESIGN DATA FOR SOME SUITABLE TYPES

In Fig. I (a) is shown a plain di -pole Owing to the manner in which the aerial each half of which is a quarter -wave- aerials at the transmitting station are length long, and to the centre is joined a arranged the receiving aerial must be low -impedance feeder. The arrangement mounted vertically, as shown in the dra- depicted at (b) Fig. i is a di -pole also, but ings. Signals could be obtained with the with the addition of a reflector mounted aerials rotated through 90 degrees and behind the aerial. The spacing of the re- lying horizontal, but reception would not flector is a quarter -wavelength. be so good and this method of erection Fig. I (c) shows another form of half - would be satisfactory only when the wave aerial, differing only from the di- transmitting aerial or aerials were sited in pole of (a) in that the feeder is joined to the same plane. one end of the aerial. The hair -pin ar- The actual length of the aerial A for all rangement at the lower end of the aerial the types shown is not exactly equal to is part of the feeder system, and its func- half a wavelength, but is slightly less, and its length is calculated from the formula : tion will be explained later. ' shown in 492 These three aerial systems A (feet) = x 0.94 semi- perspective in Fig. i, which is a fairly F(Mc /s) close approximation to the forms they take which for the vision frequency of television, i.e., 45 Mc's, gives a length of 10.27 feet. For frequencies lower than about 30 Mc / s (ten metres) the length NEARLY all the special aerials approaches nearer now in use for television recep- to the actual half- tion are what are known as di- wave dimension. poles, or some variation of this Thus for frequen- arrangement, the total length of the aerial cies between 28 and being approximately half the length of the 3 Mc / s the factor wave used for transmission. 0.94 becomes 0.95, resonant aerial of this type does not A and below 3 Mc ¡s require an earth connection as it resonates 0.96. by virtue of its own dimensions to the Each wire in the required frequency when suspended in matching t r a n s - space. Thus the system has to be joined former Ai in Fig. 2 to the receiving equipment by a cable (c) should be ex- which, while conveying energy from one to actly half the length the other, does not form an integral part of the aerial A. of the aerial, and if the design of this part Where a reflector of the system is correct the feeder may be is used its length is run round corners, fixed to a wall, and generally made taken through several rooms without intro- slightly greater than ducing any appreciable loss. FEEDER the aerial, and the As a di -pole aerial for television reception need not exceed about ten feet in length it can be erected in a confined space, Fig. 1. -Three popular di -pole aerial though the aerial should be mounted as i I practice, are repeated in Fig. 2, but in systems. In (a) a low- impedance feeder high as possible, and for preference well shown as they are generally depicted is joined to the centre of the aerial. above all surrounding buildings, as only theoretical drawings. Sometimes a reflector is used when the by this means can a good signal with the The plain di -poles of Fig. 1 (a) and (c) aerial takes the form shown in (b). The and both respond feeder can be joined to one end by adding minimum of local interference be obtained. are non -directional, an impedance matching section as shown Of the many varieties of di -pole aerials equally well to signals arriving from all in (c). used in ultra -short -wave work, the three directions. When a reflector is added, types shown in Fig. 1 are possibly the best however, as shown at (b) Fig. T, the aerial suited for television reception. They are takes on directional properties and the re- formula for calculating the aerial length all reasonably simple to design and con - ception is enhanced when it is mounted A should be multiplied by 0.97 instead a aerial struct ; they have the advantage of taking with the reflector and the aerial in line of by 0.94. For television up little space, and they can be erected on with the transmitting station and the re- of 10.27 feet the reflector should be 1o.6 a single pole. flector is behind the aerial. feet long, and mounted 5.47 feet behind

www.americanradiohistory.com Wireless World, May 28th, 1937. 5"7

By Aerials II. B. DENT IT is generally agreed that a di -pole aerial is the most satisfactory for the reception of television as it is simple to erect and if correctly designed gives a good signal with comparative freedom from interference. This type of aerial is not difficult to design, for, as explained in this article, all the essential data can be obtained from a few simple formula.

the aerial. The spacing of the reflector is twisted wires, cab -tyre found by dividing 246 by the frequency cable, and the special low - in Mc /s. impedance feeders, or As already explained, the function of a transmission lines, as they feeder is to convey energy from the aerial are sometimes called, are to the receiver, which it should do with being taken into account, so the minimum of loss. Space does not permit that discussion on matching of a detailed description of every aspect problems will be restricted of aerial design, nor of the conditions to this kind. Ordinary elec- that make for best operation, so it must tric lighting twisted flex is suffice to say that for satisfactory opera- not recommended, since it tion the feeder must be correctly matched is not sufficiently weather- to the aerial and also to the receiver proof for use out of doors. circuit. Feeders have a natural or characteristic impedance depending (a) on the diameter of the wires and also their spacing, other things being equal. If the impedance of a di -pole aerial were the same at all `FEEDER parts the feeder - could be joined in The television aerial with matching section at any convenient for a low- impedance feeder can be seen to place, but as it varies ' L- x/4 -. the left of other aerial systems erected on from about 2,500 the roof of The Wireless World laboratory. 4 MATCHING SECTION REFLECTOR vision aerial, before the vertical turn is .- made. A The possible methods of arranging this in a practical case are shown in Fig. i (a) (c) and (b) In view of this it might be more convenient to join the feeder to the lower end of the aerial provided means could (b) FEEDER be found to satisfactorily match a 72 -ohm line to the 2,50o -ohm resistance prevail- ing at this point. In other branches of Fig. 2. -The same three aerials as shown in Fig. 1, but here depicted radio impedance matching problems often in theoretical form. arise, one such being in the output circuit of a receiver. It is often necessary to ohms at the ends to The other styles, however, are quite suit- match, say, a 2 approximately -ohm loud speaker to a 72 able for use on television frequencies. valve requiring a load impedance of ohms some at the centre For ordinary reception purposes the im- thousands of ohms and a solution is found the position of at- pedance of cabtyre cable may be regarded in the use of a step -down ratio trans- tachment of the as being reasonably well matched to the former. feeder must be care- centre of a di -pole aerial, and it can be The same principle can be applied to fully chosen to joined to the two halves, with possibly an aerial and the quarter-wave matching achieve the correct a short " fanning " for a length of about section Ai shown at the lower end of the matching condi- ift., and by spacing the two sections of aerial in Fig. 2 (c) is in effect an imped- tions. In this article the aerial 8 or gin. apart at the centre as ance matching transformer, and it consists only feeders of low shown in Fig. 3. With the 72 -ohm feeder of two wires run, parallel, but well insu- impedance, such as this " fanning " is not necessary. lated from each other. Provided they are Some importance attaches to the way in each electrically a quarter- wavelength Quarter -wave match- which the feeder is run from the aerial. long the transformer will resonate at the ing section at the It must not run parallel to it, but be required frequency even though the wire foot of a half -wave taken away at right angles from the centre diameter and spacing be varied di -pole aerial designed over quite for the reception of for a distance equal to about a quarter a wide range. Yet the characteristics of television. wavelength, or 5ft. in the case of a tele- no two transformers with different wire

www.americanradiohistory.com 5o8 WAp@Il®00 * MAY 28th, 1937 WopIlc1 Television Aerials - characteristic surge impedance of the regarding stay wires for supporting the size and spacing will be the same. The quarter -wave matching section, Ai, is the mast or pole mounting the aerial, Since characteristic impedance will vary with geometric mean of the two end imped- wires one half -wave long or any number any change in either of these two dimen- ances, and it is given by the formula :- of half waves in length, become resonant sions. systems they will absorb energy, and so If, for example, No. 14 SWG wire is Zt = V Za x Zf reduce the efficiency of the aerial. Thus, used, and the spacing is 4in. the charac- when Zt = surge impedance of matching all long stay wires should be broken up teristic impedance will be approximately transformer. by insulators so that no one piece is Za = impedance at the point of exactly equal to one or more half- waves. attachment to the aerial. Zf = surge impedance of feeder. Taking our own particular case we can insert values for the aerial and for the feeder, thus Zt = , 2,500 x 72 = 424 ohms. To correctly match the feeder in the case of Fig 2 (c) the matching section

A must, therefore, have a characteristic surge impedance of 424 ohms. Since variation both in the wire size, and in the spacing, modify the impedance value some curves have been prepared for Fig. 3. -When the impedance conductors of the most likely sizes to of the feeder is higher than be used in the construction of these 72 ohms matching can be aerials. They are given in Fig. 4. effected by " fanning " the No. 14 SWG enamel wire is a satisfac- wires where they join to the aerial. tory size for a slung or fully supported aerial while i -in tube serves quite well for partially supported and self -supporting systems. 55o ohms, but if the spacing is reduced to From the curves in Fig. 4 it will 2111., the wire size remaining the same, be found that using No. 14 SWG wire the the impedance value falls to 470 ohms. spacing should be r.4in., centre to centre, With a resonant line, or transformer, of to give a characteristic impedance of 424 this type the effective impedance at one ohms. With 4 -in. tube the spacing be- . end can be made to vary by changing the comes 44in. McMICHAEL value of a resistance, or impedance, In this brief treatment of the subject MODEL 137. shunted across the other end. Take, for much relevant matter has had perforce to Twin fit- . speakers are .example, a transformer designed to have be omitted, but sufficient data is given to a characteristic surge impedance of 500 ted in this new all - enable a perfectly satisfactory aerial for wave superheterodyne just released ohms, and RF at the optimum frequency television reception, or for that matter for by McMichael Radio Ltd. The Io- is fed into one end. If the far end is work on any of the ultra -short waves, to inch square dial tilts forward as shunted by, a 5oo -ohm resistance the be designed. the lid is opened and has a glass cover with- effective impedance at the input end will a specially prepared surface upon which the In conclusion a few words night be said settings of short -wave stations can be marked. also be 500 ohms, or the same as the surge impedance of the transformer. On changing the output end resistance to 1,000 ohms the impedance at the input end falls to 25o ohms. Thus a matching is effected between r,000 ohms and 25o Spanish Broadcasting ohms without any appreciable loss in energy. Transmissions in English from the Seat of Civil War In all matching systems of this kind the By IVOR MANLEY

600 VER since Civil War broke out in hours, only transmitting when they think

I I No 15 SWG WIRE the Peninsula many listeners have they have some news of topical import- 550 been regularly receiving the Ó broad- ance. Others are hard to receive during z No 14 SWG WIRE F casts of war news from the various the usual broadcast hours as their wave- w 500 Spanish Government and insurgent lengths coincide with some of the more CI- rn îï stations. Other listeners, however, have powerful European stations ; in other 450 U had little success in locating the stations, cases when one Spanish station starts F z 4 TUBE owing to the constant changes of wave- transmitting an enemy station will 400 start wQ o length made by some of them, and on the same wavelength, making recep- r N also through lack of knowledge of the á 350 tion impossible. This is done purposely cc times during which transmissions are so that the transmission will not be heard ; _ O 300 made in a familiar language. The accom- such are the tactics of war in the ether. panying list of stations, which is as com- The best time to listen is after 8 p.m., 2500 plete as circumstances will permit, should as by then nearly all the 2 3 4 5 6 stations are work- help to overcome these difficulties. When- ing, though it is improbable SPACING (S) IN INCHES that more ever news items are in English the times than six stations will be heard on the of transmission have been inserted, medium -wave band before ii p.m., as so Fig. 4. -The characteristic impedance of though they are liable to variations. many of them are drowned by the more quarter -wave matching transformers using found wires or tube of the sizes given here and with It will be that many of the powerful European transmissions. On the different spacings between conductors can be stations are very hard to receive, purely short -wave band several official stations obtained from these curves. because they have no fixed working have sprung up, besides a host of

www.americanradiohistory.com MAY 28th, 1937 WAT@Il@@0 509 WOpIld amateurs who are difficult to identify, as is very often followed by patriotic Germai :onstantly changing their wavelength and they rarely give their proper call signs. and Italian songs or marches, such as hours of transmission, and what is more Some of these short -wave stations, such Giovanezza." Reference to the important is that he should persevere, as Barcelona ECNI, for instance, relay " Frente Popular " is an indication that otherwise he will not be rewarded by hear- their transmissions simultaneously from the station is controlled by the Govern- ing many of the lesser stations. the medium -wave band. ment ; their stations usually 10 GOVERNMENT STATIONS Distinguishing and verifying the various close down with the " Inter- NATIONALIST STATIONS SANTANDER stations is not at times an eàsy matter, as nationale." COR UN NA / OVIEDO SAN SESASTI AN they sometimes borrow the call signs from The foregoing should be OIL BAO other stations, and especially from those a help to the intending PORTE VEN ORA stations belonging to the opposite party. listener, but he should UR O OS By listening to the news bulletins one can bear in mind that many of VALLADOLID soon find out for which side the station the smaller stations are *3 .3 L AM ARC O works, as they nearly always criticise the O DAL CALA other party. All the Nationalist stations MADRID The principal broadcasting E TO LE DO close down with the following announce- stations of the contending AL EN CIA : ment " Viva Franco, Viva España " parties. O (Long live Franco, Long live Spain), this AL9ACETE o

S_""VILLE

MALAGA LIST OF SPANISH STATIONS CADIS

IN ORDER OF FREQUENCIES TE TUAN 0 x0 U. lSO 200 SCALE IN MILES Abbreviations : P, Party ; G, Government ; I, Insurgent, All times B.S.T.

No. P. Station Name. Call Sign. kc /s. Metres. kW. Transmission Times and Notes. 2115 General Quripo de Llano 1 I Seville ...... EAJ 5 731 ' 410.1 5.5 News in English between 1900 and (time varies). speaks nightly at 2330. 2.\ G Madrid ...... 1,-\.12 731 410.1 3.0 German, English and 3 G Barcelona ... I; \.I I 795 377.1 7.5 Transmits at intervals from 0900. News in French, Italian, Portuguese from 2315 to 0100. 4 G Valencia ... -- 550 352.1 3.0 Relays No. 3, EIJ1. Also transmits a separate programme. 5 0 Barcelou:t EAJ 15 1.022 293.5 3,0 ti L Oviedo ... 1.1122 293..5 (1.7 - liberación de Espana." 7 I Salamanca ... 1,085 271,9 50.0 " Atención, Atención, Aqui Radio Nacional al servicio de la - Transmits from 1500 to 1600, 1900 to 2100 and 2230 to 0130. News in French, 21.50 ; male announcer. News in English, with a woman announcer. at 2255 and at 0100 ; also sometimes in English from 2200 to 2230. Frequency as 'measured by Tatsfield is 1096 kc /s (273.5 m.). 8 G Madrid ...... P \.17 1,095 271.0 5.0 Very rarely heard. 9 (1 Bilbao ... ,.. 1:_\03 1,258 233.5 1.0 " Habla Itadio Bilbao." News in English at 2100, except Sundays. Ex San Sebastian, EAJS. Requests reports. Address : 111.18, Bilbao, Spain. 10 I Burgos .,. ... 1,238 233.5 - " Habla Radio Castilla del Burgos del servicio do la liberación de Espana." - Transmits from 1500 to 0100. la 11 I San Sebastian .., 1:_\03 1,253 238.5 1.0 " Aqui Radio Requetó de Gnipuzcoa at servicio de Espana y por Espada." News English at. 1320 and 2040. Tra.n.sntitter situated at Monte Igueldo. Espana." Operated by the 12 G Barcelona ,,, ECNI. 1,313 222.5 - " Aqui E.0 :N. uno, Radio C'.N.T. /F.A.I., Barcelona, C.N.T. News in English at 21.50 and 22330 ; French at 2210. 13 G Santander ,.. - 1,129 209.9 - " Aqui Radio I3asque." 11 I Burgos ...... EAJ27 1,142 205.0 - Alternative wavelength for No. 10, Relays Bilbao (41 in.). 15 G Bilbao ... 1 ?_\.1st 1,113 207.0 - 16 I Valladolid .,. EA.117 1.192 201.1 - Relays Valladolid (42.83 m.). 17 G Radio Alcala .,, - 1,5110 21)0:0 0.2 18 G Madrid ...... EAQI 4,000 75.0 2(1.0 Alternative wavelength for Madrid (30.43 in.) with which it usually works simultaneously. The wavelength is approximate. 19 G Barcelona ,,, ECP2 0,100 . 49.19 - 20 I .., .., 6,230 48.0 Works simultaneously with Burgos (20S Burgos - - Espanol News in English at 21 I Radio Tetuan ... - 6,507 40.1 5.0 "Aqui Radio Guardia Civil Tetuan Marnecos 2100 ; French at 2145 ; Arabic at 2200. ('roses at 23 00. 22 G ... ECNI 6.995 42.85 Relays Barcelona (222.5 in.). Barcelona - Valladolid." At 1915, 23 I Valladolid ... FEL 7,000 42.S3 - " Transmite Falange Espanola Itadio E.stacion F.E.L. French ; 1930, English. 24 I Vitoria ... ,.. - 7,040 92.5 - " Transmite Radio Requeté Vitoria." 2a I Malaga ...... - 7,1(I6 42.26 - 26 I Corinna ... ó.A.111 7.113 42.0 Wednesdays. . 27 G Madrid ...... EAIFIG /FGL 7,143 42.0 - News in English from 2330 to 9109 on Sundays and 28 I Jaca ... EA2BH 7,177 41.8 - News in English at 1615. '29 San Sebastian ... EUJS 7,200 41.65 1.0 Relays San Sebastian (238.5 m.). I al -servicio de Espana y por 30 I Durango ... 7,230 41.5 . " Atención, Atención, Aqui Radio Requetó Durango - Espana." 0230. 31 I Radio Requeté... 7,233 41.5 "Aqui Radio Requetó del trente de Madrid." Transmits from 2015 to Situated - - on Madrid front. 32 I Burgos ...... 7,230 41.5 Alternative wavelength for Burgos (18 in.). - - in English at 2150. 33 G Barcelona PSI I 7,29.3 91.15 - Relay station. Sometimes gives news 34 Cl Bilbao ,.. ,,. 7.297 41.1 llelays Bilbao (238.5 m.). - - 0100. News 3.5 (1 Bilbao ...... EAJ28 7,300 41.0 " Habla Radio Bilbao FJ'2." News in English at. except Sundays. - in French at 2330. Closes with " Viva la Republica." 3(; G Madrid ... ,.. t1GT 7,400 40.6 - News in English at 2130 ; in French at 2200. Closes 2300. 37 1 ...... E A.119 '7,430 40.1) Toledo - 2015 33 G Madrid ...... EAQ2 9,150 31.65 20.1) "Aqui la Voz de la Liberdad." News in English on Tuesdays and Fridays from to 2200 ; also sometimes after 2100. News in English on Sundays at 2100. Situated at Vallecas. Ex EDZX station. when Madrid EAQ1 is not working. 39 G Madrid ...... II TOT 9,400 30.43 - Relays Madrid (19.6 in.) and works at times 40 G Madrid ...... 1:AQ1 9,500 ::0,43 20.11 " Aqui la Voz de Espana." Transmits daily from 2315 to 0330 ; Saturdays at 1900 to 03316 News in English at 0030 and 0200, except Sundays ; also sometimes at 2150 on Saturdays. News in German at 191.1 on Saturdays. News in French at 0015 daily and 2015, and 0015 on Saturdays. The programmes at this station are not very regular at present. Situated at Aranjuez. 2315 41 I Tenerife ... E 1.143 10,36(1 23.91 4.0 " Aqui Radio Santa Cruz de Tenerife." Transmits daily 2000 to 2120, to 0100 and 0145 to 0215. News in English at. 1900, 2200 and 2400. 42 I El Tablero ... TDR3 10,362 21.93 - 'Radio Club of Teneriffe. News in English at 219920 and 0030. 93 I Salamanca ... - 12,820 23.4 - Short -wave station for Salamanca (271 in.). Usually transmits C'W.

www.americanradiohistory.com 510 Wireless World, May 281b, 1937. The Hartley Circuit

PROPERTIES AND By M. G. SCROGGIE, B.Sc., A.M.I.E.E. SOME UNUSUAL AFTER having traced in last week's issue the evolution of the APPLICATIONS Hartley circuit, the author goes on to discuss the general J properties of the single -coil oscillator and to show how it can be (Concluded from page 487 used as a simple valve tester. May 21st issue) tion voltage across the grid portion of the with this material it boils down to the rela- THE ready oscillation for which the coil is (for simplicity) i volt. This is tively simple form (Ra + R)S2 + (2Ra is noted is due the amplified by the valve in the usual way, Hartley to pR)S + Ra(i + = o. Even this looks very close coupling that it pro- according to which the amplification is -) vides. Even if the grid and tiP rather involved, but there is no need to R- - , where p is the load in the anode puzzle anode sections of the coil are entirely P. over it unduly, for what it means separated, the tuning condenser causes circuit. As the grid voltage in our case can best be gathered from studying the enough coupling to make oscillation pos- is I, the voltage developed across the curve sheet, Fig. ii. As there are five sible in most cases. But, in the investiga- quantities, and a single curve on a sheet tion that follows, close inductive coupling anode portion is Ra `P ; and, as has just of paper can show the relationships is assumed. In fact, the coupling is P between only two, some fixed values must assumed to be too per cent., so that the been explained, p is equal to R(-, be assumed for the others. The valve is voltage ratio between anode and grid is - / assumed to have easy round numbers for the same thing as the turns ratio, S, which and this is substituted for p to give .the its characteristics : p = to and Ra = to,000 ; anode turns. voltage in terms of the quantities entering g is therefore t milliamp. per volt. What is equal to The other grid turns into the problem. But we already know happens with other characteristics can quantities involved are : this anode voltage in another way, because easily be deduced. as will be explained R, the dynamic resistance of the tuned presently. Suffi-. M. IMEwMEN. 100,000 cient values of S circuit. M-ISMMMI MII INMNIMEEE,NMMEtEEI1- MMEE=E1E MiNIini1.1 1 are Ra, the anode AC resistance of the 1=111111111111111 11...IImolo1m... =11MMM..1NIIIIIMIZEMIIM given to show valve. 1, M111IMMMII \\II11111111111111111111=111- 50.000 quite clearly the Rg, effective AC input resistance smmm 1111 111\\IIIII effects of varying 111111=11 between grid and cathode. . I11IME1III the tapping point p, the amplification factor of the valve. 111IÌlf II11\ 121IIÌüiMP!MII 20,000 on the coil. g, the mutual conductance of the valve. Examining the curves, look first at iIMMENMI=MIEE.II1111111MiiISHERIIIR111 MMEIMmMENNMMMEMMZ.ME 10,000 (= R-1à). R is assumed to take account of 1M.I=MMEEMINE M ...1...>_..I I E-N\ MMEI MM-MINO EE-NMI-MII the top of the all causes of loss or damping except Ra 1M1N sheet, where Rg is 1U 1\\111N: _-__- 5,000 and Rg. I\\1 l1\11B11M1. about ioo,000 It has already been mentioned that thI 111111 Imeicrimm.mmillimm! ó ohms. This is the oscillating voltage across any part of tht ÌRMeeMi! order of resistance 111 2000 CC coil is in proportion to the turns -this introduced when assuming it to be a perfect transformer. the grid leak is 111111 I \;;!11111111-C-IN:.....MI=MI about a quarter of a The other important working principle is ..IMMI.11111. .1=-.,.E.__.101. -MENI.. that any resistance VMM. M.:\\ lameN aS=M..-.... megohm. For tap- connected across an MEMINI111u -6=spiTih11111 nth part of the coil is equivalent to n- x ._..._ wmmo.. 00 pings that are not too near the anode that resistance connected across the whole /r -so -1 coil. Thus if S = 2, the grid turns are one - end (i.e., for S not third of the whole, and the effect of Rg is 1IIIIII MGM111111 200 much less than t) the same as that of putting nine times Rg Rg can vary con- across the whole coil. And R, the whole iiiiiiiiuiuiniiiiiiiiii 100 siderably without § ö g affecting things R coil, looks like R x (3)z to the output from ó gn R OHMS the anode of the valve. Having grasped this, one can calculate the proper place for the tapping. In it is proportional to the coil turns on the Fig. 11.- Diagram from which the best highbrow technical circles, after saying anode side ; in fact, it is equal to S. So tapping point on the oscillator coil can be " one can calculate," it is etiquette to the voltage, as a quantity, can be elimin- determined for various conditions. Other ated from the problem entirely, and any uses of the curves are explained, and still leave it at that in order to sustain the others can easily be thought of. polite fiction that all members of the said one from among S, R, p and Ra can be circles can dash off any mere calculation calculated when the remainder are specified. The effect of Rg has. been neglected on a shirtcuff or in the mind. Actually much. Take S =I ; Rg can drop to Io,000 they, as well as everybody else, really like so far ; when it cannot be assumed to be ohms before the power of oscillating low to have the results displayed clearly and infinitely large it can be allowed for by values of R is impaired appreciably. concisely without the labour of working converting it to the equivalent resistance When one considers that a good radio - them all out. So only the general method across the whole coil (i.e., in parallel with tuned circuit has a R of over ioo,000, and will be indicated here before showing the R), which is Rg(S + t)'. So instead of R that under the conditions selected a valve RRg(S+ t)2 results as curves. we must use of even such a moderate conductance as Assume that steady oscillation has R +Rg(S+ t)=' I mA /V will oscillate with a R as low as already been set up and that the oscilla- When all the heavy work has been done 5,000 ohms, the readiness of the Hartley

www.americanradiohistory.com MAY 28th, x937 3®l® WOPld The Hartley C;rcuit- wards, giving the well -known phenome- be small compared with u, then for ordin- circuit to oscillate can be appreciated. non of " squegging." ary practical accuracy the resistance across Naturally, as the grid loss increases (Rg But the valve may have no grid con- which oscillation can just be maintained decreases) the power available for the denser and leak. In that case no bias is is inversely proportional to the mutual oscillatory circuit is correspondingly less, applied ; the average Ra is, if anything, conductance, g, of the valve. The thing and R must be greater to keep oscillation reduced, driving oscillation all the more can be worked out in this way :- g oin fiercely ; but against that a large amount Fig z2 shows the circuit diagram ; it is But note what happens to S. When Rg of grid current flows, causing Rg to drop easy to see that it is based on Fig. 4. In is large, the most persuasive S seems to be away down. In this case the working fact the only difference is a variable resistance about z -a centre -tap (to be more exact point falls to meet the S line ; in the former r with a maximum of about the S line rushed up to meet the working 25,000 ohms, which serves to adjust Rg. it is + , or 0.83 in this example). But The grid leak is so high -a megohm, for very large, so that all the power instance -that it affects Rg very little. The when R is tuned goes to overcome grid losses, it is more circuit has as high a dynamic resistance as effective in doing so if the tap is moved possible, but this is preferably achieved by a minimum of losses rather nearer the grid end (S =2). than by using a very small tuning capacity ; the latter would allow stray It is only at ultra-short wavelength, capacities to upset the tapping ratio. The that one is likely to want the full capabili- coupling between the two sections of the ties of the circuit merely to keep oscilla- coil should be as near zoo per cent. as tion going at all. Then R cannot be verb possible, in order to justify the assumption high, and Rg is lower than most people on which the curves were based. To imagine -1,000 ohms, or that sort of fulfil these conditions the coil may be an thing. But at ordinary wavelengths the efficient iron -core transformer with a ratio working point is much more likely to be of i : 3 or thereabouts and a total in- well up in the postage -stamp corner of th.. ductance (with windings connected in sheet. Suppose R is 112,000 ohms and series as shown) of about 3 henrys, in Rg is 100,000. Then S can have either parallel with a good condenser of 0.005 of two values to bring the valve to the Fig. 12. -A simple form of valve tester, mfd. giving an oscillating frequency of oscillation point -9 or 0.02. This means giving direct readings of mutual conductance, rather more than z,000 c /s. that the tap is near one end or the other. based on the information given on the curve The resistance r may be calibrated to It can never quite be as large as u, but sheet, Fig. II. read g direct in milliamps. per volt. The it can be -but seldom is in practice --very valve to be tested is plugged in, the volt- close to the anode end. It is rather in- point. Other contrasts are that the anode ages at which the test is to be made are teresting to notice that if Rg _is equal to current rises instead of dropping, and applied, and r is slowly increased until Ra the two alternative tappings are at there is no squegging. But the valve may the milliammeter reading begins to fall, equal distances from the two ends of the destroy itself in the effort to stabilise indicating the start of oscillation. Phones coil, whatever R or u may be. But what operations. could be used instead, except that unless happens, you ask, if both R and Rg are To find how matters stand when the they are shunted down to a very low re- large, and instead of tapping near the end valve characteristics are different from sistance they would introduce some error ; you go right into the middle of the coil? those assumed one is greatly favoured by also the milliammeter reading is an extra The working point is then nowhere near the fact that if the curves are plotted to check on the valve. the proper S line. logarithmic scales they are all of the same shape. A piece of paper can be cut out Cheap and Rapid Testing Negative Bias and moved over the sheet to show these other conditions. The rule for different This scheme has been tried, and works What happens is that the valve pours Ra is easy. Move the curve along a quite well. It is about as cheap and so much more power into the circuit than diagonal line so that if Ra is reduced rr simple a tester as could be devised, and is needed merely to maintain the status times R and Rg are both reduced n times. allows of rapid testing of large quantities quo of oscillation that the amplitude goes and vice versa. An example is shown of of valves. On the other hand, the on growing until something shifts. If the Ra reduced to one -third -3,333 ohms. accuracy is not of a high laboratory pre- to an in- circuit includes a grid condenser and leak, This is, of course, equivalent cision standard ; and -a more serious the oscillation is rectified thereby, pro- crease of g to 3. It is possible to increase drawback -while the range of measure- ducing a negative bias which causes the g to 3 in another way by increasing u to ment in the upward direction is unlimited, internal resistance to rise, and the whole 3o, leaving Ra, as before, at zo,000 ohms. it is not practicable to measure very low set of curves in Fig. xi ceases to apply The result is nearly, but not quite, the values of g such as are obtained with vari- (they were based on the assumption that same ; changing Is is a little more compli- able-mu pentodes under conditions of Ra is 10,000 ohms). Actually the whole cated, as an increase from to to u, neces- maximum bias. The limit is set by the lot are shifted bodily towards the top sitates multiplying the R and Rg figures dynamic resistance of the oscillating cir- working spot I() S. cuit, and 0.03 mA /V is about as small as right-hand corner until the by - When S is small compared is touched by the right S line. Any fur- u, -S one can go to. ther move would bring it to the lower - with either io or u, it can be neglected, Incidentally, it not essential for r to be left of the S line, which would have the and the process is then as simple as for across that particular section of coil ; it effect of causing oscillation to die out, so Ra. may be across any or all of it, according to reversing the movement of the set of the range of resistance that may happen curves. If the working point (Rg, R) had Determining the Tapping Point to be available. been only just inside the S line, the adjust- Summarising the whole business : ment would settle down quietly, with a Some of the many uses of these curves The Hartley oscillator circuit is the most steady negative grid bias and reduced Ra. have been shown-to calculate the correct generally useful and freely oscillating, and But when it is far inside the growth of tapping point for known conditions ; to by slight modifications can be adapted to oscillation is so violent as to cause the S find what happens with a given tap ; or to meet almost ail conditions. line to shoot past the mark ; the working discover whether a valve of certain charac- The shape of the curve connecting tuned point finds itself right outside, where no teristics will oscillate under given condi- circuit dynamic resistance (R) and grid oscillation is possible ; there is a violent tions. They can also be made the basis input resistant a (Rg) at the point of oscil- reversal, and so on, backwards and for- of a valve tester. If S is chosen so as to lation is the s: me irrespective of the valve

www.americanradiohistory.com WATISE®Ego MAY 28th, 1937 WCglid The Hartley Circuit- - dition (for overcoming grid loss Rg) is symptoms of the April storm, which was characteristics or coil tapping point ; and the worst for 5o years, point to neutralisa- varies only in position (assuming loga- when S = tion of the F region ionisation (negative 2 electrons) by positive rithmic . particles gathered up scales) When R and Rg are such as to bring The effect of changing the internal re- by the earth's magnetic field, this type of the working point to the lower or left side storm! therefore, being the complete reverse sistance of the valve (Ra) is to shift the of the appropriate S line there is no oscil- of that due to the bright hydrogen eruption. curve so as R diagonally to alter both and lation. When it is on the upper or right It is significant that the latter variety of Rg in the same proportion as Ra. side oscillation increases until the working short-wave fade -out has but little effect The effect of changing the amplification point and / or S -line are automatically upon the earth's field, what effect it has factor (!I) was first discovered of the valve is to shift the shifted so as to coincide. The way they by an English amateur curve diagonally so that R and Rg are astronomer in 1859, before the radio era, shift depends on whether or not a grid strangely enough. proportional to and when S, the leak and condenser are used. The large changes, or the fall of ionisation p. -S To obtain oscillation S must always be ill the F region, do seriously affect the ratio of anode turns to grid turns of the coil, less than p. earth's field, however, it being rather a curi- is small compared with IL, R and Rg are If R, Rg, and S in the just -oscillating ous case of cause and effect via the same inversely proportional to g, the mutual condition are known, the valve charac- agent. conductance of the valve. teristics can be derived from the curves. In the first place, the steady magnetic field When the grid loss is unimportant, the The most convenient formula for calcu- gathers up the charged particles, these in turn decrease the ionisation of the F is : most powerful oscillating condition is lating curves (and, perhaps, lower) regions, which fall in reached when the tapping point is S = A Rg (+r)z Ra electron flow again, as in an electro- R= , where A= magnet, and give rise to changes in the '`' , which is practically a centre tap un- Rg-B' S(µ -S) p+ 2 earth's magnetic field. Ra To suggest, therefore, that short -wave lessµ is unusually small. When R is very and B= high, the most powerful oscillating con- S(p, -S) fade -outs are due to magnetic storms is in- correct, the reverse being true. A further point of considerable interest is that during the sunspot minimum years auroral displays are seen, when ionisation levels in the polar regions at times fall normally to very low values, due to darkness On the Short and lack of solar activity. It might, therefore, be true to say that low levels of ionisation in the F region are productive of aurora, whether these low NOTES FROM ionisation levels are produced naturally or waves by the ejection of charged particles by the A LISTENER'S LOG sun. It should, perhaps, be explained that were the particles not charged they would IT was most fortunate that the period of a service directly from this country to not be affected by the earth's magnetic very poor conditions occurred before Australia during the summer daylight hours field, and the disturbance would then not May 12th, otherwise the elaborate arrange- here, but all was well because Australia be concentrated in the polar regions. ments made by the B.B.C. at Daventry to picked up the broadcast relayed by Hong Owing to absence from London I am give world coverage to the Coronation Kong, Schenectady and Montreal. afraid the report on station reception will broadcast would not have been so successful Although Capetown and the Union gener- be short this week. as they seem to have been. ally fared badly, the King's speech arrived On Friday, May 7th, conditions appeared In all, six transmitters and a large propor- safely via kugby, however, the rest of to have become good again, and a station tion of the X25 arrays at Daventry were in Africa appears to have enjoyed excellent on r8 Mc /s, relaying the Kalundborg- practically continuous use from May 9th results on GSH 21.47 Mc /s during the Copenhagen programme, was heard at excel- hours of May 13th, when Abbey ceremony and the commentaries on until the earlier lent strength around 8 p.m. . the last recording of the ceremonies and the processions, and on GSI 15.26 Mc /s in Good results were also obtained from all H.M. the King's speech was broadcast to the evening. the stations regularly received in this the Antipodes. S. America was very enthusiastic, too, country, especially W2XAD and WIXAL, Two of the six transmitters were of 10 -kW about reception on GST 21.55 Mc /s until but excepting W3XAL. power, the original transmitters installed quite late in the evening, including the At 5 p.m. on Saturday, May 8th, very in 1932, two of 20 -kW power, one old G5SW, broadcast of His Majesty's speech. good signals were noted from W2XE on plus a new power- amplifier using a push - "In all, during the day, three 14 -metre 21.52 Mc /s, this station with his new trans- pull demountable screened -grid valve,, and transmitters were used, the third being GSJ mitter is certainly a valuable addition to the finally two new 50-kW transmitters, the 21.553 Mc /s directional east and west, and, short -wave spectrum, and would do well to figures, of course, refer to output to the perhaps, it was due to this latter trans- stay on 21 Mc /s until much later in the feeder lines, and not the input . power, mitter that Singapore reported good recep- evening. figures given for input power are always tion, even though a thunderstorm was in Later on Saturday evening W3XAL was very misleading. progress locally ! fair, but W2XAD was really very good at One point of interest was that during the After the final Coronation broadcast of II to 11.30 p.m. with a Coronation pro- evening, owing, presumably, to the shortage May 13th, two of the transmitters were gramme by the Schenectady " Kiltie of channels in the 17 -Mc /s band, two trans- taken out of service, and Daventry is now Band," all the pipers being ex- service men mitters were announced to be in operation on . normal schedule with the . other four, from the Scots Guards. This broadcast simultaneously on GSG 17.79 MC /s, one some of which give almost 'local station was relayed from the lawn outside WGY serving N. America and the other the West signals in London during the evening. itself. Indies. During the remainder of the period listen- This is probably the first time that syn- Sunspot Activity ing was mainly confined to W3XAL, in par- chronised, or more correctly isochronised, ticular to Howard Marshall on " They short -wave transmitters have been used Conditions have continued to improve say in London " at 8.4o p.m. on Sun- under service conditions. during the past few weeks, although there days, and to W2XAD, particularly for the It is understood that reception of the is again signs of very considerable sunspot Tuesday 11.30 p.m. " Mailbag." Coronation Day broadcasts was excellent in activity, and the disastrous spot of April A good Nirom programme was inter- nearly every corner of the world, the only 22nd -29th is " back again," following the cepted from PMC on 18 Mc /s at midnight poor reports of direct reception of Daventry 27 -day solar rotation cycle. on May 16th. however ; a mixed bag of coming from Australia and Capetown, when There has, so far, been no evidence of a Javanese and Western music. the morning broadcasts was not very well further burst of positively charged particles Finally, W2XE was noted as being really received. from the sun, which gave rise to the violent excellent on 21.52 Mc /s at 1 p.m. on Whit - It is, of course, almost impossible to give changes during the end of April. All the Monday afternoon. ETHACOMBER.

www.americanradiohistory.com Wireless World, May 2Sth, 1937 '513

EVENTS OF THE WEEK IN Current Topics BRIEF REVIEW Television in New York Sundays, the time of transmis- Another Broadcasting mitters has, as a matter of fact, THE new 441 -line television sion being ¡loo to 130o, and will House already begun, and it is hoped station which the Columbia use the same wavelength as THE construction of the new that the stations will be in opera- is to erect Sydney. tion by the late summer. The Broadcasting Service station building at Katowice, total number on top of the Chrysler Building, Poland, has now been com- of Italian listeners the city's second loftiest sky- Wireless Exports menced. It will be completed on March 31st was only 719,000. scraper, will have an estimated DURING 1936 American radio in 1938. range of about 40 miles. manufacturers exported New N.P.L. Director 642,368 receivers, valued at Italian Plans Radio N the new Convention signed DROFESSÓR W. L. BRAGG, Automatic Car 15,000,000 dollars. O.B.E., F.R.S., at present THE preselector principle in between the Italian Broad- casting Company and the Langworthy Professor of gear- changing which is avail- Thumbs Down for Physics in the University of able on certain cars is to be Government there are extensive Television plans for expansion. Five short- Manchester, has been appointed applied to car radio in the Director of the National are being brought is reported that the Italian wave stations are to be built U.S.A. Sets IT to the Physical Laboratory. H3 will out whereby the car -driver can broadcasting authorities have for broadcasting Italian definitely decided not to attempt colonies. Two of these stations assume his duties during the bring in any one of half -a -dozen autumn. broadcasting stations to put television on an entertain- are to have a power of zoo kW ; preselected ment basis at present. of the remaining three, two are by pressing the appropriate They are of opinion that it has not yet to have a power of 40 kW and Another Beam Station button. attained a sufficiently reliable one of 5o kW. Two Too kW AT present a telephone sub- Radio Histrionics technical standard. Transmis- medium -wave stations for Rome sions are, however, being made and a new broadcasting house scriber in Scotland can is hoped to establish shortly speak to America or Australia, IT in at intervals from an experimental for Turin are also to be erected. the first radio academy station. Work on the two Rome trans- but not to many of the Outer Vienna. The proposed institu- Hebrides. There is already a tion will cater for the training cable to Lewis, but the Post of announcers, commentators, Office are considering the ques- and others in the special require- tion of improving communication ments of the microphone. Artists with the Western Isles by means will also be instructed in the of a wireless link. technique required for broadcasting. Wireless in " el Campo " More Interference THE Argentine Government is THE growth of " wired wire- very anxious to extend the less " for inter -office com- number of broadcast -listeners in munication in the U.S.A. has remote country districts, and led to fresh complaints of inter- with this end in view the Ministry ference with broadcasting. In of Agriculture has appointed a this system of communication, committee to determine the type modulated radio frequencies are of receiver most suitable for use passed along the ordinary electric in places far removed from the lighting mains. Complaints are amenities of towns and cities. being made that conversation can wire- be picked up on ordinary Gold Watches for less sets in the neighbourhood. Listeners SW Conference IN Poland the number of THE Vienna short-wave con- licence -holders shows a rapid gress will be held from July increase since the introduction ¡rth to the 17th. A certain' of an inexpensive " People's amount of inconvenience has Set." Many, however, attribute been caused owing to its follow- the public's new zeal for licence - ing immediately after the Inter- buying to the fact that a gold national Conference of Radio watch is being presented to the Art, which is being held in Paris buyer of the licence completing from July 8th to loth. Dele- each ioo,000. The buyer of gates who wish to attend both licence No. 600,000 has just re- these events will be compelled ceived his watch. to make a very hasty all-night journey across Europe. An Interesting Experiment AYEAR ago the directors of Australian SW a large hat factory in Programmes Vienna decided to provide DURING June Sydney workers with broadcasting pro- (VK2ME), working on 9,590 grammes, as they had heard so kc /s (31.28 metres), may be much of their beneficent effect heard on Sundays from 050o to on output. After a full year's 0700, 1000 to ¡400, and 1630 OUTSIZE IN RECEIVERS. -Almost every conceivable refinement is trial the directors have failed to to 1830. Melbourne (VK3ME), embodied in this 37 -valve American Crosley receiver, which is fitted note any improvement in this using a frequency of 9,510 kc / s with no fewer than six speakers, which between them are stated to respect. They admit, however, (31.5 will be working cover a frequency range of from 20 to 26,000 cycles if required, though music does metres), the cut -off is generally set at 12,000 cycles. Automatic tuning and that the not appear from 0900 to 1200 daily except volume expansion are included, and, in addition to a general control to have any distracting in- Sundays. Perth (VK6ME) will, of tone, provision is made for individual adjustment of the lower, fluence. as the workers' output also be heard daily, except middle and upper registers. Maximum power output is 75 watts. has not fallen.

www.americanradiohistory.com j T1 Wireless World, May 28th, 1937

T'1e Television Receiver X.-VISION -FREQUENCY AMPLIFICATION

By W. T. COCKING

l -ST as in the case of the AF amplifier of a sound receiver, there are many possibilities of distortion in a vision frequency stage, and careful design is necessary if a high standard of performance is to be secured. The design of a VF amplifier is discussed in detail in this article.

T was shown in Part IX of this series sponse, and this is usually taken as the that the use of vision -frequency am- frame frequency -5o c / s. The upper plification does not prevent good limit is fixed largely by imperfections in synchronising from being obtained, the rest of the apparatus, including the for it is possible by an artifice to replace transmitter, and is taken as 1.5 2.o the DC component of the signal after it Mc /s. Let us take it at 2.0 MC s. has passed through an amplifier which is The other two forms of distortion are not responsive to very slow variations in ones which are rarely considered whe,n its input potential. Since it is possible to dealing with sound apparatus ; they are secure greater gain per stage and a larger phase and transient distortion. Phase dis- output from a given valve at vision fre- tortion occurs when signals of different frequency than at radio or intermediate quencies take different times to pass frequency it will obviously pay us to through the amplifier. The response to adopt at least one such stage. It is con- an amplifier embodying pure resistance sequently necessary to consider methods couplings is, practically speaking, instan- Fig. 26. -A typical VF stage is shown here. ' of VF amplification in much greater detail taneous, but if the couplings are reactive, The condenser Cr represents the stray than we have done hitherto. then a certain time elapses before the full capacity. There are four types of distortion which response is secured. Such a time delay can occur in a VF amplifier and each is would not matter if all frequencies were has negligible frequency distortion over important in television. Frequency and equally affected, but they are not, with the same range, but the converse is not amplitude distortion are, of course, well the result that the output waveform of the necessarily true. known, for we are familiar with them in amplifier differs from the input. Now let us consider transient distortion. sound equipment. In such apparatus Now, with the "types of coupling em- If we change the input voltage of an am- amplitude distortion is by far the more ployed -that is, resistance -capacity with plifier suddenly we are in effect applying important, for the ear is very sensitive to or without correction -phase shift occurs a signal of the waveform shown in Fig. 25 it and remarkably tolerarit of frequency whenever the circuit impedance becomes (a) ; the voltage rises instantaneously from distortion. In television, however, the appreciably reactive. At low frequencies one value to another, at which it is main- position is reversed and quite a large the coupling condenser and grid leak are tained. With a perfect amplifier the output waveform would be identical, but with a good practical amplifier it is more like that shown at (b). Owing to the time delay (phase distortion) caused by reactive circuits the voltage cannot rise instan- taneouslx and the final value is not reached until after a certain time has elapsed. This is distortion, but it is unimportant if the time is small enough. With certain circuits, however, notably those in which a choke is used for high - frequency correction, the output waveform may be quite different. The effect obtained is shown in Fig. 25 (c), and it will be seen that the output voltage rises rapidly to a value greater than the normal Fig. 25. -A sudden change of voltage such as that shown at (a) will be distorted in the manner depicted at (b) by an amplifier with a limited high- frequency response. With an amplifier of level, then falls below it,- rises again above the type of Fig. 26, however, the output voltage may be like that of (c) if the values of it, and so on until after several oscillations components are not properly related. about the normal level it finally settles down at this value. In other words, a amount of amplitude distortion can be responsible, while at high frequencies the damped oscillation is set up in the inter - tolerated ; indeed, a certain amount may coupling resistance and stray shunt capa- valve coupling. Under suitable conditions actually be desirable. The range of fre- cities produce the effect. Phase shift is the effect may be very disturbing. The quencies over which amplification must be thus caused by precisely those elements waveform of (a) occurs when there is a maintained at a uniform level, however, is which produce frequency distortion, and sudden change from black to white in the very wide and ideally would extend from the two forms of distortion consequently picture. If the corresponding output zero to some 2.5 Mc / s. Since the use of occur together. It is probably true to say waveform is that of (c) then, with a suffi- a DC amplifier is impracticable an arbi- that an amplifier which has negligible cient interval between the peaks for the trary lower limit must be placed to the re- phase shift over the working range also effect to be visible, we should expect to

www.americanradiohistory.com MAY 28th, 1937 VrAT,shea Wopld '515 The Television Receiver - tween an even frequency response and Mc /s is 3 db. for all values of L /CR2. find that at the edge of the black object high amplification occurs when L /CR2 = It will be seen that, the value of L/ CR2 = there is a band of unusual whiteness, 0.5. 0.25 gives the lowest phase shift of 51.5° corresponding to the first peak, followed This circuit, however, is one in which at 2.0 Mc /s. This corresponds to a time by successive bands which are duller than transient distortion normal and brighter than normal white, can occur, for L and 70 corresponding to the successive troughs CI form a timed cir- 11 and peaks. cuit which is damped , 1101 111 11111110 effect is 11 If the present to only a small by the resistance R2. 11111 degree and the natural period of oscillation If the damping is not IMIIP is sufficiently short it is barely visible, great enough, any G 01M2 2 and it is normally possible to detect no suddenly applied volt- GI more than a slight increase in the bril- age will cause it to 1111 3 Ia\ liartty of white immediately adjacent to oscillate at its natural 1U1í1 1111 1111 the right -hand side of a black object. In frequency, and we 20 6 fact, when present in this degree only the can obtain the \M 11111111 1111 1111 effect may be useful in that it tends to damped oscillation 1/`\ 6 make the transition from black to white 0111 11iiiEZE IN shown in Fig. 25 (c). ,11111111111 1111111111 111111111111 appear sharper and more clean -cut. If It has been shown by 6 9 10 the oscillation is absent and the time delay McLachlan` that the t.,C2R2 is appreciable, so that the waveform is like effect just disappears that of Fig. 25 (b), Fig. 29. -The response and phase shift at there will be some low frequencies caused by the coupling condenser C2 and grid leak R2 are shown blurring at the trans - 1 2 here. sition. 111riiiii :011Mi`SI L The circuit most 11 0'S -2 delay of 51.5 /36o = 0.143 cycles =0.143 / 2 CR2 - widely adopted for a / 62 vsa 4 = 0.0715 ,u Sec. ; with a picture 25 cm. x W > L VF stage is that 0.25 1101 6 20 cm. this corresponds to a displacement F CR2 t9' shown in Fig. 26 ; L =0'332QSr_nrG_ií e of the spot position by about 0.18 mm., the value of R2 must S 7 CR2 /'.`1M\711 which is probably sufficiently small to be Mr'S4 01íZi unimportant in normally be very w a single stage. w o with _N+ilßi If we adopt this arrangement with large compared 0 that of RI. Now at L /CR2 =0.25, so that the damping. is 0 50 °R2 high frequencies C2 01I11 critical and transient distortion is avoided, z SON we see from Fig. that for response and R2 have a negli- 4 i L 27 a of LL 19II!)/ CR2 -0'S 3.o db at 2.0 Mc /s, f /fr =0.72, so that 27. These S Fig. - N the resonance frequency f. of curves show the fre- 01E the circuit w quency response and v, 11,iiVA must be 2.78 Mc /s. Consequently, if phase shift for the x 20 35u1sF -a likely value in an output o. //0'332 C= amplifier of Fig. 26 M/-K/ CR2 - stage -L =95µH and R = 3,3oo ohms. If for three values of L /CR2. The fre- 10 y, the valve has a mutual conductance of 6.o quency scale is ex- mA /V, we can obtain a stage gain of 19.8 pressed in frequency o times. ratios so that the 10 12 14 16 1e 20 Now let us consider curves are of the low-frequency universal application. response. In the coupling only C2 and R2 (Fig. 26) have any appreciable effect gible effect and the coupling consists when L / CR2 = 0.25, which is the critical in causing unevenness of response or phase of L, RI and CI, this last con- essentially value of damping, and that it is absent shift, unless a decoupling circuit is in- - of the total of the strap capacities. for all sisting smaller values of L /CR2. cluded. The curves of Fig. 29 show the This form of coupling was discussed in The frequency and phase distortion for performance in this respect ; the curves are some detail in Part IV with particular re- this circuit are shown in Fig. 27 for three plotted against wC2R2 where w =6.28x its use as an IF amplifier, and different ference to values of L /CR2. These curves frequency (c/s) and C2 and R2 are in shown the best compromise be- are plotted in it was that frequency ratios to render farads and ohms or microfarads and meg= them of universal ohms. 10 1 N application ; actually A drop in response of r db. at 5o c/s o fr = I /2r. N/LC. m The is probably unimportant and is obtained 9 1 same three curves when o,C.,R2 = 2 ; the phase shift, however, / !11 2 are shown in Fig. 28 is 26.5 °. It is probably wise to keep the > 8 ì 3 . ? replotted for the - 1= par total phase shift of the order of 10° only, tl, CR2=o5 w L 4 titular case when for á 7 0332 and this value in this one coupling CR 2 5 the response at 2.0 (.,C,122 =5.6. We may have more coup- en w 6 L2 = 05 lings than one, however, and as will be - 1 " The Reproduction seen later the bias circuit can also cause a w of Transients in Tele- we 5 vision," by N. W. phase shift. If can manage with one z McLachlan, coupling and the bias circuit, we ought to ` The Wireless I- 4 .f Engineer, October, 1936. allow only 5° phase change in each, and LL -0'332 _ CR2 for this wC2R2 is about 12, and since 3 (0=314 at 5o c /s, C2R= 0.0382. Now if w -0 =0'25 ! R2 is be very large á a Fig. 28. -These to compared with R it aX 2 : curves are the same should not be less than about o.3 megohm, as thosa of Fig. 27, ...... , ./` since R=3,300 ohms. Suppose we choose but with a frequency the standard value of 0.5 .megohm, then : scale and resonance C2 should be 0.0382/0.5=0.0764 p.F. o frequencies such 14 16 18 26 that the response at Again, it is convenient to choose a stand- FREQUENCY IN MEGACYCLES PER SECOND 2.0 Mcls is-3.o db. ard value, and thr nearest is o.i 11F., which makes C,R2 =o.o5 and wC2R2 =

www.americanradiohistory.com 516 7fipisIliso@ MAY 28th, -1937 Wop11c! The Television Receiver- when 123= ioo ohms and gsg is about 1.5 flows until the grid potential is more nega- '5.7 ; the phase shift will be under 5° and mA /v, so that we can use the curve for tive than - I.o volt, however, we can only the attenuation negligible, since it is less g1R3 =o.75. For a phase shift of 5° only use the range between -1.o and - 3.5 than 0.05 db. we see that °0C3R3 = 8.5, so that at 5o c / s volts. The anode potentials correspond- We must next tackle the bias circuit we find that C3 =2.7 x 10-; F =27o F. ing to these grid voltages are 173 volts and C3R3 (Fig. 26). This is a little more corn- Electrolytic condensers of 25o uF and 222 volts, and the valve is thus capable of plicated, since the performance depends 500 ,uF are readily obtainable, so that we an output of 222 -173 = 49 volts peak -to- not only upon the value of the product can easily meet the required conditions in peak.. C3R3 but also upon g,R3, where g, is the a single stage. As there is little difference The valve input is 2.5 volts p -p, so that in the price of such the stage gain is 19.6 times, and for nor- 100 i=1=.______,0 condensers, we mal operation with a resistance -capacity g R3=1 __.__ s h a l l naturally input coupling the steady grid bias should 90 9 i choose the larger of be -2.25 volts. With full input the valve, Qe/,° 500 ,uF and obtain if operating as a sound amplifier, would > 80 11 Q,%, 2 a response even a then be said to introduce some 3 per cent. u, little better than is second-harmonic distortion. This is quite / 3 á70 `,J.3 really necessary. small and quite negligible in television. w N a3 Before we go any Under these operating conditions the w 60 4 w o further in this anode current -is 14.5 mA and the screen matter it is neces- current 2.6 mA ; the cathode current is 0 50 5 ? sary to consider thus 17.1 mA. within the maximum 2 the and question of ampli- rating of 20.0 mA. I- 40 6 z LL Q = a t u d e distortion. We do not, however, require an output N 30 7 w ¢ d, Q a= 20 pHA 8 j .' SfflFr lo Ì..'`_ km 9

0 I0r.7 I 10 1 2 3 4 5 6 7 8 9 10 CJC3R3

Fig. 3o. -These curves show the effect of the bias resistance R3 and its by -pass condenser C3. effective mutual conductance of the valve in A/v and R3 is in ohms. When the screen grid is effectively decoupled to the cathode, g, is the normal mutual conductance between control grid and anode. When no screen decoupling is used, how- 'ever, or when it is returned to earth, g1 is the sum of the mutual conductance g between control grid and anode andof that gog between control grid and screen grid. This latter figure is rarely quoted, but it is usually about 20 per cent. of the ordinary mutual conductance, so that when the pre - cise figure is not available it is reasonable to take g, = 1.2 g., The effect of the bias circuit is shown in. Fig. 3o two for different values of Fig. 32. -The complete circuit of the end of a television receiver showing the detector, VF g1R3 ; with a TSP4 valve, g _ 6. o mA /v amplifier, DC restorer, and sync separator.

320 32 For a normal tube the total output of the of as much as 49 volts, for 3o volts p -p last valve must be about 3o volts p -p ; this will fully load the tube, and we can take 280 28 is a voltage change equivalent to that pro- advantage of this to simplify the circuit -. ¢w gb w duced by a sine wave of 15 volts peak or somewhat by omitting the coupling con- 240 - 24 §` 10.6 volts RMS. If the load resistance is denser from the diode We $o: a output. shall oz. ñssT 3,000 ohms, the valve must consequently then have direct coupling between the 200 5//Ov 20 J S.,/''%%ó° 2 be capable of an output of 10.62/3,000= detector and the VF valve and avoid all 0.0375 watt. This is quite a small amount frequency and phase distortion at low 160 '/'P ' 16 `IÌI of power and is by no means difficult to frequencies at this point. cc obtain. 120 /!° 2 ¢ With direct coupling the operating con- 6p ° '\ti; The dynamic characteristics of the ditions of the VF valve are different, 11 0 for .4., 80 6 w TSP4 valve are shown in Fig. 31 for a the input voltage will not swing about the Pr ó number of different load resistances. As bias point but will always drive the grid 4 á 40 4. this valve has quite a low anode- cathode negative with respect to its initial bias. ``~` capacity we shall probably be able to Consequently, we may have to use a -1 -2 -3 -4 -5 - use a load resistance of 3,50o ohms. smaller value of initial bias. We want to GRID VOLTS Looking at the curve for this value make this as high as possible, however, we see that it is reasonably straight because this will keep the current con- Fig. 3r.- Dynamic grid volts -anode volts over grid potentials, ranging from sumption at a minimum. We have seen curves of the TSP4 are given here. zero to - 3.5 volts ; since grid current that we can drive the grid so that the

www.americanradiohistory.com MAY 28th, 1937 WATamg 577 WopIld The Television Receiver. working conditions if we adopt this stand- this interference could be so easily and so anode potential rises to 222 volts without ard value of resistance. quickly eliminated if only the Government serious distortion. For an output of 3o The. circuit diagram of the detector, VF would take action. The cost of suppressing volts p -p, the anode voltage would then amplifier, DC restorer and sync separa- the radiation of interference at the source is not, as a rule, great, and, since most change between 222 volts and 192 volts in 32, tor thus takes the form shown Fig. motorists are probably owners of " all - and the corresponding grid voltages are and is extremely simple. Nevertheless, it wave " sets which are affected by ignition - 3.5 volts and -1.98 volts, this latter gives good amplification and reliable interference when the short -wave range is figure being the no- signal grid bias re- synchronisation, and it is in no way in use, all stand to benefit whether or not quired. critical as regards values of components. they are actual or possible owners of tele- At this bias the valve will take about Naturally there are optimum values, as vision receivers. As it is, hundreds and 16.1 mA anode current and about 2.9 mA has been pointed out in this article, but hundreds of new vehicles, private and com- screen current, so are no mercial, go on to the roads each week, and that the total cathode they by means critical and the nor- many them current of 19.0 mA is just inside the of produce the most poisonous mal tolerances in components have a negli- interference. We have waited far too long makers' rating. A Too -ohm cathode bias gible effect on the performance. The sync already for anti -interference regulations. resistance will thus produce 1.9 volts of separator is the most critical part, and here The more delays there are the greater will bias, and as the no- signal detector anode it is generally advisable to make provision be the difficulties in the way and the heavier current will also produce a small bias volt- for adjustment of its grid bias under will be the handicap upon the developments age, we shall not be far off the correct operating conditions. of both television and short -wave broadcast reception. ti ti ti Still Going Ahead WE still seem to be quite a long way off RANDOM RADIATIONS that saturation point in the matter of broadcast receiving sets that has so often Microphone Gate - Crashing By "DIALLIST" been talked about. At the end of -March oNE of the most astonishing instances of the total number of licences in force was broadcast gate- crashing - the gate in 8,122,250, an increase of 42,381 for the question being the door of an observer's from the Alexandra Palace were started. month. It is curious to notice that there box -took place on the evening after Coro- It's a little difficult to put one's finger on are comparatively, small increases in places nation Day. A youngster from the crowd the reasons why television hasn't made where one would expect big ones. Despite walked into the box in the Green Park, and more rapid progress into popular favour. At the opening of the Penmon station, Anglesey stated airily that he was the official observer. first the programmes were distinctly poor shows only three new licences, Carnarvon- The engineer in charge didn't know the and unexciting, to say the least of it, but shire 53, Denbighshire 17, Merionethshire s8 observer, who ought to have been there, by they have improved enormously of late. It and Montgomeryshire 17. Flintshire has sight, and thought that all was well. The is possible that some of those who might actually a drop of five in its total. Just microphone crasher settled down to his work have purchased sets last autumn were put across the border Cheshire's total is up by at once, and actually managed to broadcast off by the rather dreary programmes that 47o and Shropshire's by 193. to the world for a couple of minutes until they saw at demonstrations, and haven't The increase for Scotland. is much more the control -room operator, failing to recog- realised what an improvement there has satisfactory, totalling, as it does, 4,825. nise his voice, played for safety and cut out since been. I don't think that the cost of Glasgow shows the surprising rise of 1,639 the commentary. One has often heard re- television receivers is holding back possible (which is not a long way off 1 per cent.), marks shouted into the microphone by mem- buyers, for in years gone by there has been whilst Aberdeenshire, Morayshire, Banff- bers of football crowds, and so on (" Can a ready sale for radiograms costing quite as shire, Inverness -shire and Ross and Cro- you hear me, mother? " is an old favourite), much. I should be inclined to narrow down marty reflect the influence of the North of but this is, I think, the first time that a the most important brakes on the wheels of Scotland transmitter by respective rises of two- minute commentary has been achieved. television's progress to two. 309, 143, 85, 174, and 63. The B.B.C. admitted the fact in its news Though the total for Northern Ireland re- bulletins, recounting the incident as a good Two Big Snags mains small, the increase for March was a story against itself. particularly good one, being 1,217, which I can tell them another story against Just now I mentioned there had always represents more than 1 per cent. themselves which I am certain they don't been a pretty good market for expensive know. Not so very long ago the offspring radiograms. But the radiogram is an instrument which can, and will, provide of a friend of . mine were giving a party to other young folk. Music was provided by entertainment just whenever you want it. the wireless set from whose .loud speaker On the other hand, the sound -and -vision issued the strains of a well -known dance receiver for the ultra -short waves can be orchestra. " I wish," said one young thing, used at present only for two, hours on week- " that we could get them to play such -and- days and not at all on Sundays. It has such a tune." " Easy," said her partner; already been suggested in The Wireless " I'm sure I could make them do it in a World that the radiation of the whole minute or two." Several bets having been London Regional programme every day and made, he went to the telephone, rang up the all day by the ultra- short-wave transmitter B.B.C., announced himself as Lord Clarence at the Alexandra Palace or that at Broad- Marjoribanks, and demanded to speak to the casting House would have highly beneficial dance band leader. The latter was soon at effects, since owners of television sets (pro- the other end of the line, and having heard vided, of course, that the vision part can be what was wanted expressed himself as most switched off) would be able to receive the London programme with far better quality willing. " Yes, my lord ; certainly, my lord ; we shall be delighted to oblige your lord- than is now possible on the medium waves. ship." And, sure enough, in a minute or The second snag is interference, particularly two, the desired tune was announced as that caused by motor vehicles. It is all very being given by special request! well to say that the images on the screen are not very badly affected. One could put 11. ti up with the visual part of the hailstorms that car ignition systems produce, provided ? Why the Slow Progress they do not affect the sync ; but when every THOUGH considerable numbers of tele- other car gives rise to the sound portion of THE VISION MONITOR. Television Control vision receivers have been sold there's a hailstorm of the most intense kind beat- Engineer at the N.B.C. Studio in New York. no denying that the new hobby has been ing on a tin roof, interference becomes some- He controls the outgoing vision transmission slower in catching on than was anticipated thing much beyond á joke. and is in direct telephonic communication at the time when the regular programmes And the pity of it is that the bulk of with the camera operator.

www.americanradiohistory.com 518 Wireless World, May :8th, 1937

the lengthening WITHdays comes an ever- growing number of Outside Broadcasts. Some, of course, are the old and well -tried perennials, Listeners' Guíde for t whilst a few new sources are will be made and re- broadcast Charles Mason; a gondolier, this thought in mind, Ernest being tapped. This week the later in the day for those un- Kaye Seely; and the Man with Longstaffe has prevailed upon outstanding O.B.s come from able to listen to the actual the Cloak, Wilfrid Rooke- Harry Hemsley to bring his the Royal Tournament at broadcast which will be given Ley. " four children " round a Olympia on Monday, the at 2.45 (Nat.) . Mr. Hanson, the producer, radio set for the benefit of realising one day listeners. The broadcasters that there was a which they will hear include fund of beautiful Joan Young, Harry Cham- Italian music avail- pion and Neil McKay. The able in the B.B.C. part of the four children and Record Library the father who will be listen - which would pro- ing-in with their mother vide an attractive (Gladys Young), will be taken by Harry Hemsley, the child THE GRANDSTAND impersonator. This novel pro- VIEW which Alan gramme, entitled " Tune in, C. Hess will have when describing the Daddy," will be heard on R.A.C. International Saturday at 8 (Nat.) . Light Car Race at Douglas, Isle of Man, FROM THE VELDT for National listeners AN interesting and unusual at 5 on Thursday. Photo: Victor broadcast comes to National " The Smythe will Autocue." also be commenting listeners on Sunday afternoon at the Douglas Bay at 3. It will consist of a short Hotel corner. tour of the Kruger National Derby on Wednesday, and the light programme for the Park near Johannesburg, R.A.C. International Light " DERBY DAY " summer months, hit upon the South Africa, which will be Car Race at Douglas, Isle of No dates could be more idea of presenting this series of conducted by the Warden of Man, on Thursday. suitable for A. P. Herbert's light entertainments. He has the Game Reserve. The com- comic opera, " Derby Day," assembled a gifted band of mentator will give listeners an THE FIGHTING FORCES than the actual days of the players, who will provide the intimate picture of this sanc- ON Monday, at 8.3o, from great race and that of the Oaks medium for tuary of wild life. The Park Olympia, Regional listeners giving listeners (June 2nd and 4th). some of the tuneful lies in the north -eastern por- will hear a running com- melodies The story opens the day for which Italy is famous. tion of the Transvaal, border- mentary on three events of the before the Derby in the gar- The first of the series will be ing on Portuguese East Africa. Royal Tournament. This gay den of the " Old Black It has a length of some 220 annual military heard by Regional listeners on spectacle, Horse "; then comes the great Sunday at 9.5. miles and an average width of which raises money for the 'day, with scenes on the road about 40 miles, so that it is Army Benevolent Funds, to Epsom, in the paddock, and JUTLAND rather larger in area than never ceases to draw great on the rails. The last act deals ON May 31St, 1916, the Wales. crowds. The events to be de- with the day after the race and largest naval engagement of The Kruger National Park scribed will be a physical train- also takes place in the garden the Great War, the battle of had its origin in 1898, when ing display by the R.A.F. ; the of the " Old Black Horse." Jutland, took place. A drama- Interport Field Gun competi- Gordon McConnell, who tised story of the events of this tion by the Royal Navy, and will produce this on Wednes- great North Sea battle has been the musical drive by " K " day at 8.15 (Reg.) and written by " Taffrail " (Cap- Battery of the Royal Horse Nationally on Friday, June tain Taprell Dorling, D.S.O., Artillery. The scenes in the 4th, has chosen a very strong R.N.) , which will be pre- arena will be doubtless fit- cast, which will be supported sented for National listeners tingly described for listeners by the B.B.C. Revue Chorus on Sunday at 9.5. and with the background of and Theatre Orchestra, con- The B.B.C. has stated that martial music will provide a ducted by the composer of the this broadcast is in no way colourful sound picture. score, Alfred Reynolds. .. intended to add fuel to the controversy which has raged THE SPORT OF KINGS VENICE AGAIN around this battle, but to com- THE arrangements for the A. W. HANSON, the im- memorate broadcast the 8,642 officers of the Derby follow presario of " In Town To- and men of the British and exactly those of last year. An night," has devised a new German Navies who lost their effects microphone will be at form of entertainment, which lives in the action. Tattenham Corner to pick up he has entitled " In a Gon- the hoof beats of the approach- dola." He has recruited Wil- THE CHILD LISTENER ing horses, whilst an observer frid Rooke -Ley, the author of THE remarks of children will, as far as possible, call out " The Table Under the Tree " when listening to broadcast the names of the leading horses and " Musical Ghosts of Lon- programmes are often, though as they pass him. The Derby don," to write the script tell- amusing, very sensible. With is always a tremendous mix - ing of an English family party up for commentators, for it is touring the canals of Venice. HARRIET COHEN, the famous frequently difficult to deter- The party will consist of an pianist whose playing inspired mine the colours of the elderly lady, to be played by Henry Hall to study the piano, will be heard with the Edric Cundell jockeys. Elaine Innescourt; her niece, Chamber Orchestra at 9 (Reg.) on A record of the commentary Joan Carr; a young man, Saturday.

www.americanradiohistory.com Wireless World, May 28th, 1937 - 519 Outstanding ee Broadcasts an area lying between the Sabi at Home and Crocodile rivers, about 1,500 square miles in extent, and Abroad was proclaimed a Game Sanc- tuary. It-has since been added to at various times, and now covers nearly 9,000 square miles. There is to -day probably a greater variety of wild life in this park than in any area of similar size in the world. The commentary will be given at Skukuza, one of the twelve rest camps, it being Photos: The South African Railways. conveyed by land line to REST CAMPS are established at twelve points in the Kruger Johannesburg and on to Cape National Park, Transvaal, for the benefit of travellers. Town, a distance of This natural home of wild life of every description will about provide a twenty- minute descriptive broadcast for National 1,000 miles. It will then be listeners on Sunday. This photo is of Skukuza whence the sent via Radio Telephone commentary will be given. Inset are Wildebeests, which Beam Service to this country. are exceedingly tame, and Zebras at a waterhole. Camp in the On OPERA mountains. Monday brings two opera Home: Tuesday at 10.5 National events, a new fairy opera, Two relays from act of Bizet's " Carmen," with listeners Covent Garden and will hear Act 3 of " La Cloche Engloutie," by the one from Renée Gilly in the name -part. " Gotterdämmerung." Both French composer, Manuel Glyndebourne come into this The action takes place in of these relays are from Rosenthal, from Paris at 8.3o, w e e k's programmes. On Seville in the early 19th Covent Garden. From Glynde- and a complete recording of Saturday at 10.15 (Nat.) century, and the scene for this bourne on Thursday, at 8.15, " The Barber of Bagdad," listeners will hear the third is act set in the Smugglers' the third act of Mozart's by Cornelius, from Frankfurt " Figaro " will be heard by and Stuttgart from midnight HIGHLIGHTS OF THE WEEK Regional listeners. until 2 a.m. The latter is the Abroad: Dvorák's extraor- work in which Cornelius, a FRIDAY, MAY 28th. Monday, May 31st (continued). dinary and poetical opera, devout disciple of Nat., 8, The Air -do- Wells. 9, Abroad. Wagner and Responsibilities of Empire -VI, Strasbourg, 8.30, " The Ten " Rusalka " (The Water - Liszt, embodied the ideas of the Rt. Hon. W. Ormsby -Gore. Czardas Virtuois "-Cigány Or- Sprite) is, of all the com- the " new " music of the 9.45, Mabel Constanduros. chestra from Budapest. poser's works, the greatest Weimar School, of which he Reg., 8.15 and 9.30, Concert from favourite the the Queen's Hall. 9.10, " Paste TUESDAY, JUNE Ist. with Czech was a member. and Paper." Begging letters Nat., Callender's Senior Band. public. It was first produced On Thursday at 9, Milan received by a winner of the Irish 7.50, " Down Memory Lane " : at Prague in 1900, four years gives us something really old, Sweepstake. old melodies that still linger. before Dvorák's death. It will Monteverdi's " L'Incorona- Abroad. 8.15, " The Purple Pileus." be heard from Prague to -night zione di First Hilversum 1, 7.55, " Stabat Mater," Reg., 9, Music for Worship -IV. Poppea." pro- oratorio (Dvorak). 9.30, " Intermission " : Novelty (Friday) at 7.30. This even- duced in 1642, it is the work numbers and solo pieces by the ing brings us yet another ,in which Monteverdi gave final SATURDAY, MAY 29th. Variety Orchestra. magnum opus of the Czech proof of his genius for dra- Nat., 3 and 5.15, Athletics, the Abroad. master, his magnificent Ora- Kinnaird Trophy. 8, " Tune in Strasbourg, 8.30, " Cosi fan tutte " matic presentation and truth- Daddy." 9.35, Quintette du Hot (Mozart) from. the Municipal torio " Stabat Mater," from ful characterisation. Poppea, Club de France, from Paris. Theatre. Hilversum I at 7.55. as all know, was the second 10.15, " Carmen," Act 3. Saturday's principal opera wife of Nero, her third hus- Reg., 6 The Air -do- Wells. 7.30, WEDNESDAY, JUNE 2nd. The trial of James Stewart of the Nat., 2.45, Commentary on the comes from Rome at 9, and is band and her last, for she soon Glen. 1752. Derby. 6.40, The London Verdi's " Ernani," founded died through his brutality. Abroad. Theatre. 8.15 and 9.30, Concert on Victor Hugo's " Hernani." Radio Paris, 8.30, Italian music. from the Queen's Hall. When produced at Venice in Reg., 7.30, " The Vagabond Lover." SUNDAY, MAY 30th. 8.15. Derby Day. 9.40, Men 1844 its success was enormous. DANISH MUSIC Nat., 3, The Kruger National Park, Talking (prison visiting). Sunday brings us still more THE first of a series of muni- S. Africa -a descriptive relay. Abroad. Czech opera in the shape cipal park concerts by a band 9.5, Jutland-A history in dra- Luxembourg, 9.50, Dances of the of the of 7o Copenhagen musicians matic form, by Taffrail. 10.5, Nations, by the station orchestra. perennial delight, Violin recital, Eda Kersey. Smetana's " Bartered Bride," will be radiated on the Danish Reg., 5, Orchestre Raymonde and THURSDAY, JUNE 3rd. which comes from Stuttgart wavelengths on Sunday after- Williams Brownlow (baritone). Nat., 5, Commentaries on the at 7.45. noon at 4. The programme, 9.5, " In a Gondola " -a Vene- R.A.C. International Light Car exclusively of tian silhouette. Race. 8, Variety from the Union Twice this week, on Sunday which consists Abroad. Cinema, Kingston -on- Thames. from Milan at 9 and on Tues- Danish music, will open with Milan, 5, Léhar's " Merry Widow." 9.20, Recital, Kathleen Moor - day from Rome at the same the King Christian X Jubilee house ('cello) and Frank Merrick hour, the veteran 74- year-old March. The concert comes MONDAY, MAY 31st. (piano). Nat., 7, " Monday at Seven." Reg., 6.15, " The Purple Pileus." Mascagni conducts his own from the biggest park of 9.35, " Between Ourselves "- 8.15, Act 3 of " Figsro " from opera, " Iris." Since its pro- Copenhagen, Faelledpark. an intimate entertainment. Glyndebourne. duction in 1898, it has won Subsequent to this transmis- Reg., 7.30. English -American folk Abroad. even more favour than any of sion, three large provincial Songs : The B.B.C. Midland Kalundborg, 8, " Les Cloches de Singers. 8.30, Commentary on Corneville," operetta (Plan- the composer's score of operas choirs will render popular the Royal Tournament, Olympia. quette). since the delightful " Ca al- Danish songs. leria Rusticana." THE AUDITOR.

www.americanradiohistory.com Wireless World, May 28th, ig37 Ultra -short -wave

By " CATHODE RAY" broadcasting MORE ARGUMENTS SO there is one department of broad- 15,0óo or even 20,000 cycles per second casting, and that not the simplest, IN FAVOUR OF THE should be included ; actually, broadcasting in which this country has not merely stations do not attempt to go beyond about done to-day what America did PROJECTED SERVICE 8,000 ; and except at very close range the yesterday- Television. For this we are practical limit of reception without inter- grateful to the enterprise of our B.B.C. ference is about 4,000. Some receivers and others concerned ; even although are cutting off badly as low as i,000 ! nobody seems to know exactly what to do The ultra -short waves are as yet wide that the cost of special ultra -short wave we rather, the fast - open spaces ; a television transmitter with it now -or local areas is wealthy members of the transmitters for covering occupies several times as much frequency disappearing that of a television got it. But when we small compared with space as the whole medium and long community-have The point is that it affects consider the manner in which the proved service. wavebands combined, and still leaves does not want it ; there is no and established demand of the seething nobody who plenty. I gave some idea of this in a dia- of existing services, but it would Metropolitan millions is being supplied upsetting gram that appeared on December 4th last. be a real boon to keen listeners. with sound broadcasts, the intensity of our So a real " high -fidelity " transmitter is how? It is probably too well drops off by very many Why and entirely practicable from this standpoint. congratulations known even for " Cathode Ray " to have db. Moreover, the interference that one must Presumably, it is not the intention of expect from stations working on an the B.B.C. that the Home Counties be adjacent or even the same wavelength is omitted entirely from the scheme of negligible compared with that on the things ; and therefore the London station longer waves, although the approach is more correctly described as the South - within the next year or so of maximum East station, at least. Yet even within sunspot activity makes it unwise to be too the boundary of the County of London dogmatic about this aspect of the matter. itself, in the south-easterly direction, the Anyway, there are still plenty of well - London National programme cannot be spaced wavelengths. relied upon to be free from serious interference except by treating it as a distant Perfected Contrast Expansion station and accepting a correspondingly low standard of reproduction. By Then there is an idea for improving adopting every available device -high reproduction, which is lying dormant just selectivity, tone correction, and a whistle now because there seems to be no hope filter as narrow and deep as an Alpine under present conditions of putting it pro- crevasse- something approaching the perly into effect- contrast expansion. I moderate fidelity standard of the original explained some time ago why an attempt transmission may be possible. But why to restore the original pp and ff contrasts should one be obliged to do all this to at the receiver fails ; the variations in in- get the local National programme, in the tensity of the programme are compressed central ring of its service area? Con- by the transmission control engineer in a ditions are naturally worse still in the manner which he judges will give the most extreme parts of the area, and have pleasing effect when reproduced in the steadily deteriorated since the Regional ordinary way, with no re- expansion. But scheme was established. a special service, of the kind suggested, need not necessarily be bound by existing Something for Their Money receivers everywhere, because it would be intended mainly for those who are suffi- Seeing that listeners in general are con- Apparatus for radiating programmes on ciently interested in the best reproduction tributing the money which is being used ultra-short waves is already installed at to use special receivers for the purpose. to finance television-a venture likely to Broadcasting House. The programme could be " compressed " be out of reach of the vast majority of automatically, according to a definite them for years at least-it seems to me to explain that the broadcasting of pro- scale, and the receiver could be arranged that they have rather a good claim to grammes from a station occupies a band to expand it again to the original. Prob- derive some benefit from the equipment of wavelengths, not just one single wave- ably the best way -and it is one for which 'now in existence, especially when the length as during a silent interval, and that there is room only on ultra -short waves - regular broadcast service leaves so much consequently only a limited number of would be to radiate a pilot wave which to be desired. I am referring, of course, stations can work within fixed limits of would fluctuate in strength according to to the proposal that when the ultra -short wavelength without overlapping. Stations the degree of compression effected, and wave sound transmitter is not being used on all ordinary wavebands are already so which would be used by the receiver to to supply the accompaniment to television crowded that, unless the desired trans- govern the corresponding expansion. it should radiate the National programme, mission is overwhelmingly stronger than But perhaps that is too much to expect or whatever programme is most likely to others adjacent to it in wavelength, it is at first. However, apart from the things benefit thereby. Or if it be objected that necessary to reduce or cut off at the named, ultra -short waves have the advan- television hours are going to be extended receiving end the highest audible fre- tage of being free from most forms of so much as to make serious holes in any quencies, essential to life -like reproduction noise, interference, and atmospherics ; such supplementary service, it remains of sound. Ideally, frequencies up to with the important exceptions of motor

www.americanradiohistory.com MAY 28th, 1937 VIpA@@0,opIll Ultra -short Wave Broadcasting - ordinarily simple and compact receiver, of ignition and certain types of electro- pocket dimensions, using the super- regen- medical apparatus. Aerials offer far more erative principle. Some of the extreme scope for high efficiency, directional pro- fidelity is sacrificed, but then it is hardly perties, and reduction of interference. No expected from such receivers, for which person ordinarily situated is able to put up 'phones are generally used ; and on the anything that is more than a mere part of other hand the super- regenerator is re- an aerial on medium and long waves. The markably immune even from ignition proper length for a Droitwich aerial is interference. Besides which, it is the only WICA IQT Q nearly half a mile, or quarter of a mile if single -valve receiver to include AVC ! erected vertically from the ground ! But the ten feet for ultra -short waves is much Who is to Blame ? more manageable. NEW BATTERY Another thing is that an ultra -short wave Although I may appear to have implied programme can be picked up on an extra- that it is the B.B.C. that is solely guilty of Ad-WAVE SUPERHET holding up ultra -short wave broadcasting, they profess to have the best reproduction of their programmes at heart, and would Television Programmes be unlikely to oppose such a suggestion ; £7 but it seems that the receiver manufacturers are nervous it, Transmissions are from 3 -4 and 9 -10 about though daily. whether it is on the ground that the real Vision Sound high -fidelity might show up commercial Mc/s. 41.5 Mc's. 4.5 "r high -fidelity " for what it is, or because FRIDAY, MAY 2Sth. they think the public would instantly refuse to buy any sets not including ultra - 3, Starlight : Billie Houston and Nina Devitt. 3.5, Polo ponies and players from the Hurling- short wave reception, is not clear. One ham Club. 3.20, British Movietonews. 3.30, would have thought that any pretext for Play Parade : repeat performance of scenes offering the new season's products as an Compiete from " The School for Scandal." with 6 advance on the old would be welcomed by B.V.A. 9, Starlight : Hildegarde. 9.15, Piatigorsky an industry in which new ideas are run- valves. ('cello). 9.35, Gaumont- British News. 9.45, ning short. The only receiver of its type now on the British market. Friends from the Zoo ; programme arranged Results on all 3 wavebands equal to mains receivers of for Dominion guests at the Z6ological Society's Of course, the fullest benefit from a equivalent, type. Latest technical developments in- Party. corporated iu circuit. Latest types valves, transformers, Coronation " wide range " transmission of the type taming coils, switches, etc. proposed could not be gained simply by Specification in brief: radio frequency amplifier, first SATURDAY, MAY 29th. detector with separate triode oscillator, I.F. amplifier, adding the, extra waveband to the standard double diode detector, L.F. amplifier, low consumption 3, Oliver Wakefield. 3.10, Film Cartoon. 3.20, receiving sets, although pentode Output. D.A.V.C. volume control and tone Pasquinade No. 2. Cast includes June Clyde no doubt they control both operative on gramophone. Illuminated and Richard Ainley. 3.45, National Cycling coúld be made to give better reproduction dial with station names. Wave- ranges: 16 -52, Festival. The start of the Cycle Road Race than is possible now from the 'National 200 -550, 900 -2,000 metres. in Alexandra Park. medium -wave stations, especially if the 9, Gillie Potter. '9.15, British Movietonews. B.B.C. werê to co- operate by=t putting out ALL -MAINS ALL-WAVE SIX 9.25, Darts and Shove -ha'penny. Competition the full audible spectrum: between rival teams of two well -known hos- It is the design with radio frequency stage telries. 9.35, Grill Room -Dim Dremo and of sets primarily intended for high -quality Georges Gladyrevsky (guitarists), Bela Bizony local- station reception that would be given (violin) and the Hungaria Gypsy Orchestra. the greatest impetus, for at present there is no inducement MONDAY, MAY 31st. to make them anywhere near as good as one knows how. It is 3, Sports Review No. 2 : Howard Marshall will introduce personalities who have been in the about time for the stagnation here to be sporting news during the past month. 3.20, stirred up. Gaumont-British News. 3.30, Ivy St. Hellier in " Queue for Song." 9, Repetition of 3 programme. 9.20, Viennese Honeymoon ; revue for television by Hans Kafka. 9.50, British Movietonews. Radio and Aviation

TUESDAY, JUNE 1st. MR. R. P. G. DENMAN, well known in Complete radio and aeronautical circles, and a with 6 3, Starlight : Charles Heslop. 3.15, British contributor to our pages, was formerly B.V.A Movietonews. 3.25, " Polly " : an opera by in valves. John Gay. This is a sequel to " The Beggar's charge of the electrical engineering section ' Dc Luxe " 6 valve receiver, with S valve performance Opera." at the Science Museum; and later a director specially recommended for tropical and foreign reception of Heston Airport. Now, consequent on conditions). Built on special cadmium -plated 16 gauge 9, Personalities -IV. 9.10, Gaumont- British steel chassis. Varley iron -cored I.F. coils. Litz -wound News.. 9.20, Repetition of 3.25 programme. the Government's decision to purchase using coils. 3 waveranges-16.5 -2,000 metres, Illumin- Heston, Mr. Denman has been left free to 'tted " Airplane " dial with principal station names. WEDNESDAY, rejoin his former colleague, Mr. Circuit comprises : Pre -selector radio frequency amplifier JUNE and. E. S. L. operative nn all wavebands), triode -hexode frequency 2.55, The Derby. Viewers will see a plan of Beale, who in 1935 established a consulting changer, double bandpass coupled I.F. amplifier, double practice in engineering physics limbs detector, D.A.V.C. applied to 3 preceding valves. the course and hear the commentary to be at 129, Ehury S.F. amplifier and pentode output. Variable tone control broadcast nationally. 3.10, Anne Ziegler Street, London, S.W.1. and volume control operate on radio and gramophone. (songs). 3.20, Gaumont -British News. 3.30, Apart from radio work generally, Messrs. All McCarthy receivers supplied Fifty -ninth Picture Page. Beale and Denman are engaged on investi- Important ! complete with valves, knobs, pilot 9. " Queue for Song." 9.25, British Movie- The prices at which lamps, leads, mains cable and plug. gations in sound and vibration engineering, McCarthy Chassis are ad- 12 months' guarantee. Cash with tonews. 9.35, Sixtieth Picture Page. vertised include Marconi the development of photo -electric devices Royalties. order on 7 days' approval. and cathode -ray tube applications. Readers should, for their Deferred terms on application or THURSDAY, JUNE 3rd. own protect inn. make through London Radio e before purchasing Supply Co., Display in Alexandra Park by any receiver that the 11, Oat Lane, E.C.2. 3, Prunella quoted price inclndea the and members of Royalty payment. Write for catalogue of complete Stack the Women's League of range of McCarthy receivers. Health and Beauty. 3.20, Maria Luth (songs). "Resistance-Coupled AF Oscillator" 3.25, British Movietonews. 3.35, Theatre MCCALfl It-1' 11FALIIC ALTr Parade. In this article (The Wireless World, May 44a, Westbourne Grove, London, W.2 9, Music Makers. 9.10, Architecture -V. 9.25, 14th) the first two diagrams were inadvert- Telephone: Bayswater 320112. Gaumont- British News. 9.35, Revue. ently transposed.

www.americanradiohistory.com 522 Wireless World, May 28th, 1937

" news -flash " from the B.B.C. box outside Buckingham Palace had no credentials but a plaus- ible manner. In future, how- roadcast Brevities ever, broadcasters will have to offer more tangible evidence of Separating Wales from NEWS FROM PORTLAND PLACE identity. the West Microphone " Passports " ? for B.B.C. introducing the " wipe " effect, THE final separation of Wales tables and chairs It is being suggested that from the West Region will workers cry to high Heaven familiar to all students of filin everyone having access to a take effect early in July, as their alien origin. Whether the technique. Another interesting B.B.C. in microphone should already foreshadowed in these staff who have to write upon the effect, to be introduced the henceforth be provided other are next Coffee Stall " pro- with a columns. This raises the ques- one and sit upon the " special ticket. In the case of tion of the allocation of a separ- inspired to frame programmes gramme, will be the simultane- regular broadcasters all- British of film and a and an- ate wavelength to the West on British or nearly ous transmission nouncers a "season" would be The scene. One -half of the Region. It is definite that some lines is a debatable matter. studio required, probably designed like reshuffling will be necessary for only certain fact is that British picture will show a busy street a passport, with the speaker's the comfortable accommodation listeners pay, both for wood and and the other half the specially portrait inside. of the newcomer, and the solu- talent. And let us assume in constructed coffee stall round tion that probably springs first the name of charity that when which the entertainment re- to the mind is the extinction the B.B.C. can get equal quality volves. " of the three medium -wave at home, whether. it be in talent We Want the King " Nationals- London, West and or in wood, the home product The Radio Link NOT often is a dream trans- North. takes precedence. The televising of the Corona- lated into reality as it was ea a c, ea tion procession showed the capa- in the case of Davy Burnaby in Should the Nationals Go ? bilities of the new twin -wire and the Box Coronation Week. The popular This would release the 261.1 - Toscanini balanced cable; but interest is compère retired to bed on meter wavelength, already be- Office now centring on the possibilities Coronation Night with the ing used by the West Region, so THE old idea that broadcast- of the radio link. If this is a crowd cries of " We want the that it became exclusive to that ing has a detrimental effect success, the scope of television King ! " ringing in his ears. He Region ; but under this plan on concert and theatre attend- O.B.s will be increased enor- dreamt about it, so vividly, in there would cease to be London ances dies hard, but the coup de mously. Already the likelihood fact, that at 3 a.m. he woke to and North National t r a n s- grcice comes with the news that of televising Wimbledon tennis find that he had the words of a missions. If these were shifted all seats for the B.B.C.'s London is being freely discussed, and it lyric. At once he 'phoned over to the 2o3.5 -metre wave- Michael North, and the two of length which is now used by them evolved, on the telephone, Plymouth and Bournemouth, the rousing song which formed representations would almost THE STROLLING the finale of the Coronation certainly be made that it was TRANSMITTER Music Hall broadcast on the fol- unprocurable on many sets. lowing Saturday. Will Scotland Solve the Riddle ? Appearances Not Deceptive It would seem, therefore, that the B.B.C. will have to decide A FEW days ago the B.B.C. on the use of the Scottish received a letter addressed National wavelength (285.7 to " Him with the two gold metres) for the West Region, To permit impromptu teeth and brass earhole, Alex- bringing Scottish National into interviews with the andra Palace." It was at once man in the street, the handed to the rightful owner. line with the London and North Columbia Broadcast- Nationals on 261.1 metres. The Gypsy Petulengro. ing System of New No one Newcastle wavelength of 267.4 York have designed can doubt that high - metres could then be retained low ultra - definition television has " ar- a -power rived." for the new North-Eastern trans - short wave transmit- to be carried ,by a . nitter at Stagshaw, and Aber- ter strolling announcer. . deen could keep its 233.5 metres. An The walking stick Captains and Kings as at present. experimental conceals an aerial and period of working on this basis RF stage, a binocular case carries the modulator and AF amplifier, Depart is the most promising solution of whilst batteries are supported by a waist belt. A wrist microphone HARD on the heels of Mr. a by no means simple problem. completes the equipment, which is stated to have a range of one mile. E. R. Appleton's retirement American of an even less conspicuous kind was used by WI equipment from the position of West Mr. Cornelius Vanderbilt for his journalistic " scoop " transmission from Regional Director comes that of Abbey the Coronation. To Be or Not to Be- Westminster during Mr. E. G. D. Liveing, North British Music Festival, conducted by is also being suggested that the Regional Director. The reason ; is given, in Mr. Appleton's ART is universal thus it is Toscanini, were sold out a fort- mobile unit be taken to Henley case, that broadcasting reaches night ago, although the last con- for the Regatta. The distance as his desire to found a League out its tentacles to obtain the cert will not be given until June from Henley to Alexandra of Youth with a spiritual back- best that any country has to 16th. Palace is thirty -five miles. So ground ; in Mr. Liveing's case, offer in the way of musical Seats for the first concert were the engineers are not unam- as his wish to devote himself to genius. The Toscaninis and sold out two hours after the bitious. literary and journalistic pur- Taubers, perhaps rightly, know opening of the box office. suits. less about international bound- WI WI It is significant that both are aries than about the dominant hey positions and among the seventh, and the B.B.C. can Film " Wipes " for More Gate -crashing plums of broadcasting, and that therefore loosen its purse- strings Television ? THE microphone still seems to both these officials have chosen with a good heart and without HILE intensive research be fair game for anyone June 3oth as the day on which hurt to patriotic fervour. \ Y continues on the O.B. side who really has designs upon it, to go out into the wide open of television, the engineers at and the amazing thing is that so spaces. The influence on the Foreign Wood Alexandra Palace are still busy few people take advantage of broadcasting service exercised But counterpoise must be improving technique. its comparative defencelessness. for thirteen years past by Mr. secured somehow, and so Port- The engineer who " rocked the The latest example of micro- Liveing and Mr. Appleton will land Place has been going into ship " in " Cabaret Cruise " by p h o n e " gate- crashing " had be sorely missed, both inside the vexed problem of " how to means of a gently tilting mirror almost a comic -opera touch. Broadcasting House and by lis- furnish out of income." New is now at work on a device for The stranger who gave the teners in the North and West.

www.americanradiohistory.com Wireless World, May 28th, 1937 523 LARGER TELEVISION SCREENS A Suggestion for Increasing Area cT IN the Iconoscope type of cathode -ray ence of the electron stream. For in- c HEN we Ji nd tube as used in television the familiar stance, certain phosphorous compounds fluorescent screen is replaced by a are found to absorb less light, when sub- "mosaic " screen built up of tiny jected to the action of electron bombard- photo- sensitive cells which form an in- ment, than under normal conditions. T.C.C. condensers we visible " electric " image of the picture to Whether or not they produce phos- be transmitted. This change in the func- phorescent light at the same time is im- tion of the screen represents an outstand- material, since it is the variation in trans- look for the trouble ing development in cathode -ray tech- parency, or opaqueness, that is utilised in nique, as applied to transmission. reproducing the picture. Quite recently attempts have also been When such an electrode is inter- made to oust the fluorescent screen in posed between a powerful arc lamp L SOMEWHERE ELSE and a ground -glass viewing screen S, the A SERVICE ENGINEER s light from the lamp is so controlled that So said a service engineer it can only to us recently. The mere pass fact that T.C.C. Conden- freely through those sers are in a Receiver, points in the elec- tells him straight away trode that follow the that at least a dozen poss- the electron ible breakdown points can track of be eliminated. stream from the The most prolific cause of " gun " part of the breakdown in a modern Using a cathode -ray tube for controlling a beam of light from an its external source. tube in scanning A. C. Receiver is the motion. momentary building-up of reception, where the arguments against its In effect the scanning stream opens a HIGH -SURGE VOLTS at the instant of switching - use are two -fold. First, it limits the size succession of small " windows " in the on. It may result in a of the received picture, since the screen electrode E, and so allows the light from complete set of "blown" resist- - must necessarily be mounted inside the the lamp L to pass through and valves, burnt out glass bulb, and, secondly, the fluorescent build .up the light and shade of ances or transformer windings, and other mys- " glow " produced by the electron stream the : received picture on the screen terious ' faults. Eliminate is, at best, only a poor substitute for direct S. The transparency of each " window " the cause itself... at source, light from a lamp. is graded by the intensity of the electron by fitting T.C.C. ' Wets.' the arrangement shown in the stream, and this, in turn, is varied fróm With these perfect safety In valves in circuit high surges is Figuré the usual screen replaced by an point to point by the amplitude of the sig- cannot develop, voltages - electrode E which is capable of changing nals applied to the control grid of the are kept below peak work- its optical characteristics under the influ- cathode -ray tube. ing. Not only are the T.C.C. Condensers themselves SURGE -PROOF, but their very presence makes all associated components secure against THE " MAG- NICKEL " FUSE damage. Play for safety ... use T.C.C. ' Wets.' Specially Designed for Receiving Set Conditions FOUR STANDARD TYPES THE ordinary wire fuse is a thing of capacity for overloads of short duration. 802. 16 mfds. 440v. Continuous Peak wkg. simple reactions, without the reason- The Belling Lee " Mag- Nickel " fuse 6C2. B mfds. 440v. Continuous Peak wkg. ing powers which would seem to be neces- satisfies these requirements and makes use 805. 8 mfds. 500v. Continuous Peak wkg. of fuse in a receiv- of sary for the post main an ingenious new principle. The main Continuous Peak wkg ing set. If it is heavy enough to survive conductor (not itself the fuse) consists of 809. 32 mfds. 320v. the initial surges of switching on it will be a thick nickel wire capable of carrying insensitive to rises of primary current an overload of at least 400 per cent. On -that STOP which, although small, may, nevertheless, it are fixed two small blobs containing HIGH SURGE be symptomatic of serious trouble some- magnesium powder which oxidises spon- Y where inside the set. What is really re- taneously with the generation of intense VOLT DAMAGE quired is a fuse with a reasonably narrow local heat when the temperature is raised margin between its normal working cur- above a given point. This burns through rent and fusing currents of sustained value, the nickel and interrupts the supply yet with a high enough current- carrying current. It has been found that the gauge of nickel wire required to keep the MAGNESIUM tempera- MIXTURE ture below the critical point for the normal working current has a sufficiently high thermal content to absorb momentary S urges; but a sustained excess current rapidly raises the temperature to the point ALL-BRITISH at which the chemical reaction takes place. NIOKEL WIRE The fuse rated to carry } amp., for in- CONDENSERS stance, is stated to blow 1 second after the application of a 75 per cent. overload. The Telegraph Condenser Co. Ltd., Wales Farm Road, N. Acton, W.3. Sensitive to small sustained rises of current, Three ratings are available, namely, 250, 50o and 75o mA. The dimensions the Mag- Nickel " fuse is, nevertheless, 61 1.887 unaffected by the surges which occur when are the standard 'kin. long x tin. diameter, the receiver is first switched on. and the price of all three types is 9d. each.

www.americanradiohistory.com 524 Wireless World, May 281h, 1937

The Editor does not hold himself Letters to the Editor responsible for the opinions of his correspondents tion, I naturally mean the instrument as set he appears to have misunderstood me. I did up ready for work, i.e. on a baffle, and not not imply that transient response was more separated as indicated by Mr. Barden. or less independent of frequency response, Pirated Call -signs I would therefore state in full that, assum- but that their conjunction was not a sine FOR some ten years I have held a trans- ing the diaphragm to be a non -resonant qua non. mitting licence, first with the call -sign piston :- I must apologise for calling Fourier's 2MQ and later, when the " G " was added, (i) With a baffle speaker mounted on a Theorem his Analysis, but did not mention G2MQ. As most of my experimental work baffle, the air loading is a maximum for his Integral Theorem as it does not seem to in radio has been confined to receivers and wavelengths so small that the sound is be rigorously applicable to loud speakers. receiving circuits, very little transmission thrown off as a beam. (At these frequencies It is perfectly true that " other things has taken place from this station, and, as a the baffle does nothing useful.) being equal, every increase in frequency res- matter of fact, no transmitting apparatus (2) As the wavelength increases, the load- ponse improves fidelity on transients," but whatever has been used here for at least six ing becomes lighter and lighter (and would the trouble is that other things do not re- years. collapse utterly but for the presence of the main equal if the frequency response is For well over a year now I have been regu- baffle). improved. Consider a single RC coupling ; larly receiving QSL cards from all over the The table below gives approximate mean inductances in serk3 with the resistances can world, but mostly from countries adjacent 6ir loading in dynes per sq. cm. on a roin. improve the frequency response, but transi- to England, proving conclusively that my diaphragm, velocity r cm. per second. ent fidelity is usually impaired. call -sign has been regularly pirated. May I Some of the figures have been quoted in my His desiderata for a good transient res- avail myself of the publicity of your Corre- letter of March 26th, but by tabulating them ponse do not seem to hold for the general spondence columns to inform experimenters the great change in loading will be more case. Headphones, loud- speaking telephones generally that I am not in any way respons- obvious. and the older pick -ups (though the latter ible for signals so sent out, that I have not Estimated mean air pressure in dynes'sq. cm. are the inverse of speakers) have restricted transmitted from this station (or from any frequency responses and a multiplicity of I should Baffle Speaker on Same Speaker on resonances, but are really quite good on other) for several years, and that Frequency. Baffle. 1 :1 Horn. be much obliged for any information which transients. would enable me to identify the man in Working Face. Back. Working Face. Back. It is certainly unfortunate that a classical question. Numerous examples of this piracy 5000 40 40 42 40 analysis has not appeared, and until it comes have been brought to the attention of the 500 13 13 42 0 Postmaster -General's department concerned and the possibility of confusion with similar 50 0.18 0.13 42 0.09 letters seemed ruled out by the fact that occasionally the transmitter in question has I think, after studying the above figures, used such words as " Montreal " and that Mr. Barden will agree with me that " Quebec " to identify the letters, although with a baffle the air loading is greatest at obviously the station is somewhere in this the high frequencies. country. His comment that most talkie equipments In the event of the pirate being identified use a baffle speaker for the low notes, only the writer proposes to take legal action, not emphasises the argument. Firstly, because only in his own interests but in those of all the low -note speaker deals only with a amateur transmitters who conscientiously limited frequency band, and its transformer adhere to the regulations laid down. can be matched to its average impedance PERCY W. HARRIS. over that band, regardless of how the im- Wimbledon, S. W.19. pedance may vary outside that band. Secondly, he will usually find that more Horn - loaded M.C. Speakers than one speaker is used, and that they are clustered together, so that the pressure field INOTE from r. -:. Barden's letter that, in misquoted of each one helps to load the others. mine of March 26th, I the I am told that, in a recent arrangement, passage which originated the discussion. I the bass section comprises not only four ask you and Mr. Barden to accept my speakers, but that 'they are mounted in a apologies. I would like to point out, how- ", directional baffle (these important differ- " are really ever, that the subtle but straight-sided wide -angle horns), so ence which Mr. Barden indicates is not, in that it will be seen that everything possible is done fact, there. to loading low The original paragraph referring to air get at frequencies. With regard to the relative advantages of read : " With baffle the loading is loading a a horn speaker below the -off for wavelengths so horn cut and a maximum small that a baffle speaker, the baffle speaker would the sound is thrown off as a beam, and normally have lighter and lighter with increasing the advantage, since it is becomes intended to be I.sed in this manner. If, wavelength." I could amplify this by stat- however, the frequency ing high frequencies the baffle has range of the horn that at speaker has been extended by the use of a practically no effect, but at low frequencies bass chamber, other factors come air loading collapses in its absence. The in, not the the least of which is that full use can be baffle, by preventing this collapse low at made of the improved constancy of the im- frequencies, becomes effective at these fre- pedance curve. quencies, it cannot maximum but preserve Whether the overall result of the one loading on the diaphragm. This is the arrangement or the is vital and fundamental point. of other the better is a matter which can only be settled by a When Mr. Barden attributed to me a listening test. statement " that a baffle affects the loading If Mr. Barden cares to make such a test, at high frequencies only," I corrected him I have no doubt of his verdict. claiming to have said with baffle by " P. G. A. H. VOIGT. speakers, the loading is a maximum at high London, S.E.26. frequencies." I words TELEVISION AERIAL. A practical inter- Although admit the actual to be pretation of a di -pole television aerial with different, my meaning is the same. When IMUST thank Mr. Turner for his response centre- connected feeder as shown in Fig. speaking of baffle speakers in this connec- (May 7th) to my letter (April 16th), but 1(a) on page 5o6 of this issue.

www.americanradiohistory.com MAY 28th, WIp@Il200 1937 OpIl 525 it seems necessary to glean what ,we can matical ability to realise the " ingress " from a good -natured interchange of opinions. channels of a superhet are manifold. Polegate, Sussex. - J. K. TODD. Contrasting with this, the TRF receiver has but one channel, and so confers many benefits under these circumstances. IHAVE been particularly interested in the Dealing discussion on horn -loaded M.C. speakers, now with the superhet under Section (b), we must enumerate the benefits and it seems to me that a little confusion conferred ought to be cleared up. by the superhet circuit over the I refer to the fact that several readers have TRF set. I consider these to be as mentioned obtaining good results from a follows : - speaker designed for baffle -loading but used (1) Greater intrinsic selectivity. with horn -loading. (2) More uniform amplification over the Now, the efficiency of a speaker depends, whole tuning range. up to a point, on the loading, and one of (3) Easier facilities for advantages of horn -loading is (he the provision of the that variable selectivity. loading is constant (roughly speaking) for all frequencies down to the cut -off frequency, (4) Possibly greater overall efficiency whilst with baffle- loading it varies from a for a given number of valves. maximum at high frequencies to a minimum On the debit side I enumerate the follow - at low frequencies. For this reason a MC unit designed for ing:- horn -loading is unsuitable for use with (r) The average 5 -valve is still too baffle -loading except as a " tweeter." noisy in the matter of hiss if the con- Conversely, then, it seems that the method ditions approaching " high fidelity " are of using a MC unit designed for baffle -load- attempted. ing with horn -loading must give equally (2) Self -generated whistles, even though unsatisfactory results. there may be only two, are two too many. Hampstead. JOHN BRIERLEY. (3) The increased sensitivity of super - hets has resulted in " cheese -paring," with result valves v. the that over -complex Superhets Straight Receivers have been developed to " pay the piper." NEW METAL SHIELDED e YOUR leader in the issue dated May 14th (4) The quality of reproduction from raises a multiplicity of questions which some of these receivers with their double TRANSFORMER GIVES may be broadly divided into two classes, diode output pentodes leaves much to be viz. : - desired. LONGER LIFE AND (a) Local characteristics. (b) Universal characteristics. Summarised, then, instead of the benefits UTMOST RELIABILITY I propose to deal with Section (a) of superhets being utilised on sound pro- initially as applicable to my own conditions gressive lines, they have been appropriated Not even moisture, let alone as a resident on the south coast in the to the base purposes of cheapening every- dust, can penetrate the newly thing with little regard to either quality designed metal and compound vicinity of the Solent and as a user of both shield of the universal trans- TRF and superhet receivers. reproduction or replacement costs. Therefore I contend finality in choice of former on the Rola F742 -P.M. As is common to almost every sea coast And important though this near a naval or merchant seaport, the most circuit has by no means been reached. logical develop- special feature is. the popu- common source of interference is morse Moreover, I contend further larity of this new 92" unit transmission. This may be CW- or' ICW ment of TRF receivers of 5 -8 valves is very will probably rest even more and even spark transmission. desirable. upon its wonderful perform- Now let me analyse the possible sources I seriously consider that a really exhaus- ance. With 11,500 lines per in which such transmissions may be received tive analysis of present-day bands should sq. cm. in the gap the flux be made, starting with the idea that repro- density is equal to the famous by a superhet receiver : - duction as faithful as can be achieved, G.12 -P.M. It employs the (i) IF channel. should be the starting point in design. new magnet metal " Alnico," (2) Signal frequency. This step alone will prune the unwieldy and is so sensitive that it sets (3) Self -oscillating frequency. valve list no end. a new standard for battery In the case of (r) the suggestion of reserv- Now to satisfy listeners' requirements, set reproduction, whilst as an ' ing a specific channel for this frequency is They are really simple and fall under two extension speaker it gives not likely to be successful as it would restrict headings :- truly remarkable results. Let from us send you full particulars. naval ships using it. It is generally (a) Real programme value (that is, .known that restrictions of this nature are genuine high fidelity). not feasible to essential Services, who must have free access to any part of the RF (b) Receivable programmes. spectrum. The first section is self -explanatory. The Item (2) is a variable quantity extending second I interpret as meaning intelligible over the broadcast band, which now in- speech or music, but of such quality as to eludes SW. Thus it is quite impossible to make long -period listening a strain. It does F 742- prevent morse signals from being received not need a psychologist to tell us that no in this circuit. " top " and perpetual " boom " is distract- PM Likewise (3) is a variable quantity, but ing to even those professing to be quite greater precautions in receiver design can unmusical. WITHOUT TRANSFORMER 42 - effectively prevent the reception of morse Who says, then, the TRF is a that set USE transmissions at this frequency. I regret nonentity, either on the grounds of selec- OVER 8 MILLION IN to note many commercial receivers do not tivity, range or quality reproduction? Who provide adequate isolation of this circuit cares to claim unquestionable superiority in from the aerial circuit in this respect. all these respects for the superhet? Furthermore, the radiation of the self - Finally, which manufacturer claims the oscillator frequency into the aerial circuit superhet is cheaper to make good than the is far too common. To (3) must also be TRF, and which type gives the most added the question of either the reception trouble? JZE' Grat/ta Thleig IÍOthiCe`L4 of interfering signals on harmonic fre- My deep regret -is that the public per- quencies or production of audible beats on mitted themselves to be swept off their feet THE BRITISH ROLA CO.. LTD. or fundamental harmonic frequencies from with the term " superhet." What of super - MINERVA ROAD, PARK ROYAL,N.W.10. CW. inductance, so well developed by Philips? PHONE : WILLESDEN 4322- 3- 4 -5 -6. It does not require advanced mathe- Portsmouth. ' NAUTrcus."

www.americanradiohistory.com Wireless World, May 28th, 1937

SHORTWAVE AERIALS IN order to ensure the efficient reception of a wide band of short waves, the aerial comprises Recent Inventions two conductors arranged, as shown, to form four diverging Brief descriptions of Litter case, the resistances are in CATHODERAY TUBES arms A, B, Ar, Br. The trans- the more interesting circuit and serve to broaden the OCCASIONALLY the external mission -line feeding the set is con- response curve. pressure on the walls of a nected to the arms at a non -central radio devices and im- When the switches are closed, cathode -ray tube is too great for point. such that the arms A. Ar provements issued as the resistances are cut out. and the strength of the glass, and the are both equal in length, and selectivity is increased. The tube collapses. In an " implo- form a half -wave resonator at the patents will be included coupling between the valves is sion," as it is called, the frag- lower end of the desired frequency' in section then almost completely an induc- this tive one, since both plates of the condenser C are effectively earthed SHORTWAVE SIGNALLING so far as high -frequency potentials T'v(1 short -wave stations A and are concerned. The resistances B, outside the normal range are made variable, so that the de- of intercommunication, are kept in gree of selectivity may be con- touch with each other by an inter- trolled over a given range. mediate relay station C, which E. K. Cole, Ltd., and A. E. may be unmanned. Short-wave Falkus. Application date Septem- signals from A are picked up by ber 14th, 1935. No. 460787. station C, and, after being recti- 0 0 0 0 fied, are used to modulate an out- RADIONAVIGATION SYSTEMS which be of going carrier, may -kno e n method of guid- any desired wavelength, so long well as it reaches station B. Signals ONEing an aeroplane in flight is to from station B are similarly re- transmit two directed beams of energy, so that they overlap ceived by station C and retrans- is mitted to stat'.on A. slightly. The desired course The relay station C uses the the centre-line of the overlapping same wavelength in both direc- part, which is indicated by the r tions. The same aerial can also merging of two separate morse signals into a continuous note. In -42 be used at the relay station, both ' reception, practice, however, the radiation S1' for transmission and beacon is provided it is connected at appro- from the transmitting not entirely confined to the path priate nodal points. There may be O. Póschl ; A. Dietrich ; and P. of the main beam. Automatic voltage cut -out for cathode -ray tubes. Habig. No. 461204. secondary lobes of radiation which are liable to give a false indication o' o o 0 to the pilot. ments of glass usually blow in- band. Similarly, the shorter arms VARIABLE SELECTIVITY The invention consists in modu- wards so that there is little danger B. Br are equal to each other and TIIE coupling between two of lating such secondary lobes with a of mechanical injury. But the resonate at a frequency towards the intermediate - frequency warning note, which clearly dis- electrical risk is more serious, be- the upper end of the wave -band amplifiers in a superhet receiver is tinguiShes them from the naviga- cause some of the internal elec- range. The impedance of the trodes may be at a pressure of down -lead is chosen to give a sub- several thousand volts. stantially flat response to fre- As a safeguard the circuit to the quencies lying between the two high- pressure electrodes is main- extremes represented by the tained by a make -and -break dipoles. The two dipoles may be switch S, which is held in the arranged in the same plane ór closed position by the pressure of otherwise, and may be set at right the end wall of the bulb. Should this break, the switch is automatically thrown open by a spring Sr, and the internal electrodes at once become "dead." The General Electric Co., Ltd., and L. C. Jesty. Application date December 5th, 1935 No. 461374 o 0 0 0 TELEVISION " CAMERAS" -Fin: picture to be televised is 1 first focused on to a photo- electric cathode mounted at the large end of a cathode -ray tube. The electrons emitted from the cathode are controlled by the field from an external winding, so that they traverse a " line " anode. This consists of a number of small conductors. mutually insulated from each other. but forming in conjunction with a common Variable selectivity circuit for superhet IF amplifiers. . earthed element an equal number of small condensers. Each condenser thus acquires an overall selec- t. ' ril signals sent out altered. to vary the along the which of the set. by switches S, main beams, thereby relieving the electric charge simulates the tivity -shade value of a line -ele- SI, Which cut resistances R, Rr in pilot of any doubt as to which is light -and tuned circuits. The the correct course. ment of the original picture. The Aerial designed for efficient and out of the discharged in total coupling is partly that be- Telefunken Ges. Fite Drahtlose condensers are reception over a wide band of the coils L, Li. and partly Telegraphic tn.b.ii. Convention sequence by a scanning beam from short -waves. tween " part of the cathode - that due to the condenser C when date (Gertuanr) September 24th, the " gun are open. In the Nu. 41x0883. ray tube. The arrangement is de- the switches 1935. signed to increase the time during angles to each other as shown in _____ which each picture element can the drawing or at any desired r- angle. I published here prepared. with the permission build up its equivalent electrical The British abstracts are 3 of the Controller of H.M. Stationery Office. from Specifications charge. Alarconi's Wireless Telegraph obtainable at the Patent Office, 25, Southampton Buildings, London, V. A. Jones and Baird Tele- Co., Ltd. (Assignees of I'. D. Lan- V1'.C.2, price r'- each. A selection of patents issued in U.S.A. Is vision, Ltd. Application dates don and J. D. Reid). Convention also included. August r4th, 1935 and March date (U.S.A.) April 2811,, 1934. loth, ¡936. No. 461197. No. 460570.