VOL.2 NO.10 rL'i[r@ [email protected] from. Model 236 (illus-trated) is the latest console...

rL'i[r@ i@molitZMISCH iNV

VOL.2 NO.10

SEPTEMBER

1935

WIRELESS September, 1935

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The D.C.AVOM INOR

CURRENT0-C m amps.0-300-120

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WIRELESS

CCN1FIENTSPage

The Editor's Chat .. .. 135Is Foreign -Reception Enter-

tainment ? .. 136The S.T.600 Battery Radio -

137Broadcasting and the Indian

Empire .. . 139Tuning the Aerial .. .. 141B.B.C. News .. .. 143Intelligent Listening .. .. 144A Four -Valve Battery Super

with A.V.C. 145Developments In World Com-

munication .. 149

PageQuestions I am Asked .. 152In Lighter Vein .. 153Below 100 Metres .. 154Short -Wave Notes .. 155Busman's Holiday .. 157Round the World of Television 159" Wired " Television .. .. 162From My Armchair .. .. 163" Hard " and " Soft " Scan-

ning Circuits .. 165Television for the Cinema .. 167There are Ns LISTENERS in

America . . .. 169

AR some of the arrangements and specialties described in this Journal May he thesubjects of Letters Patent the amateur and trader would be well adrised to obtain

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WIREL ES3 September, 1935

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Septcmber, 1935

rlliielessi

Wig ZLESS

&TELEVISION REVIEW,Good News for "Wireless" Readers-A Fine Battery Super

DURING the forthcoming monthsreaders will notice considerabledevelopments and even some

changes in WIRELESS AND TELEVISIONREVIEW. But the essential characterof the magazine will, of course, remainunaltered. We have every reason tobe satisfied with the position that hasbeen attained and held by what isprobably the most widely read monthlyradio journal in the world.

Nevertheless, we are determined topress still further forward, and in thepursuit of this ambition no effort isto be spared to create attractive newfeatures and methods of presentation.Believing that our readers wouldwelcome contrast to the more technicalmaterial which must obviously alwaysconstitute a large proportion of thecontents Of. WIRELESS AND TELEVISIONREVIEW, we have already introduceda " breakaway " item in the form ofshort stories. And it is clear from ourcorrespondence that these have provedmost acceptable.

Improvements and AdditionsThey have not been and never will

be the effusions of unskilled authorsor " pot-boiler " offerings of quick -firejournalists, but carefully selectedstories by sincere and competentcraftsmen.

In so far as our established featuresare concerned, there will probably berevision, improvements and additionsrather than any contraction. JohnScott -Taggart, who is indisputably theworld's leading radio designer andwriter, will continue to contributeexclusive articles, and so will VictorKing, Dr. Roberts and others of thepopular team which gives strengthand distinction to the magazine.

But you can anticipate some veryimportant developments. And all inthe right direction. There is no need

for us to say " look out for them."You'll see and appreciate them clearlyenough in due course so long its youregularly collect your WIRELESS ANDTELEVISION REVIEW from the book-stall or newsagent or, better still,have it delivered to your house. -

At the BeginningAnd don't forget that from now on

your favourite radio monthly is to bepublished at the beginning of themonth, instead of in the middle of it ashitherto. It may take you an issue ortwo to accustom yourself to thischange, but afterwards you will find

AT THEASTORIA

This is Joe 10384, leader of the AstorbDance Band, and a popular broadcaster

it very much easier to remember thatWIRELESS AND TELEVISION REVIEW" comes out " the first of the month,which is extremely appropriate aswe hope you will agree when yougrasp the subtle significance of thatstatement !

The Great Radio Show at Olympiais still in full swing as we pn these

words. What an exhibition ! What anorgy of technical delight and tyrowonder ! it staggers the imaginationto try and visualise the tentacles whichspread away back from it into thedepths and intricacies of scientificresearch and industry.

Over five thousand sets, and most ofthem different expressions of' amazingachievement in the mass productionof first-class apparatus for fourth-class pockets.

It isn't so very long ago that a wire-less set was an individual construction,the result of the efforts of individualworkers. But these 1936 sets are almostinvariably cast in the moulds of theconveyer belt, the multi -functionalmachine and other aids to scientificmass -production.

And no one will shed a tear for thepassing of the older, cruder; moreexpensive and vastly less efficientmethods !

A "Hot -Stuff" SetThere are many, though, who prefer

to build their own sets. There has beenjust as much, if not more, progress inhome -constructor designs. Evidence ofthis is provided by the battery receiver,which we describe in this issue.

It is a " hot -stuff " super with1. V.C. and other up-to-the-minuterefinements. In view of the fact thatit uses only four valves and consumessomething round about a mere tenmilliamperes of H.T., the performanceit gives is really rather startling.

On a short aerial in the very centreof London during the daylight, itpulled in a number of stations at fullloudspeaker strength, the A.V.C. giv-ing a wide compensation.

At night, in a provincial town,practically every station in Europeseemed to be available for the pro-vision of programmes.

135


Is FOREIGN -RECEPTION ENTERTAINMENT ?Following on the opinions expressed recently by Mr. G. T. Kelsey, particularinterest attaches to the remarks on the entertainment value of foreign

programmes in this article.

By ALAN HUNTERWII EN my fellow scribe and friend,

G. T. Kelsey, takes up thecudgels on behalf of short

waves-as he so piquantly didrecently in this journal-one expects aforcible expression of faith: ForMr. Kelsey, more perhaps than anyother radio writer, believes in shortwaves.

Medium Waves DefendedThat his faith is shared by an ever-

growing band of short-wave fans isobvious to anyone able to read thesigns. The thrill of the chase isnowhere keener than " down under "-where a flick of the tuning knobmagically transports the listener fromone end of the earth to the other.

Short waves, to anyone who reallyunderstands them, need no defence.Far flung Empire 'phone routes give21 -hour testimony to the uniquevalue of short waves in spanningenormous distances with relativelysmall power. The B.B.C.'s Empireprogrammes radiate to every partof the civil sx1 earth. Indeed, froma communication point, of view thecase for short waves is proved. Theyhave verily put a girdle round theearth.

But in defending the short wavesMr. Kelsey seems to me to haveattacked somewhat ruthlessly anotherpreserve of the ether in which he isobviously not quite so interested --the medium waves. He suggests thatno one can honestly claim to be ableto listen to a foreigner on the medium -waves for an hour or more for enter-tainment as such. That is where Idisagree-and I feel fairly sure thatthousands of other listeners are withme.

Question of DistanceLet us clear up one rather important

point right away. If you live within10 to 15 miles of a 50 -kilowatt Regionalyou enjoy a field strength from thatstation enormously greater than youcan possibly hope to from any otherstation-whether it is at home orabroad.

Indeed, if all reception were carriedon under such very nearly ideal con-ditions, I doubt if these elaboratesuperhets would be needed. As it

happens, of course, thousands oflisteners are much farther than 10 to15 miles from a high -power station,and some kind of pre -detector amplifi-cation is essential. For at greaterdistances the set must be moreselective-and the signal must besustained in strength after passingthrough its successive filtering.

Take my own case. I live in theheart of Sussex, some 55 miles southof Brookmans Park. It can hardlybe said that I have a local station.Certainly I have not the boon of avery high field strength signal, greaterthan all others.

As a matter perhaps of surprisingfact the little Normandy station ismore strongly received at my placethan London Regional. But then,of course, the French signal is travel-

HIGH -P OWER COOLING

"Even now, with the high -power stationspumping out 100 hilozvatts or more, theselection of daylight -range foreigners isvery limited," writes the author of thisarticle. Here is the massive control gearfor the valve -cooling plant at one -of the

powerful German stations.

ling part of the way over water,and I am perfectly certain its poweris higher than advertised.

I am not going to quote this stateof affairs as a direct refutation ofthe thesis that foreigners can't hold

a 'candle to the locals. All I sug.gest is that it gives us a line of thoughtpossibly unlikely to occur to thelistener living-as I believe Mr. Kelseylives-extremely near a high -powerprogramme centre. -

In spite of modern automatic -volume -controlling, London Regionalsometimes fades at night time downhere. Fancy that-the local stationfading ! And, believe me, such arethe peculiarities of the Kennelly -Heaviside layer, my home station'sfade is occasionally much more violentthan the fades of certain foreigners.

Far -Off LocalsOur Regionals were put up to enable

the majority of listeners to enjoya high field strength signal-at leastone, and possibly two. Millions oflisteners live within the 30 -mile radiusof these stations, and thus find them-selves confronted with local signalsvery much greater in field strengththan even the highest -poweredforeigners. But there are vastnumbers living on the fringe of theseareas, and some fair proportion, likemyself, outside the_ nominal fade -freerange.

It is these less sheltered listenerswho are likely to be a little astonishedby Mr. Kelsey's dismissal of theforeigners as potential sources ofentertainment-of sustained enter-tainment. To those suffering fromnearest station fading and distortionthe objection to variability . byforeigners is hardly valid.

Altered My OpinionA few years ago, when I, too, lived

under the shadow of a local station,I used to consider that all the for-eigners were " also rans." But thenin those days the power of the foreignerswas much less than it is now. Ourmodern sets worked under old con-ditions would not give us anythinglike the present spate of programmes.For it is axiomatic that a signal isonly as good as its ability to riseabove " static level "-and that is afunction of transmitting power, notreceiving amplification.

Even now, with the high -powerstations pumping out 100 kilowatts

(Please turn to page 172)

136

September, 1935lks1GATT

IDON'T supposeI need to tellyou how to

change over to"gramophone"and put the needle on the record!That's all there is to the " gram" partof this de luxe " battery " combination.

But to get the best out of the radioportion calls for some element of skill-not much, but enough. First of all;learn what the various controls are forand what happens when the knobs areturned.

1:4600RAIDIORA

For Local ExtractionThe Extractor condenser which is

at the back is not really one of thetuning controls at all. It is solelyfor cutting out the interfering " local "B.B.C. station. On the medium wavesthis may be a. B.B.C. relay or aNational programme regional or aRegional programme regional station.These stations will cause overpoweringinterference in certain localities andover certain portions of the dial.

If, therefore, you desire Berlin andLondon Regional blots him out,you just turn the Extractorcondenser till London Regionaldisappears. You will find thatthere is only one adjustment ofthe Extractor when this disap-pearance takes place; on eachside of this point, the " local "comes back.

It only takes a few secondsto adjust and there is no needto look at the Extractor knob;you just put your hand behind the set,turn the knob till the local disappears,and then get on with the ordinarytuning job.

Very often only one of the localscauses really serious interference, inwhich case one setting of the Extractoris good for the whole of the medium -wave band. But when you go overto the long waves, Droitwich may veryeasily cause terrible interference,wiping out Luxembourg and Radio

Paris in someparts of Britain.

The Extractoris once more quitemiraculously

effective and Droitwichis cut down in strengthtill it remains a tenth -rate station. But youhave, of course, to retunethe Extractor condenserif you have beenworking on themedium waves.

The Extractorcoils have a mediumand a long wavewinding, but the switching over isautomatic and occurs in the set whenyou,. change -over on the receiver.Thus, when you are over on the longwaves the Extractor is ready to ex-tract the long wave jammer, viz.,Droitwich.

There is, of course, a disadvantagein having to retune the Extractor forDroitwich, but the whole process isonly a matter of seconds. The only

WIRELESS

a moment you may wonder why.Actually, the Extractor will extractany station, weak or strong, but it isprimarily for cutting out powerfullocals of B.B.C. manufacture.

This may sound slighting to the-B.B.C., and you may well ask whatis to happen if you actually want the" local." You can, of course, get theB.B.C. at full strength by cutting outthe Extractor circuit by tuning it off

the B.B.C. wavelength. Forexample, you could turn thecondenser to maximum (movingvanes fully inside fixed vanes).

B.B.C. ProgrammesUsually this is unnecessary

unless you live a long way awayfrom the B.B.C. Ordinarily,even when the Extractor is atthe best position for cutting out

Mr. Scott -Taggart gives some valuable information ongetting the best results from his latest design, constructionaldetails of which opeared in our special exhibition number." With these hints," says S. -T .," every constructor afteran evening or two should become expert and bring in thehundred stations which this superlatively sensitive set is

frequently capable of receiving."

risk is that you may, on going back tothe medium waves, forget to read justthe Extractor condenser. Rememberthat wherever the Extractor con-denser is tuned (even if you have for-gotten about it !) then will it extract astation.

Thus it might easily extract astation you are wanting. For ex-ample, if the condenser just " happens"to tune the Extractor circuit to Buda-pest, you won't get Budapest, and for

a " local," there remains a fainttrace of the latter, and this may bebrought up to loudspeaker strength byincreasing the reaction, aerial coupler,and volume control-or perhaps onlyone (or two) of these controls.

Where you cannot bring back theB.B.C. by increasing the sensitivity ofthe main set, you have only to de -tunethe Extractor condenser a trifle. TheB.B.C. station will then, as regardssignal strength, become similar to anon -fading foreign station.

137

W!RELESS September, 1935

So much for the non -tuning control.There is also a tone control whichcomes into somewhat the same cate-gory. It is adjusted to suit the tasteof the individual listener. It will. befound that when listening to distantstations any heter-odyne whistle andhigh - note inter-ference can bewhittled down bya mere turn of thetone control. Butdo not forget allabout this control;on a strong stationyou will need allthe higher noteresponse, and thetone control canbe adjusted to givebright reproduc-tion.

Single KnobAs regards the

main tuning of theset, this is done bythe single knob ofthe gang conden-ser. There is asmall concentricknob projectingfrom the main,thus providing afinal titivating "

CUTS

adjustment to the tuning. The gangcondenser does not require trimming inthe ordinary sense of the word, but afew remarks on this point are givenlater.

The aerial coupler does not affect

OUT ALL LOCAL B.B.C. INTERFERENCE

The 11.17. end of the set. The Extractor condenser on the terminal strip provides aready means of culling out any interference front a " local " B.B.C. station. Fit

instructions on the use of this control are given in this article.

timing to any degree that affects thetechnique of operating the set. Theaerial coupler provides greater selec-tivity for the aerial circuit ; byturning the knob anticlockwise (to theleft) signals will be reduced in strength

but selectivity willbe improved.

The volume con-trol is far moreuseful than itsname implies. Itcertainly controlsvolume (althoughthe aerial couplerwill do the same),but its chief meritlies in providinggreater selectivity.When you needthis, you reducethe volume control(turning the knobanticlockwise- tothe left), a n dbring up anodereaction,

Aerial ReactionNeedless to say,

the beginnershould not use theaerial reactionknob until he isquite familiar with(Please turn to page

176.)

THESE ARE THE PARTS USED IN THE S.T.600 RADIOGRAMComponents. Make Used By Designer. ,Components. Make Used by Designer.

1 Tone control, .00075-mfd. soliddielectric variable condenser

1 Aerial coupler, .0005-mfd. solid

Polar (Compax)

B.T.S.

9 Terminals, A., E., H.T.+ 1, H.T.+ 2, H.T.-- 3, L.T.+ , L.T.-,L.S.-, G.B.-1

Belling & Lee (type II)

dielectric variable condenser1 Aerial reaction condenser 0005-

mfd. log. mid lineGraham Farish ( Litlos)

8 Wander plugs, G.B.-2, G.B.-3,G.B.-4, G.B.- , H.T.-, H.T.+ 1, H.T.-r- 2, H.T.+ 3

Clix

1 Main coil assembly S.T.600 Colvern 1 Volume control with 3 -pt. switch Bulgin G.M.251 Extractor coil S.T.600 Colvern (on radio chassis for radio vol.1 Two -gang condenser with drive J.B. type S.T. 2121 and control)

incorporating front trimmer S.L.9A Dial 1 Volume control for gramo Graham Farish -megohm(special to this set) (mounted on motor -board)

1 1-mfd. fixed condenser Graham Farish (Mansbridge 1 Extractor tuning condenser Ormond (S.T.600 type withtype) 0005-mfd. air dielectric knob)

1 1-mfd. fixed condenser Dubilier (type 9200) 1 L.F. transformer Varley Niclet (standard 1: 3.5)2 2-mfd. fixed condensers T.M.C. Hydra(300v. working 1 Terminal strip, 16 x 3 X ,i16 in. Pete -Scott

I .00005-mfd. fixed condensertype 30) 1 Baseboard, 16 x 10 x in.,

Lissen mica with part Metaplex (MetaplexPete -Scott

1 .0003-mfd. fixed condenser Lissen mica covers 16 x 71 in)I .006-mfd. tubular condenser T.M.C. Hydra (600v.working I Panel (walnut or oak -ply), 16 x Peto-Scott1 0.1-mfd. tubular condenser T.C.C. (type T.250 -350v. 9'. in.

D.C. working) 4 Valveholders, 4 -pin anti -micro - Benjamin Vibrolder1 0-5-mfd. fixed condenser Dubilier ( type 9200) phonic1 Anode reaction condenser .0003-

mfd. differential solid dielectricGraham Farish ( Litlos) 1 Pick-up Rothermel-Brush Piezo-

Electric, type S.82 1-megohm mounted resistors Ferranti ( type G.H.1) 1 Radiogram switch 4 -pt. two - Bulgin S.81125,000 ohm 1 -watt resistor Dubilier metallised circuit1 75,000 ohm 1 -watt resistor Dubilier metallised 1 pair needle cups Bulgin N.C.51 20,000 ohm 1 -watt resistor Dubilier metallised 1 Loudspeaker British Rola (type F. 6241 300,000 ohm 1 -watt resistor Erie P.M.00 with terminals)1 50,000 ohm 1 -watt resistor Erie 1 Cabinet (special to this set) Peto-Scott1 Anode reaction choke Wearite H.F.P.J. 1 Turntable motor Garrard (type No. 20), with1 Aerial reaction choke B.T.S. 7 -inch handle

VALVES. 2 COSSOR 210 V.P.T. 4 -pin, 1 MULLARD P.M. 2 D.X., 1 MULLARD P.M. 202

*

138

September, 1935 WIRELESS

1noadcasti11g and le

LYndidn finpimBy The Rt. Hon. LORD STIIABOLGI

T is customary to speak of the Un-changing East ; but the East ischanging rapidly. The develop-

ment of broadcasting, for example, islikely to change the mental outlookof India's 350,000,000 inhabitantsfaster than any other discovery of thetwo thousand years of the Christian era.

Caxton's printing press eventuallybrought great changes in the world bygiving the masses of the people accessto the printed word in literature andthe newspapers. But of India's vastpopulation only about 23,000,000 canread and write ; so the printing presshas not affected them to anything likethe same extent.

Few Can ReadIt is true that the vernacular news-

papers circulate in the villages, and thefew people who can read pass the newson to their hearers ; but with broad-casting, every one of India's teemingmillions can be reached. And nine -tenths of the population live in thevillages.

The wonder is that the Governmentof India, and the India Office inLondon, have not moved more quicklyin establishing, a broadcasting servicethroughout the vast peninsula. Astart has, however, now been made.

It is intended, within the next fiveyears, to establish a chain of stationsthroughout India. Mr. Lionel Fielden,well-known in the broadcasting world,has received the important appoint-ment of General Manager of Broad-casting, and is leaving for Delhi. Thefirst station was opened at Peshawar,the capital of the North-West FrontierProvince, this spring ; and the secondhigh -power station, one of the mostpowerful in the world, is under con-struction at Delhi at a cost of £22,500.

The Financial PositionNow there is this excuse for the

Government of India : our IndianEmpire has passed through the sameeconomic crisis as the rest of the world

Unique in its large number ofspoken languages, India pre-sents quite a big problem wherethe provision of an organisedbroadcasting service is con-cerned, The vital considerationsare clearly set forth in this

authoritative contribution.

II

and the revenues have been strainedto the uttermost. For the present it isadministratively impracticable tocharge a licence fee for receivingapparatus. The bulk of the public wholive in the 700,000 villages of India are

THE AUTHOR

The Rt. lion. Lord Strabolgi, who writesthis interesting article on a subject whichis of considerable moment at the present

time.

miserably poor, and could not possiblyafford to pay a licence to an amountworth the cost of collection; so that,whereas in Britain the B.B.C. not onlypays its way but contributes substan-tially towards the general expenses ofthe nation, in India the cost of awireless system will be a direct chargeon the Exchequer.

A Difficult ProblemAnother difficulty is the number and

variety of the languages. India is aconglomeration of races, many ofthem differing widely from the others.Only about 10 per cent of the popula-tion understands English. There are220 spoken languages! The vastmajority of the inhabitants onlyspeak their own language. These 220different languages are divided intothree main groups-the Aryan, theDravidian, and Hindustani itself. TheAryan languages are spoken by thedescendants of the great waves ofimmigrants and invaders who passedover the mountains into India in thelong lost past ages of history at thesame time that another great wave ofthe same races occupied Europe.

The Chief DialectsJust as the Aryan languages in

Europe are now divided into Spanish,French, German, English, Russian, andso on, so the Aryan languages in Indiaare divided into a number of chiefdialects, of which the principal areHindi, Marathi, Punjabi, Bengali,Uriya and Gujarati. These languagesare spoken by 257,000,000 people.Entirely distinct from this group arethe Dravidian .languages spoken bythe pre -Aryan indigenous inhabitantsof the South of India, of which thechief are Tamil, Telugu, Kanarese andMalayalam. These are the languagesof another 71,000,000 people.

Four hundred years ago occurredthe great Moslem invasion of India ;and there was evolved an officiallanguage, Hindustani, which is a

139

WIRELESS

corruption of Hindi mixed with Persianand Arabic and ranks with Englishas the official language and generalmeans of communication. Hindustaniis spoken by the small percentage ofeducated people.

Broadcasts in VernacularNow broadcasting will be of most

value if it reaches the masses. It istherefore obvious that programmesmust be broadcast in the vernacularlanguages, and the changes will haveto be rung amongst at least a score ofleading dialects if the villagers are tobe able to understand what is comingover the ether. Furthermore, theservice must be under strict Govern-ment control, because the greatestcare will have to be taken not toupset the religious and social sus-ceptibilities of the various creedsand castes. Thus, while thereare 240,000,000 Hindus, thereare 77,000,000 Mohammedans, and13,000,000 Buddhists, not to mentionthe 6,000,000 Christians, the Parsees,Jews and others.. The adherents ofthe creeds are in fierce rivalry witheach other, especially the Hindus andMohammedans, and the greatest carewill have to be taken that nothingappears in the programmes to upset thefeelings of any of these people.

The first station at Peshawar hasbegun to function, and the first pro-gramme was made in the language ofthe Pathan tribes. The reason thisNorthern station was erected first of allis that we have had great difficulty withthe independent and semi-independenttribes on the frontier. Fierce fighters,Moslems by religion, they have causedus trouble ever since we assumedresponsibility for the peace and orderof India. If they can be reached bywireless, the results should be good inhelping to preserve peace on thistroubled frontier.

"Speech from Heaven"The first spoken word by wireless in

India was during the initial broadcastlast March, when Sir Ralph Griffith,the Governor of the North-WestProvince, broadcast a message to thePathans in their own dialect. Thiswas received with astonishment by the -tribesmen who have named the systemwith a native word meaning " speechfrom Heaven." I have never heardany listener in this country talk of theB.B.C.'s programmes as " speech fromHeaven," and I should think that LordBridgeman and the other Governorswould be highly flattered if thisexpression were applied to their pro-grammes I

THOUSANDS OFLANGUAGES

It is intended to broadcast nativemusic and also talks on health, sani-tation and, most important of all,agriculture. Apart from the politicalvalue from the Government's point ofview in reaching the villages of Indiaby wireless there will be an undoubtededucational effect. One of the troublesin India is the out-of-date system ofagriculture. The ploughs are the sameas those in use for thousands of years,and they do not plough deep enough.The use of modern fertilisers is littleunderstood, veterinary practice isvery backward, and, by way of anexample, the Indian peasant pro-prietors for the most part, that is tosay. the Hindus, are prejudiced againstkeeping poultry, which they regard asunclean. So poultry farming, the greatstandby of the European smallholder,is neglected.

THE MAN IN CHARGE

Mr. Lionel Fielden, well known in con-nection with British broadcasting, hasbeen chosen as General Manager of the

India Broadcasting Company.

Indeed, the greatest problem ofIndia is not political at all. It iseconomic ; the extreme poverty of theteeming millions, whose numbers haveincreased under peaceful rule, andwhom the land will barely support.Any better methods, therefore, offarming and irrigation, that can betaught to the villagers will be oftremendous benefit.

One-third of India is under the ruleof the semi-independent princes.

September, 1935

Certain of the great states, Hyderabad,Mysore, Kashmir, and others, rank insize with European countries. TheIndian Princes have shown greatinterest in the Peshawar station, andare investigating the possibility ofestablishing their own radio stationsin co-operation with the main Indiansystem. This will be a great'help also.From what I know of India, I cannotvisualise a peninsula wide hook-upsuch as is practised in America, withone message or programme goingthrough all stations ; and that becauseof the language difficulty. I believe thesolution will lie in a multiplicity ofsmall low -power stations, each servingits own district where one or twoleading languages are used ; and twoor three high -power stations, princi-pally for official communications.

Public Speaker SystemThere will be few independent

" sets " bought in proportion to thevast population ; but probably theRussian system will be adopted bywhich a loudspeaker is installed freein each village square. This will becostly, and it will strain the resourcesof the Finance Department of Indiato complete it within five years ; butit will be money well spent, and shouldhave important and beneficial resultsof almost incalculable value.

SIMPLE AERIALSEPARATORS

By A. H. CUTT

FOR short-wave work it is becomingcommon practice to use doublelead-ins, or " feeders " as they

are termed. If these feeders arecrossed at short intervals there is agreat reduction in background noisedue to man-made static, etc. Specialseparators are sold for the purpose,but they are rather costly. The follow-ing is a cheap way of making them.

The material used is ordinary ply-wood. This is cut into narrow stripsand four holes drilled in each piece.They are waterproofed by soakingthem in a solution made by dissolv-ing a tallow candle in petrol.

The feeder wires can be of rubber -covered flex or high-tension cable.Thread the wires through a sufficientnumber of the separators, allowing atleast one for each foot of the feeder.They are then grouped in pairs, thewires crossed, and each pair tied to-gether with short pieces of cord toprevent the wires from untwisting.

140

WIRELESSSeptember, 1935

Tunin'r-thoAorialTins is going to be an article for

the amateur experimenter orthe constructor who likes tin-

kering about with his set to get betterresults. Like I do. I sometimes findit very difficult to leave a set aloneeven when it is supposed to be workingfor the entertainment of others. Iitch to adjust this, turn that andgenerally mess about with the thing.

The Urge to TinkerOne of these days I suppose I shall

relax and the urge to tinker willdisappear-and so will I, 'from radiojournalism ! However, that day is inthe distant future. In the meantime,one still experiments. That there arevery many readers of WIRELESS whodo likewise I have complete proof. .

Not so long ago.

I said somethingabout the hotting -up of modest two -and three-valvers togiv e performanceswell above their sup-posed powers. Ittook me about amonth to clear offthe correspondencewhich arrived. Not that I minded ascrap, and I don't think there is onecorrespondent of that period, or anyother for that matter, who can saythat he did not in due course get areply to any questions he may haveasked me.

Hey, there ! Put down that pen,I'm just away for a vacation dcwnsouth !

"Coddling"Now about this

experimenting. Youcan do some ex-tremely interestingthings with the aerialcircuit of your setor any other set-owner willing.

You know, wedon't use our aerials these days. Am-plification is so liberally applied thatthe average set doesn't properly startbeing a scientific job until the grid ofits first valve is reached.

In the sterner days we used toconserve and coddle every possibleparticle of energy which could be

A VALUABLE CONTRIBUTIONOF 'INTEREST TO ALL

EXPERIMENTERS

wrung from the ether. Our aerialswere boldly thrust into the sky andmade to form part of a circuit whichcould be tuned exactly to the wave-length of the station we wanted topick up. Made receptive to theumpteenth degree, in fact.

What we do now is mostly to regardthe aerial as a collector pure and

SIMPLESCHEMES

The circuit on theleft shows a sim-ple untuned aerialscheme, the onetapping servingboth medium andlong waves. On theright is a similarcircuit with an

additional coil L2 and a condenser C2 fortuning the aerial circuit. The wave -change switch is omitted for simplicity.

simple in the broadest and mostgeneral sense. And a collector notof the one station but of every one,leaving it to the set to apply thediscrimination and a whale of ampli-fication, to make up for the loss of

INCREASED

SELECTIVITYIn Fig. 3 a smallpreset condenser isconnected in serieswith the aerial toimprove selectivity,while in Fig. 4 theaerial is taken tothe centre tappingon the tuned aerial

coil and a coupling condenser is insertedas shown.

power. Maybe that method has itspoints. I said maybe.

Often though, when applied rathermore carelessly than usual, you getdiscrimination of a very much un-

wanted kind. Look at my first littlediagram. It's all most theoretical andso on, but, alas, as the Polynesian saidwhen he picked up the ripe endof a thousand volt supply, experimentwithout a little theory is as a bookwithout its pages.

A Well -Known DefectFig. 1 shows a simple aerial arrange-

ment such as has been widely usedand is still frequently encountered.The aerial taps into the coil, whichforms part of a tuned circuit. Ashorting switch cuts out part of thatcoil for the medium waves but enables

the whole of it tobe employed forlong -wave tuning,Actually, the coilmay consist of twowindings, but ineffect it is one coilfor our purposes.

The aerial is sup-posed to be untuned,but it is not " aperi-

odic." That is to say, it will not" accept " all stations equally andgive no favours. It possesses induc-tance and capacity and will, therefore,respond to one wavelength, or a moreor less narrow band of wavelengths,better than the others.

Now it has happened very often, tothe great discontent of listeners, thatthe " natural " wavelength of the

aerial system whenthe switch is over to" long waves " fallsclose to that of amedium wave stationowing to the factthat its self -capacityand inductance, plusthe inductance ofthat part of the coilwhich is included in

the aerial circuit, " tune " to themedium wave 'station. Hence, break-through!

And how is break -through some-times cured ? By sticking another smallcoil in the aerial circuit to raise the" natural" wavelength above that ofthe medium -wave broadcaster which is

141

WIRELESS

broadcasting its way unfairly andunethically into the long -wave pasturesof the set.

Now you who have experiencedbreak -through, let me ask you aquestion. Have you ever noticed howloud that break -through is despite thefact that all the tuning circuits in theset are wielded against it ? I bet youhave. And the reason ? The aerialtunes to the interferer and grabs somuch power from it that you want aminifier not an amplifier, to deal withit ! (I fancy that crack's a trifle toosubtle ; still, let it pass.)

An Interesting ExperimentThe moral of all this is quite

obvious and it is that if there is astation you want to bring in with thebiggest punch possible on a given set,or, for that matter, if you want toboost up all the stations, then youhave a method right to hand. It issimply that you should tune the aerialsystem in the same way as you tunethe grid circuits in the set.

Try it. You'll meet with some sur-prises. Let me explain the idea indetail. Take our little Fig. 1 circuit.I'll simplify that still further byknocking out the wavechanging. Wenow have Fig. 2. But there is a coiland condenser AV. The added coil(L2) is for the purpose of increasingthe inductance of the aerial circuit.There won't be enough without it. Ican't tell you exactlywhat size of coil willbe needed, for somuch depends uponthe coil in the set andthe position of itstapping. This iswhere the experi-menting begins tocreep in.

As a start youcould wind twenty turns on a two-inch former, using 24 -gauge wire (or26 or 28 if either of these is more con-venient), and decrease or increase theturns after a test or two.

Strength Will IncreaseA .0005 mfd. solid dielectric

condenser will do for the tuning.This condenser appears as C2 in thediagram.

With such a scheme you will findthat the strength of the medium wavestations will bump up considerably.But they may be too powerful for theselectivity of the set, for there will bea fairly strong coupling between theaerial and the grid circuits.

You can, therefore, see what a seriespreset as in Fig. 3 will do. That will

STATIONS WILL BELOUDER

give you some control over selec-tivity, and I'll eat my only trilby ifyou have to apply so much seriescapacity that your stations will fallto their original level of strength.

Some of you might conclude thattapping down the new coil as in Fig. 4would give similar results and save a

EASY TO TRY

Fig. 5 shows theFig. 3 arrange-ment adapted toboth medium andlong waves. Fig.is a very efficientscheme giving ex-cellent selectivityand volume, andFig. 7 (above) is apractical circuitbased on this

scheme.

condenser. Don't believe me if I say" No " to that, but experiment foryourselves. If you tap down and usea series coupling condenser as shown,your results will be controllable. ButI like the coupling condenser ideaapplied as I shall describe later.

So far we have tackled only themedium waves, and that might be allright for the U.S., where they don'tbelieve in big things ; but we inEurope have to consider the longwaves, too.

Well, there is no reason why youshould not wave -change your aerialbooster, is there ? Fig. 5 shows youFig. 3 adapted to both medium- andlong -wave stations.

September, 1935

Yet we haven't gone as far as wecan go along the route of aerial tuningexperiments. It is quite on the cardsthat some of you would get astonish-ingly superior performances by meansof simple expedients such as I havealready described. But there will beothers. There always are.

A Complete TunerTo those I commend Fig. 6. Here

we have an aerial tuner complete withseries condenser coupled to the set bymeans of the aerial winding (or tap) ofits aerial coil and a coupling condenser.This last should be one of those'00015 mfd. maximum air types.Fig. 7 gives you a practical circuitbased on this scheme. But this againis only for medium waves, and for thereception of long waves a long -wavewinding and a wave -change switchwould need to be provided.

This Fig. 6 circuit not only tunesthe aerial and therefore increases itspick-up, but it provides another com-plete tuning circuit and increases theselectivity of the set. Though I warnyou that if you chase selectivity upto super degrees you are bound to losesensitivity. You always will.

On the other hand, I fitted such acircuit to a commercial battery setnot so long agg and improved itsselectivity no end, and at the sametime I reckon the strength of mostof the stations was pushed up at least

five times, if notmore, believe it ornot.

When your ad-ditional circuit isloosely coupled tothe circuit in theset itself you will getsharp tuning on theset, although theaerial circuit, the

new one, is bound to be somewhatflatter. It is for this reason that oneof those better quality solid dielectriccondensers will serve the purpose quitewell.. There is not much to be gainedby using an air condenser completewith calibrated dial. With a tightercoupling, band-pass effects will beginto creep in. But you need not worryyourself about that. It is more likelythat the overall curve of the set willbe improved rather than otherwise.

Harking back a bit to the questionof aerials, I want to leave this thoughtwith you. It has been commonlyaccepted as a fact that modern setsare so good that you don't have tobother much about the aerial. Butmightn't many of us take this tooliterally ?

142


More Jobs GoingIHEAR there are lots more jobs going

in the B.B.C. For example, thepromotion of Mr. J. Beresford

Clark to succeed Mr. Cecil Graves asDirector of the Empire Departmentmeans the appointment of a new Pro-gramme Director for the Empire.Another job that is going is that ofInformation and Talks Assistant atBelfast, on the promotion of Mr.MacMullan. There will be at least adozen similar appointments to fill inthe autumn.

The procedure now followed by theB.B.C. is to give present staff the rightof first refusal of all such posts. If thisdoes not lead to the application ofsuitable candidates, then the posts ar.-advertised and the short list of candi-dates is interviewed by an Appoint-ments Board. This procedure isobviously much better than the oldmethods.

Jack Hylton's Radio RevueAt Broadcasting House there is much

interest in Jack Hylton's Radio Revue,which will be given in the RegionalProgramme at 8 p.m. on Saturday,September 21st. Mr. Hylton is pre-paring some surprises in the way oflight entertainment. If the programmeis as successful as expected it will marka new era in B.B.C. entertainmenthistory.

Commercial Information forthe Empire

Beginning this month, the B.B.C.will provide a new service of commer-cial information on all the short-waveprogrammes. The idea is to encouragethe spread of accurate commercial

Jr newsLight Entertainment Surprises-Augmenting the EmpireService-The New Post Office Cable-Children's Hour

To Tour

By Our Special Commissionerinformation on all subjects affect-ing the development of tradewithin the Empire. It will beinteresting to observe whetherthe B.B.C. succeeds in this laud-able enterprise.

Lady ReadingI am told by a member of the Ills -

water Committee that Lady Readinghas been " the life and soul " of theirlittle parties. Her vivacity, alertness,and interest have helped to penetratemany an obscure problem. She has

nA00

AWARDEDTHE O.B.E.Miss MarySomer rifle,Director ofSchool Broad-casting M theB. B. C., wh owas recentlyawarded the

TheB.B.C. broad-easts toschools mainlyaim at stirringchildren b e -tweets the agesof 11 and 14.

vAva

now mastered all that there is to knowabout broadcasting, and it is generallyexpected that she will be chosen tosucceed Mrs. Mary Hamilton as womanGovernor of the B.B.C. when the latterretires at the end of 1936.

TelevisionThe announcement of the sensa-

tional new Post Office cable capable

of carrying two hundred messagessimultaneously may have, an importantbearing on the development of tele-vision. A limiting factor so far hasbeen the accepted fact that highdefinition signals could not be satisfac-torily transmitted by land line. Thusan uneconomic duplication of pro-grammes seemed inevitable.

Now, however, it is promised for thenew cable that high -definition tele-vision signals can be carried any dis-tance and faithfully reproduced at theend. If this is proved in practice, thenthere will be an enormous saving in thecost of covering the whole country foradequate television. It would bringthe national coverage stage muchcloser.

A Trade Union in the B.B.C.Encouraged by the concessions

granted as a result of complaints bymanual workers and junior engineersat a staff meeting some weeks ago,members of the staff of the B.B.C. arebeing canvassed secretly to secure theiracceptance of the idea of a staff councilor trade union which will be entirelyindependent of official control.

The movement so far has beenignored by the administration of theB.B.C. If this attitude is maintained,it is difficult to see what go6d the stafforganisation will accomplish, becauseit is only through being recognised forpurposes of negotiation that such amovement can justify its existence.The fact that it has begun even in atentative way reveals a degree of dis-satisfaction which should call for theattention of the Board of Governors.

My information is that conditionsof work and pay are do the whole,good. The chief cause of trouble isthe attitude of autocratic authorityand despotism, however benevolent.

Mr. Fielden Off to IndiaMr. Lionel Fielden, the new General

Manager of the India Broadcasting(Please turn to page. 174.)

143

WIRELESS

INTELLIGENT LISTENINGOur short-wave expert deals on this page with animaginary day's listening, telling you on what wave-lengths to listen at the various times of the day.

SHORT-WAVE reception is an art initself, both on the technical sideand when it comes to handling a

receiver. On -the average broadcastreceiver we simply know, from experi-ence, that certain stations can be heardthroughout the hours of daylight,while many more appear in theevenings.

On the short waves, until we havehad first-hand experience of -things, wecannot form any assumption of thatkind. Certain stations can only beheard in the small hours of themorning, others at breakfast -time, andothers during the afternoon andevening.

Always SomethingAt any hour of the day or night there

is something coming through, if welisten on the right wavelength for it.Suppose we are starting an imaginarybout of listening at about2.30 p.m. on a Saturday.Personally, I should goeither to 16.87 metres andlisten to Bound Brook(W 3 X A L) or to 19.72metres for Pittsburgh(W 8 X K). The 16 -metrestation will probably be thestronger of the two, andif it's a bad day they'llboth be pretty weak untillater in the afternoon.

Other programmes thatwill definitely be on the airare those from the EmpireStation at Daventry andfrom the various Zeesenstations-probably on the19 or 31 -metre bands.

On the 20 -metre amateurband, during the afternoon,there will be a profusionof signals from the U.S.A.,and probably from Asia as well, but ifyou're not a Morse enthusiast yourchance won't come till later in theevening.

Early EveningBy tea -time the 16 and 19 -metre

bands will have livened up consider-

ably, and W 8 X K, in particular,should be fairly strong and reliable.If you're lucky you might hearBombay between 5 and 6.30 p.m., on31.36 metres. He often puts over quitea strong transmission nowadays.

Since I'm not suggesting that youput in a 24 -hour. bout of listening-a feat that only appeals to super-men-I think it might be a good plan toshut down until 8 o'clock or there-abouts. Punctually at eight you willhear W 2 X AD start up on 19.56metres for an hour's programme fromone of the American medium -wavestations.

He will be about the strongestAmerican station you will ever hear,

hardly any ochance ofmissing him if your receiver is any-thing like a receiver.

If you care to 'get on by 7.30, andatmospherics aren't too bad, you ought

AN AMATEUR OF THE FAR EAS

Seichiro Ilanda, an eighteen year old Japanese student, whosotransmitting station J 1 D M has proved very successful in long-

distance contacts.

to be able to bring in Nairobi (VQ 7 LO)on 49.4 metres. He hasn't been stronglately, but an ordinary two-valver hasbeen fetching him in night after night.Johannesburg (Z T J) on 49.2, is

weaker still, but keeps on till a laterhour and is generally quite goodbetween 8 and 9 p.m.

September, 1935

From 9 p.m. onwards a bout of" all -in " reception is indicated, sincestations are becoming more numerousand you are liable to hear interestingtransmissions on practically any ofthe wavebands - 19, 25, 31 or 49metres. W 8 X K starts up on 25.27metres at 9.30, having closed down his19.72 -metre transmission 'at that hour.

By the time 11 -o'clock arrives, the49 -metre band will be filling up withNorth and South Americans, workingso close together that identification isno easy matter unless one hears anannouncement.

Most of these stations will steadilyimprove in strength until the earlyhours of the morning. By the timemidnight arrives, by the way, therewon't be much point in listening foranything below the 31 -metre band.That and the 49 -metre band will becarrying practically all the traffic.

The Best TelephonyThe 40 -metre amateur band, by the

way, will be fairly full of Americans,but they are not licensed to usetelephony on that band. The telephonyis at its best on the 20 -metre bandbetween 10 and 11 p.m., althoughsometimes, on freak nights, it persistsin coming through until after mid-night, in spite of what I have justsaid.

By the time 6 a.m. arrives you wiltbe able to go down there again. If you

have a really good receiver,you may hear telephony onthe 20 -metre band fromamateurs on the West Coastof America, or even fromHawaii. In any case at6.30 you might be able tohear Suva, Fiji Islands(V P 1.A) on 22.94 metres.

AustraliaMost of the 49 - metre

stations close down at 3 or4 a.m., and there are reallyvery few transmissions onthe air between those hoursand 8 a.m. If it's Sundaymorning, however,. Sydney(V K 2 M E) will start upon 3F28 metres at 7 a.m.,and should be received welluntil 10 a.m. If it is aweekday you will haveLyndhurst (V K 3 L It) as

an alternative Australian transmission,although he does not switch on until9 a.m.

You can see from the above that youstill have to treat the shorter wave-lengths almost as " daylight bands,"going steadily up your wavelengthscale as darkness draws near. W.L.S.

144

September, 1935

Economy combined with great efficiencymakes this receiver an attractive propositionfor all battery users. Using only four valves,it gives a wide choice of stations and providesample selectivity to cope easily with modern

conditions.

NE of the greatest problems indesigning a really powerful setfor the battery user is that of

getting the desired results withoutexcessive H.T. current consumption.Undoubtedly one of the most populartypes of set at the present time isthe superhet and this popularity isfully merited.

In the Front RankFew receivers can compare

with the superhet for selec-tivity. This is due to thesuperhet principle itself,although obviously first-classtuning coils must be incor-porated in order to achieveanything approaching 100 percent. efficiency. In manyways the superhet has beenlooked upon as the mainsusers' pigeon. People oftensay : " He's a lucky fellowbecause he's got the mains,and therefore H.T. and L.T.current consumption don'tbother him."

This, as a matter of fact,

ALL THE PARTS --

WIRELESS

DESIGNED AND DESCRIBED BYTHE "WIRELESS" RESEARCH

DEPARTMENT

until fairly recently, has been justified.The battery user has had rather a thin

time as compared with his morefortunate brethren, who have the

advantage of A.C. or D.C. supply;and yet, curiously enough, thereare more battery set owners thanthere are owners of all -mainsdesigns.

Better and CheaperWe, in this country, have

not yet gone " all electric,"for the simple reason thatthere is no electricity laid onto many thousands of housesin various parts of the BritishIsles, outside the immediatei inity of the larger towns.

Perhaps one day the gridscheme will solve the prob-lem, but that day seems along way off at the moment.Until then the battery usercan only hope that the valvemanufacturer will go on con-ducting intensive research onhis behalf, as he is doing atpresent, with the object of

1 Polar 3 -gang tuning condenser Modernity, both in appearance and design is a distincliresuperhet type. feature of this fine battery superhet.

1 Polar semi -circular drive for above.1 Set Colvern superhet coils type K61, K82 and 863.2 Colvern I.F. transformers type 110.1 Ferranti L.P. transformer type A.F.8.1 Bulgin screened superhet H.F. choke type H.F.10.1 Varley screened Nicore H.F. choke type B.P.28.1 Dubilier 1 -mid. fixed condenser type B.B.1 T.M.C.-Hydra 1 -mid. fixed condenser type 30.1 T.C.C. -1-mfd. fixed condenser type 50.2 T.C.C. 1-mfd. tubular fixed condensers.2 T.M.C.-Hydra 1-mfd. tubular fixed condensers.1 Dubilier .1-micl. tubular fixed condenser type 4503.1 Dubilier 0005-mfd. fixed condenser type 665.1 Dubilier .0001-mfd. fixed condenser type 820.3 Graham Parish i-meg. 11 -watt Ohmite grid leaks in horizontal holders.1 Erie 100,000 -ohm resistance 1 -watt type.1 Amplion 100,000 -ohm resistance 1 -watt type.1 Bulgin toggle onfoff switch type 5.80.1 Peto-Scott mounting bracket type 22.1 Peto-Scott mounting bracket type 2211.1 Erie 50,000 -ohm volume control graded type.1 Formo preset condenser -002-mfd. (max.).3 Clix 7 -pin chassis -mounting valveholders with screw terminals.

-YOU WILL NEED1 Clix 5 -pin chassis -mounting

valveholder with screw terminals.1 Westinghouse Westector type W.6.

1 Peto-Scott baseboard covered both sides with copper foil or " Metaplex,"12 x 10 x hin. and runners 10. 3 in.

2 Peto-Scott terminal strips, 2>.111 in.4 Clix indicating terminals type B.2 Belling -Lee accumulator spades.1 Belling -Lee wanderfuse.7 Clix wander plugs.1 coil B.R.G. " Quikon " connecting wire.Screws, flex, etc.

Marconi orOsram

VALVESSignal H.F. Mixer. I.F. OutputV.P.21 X.21 V.P.21. P.1.2

BATTERIESH.T.-120 volts. Drydex, G.E.C. Ever -Ready, Lissen.L.T.-2 volts. Exide.G.B.-4f volts. Drydex, Ever -Ready, Lissen.Loudspeaker. --W. B. Stentorian.

145 0

3I

WIRELESS. September, 1935

getting better results with fewer valvesand a lower current consumption.

This month we are describing asplendid example of the most modernradio technique in the form of a four -valve superhet with automatic volumecontrol. It is a set, we can assure thehome constructor, that will giveexceptional results as regards range,selectivity and quality of reproduction.

These results are due to the fact thatthe most advanced technical develop-ments have been combined togetherto form a compact and extremelyefficient whole.

Saving a ValveWe have been able to reduce the

number of valves to four and yetobtain remarkable efficiency and ahigh degree of selectivity. As you willall realise, every superheterodynerequires two detectors, and in thepast both of these detectors havebeen of the thermionic valve type.But now the designer is able toreplace one of these valves, namely,that which carries out the func-tions of the second detector,with a small dry rectifier called the" Westector."

This is a device similar in mostrespects to the familiar Westinghousemains rectifier, but has been speciallyadapted by the manufacturers to.

THE "WESTECTOR" RECTIFIER SAVES H.T.

Pentode amplification is employed throughout, the intermediate -frequencyand output raires being of this type. This arrangement. together with a heptodemixer valve and a " Westector " second detector produces an exceptionally powerful

combination.

/2.Apo, r Lw your 4,0 CA6Wver OR/ct,NC 06.GIMM

THERE ARE NO PANEL MOUNTING COMPONENTS

3 GANG COIL .3 GANG 7-1//V//VG ( .542 000 °HA'S/ CONDENSER 7".* voz.Conenaot

2

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carry out the important duties ofrectifying H.F.

The Westector " is an ideal seconddetector in a superhet., and we haveused it in this receiver with highlysuccessful results.

Though the "Westector " allows avalve to be cut out, credit is due tothe valve manufacturer, because it ishe who has enabled us to get suchremarkable efficiency. In this par-ticular design, for example, thefirst valve is a variable -mu pentode.It carries out the important work ofamplifying the incoming impulses attheir ordinary broadcast frequencies.This scheme not only produces highinitial stage gain, but also providesa much greater degree of selectivitythan other methods.

Mixer and OscillatorThe second valve is an X21, which

acts as a mixer, that is, a combinedfirst detector and oscillator. Theincoming impulses, after passingthrough this valve, are then amplifiedat intermediate frequency by a secondvariable -mu pentode, finally arrivingat the " Westector," where t1iey arerectified, and afterwards amplified atL.F. by a high -efficiency pentode out-put valve.

Although the stage gain is socolossal, the set is, nevertheless,

The diagram on tlw left shows theabove -chassis layout. It will be seenthat all the controls are actuallymounted on the chassis itself, so thatonly the clearance holes for thespindles have to be drilled in thecabinet front. The dimensions forthese are given in the small diagram.

146

September, 1935

absolutely stable in operation. It willbe appreciated that the greater theamplification per stage in a receiverthe greater also are the chances ofinstability taking place. There needbe no fears on this score in the case ofthis superhet.

All the vital parts are screened, andwe have used a foil -covered baseboard,which serves to separate variousleads and components which 'nightotherwise interact.

Very Clean LayoutOn the top side of the chassis are

mounted the tuning coils, gang con-denser, manual volume control, andintermediate frequency transformers,and, of course, the valves.

On the under -side are the remainingcomponents, together with most of thewiring.

This gives an extremely neat ap-pearance to the assembly, although wewould add that this neatness is simplyincidental, efficiency having been ourprimary consideration.

There is also a three -gang tuningcontrol giving single knob tuning forthe broadcast wavebands. Once thetrimming of the three sections of the

A DESIGN WITH EXCEPTIONALLY SIMPLE WIRING

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WIRELESS

This photograph provides a usefulreference to the practical run of thewires when used in ccnjunction with

the diagram below.

gang condenser has been carried out,the whole operation of tuning in astation becomes merely one of turningthe knob until the pointer indicates thewavelength required.

The Coil KitThe three Colvern coils are, of course,

very accurately matched up anddesigned for use in conjunction withthis type of superhet receiver. Andthey, are, of course, intended to beused with the intermediate trans-formers specified ; in fact, the coilscan be looked upon as one completekit and no attempt should be madeto use mixed coils in this set. Onlyby adhering strictly to the specifiedparts is it possible to achieve thedegree of efficiency which the receivergives.

From the construction standpoint,everything is straightforward and freefrom snags. As we previously pointed

Most of the wiring is carried outbelow the baseboard, as this sub -chassis diagram illustrates. Whereleads pass through to the corn-ponents above, the holes arenumbered to correspond with thenumbers in the wiring diagram on

the preceding page.

117

WIRELESS

out, the baseboard must be metalcovered, either .with copper or thepopular " Metaplex." And, moreover,it is essential that this metal coveringshould be bonded so that both sidesof the baseboard are common fromthe electrical point of view.

If copper foil is employed onepiece can be used and wrapped roundboth sides of the baseboard in onecontinuous sheet. In the case of a" Metaplex" baseboard, cut to size, it isadvisable to run a bolt, terminatingin a nut and washer, right through,so that the top and underneath sur-faces are electrically short-circuited.

Chassis Earth PointsSome care is necessary when cutting

the four holes for the valve holders toensure ample clearance between theedges of the holes and the socketswhich take the valve pins. Eachpin should be well clear of the metalbaseboard covering. Adopting theaccepted modern principle in setdesign, we have connected certainleads direct to the metal coating on thebaseboard. This coating is, of course,earthed, and each lead connected to itis thus also earthed. Hence, the metalwork forms a common earth, and it isfar more effective to carry out thisearthing by means of short wires onto the nearest point on the baseboard,

ii

ENSURING THE BESTSENSITIVITY

than to take each wire to the earthterminal.

It is more efficient from the radiopoint of view, and, of course, itsimplifies the con-struction'. Eachpoint where a lead isjoined to the base-board is markedM.B. on the wiringdiagram, and it isessential that theseconnections shouldbe firmly made, sothat the electricalcontact between thelead and the metalcoating offers thevery minimum resis-tance path to thealternating currentsflowing in the circuit.

And now for a fewhints on adjustingthe trimmers. Firstof all, make a start

September, 1935

trimmertl:midway. You will find thetrimmers on the two I.F. transformersat the base of the coils, a little leverprojects through a slot, and you canmove this either way as desired.

Now tune in a station at the lowerend of the dial on the medium wave-band. Adjust the oscillator trimmer-that is the rearmost one on the gang

HOW THE COIL UNIT IS WIRED

The wiring to the coil unit terminals is clearly seen heresince the screening cans which cover the individual coils havebeen removed. The preset condenser on the right is a

trnummg adjustment for long waves.by screwing thegang condenser trimmers right in,and then unscrewing each one half aturn. Set the intermediate -frequency

BALANCING UPTHE TUNING

The operation of adjust-ing the gang condenseris simple, and full in-structions are given in

the article. Note that the ends of theivorine scale are cut away so as to clear the

baseboard.

condenser-so that the station's wave-length corresponds with the wavelengthmarked on the dial. For example, ifit is a station on 300 metres, then youshould adjust the oscillator trimmeruntil you get the loudest results whenthe pointer is opposite the 300 -metremark on the scale.

Now adjust the remaining gang con-denser trimmers.

Next, tune to a station at the upperend of the dial and adjust the inter-mediate -frequency trimmers. Finally,switch over to the long waves by turn-ing the wavechange switch to theleft, and adjust the .002 presetcondenser, which is located just behindthe coil unit assembly, until thevolume of the long -wave transmissionsis the best you can get.

The "Local" SwitchIncidentally, the H,T. voltages we

recommend are as follows : H.T. + 1,60 volts ; H.T. 2, 36 volts ; H.T. +3, 45 volts ; H.T. + 4, 72 volts ; and.H.T. --I- 5, the maximum of the H.T.battery, say, 120 volts.

The G.B. plug should be insertedin the 3 -volt tapping on the G.B.battery.

The automatic volume control willprevent any overloading and serve tokeep the volume constant on prac-tically all stations. But there are

(Please turn to page 174.)

148


DEVUOPMENTS _,WORLD-.

A Special Article of Interestto All Our Readers

IT might be said with a good deal oftruth that this is the age of worldcommunication. Certainly deve-

lopments in methods of communica-tion between different parts of theearth have been one of the outstandingfeatures of the present age. Those ofus who are particularly interested inradio broadcasting do not need to betold of the,numerous milestones whichmark the road of progress in our par-ticular science. We are sometimes aptto forget, however, that this is onlya part of the whole vast scheme ofnational and international communica-tion. Whilst radio broadcasting hasbeen going forward, long-distancetelephony, short-wave transmission,cable communication and many otherbranches of this great science have notbeen standing still.

A Comprehensive SurveyThese thoughts are prompted by a

remarkable paper which was recentlyread before the Institution of ElectricalEngineers by Colonel A. S. Angwin,the Chief Engineer to the Post Office,whose name will be well known tomost of you in connection with thePostmaster - General's TelevisionReport issued some time ago. Thepaper is an amazing document andcomprises a comprehensive survey ofthe work which is being done in allthe various fields of communicationwhich come directly or indirectlywithin the scope of the Post OfficeEngineers.

The Editor has asked me to give youa digest of this information, but, asyou will appreciate, it is only possiblein this short article to give you a mereoutline of so large a subject ; those ofyou who wish for more detailed infor-mation, however, should consultColonel Angwin's original paper whichis printed in the Journal of theInstitution of Electrical Engineers for1935, page 177.

Progress in BroadcastingIt is natural that radio broadcasting

is the first subject to which yourinterest will turn, and therefore I willbegin by giving you a few observationson the principal developments of thisscience during the past year or two.In the first place, you may get someidea of the general development by

MMUNICATIONBy Dr. JOSEPH

HARRISON ROBERTS, F.Inst.P.

the increase in the number of licensedlisteners. In Europe in the beginningof 1932 this number was 13,678.320,and by the end of March 1934 hadreached the figure of 19,626,315.

This may well be described as theage of communications. In thefollowing pages our ScientificAdviser gives a rapid survey of theimmense strides that have beenmade in recent years not only inbroadcasting but in the variousother methods by which communi-cation lints together the uttermost

ends of the World.

In 1932, as you may know, therewas a great Convention, called theMadrid Telecommunications Conven-tion, which laid down certain impor-tant provisions with regard to thepower of broadc.asting stations ofEurope. According to the arrange-ments arrived at, the power waslimited to 100 kw. in the mediumwaveband (200-500 metres) and to 150kw. in the long waveband (1,000-2,000,metres). There is, however, the excep-tion of one station at Moscow, whichhas a power of 500 kw.

CAN BE HEARD

This brings us to the establishmentof the Droitwich station, which cameabout in this way. The B.B.C. re-tained the long wavelength in use atDaventry as a result of the LucerneConference, but it was felt quite earlyon, even in 1932, that this channel,which was regarded as a valuable one,was not being made the best use ofby the seven -year -old transmitter atDaventry, which was radiating only25 kw. The quality of reception indistant areas in the case of Daventry5 X X was found to be much inferiorto that of the more modern medium -wave Regional stations and conse-quently it was decided to build a newlong -wave station with a much greaterpower. This is how the Droitwichstation came about, with a transmitterof 150 kw. The transmitter, as youknow, has now been completed, and itis expected that the signal strengthwhich it provides will eventuallyrender unnecessary the relaying of thesame programme by a medium -wavetransmitter in the North, London andWest regions.

As regards the "little National"transmitters sending out the National

ALL OVER EUROPE

ONE OP THE LATEST WORLD VOICES, the West Regional transmitter at Wash -ford Cross in Somerset. This is the peteer house, with its four Diesel engines and

generators.

149


programme, an interesting problemarises, namely, the problem of syn-chronising high -power transmitters.This problem had to be faced by theB.B.0 because the international wave-length situation prevented certain oftheir transmitters from having separatewavelengths. This synchronising, ar-rangement has been found to workout very well and the B.B.C. are nowoperating not only three stations on onewavelength, but have actually inpractice operated as many as sevenwith an accuracy of one part in 100,000.

The Use of Telephone LinesGreat progress has been made in

relaying broadcast programmes overtelephone circuits and, in addition toproviding for therelay of foreign pro-grammes, practicallythe whole of the in-ternal simultaneousbroadcast systemhas been changedover from the oldoverhead open wirecircuits to under-ground cable cir-cuits. It will beinteresting to manyof you to know thatthe B.B.C. per-manently rent fromthe General PostOffice close upon5.000 miles of under-ground circuits forthe purpose of link-ing up the variousstations and regionalheadquarters.

A FurtherDevelopment

Another importantdevelopment in thelong-distance relay-ing of programmeshas been the in-creasing use of radiotelephony circuitsfor linking up thebroadcasting organ-isations in differentparts of the world.You will remember how various pro-g,rammes from distant parts havebeen provided in the Christmas -dayprogrammes, culminating so fittinglyin a message from His Majesty theKing to the entire Empire.

You will readily appreciate that thequestion of the acoustics of broadcast-ing studios is very important to theB.B.C. and this has consequentlyreceived a great deal of attention

AN

LONG-DISTANCERELAYS

during the period under review. AtNewcastle, Manchester, ,Leeds, Bir-mingham, Cardiff and Bristol newstudios have been completed, whilstin London a large studio has recentlybeen built at Maida Vale for the useof the B.B.C. Symphony Orchestra of119 players. This new studio has beenconstructed inside part of the MaidaVale skating rink. A very interestingfeature of this studio is that it formspractically a separate building insidethe skating rink, separate walls androof trusses having been provided soas to prevent the transmission of

OTHER BIG VOICE

OUR NATIONAL GIANT, the Droltwieh station, with itshuge masts supporting bath the tong -wave and Midland

Regional aerials.

sound through the roof of the studioand via the fabric of the building toany further studios which may beconstructed in the future in other partsof the skating rink building. In otherwords, any studios inside the buildingwill be acoustically separate and dis-tinct from one another and will notinterfere with each other to anyappreciable extent, incidentally, thisbroadcasting studio is the largest

which has yet been built in thiscountry and has a content of about230,000 cubic feet.

Empire Service TransmissionsAs you will remember, a short-wave

service was started some considerabletime ago from Daventry for servicingthe British Empire. The actual date,as a matter of fact, was December 19th,1932. This is done on two transmitterseach capable of delivering 15 k toan arrangement of directional aerials,the wavelengths being in the shortwavebands between 13.9 metres and50 metres for reception in the variousparts of the Empire. A good deal ofwork had to be done in this, connectionon the design of suitable aerials forshort-wave broadcasting service, sincethe requirements here are very differentfrom those of point-to-point services.As a result of the -experiments andtrials a good deal of experience hasnow been gained on the design of suit-able aerials and the original aerialswhich were used at Daventry havebeen replaced by others which haveproved more suitable in practice.Further improvements in the serviceare still being made.

This brings us naturally to thequestion of the fading of broadcasttransmissions. The earlier broadcast-ing stations were all comparativelylow -power, and the service area waslimited owing to the fact that theattenuation of the received signal soonprevented it from being able to over-ride the local interference. It has beenfound, on the other hand, that modernhighpower stations will give adequatesignal strength at distances far beyondthe points where serious fading hasset in, showing that the service area isdetermined by the radius at whichfading becomes intolerable, ratherthan by considerations merely ofsignal strength.

Improving Radiation EfficiencyIn the light of this information

various kinds of aerials have beentried in an endeavour to improveefficiency of radiation. You will notethat the efficiency of radiation de-pends not only upon the actual powerradiated at the transmitter, but alsovery much upon the design of theaerial. It has been found that theheight of the aerial in relation to thewavelength used is very important, afigure for the height of 0.58 timesthe wavelength having been found tobe the best. In the new transmitterwhich is at present under constructionat Belfast, an experimental verticalmast radiator will be used having a

'150

September, 1935

height which is in the neighbourhoodof 0.58 times the wavelength in use,but being adjustable for experimentalpurposes.

Receiver DesignI do not think I need say very much

about developments in receiver de-sign, as these will be pretty well.familiar to most of my readers. Thesuperheterodyne receiver has, of course,largely superseded the " straight " set,mainly owing to the fact that unwantedsignals can be filtered out at an inter-mediate frequency with great ease.Receiver design has been greatlysimplified by.the introduction of multi -electrode valves and. also by improve-ments in valve performance generally,so that the number of actual stagesrequired for a given amplification hasbeen reduced. Automatic volumecontrol is prac-tically universal onbetter class sets,whilst amongstcomponents metal-lised resistancesa n d electrolyticcondensers are nowin wide use. Forspecial purposeswhere a minimumof space is impor-tant, e.g. in motor -c a r equipments,valves of very smalldimensions a r ebeing producedwhich are perfectlyefficient.

Telephonyon Ships

Considerable in-crease has beenmade in thenumber of shipsequipped with tele-phone apparatus tofacilitate com-munication be-tween passengersand telephone subscribers on land.Even trawlers are now mainly equippedwith a simple and robust type of tele-phone apparatus which enables themto communicate with coast stations.These transmitters work on a wave-length of 177 metres, with a power ofabout 50 watts. The correspondingequipment has been installed at allcoast stations ; but the transmittershere are of higher power, with- inputsranging from 500 to 3,000 watts.

To those of us who only use the tele-phone for local calls, or at most fortrunk calls in this country, it will come

STRINGENT STANDARDSEMPLOYED

as a surprise to know the extraordinarydevelopments that have, been madewithin the past two years in long-distance telephony. It is now possiblefor telephone subscribers to speak toone another from the farthest cornersof the earth. I would just like to giveyou a case in point to illustrate theingenuity of this method of communi-cation. The chief engineer cites as anexample a subscriber in Sydney com-municating with one in Bulawayo ;the circuit in this case would be fromSydney to Baldock by radio, Baldockto London by land line, London toRugby by land line, Rugby to CapeTown by radio, and finally Cape Townto Bulawayo by land -line.

DOWN IN SUNNY CORNWALL

WIRELESS

in fact, they were separated by thou-sands of miles from one another. Onemight be permitted to say that thissurely represents the high-water markin world communication !

Frequency StabilisationThe improvements in radio trans-

mission and the increasing congestionof the ether call for' more stringentstandards of accuracy of the frequencyand stability of radio waves. Experi-ments have for a long time been goingon at the National Physical Labora-tory, and these show that internationalagreement as regards frequency stan-dards can now be attained to a fewparts in 100 millions ; whilst in thelaboratory comparisons of a researchcharacter can actually be made to afew parts of 1,000 millions. Theseexperiments are very important in

their bearing onnew systems ofradio transmission,

ON THE WESTERN SEABOARD. Land's End radio station keeps up constant touchwith ships. Up-to-date gear and direction -finding apparatus are installed, and have

kept this old -established commercial link well to the fore.

A kind of world round -table con-ference was held some little time backbetween the representatives of acertain firm, these representativesbeing situated in Bombay, Sydney,Johannesburg and London respec-tively. Each representative addressedthe conference in turn, whilst listeningpoints were also provided in Paris,New York, Montreal, Calcutta, Mel-bourne and Perth (Australia), at whichother members of the company wereable to hear all conversations. It wasas though these various members weresituated at the same table-and yet,

such as the singleside band sup-pressed carriersystem, where thecarrier has to beinserted at the re-ceiving end, andthe inserted fre-quency must bewithin a few cyclesper second of thatof the originalcarrier.

The interferencedue to electricalmachinery andelectric signs andsuch -like apparatuswe have alwayswith us, and Ihardly need to tellyou that this is re-ceiving the carefulconsideration of thePost Office researchengineers. Those, ofyou who live inopen country dis

tricts will not be troubled very muchby interference of this type, but thosewho live in large towns know itonly too well. A committee of theInstitution of Electrical Engineers,which is representative of all thevarious interests concerned, is nowactively dealing with this importantquestion. At the same time collabor-ation is being sought through theInternational Electrotechnical Commis-sion, who are seeking 'to correlatemethods of measuring interference andinternational standards of permissiblestrength of the interference field.

151


(RactionstamitsledQ. 149. As the Hexoverter will

be connected to the family set, willnot the calibration vary, since it isunlikely that one should go back tothe same point on the long waves ?

A. Why unlikely? It is the ob-vious thing to do, surely, if onlybecause it is desirable to select a point

at the top end of the long waveswhere direct pick-up of a long wavestation is not experienced.

But you are quite right in sayingthat an alteration of the long wavetuning will throw out the, oscillatorcondenser calibration since the longwave tuning is really the intermediatefrequency setting.

If you have selected a given inter-mediate frequency by tuning to acertain point on the long waves, thecalibration of the oscillator condenserwill only apply to that frequency.You do not need to know what thefrequency is.

If you forget where you " were "on the long waves, it means a newset of readings on the oscillator,although you could set the twocondensers of the Hexoverter to theirrecorded readings and then tune thelong wave portion of the main setuntil the desired short-wave stationis heard.

Q. 150. When are you going tobring out a new set ? Is it going tobe a three-valver ? If not, why not ?

A. My next set will be the S.T.700.It will be published-periodical un-known-in two months' time. I donot reveal what the circuit is like tillzero hour. But why the craze forspecial numbers of valves ? A valveis only a component, after all. Put-ting it in glass does not make it anydifferent. The only factors that in-fluence me are initial cost and runningcost. Extra valves may quite easilyreduce both. I have never trackeddown the reason for preferring threevalves unless it has something to dowith complexity of construction orexpense.

On the whole, the more valves themore outlay, but where performanceis concerned an additional valve addsproportionally far more than itscost.

ti

This month our distinguished con-tributor goes at some length into thequestion of valve overloading, and

gives some very valuable advice.

Q. 151. How can I tell if my setis overloading ? What are the dis-advantages of overloading ?

A. Overloading can occur at anystage in a receiver, e.g. at the H.F.valve, the detector, the so-called 1stL.F. valve if there is one, and theoutput valve. Overloading may occurin an H.F. valve, especially wherethis is of the " fixed " S.G. type.As little as one or two volts may causethe operating point on the charac-teristic curve to travel on to a bendon the anode current curve, or gridcurrents may be set up when the gridbecomes positive due to excessivelystrong input signals.

Overloading simply means that thevalve no longer operates under theintended conditions. As long as theseconditions are maintained all is well,but if the applied signals (high -frequency or audio frequency) are toostrong, the conditions are altered andthings begin to happen. In the caseof the H.F. valve, distortion of theH.F. currents may take place andcross -modulation between two signalsmay occur ; thus a strong local "and a foreign station may become

inextricably mixed, and subsequentselectivity will not separate them.

In the case of a detector valve using" leaky grid " rectification overloadingmay actually reduce signal strength ;this is occurring when a certain" double -hump " tuning effect isnoticed. It will be found whentuning to a strong signal that itappears to come in best at two separatetuning points, while it is weakerbetween these points. Actually, theH.F. signals are strongest betweenthe two points but the output fromthe detector falls off because it is beingoverloaded ; a weaker H.F. inputunder these conditions will give alouder signal than will the strongerH.F. input. This, of course, onlyapplies to the special case of operatingthe detector near the point where itssensitivity falls off.

Two Kinds of DetectionOverloading such a detector will

set up two kinds of detection orrectification : the first is the normalgrid -leak 'rectification which calls fora straight anode current curve; thesecond is due to curvature of the anodecurrent curve, i.e. anode bend detection.A strong signal will cause the averagegrid voltage to fall, i.e. become morenegative. If the average operatingpoint approaches or reaches thebottom bend of the grid-voltage-anode-current curve-anode bend recti-fication sets in.

Grid -leak rectification causes theaverage anode current to decrease;anode bend rectification results in theanode current increasing. Theseeffects may oppose each other in caseof overloading.

The commonest example of over-loading is the application of toostrong a low -frequency signal to theoutput valve. Such a valve hasjexcluding Class B and special cases)a negative bias applied to its grid.It is worked so that only the straightportion of its grid voltage-anode-current curve is employed. If theinput signal is too strong, the operatingpoint on the curve will momentarilystray on to a really curved part of the" curve." For example, a strongnegative half -cycle may carry the


152

September, 1935 Wi REISS

LOOK here ! " I said to ProfessorGoop, " we must really pullour socks up about the Exhi-

bition this year! "" And why," inquired the sharer of

my labours in the field of wireless," and why is it incumbent upon us totauten our hosiery, as you suggest ? "

Last Year's "Report"" Why," I said, " don't you re-

member that last year we somehowspent the whole of our time lunchingand teaing and dining in one or otherof the restaurants of Olympia andnever managed so much as a walkround the stands ?

"True," re-turned the Pro-f e s so r; "butdidn't we reportupon the rest-aurants ? "

" We did."" And are they

not an importantpart of any ex-hibition ? "

" They are.""Very well,

then. What is the trouble ? I amsure that many readers found ourhints most valuable."

" Possibly ; but you must rememberthat our first duty is to tell wirelessenthusiasts all about wireless. There-fore I insist that this year we shall do'the thing properly, visiting each standand recording our impressions."

" And shan't we have any lunch ? "" Just a sandwich.""Or tea ? "" Another sandwich."" Or dinner ? "

"Made an Early Start"" If our consciences will allow us to

spare the time we may go as far astwo sandwiches a head for dinner."

It took me a little time to convincethe Professor, but once he had appre-ciated my point of view he agreed thatthis year we would stick entirely tobusiness, sacrificing, if need be, evenour meals in the interests of readers.

at the Car and

TWO CUPS OF COCOA

We staggered the ?railerStarter.

OUR WIRELESS FRIENDS

TRY TO VISITTHE RADIO SHOW

On the opening day we made anearly start. Since neither of us isvery good at rising with the lark orthat kind of thing, we thought itbetter to sit up all night so that wecould easily catch the 9.35 a.m. fromIltudbury Wallow. The trouble aboutgetting to Olympia (if you can'tcommandeer Sir K. N. Pepper's car, aswe did a year ago) is that you have

to change atWillesden Junc-tion, which hasplatforms andtrains simply allover the place.That is probablywhy we presentlyfound ourselvesat Richmond in-stead of at Addi-son Road. Dis-covering that the

only way of getting back to Olympiafrom Richmond without buying freshtickets 'was to return to WillesdenJunction, of which we had both hadmore than enough, we decided to trya 'bus this time.

We both felt,though, that afterour somewhat ex-hausting experi-ences a breatherwas necessary be-fore our travelswere resumed.Having thereforestaggered thewaiter at the Carand Starter by or-dering two cups ofcocoa, we hired a skiff and spent anhour or so snoozing happily upon thebosom of old Father Thames.

A kind policeman gave us the num-ber of the 'bus-which, as he put it,would take us past Olympia.

"GOING UP!" OR "DOWN?"

Demonstrating the bracing powers of cocoaby descending the ascending staircase.

He was right. It did. The Pro-fessor somehow got into an argumentwith a fellow passenger about theHeaviside Layer, and before we knewwhere we were we had reachedTrafalgar Square. Braced by anothercup of cocoa apiece (we are sending therecord of these cups of cocoa to Ripleyfor' his " Believe It Or Not " series),we set ourselves to tackle the problemof transport seriously.

Down the "Up""So far," I said, " we've tried

overground trains and 'buses, andthey haven't been successful. Let ussee what Lord Cinderpath can do forus with his UndergrounD. If he canget us to OlympiA we shall be DulYGratefuL." We walked up to Picca-dilly Circus, whose station is wellnamed. I suppose we went aboutseventeen times round its subterraneanpromenade before we found our wayto the escalator. And once we had -reached this our adventures were byno means over, for the Professor wouldinsist on demonstrating the bracingpowers of cocoa (see Ripley above)by descending the ascending escalator.Time after time he nearly did it.Time after time he was borne back tothe top and swept off at the gratingthing. Odds were being freely laidamongst the crowd of spectators whichhad assembled by this time, and I

think that theProfessor wouldhave succeeded athis last attemptin landing thepacket for whichhe had backedhimself had notthe authorities in-tervened and for-bidden furtherattempts.

At long last wereached the platform. Exhausted wesank into our seats and who shallblame us if for a moment or two ourtired eyes closed.

We were aroused by loud shouts of" Amos Grove." We enquired whether

153


the next station was right for Olympiaand having been assured that it mostemphatically was not, we disembarkedhastily.

" Every form of transport that wehave tried so far has let us downbadly," I lamented. " What can wedo now ? "

The Professor suggested an aero-plane, but on enquiry we found thatthere was no aerodrome in theimmediate vicinity and that, anyhow,the nearest landing place to Olympiawas probably Croydon.

" I Hailed A Taxi"Another kindly policeman whom we

consulted told us that by walking amere mile or two we would find a tramthat would take us to TottenhamCourt Road. Let me tell you here andnow that trams are jolly fine. Thisone, unlike all the other things, wentwhere it said it was going and dulydelivered us at our intended destina-tion. We felt that we were gettingwarmer and decided that we wouldfinish the journey by taxi, though aswe were rather cramped by so muchsitting we felt that a little walk tostretch our legs was indicated.

We hadn't walked far when we cameto a particularly jolly wireless shop.Having flattened our noses against itswindows for some minutes, we enteredand found a most genial chappiebehind the counter. He was one of thebest salesmen that I have ever comeacross, the sort of fellow who wouldhave made a real success of sellingtinned vegetables to cannibals. Any-how, before we knew what had hit us,we found ourselves the proud ifsomewhat staggered possessors of 17variable condensers, a complete outfitof shop-soiled short-wave coils, a dozenvalves of the most complicated typesand half a score of assorted low -frequency transformers.

A FINE SALESMAN

The sort of fellow who would leave soldtinned vegetables to cannibals.

Just as we left the shop a taxicame bowling along with its flag up.I hailed it. " Olympia! " I cried. Weheaved our parcels inside and followedthem ourselves.

"Phew ! " I ejaculated, sinking backinto my corner ; " this has been a

day. By Jove, wasn't that fellow amarvellous salesman ? Pretty wellcleaned me ' out."

" Me too," sighed the Professor." However, it's all in a good cause andthough we've had a tiring time I'mfeeling all keyed up for running roundthe stands at the Exhibition."

The last stage of our journey wascomparatively uneventful, despite theantics of those queer pedestrians whobelieve that you can really take Mr.Hore-Belisha at his word when youwant to cross the road between two ofthose toffee -apple things of his.

" And here," I remarked with a smileas we swung round the corner towardsthe entrance, " and here, my dearProfessor, is Olympia. It takes somegetting to, .but it's dogged as does it,

"FOUR AND NINE, PLEASE"

Would he take it out in condensers Hewould not. Or transformers ?

and by sheer perseverance we havearrived."

We stopped ; the taxi man got downand opened the door. We descended.Each of us looked at the other.

" If you wouldn't mind " Iventured, looking at the Professor,after an exploration of various pockets.

" I am afraid I must ask you,"smiled the Professor, who appeared tobe turning most of his clothing insideout.

The "Simple Cell"" Four and three, please," remarked

the taxi -man, " and sixpence for theluggage. That makes four and nine."

Simultaneously the Professor and Itried to explain that though we werereally men of substance we had spentour very last penny at the wirelessshop.

Would he take it out in condensers ?He would not.Or valves ?No.Or transformers ?No.We were both distinctly disap-

pointed in London policemen. Thetwo that we had previously consultedhad done their best to be helpful.The one who now strolled up was not.

If anybody now wants a thick ear,all that he has to do is to ask us for adescription of a simple cell.

BELOW 100METRES

By A Special Cerrespandent.

E are now just over two monthspast the longest day, andshort waves are beginning to

conform to what we may call " Autumnconditions." The fade-out, on wavesbelow 25 metres, is occurring at anoticeably earlier hour, and the 49 -metre band, in particular, is liveningup quite early in the evening insteadof remaining dead until most peopleare thinking of bed.

Coming back to conditions, however,I predict that the Americans will beextremely good for the next fewmonths between 2 and 7 p.m. (thisreferring, of course, to wavelengthbelow 30 metres, and including the20 -metre amateur band). Most ofthe broadcast stations are increasingtheir powers still further-why, I don'tknow-and the " hams," of course,live perpetually in a state of growth.

"DX" Ultra -ShortsBy the time the shorter wavelengths

begin to fade, the 31- and 49 -metrebands and the amateur 40 -metre bandwill be well away. The only dulltimes of day will be the mornings,and even then one may often bearNew Zealand and Australia in the20 -metre band.

The 49 -metre band is far from goodat the time of writing, the chief dis-advantage being atmospherics andgeneral noise. I invariably find thatit has bucked up by the beginning ofSeptember, however, and I think itwill soon be possible to go slowlydown the band and tick off eight orten " Yanks " on the log -sheet.

If there is a dead period this comingwinter, it seems to be due in Decemberor January. The autumn should,from the look of things, be unre-lievedly good.

We have been accustomed to lookupon the so-called ultra -short wavesas immune from variations in con-ditions. The 10 -metre band, of course,has completely given that theorythe lie by the way in which it hasturned into a real " D X " waveagain this year. Contacts betweenEurope and America (both North andSouth), between Australia andAmerica, and between Australia andJapan have been frequent during thepast few months.

It seems quite within the boundsof possibility that 5 metres will showsimilar symptoms by next year.

154


`®sNOTES

millimmemillellonlinummenemenunimilimill3 wLs iiiimmovon inniumuniumnimminionyTills year's Radio Exhibition has,

without a doubt, interestedmore people in short waves than

any of its forerunners. One has pre-viously had to hunt round for a merehandful of stands to find anyone be-traying even a passing interest in theshort waves. This year we have foundthe all -wave type of receiver verymuch in evidence, and really goodshort-wave components are relativelyplentiful.

The "Straight" SetUp to now I have only dealt in these

notes with the more simple types ofshort-wave receiver, suitable for thosereal enthusiasts who like to do a littleexperimental work on their own, andto whom a weak headphone signal isjust as interesting as real wall -bendingloudspeaker reception from a distantstation.

The difference between the twotypes of result, it might be thought, isonly one of degree, and to a certainextent this is true. A set using thecircuit I showed last time will givecomfortable headphone reproductionon any of the better-knownstations, and the additionof a good big L.F. stagewill make it most definitelya loudspeaker receiver.

Single ControlMany people who visited

the Show, however, willonly be content, for thenew season, with a short -waver that handles just likea single -control broadcastreceiver, and gives equallyreliable results. That, I amafraid, cannot be achievedby a detector -and -two L.F.arrangement; it callseither for a set with one or two H.F.stages or for a really good superhet.

The accepted fashion for a good all -wave receiver seems to be to make useof a separate short-wave detector(possibly with an H.F. stage ahead ofit) which, by means of the ordinarywavechange switching, comes into useas a superhet adaptor when short-wavereception is desired. This, of course, isin every way an excellent scheme.Wavechange switching for the two

broadcast bands is quite complicatedenough,, in some commercial receivers,without having to introduce a thirdrange about which one has to be con-siderably more careful.

The large effect of valve noise onshort-wave reception is discussedin this article, which containsdetails of a new superhet on which

the author is working.

The use of a " built-in " short-waveadaptor is by far the easiest method ofdoing the thing properly. The schemehas only one disadvantage, and that,probably, will not concern the peoplewho make use of it. I refer to thebackground noise that is, unfortun-ately, inevitable when a large numberof valves is used.

The chief feature that distinguishesthe short waves from the medium andlong waves is, of course, that mostsignals are relatively weak-in otherwords, the background noise assumesa position of far more importance.

A GOOD S.W. SUPERHET CIRCUIT

2N/

f

IF'

i Z.

_ _ J

/F Ocr LF

NT -64/vaec+ /

This circuitralver with a

is a good compromise between the huge multi -4 -watt output and the really quiet little affair with

two valves.

We hardly ever fail to receive a stationbecause the set isn't " powerful "enough-it's nearly always becausethe set isn't quiet enough.

This is where the short-wave super -het, in its present stage of development,leaves room for improvement. Allthe good commercial short-wave super-hets will give really excellent results on,say, rather more than a dozen Americanstations, Sydney, Nairobi and Johan-nesburg and, of course, all the Euro-

pans. If they receive that much onthe loudspeaker with fair quality andvolume they are doing all that anyonecan reasonably expect from them, andare obviously providing a tremendousamount of entertainment that cannotbe derived from a set that only coversthe medium and long waves.

The real short-wave fan, however,has a perverted mind (forgive me-I'mone myself !) and wants to dive deeperinto the subject than that. His onecrowning desire is, so to speak, to borea little hole in that omni-presentbackground noise and to hear some ofthe stations that, at present, are un-derneath it.

Small But SensitiveSo long as valves depend upon

jostling streams of electrons, he standsmore chance of doing that with a fewvalves than with many, since eachsucceeding stage will introduce a littlemore hiss.

If we can get in between the twoideals-the huge multi -valuer with a4 -watt output and the really quietlittle affair with two valves-we are

more likely to be able toplease everybody.

I am working, at present,on a fairly small superhetusing a heptode frequency -changer, one H.F. pentodeas LE, another as seconddetector, and an outputpentode. Four valves, eachone going " all out "-com-pletely at variance with theAmerican ideal of thegreatest possible number of" tubes."

Local "Background"The circuit and the rough

layout of this midgetsuperhet are shown on these pages.; Atthe moment it doesn't seem as if itwill be necessary to add another valveas pre -selector before the heptode ;but even if it is, the set will still bereasonably small. The new X 41 triode-hexode is, of course, interchangeablewith the beptode, and I am carryingout comparative tests between the two.

The actual " radio " backgroundnoise with this scheme appears to bevery small indeed. My own main

155


trouble is local background, mostlyfrom electrical apparatus, and manyof the noise -reducing aerial schemessimply have no effect upon it at all.

These, by the way, were much inevidence at the Show, and, in general,their use will be found tremendouslybeneficial. It just happens that mostof my own special interference doesdefinitely come down the aerial and isnot picked up and re -radiated by thehouse -wiring, as it is in so many cases.

To be really useful on short waves,these aerial coupling schemes shouldemploy a low -impedance down -lead,necessitating the use of an auto -transformer at the junction betweenthe down -lead and the aerial proper,and another one at the point of couplingto the receiver. Such a down -lead,completely screened, will certainly notpick up local interference, and if thehorizontal part of the aerial is right out" in the clear," a very efficient systemwill result.

Worth the MoneyIn one or two extreme cases I have

met, the only way to eradicate theinterference completely has been totake the lead-in from the far end ofthe aerial, bringing it down verticallyand along underneath the ground (seebelow). This, of course, costs rathera lot for screened cable-but if there'sno other way out it is worth themoney.

Overseas readers who are cursedwith irregular mains often complain ofnoises from the power station beingtransmitted along the mains-sparkingof brushes on ancient commutators,arcs at age-ola " power -leaks," and soforth. Most of us in this country,fortunately, have little to complainof in this way. Mains filters areavailable, however, consisting of twoH.F. chokes and two pairs ofcondensers.

The whole range of " suppression "devices, as seen at the Show, is wellworth studying, as there is almostcertain to be something that will beright for your particular trouble.

Midget Short -WaversAn aspect of short-wave reception

that must not be neglected duringthe coming season is the popularityof the " midget " receiver. Thanksto the various types of tiny valvesthat are now being marketed, it ispossible to compress a two -valveshort -waver into a very small space,and there is a certain charm in theuse of a short-wave portable whichcan he taken out to the top of a nicequiet hill, far from all electricalinterference.

NOISE -REDUCINGAERIAL SCHEMES

I have lately been using a super -regenerative set for ordinary short-wave listening, as well as for the" ultra -shorts," and provided therearen't too many stations workingin adjacent channels at the time, itsselectivity is just about adequate.Its sensitivity, of course, is terrific.I have listened to W 3 X AL on16 metres at good loudspeaker strengthin a moving car with four feet of aerial !This, by the way, on three valvesbuilt into a set about the size of a fatcigar -box.

COMPACT LAYOUT

8.4,0 SAPIWO

The circuit on the previous page lendsitself to a small, neat layout as shown

above.

The charm of a really small andreally portable short-wave set is simplythat of novelty, I suppose. One isthoroughly used to portable broadcastreceivers, and to the programmes thatthey bring in, and car -radio is wellbeyond the " novelty " stage thisyear.

To take out a small short-wave setduring a country picnic, though, andto produce dance music from Americaat teatime, means the establishing ofone's reputation as a real wizard. Inpassing, I may as well remark that it'snot nearly so easy as it sounds.

Those readers who are not going infor " all -wave " sets this season will

FOR SILENT WORKINGISM o. ORM.

-.-

SceAwevra, Vonev-Lzaa-

Zono...-oameaCbray-wa rekser

-- .

iii

IZ:zt''1;; : '61'.2.2Z...;27:1-. '4C

Vhere interference is especially bad thismethod of taking the down -lead from thefar end of the aerial may prove valuable.

probably be thinking seriously ofbuilding a small short -waver to use asan addition to their own broadcastreceiver. Whether it is a two -valveheadphone receiver or a converter ofsome kind doesn't matter very much-in either case they will be makingavailable some scores of programmesthat otherwise could not be heard.

I believe I have already referred tothe fact that the erection of a separateaerial for the short -waver is not neces-sary. If your broadcast receiveroperates from a fairly good outsideaerial, use the same one for yourshort-wave listening, even if both setshave to operate at once.

Several alternative schemes may betried, among them that of tapping thebroadcast set on theend of the aerial,andtaking another lead-in from the centreof it (roughly) to the short-wave set.

Try Two Earth LeadsAnother method is simply to feed

the end of the aerial to the two sets,using a small midget or pre-set con-denser in series with the lead to theshort -waver. A common earth some-times causes slight difficulties, althoughtwo separate leads down to the sameearth -tube will usually work well. Itis the common lead that causes inter-ference between the two sets.

In case there is anyone who has readthus far, and who has, as yet, nointention of becoming a short-wavelistener during the autumn and winter,let me appeal to him to think thingsout and to estimate how much radioenjoyment he is going to miss.

Roughly a hundred programmesmay be heard, for the expenditure ofa very modest sum, that simplycannot be heard by any other meansthan short waves. But it is not themere.thrill of listening to long-distancetransmissions that constitutes the chieffascination of short waves. It is thefact that there is still plenty of experi-mental work to be done, even by theunskilled home -constructor.

Sure of ResultsYou may try out the new circuits

that I show occasionally in these pages,and for no particular reason, you maysuddenly find yourself obtaining tre-mendous results with one or other ofthem. Whatever happens, you willfind no difficulty in getting someresults right at the outset, whateverarrangement you use.

Let 1936 be a real short-wave seasonfor you. Conditions should be improv-ing for another two years yet, and evenwhen the next " trough " in the cycleof conditions comes round, there willstill be plenty to go for.

156

September, 1935

IrT happened almost ex-actly at midnight.How many million

aural witnesses theremust have been to thecrime will probably remain a matterof dispute.

But if a hundred thousand listenersheard the famous Studio Murder, whenthe actor Parsons was strangled beforethe microphone in the course of a radioplay, a few millions almost certainlyheard the shot that killed BransonPotts in the Cuba night-club.

For an hour and a half dance -musichad been relayed from the Cuba ;dance -music played by a new RumbaBand of some celebrity. About aminute and a half before twelveo'clock there came the voice of theannouncer : " The dance -music youhave just heard has been played to youby Carlos and his new Rumba Orches-tra, from the Cuba Club. As thecabaret entertainment is beginning atrifle early, the National Programmeis now closing down until to-morrow. Good -night, everyone, good-heavens ! . . ."

Several million listeners stared ateach other, unable to believe theirears. But their sets were silent. TheNational Programme had closed downuntil to -morrow. And they had towait for the next morning's papers tosatisfy their curiosity. Even thensome of them were not satisfied, andthe B.B.C. postbag was proportion-ately the heavier.

Scotland Yard, however, in theperson of Detective Inspector SimonSpears, was not doing any waiting.For Spears, by the irony of an in-scrutable fate, had been sitting in theCuba, enjoying his first holiday formonths, and pretending very fairlysuccessfully that he had forgottenwhat the word " policeman " meant.Miss Topsy Levine, that blonde youngperson who was such an asset to thesecond row of the PallodroMe chorus,had been helping Spears considerablyto the degree of forgetfulness hedesired.

And now, at a little after three,instead of escorting Miss Topsy on

an agreeably pro-longed taxi -driveto the confines ofHendon where shelived, Spears found

himself facing Inspector Moresby,a colleague whom he rather disliked,across the table of the manager ofthe Cuba's private office. The contrastwas both striking and depressing, norwas the depression appreciably liftedby the manager's expression. Ofnormally dark features and with a faceto be described charitably as Levan-tine, Gipsy Ricardos as he stoodbetween the detectives, was a muddygrey, and quivering at that. " Agrubby blancmange improperly set"was Spears' description of him later.

AThrilling Mystery Story

By VAL GIELGUDB.B.C. Drama Director and co-authorof " Death at Broadcasting House."

" Well ? " inquired Moresbyabruptly. " You took charge, ofcourse. Any luck ? "

Spears scratched his jaw." It's a teaser," he said." What do you mean ? "Spears grinned. He still felt

sufficiently on holiday to be ableto think of Moresby as having thereal responsibility for the case.

" Listen, Moresby," he said, " andsee if you can piece it together.Bramson Potts was sitting alone at acorner table next to the dance floor."

" Wait a minute, Spears. Who thedevil was this fellow Potts ? "

" The best -hated theatrical agentin London, which makes it so mucheasier," said Spears. " He was a swinein private life, and a crook in business.I've no doubt we'll find within twenty-four hours that about a quarter of thepeople- in the club had it in for himone way or another. The Cuba's the

WIRELESS

latest thing in the pseudo -fashionabletheatrical set."

Moresby's face assumed a puritanic-ally grim expression ; and Spearsgrinned.

" I know it all from Topsy Levine,"he said, " the girl who came withme."

" Your prospects would be better,Spears, if you kept away from stagedoors, said Moresby virtuously." Especially as you're a married man."

" Oh, grandpa, what a blue noseyou have," murmured Spears. " ShallI go on ? "

Moresby nodded irritably." Very well. The medical report

tells us that Potts was shot at closerange. Almost the whole of the topof his head was blown away-messy,very. Gun with a silencer, of course."

" Yes," objected Moresby, " buteven a silencer--"

" Wait. I happened to be lookingat my watch-Topsy asked me thetime. As I did so the lights wentdown, and the dance music died awayalmost to nothing while the announcerwas talking into the microphone. Icould hear him, because I was at a tableon that side of the floor-the sideopposite to Potts."

Well ? "" I couldn't see my watch when the

lights went. I looked up, and justat that moment there was the devilof a crash from the cymbals and thedrum. That must have covered theshot-just as the darkness covered theshooting. After thirty seconds thelights flashed up again-and there wasBramson sprawled all over his table."

Moresby nodded slowly." The murderer must have known

that band routine for the cabaretopening," he said shrewdly. '

" Yes," said Spears. " But aboutthirty people can be picked on ashaving been in the club more than onceduring the last week. Besides "-he paused dramatically, enjoying inanticipation the shocking of Moresby-" there's no weapon ! "

" What ! "" I tell you there's no weapon-not

the ghost of one ! I've had every

157

WIRELESS

man-and woman, too-searched tothe skin "

" Yes," groaned Ricardos, fiddlingwith a cigarette -holder with shakingfingers, " it is that that ruins me.No one will come to a place wheresuch . . .3,

"An outrage is perpetrated," con-cluded Spears sarcastically. " Theladies didn't object."

" Of course not," sneered the Levan-tine. " But an Englishman will notrisk such a thing happening to the ladybe takes to a club."

" Anyway, it was done," saidSpears, " and it was done thoroughly.There wasn't a revolver in the place ;not so much as a water -pistol."

" You're sure nobody left the room ?"" Positive. I've good eyes and a

loud voice, Moresby. I used both.I got the doors shut in a jiffy, and I'vethe whole boiling lot still there, in viletempers and wilting boiled shirts ! "

" Don't be so dam' bright about it,Spears ! "

" Sorry. Well, what next ? "Moresby got to his feet and took

the shaking Ricardos by one elbow." I imagine you've got the table and

the body isolated," he said. " Takeme there, please."

The Levantine ledthe way, and Spearsbrought up the rear.

The Cuba ballroomwas a pathetic spec -t a c l e of pleasure -seekers who for oncehad been providedwith a real sensation.Frayed tempers, in-cipient hysteripompous indignation,naked fright wereall being displayedin their several andunedifying ways.Only Miss TopsyLevine, who wassmoking calmly atSpears' former table,scandalised InspectorMoresby by wavingcheerfully to his col-league and asking shrilly if she couldorder another packet of cigarettes

The gross carcass of Branson Pottshad been removed to decent seclusion,but the stained tablecloth and splin-tered glass lay clear for Moresby tosee. He stood and peered down atthe table, frowning, his massive jawclamped. Then he picked up thebroken glass.

" There was champagne in thatglass," he said quietly.

HOW THE WEAPONVANISHED

" You surprise me," said Spears." Champagne is drunk in the Cuba,you know."

" I know," said Moresby calmly.Where's the bottle ? "

The bottle ? "" I said ' the bottle.' "" All bottles taken away at mid-

night," said Ricardos smugly, as be-fitting a man who broke every lawbut one.

" I thought no one left the room,"said Moresby, turning to Spears.

Spears flushed and said nothing." Like Chesterton's postman, you

didn't notice the waiters, Spears, didyou ? No one does, do they ? That'show your weapon vanished. It wasdropped into an ice -pail. Go andempty them, Spears. But first lookinto them and prove to yourself justhow opaque is the ice -pail when it'sfull of ice."

"Yes," groaned Ricardos, fiddlingwith a cigarette -holder With shak-ing fingers, " it is that that ruins

I'm sorry, Moresby, That's con-foundedly ingenious of you."

" It was darned ingenious of thekiller, especially as you won't beable to identify the particular ice -pailwith any particular table. Still, themedical report allows us to cut downthe possibles to the people at abouthalf a dozen tables. When we've goneinto the motive and personalityquestions

But Spears had gone. In tenminutes he was back, and there was a

September, 1935

heavy revolver, complete with silencer,wrapped in a cloth in his hand.

" You were right," he said." Did you look at the brand of

champagne ? ". asked Moresby." I did," said Spears, raising his

eyebrows. " Why? It was Lanson '21."Moresby turned to Ricardos." Send over the waiters who looked

after this lot of tables," he said.The proprietor obeyed, and four

waiters came slowly across the room." Which of you served Lanson '21

this evening ? " asked Moresby.Then Spears could grin again. It

appeared that all four had servedLanson '21 that evening. They weresorry. The year was popular withdiscriminating clients . . .

Suddenly Spears jerked up his chin." Which of you served Mr. Branson

Potts ? " he demanded.The second waiter in the line took

a step forward, a pale, weedy youthwith a spotty face and a smudge of amoustache which only accentuatedhis lack of chin and his pallor.

Spears put out his long arm and,twitched the second waiter's napkinfrom his arm.

" Hold him, Moresby ! " he said.There was a"futilely pathetic scuffle,

and the weedy little man stood still,swaying on his feet.

" All right," he said. " I did it allright. I had my reasons-the swine II don't care. I'll go quietly:"

" How the blazes--" began Moresby..Spears turned the napkin over.

There was a long smudge of powderblackening across the linen.

" Inspiration," said Spears quietly." He knew the dance band routine.He knew Potts always drank cham-pagne. He thought of the ice -pailtrick ; I give you marks for that,Moresby. He shot Potts under coverof the napkin at close range during,those thirty seconds of black -out,and he dam' nearly got away with it.I'm glad you're on duty, Moresby.I'm still on holiday, and now I cantake Topsy home. Good -night."

RELAYS FROM BUDAPESTON September 24, 25, 27, and

28, listeners will hear fourrelays from Budapest.

These broadcasts will be repre-sentative of night life in thatcity and will necessitate the useof forty microphones located atvarious points. If the experi-ment is successful there is apossibility that the idea may beextended to other cities of Europe.

158

September, 1935

,4?,;.%$,

ti

"* 1

Television Patent PoolIUNDERSTAND that anarrangement has beenentered into between the

Farnsworth Television Inc.of America, and Baird Tele-vision, Limited, whereby there willbe a complete interchange of patentsand technique. Already the Farns-worth Company has made a similaragreement with Fernseh A.G., theGerman Television Company, andFernseh A. G. in turn have madea similar arrangement with the BairdCompany. According to this, thepatents and technical data of each ofthe three companies is available to theothers.

According to reports which havereached me from Philadelphia, Mr.P. T. Farnsworth, the vice-presidentof Farnsworth Television Inc., andinventor of the various televisiondevices used by that firm, predicts thattelevision will open up new fields foremployment and will be a tremendousfactor in giving a renewed impetus tobusiness.

What Definition?At present there does not appear to

be any very set policy with regard tothe degree of definition which is to beused in television transmission andreception in this country. As hasbeen arranged, the Baird people are touse a definition of 240 lines ; whilstElectrical and Musical Industries areto supply a transmitter working on405 lines.

There has been a good deal of tech-nical argument about all this. TheBaird experts say that, although theo-retically the higher the number of linesthe higher the definition, best resultswill be obtained at present from 240lines, and that to adopt a highernumber of lines at this stage would bepremature. It has also been sug-gested that whilst 240 lines can besent out on a wavelength of 7 metresor thereabouts, if we go to 400 oddlines it will require a much shorterwavelength to obtain the full effect.

tiv2 atoAdd

EV ISA REVIEW OF DEVELOPMENTS IN

THE VARIOUS COUNTRIES

By Dr. J. H. Roberts, F.Inst.P.

But the 7 -metre wave has an esti-mated range of some 25 miles, whereasthe shorter waves will have, it isbelieved, a still shorter range.

"Lacing"The experiments of Electrical and

Musical Industries have naturally beenconducted in considerable secrecy, butit is known, or rather it is believed,that a special system of " lacedscanning " is used and that the short-ening of the wavelength can beavoided.

Some people say that there has beenfar too much secrecy all round amongst

THE "ULTRA -SHORTS"

A combined Telefunken micro -wavetransmitter and receiver for two-waycommunication. The same aerial andreflector are used for both transmission

and reception.

W1RELES

10the different firms who areworking on television, andthat this secrecy is a greatbar to progress. Germany isgoing ahead, and many peoplecomplain that we in this

country are allowing ourselves to fallbehind. On the other hand, I amtold that the buying of sets inGermany has not yet reached anygreat proportions, although the serviceis actually existing. At any rate, itseems pretty certain that when theBritish television service does start weshall have a much higher standard ofexcellence in our television receptionthan any other country in the world.

P.E. MosaicTalking about Electrical and Musical

Industries, by the way, I understandthey are forging ahead with their tele-vision system which employs a photo-electric " mosaic," based on the fashionof that of Zworykin, the famous tele-vision expert of the R.C.A. VictorCompany of New Jersey, U.S.A. Ibelieve the Electrical and MusicalIndustries are working in pretty closeco-operation with R.C.A. of Americaunder some kind of patent poolingscheme.

"Aerial Movies",The Radio Corporation of America

has allotted more than a million dollarsfor the erection of a television broad-casting station and the manufactureof receiving equipment. The well-known president, Mr. David Sarnoff,said that his company's " aerialmovies'" would be a reality withineighteen months.

The Philco Radio Company, oper-ating more secretly, was reported tobe spending a similar sum in its Phila-delphia Laboratories ; while theAmerican Telephone and TelegraphCable Company are reported to beready to instal the first of the " electricpicture pipes " between Now Yorkand Philadelphia, which I mentioned inthese Notes last month.

In fact, there seems to be a kind ofrace between England, Italy. Germany,

159

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Belgium and the United States, to seewho can get ahead first in practicaltelevision.

Progress in BerlinTalking about Germany, Berlin does

not intend to be outdone by Londonin the matter of television. Accordingto reports, plans are going forwardswiftly for an expansion of visualbroadcasting in the Reich. TheGermans have already started a publicservice with a station of 4,000 wattsoperating in Berlin to send out visionon the ultra -short waves at 41.7 kc.,with accompanying sound at 12.9 kc.

The Germans started to broadcast240 -line television nearly two yearsago, but limited the reception toscientific laboratories and 'amateurswho built their own sets... It was foundthat a radius 'of about 30 miles couldbe obtained, covering the whole ofBerlin. From this station it is intendedto continue visual broadcasting,. but itis also planned to erect a station onthe Brocken mountain and to connectit with Berlin to serve the westernportion of Central Germany.

Ready for the Market?One German firm, ,I am

informed, has a large stockof television receivers allready for the market. Pro-grammes at first will consistof ordinary news reels,changed every week. TheGerman Post Office, whichhas television in charge, hasordered a special televisionvan to go to places to obtainnews events and to makespecial reels for immediatetransmission to owners ofvision receiving sets.

Television and theTheatre

" Television in the theatreis a development for thefuture and for many yearswill not affect the attend-ance at cinemas." At anyrate, this is the opinion ofMr. H. R. Lubrke, directorof television for the Don LeeBroadcasting System, of theWest Coast, U.S.A.

" Television," he says, " isadapted to reproduce a fewevents for many individual -in many small groups-inother words, to reach thepublic in their homes. Themotion picture and thetheatre, however, areadapted to reproduce a fewevents to many individuals

AN INTERNATIONALTELEVISION RACE

in a few large groups-that is, toentertain the public in theatres. Weshall look to television as a sourceof news and timely presentation, whilstto the theatre we look for artisticproductions. Television can presentevents as they happen, as well asrecorded versions of the samehappenings."

The great purpose of television inhis belief is not to supersede otherforms of entertainment, but to supple-ment the broadcast of sound in thesame manner that sound supplementedvision in motion pictures.

The IconoscopeI referred previously to the Icono-

scope, which is sometimes called the" mosaic electrode." In this arrange-ment the scene which is to be trans-mitted is focused, by means of acamera optical system, upon a photo -

ITALIAN BROADCASTING HOUSE

C:

This is the studio centre of the South Italian stations. Notethe anti -near -fading aerial of the Rome 111 transMitter, hethis building the Italian television developments and experi-

ments will probably be tarried out.

September, 1935

sensitive surface ; this surface is madeup of a very large number of smallindividual photo -sensitive cells. Thearrangement, in fact, is somewhat likethat of a very coarse photographicplate, but instead of a chemical changebeing produced, a photo -electric orcervical -electric effect takes place. Theresult is that the current emitted bythe mosaic varies as the scanningspot pasies from point to point.

It would seem that some arrange-ment of this kind is about the onlyreally practical method so far_ dis-Covered for the direct transmission ofa scene or an event as it takes place.

Short -Wave CircuitsOne of- the few things that does seem

to be definitely established about thenew television broadcast scheme isthat the transmission will be on ultra -short waves of 7 metres or less.

This raises the question as to whattypes of circuit will be most convenientfor receiving at these high frequencies.The superheterodyne circuit has beenused very largely during recent yearsfor reception even down to compara-

tively short waves, butwhether it will be just asgood in the ultra -short-waveregion remains to be seep.

Another scheme is thecircuit with the quenchedvalve which was used quitea good deal some years agobut has not found muchfavour in the meantime.

Another SchemeThe Barkhausen circuit is

another one on which agood deal of work is beingdone at the present time onultra -short-wave reception ;the most important featureof this circuit is the factthat the valve works witha high positive potential onthe grid and no potential 'opthe anode. The result ofthis unconventional arrange-ment is that the electronsoscillate in and about thegrid at enormously highspeed. The point is thatthe electrons do not have totravel right across the valveand since they have onlypart of the distance to gothey tan be made to oscil-late at a correspondinglyhigher frequency. You willappreciate this when youbear in mind that a 7 -metrewavelength corresponds to afrequency of about 40 millioncycles per second.

leo

September, 1935

There's one booklet you mustn't fail to get whenyou visit Kelvin Hall-" The All Metal Way, 1936."It's more than a catalogue of WestinghousRectifiers and Westectors-it's a treatA.C. Mains Radio, distortionless detectiAutomatic Volume Control. It contains con trickle -charging both H.T. andaccumulators, operation of moving coilspeakers from the A.C. Mains, Universal Recetc., etc. Get a copy from Stand 9, andyou're there, don't forget to ask fo

technical information you may requir

Westinghouse Brake & Signal Co,82, York Road, King's Cross, London, N

WESTINGHOUSE

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WIRELESS

AFTER wireless came " wired "wireless, and now, close on theheels of television, comes the

prospect of picture programmes, dis-tributed not via the ether, but over aspecial form of high -frequency trans-mission line or cable.

Following Radio PracticeIt should, however, be made clear

that the plan proposed for " wired "television has very little in commonwith the well-known method ofrelaying broadcast programmes to anumber of subscribers over low -frequency lines. Although this isoften called " wired wireless," it isstrictly speaking only a modified formof telephone relay.

FOR LONG DISTANCES

September, 1935

ArNewel/IslamThe latest types of cables make it possible to send wide bands of frequencies,such as are required for high -definition television, over land -lines. Below,

Carden Shiels describes the practical details of this valuable development.

But if one speaker's voice is firstapplied to modulate a high -frequencycurrent of, say, 30,000 cycles, and thesecond speaker's voice is similarlysuperposed on another high -frequencycurrent of, say, 60,000 cycles, thenboth the " carrier " currents willtravel along the same line, withoutmerging or mutually interfering witheach other.

This kind of wired wireless is verymuch on all fours with what happens inbroadcasting. So long as they remainin the ether, carrier -waves fromdifferent stations do not interfere inthe least with each other. They maydo so in the receiving circuits of the

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The whole secret, of course, liesin finding a wire circuit capable oftransmitting the carrier -frequenciesover long distances without seriousattenuation. The ordinary " plain "wire circuit will not serve the purpose,though carrier -frequencies of the ordermentioned can be transmitted overtelephone lines which are " pupinized,"or loaded at intervals with inductancecoils. In practice, several telephonemessages are now being transmitted inthis way simultaneously over the sametrunk line, with a considerable savingboth of time and money.

A Million CyclesBut in order to transmit a television

programme of high -definition picturesby wire, the line must be able tohandle frequencies of a much higherorder. Instead of 60,000 cycles, itmust carry currents ranging well over amillion cycles, and this without losingthe higher frequencies at a greaterrate than the low. In the first place,

A DUAL LINE

A ,3344c/Na- kv4.pizes

/763Two distinct channels are prorated with

This special double " cable."

the overall attenuation must be small,otherwise the signals will not " carry "for any distance ; and, in the secondplace, whatever loss does occur mustbe equally distributed over the entireband of frequencies.


September, ! 935 WIRELESS

Ts an interest in radio the first sign1 of unhappiness in marriage ?

Does it reveal the first rift in theeternal lute, the initial crack in thefabric of everlasting bliss ?

It would seem so from an advertise-ment I have just read. It shows a wifelooking tired, drawn and run-down,She looks so unappetising that I wasnot at all surprised *to find her writing :" My husband got restless." But letme recount her tale of woe-woe,that is, before she finished the firstbottle.

"Tired and ' Drawn "" I kept the home lovely, but my

husband got restless. Houseworkmade me so TIRED and run-downlooking-thank goodness I did some-thing. We live in an awkward house-lots of stairs and soot settling oneverything. But ever since we weremarried.I've taken a pride in keepingthe home lovely. I even soda the bathevery day. Last winter all mystrength seemed to go. I got tiredright out-but I had to keep going.

" Then suddenly I noticed that myhusband was less interested in thehome. Being run-down made me looktired and " drawn." He was restless inthe evenings, fiddled with the wireless.Thank goodness I was sensible aboutit. No use blaming him. The truth isthat any man gets tired of a tired -outwife."

A Sad StoryThe good lady, I feel, has worried

needlessly. Surely a sudden interestin wireless has a simpler explanation ?The good fellow has probably justread all about the S.T.600. The pictureof him in the top right -band cornershows a very decent vague -facedenthusiast in his shirt sleeves, obvi-ously constructing a very vaguereceiver from an undecipherable blue-print in a fog -bound kitchen.

He is, of course, as vague and asmuch in the background as most

11110air

Radio and Marriage-Seeing One's Name in Print and The " 700 "are among the topics dealt with by Mr. Scott -Taggart this month.

husbands, but on this occasion theheroine, lined, dyspeptic, washed-out,must occupy the front of the stage.The danger, of course, is that thou-sands of wives will see that advertise-ment and, looking over the edges oftheir newspapers, will find theirthroats clutched by' fear as they seetheir harmless Harrys screwing downvalveholder V3 nearest baseboardedge.

Laying down her newspaper withtrembling fingers, she whispers :

" Harry, don't you love me anymore ? "

Harry looks up. " What's that ?I can't hear you. This confoundedscrewdriver's too big."

" Must you swear, Harry ? Youdidn't use to when we were firstmarried," says Jeannie wistfully.

Harry grunts as he fits the grid -leak holder. " That was before I tookup wireless."

Jennie dabs her eyes. " You didn'tuse to fiddle with the wireless then."

" There was no wireless then,"

Harry remarks brutally, screwing theterminal strip to the baseboard.

" Are you," she asks tremulously," building this set because I amtired -out, done -in, and washed-up ?You no longer seem to admire thesoda -cleaned bath."

" Hallo, what's the matter withyou ? " cries Harry, seeing the tearsroll down the sunken, lined cheeks andon to the crepe neck and triple chin.Jeannie sobs against his shoulder :" I was so happy till I read thisadvertisement. Now all my life isshattered."

Sowing Grave SuspicionHarry says something about rub-

bish, clumsily wipes away her tears,kisses her absently and fits the L.F.transformer. Jeannie smiles happily.But she buys a bottle,. and givesHarry some. He likes it and buildsanother six sets.

But will all such stories end ashappily ? Will not grave suspicionbe sown in many a home ? It seems

THE CONCERT STUDIO AT W S U I

This is the concert studio and lecture hall at Iowa City Broadcasting Station (II' S U I).It is large enough to hold an audience of two to three hundred.

163


so unfair to pick on wireless as arestless diversion from a washed-outwife. And even if, here and there,wireless is an escape from a nagging,hen-pecking or merely dull wife, whatof it ? Surely it's better than gaddingabout with stamp collectors or beingout half the night gathering mush-rooms.

There are many worse occupationsfor a bored husband than " fiddlingwith the wireless." Let " washed-outwife " rejoice lest worse befall. Andwhat is the moral of all this ? Simplythat even a bath washed daily withsoda will not hold a wayward wirelessman's love.

From a reader.Dear Mr. Scott-Tagert,-Y our name

is a household word. . . .

Then why not spell it correctly ?

My First CompetitionHe goes on to suggest that I write

to see my name in print. No ; afterall these years-twenty-one, about-it makes me feel faintly sick. Aboutthe only fun I now get is -to jugglewith the diploma initials at the end,changing their order, acquiring newones, deciding which to use on specialoccasions, and so forth.

At first, of course, it is great fun tosee an article in print. Or even to seeyour name. I remember how proud Iwas-at eight years of age-to seemy name amongst five hundred otherfirst prize -winners of a competitiondealing with station names-you knowthe kind of thing : picture of a pieceof liver lying next to a pool of water.Usually the piece of liver is meant tobe a rock and the pool something else,but I seem to have been lucky. Asyou couldn't expect the Editor todivide ten shillings amongst fivehundred, we prize -winners each re-ceived a bag of filthy sweets.

Wielding the PenThe first time I ever made any

money out of my pen-one of the chiefraisons d'être of this useful implement-was when I contributed not one buttwo jokes to the Royal Magazine. Iwas seven years old at the time, and Ireceived half-a-crown each. My friends-inventors occasionally scrape to-gether a few-declare that these werethe last jokes I ever made. I remem-ber distinctly the day the moneyarrived ; I was sick the whole of thefollowing night. It was no joke.

My next effort was a puzzle magazinejointly edited by myself and my bestfriend, who was the son of a clergyman-believe it or not. We charged 6d.

SHOULD RADIOENGINEERS WRITE ?

per copy, sold about a dozen copies perweek, and made a good thing out of it.It died after a month. In 1914 Istarted writing wireless articles. Thefirst was about quite an ingenioustapping key which enabled you to sendand receive at the same time, or ratherto " break-in." Since then I musthave written a thousand articles,several million words and aboutfourteen books on wireless, of which850,000 copies have now been sold.

I think the pleasure of seeing one'sname in print wears off very quickly.Some foolish people think that " popu-lar " writers become conceited ; thosewho think that usually cannot write ordon't write or are not permitted bytheir jobs to write. I've yet to meet aregular technical -writer who is withouta sense of humour as regards his ownimportance, or lack of importance.

He gets a great deal of publicity, ofcourse, but it is essential for thedissemination of knowledge. Pro-fessionally he does not benefit at allfrom .the publicity, although much of

the old prejudice is dying since somany famous scientists have takenup their pens to write for the publicand not merely for learned societies.

Sometimes young radio engineersengaged in research ask my advice asto whether they should supplementtheir incomes by writing. Usually IdiScourage them, although I urge themto develop prestige in their technicalsocieties provided this meets with theapproval of the companies employingthem. Jealousies are very easilyaroused the moment you put pen topaper-and the young engineer cannotafford to arouse the jealousy of hisseniors.

During the WarThe only time I myself have aroused

feelings which could injure me wasduring the war, when I was writing-often from a trench-the first compre-hensive accounts of the new valvetechnique. My articles-so the chiefsin France thought-ought to havegone through them. It appeared tobe unknown to them that militaryregulations permitted the submissionof such articles direct to the PressBureau in London.


MAX KESTER WRITES SONG FOR NEW FILM

In the Fox film " The Price of a Song." the composer wAtes a new number called" My Heart's Beating out of Rhythm." H kite he is playing it over he is murdered,but the song remains fixed in the murderer's mind. This tune brings about thesensational climax and discloses the murderer. " My Heart's Beating out of Rhythm "teas specially written fm. the film by Ronald Hill and Max Rester. of the B.B.C. Inthe photograph are Erie Manturin Charles Mortimer, and Oriel Ross. The general

release ;late is October 7th.

164

September, 1935 kXr:RELESS

11 ff 117"-N

n I Yo dallagerakinStevens

N designing scanning circuits usingIL high vacuum valves, the aim is

to reproduce exactly the actionof the gas -filled relay connected acrossa condenser. Unfortunately there isno simple method of doing this, sincethe peculiar action of the relay cannotbe imitated by a thermionic valve.

In the former the anode currentstarts instantaneously at a givenanode voltage and is more or less un-affected by variations in anode or gridvoltage, but in the valve we have adefinite relation between current,anode and grid volts and with evena steep characteristic the anode currentrises gradually as the anode voltageis increased.

VERY INGENIOUS

Fig. I. The circuit of the " multi -vibrator " oscillator which can be made

to produce saw -tooth oscillations.

The valve, to act as a dischargingrelay, must be adapted so that theanode current is delayed until a givenvalue of anode voltage is reached, andthen, once flowing, must be increasedvery rapidly, the impedance of thevalve " coming down with a run," soto speak.

The " Multivibrator "In the July article we had an example

of the adaptation of hard valves tothe discharge of a condenser, and thesecond one is of sufficient interest toconsider in detail, as a number ofhard valve circuits are based on itsaction.

The " multivibrator " circuit, whichis reproduced again in Fig. 1, belongs

*Continuing his discussion from the Juiynumber, of cathode-ray time -base cir-cuits, Mr. Stevens here explains how the

hard valve type operates.

to the type of circuit in which theanode current can be made to altervery rapidly in either direction, andthe curve of current is approximatelythe same as that of the ideal saw -toothwave that is required for linear tele-vision scanning.

To make the action of the circuitclear, the valves and components havebeen lettered. The valves V, and V2are connected to the H.T. throughthe anode resistances R1 and R2.Each anode is coupled to the grid ofthe other valve through the couplingcondensers C, and C2, and each valvehas a grid leak. In practice theseleaks would be low, about 100,000ohms.

How it WorksWith R, and R2 equal and Cl and

C2 equal, at the moment of switchingon, the anode currents of both valvesshould be theoretically equal and thecircuit should be stable. Owing toslight momentary .variations in theemission, however, one valve will havea slight increase in anode current.Suppose it is V1. Then the currentthrough R1 increases and the voltagedrop across R, increases. Since theH.T. battery volt's are equal to thesum of the anode resistance drop andthe volts across the valve itself, it

A SUCCESSFULCIRCUIT

Fig .3. A useful hard-valvetime-basecircuitdeveloped by theCossor Co. It uses atriode actuated by apentode for discharg-

ing the condenser.

follows that the voltage across thevalve will fall.

This falling voltage will he com-municated to the grid of V2 throughthe coupling condenser C1. The gridof V2 will thus become more negative,and will reduce the anode current ofV2. Owing to the amplification ofthe valves, this reduction in current

THE SAW -TOOTH

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Fig. 2. Top: The wave -form of the anodecurrent change in the "multiribrator."The curve below is of the condenser dis-charge, which can be made linear (dotted

line) by the use of a diode.

will be much greater than the rise inV, which caused it. The voltage dropacross R2 will therefore become muchless, and the volts across V2 itself willrise. This rise in voltage will in turnbe handed on to the grid of V, throughthe coupling condenser C2. V, gridwill therefore become less negativestill, and will rapidly increase thecurrent in V.

Since each interchange of voltagebetween the valves is magnified by

165


the amplification factor of the valveitself, we can see that the initial smallincrease in anode current becomes likea cataract in growth. The limit tothe increase is set by the grid of V2,which is becoming more negative witheach increase of anode current in VI.Eventually V2 will be so negative thatthe anode current will cease altogether,leaving the coupling condenser fullycharged. This condenser will nowdischarge through the grid leak andthe conducting valve V1 at a ratewhich is determined by the values ofC and the grid leak.

Valves Used AlternatelyAs the condenser discharges, the grid

of V2 gradually becomes less negativeuntil the anode current starts to flowagain. This builds up in the sameway as the current in V1, until V1'sgrid becomes negative and shuts down.The process is thus one of a rapidrise and fall of anode current, eachvalve in turn acting as the brake onthe sustained oscillation.

The interval between the condensercharge and discharge can be made as

AN ORIGINALSCANNING SCHEME

long as desired by increasing the valueof the coupling condensers and leaks.With couplings of 2-3 microfaradsand a high grid leak, the time takento reverse the oscillation will amountto several seconds.

From the television circuit point ofview the most important point is thewave -form of the oscillation produced.This is shown in Fig. 2, and it will beseen how closely it approximates to areversed saw -tooth. If the resistanceof the grid leak is replaced by a diodeor constant current valve such as apentode, the curve of the condenserdischarge becomes practically a -

straight line.The advantage of such a circuit is

its remarkable stability, and the easewith which it can be synchronised to asignal of a definite frequency such asis obtained in television. If a lowvoltage is injected into the anodecircuit of the. valve and the constants

THE LONDON TELEVISION STATION

are adjusted to the approximate valueof oscillating frequency required, thecircuit will " lock " itself easily andmaintain the rate of oscillation withoutwandering.

An original and very . successfulscanning circuit has been developedby Q. S. Puckle of the Cossor Company.The circuit is shown in Fig. 3, and itw ill be noticed that two valves areused, marked V1 and V2 in thediagram.

The Charging CondenserThe main charging condenser,

marked C is charged through thepentode P, whose impedance is con-trolled by the voltage applied to thescreen from the potentiometer. V1,the discharge valve, is connected acrossthe condenser in series with a resistanceR1. The grid of this valve is con-nected directly to the anode of anotherpentode, V2, which has an anoderesistance R2. The grid of this pen-tode is connected back to the anodeof the discharge valve through a con-denser C1. The deflector plates ofthe tube are connected across the

discharge valve in the simple circuit,as shown in the figure.

At the instant of switching oncurrent will flow through V2 andthe resistance R2. The voltage dropacross R2 is applied to the grid ofV1, and makes it negative withrespect to its cathode, which is atfullH.T.± potential at the instantof switching on. No anode currentwill, therefore, flow through V1,and the condenser starts to chargeat a linear rate through the resist-ance of the pentode. Eventuallythe condenser potential reaches asufficiently high value for anodecurrent to start in V1.

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The choice of the Alexandra Palace for the London television station enables a very well-balanced area to be covered, as is shown in this map. About 25 miles radius is statedto be the real service range of the transmissions, and the circle shows the limit of thisradius It is probable, however, that places outside the circle will in many cases obtain

perfectly satisfactory reception.

Altering the SwingThis produces a drop in voltage

across R1, which in turn is appliedto the grid of V2 through C1. V2is thus made more negative, andthe anode current is reduced.This in turn lessens the bias on\ "1, and the anode current riseswith a rush, discharging the con-denser rapidly. The condenser dis-charged, the voltage acrossfalls again, and the circuit is re -setready for the next condenser chargeto take place.

The potential at which the dis-charge takes place is determined bythe value of R2, which thus con-trols the amplitude of the swingof the beam. R1 has the effect ofaltering° the rate at which the con-denser discharges and is normallyof a low value.

160

September, 1935

di

tiofin

THERE are various methods ofproducing large screen pictures,the three most important

methods being the mechanical, theintermediate film, and the high -powercathode-ray projection tube.

Television has been projected onto a large -size screen by means ofmechanical methods, using large mirrordrums rotating at high speeds. Thisis the way in which the televising ofthe Derby from Epsom was carriedout and reproduced on a screen in theMetropole Cinema, Victoria, threeyears ago.

Intermediate Film MethodMr. Baird has now developed a high -

definition method of projecting largepictures, limited, however, at themoment to close-ups only. In thismechanical method he uses a systemcalled interlacing, where lines are notscanned sequentially in order, but outof turn, which has the effect of reducingflicker.

The method for which I have themost hope, at the moment, is theintermediate film method,which gets over the greatdifficulty, experienced withmechanical and cathode-raysystems, of insufficient light.

We are now working onproviding a complete equip-ment which projects full-sizepictures on to the cinemascreen having ample light anddefinition.

Two FormsThere are two forms in

which it can be made :Firstly, an arrangement

which has been developed andconstructed by the BairdAssociated Company in Ger-many, Fernseh A. G., inwhich a continuous loop ofcelluloid film passes through themachine again and again. The film,with the unexposed emulsion on it,passes through a continuous motioncamera, on which is projected a tele-vision image received by radio by

means of a rotating disc, the modu-lation of the light from black to whitebeing carried out by means of the Kerrcell.

This film is then developed, fixed,washed and dried, and is seen at this

A review of various methods ofprojecting television on a largescale, and the possibilities of its

application to cinemas.

By A. G. D. WEST, M.A., B.Sc.(Technical Director ofBaird Television Ltd.)

point as a finished positive print, whichis then immediately projected on tothe cinema screen. After leaving theprojector it passes through tankswhere the emulsion is scraped off, andthe remaining clear celluloid is dried,and then it runs through a chamberwhere new emulsion is applied anddried, before running into the cameraagain.

I have seen this system working inBerlin, giving quite excellent results,

TRANSMITTING THE FILM

IEELESS

transferred to a cathode-ray tube. Thepicture is then photographed on to acontinuously moving film using aspecial form of camera. The camerahas two rotating drums inside it,both moving at a constant speed.One is in the position where the pictureis recorded, the other is for therecording of sound.

How It Is DoneThe film, after being exposed to both

vision and sound, runs straight into adeveloping bath, where it is developedfor twenty seconds, washed for fiveseconds, fixed in twenty seconds,washed for a further fifteen seconds,and dried in less than a minute. Aftera total period of under two minutes,it then passes immediately into theprojector and, after leaving the soundgate, is taken up on the pick-up spool.

The method has one disadvantage,namely, that the cost of film is ratherhigh. This is, of course, saved inthe continuous loop process. On theother hand, better quality is obtainedand the event, having been televised,

and reproduced, is in a re-corded form, and the spoolcan be removed, re -wound,

This is the Baird disc apparatus used to transmit films fort le purpose of television reception. Either ordinary or

intermediate film process can be used.

but I think that the quality is not asgood as that obtained by the methodwhich I am going to describe.

In this case, which is a developmentof the Baird Company, a televisionpicture is picked up by radio and

and projected on any subse-quent occasion.

For instance, if the Derbywere televised in this wayand thrown on to the screenat 3 p.m., the same film couldbe used again at 4 p.m., 5p.m. and 6 p.m. on the sameday, until replaced by thestandard news reels.

A Third SystemBefore considering the com-

mercial possibilities of thissystem, I want to refer to athird method, which is nowin process of development,called the projection tube.

This is tone other than a specialform of cathode-ray tube havirig anintensely brilliant picture, somethingbetween 3 in. and 6 in. square, sobright and well defined, in fact, thatit can be projected by means of a

167


lens on to a screen with good brillianceand detail.

At the present moment, only smallscreens about 3 ft. or 4 ft. square canbe filled in this manner. A brighterpicture can be obtained on the tube,but there is then so much powerput into the screen that it disintegrates.

In any case, a voltage of up to 10,000volts is necessary to produce, enoughbrilliance to be able to project picturesof the small size mentioned, but it is aform of development which the cinemaindustry must certainly keep an eyeon, because when it does become prac-ticable, as it will do in the course ofthe next five years, it will possibly'do away with the standard projectormechanism itself.

Radio and Cable ChannelsThe projectionist will become the

electron engineer, and, instead ofcleaning his gate and spooling his films,he will be adjusting his voltages andwatching his modulation metres. Inthis case, of course, the television isinstantaneous. There is no delaywhatsoever, but, on the other hand, norecord whatever is made of any eventwhich passes Over its screen.

Its application can well be compared.with the effect of broadcasting where,"

LINKING UPTHE CINEMAS

cinemas will be -linked up with thesource of programmes. There are possible radio links and cable links. Itseems clear that the first cinemas toreceive their programmes by means oftelevision will do so by radio links,from large high power central trans-.mitting apparatus on ultra -shortwavelengths sending out signals whichcannot be resolved by any homereceiver, and which will therefore besecret, picked up by radio receiver andprojected on a screen.

Later on a big central radio trans-mitter may quite easily, with the futuredevelopment of the concentric cable, bereplaced by a central distributingexchange point, say, in the centre ofLondon, and the same method willalso be of use in connecting up adistant programme item with thecentral distributing radio transmitteror the central programme distributingexchange.

In this latter case, however, it ispossible that micro waves, with wave-lengths of the order of one metre or

THE APPARATUS AT THE RECEIVING END

The televised scene is produced on the end of the cathode-ray tube shown in th sillustration. It is then photographed on to film by a cinematograph camera.

like sound, it is transmitted once andfor all, projected and sent out, "and isnever seen again, whereas the inter-mediate film can well be compared withsound recording, where events areshown and recorded and filed for futurereference.

There is one important point, towhich I have referred before, that isthe answer to the question as to how

less, will also be used for relay purposes.A micro -wave transmitter can be built,whiCh will operate over a distance ofperhaps 10 or 20 miles on very lowpower on a highly directional basis,that is to say, transmitting its powerin the form of a beam or searchlightfrom the outside point to the distribut-ing centre.

To take a practical example. if I

were asked how, at the presentmoment, a picture of the Boat Raceor of an Albert Hall Boxing Contest,could be relayed to cinemas in London,I would say that it could be done bythe following method.

An outdoor scanner, of the inter-mediate film or electron camera type,preferably the latter, could be installedin an aeroplane for picking up the BoatRace, or in the Albert Hall for scan-ning the .fight. The signals developedwould modulate a low -power micro-wave radio transmitter, which wouldshoot the vision signals straight at theCrystal Palace, to be picked up thereand relayed from the high power ultra -short -wave transmitter to the wholeof the London area. This would thenbe picked up by radio receivers incinemas and projected by the inter-mediate projection process on to thefull-size screen.

Competent Staff RequiredNow, thete are certain qualifying

points which I must mention. Firstof all, the apparatus, although it worksadmirably well, is still in an experi-mental stage.

Secondly, no official permission hasyet been given for a service of thisnature to be instituted.

Thirdly, it will need a highlytrained and competent staff to lookafter all the apparatus. No morecompetent, however, than that neces-sary for sound recording on film in itsearly stages and before it became amatter of rule of thumb.

You would not like me to finishwithout referring to some of thecommercial aspects of television andthe cinema.

In Experimental StageFirst of all, I must emphasise, again

that the results which are obtainedat present with this -system are still inthe experimental stage, but I wish toimpress upon you that in my opinionall the fundamental problems havebeen solved and that it is only a matterof attention to detail to put the resultsof this work into commercial form toarrive at a satisfactory service, withfull programme value.

The apparatus, photographs of whichI have already shown to you, will nottake up very much more room in thecinema than the ordinary projector,the same width and height but possiblyanother three or four feet more fromback to front lens. It is, of course,very difficult to say at this stage whatwill be the cost of providing a tele-vision programme to cinemas and whatwill be the cost of expenditure in the


183


ThereAre No LISTENERSIn America I

S'cup-Scifim att affm Hank'?DoN'T ask me how I enjoyed my

holiday in the States," warnedJohn Watt when at last 1

hailed him between shows at St.George's Hall. " Because, you see, itwasn't really a holiday at all. I wentover there to take a look-see atAmerican radio. And that meantkeeping my nose pretty well to thegrindstone-for radio's a big thing onthe other side of the Herring Pond."

Switched On All Day !I suggested that he was looking allpepped up " as a result of his recent

trip across the Atlantic, at which hemopped a furrowed brow. And thendazzled inc with the famous John Wattsmile.

" Well, I did three shows overthere," he confessed. " The wholebusiness is so different,, all the same.The average American seems to switchon his set at about 9 a.m. and leave itswitched on until midnight. I shouldsay there are between twenty andthirty million sets installed in America.But there are no listeners-not reallisteners !

" Over here we have built up some-thing like a real audience-a millionor so people at least. These folk turnon their wireless sets because theywant to listen. We have educatedthem to believe that B.B.C. programmesare worth the effort of listening.There's nothing comparable with thatin America. - There the radio-not thewireless, you note !-is just a back-ground.

"A Kind of Monotony"" Is that the only way American

radio differs from ours ? I shouldthink not ! Their basic standard ofjudgment is quite different.

" They are not primarily concernedwith whether a programme is goodbroadcasting. With sponsors it is notenough that the programme should begood-it must be demonstrably popu-lar, or have a high prestige value.Over here, of course, our only corn-

ni% ercial concern is whether the turnor programme is costing too much !

" Are they snappier ? Yes, I supposethey are. But there's a kind ofmonotony you don't often see men-tioned by people Who are praisingAmerican programmes at our expense.I mean the monotony of the shape oftheir programmes. The commercialsystem forces the broadcasters to stickto an approved formula. Experimentsare not too kindly looked upon-incase they fail to sell the toothpasteor cigarettes or whatever it is.

JOHN WATT

Famed for his "Songs from the Shows"anti similar programmes, John Watt isone of the most energetic producers in

the B.B.C.

" The sponsor pays for his comicturn, for example, and expects thesame old sequence to be followed.The comic comes on the air with a fewgags, cracks them and then goes offwhile a band plays a tune or two.Then he comes along with a few moregags, and so on.

" That's the general formula. Thejokes may be different-or not. Thetunes will certainly bear a strongsimilarity, for a reason I'll talk aboutin a moment.

" In this country only the MusicHall shows conform to a definiteshape or pattern. All the other varietyshows have something individual aboutthem. In that way we certainly ringthe changes better than the averagesponsored show in the States.

Length of Programmes" Of course we have our monotony,

too. Our one -hour light orchestralprogrammes must seem monotonous tothe. American, because he is not usedto such long stretches of broadcastingwithout gags or high lights.

" Their programmes are much shorterthan ours ? Well, everyone seems tothink that a quarter of an houris the limit on an American network.Actually, that is not true these days.They have more and more half-hourshows. And even some hour shows-like that sponsored by Ford, forexample.

" Jazz mad ? Certainly not ! Theirentertainment idiom is expressed muchmore often in dance tune .tempo thannot. You hear the same current dancenumbers running right through theAmerican programmes-in a way thatwe do not exploit over here. I shouldsay that they use dance numbers inthe same way we use light musicnumbers over here.

Prepared to Learn, But ..." Did 1 really learn anything from

my visit ? Well, that's a hard one !I may as well tell you that I went overthere prepared to learn a lot-but Ididn't find they had it to teach !

" I got into New York on a Saturdayafternoon-and for the first fortyminutes heard not a word of honest -to -goodness American. Plenty of Yiddish,Italian and German-but no American!Still, I did discover America in the end-by going to my bedroom and

169

WIRELESS

listening to the radio from about 4 inthe afternoon until midnight.

" My impression ? One of intenseamazement at the way programmesflipped from place to place without abreak or an interval. I certainlymissed the Bow Bells !

" The Americans have developedthis programme change -over businessto a fine art. I must say it is mostimpressive. And yet,- as I laterdiscovered when I --put my own showsover, there is nothing particularlydifficult about it.

How It Is Done" How they work it is this. In the

studio there is a clock with a largesecond hand, carefully watched by thecontrol or monitor engineer from hissilence cabinet adjoining the studio.

" As the second hand begins its slowsweep round for the last half minute-representing a 180 degree travelround the clock face-he begins toturn the knob of his fade ' pot '-alsocalibrated in 180 degrees.

GETTING READY

"I NEARLYWENT MAD"

network or which programme one isabout to crash into. By the time hehas finished, the engineers have donetheir work-and the show goes on.

" From a production point of viewthe whole thing is perfectly simple.These large clocks with their con-tinuously moving second hands giveone a feeling of moving along withtime-and it is perfectly easy, as Isay, to synchronise the fade knob withthe movement of the clock."

Those Long IntervalsAll of which interested me strangely.

Some time ago I made an investigationof the long delays in some of ourprogrammes, discovering to my sur-prise that it was a programme timingfault, not an engineering hold-up. TheControl Room at Broadcasting Houseas good as admitted that they could

FOR THE SHOW

.it:n.c. musieal comedy being rehearsed in St. George's Hall. This building has now

been taken over on a long lease by the B.B.C. and is undergoing alterations to permitof built-in nv',.!rophortes and other improvements.

" The result is that the programmefades dead on the stroke of the houror half-hour or .quartei-and the lineengineers have precisely 17 secondsgiven them to switch over-possiblyin a coast -to -coast hook-up extendingover thousands of miles.

" While this is going on the local,announcer is stating in brief teimswhich station one is tuned to and which

speed things up if necessary-but whatwas the hurry ?

There is nothing to prevent usinstalling suitable clocks and fadeknobs in our studios. Further, thetask is much simpler than it is inAmerica. Our " S.B." land -line systemis obviously much more self-containedthan the vast trans -Continental net-works over there.

September, 1935

As far as I can see it simply needssomeone in high authority to passalong the word-and all those annoyingintervals in the programmes woulddisappear overnight. John Watt bearsout a contention I have long held.Cut the intervals and make thingssnappier !

American'Continuity" FeaturesBut I hadn't done with the good

John-even if, obviously, hp had verynearly done with me.

" Humour ? No, they don't exploitstraightforward humour any betterthan we can. They seem to concen-trate on witty commentaries of currentaffairs-giving them a humorous slant,so to speak.

" Amos 'n' Andy are the mostfamous exponents of this kind of thing.They come on the air every night.There are other ' continuity ' featuresof a similar kind. They all work onthe idea that characters can be builtup and sustained over a serias ofbroadcasts. It is the exploitation ofhuman interest rather than humour,this.

" Supposing all our producers weresent over to the States for an educa-tional period ? " I suggested. " Ishouldn't suppose anything of thesort," replied John. " Why not ?Because they'd all go mad-I nearlydid myself !

Yes, I did a certain amount oflistening to Empire programmes-which certainly come in very wellover in the States. All -wave sets seemto have caught on there, and manylisteners tune in the European pro -.grammes on short waves as a changefrom their own stuff.

Our Methods BestPlenty of folk are saying out therc

that our system of broadcasting isbetter than their commercialised idea.It is significant, I think, that onehears a good deal more emphasisthrown on to the occasional broad-cast of a symphony orchestra thanon the unending supply of, lightentertainment."

So John comes back to St. George'sHall convinced that all's for the bestin the best of possible worlds. Thatour system is the right way for us.And the American system probablyright for the States.

I left John clearing up to go awayfor a real holiday-climbing andswimming and all that in the BavarianAlps. When he gets back he will getdown to some more " Songs from theShows "-as well as plenty of othershows all for our delight.

170

Se,ptember, 1935 WIRELESS

TELEVISION FOR THECINEMA

-continued from page 168.

rental or purchase of such apparatus,neither can I give you any comparisonwith present news -reel costs.

Neither can I say definitely thattelevision will be applied only to thefield now covered by news reels. Withan entirely new science, new technique,art ,and presentation follow. To comeback to more practical points I haveto say that good television pictures inone form or another will be shown inLondon cinemas before the end of theyear. They will show results of fairentertainment value and should attractthe public from this point of viewrather than from the point of view ofnovelty, or from the fact that televisionis a matter of the moment.

In a Few YearsI think I am right in saying that

within two years from now severalLondon cinemas will be taking regulartelevision items in their programmes.Perhaps within three to four years,from now provincial cinemas will have

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their own distribution stations to coverlocal areas only. But it will take manyyears before every cinema in thecountry is equipped to give full screentelevision' of programme value. Thiswill depend entirely on the technicalprogress which is made with regard tocable and radio relay links.

In the meantime television for radiobroadcasting will have gone aheadvery rapidly. Will it have any effecton the cinema box office ? In myopinion it will bave no effect at all.There are two main reasons for this,one is that television broadcastingprogrammes will have presumably thesame limitation in conception as thepresent sound broadcast programmes.The cinema will, however, continue togive the public what it wants. It

must do that, otherwise box officereceipts will go down and the cinematrade will cease to exist.

Unconscious AttractionSecondly, I am convinced that even

if programmes for the home were madereally attractive the average memberof a family will still want to go outto his local cinema or theatre, andlaugh and cry and enjoy himself incommon with many hundreds ofothers. One cannot get away from thefact of the influence of mass psychologyand its unconscious attraction.

Summing up, I venture to say asfollows : Television broadcasting for

the home is here now and will soon beseen in a large number of homesthroughout the country.

Television for the -cinema is in anexperimental form now, but it isgradually developing to become afeature in the programme presentation.

The cinema need have no fear oftelevision in the home as regardsreducing box office receipts. Televisionwill result eventually in new techniquein presentation which will graduallydevelop in its own style and in the formmost suitable to it.

Note : The foregoing article by Captain A. G. D.West was taken from the special lecture given recentlyby the author before the Conference of the Cinemato-graph Exhibitors' Association.

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" We consider the advent of this new rangeto be of such importance to constructors that noreview would be complete without a referenceto this remarkable speaker development."When you hear a 1936 Stentorian youwill realise that this striking tribute isindeed well merited ; for never beforehas such a high " laboratory" standardof reproduction been available to thepublic at popular prices.New production methods makepossible a vastly improved performanceat no price increase. New designs ofmagnet and component parts bring anorder of efficiency hitherto beyond thebounds of possibility. Hear the 1936Stentorian to -day! Listen to theenormous volume from weak inputs.Notice the marvellous definition,incisive top notes, and magnificentnatural bass. You will find it hard tobelieve that prices remain at the samelevel as last year !In this startling new range of instru-ments, W.B. engineers again givetriumphant proof of the value ofconsistent and intensive research.

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Sole Agents in P.S.L: Kelly & Shiel, Ltd., 47, Fleet Street, Dublin.171

W;RELESS September, 1935

IS FOREIGN - RECEPTIONENTERTAINMENT?-continued from page 136.

or more, and receivers building up toa loudspeaker power of 3 watts ormore, the selection of daylight rangeforeigners is very limited. Those thatdo come in-down here, for instance-are, of course, quite free from fading.

Cologne, Brussels, Poste Parisienand Fecamp are daylight signals ofgreat merit-but not necessarily sogood at night, when the layers begintheir fun and games. London Regionalis not a very strong signal in the day-time, while the London National ispitiable.

Alternatives to B.B.C.I have not mentioned the long waves,

which provide day and night - timesource of programmes of real enter-tainment value to the .countryman.Droitwich gives us our only reliableNational signal. Kootwijk, RadioParis and Luxembourg always comein well.

These are odd examples, nct toosignificant because they affect, perhaps,only a minority of listeners. I quote

them merely to show that, withoutthinking or checking up, here are somestations as engrained upon my listen-ing consciousness as the locals and theshort wavers are upon Mr. Kelsey's.

But there is a larger issue at stake-the issue of the method of listening.For my part, I treat my wirelessreception in two distinct ways. I makea date with the set for special broad-casts or talks or plays or musical itemsI am interested in. Or, more usually,I simply switch on, twiddle the tuningknob until I come upon somethingtuneful-and leave that to provide mybackground until such time as theblather of an unknown foreign tonguedrives me to seek pastures new.

I do not wish to make out a won-derful case for the foreigners. All Isay is that, time after time, one orother of the foreigners does provideme with tuneful music at periodswhen nothing of the kind can beextracted from the home programmes.

Very often when some elaborateshow is being put over by the B.B.C.in a vain attempt to compete with thelegitimate stage, music -hall or concert -hall, I turn with a sigh of relief tothe relative simplicity of Hilversum'smusical entertainment, or a Germanstation's lilting melodies.

Am I obsessed with the awful

variability of such stations ? In truth,no. My automatic volume controlhelps to hide the modest fades.And when a particularly horrid momentof distortion blurs the programme Icannot grumble-because my homestation does much the same thing.

I have long since lost any thrill insaying to myself, " How wonderfulthis is-music coming from 800 milesaway." We all talked like that at thebeginning.

A Question of MusicNow, as I say, it is merely a

question of getting on to some reason-ably tuneful music-and hanging whereit actually comes from. I feel no" latent desire " to conquer otherterritories, and in that, possibly, Idiffer fundamentally from the short-wave fan.

But then so do thousands of" B.C.L.'s." who nightly find amuse-ment in prosaic reception of medium -wave foreigners. I am perfectly surethat no one-after the first fine carelessrapture has gone-would willinglystay put on a foreigner just because itwas a foreigner. No, only because itso happened that that foreigner wasgiving them something they could notget from perhaps a more reliable localSource.

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QUESTIONS I AM ASKED-continued from page 152.

grid voltage into the dangerous lowerbend region, where distortion willarise. It will be noticeable in theloudspeaker but far more easilytraced by including a milliammeterin the anode circuit of the output valve.When extra loud passages of music arereceived the needle of the milliam-meter will kick forward to highercurrent readings, due .to the rectifica-tion at the lower bend. Small kickscan be ignored, but violent onesindicate definite -distortion.

Insufficient Negative BiasAnother effect will be obtained if

the negative bias is insufficient ;this time the positive half -cycleswill-on a very strong signal-exceedthe negative bias and the grid willbecome momentarily positive. Thiswill set up a grid current and the fullpositive half -cycle will not be properlydeveloped on the grid. This effect istraceable by the use of a micro -ammeter of suitable range in the gridcircuit. Normally, when no signalsor medium strength signals are beingapplied to the grid of the output valve,the microammeter will show noreading. When overloading occurs,due to the signal causing the grid tobecome positive, the microammeterat once shows a reading indicating agrid current which, no doubt, will causedistortion. By using two currentmeters, one in the grid and the otherin the anode circuit, it is possible tosee at once when overloading occurs.Usually it happens at a signal levelmuch below that at which it becomesobvious to the ear.

Similar distortion may occur at the1st L.F. valve, when such a valve isused. The tests are the same.

FROM MY ARMCHAIR-continued from page 164.

Since then, I have always had com-plete charge of a department or of acompany or been completely inde-pendent. I have been able to writeas I like with no consequences toconsider. The chief disadvantage ofmuch writing is that one is apt to beconsidered a writer ! I attach solittle importance to writing that I havenever regarded it as anything but a by-product (albeit a remunerative one) ofpractical work or a relaxation fromlegal and patent study.

Our West Country doctor writes :Eddy currents are what swirl about

small boys after currant cake and a doseof castor oil-I can prove this.

* * *

A. E. I., of Brewery Buildings (whata gorgeous address !), Cainscross,Stroud, Glos., would like a visit butasks nervously : " Does it entail anyobligation financially ? "

I should be glad to pay to come.But we might get twice as manystations as in the Lucerne Plan.

The charge for visiting Chorlton-cum-Hardy would be 50 guineas peraerial. -,*

In between spurts of deciding whatto do about Abyssinia, I am completing

my big set of the year. Which means,of course, that while you are revellingin the glorious sunshine, I am im-prisoned in a laboratory.

Vast Amount of WorkI suppose that no one would need a

dozen guesses before arriving at themagic figure 700, and .believe me,there are many times seven hundredcircuits leading up to this latest set.It is going to create a bigger 'sensationthan any of its predecessors, if I amany judge.

A vast amount of laboratorymeasurement work has been neces-sary-far more than with any previous

(Continued on next page.)

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173


FROM MY ARMCHAIR-continued from previous page.

set-the reason being that entirelynovel principles are being applied forthe first time, and the results have beenso-what's another word for thatoverworked and wilted " amazing " ?-that I .have wanted to be certainthat the performance is easily obtainedunder all sort of conditions.

The circuit itself is fascinating inthe extreme, and those who expectsomething really new and exciting inmy chief annual set, are going to havesomething to make their tongues lollout. There are also other interestingfeatures which will whet the appetitesof even the most blase constructors.

Still Very Much AliveOnce again we shall prove that there

is still rich red blood flowing in theveins of the amateur movement. Thedays of indiscriminate building areover, it is true. Once upon a time,there were hundreds-perhaps thou-sands-ready to build each and every

- design published. Merit did not mat-ter. Who was to decide which wasthe most meritorious ? The periodic isthemselves did not seem to know, formasterpiece followed on the heel ofmasterpiece, and a new epoch-mak( rwas born in the dust left by its recent.predecessor.

Bad old days. Self-righteously Ideclare I had no hand in it. Foryears the public knew me not. Foryears I had just disappeared and wasunheard of by the general public-unless I was wrecked in my aeroplanein the Channel. I became severelyprofessional, and the limelights ofpublicity were dimmed. But I waslured from the plough by very larg.ioffers of, gold, and promised greatfreedom of expression.

Fewer and BetterFreedom and high reward-who

would refuse ? In the autumn of1931 I realised that home -constructionwas at the cross-roads, and with theS.T.300 I initiated the fewer -and -better sets policy. It certainly gavenew life to the constructor movement.I have been criticised for " cornering "the set -construction field, and creatinga monopoly. If, in fact, anythinglike this has occurred it is more acompliment than a criticism. Believeme, I am always very much on mytoes. I have seen many a designereclipsed and I never risk resting on,my laurels. The S.T.700 is being

evolved with desperate efforts toproduce a set of overpowering per-formance and appeal. I have nohesitation in recommending you tobuild what will be my best set, of1935-36.

I see an enterprising inventor hastaken out a patent for a gramophonerecord made of chocolate. The ideais that if you weary of a particulartune you just eat the record. Thescheme, of course, is not new. Ionce met an inventor who had a setwith valves made of marzipan. Hestarted experimenting with a 10 -

marzipan -valve circuit, working nightand day. As he grew hungry he wouldeat the output valve and this resultedin a rapid diminution of signal strength.

Fortunately, this was compensatedfor by the extreme ingenuity of theinventor, so that as the number ofvalves was reduced the improvedefficiency made up for the expectedloss of signal strength. He claimsthat most modern developments derivefrom his enforced inventiveness.

When I visited him in his laboratory,there was only one marzipan valveleft, and he claimed that, thanks to hiscircuit -mongering, just as good resultswere obtainable as with ten of thevalves. In a careless moment I atethe sole remaining valve. Signalsremained as good as ever.

J. S. -T.

B.B.C. NEWS-continued from page 143.

Company, departs this month to takeup his duties. He has been for thepast six or seven years one of the mostvaluable members of the Talks Staff ofthe B.B.C. He plans' to take with himto India a small nucleus of B.B.C.officials.

His Director of Programmes islikely to be Mr. R. A. Rendall, who isnow in charge of programmes for theWest Country at Bristol. Mr. Rendallis the nephew of Dr. Montague Rendall,formerly Governor of the B.B.C.

Children's Hour to TourI heard the other day of an interest-

ing suggestion that the London Chil-dren's Hour should make itself betterknown to the public, and in particularto its most devoted listeners by touringthe children's wards of hospitals.Already it has visited the GreatOrmond Street Hospital with success.The idea is likely to be adopted.

174

A FOUR -VALVE BATTERYSUPER WITH A.V.C.

-continued from page 148

times when the local transmission-ifone resides only a short distance awayfrom a powerful B.B.C. Regional-tends to become overpowering.

In cases of local station overloading,it is quite easy to rig up a localdistance switch, consisting of 100 ohmsresistance and an ordinary on -offswitch.

All that has to be done is to joinone side of the switch to the aerialterminal, and the other side of theswitch to one side of the 100 -ohmsresistance. Then connect the remain-ing side of the 100 -ohms resistance tothe earth terminal. When the switchis in the " on position, the resistancewill be connected across the aerial andearth and will reduce the volume of thelocal station sufficiently to preventoverloading. For the reception of allother transmission the switch shouldbe " off," so that the resistance is notin circuit.

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September, 1935

A LOUDSPEAKERDEVELOPMENT

Results of our tests of the newStentorian Senior.

SENSITIVITY has always been oneof the outstanding features ofW.B. speakers, and the new ones

are more sensitive than ever.This year larger and stronger mag-

nets have been fitted and, in addition,a new type of baked speech coilformer is employed. This providesimproved centring, besides givinggreater rigidity and lightness to thecoil.

Since the' details of the firm's rangewere published in our last issue, wehave had the opportunity of tryingout the new Stentorian Senior model36S. This is a permanent -magnetinstrument, and incorporates the" Microlode system of matching upto any type of output circuit.

The Two Switches -

On the back of the chassis thereare two switches. One of themcontrols the matching, while the otherone is for high or low resistanceextension work. Terminals are pro-vided so that the speaker can beemployed in conjunction with poweror pentode outputs, as well as push-pull, Q.P.P. or Class B. Two furtherterminals are provided for connectingup to a volume control.

A useful innovation is the provisionof information-actually on the chassis-for connecting up the speaker as anextension with most of the well-knowncommercial sets. Incidentally, the coneitself is of hand -made paper, andthe makers state that this im-proves attack and eliminates frequencydoubling.

"Very Sensitive Indeed"On, test, we found the instrument

to be a very fine example of loud-speaker design. It is very sensitiveindeed, and the" reproduction isexcellent.

Given a good undistorted input andthe correct setting of the inputtransformer switch -arm, the high andlow notes are brought out withremarkable clearness and fidelity.It is suitable for use with everyclass of set, big or small, and is aspeaker that we have no hesitation inrecommending.

The price of the model 36S istwo guineas. The results of our testsof the other models will be given inan early issue.

"WIRED" TELEVISION-continued from page 162.

A special type of high -frequencyconductor has recently been developedfor this kind of work. It consistsessentially of an outer conductingtube and a central wire core, arrangedso that the high -frequency currentstravel along the space formed betweenthe inner surface of the tube and .theouter surface of the centre 'wire.

The signal currents travel by skineffect, i.e., they are confined to thesurface of the metal, and do notpenetrate through to the outer surfaceof the tube. The latter, therefore,acts as an effective protection againstoutside disturbances.

Figs. 1, 2 and 3 illustrate differentconstructions of modern high -fre-quency carrier -lines.

The cable shown in Fig. 1 is abouthalf an inch in outside diameter, andis capable of transmitting a frequencyband of one million cycles over a dis-tance of about 10 miles. By insertingrepeaters or amplifiers at this distanceapart, the range of transmission can,of course, be extended almostindefinitely.

An Ingenious DesignThe inner conductor A is a solid

copper wire, which is insulated fromthe tubular conductor B by a spiralwrapping C of cotton string. Theouter conductor B is a tube made ofoverlapping copper strips, held inplace by a brass binding -tape D. Anexternal sheath E, of lead, protectsthe line as a whole from moisture.

If the repeaters are inserted every5 instead of every 10 miles, the linewill transmit a frequency -band offour million cycles without appreciableloss. Alternatively, by doubling thediameter of the outer tube thefrequency is squared.

Fig. 2 .shows a modified form oftransmission -line, in which the outertube A is spaced apart from the centrecore B by a series of hard rubberinsulating washers C.

In Fig. 3 the outer copper tube Ais 21 inches in diameter, and surroundsa small tube B which, in turn, con-tains the centre wire C. This arrange-ment provides two separate trans-mission lines, one between the outerand inner tubes A, B, and the otherbetween the inner tube B and thewire core C. Spacing -discs or washersD E are inserted at intervals.

175

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1 Peto-Scott Ready -Drilled Metaplex Chassis 4 01 Polar Midget 3 -gang Condenser, with drive 1 2 31 Set of 3 Colvern Coils ... 110 02 Colvern I.F. Transformers ... ... 1 5 01 Set of 4 Specified Valves 219 0

S.T.600 RADIOGRAM

KIT "A". Pad E511.6Comprises all components as first OR YOURSspecified by Mr. J. Scott-Taggatt, FORincluding Peto-Scott Structakit, lessValves, Cabinet, Needle, - Cups, 1 0 meGranto Motor, Pick-up and Speaker.

and 11 monthly' payments of 10/3.

-S.T.600 RADIOCRAM CABINET --Exclusively Specified by Mr. John YoursScott -Taggart, this oxquisite Peto-Scottcabinet has a modern two-tone finish with Forinlaid walnut veneer panels. Cash or C.O.D.Carriage Paid £31310. (Carriage and Pack-ing 2,6 extra. Speaker Baffle assembly, 3j6extra.)

and 11 monthly payments of 6!3.(iurindfag carriage and speaker baffle assembly.)

KIT -BITS1 ou pay the Postman. We pay, postcharges on all orders over 101 -Or. BR11,I1N ONLY

S. d1 Garrard No 20 Motor with 7q handle ... 17 01 Rotherinel-Brush Mem-Electric Pick-up 2 2 01 Rola F624 P.M 00 Speaker ... 1 171 Set of 4 Specified Valves ... 2 4 6

Model A.C.12. For AV).mains, 200/250 volts, output120 volts at 12 mta. Four tap-

pings 40v.,60v., 90v.. and120v. Cash. orC.O.D. Car-riage Paid.£111010 or2)6 down and10 monthlypayments of

Model D.C.1. Cash or C.O.D. Carriage Paid£1/7/6, or 2/6 down and 11 monthly payments of 2/6.Model A.C.25. Cash or C.O.D. Carriage PaidR2/916, or 51- down and 10 monthly payments of 5/.Model M.A.1O/30 With Trickle Charger. Cashor C.O.D. Carriage Paid ,E2119/6, or 5/- down and 11monthly payments of 5,6.

Peto-Scott 1936 PERMANENT MAGNETMOVING COIL SPEAKE RS

FIDELITY REPRODUCTION.Type New Babyfor Power or Pen-tode. Complete withinput transformer.Send 2/6 with order.Balance in 8 monthlypayments of 2/6.Cash or C.O.D. Carr.Paid, 15/6.3.1 Chassis for Poweror Pentode. Cash or

C.O.D. Carriage Paid, 19/6, or 2/6 down and 8monthly payments of 2/6.S.3 Chassis de Luxe for Power, Pentode or ClassB. Cash or C.O.D. Carriage Paid, 32/6, or 2/6down and 11 monthly payments of 3/-.

HIGH

PETO-SCOTT Co. Ltd , W2, CITY RMI L

77ONDON,E.C.1D,

West Lad Showrooms : CS, W.I, High Holborn, London, W.C.

W I REL ESS

THE S.T.600BATTERY RADIOGRAM

-continued from page 138.

the ,operation of the other controls.The aerial reaction knob (at the bottomleft-hand corner) should be at zero-i.e. fully anticlockwise (to the left).

The greatest fault in tuning wirelesssets is to have the signal too loudbefore applying reaction. The resultis that poor selectivity and distortionare needlessly experienced. Even withfull reaction, with the set on the pointof oscillating, signal strength shouldbe just below the maximum possible.

Of course, when the signal is verystrong and reaction is not necessary,the only limit is that where distortioncommences. But when receivingforeign stations of average strength,reaction is desirable-if only to givethe required selectivity ; it is thenthat it is wisest to keep the normalsignal weak and bring it up to goodloudspeaker strength with reaction.

Extremely EffectiveAerial reaction on the S.T.600 is

extremely effective, and it works moresmoothly even than the anode reaction.When first testing it out, leave theanode reaction at zero (full left). Youwill find you can get all the usualreaction effects perfectly with aerialreaction. A slight readjustment ofthe front concentric trimmer will help.The previous rule applies : Do notapply reaction to signals that -arealready strong ; cut them down withthe aerial coupler.

It is very important to know thataerial reaction comes from the screen -grid circuit of the first variable -mupentode. If, therefore, the volumecontrol is cut down too much, therewill be so much negative bias on thecontrol grid of this valve that therewill be insufficient reaction currentflowing in the screen -grid circuit, whichis robbed of its H.T, current. Inpractice, this simply means that youcannot get aerial reaction unless you

have the volume control turned up (tothe right) enough.

Having noticed the aerial reactioneffect you can try combinations ofaerial reaction and anode reaction.At first try just a little anode reactionand a little aerial reaction. Thenadjust either to give " critical reaction"effects. Once more let me remindconstructors that signals should bereally weak before applying the tworeactions. As the volume controlmay require to be turned up to permitaerial reaction, signals can best beweakened by reducing the aerialcoupler-i.e. turning it to the left.

As regards the trimming of the gangcondenser, this is extremely simple aswe do not rely On trimming in theordinary sense, since the operator canadjust the front trimmer at any time.All you need do is to set the fronttrimmer about half -way, leaving theaerial coupler turned about one-thirdway from zero (full left) to theright.

You now choose some fairly weakstation about half -way along the dialof the medium waves and try pro-gressively different adjustments of therear trimmer on the gang condenser.At a certain position of this trimmerloudest signals will be obtained whenthe main condenser knob is moved.Likewise, signals should weaken if youadjust the front trimmer to.either sideof its half -way position.

Enginces s Guidecontaining the_widestchoice of engineeringcourses in the worldCutlines The T.I.G.B.'s up-to-date, homestudy Courses in Wireless, Electricaland Mechanical Engineering. etc. Showshow to become A.M.I.E. E., A.M.I.W.T.A.Rad.A., etc. and how to Qualify for awell -paid post . Traininguntil Successful Guaranteed.VI RITE NOW for Free Guide

THE TECHNOLOGICAL INSTI-TUTE OF GREAT BRITAIN,21, Temple Bar HouseLondon. E.F4 (Founded 191719,000 Successes.)

MIS

To SUCCESS2

1!

Gilbert, J. C. (Cabinets) 174

INDEX TO ADVERTISERSLectro Linx, Ltd...Marconiphone Co., Ltd.

174134

Peto-Scott Co., Ltd. .. 175Pifco, Ltd. .. .

173PAGE Technological Institute of Great Britain 176

Answers Football Annual .. .. Cover ii Varley Products .. . 172Automatic Coil Winder & Electrical Westinghouse Brake & Saxby Signal

Equipment Co., Ltd. .. .. 133 Co., Ltd. .. 161

Cole, E. K., Ltd. .. . . Cover iv Whiteley Electrical Radio Co., Ltd. . . 171

Ferranti, Ltd. .. 161 Wingrove & Rogers, Ltd. 172

September, 1935

You may find that at the extremebottom of the medium waves, theaerial coupler will affect wavelength to

THE POWER SUPPLYBATTERIES.

Drydex, Ever Ready,Lissen.

G.B. Drydex, Ever Ready, Lissen.L.T.Exide, Block.

a small extent and it may be necessaryto keep the aerial coupler at a lowvalue (nearly full -left) when receivingsuch stations ; otherwise the fronttrimmer may just fail to give a sharptuning point.

With the above hints on tuning,every constructor after an evening ortwo should become expert and bringin the hundred stations which thissuperlatively sensitive set is frequentlycapable of receiving.

A FINETESTING INSTRUMENT

of the popular AvoOscillator has been introducedby the Automatic Coil Winder

and Electrical Equipment Co., Ltd.It is priced at £5 10s., but as a timesaver it should be almost invaluable toservice -men and others who haveoccasion to test radio receivers.

The dimensions of this Avo-Oscillator areonly 6" x x3e,

This instrument provides a steadylocal signal, modulated if desired, at afrequency which can be varied overthe whole of the long, medium and I.F.wavebands. It can also be used onshort -waves by harmonic working,has a variable adjustment for strength,and is completely self contained withbatteries and valve.

Printed in Great Britain and published on the 1st of each month by the Proprietors, THE AMALGAMATED PRESS, LTD.' The Fleetway House, Farringdon Street,Lond n,i E.C.4. Advertisement Offices : John Carpenter House, John Carpenter Street, London, E.C.4. Registered for transmission by Canadian Magazine Post.Subscription Rates : Inland and Abroad, 8/- per annum ; Canada only, 7/6 per annum. Sole Agents for South Africa Central News Agent' Ltd. Sole

Agents for Australia and New Zealand : Messrs. Gordon and Gotch, Ltd. S.S.

176


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0


!CLEAR-CUT REALITY' made Radiolympia

atothA EKCOskoIn the search for realistic reproduction, Clear-cut Reality', exclusive to Ekco, emerges as thesupreme triumph of the 1936 season. Experts describe it as " reality . . . a clearly audibleimprovement upon ordinary radio tone " . . . an improvement that only Clear-cut Reality'can bring to radio.It gives tone as true as a tuning fork to this amazing model-a receiver already predominantfor beauty of cabinet and outstanding performance.

* Eight -stage superhet circuit withband-pass tuning, for A.C. mains.

* New type Clear - cut Reality'moving -coil speaker with extra largeand efficient output transformer.

* Station pre -selector and automaticnoise suppressor.

* Magnificent moulded cabinet in newwalnut shade or black with chro-mium -plated fittings.

* Quiet Automatic Volume Control.

* Large size station scale with namesand wavelengths.

* Continuously variable tone control.

* Light -beam and shadow stationindicator.

* Tone -compensated volume control.

* Gramophone pick-up sockets withswitch.

* External speaker sockets.

* Internal speaker switch.

* Latest type valves: Octode, H.F.Pentode, Double - Diode, Triode,L.F. Pentode and full wave rectifier.

* Output 3 watts.

MODEL AC86 irni"'" ""G8 -STAGE

SUPERHETBlack anti Chromium 10/6 extra.

SN

Initial payment of L1.2.6 and 1 2 monthlypayments of L1..2.6.

MODEL B86. Eight -stage BatterySuperhet version of AC86. Incor-porates Q.P.P. output and 111Gus.latest valve combination. (without batteries)

To : E. K. COLE LTD. Dept. D.11. Ekco Works, Southend - on - Sea. Please sendEkco 'Clearcut Reality' Radio.

me illustrated literature of

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VOL.2 NO.10 rL'i[r@ [email protected] from. Model 236 (illus-trated) is the latest console...

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Transcript of VOL.2 NO.10 rL'i[r@ [email protected] from. Model 236 (illus-trated) is the latest console...