Engineering - World Radio History

ectroricEngineering

INCORPORATING ELECTRONICS, TELEVISION AND SHORT WAVE WORLD

PRINCIPAL

CONTENTS

R. W. Paul - Pioneer Cinematographer

Dust Cored Coils

Physics of the Hard Vacuum Valve

F. M. in Record Reproduction

Aerial Characteristics - Data Sheet

2r- AUG.,1943

PDF compression, OCR, web optimization using a watermarked evaluation copy of CVISION PDFCompressor

ii Electronic Engineering August, 1943

one in a thousandTen years ago we introduced the first British -Made low -loss ceramic. To -daythe range of FREQUENTITE components covers more than a thousand piecesof every shape and size.With such a store of manufacturing experience we are able to offer advicebacked by practical knowledge on your insulation problem. Please consult usbefore you finalize your design.

STEATITE & PORCELAIN PRODUCTS LTD.Head Office: Stourport-on-Severn, Worcs. Telephone: Stourport Ill.Telegrams: Steatain, Stourport.

B.P.28

The fact that goods made of raw materials in short supply owing to war conditions are advertised Inthis magazine should not be taken as an Indication that they are necessarily available for export.


August, 1943 Electronic Engineering 89

Cathobe coatitis

THEcathode is the heart of a

valve and it is of primary im-portance that the extremely finelimits stipulated by the designer arerigidly adhered to in production.

Our illustration shows the cathodebeing sprayed and a sample beingweighed to a limit of 0.5 milligram(.000017 oz.).

BRiMAR

VALVES

STANDARD TELEPHONES AND CABLES LIMITED, FOOTSCRAY, SIDCUP.


90 Electronic Engineering August, 1943

.,-.41stogeVe aFtiteil/A*PC4,1,,:&V,

Value provenbg long service

ClArS ra

desfor

INDUSTRIAL APPLICATIONS

ELECTRO MEDICALEQUIPMENT

THERMIONIC INSTRUMENTSand TEST GEAR

VITAL COMMUNICATIONSand WARNING SYSTEMS

ETC.

THE GENERAL ELECTRIC CO. LTD.Magnet House, Kingsway, London, W.C.2



THERE IS NO SUBSTITUTEFOR

ENGINEERING EXPERIENCE

And this is obviously a matter of extent, intensity and time.

Take Electrical condensers for instance-simple in conception maybe-

but demanding infinite experience and skill, to satisfy the exacting

operating conditions of modern requirements. The fulfilment of these

has meant the whole time occupation of highly skilled specialists,

working at high pressure, in this way to earn, along with their

countrymen in other spheres, the right of survival.

What a wealth of experience and technical excellence will be available

to all, when happier times arrive ; and nowhere more than in

Dubilier Condensers.

DUM HERCONDENSER CO (1925) LTD.



The AvoMeter is one of a useful range of " Avo " electricaltesting instruments which are maintaining on active serviceand in industry the " Avo " reputation for an unexcelledstandard of accuracy and dependability-in fact, a standard bywhich other instruments are judged.

Some delay in delivery of Trade Orders is inevitable, but weshall continue to do our best to fulfil your requirements aspromptly as possible.

THE Model 7 Universal Avo-Meter is the world's most

widely used combination elec-trical measuring instrument. Itprovides 46 ranges of readingsand is guaranteed accurate toB.S. first grade limits on D.C.and A.C. from 25 to 100 cycles.It is self-contained, compact andportable, simple to operate andalmost impossible to damageelectrically. It is protected byan automatic cut-out againstdamage through severe overload,and is provided with automaticcompensation for variations inambient temperature.

Sole Proprietors and Manufacturers:AUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT Co., Ltd., Winder House, Douglas Street, London, S.W.I. Phone : Victoria 3404/7.

SILVERED MICA CONDENSERSIncessant progress in methods ofmanufacture and research linkedwith the most thorough mechanicaland electrical inspection, are reasonsfor the outstanding superiority ofU.I.C. Silvered Mica Condensers.Available in all standardized sizes.Suitable for tropical and arctic con-ditions. Type approved.

UNITEDINSULATOR

V VD

12-22, LAYSTALLSTREET,

LONDON,E.C.1

Tel: TERminus7383

(5 lines)

Grams: Calanel,Smith, London



1

for Outstanding reliabilityHighest efficiencyPerformance proved by 17 yearscontinuous service all over the

World

WESTINGHOUSE BRAKE & SIGNAL CO. LTD.PEW HILL HOUSE, CHIPPENHAM, WILTS.

'Designed by engineersfor engineers, theSolon electric solder-ing iron gives neater,cleaner, more efficientwork in less time.The heating elementis right inside the bit ;giving constant heat atthe point-where youwant it. All internal con-nections housed at end ofhandle-away from heat andeasy to get at. Completewith 6 ft. of Henley 3 -core flex-ible. Made for the followingstandard voltages - 100/ I 10,200/220, 230/250. Supplies are, ofcourse, only available for essentialwar work. Early ordering is

advisable as the demand is heavy.

sCILONSOLDERING IRON

Made in England

Mode/ shownis a standard125 wattround pencilbit Solon.Other sizesand typesavailable.

W. T. HENLEY'S TELEGRAPH WORKS CO. LTD.(Eng. Dept.) Milton Court, Westcott, Dorking, Surrey.

ElectronicEngineering

AUGUST, 1943

Volume XVI. No. 186.

CONTENTSPAGE

Editorial 95

Dust Cored Coils-Part I ... 96

Robert W. Paul .. 99

Physics and the Static Characteristics of HardVacuum Valves ... 103

Effect of Lightning on Receiving Aerials 107

Mass Radiography ... 108

Aerial Characteristics and Coupling Systems-Data Sheets ... . . 109

The Synchronisation of Oscillators-Part IV 114

Synthetic Reverberation ... 117

Television after the War 118

Frequency Modulation in Record Reproduction 121

Book Reviews 126

Abstracts of Electronic Literature 128

Notes from the Industry... 128

A Note on the Puncture Strength of Porcelain 130

CONDITIONS OF SALE-This periodical is sold subject to thefollowing conditions, namely, that it shall not without thewritten consent of the publishers first given, be lent, re -sold,hired out or otherwise disposed of by way of Trade except at thefull retail price of 2/- and that it shall not be lent, re -sold, hiredout or otherwise disposed of in a mutilated condition or in anyunauthorised cover by way of Trade, or affixed to or as part ofany publication or advertising, literary or pictorial matter

whatsoever.



:DMA SWAN ELECTRIC CO. LTD. 155, CHARING (ROSS RD., LONDON, W,C.2

For full particulars write to Technical Service Department


95

PROPRIETORS s

HULTON PRESS LTD.,EDITOR:

G. PARR

EDITORIAL, ADVERTISING AND PUBLISHING OFFICES, 43-44, SHOE LANE, LONDON, E.C.4

TELEPHONE:

CENTRAL 7400

Monthly (published last day of preced-ing month) 2/- net. Subscription Rates :Post Paid to any part of the World -3 months, 6/6; 6 months, I3/- ; 12

months, 26/-. Registered for Trans-mission by Canadian Magazine Post.

TELEGRAMS :

HULTONPRES LUDLONDON.

OUR contemporary, Radio News,which is published in Chicago,has announced its intention for

the future of referring to the scienceof " pure and applied radio " asRADIONICS.

In a long Editorial note* justifyingtheir decision, the word is definedliterally as " travelling radiation "with additional emphasis on the" ion " part, denoting a chargedparticle.

. . . . The word thus takes ona greater significance. We have init radiation, charged particles, thecoverage for future developments inradio technique (an act or processusing some new ultimate particle) . . '

The word ELECTRONICS is con-demned on three counts :

(1)

(2)

(3)

Its literal meaning is " wan-dering amber."The scientific connotation canstand for only a particularcharged particle, justified pri-marily by being a fundamentalcharge and historical value(sic.).There is no implication ofradio technique as thoughtof by the public, and thiscauses misunderstanding . . . .

Finally, we are surprised to learnthat ELECTRONICS is a Britishterm, whereas RADIONICS is pureAmerican. It is the general im-pression over here that ELECTRONICS

* Radio News, May 1943, P. 4.

Wordswas coined by the McGraw Hill Co.,so we are smarter than we thought.

Anyhow, whoever coined it, it isa most useful word, and we thinkthat Radio News should make outa better case for abandoning -it. Onthe first count, it is not profitableto attack the etymology of anyEnglish word-you never knowwhere you may land. Talking ofetymology, why not start a cam-paign for altering electrocution intoelectrocussion, which is moreaccurate ?

The justifications in the secondcount seem quite sound. The elec-tron is both a fundamental chargeand an historic term, and thescience should therefore be associatedwith this basic word.

On the third count, the muddle-headed attitude of certain membersof the public to science is the despairof scientists, and it is doubtful

Index to Vol. XV.A full cross-referenced index for

Volume XV of Electronic Engineering isnow available, price 6d., post free.

Applications should be addressed tothe Circulation Dept., Hutton Press,43 Shoe Lane, E.C. 4., and be accom-panied by a P.O. or stamps to thevalue of 6d.

ImportantSubscribers who have their copies

of the journal sent direct from theCirculation Dept. need not applyseparately for the Index, which will besent in due course.

whether the use of one term insteadof another will help to clear theirbrains. It is up to scientists tohelp the public appreciate the truemeaning of electronic developments,and they are not helped in this bythe ballyhoo which has appearedrecently in certain publications.

In judging the merits of thetwo words, we would sooner applythe tests suggested by A. P.Herbert :t Ask the new word thefollowing questions : Are you in-telligible ? Are you pleasing ? Areyou legitimate ? Are you needed ?

And judged by these standards,we respectfully suggest thatRADIONICS is an also ran.

Mr. Hugo Gernsback, of Radio -Craft, has also taken up the cudgelson behalf of ELECTRONICS. Thereis only space to quote the beginningand ending of his remarks :$

" We have noticed an unfortunateattempt from several quarters tobefuddle the public with the termRADIONICS. Why this redherring should be dragged acrossthe well -established ELECTRONICStrail at this late date seems aprofound mystery

. In 1924 I coined thehumorous word RADIOTICS for aradio joke column. Maybe that isthe less befuddling term.'

Good for you, Mr. Gernsback !In the meantime, we should worry.

t What a Word! (Methuen) p. x37.Radio -Craft, May 1943, p. 463.



Dust Cored Coils'Part I. The Development of Dust Core Materials

A review of the design and applications of dust -cored inductance coils, showing how a detailed analysis of thelosses enables the performance of a given coil, to be calculated from a limited number of test measurements

By V. G. WELSBY, B.Sc. (Eng.)*

IT is well-known that if an alter-nating current is passed through acoil surrounding a solid ferromag-

netic core, circulating currents, oreddy currents will be induced in thecore. These currents, flowing againstthe electrical resistance of the corematerial, will dissipate energy in theform of heat. The- amount of energylost in this way and the resulting tem-perature rise may be quite insigni-ficant, but what is usually far moreimportant is the damping effect pro-duced in any resonant circuit of whichthe coil may form a part. Otherfactors being equal, the eddy currenteffect increases approximately asthe square of the frequency of the ap-plied voltage, with the result that the,problem of minimising these lossesrapidly becomes more acute as the fre-quency is raised. At low frequencies,eddy current losses can be kept suf-ficiently small by dividing the coreinto a series of laminations, insulatedfrom each other so that the effectiveresistance presented to the eddy cur-rents is increased. As the frequencyis raised, the tendency for the lossesto rise can at first be compensated by

Post Office Research Station.

dividing the core into thinner andthinner laminations, but this processobviously cannot be continued inde-finitely. Generally speaking it is notpracticable to use laminations with athickness less than about 0.002 inch,owing to difficulties in manufactureand assembly. From the point ofview of economics, too, the cost wouldrapidly become prohibitive as thethickness of the lamination was re-duced owing to the increased numberof laminations and the rising labourcosts. As an alternative, a furthersubdivision of the core can be ob-tained by imagining the laminationsas being split into thin strips separatedby layers of insulation; in other wordsby building the core up in the formof a bundle of insulated wires of mag-netic material. Such cores have beenused, (e.g., induction coils used intelephone instruments, etc.) but theirapplication is limited by cost and thedifficulty of forming cores with closedmagnetic paths.

The idea of building cores of dis-crete particles of magnetic material,each surrounded by insulation, is byno means new, but some yearselapsed before any satisfactory results

were obtained. The first commercialdust -core material was produced inAmerica by the Western Electric Co.about 1915.1 The magnetic materialused was iron which was reduced topowder by casting it (or depositing itelectrolytically) in a brittle form andpulverising it in a suitable mill; thepowdered iron was then coated withshellac and pressed into ring -shapedcores under a pressure of about iootons per square inch. Materials ofthis type were extensively used atspeech frequencies in loading coilsfor telephone circuits. The nextstep forward was about 1928, whenthe Bell Laboratories in Americaperfected a method of producingcores composed of compressed pow-dered " permalloy '" (a high -perme-ability nickel -iron alloy). The perme-ability of this material showed an in-crease of about so per cent. over thatof the iron -dust cores, resulting in acorresponding reduction in the dimen-sions of coils having a given per-formance.

The early dust -core materials werestill not sufficiently finely -divided toenable them to be used at radio fre-quencies, and an interesting material,

The illustration at the head of this page shows a typical selection of dust -cored coils in use at the present time. (a) ' pot' core, (b) ' pot'core with screw adjustment, (e) ' Cotton -reel core, (d) ' E & I core, (e) ' L' core. (Approximately I full size).



known as " Ferrocart,"' was de-veloped at about the same time inGermany in an attempt to overcomethis difficulty. It was formed bysprinkling long thin particles of ironon a sheet of paper, orientating theparticles by means of a magneticfield so that they were all lying- parallel, and then securing them inposition with a suitable adhesive. Anumber of such sheets were thenformed under pressure into a solidmass which could be worked into anyrequired shape. The material was,of course, used in such a way that theaxis of the particles lay along thepath of the magnetic flux in the com-pleted coil. The fact that the par-ticles were widely separated and eachpresented a small cross-sectional areaat right -angles to the flux enabled theeddy -current losses to be reduced suf-ficiently to make Ferrocart suitablefor use at frequencies hitherto unat-tainable with any form of iron core.Ferrocart has now been largely super -ceded by improvements in the tech-nique of producing finely -dividediron dust. Nowadays, iron dust isoften produced chemically by the" carbonyl " process.' The first stageis the formation of a compound, ofiron and carbon monoxide, known asiron pentacarbonyl, which exists atroom temperatures as a liquid. It iseasily vaporised, and on further heat-ing, decomposes once again into car-bon monoxide and metallic iron.Under suitable conditions, the ironcan be condensed in the form of tinyspherical particles ranging in dia-meter from o.5 to 5.o microns (imicron = o.00i mm.). Dust obtainedin this way is particularly suitable be-cause not only is it finely divided, butalso the spherical form of the par-ticles reduces the tendency of the lat-ter to burst through the insulatinglayers when the core is subjected tothe forming pressure. " Carbonyl'"cores are extensively used for radiotuning coils and for apparatus (suchas wave filters) used in carrier tele-phony..

Specific PermeabilityThe specific permeability A of a

dust core material is defined as theaverage permeability of a samplewhich is sufficiently large to enable itto be regarded as homogeneous. Ifsuch a sample is placed in a magneticfield, the flux will pass successivelythrough particles of high permeabil-ity and insulating layers with a perme-ability which may be taken as unity.It is easy to see, therefore, that thespecific permeability is going to de-pend rather on the number and thick-ness of the insulating layers ratherthan on the permeability /.4 of the par-ticles. Fig. i gives some idea of the

B

Fig. I.I. Relationship be-tween specific permeabilityand particle permeabilityfor different percentages

of insulation.

/50 /'S$\PERCENTAGE

OF INSULATION:--, 100-- BY VOLUME

3%`/CC

c50-

:-. -------.90/

0

U1u

0 200 400 600PART/CIE PERMEABILar)tto

way in whichµ depends on pc, and onthe percentage of the total volume ofthe material which is occupied by in-sulation.' It will be noticed that asthe percentage of insulation is in-creased, A tends to become indepen-dent of Igo, so that from the point ofview of permeability there would beno advantage in using high -perme-ability alloys in place of iron in suchcases.Effective Permeability

The effective permeability Ile is de-fined as the ratio between the induct-ance of a coil in air and the induct-ance of the same coil when the coreunder consideration is introduced. Ifthe coil could be completely.embeddedin a large mass of the core material,ILe would obviously be equal to Ito. Inpractice, however, this maximum can-not be attained,* since, as a result ofthe relatively low specific permeabil-ity it is impossible to ensure that allthe flux linking with the coil will flowin the core without any leakage. It

. does not follow that the design ofcore which gives the highest value ofA. for a given material is necessarilythe best. This point will be dealtwith in more detail in Part 2, but thebroad principle will be stated herethat the optimum value of au. tends ,tofall as the frequency is raised. Thusthe best design for a certain frequencymight be a toroidal core in whichµ. p = 12 ; while at some higherfrequency, better results might be ob-tained with the same material bychanging over to a different shape ofcore for which A. might be as low as3. It can be shown, in fact that alimiting frequency exists for a givenmaterial and coil size, above which noadvantage is gained by introducingthe dust core. This limit is reachedwhen the increased- losses due to theintroduction of the core begin to out-weigh any advantages gained by therise in inductance, even for very smallamounts of core material.Other Sources of Power Loss

Up to now we have considered theproblem of core materials from thepoint of view of eddy -current losses

It can be closely approached in carefullydesigned toroidal (ring -shaped) cores.

only, but there are two other sourcesof loss which have influenced the de-velopment of dust cores and whichwill be referred to briefly here. It isproposed to discuss them more fullyin Part 2. Firstly, there is thehysteresis loss which takes place whenany ferromagnetic material is placedin an alternating magnetic field.Although hysteresis may contributeonly a small proportion of the totallosses, nevertheless it may be veryimportant because it causes distortionof the waveform of currents flowingin the coil. This means that if asinusoidal alternating voltage is ap-plied to the coil, hysteresis will causedistortion of the current wave, result-ing in the production of componentsat harmonic frequencies which did notexist in the applied signal. This pro-duction of unwanted frequencies maycause serious difficulties in apparatussuch as a multichannel carrier tele-phone system. The second source ofloss is, for the lack of a better term,usually referred to as the "residualloss," although in some literature onthe subject, .the German term " nach-wirkung " or " after-effect " will befound. The exact significance of thisloss has led to some controversy, butit seems to be generally accepted thatit is due to internal stresses in thematerial, produced by the magneto-striction effect. Residual loss can beminimised by careful annealing ofthe dust particles. The existence ofthese two sources of loss has led to thedevelopment of several alloys havingcertain special properties, although.particularly at higher frequencies, thebest results have so far been obtainedwith carbonyl iron dust.Types of Core

Dust cores can be pressed in a widevariety of forms, but these can beclassified roughly as follows :I. Solenoid

The simplest type of core consistsof a " plunger," usually of circularcross-section, " which is insertedthrough the centre of the coil bobbin.For reference purposes, this will becalled the solenoid type. Since themagnetic circuit is not closed, theeffective permeability will be low, so



that solenoid cores are most suitablefor use at high frequencies. Theplunger is often fitted with a screwedbrass rod to enable fine adjustment ofthe inductance of the coil to be car-ried out by changing the relative posi-tion of the core.2. Toroid

The toroidal or " ring "-core maybe considered as a. long solenoidwhich is bent round into a ring andjoined up to form a continuous core.This type has the advantage that, byplacing the winding in close proximityto the core, the external leakage fieldcan be made very small. This meansthat the effective permeability ap-proaches that of the material and alsoenables the coil to be surrounded by aclosely -fitting screening -can withoutintroducing excessive losses.

Toroidal cores are used at relativelylow frequencies where the maximumeffective permeability is required; atypical application being to loadingcoils for telephone circuits. The factthat the full permeability can beclosely approached leads to the use oftoroidal test cores for the accuratemeasurement of the specific perme-ability of core materials and also forthe experimental investigation of corelosses.° One disadvantage of thetoroid is the difficulty of applying thewinding, since this cannot be woundon a bobbin and then slipped on tothe core as with other types. Specialwinding machines have been designedfor winding toroidal coils, but theseare limited as to the range of wiregauges and the sizes of cores whichcan be dealt with. Another disidvant-age is the difficulty of obtaining an

Toroidal filter cans, coils, and dust cores.(By courtesy of the Telephone Mfg. Co.)

accurate final adjustment of the in-ductance value, particularly when thewinding consists of only a few turnsof wire.3. Ironclad or " Pot " Core

In this type the core is extendeduntil it completely encloses the bob-bin. There are several versions whichdiffer mainly in the way in which thecore is split in order that the bobbincan be inserted. A central hole isusually provided for adjustment of in-ductance, which can be carried outeither by placing a suitable piece ofmaterial in the hole and sealing it inposition, or by means of a plungerattached to a screwed rod as describedabove. A range of adjustment ofabout to per cent. of the total induct-ance can be obtained'in this way. Thistype of core combines the advantagesof a fairly high effective permeabilitywith ease of construction and adjust-ment, and it is extensively used atmedium and high frequencies.4. " Cotton -reel " Core

The shape of this core is explainedby its name. It may be regarded asan intermediate stage between thesimple open solenoid and the closed

" pot " core, since it has a centralcore (which may or may not containan adjustable plug and two flanges)which give the complete core a " cot-ton reel " shape. As in the case of the" pot " core there are several versionswhich differ in the way in which thecore is split to enable the bobbin tobe assembled.5. " E and I" Core

This takes the same form as thefamiliar laminated core. It is simpleand easy to construct, but its loweffective permeability make it suitablefor higher frequencies only.6. " L " Core

This is merely a variation of theabove type which requires only asingle mould to form the two parts ofthe core. It has an even lower 'effectivepermeability. Both the " L " and" E -and -I " cores cannot be adjustedand are often used in transformersfor use at radio frequencies.

Dimensions of CoresIt will be shown later that for the

best results, the power losses due tothe resistance of the winding and theeddy currents in the core should beapproximately equal. At low fre-quencies the main problem is to keepthe winding resistance down, so thatcores tend to be massive in order toobtain the necessary winding space.At high frequencies the reverse is thecase and the cores are kept as small aspossible to reduce the eddy currentlosses. As a result, cores are madein many different sizes, ranging fromtoroids several inches in diameterdown to tiny solenoids which may beonly a fraction of an inch in lengthand diameter.

The table which follows gives someidea of the way in which the fre-quency spectrum is covered by thevarious types of core. The frequencyranges have been deliberately leftvague because no definite limits canbe set :

BibliographyI SPEED and ELMEN, Trans. A.I.E.E., 1921, p.1321 SHACKLETON and BARBER, Trans. A.I.E.E., 1928'

p. 429. HANS VOGT, Wireless World, 1932, p. 272.

SCHNEIDER, Electrician, 1934, Dec. 14.4 CHASTEN, Elec. Comm., 1935, p. 142.6 Eleh. Tech. Zeitschr., 1937, Dec. 23.6 WELSBY, P.O.E.E.J., 1942, p. 48.

Freq. Range Material r, Core Type V

Power (<100 cfs)_ Laminations

Speech (100 c/s-10Kcis) Permalloy Dust 100 Torold IOD

Carrier (10Kcis-500Kc/s) Iron Dust 20 Torold 20Pot 6E ands 4

12 Pot 5Cotton -reel 4

Radio (>500Kc/s) Iron Dust E and I 3L 2Solenoid I

Air Core I Solenoidor " Slab "



ROBERT WILLIAM PAUL wasborn at Highbury, on October 3,1869, and died in London on

March 28, 1943. His father was aLondon shipowner, whose ships sailedout of the Pool of London to the Balticand the Levant. He was educated atthe City of London School and at theCity and Guilds of London TechnicalCollege, newly opened near FinsburySquare. During vacations he tooklong trips on his father's ships andacquired a taste for travel that en-dured throughout his life.

At Finsbury Technical College heexcelled on the electrical side and dis-covered his abilities for electrical andmechanical design. After leavingcollege he went to Elliots to learn in-strument -making and also to the fac-tory of the Bell Telephone Companyat Antwerp. In 1891 he started hisown business as an instrument makerin small premises in Hatton Garden.He kept up his contacts with FinsburyTechnical College by getting theteachers there to suggest and partiallydesign instruments. In this way hemade instruments outlined by Ayrton,Perry, Mather, Sumpner, Walmsleyand others. His personal contributionto the designs at this date was mainlyon the mechanical side, for which heearly showed great ability. Many of

Robert W. PaulPioneer Instrument Maker

and Cinematographer

By W. H. ECCLES, D.Sc., F.R.S.

the instruments that spread all overthe world bearing the above famousnames owed much of their practicaland commercial success to Paul'sgenius for soundness in mechanicaldesign and workmanship. It is astriking fact that his business ex-panded so fast that the works hestarted in Hatton Garden in 1891 hadto be augmented by a four storey fac-tory in Great Saffron Hill close by in1894.

Now in 1894 two Greek showmenbrought from America to London oneor two of Edison and Dickson's newKinetoscopes. Charging twopence atime for a peep through an eyepiece atthe short " living picture " given bya film of 4o feet arranged as an end-less belt, the showmen had difficultyin dealing with the crowds that be-sieged their shop near LiverpoolStreet station. They sought out Pauland asked him to make six similar in-struments ; this was permissible asEdison had not patented it this sideof the Atlantic. During the next yearPaul made sixty more with improve-ments. As the American originatorsnaturally refused to supply new pic-tures for use in these machines, Paulstarted from scratch on the design,manufacture and use of cameras fortaking pictures. He was thus the first

cinematographer in this country. Thenhe designed a machine for perforatingthe film so that it engaged thesprocket wheels without undue wearand tear. At each stage, it has beenstated by users, he introduced newideas and great improvements. Someof his pictures were shown at theEarls Court Exhibition of 1895. Herethe sight of the queues of people wait-ing for their turn at each of the fifteenmachines on show, roused Paul to theendeavour to project living pictureson to a screen, a feat as yet un-attempted or, at any rate, unachieved.

The principal difficulty was to givethe film a step-by-step motion suchthat it was standing still for a largefraction of the time, for only thuscould sufficient light be transmittedthrough each picture or " frame " inturn. He worked at the problem withgreat energy and towards the end of1895 he obtained success with amechanism consisting of a fingerwheel rotating uniformly which en-gaged with slots in a star wheel. Thisis on the same arbor as the sprocketwheels, moves forward one frame -length at each engagement with thefinger wheel and is held stationary be-tween whiles. Embodying this in aform which could be attached to thestandard pattern of lecture lantern hewas then manufacturing, he fed theintermittently moved film from aspool through the stage of the lanternand collected it in a basket beneath.The light was made suitably inter-mittent by an oscillating shutterwhich, through gearing, opened eachtime the film came to rest. With thisfirst machine he gave a demonstrationat the Finsbury Technical CollegeConversazione on F ebruary 20, 1896.As it happened the Lumiere Brothers,who had been working independentlyat the same problem in Paris, gave anexhibition with their projector at theRegent Street Polytechnic the sameevening. Paul patented his projectoron March z, 1896 (patent No. 4686).This patent covers in particular thestar wheel with slots, now called theMaltese Cross intermittent motion,which is to -day universally used, hav-ing driven nearly all rivals off themarket.



Drawings from Paul's Patent Specification showing the Maltese Cross Mechanism (Pat. No.4686. 1896).

Paul now began to receive pressinginvitations to give a show at variouspublic places. For instance he wasengaged by the Alhambra manage-ment to give an item in the eveningprogramme lasting ten minutes. Theengagement was for a fortnight onlyas everyone knew that the publicwould soon get tired of living pic-tures, even under the new name of theAnimatograph. To test the publictaste, however, a short playlet wasstaged on the flat roof of theAlhambra and " shot " by Paul. Itwas called " The Soldier's Court-ship," occupied 8o feet of film andwas a. roaring success. In the makingof this film Paul met his future wife,who comes of an old theatrical family,and who played the principal char-acter. With amazing energy Paulalso shot topical events, for instancethe Derby of 1896 when the Prince ofWales's horse Persimmon won therace. On the following day the filmwas shown at the Alhambra in thepresence of the owner. The publicenthusiasm was overwhelming; Paulwas called before the curtain manytimes and received a great ovation. Ofcourse by this time the original twoweeks engagement had been exceeded ;actually it extended itself two years.

An obvious result of these strikingproofs of popularity was that a greatdemand arose for projectors andfinished films. It came from everyEuropean country, from Kings andfrom professional entertainers, fromvariety theatres and fair ground show-men. He therefore enlarged his factoryand engaged a staff of photographers.The office and works were besieged bywould-be purchasers speaking every

language, who waited impatiently foiequipment and meanwhile tooklessons in a school for operators whichPaul improvised. Over a hundredprojectors were sold at a price of £8oeach in twelve months-and whencameras, films at ninepence per foot,and fees earned by shows, were addedinto the account the turnover wasLi8,000. Paul had accomplished thiswithout borrowing any outsidecapital ; it grew out of his own fewhundreds with which he started his instrument works in 1891. But as busi-ness was expanding so rapidly he andsome friends tried to float a companyto take over the cinematograph sideof his interests, patents and all. Itwas a fine opportunity for the publicto get in " on the ground floor " ofthe vast cinema industry of the future.But the subscription was so small thatthe company did not go to allotment:The cautious investing public did notbelieve in " living pictures."

During 1897 a fatal fire at a cinemademonstration (not Paul's) in Parismade him redesign his projector so asto be encased in sheet steel and thefilm after passing through the pro-jector was wound on an internalspool. Various troubles in drivingthis spool were admirably overcome.Meanwhile he frequently headed hisphotographic staff when shootingtopical events, and always did theevening round of some half dozenLondon music halls where he had aturn. Nevertheless he found time todevelop new electrical instrumentsand improve old ones for use in uni-versity laboratories and in industry.In 1897, also, he found time to getmarried. Thereafter his wife was pro-

ducer, stage manager or principallady in many a playlet for which herexpert knowledge eminently fitted her.In the same year he bought a field atMuswell Hill for the erection of aspecial studio-the first of its kind inEurope. It comprised a miniaturestage, a movable hanging bridge,many trapdoors, a trolley system forrunning the camera to and fro atspeed, and means for turning thecamera accurately on its axis. Therewas also a scene painting room, where,at first, Paul himself painted all thescenery at night " after. the day'swork was over " as he said. Actorsfrom the London theatres came to thestudio to play their parts. Gradually,at this studio the " trick film " wasdeveloped; ghosts, ogres, fairies,dwafts and giants became everydayproducts. Deep sea divers found boxesof treasure with live fishes apparentlyswimming round them. A very greatsuccess was a collision between twotrains on an embankment beside alake; this was so realistic that theaudience usually screamed. It waspirated in many countries, especiallyin America, as sale of the film inLondon was outright. A great author-ity on the history of the cinema hassaid " Paul's trick films were the firstand best of their kind in England and

Original Maltese Cross Mechanism incor-porated in a film projector.



The Development of the Animatograph.

An illustration from an early booklet issued by Paul, describing his' machine forthe most perfect manner.'

eclipsed anything produced through-out the world."

In 1898, feeling that the amount oflight passed by his existing intermit-tent motion and shutter was less thanit might be, Paul invented and de-veloped an ingenious improvementwhich is described in patent specifica-tion No. 487 of 1899. It eliminatesjerkiness in the motion and is capableof working at high speeds. He alsodeveloped a high speed camera cap-able of taking 120 pictures a second.This was employed by Vernon Boysfor making slow-motion photographsof sound -wave shadows. It was alsoused by Worthington for making pic-tures of the splashes produced in astill water surface by falling objects.Another set of historic scientific filmswas made in collaboration withSilv anus Thompson, who made thenecessary numerous drawings forillustrating the motion of lines offorce in changing magnetic fields.This last led to the making of cartoonfilms ---a long-distance forerunner ofWalt Disney's present-day speciality.By this time the amount of film Paulwas processing for public exhibitionwas about 8,000 feet a day.

Although the cinema side of hisbusiness was rising to a profitablecrescendo between 1905 and 1910, Paulresented the fact that it distracted himfrom electrical instrument making.But this side was also growing. Hewas a master of design and his instru-ments were distinguished by theirmechanical as well as electrical quali-ties. About 1903, in the midst of therush of work described above, he in-vented the famous " Unipivot " tablegalvanometer. The conventional in-strument had a cylindrical iron core

projecting pictures in

fixed between the jaws of a permanentmagnet for the purpose of concentrat-ing the field and had a cylindricalmoving coil carried by top and bottompivots so that its sides moved in thespaces between the core and the jaws.The new uni-pivot form of instrumenthad a spherical iron core fixed be-tween embracing jaws and had a cir-cular moving coil. There was avertical hole drilled from the top tothe centre of the sphere and the singlejewel was fixed at the bottom of this -hole very accurately centred. An in-ward radial spike starting from thetop of the coil rested with its pivot -point on the jewel, and control wasobtained by two external helicalsprings carrying current in and out ofthe coil ; the coil and its attachmentswere accurately balanced to bring thecentre of gravity to the pivot point.This construction besides its advant-ages in use permitted the clamping ofthe movement for transport ; fre-quently this clamping was ar-ranged to be done automaticallyas the instrument was lifted oflthe table. This design eliminatedlevelling, reduced friction, anddeservedly became a great com-mercial success. From 19o5 Paulreduced his attention to thecinema and developed instru-ments suggested or invented byCampbell, Darling, Duddell,Drysdale, Irwin, Jolley, andothers. Many of these instru-ments sold well ; indeed he had toset up a branch works in NewYork in 1911. But he frequentlyassisted rese arch workers bybuilding non -such instruments ofa kind never likely to sell. Itwas in connexion with two or

three such research instru-ments for high frequencythat the writer first met Paul.

In 1904 his instrumentswere awarded the goldmedal at St. Louis, and in1910 the gold medal at Brus-sels. In this latter year hemade up his mind to dropthe cineina department,which he had always calleda " side -line," and to concen-trate on instrument making.He burned his large stock offilm and disposed of thespecial plant. He then laidout his works for the moreintensive production of elec-trical instruments with theresult that output was risingfast in 1913-14. The warcaused the demand for test-ing and measuring instru-ments to come mostly fromgovernment departmentsduring the next four years.

Paul's personal contributions to newdevices included suggestions andmodels for acoustic mines and mag-netic mines, and the apparatus for thelocation of mines and submarines.And, of course, his factory turned outa great volume of testing instrumentsneeded by the Services. At the end ofthe war an amalgamation with theCambridge Scientific Instrument Co.was arranged. Thereafter Paul grad-ually withdrew from the drawing officeand the factory and concerned him-self more with the finance andeconomics of the industry. And hetook up again his reading of classicaland modern literature in which he wasvery well grounded.

Although semi -retired, his construc-tive energy surged up strongly if apractical problem were put beforehim. In response to one suggestion

Moving coil system of3aoe Paul's " Unipivot " gal-

vanometer, which'greatlyimproved the robustness

and reduced friction.(By courtesy of theCambridge Instrument Co.)



he equipped his car with an excellentforced ventilating system ; he also de-signed and made a very neat non-electrical petrol gauge. He enteredthe loud speaker field with the newidea of a diaphragm of balsa wood.When Sir William Bragg placed be-fore him the problem of keeping thelungs of a paralytic friend going, Paulproduced a machine, which he calledthe " pulsator," which has since beenmade by the dozen for hospitals.Again, when the Faraday CentenaryExhibition was planned he offered tomake up replicas of early apparatusfrom the descriptions published byFaraday and others, and produced amagnificent display. All these andmany other mechanisms he made upwith his own hands in his workshop athome; there is no doubt he was hap-piest when he was constructing things,and constructing them well. All hislife he hated clumsy work. It is re-lated that on going round the worksone morning he came to the benchwhere quite a good workman had beenstruggling for some weeks with anelaborate recording apparatus, addinghere and changing there. The resultby this time was a mess ; so Paul sud-denly picked it up, took a big swingand threw it against the wall." Now," said he, " start again." Hehad, it reminds one, a keen sense ofhumour.

" England produces thefirst moving picture onscreen " . . . it was inLondon in February,1895 that the firstmoving picture wasthrown on a screen.About 3 a.m. policemenin Hatton Garden heardshouting, and runningto astudio found RobertPaul and his workmenshouting with delightat having successfullythrown a clear movingpicture on the screen

for the first time.

The story of Paul's life would bevery incomplete if his charitable actswere forgotten. Many of these werenever disclosed fully even to closefriends. Others, such as supporting

Paul's CinematographCamera (1896).

This machine was usedby Paul for filmingQueen Victoria's Jubi-lee in 1897, for whichpurpose a special stand

was designed.

individual research workers who for awhile had fallen on hard times, cameto one's knowledge accidentally.Other public spirited actions areknown more widely. For example heorganised and financed the Appren-tices' Prizes at the Physical Society'sAnnual Exhibition of Apparatus. Hefounded a Scholarship which isawarded by the Institution of Elec-trical Engineers. To this Institutionhe presented a beautiful painting ofVolta, and to the Franklin Institute 'of Philadelphia he presented a fullsize replica of Faraday's statue in theRoyal Institution, London. But hisreserve and shyness and a kind oftalent for fading away unnoticed wereexceptional. For instance, probablyno voluntary worker did nearly asmuch for the Faraday Centenary Ex-hibition as did Paul ; but in the longlist of acknowledgments to personswho helped the Exhibition, even byattending a sub -committee meeting,the name of Paul does not appear.Again, many of those who knew howgreat he was in the world of thecinema did not know of his contribu-tion to applied physics-and viceversa. For these reasons, possibly,few honours came his way. Two heappreciated greatly were the Vice -Presidency of the Physical Society andthe Duddell Medal of 1938. Whenmore is known of his benefactions, itwill be recognised that he was a greatphilanthropist, as well as a greatleader in the applications of science.



Physics and the Static Characteristics of Hard Vacuum Valvesby J. H. FREMLIN, M.A., Ph.D., F.Inst.P. *

A Paper read before the Electronics Group of the Institute of Physics on April 6th, 1943,at the Royal Institution.

THE characteristics of hardvalves have been considered indetail by many hundreds of

people for a large part of their work-ing lives. It is likely, therefore, thatI shall omit all mention of manypoints that seem to some to be of out-standing interest.

I propose to confine myself mainlyto the most essential valve propertiesand shall not say much about second-ary emission for example, or anythingat all about such things as contactpotentials, cathode coating character-istics, grid emission or especially,noise.

Now the physical laws involved inhard valve design are mostly knownto adequate accuracy. The problemslie largely in the application of wellknown laws to complicated systems.This is not always easy. In order toget results of practical value it is oftennecessary to make drastic approxima-tions. illy this I do not mean merelythat we have to consider theoreticallystructures that are much simpler thanthose in which we are really inter-ested. We have also to employphysical concepts which are known tobe incorrect, in the not invariably mis-placed hope that the errors so intro-duced will be negligible, and the suc-cess of the physicist in valve designdepends less on his knowledge of thedetails of natural law than on hisknowledge of when any such laws maybe neglected with impunity.

Thus, most elementary theory ofthermionic valves can proceed quiteadequately on the assumption thatcurrent as well as potential distribu-tion is continuous through space.Knowledge of the particulate nature ofelectricity, which was gained beforeIwo, is not used and is, except bythose who have the courage to work onthe vexed question of noise, ofteneffectively banished from mind. I hopeto give here some indication of thelimits within which such simple con-ceptions are useful. These limits aresurprisingly wide and it is to me verystriking that we even now only occa-sionally need to advance from the con-tinuous fluid theory of electricity tothe particulate theory and that thefurther advance to the higher forms ofcontinuous function provided by wavemechanics seems unlikely to be calledon extensively for a while yet.

Messrs. Standard Telephones & Cables, Ltd.

Now from a practical viewpoint thecharacteristics of a valve may be re-garded as the relations determiningthe currents to the various electrodesof the valve as a function of the volt-ages supplied to these electrodes.

Consider first the simplest type ofvalve, the diode. It has been shownby Langmuir' that the current in spacecharge limited conditions will alwaysbe proportional to the three halvespower of the voltage, whatever theshape of the electrodes. This has beenshown to be true still more generallyby Wheatcroft, using the method ofdimensions, for all cases in which thevelocity of a current element at anypoint is proportional to the square rootof the potential at that point. Thiscriterion will cover certain forms ofgas discharge as well as hard valves.The range of validity of this argu-ment is not, however, quite clear. Icannot see how the required limita-tion to space -charge limited conditionscomes in.

The constants of proportionality forplane and cylindrical diodes have, asis well known, been calculated byChild and Langmuir. The physicallaws involved are solely those des-cribed in the fundamental definitionsof charge and potential, as expressedin Poisson's equation V 2 V = - 47Ptogether with the Newtonian laws ofmechanics. The way in which theproof is written out usually obscuresthe fact that a particulate theory isunnecessary so long as the ratio ofcharge to mass of electricity is cor-rectly included.

Some difficulty is sometimes foundwith the assumption of zero emissionvelocity on the grounds that in thiscase there will be no emission at allwith zero or negative field at thecathode and saturated emission withthe smallest positive field. This diffi-culty is, however, merely the familiarone of determining by inspection thevalue of # . In fact, the emission withzero field and zero emission velocityis indeterminate in the absence of fur-ther information; it is quite incor-rect to say that emission is obviouslyzero. Its value depends upon the spacecharge considerations given by Childand Langmuir, for if the current fellbelow their calculated value a positivefield would exist and full emissionwould occur till space charge betweenanode and cathode just neutralised the

field, while if the current were toogreat a negative field would occur andthe current would cease entirely untilthis field had vanished. The indeter-minacy is, therefore, resolved by thefact that any current differing by afinite amount from that calculated isquite certainly not in equilibrium.

For an infinite parallel plane diodewith anode cathode distance d we havethe current density i. given by

2.34 x io-2 V.2/.i. = mA/sq. cm.

112

for zero emission energy. A similarformula for the current per unitlength in an infinite cylindrical diodeis also obtained. For reasonably largevoltages these formulae hold satisfac-torily up to the largest current densi-ties which the cathode can give with-out saturation. For small voltages,even if allowance is properly made forcontact potentials, the current is foundin experimental tubes to be persis-tently larger than predicted by theChild-Langmuir formula, and currentactually continues to flow when theanode is at a slightly negative volt-age. We can, however, say that ex-periments on diodes have shown thatover a wide range it is not usuallynecessary to take account of the par-ticulate nature of electrons and cantherefore proceed with some confid-ence to neglect it in our first considera-tion of more complicated valves.While neglecting it we must not, how-ever, forget it.

Consider now the triode. Even withthe drastic simplification suggested itis not possible to solve Poisson'sequation for the boundary conditionsexisting in an ordinary triode. It isdifficult even to write down what theboundary conditions are until we haveleft out the grid supports and insula-tors and considered an infinite parallelplane or cylindrical system to elimin-ate all edges and ends. With theausterity triode thus produced, we canwrite down the conditions, but we stillcannot solve the equations. Resort isusually made, therefore, to a subter-fuge. The system usually employedis to determine, by intuition or other-wise, the dimensions and electrodepotentials of a diode, "equivalent" tothe triode with which we are con-cerned, in terms of the geometry andelectrode potentials of the triode. Themeaning and means of determining



"equivalence " merit some discussion.It is clear that, to the approximationpreviously decided upon, the currentemitted in each valve must be such asjust to reduce to zero the normal elec-tric field at the cathode surface. It isoften stated, therefore, without moreado, that the equivalent diode issimply a diode which in the absence ofspace charge has the same electric fieldat the cathode surface. Now the elec-tric field at any point on the cathode ofa triode can normally be found, and isfound to be a linear function of thegrid and anode voltages V. and V.respectively. If the cathode is farenough from the grid for the electricfield at its surface to be uniform, itmay be written

V. + DV.

Zg + DZ.

where D is a function of the gridgeometry and position which we shallcall the " penetration factor "; /, isthe distance between grid and cathodeand Z. the distance between anode andcathode. Any diode with a cathode -anode distance K(1, + D1.) and anodevoltage K(Vg + DV.) would give thiscathode field. We can, of course, de-fine equivalence in any way we like,but if, as is normally the case, we wishto use the diode to forecast the cur-rent density in the triode, we must notassume that all such diodes will re-quire the same current to neutralisetheir admittedly identical cathodefields. This is clearly not the case;if we look for a moment at Child'sequation,

i -2.34 X IO-s V'/2

we see that it can be written as2.34 x x0 -'3E3/,

i - mA/sq.cm.Vd

where E is the normal cathode fieldin volts/cm., and this clearly dependsupon d as well as upon E. We have,therefore, to find some furthercriterion to tell us which of the in-finite series of possible diodes to use.There is no prior reason for assumingthat the same distance may be chosenfor all currents but there is experi-mental evidence that current is pro-portional to (V, + DV.)3/2in a planetriode, so we shall add one more toour list of assumptions by supposingthat the diode distance id is indepen-dent of the voltage. We can then find'what the distance is quite readily byconsidering the potential distributionin the triode when the grill is positiveat such a potential as to he itself un-charged, when, of course, the poten-tial is al'/s. Hence

Zd = ig

and from this we find the total emis-sion current density

2.34 x .ro-'(Vg DV.)31,i= mA. per sq.cm.

a

42/ + D(le

Now there is no theoretical justifica-tion for the supposition that there ex-ists at all an equivalent diode of in-variable dimensions. In fact, it hasbeen pointed out by Rodda' and byDow' that such a diode is certainlynon-existent. The analysis which Ihave given assumes that D remainsconstant, which is untrue if spacecharge exists between grid and anode,and Rodda gives a formula allowingfor the variation of equivalent diodedimensions with voltage which forlarge current, densities and large grid -anode spaces gives appreciably dif-ferent results from the formula whichI have given above. I think, however,that the non -uniformity of current dis-tribution in the grid plane, which hasbeen neglected in both formulae, maywell be as important as the differencesbetween them. In many cases, as Dowhas pointed out, it is quite accurateenough to take the equivalent diodedistance simply as Z, + D11. As inthe case of the diode, this formulabreaks down for very small emissioncurrent densities; it has also an extraand independent condition in whichbreakdown occurs, i.e., when V, ispositive and V. is small or negative.This is quite apart from the effects ofsecondary emission.

I want now to go back a little tosay something about the determinationof the penetration factor D in theabsence of space charge, which isnecessary before any of the triodeformulae can be used. Apart frommathematical methods, which I donot intend to discuss here, it is pos-sible to do this in many cases by theuse of mechanical models, particu-larly by the use of a stretched mem-brane in a state of uniform tension asproposed by Dr. Moon-hereafter re-ferred to as a rubber sheet-or by anelectrolytic trough, As I have workedmyself with the former' and as I shallwant to mention it in other connex-ions, I will describe shortly its mainproperties.

If the sheet is stretched tightly ina horizontal plane and if points on itare then slightly displaced verticallyby suitably applied pressure, anypoints on the free parts of the sheetwill conform to the equation

ash= 0

where h is the vertical displacementof the point from the horizontal planecontaining the co-ordinate axes of xand y. This equation is of the sameform as Laplace's equationdor a poten-tial distribution independent of the zaxis, the displacement h taking theplace of the potential. We can thendetermine the form of the potentialdistribution for any system of elec-trodes whose geometry varies only intwo dimensions by applying models ofsuch electrodes to the stretched sheet,their displacements being proportionalto the potentials intended to be car-ried by the electrodes. The slope ofthe rubber sheet at any point, for ex-ample at the edge of the " cathode "model, will then be proportional to theelectric field at the correspondingpoint in the real valve. We can there-fore measure D quite easily bymeasuring the height through which it

06

04

02

1

Di

0 0 5a I Oa

Fig. I. DE is the electrostatically calculatedvalue of the penetration factor at a point onthe cathode surface. The curve shows thevariation of this according to theory with thedistance x measured from a point immediatelybelow a grid wire. The pointsCt) were obtainedexperimentally on the rubber sheet model.The dotted line shows the value of D obtainedfrom the Schottky -Miller formula.

.d = 0.0322a, Ig = 0.40a, /a = I.40a

is necessary to move the grid model tocompensate exactly the effect, on thisslope at the cathode, of moving theanode model through one unit ofheight. A small piece of mirror at-tached to the sheet and reflecting aspot of light on to a fixed scale givesa convenient and sensitive method fordetecting small changes of cathodefield.

This method has been used to checka calculation of the change of D alongthe cathode when the distance betweencathode and grid is small compared tothe grid pitch (see Fig. I), to check acalculation of the effect on D of hav-ing the grid -anode distance small com-pared to the grid pitch (see Fig. 2)and to compare the formulae given byvarious authorities for.the penetrationfactor in triodes with very thick grid



wires. Incidentally, the best of thesewould appear to be that given by011endorff which also lends itself con-veniently to the construction of anomogram for its application.

The rubber sheet method has alsobeen applied to the measurement ofinter -electrode capacities and again iscapable of dealing with cases whichare entirely intractable mathematic-ally. To show that the space -charge -free result of rubber sheet experi-ments may be of practical value, Fig.3 gives the electrostatically calculatedvalue of i/D midway between gridwires, for small grid -cathode dis-tances, together with the results froma real triode, in which the electrodeswere mechanically adjustable.

I think I have said enough to sup-port my claim that D can be deter-mined; for cases which cannot betreated on the rubber sheet, the elec-trolytic trough may be used." We arenot yet, however, quite out of thewood. The field at the cathode maynot be uniform, either because the gridis too close or because the cathode isin filamentary form; so that every

IoF-fDJHF

Dsch

05

ta- to

0 01 02 03 04 05 0.5

Fig. 2. Variation of penetrationjfactor DEcalculated by electrostatic image theory,from the value given by the Schottky -Millerformula (Dscn), as the grid anode distancebecomes small. Points 0 obtained from the

rubber sheet model

point of the cathode would appear torequire its own private equivalentdiode. When the grid is too close wecan for small current densities use thecalculable cut-off value of penetrationfactor,' but for larger currents themean amplification factor increasesrapidly and the current may increasefar more rapidly than would be sug-gested by the inverse square law.

When the cathode is filamentary wecan most conveniently assume it tobe flat with an " effective area " de-pendent more upon the distribution offilament limbs than upon their ownsurface area; I must confess that Ido .not know of a satisfactory generalmethod for determining this" effective area " except by directexperiment.

C

Now the difficulties which I havementioned so far are not physicallyvery important. That is to say, theyare difficulties due mainly to com-plexity of detail rather than to inade-quacy of the physical laws assumedto hold. If I shot a bucket of assortedball bearings down a flight of steps,my inability to determine theirexact tracks by calculation would notbe materially affected by my usingEinstein's laws of motion rather thanNewton's.

The simplification of assuming thespace current in a valve to behavelike a uniform fluid is quite closeenough to the truth within limits. Ipropose now to consider these limitsa little more closely. I think thatwe shall be able to see that many ofthem will be pushed back a very con-siderable distance by taking into ac-count our physical knowledge of theparticulate nature of electrons.

It has been known for many yearsthat when the voltage on the anode ofa diode is reduced to small values,the three -halves power law is notobeyed and that current continues toflow, falling off exponentially withanode voltage, even when the anodeis negative with respect to cathode.This may readily be explained on aparticulate theory, on the assumptionthat electrons are emitted with ran-dom energies distributed according tothe normal Maxwellian laws wherethe number having energy greaterthan any given value eV falls off as-eV

eky . We can get an immediateon this by looking at the mag-

nitudes involved; thus experiment-ally, the energies of the electronswould have to be of the order oftenths of a volt to explain the ob-served effects. If we take the energyas corresponding to 1/ io volt, or1/3,000 ESU, the energy of the elec-tron will be e/3,000. This must, ifthe hypothesis be true, be of the orderkT where k = 1.4 x io-" and T is,say, i,00do Abs. Hence e must be ofthe order 1.4 x 3 x to' x io-" or4 x ESU, which is, of course,in adequate accord with our know-ledge of the electronic charge. Thuswe are able to use the improvedphysical theory to give a quantitativeexplanation of an effect which couldnot even be qualitatively explainedby the more elementary laws pre-viously supposed. For exact calcula-tion of current in a diode we turnagain to Langmuir.'

This point is of importance in tri-odes as well as in diodes. The simpletheory suggests that we could make atriode of infinite slope if we couldonly make grids of fine enough pitchand put them close enough to thecathode. Consideration of the un-

uniform nature of the current soonshows, however, that the engineermay not be required to make grids of

g wire 5 W from the cathode, whichwill no doubt prove a great disap-pointment to him. There will in factbe a limiting slope which will not im-prove as the spacings are reduced,but will depend upon cathode tem-perature alone. For normal present-day cathodes this limit is in theregion of ro mA./v. per mA. It might

10

9

8

7

6

5

4

3

2

-o--

0

ty-0-2 04 06 0-8 I o

Fig. 3. Variation of penetration factor Dand the corresponding amplification factor

with cathode grid distance when this issmall compared to the grid pitch. The curveis calculated from electrostatic image theoryand the points 0 are the values found near

cut-off in anlexperimental valved = 0.005 cm., la - Ig = 0.539 cm., a = 0.155 cm.

appear, therefore, as if triode designin the future will have to be done bythe chemist rather than by the valveengineer though the usefulness of evenattainable slopes may lie limited bythe high corresponding capacity.

Consider next the limitation uponthe triode formula: which I mentionedabove, when the anode becomes nega-tive. The total emission current willthen be collected by the grid, but willbe in nearly all cases several timesless than that obtained from theformula. This is not easily explic-able on the continuous fluid pictureof current, but is readily explainedon the particulate theory by suppos-ing that most of the electrons missthe grid wires on their first transitand are reflected back by the anodeinto the grid cathode space; they mayoscillate from one side of the grid tothe other a large number of timesbefore collection and thus increase thespace charge in the cathode gridspace a number of times. This be-haviour may be examined very easilyby the use of the rubber sheet whichI have already mentioned; if the up-ward vertical displacements are



40

2

10

FROM eql 4 II

9m (AVM\

o

o °

o

FROM eq. XII b

e

o

o

t9

0 0,5 10 15

Fig. 4. Variation of mutual conductance gmper unit area with cathode grid distance(The equation numbers refer to Ref. 2).

taken as corresponding to negativepotentials it can easily be shown thatthe track of a small steel ball on thesheet will correspond to that of anelectron in the valve, though frictionmakes long paths inaccurate andspace charge cannot be simplyallowed for.

Now the cases in which the elec-tron theory is required for dealingwith the static characteristics of tri-odes and diodes are relatively fewand to most valve workers of small,though perhaps of increasing, import-ance.

But when we go on to considerbriefly multi -electrode valves theposition is markedly changed. Themost important characteristics of apentode, for example, are seriouslydifferent from those which would beforecast from the first approximatetheory. We can, of course, use thesame methods as earlier to calculatethe inner and overall amplificationfactors, and it may be noted in pass-ing that the " inner p." of a tetrodeor pentode is often appreciably dif-ferent from that calculated for atriode with plate in a position cor-responding to the screen in the multi -electrode valve, and is given withvery fair accuracy by the formulxbased on electrostatics. (See Fig. 5).In a tetrode, the total emission cur-rent may also be given by a formulasimilar to that which I have given fortriodes. If we attempt to determinethe current distribution betweenscreen and anode, however, we findourselves often very far from thetruth, owing to the " focusing "action of the control grid. The useof the electron theory, with the helpof the rubber sheet, enables us to de-

sign lined up tetrodes in which thecurrent distribution may be of anytype desired.

In a pentode, the situation is agood deal worse still for those wholike their currents smooth. Not onlyis the current distribution betweenscreen and anode only estimable afterrepeated recourse to the rubber sheet,but the total emission itself is appre-ciably reduced by the space charge dueto electrons reflected by the sup-pressor. Even more disturbing, theoverall amplification factor, which forsimpler valves has always been closeenough to the electrostatically cal-culated value, fails us. This is inpart due to the increase of spacecharge as a result of the reflectedelectrons which I have just men-tioned, but it is in much greater partdue simply to the change in currentdistribution between the screen andthe anode. The potential distributionbetween screen and suppressor is con-siderably affected by the anode poten-tial and, as the anode potential in-creases, the number of electrons re-flected back to the screen decreaseswith a consequent increase of anodecurrent which is quite independent ofany change in total emission. Hereagain, then, we have a phenomenonwhich cannot be explained evenqualitatively without an understand-ing of the particulate nature of elec-

10

9

0 25

020

015

0.10

-021

ASYMPTOTE

021

0 5" 10" IS

Fig 5. Variation of inner penetration factorD21 with anode position in a tetrode.

Il /a -a1=a2=a. -= 1.25, 1.0, -=0.063.a a a

The dotted line represents the value of D'21.the value calculated for a triode with itsplate in the same position as the screen gridof the tetrode. Points ® from the rubber

sheet model

tricity. As evidence for the explana-tion which I have just described, Fig.6 shows the anode current character-istic of a pentode which was obtainedby counting the numbers of steel

ANODE CURRANT IN' PENTODE MODEL. 1---1-

o1--zLJaaD0W0

,0Z

ANODE POTENTIAL (0/o OFSCREEN POTENTIAL).

70

50

4

3

2

10

10 20 30 40 50 60 70 80 90 100 110 POFig. 6. Variation of anode current, as a percentage of total current, in a pentodemodel on the rubber sheet (with lined up control and screen grid). The points I werefound by observation of the distribution of steel balls between anode and screen ; theheight of each represents the probable statistical error. The dotted line represents theproportion which would have reached the anode if there were no focusing effect by the

control grid and if no rAilexion occurred at the suppressor grid



balls reaching the anode of a rubbersheet model. The amplificationfactor calculated by purely electro-static means was about 3,30o Theeffective amplification factor deter-mined from the rubber sheet resultsdepends on the current, but at zerocontrol grid bias it would be 97, or33 times lower than would be the caseif reflexion did not occur. I think itis clear from this why the impedanceof pentodes is often lower than thatof beam tetrodes and much lowerthan would at first sight be expected.It seems, too, that the design of sup-pressor grids merits more attentionthan has usually been given to themin the past.

A further. example 9f this pheno-menon occurs in the pentagrid con-verter, where the electrons reflectedin the outer parts of the valve mayseriously upset the proper working ofthe inner. The reflexion from thesuppressor can, incidentally, beturned to good account; in the transi-tron oscillator a negative resistanceindependent of frequency has beenobtained by its use.

Now I have attempted to show yousome of the limits of the very simpletheory normally used in considera-tion of valve characteristics. It is tome always surprising that one canget results so close to reality oversuch a wide range as one does, whenit is realised that in a quite reason-able electron stream of, say, to mA. /sq.cm. at 25o volts, the average dis-tance between individual electrons isabout .00t in., the diameter of a thingrid wire. I have tried to show someof the improvements resulting fromthe application of the next approxima-tion to reality, and I am looking for-ward with some interest, not unmixedwith apprehension, to the time whenthis has been sufficiently well workedout to justify the consideration ofsome of the really very well estab-lished non -particulate properties of

the electrons themselves.

REFERENCES1 I. LANGMUIR. The effect of space charge and of

residual gases on thermionic current flow in diodes.Phys. Rev. II, 450 (1913).

2 J. H. FRFAILIN. Calculation of triode constants.Electrical Communication, July 1939.

3 S. RODDA. Notes on paper on " Calculation ofTriode Constants." Phil. Mag. 29, 601 (June 1940)

4 W. G. Dow. Equivalent electrostatic circuitsfor vacuum tubes. P.I.R.E. 28, 548 (Dec. 1940).

5 See for example :-D. B. LANGInUIR " An Electro-lytic Trough for Tracing Electron Paths." Nature139, 1066 (1937, June 17th).

6 M. BOWMAN-MAN1FOLD and F. H. Nicom. " AnElectrolytic Field -Plotting Trough for CircularlySymmetric Systems." Nature 142, 39 (2.7.38).

7 I. Lallontrint. The effect of space charge andinitial velocities on the potential distributionand thermionic current between parallel planeelectrodes. Phys. Rev. 21, 419 (1923).

The Effect of Lightning on ReceivingAerials

Extract from a paper read before the Institution of Electrical Engineersby J. F. Shipley, on " The Protection of Structures against Lightning" *

IN spite of the fact that themajority of dwelling houses andoffices are now equipped with radio

receiving aerials, and that these to alarge extent correspond to lightningprotective systems, although generallyof an unsatisfactory kind, the numberof cases in which trouble occurs is notof importance.

The author is indebted to Mr. R. A.Price for particulars of some Soo casesof damage to wireless aerials whichoccurred during the four years ending1939. The following facts emergeand from them, certain conclusions canbe drawn.

The number of cases reported wasSoo. Outside aerials were struck in405 of them, chimneys or roofs in 79cases, trees to which aerials wereattached were struck in 12 cases, andlightning entered houses by othermeans in 4 cases.

Of the 405 cases in which lightning -struck outside aerials, receiving setswere damaged in 206, house propertywas damaged in 14, fire was caused in61, and life endangered in one caseonly. When the chimney was struckthe inside aerials in attics weredamaged in 2I cases, and in the re-maining cases outside aerials or someother form of conductors were in-volved. Thirty-five receiving setswere damaged, 12 fires were caused,and there were two cases of dangerto life.

There were a few cases of lightningentering houses by means of electriclight, telephone or relayed wirelesswires, and in one case the earth neu-tral of the electric lighting systemwas most probably the route of entry.In one case, 41 receiving sets were putout of order simultaneously. Metalclothes -lines were involved in twocases, and where sets were damagedthe electric light system was invari-ably involved, with small damage tothe wiring, switches, meters, etc.

Aerials almost always melted orburned into small lengths whenstruck, whether they were indoor oroutdoor. Indoor aerials when strungin the roof or attic were invariablyused as part of the lightning path,with consequent destruction of equip-

ment and danger to property. Thedown -lead was sometimes melted, butusually formed a jumping-off' placefor the lightning stroke to damage thebuilding and to set fire to some of thecontents. The change -over switchwas nearly always useless, whetherused as intended or not. There areseveral accounts of the switch beingfused in position, and in one caseblown to dust. Earth leads whentraversed by the lightning stroke,were usually melted. Earth connex-ions wete almost always defective,there being many cases of the pipes towhich they were connected beingdamaged, with consequent fire orother trouble. In one case an earth"pipe" was reported as being blownout of the ground. The generalopinion formed is that radio earthswere unsatisfactory from a lightning -protection point of view.

From the above the following con-clusions can be drawn :-

(a) Unless the aerial down -con-ductor, earth wire and earth conformto the requirements of the new Regu-lations for Lightning Conductors,cases similar to those reported willOccur.

(b) Unless a change -over switchcommensurate with the size of downconductor recommended and withmuch wider isolating gaps, is in-stalled it will be of no use for theprotection of the set in a lightningstorm. The only use for the normalkind of change -over switch is to dis-charge the normal earth -air current infine weather. Beyond this the ideathat they provide safety is illusory.

(c) The provision of adequateequipment satisfying (a) and -02)would be uneconomical for the aver-age subscriber. Even if (b) werepossible there would still remain thedisadvantage that during the passingof the transient flash the set would beraised to an excess voltage whichmight cause alarm.

(d) The use of a very short aerialin the immediate neighbourhool of theset is recommended to ensure mini-mum risk from lightning.

To be published.



Mass RadiographyThe photograph at the head of this page shows equipment for mass radiography installed in alarge industrial concern for examination of the workers, who attend voluntarily. The tube is ofthe rotating anode type, withstanding a load of 85 kV. peak at 400 mA. for I/10th sec. Acamera tunnel is mounted on the screen carriage and the patient's identification card is photo-graphed simultaneously with the image. Electrical interlocking ensures that the film is in

position and the shutter closed before making the exposure. Considerable experimental dataon the essentials for this work has been supplied by Ilford Limited and the apparatus wasdesigned and manufactured in commercial form by Watson & Sons (Electro-Medical) Ltd.Units have also been made by Stanley Cox, Ltd., The Solus Electrical Co., Ltd., and others.

(Left) The subject in place for taking a radio-graph. A black cloth cover is worn on the

chest.(Above) Examining films for technical imper-fections. Two frames from the length of film

are shown at the left of the page.

(Photographs by courtesy of Messrs. Hoover, Ltd.,Ilford Ltd., and the Ministry of Information).


DATA SHEETS 51 & 52

Aerial Characteristics and Coupling Systems

THE theory of radiation from anaerial is too complex a subject tobe treated in complete detail in

this series of Data Sheets. It istherefore proposed to arrange them inthe form of notes, providing informa-tion on various aspects of aerial per-formance, and to include a biblio-graphy from which further informa-tion can be obtained.

Most of the modern work on aerialsin the English language has been pub-lished in The Proceedings of theInstitute of Radio Engineers and to alesser in the Journal of the I.E.E.and on this information the authorhas drawn freely.Input Impedance

For the design of matching net-works coupling the aerial to thetransmitter or to a transmission line,it is essential to know the input im-pedance of an aerial at its drive point.

However much it may offend thepurist, a useful (if only approximate)picture of the change of input imped-ance with aerial length may be ob-tained by considering the simpleaerial as an open circuited transmis-sion line (see Fig. I). If we let Zi bethe input impedance and Z,, thecharacteristic impedance of this trans-mission line, then by normal trans-mission line theory -

Z, = Z. coth (a + 0)/ ... (I)where (a + 0) = P, the Propagation

Constantand a = Attenuation Con-

stant of the lineje = Phase Constant of

the line1 = Length of line.

If we write L., Co, R0, G., for theinductance, capacity, resistance andconductance per unit length of linerespectively, then when 64,5 > R.and (X. > G. (as is usually the casewith short aerials).

a = V-i R.G. ... (2)

= calf L.C. = 27r1X cV L.C. (3)

Z. = Lo/Co (4)as At = c = 3 x Jos metres/sec. : thevelocity of light. Now the velocity ofpropagation (v) of a wave along # lowloss line is (w113) so

Iv

VL.C.and if we neglect the retardation ofthe wave along the wire, that is, make

v = c, then d = 2.73"/Xand /3l = G = 2q7 -11X radians

= 36o//X degrees (6)

D

( 5 )

2t

\N\\\\\\\\\\\\,\\\\\,zi

y A

4

Fig. I. (a) Grounded vertical aerial of length(b) Vertical dipole aerial of total length

it. (c) Equivalent circuit represented by anopen circuited transmission line of character-

istic Impedance Zs.

represents the electrical length of theline or aerial.*

With normal aerials G. is verysmall and for short aerials upto about G = 6o° or 1 = A/6 the inputreactance of the aerial is large com-pared with the resistance. Neglectingthe resistance term we can simplifyequation (I) to

= - Z. cot G ... (7)which is shown plotted in Fig. 2.From this it will be seen that the in-put reactance of a simple aerial iscapacitive up to an aerial length of1 = X4 (or G = goo) and then becomesinductive between 1 = X/4 and /=X/2(or between G = goo and G = 180°).

The use of 0 for electrical length should notbe confused with fA, for conductance, but as 0,, isusually neglected, this should not cause the readerany difficulty.

+Xi

P1 f72 n 3n 20

G 90

xi

180 270 360

i91-0

-z, cot gr 1

Fig. 2. Input Reactance of open circu ttransmission line.

ElectronicEnginEerinq

The cycle is then repeated as theaerial length is increased or theoperating wavelength reduced with agiven aerial length. (See also DataSheets No. 6 to i).

The transmission line equations em-ployed- above are derived on the as-sumption of uniformly distributedparameters (i.e., L., Co, etc.) with theresulting sinusoidal current distribu-tion.

With the exception of long hori-zontal wire aerials and conical aerialsthe distributed parameters vary inmagnitude along the length of theaerial. However, the distributed para-meters tend to become more and moreconstant along the length of theaerial as the cross-section becomes re-duced. Whatever the shape of theaerial member, if we make the crosssectional dimensions sufficiently small,the distribution of current along itslength will tend to be sinusoidal. AsZ. VL0/Co we see that with themajority of aerials the characteristicimpedance is a varying quantity. Ifwe make the cross-sectional dimen-sions sufficiently small we can, how-,ever, approximate the solution bymaking use of an Average Character-'istic Impedance of the aerial which.we will designate by ZoA where

Zoe = -fZ.6,) dy1 .

where Z.(,) is the value of Z. for aninfinitesimally short length of theaerial a distance " y " from the drivepoint (see Fig. r) and " 1 " is the totallength of a grounded aerial and halfthe total length of a dipole in freespace.

On Data Sheet No. 51 is given theexpression for Zoe for a number ofaerial forms both of the grounded andfree space variety. With the excep-tion of No. 5 and No. To the expres-sions are taken from Schelkunoff; No.io from Morrison and Smith. In thecase of the conical aerials the dis-tributed parameters are constant andtherefore Z. is constant, that isZOA = Z..

It will be seen that the expressionfor Z oh for a cyindrical groundedaerial is different from that due toHowe (Z0A =6o (log. lla - I)) usuallyquoted in text books. The thinnerthe aerial the more nearly will the twoexpressions be equal.


DA

TA

SH

EE

T N

o. 5

1o

FR

EE

SP

AC

E,L

ER

IALS

GR

OU

ND

ED

.TR

IALS

V1

1ci

le 213

5

2.a

It

A t

V 1

11it,ii

/V

t,

4

2j v

68

9

,

2

21

11

21

3v

7

\ 1

Ia

10_.

,

I

BI -

CO

NIC

AL

orH

OU

RG

LAS

S

Zo

= /2

0

.W

hen

cone

Zo=

.4/2

0log

e[0]

loge an

gle

[cot

(j6/4

20

*.: /

20lo

ge[7

]

is

ohm

s

smal

l

21: oh

ms

6IN

VE

RT

ED

CO

NIC

AL

Z0

= 6

0

Whe

n co

ne

Zol

4=60

loge

[2/#

1:--

--,6

0log

e[2-

1-]

loge

angl

e

[cot

W4

is s

mal

lohm

s

: aoh

ms

2T

HIN

SP

HE

RO

IDA

L

ZO

A =

/20

loge

[-n

a =

rad

ius

atba

se.

ohm

s

_

7T

HIN

SP

HE

RO

IDA

LZ

0A=

60

loge

[a

= r

adiu

s-1

-]a at

ohm

s

base

3T

HIN

DO

UB

LE

DIA

MO

ND

ZO

A =

/20

loge

[]a

= m

axim

um

21 radi

us.

ohm

s8

TH

IND

IAM

ON

DZ

oA=

60

loge

Kq

a =

max

imum

radi

usohm

s

4T

HIN

CY

LIN

D-

RIC

AL

WIR

EZ

0A=

120

[Ioge

a =

rad

ius

2 721

--I]

of w

ire.

ohm

s9

CY

LIN

DR

ICA

L

WIR

EZ

0A=

60

a =

rad

ius

21[lo

ge-a

- -

d

of w

ire.

ohm

s

5T

HIN

CY

LIN

D-

RIC

AL

WIR

E

V -

TY

PE

Z ;W

/20

loge

Kei

OA

a

240=

ave

rage

sep

arat

ion;

ohm

s

a =

rad

ius

of w

ire.

10IN

CLI

NE

DT

HIN

CY

LIN

D-

RIC

AL

WIR

Er2

D1

Z01

,1..4

60 lo

geL7

-oh

ms

D=

aver

age

heig

hta=

radi

us o

f wire

With

the

exce

ptio

n of

Con

ical

Aer

ials

thes

e ex

pres

sion

son

ly a

pply

to a

eria

ls w

ith v

ery

smal

l cro

ss s

ectio

nal d

imen

sion

slo

gex=

2.3"

iox

In D

ata

She

et 5

1 th

e di

stan

ce b

etw

een

the

two

elem

ents

of t

he fr

eesp

ace

aeria

ls is

ass

umed

to b

e ve

ry s

mal

l and

the

sam

eas

sum

ptio

n is

for

the

dist

ance

bet

wee

n th

e bo

ttom

of t

he g

roun

ded

aeria

l and

the

grou

nd.

With

free

spa

ce a

eria

ls, t

he a

eria

l is

assu

med

to b

e a

cons

ider

able

dis

tanc

e(s

ever

al w

avel

engt

hs)

from

the

grou

nd s

o th

at c

apac

ity -

to-g

roun

d ef

fect

s ar

ene

glig

ible

.


t(

=11

1111

1111

1111

1111

1 lim

.%11

1111

1111

MIN

VIN

IIIM

ISIO

LIM

MA

IIII M

in=

1111

1111

1111

,16.

1VO

MIO

MM

IIIIII

MIII

IIIN

MI

In II

IIMM

IIIIII

I,A

MIN

Oat

IIM

INIII

MIII

IIIIII

IIMIli

Mi

Iffila

mai

lasi

nIn

vM

IIIN

VII

NL

IO L

IMIN

INIM

UN

IVII

IME

IMU

MU

nwill

ing

lllll

III.

..1

llllll

l In1

1111

1611

11I

1111

1111

1111

1111

11V

VIN

IIIN

IMM

IIIM

IIMM

,M

N11

1111

1111

11 ll

lll 1

1111

11 1

1111

411,

1111

1111

1111

1II

1111

1111

1111

1111

111:

11O

VIII

MM

MIN

INV

II,M

INI

IIMIN

NIV

IS IP

'II

111.

1117

11W

WW

III

IV U

IPM

IIIW

VIII

IMM

IIIV

VH

MIM

MIII

IUM

ILIII

VIIM

II11

1111

11M

111

tiner

..MIT

V.

11m

1 M

I M

MM

MM

1iti

lra

''''''''

"""

''''''

riii

::::::

::Im

..E

N

,11

1"r

"ild

:::in

a=

1111

11 l.1CL

UC

CC

IC=

CE

a ''''

''''la

llM

dil

r.II

MM

1...

=11

1111

1111

1111

11.1

1M

I.16

19:1

1011

111.

5M

INU

MIB

MIIM

IM

IMI

MIN

IIN

Iniii

VIM

1111

1111

1111

111M

1 11

8111

AII

IIIM

M11

1111

1111

1111

1LII

IIII

MII

I ''''

'' 11

1111

1111

1111

III

''I. '

' MI

1111

1111

1111

1111

1111

11 ll

lll 1

1111

1111

1111

111

imum

NI

VI\

III

IIM

IIII

IIII

IIII

IIV

MII

IIII

IIII

IIII

IIIH

IIL

IIII

IIII

IIII

IIII

HII

IIII

III

WIN

IMII

IIII

IIIM

MIN

1111

11:

U11

1111

1111

11M

11,1

1111

KM

1111

1111

1111

111M

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1M10

1111

11i*

IMII

IMIg

ill R

OIN

IMM

ION

NIN

IIII

IIII

IMIO

NIN

IMM

IMM

Ill

11'1

1111

1111

111L

1111

1111

1111

iliiI

IIM

Miii

iIII

IIII

IIII

IN11

1111

111

111\

1111

1110

1111

0111

111M

INII

IIII

IM11

1111

1111

111\

1111

1111

1111

1111

1111

1111

II3,

Imiu

mp

imm

unim

min

imm

uml

1=

1.M

i "M

k .

:==

l120

:74:

=IM

IN11

12:1

11:C

gt.1

man

nini

.n.

3.

mon

101.

11.1

1011

1.M

oni.

1116

.111

11M

MI1

0111

1111

.411

1111

1111

.O

N

ME

MIM

MO

NIN

Sft

ui.II

INV

0111

1IN

IVE

RIM

' 1.4

1U

NE

11.

111

1111

1.1

imill

e.11

1111

111

llllll

lllll

1101

00:1

11i

UM!e.

ILlll

llll V

IVII0

110.

1111

1311

1111

111,

1111

1111

11U

M IV

OV

IVO

MM

IMV

M11

1111

1111

111.

111

1111

1111

1 IM

M11

111,

1111

1111

1111

111

1111

11L

1111

11.1

11

NIL

111

1111

1111

:111

1111

1M11

1111

11M

1:11

1111

111

InII

IN11

1111

1111

.1\'1

1x11

111i

iIIiIl

1111

.111

1111

11N

illtlr

''II

Ilu 1

/111

1M

1111

11.1

1111

1111

1111

1.11

1MaM

MII

IM11

1111

1111

1X:

1111

0111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

0111

1111

1111

1111

1111

1111

iN11

6111

1111

1111

1111

1111

0111

1111

111M

111

111.

1111

1111

1111

11M

1111

1111

1111

1111

1111

1111

1101

1111

1111

1111

1111

1111

1110

kIn

111

1111

1110

1111

d111

1111

1111

0111

1111

1111

1.11

1111

1

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1011

1111

1111

1111

1111

111A

I 11

M11

1111

1011

1101

1111

1111

L11

1111

1111

1111

1111

1111

1111

1111

111M

1111

1111

1111

1111

1111

1111

1111

1111

111.

1111

1111

1111

1111

110k

.11

1111

1111

111,

111k

1111

1111

1111

H11

1111

1111

1111

1111

111M

1101

1111

1111

11L

1111

1111

1111

1111

1111

1111

1101

1111

1111

1111

1111

1111

110,

1111

1111

111:

1111

:111

1111

1111

1i11

1111

1111

1111

nt. l

llll a

nilu

mei

mai

nna

llllll

ll m

um:

1111

lllll

NE

IL M

N ll

lllM

ill=

1111

0111

1115

1.1

1.11

1111

1111

11 ll

llllll

MI

gum

=11

1111

1111

4111

111

1111

1111

1111

1111

1 11

1111

1 M

IMI

1111

1111

1111

1111

1131

1111

1MM

L11

1111

1111

1111

1111

111M

111

1111

1111

MM

III

lllll

1111

1111

1111

1111

1111

1111

1111

1111

1111

1111

1Inn

3111

1111

1111

111,

1111

1111

1111

1111

M11

11

E

.1.i.

1.e=

M.E

.M111l

:a:g

,. ll

l.

tj C

CB

CC

EC

.H l

IV

new

:r

ii,p

El M

r1,

"sol

slm

n-n.

-:11

-0-

....m

. ,...

%pi

n lll

LI:

IMPL

IFIN

: .M

iliiii

3EM

S`=

EM

O. I

naM

ILM

Ilnr

1IN

IIIIM

INS

III U

TIII

IIIIII

IIMM

II I

3111

1111

11rn

i llll

l11

11...

..n.ta

irsiln

101.

.... l

llllll

101

1111

1111

111.

;,1

1111

4111

41III

IIIM

IIMII

IZO

IRIN

IIIffi

r M

ILL

ump

IIII s

il1.

1111

1111

MIL

IIIV

IIIIM

INM

INIM

1p.

iNim

miti

n, 4

11::9

1131

1101

111n

.!!

!.ht

_ini

Li l

lllll

Min

hAiii

mi,l

ison

sim

mum

km

imin

gE

lose

mul

EV

IIVA

NIM

Lla

illM

snII

IIM

OIN

IIII

num

nItil

ink.

0111

1.1.

11§M

me

MII

IIM

IIII

IIM

II11

1111

1111

1unn

lllll

lllll

1111

M11

1111

111:

1111

11M

UN

IMM

II11

1141

1111

1111

1111

11

1111

1r11

111

iII

MII

IIM

IMSI

IIII

IMIl

lk 1

1111

1111

1111

1111

1011

10:1

.r...

umnn

uinu

mii

min

nm

umni

mm

in.1

1111

6 im

mom

pim

mith

ok 1

pal

mnn

nunn

unun

n§m

umlim

mum

mum

mor

umno

mm

umm

ainn

unm

umum

miik

uum

innu

mith

ilim

muu

mm

umim

umum

mul

inim

miu

m'M

INI

MU

IL11

1111

1111

III

IIII

IIII

III

1111

1111

iillil

iiMM

MII

IIIM

1111

1111

111A

311:

1111

,

1111

1111

1111

1 IM

IN11

1111

1111

1111

1111

1.1,

all

IIII

I111

1111

3111

1111

1111

1111

1111

1111

A1

IiII

IIII

IIII

VII

IIIM

1111

1111

1111

11W

1111

1111

1111

1111

1WII

IIP1

1111

1111

1111

111M

0.

epai

nusu

miln

iala

mim

umm

ipsi

umni

n;11

1111

1111

1111

1111

1M1:

1111

0111

11k


\l2

15

10

5

..--,.. ...-

-4

i

_--, ..-

---

CA-z

,r- ..-.

..--..-- ---

-,upE

b8(10ge3/a- 4

-wit/ if/ i t"ttt / i i /-t fz

C"-

'1a

1

Liz -- - < bOOgeX-irF

: length: radius of

of rodrod

in cmin cm.

0,--Ill----

...

0ce0 ,- - -I0I--

>-t-u

,-

-'x

---..

-4-Measured Values

aa_<

.--e0

HEIGHT 'Z' OF

INCHES

ROD ABOVEI

30

METAL PLANE

I I I.7777 ID 20_1

40 5

25 50 CM. 75 100 12580 /60 240 320 400

The measured and calculated capacity to ground of a 1" dia. vertical grounded rod mounted on a metal plate 3 ft. by 6 ft.

The measured values were taken at 1.0 Mc.,s. by Foster & Mountjoy (R.C.A. Review Jan., 1939)

Input Capacity of Short AerialsFrom equations

write(4) and (5) we can

Zo = (8)vCo

when v = c we can express the staticcapacity Co in ittIF by

33.3Co = i.LAF. per cm.

ZFor aerials whose length does not ex-ceed 6o° the input capacity can be cal-culated from equation (7).

For very short aerials when Z. cot2.7//)1/4 Z0X/2crl the input capacityC. of the aerial becomes

C. 7-- C01 ... (1o)33.31

Aters.

(9)

Z.where Co and C. are calculated fromZoe where necessary.

In Fig. 3 are plotted the calculatedand measured capacity to ground ofan in. diameter grounded rod. Twocalculated curves are shown one usingSchelkunoff's expression (see 9 in

Data Sheet No. 51) and the otherusing Prof. Howe's expression. Acurve showing the results of measure-ments carried out by the RCA at

Mc/s. where equation (to) is applic-able is also shown.

In order to save labour a number ofcurves have been drawn on DataSheet No. 52 from which the values ofZoe given in Data Sheet No. 51 can beobtained. It should, however, be re-membered that these expressions arefor Zoe are only applicable for thinaerials.

Example. The average Character-istic Impedance of a dipole of cylin-drical wire cm. in diameter and 5metres total length (21) at a wave-length of 20 metres is (21/a = 2,000),Z A = 792 ohms and the input react-ance is therefore

( 360 \0Xi= - 792 cot - 792 ohms`8/1which is equivalent to a capacity of

C. - =134 APFx 1.5 X 101 X 792

In the above expression the resistiveloss has been neglected; but with anyaerial the radiation resistance isalways present even if the dissipationlosses are reduced to zero.

The expression for the attenuationconstant where R. is not neglected,but G. = 0 and R/ < r, is :

a = R.I2Z.If we designate the radiation re-

sistance referred to the current anti -node or loop by RI it can be shownthat when 1 = nX/4 (where n = I, 3,5, etc.)

R. 2R1,

Provided, therefore, that Z. or ZoAis large (as is the case with thinaerials) the approximation due toneglecting the resistive component isjustifiable.

If in Example 1 the diameter of therod were increased to 4 cm., thus mak-ing 1/a 125, then Z, ~ 54o ohms andtherefore XJ7Z -540 ohms.

It will be shown in later DataSheets that the accurate solution for

this low value of lla givesohms.



Valves and VehiclesThe connection between valves and vehicles

is frequently a very direct one - the contact padin the road surface which controls the operationof traffic lights.

The equipment consists of electron tubes andrelays, so arranged that when the contact pad isdepressed a current impulse is released into therelay circuit and initiates the light sequence.The apparatus automatically resets itself after atime interval, or after the cessation of further

impulses. Sometimes, however, even themechanical connection is eliminated. Then a" proximity " link is used, consisting of a parti-cular arrangement of valves and circuit designwhich is sensitive to the proximity of vehicles.In other words, it can " feel " the approachof traffic.

This is yet another example of the indis-pensable services rendered to the community bythe ubiquitous Thermionic Valve.

MULLARDTHE MASTER VALVE

A Valve for Every PurposeDOMESTIC COMMERCIAL INDUSTRIAL SCIENTIFIC MEDICAL EXPERIMENTAL

THE MULLARD WIRELESS SERVICE CO. LTD., CENTURY HOUSE, SHAFTESBURY AVENUE, LONDON, W.C.2. (55B)



The Synchronisation of OscillatorsBy D. G. TUCKER, B.Sc. (Eng.), A.M.I.E.E.*

Part IV. The Discrimination of a Synchronised Oscillator against Unwanted Signals mixed with the Control Tone

I. Introduction.Fig. i shows a simple feedback

oscillator of natural angular fre-quency co., with a locking tone Es,.sin want injected into the grid circuit,and a stray, unwanted signal Es sinco.t in series with it. In practice, sucha condition arises where the controltone is transmitted from a distance,over a telephone circuit or radio link,for example; circuit noise and cross-talk then represent stray signals. Inthe particular case of carrier tele-phony, the control (or " pilot ") toneis generally transmitted over a linealready carrying a number of com-munication channels, so that direct ormodulated speech signals at levelscomparable with that of the controltone are stray signals of importance.The effect of these signals on the syn-chronisation of carrier telephone cir-cuits may be to produce a " flutter "on any transmitted speech or othersignal ; this matter will not be pur-sued in this article, but it is worthpointing out that a synchronised oscil-lator produces sufficient suppressionof the unwanted signal in the carriergenerating circuit to ensure that noflutter occurs under ordinary workingconditions. Another similar casearises in radio practice, where amodulated carrier tone may be in-jected into an oscillator in order toextract a fairly pure carrier for auto-matic tuning purposes.'

Here we will investigate only theactual response of the synchronisedoscillator itself to an unwanted fre-quency in the locking circuit. It willbe assumed that the output of the P.O. Research Station.

800

0C

ca 600d

ww

E E400

3 0,O. 41-8 3 20 0

0

Fig. 1. Oscillator with locking signal Esyn andstray signal Es.

oscillator is taken from the anode cir-cuit. Paragraph 5 discusses the effect 'of taking the output from the ter-minals of the tuned circuit.

It will be seen that the oscillatoris effectively an amplifier to the in-jected signals, with tuned positivefeedback applied to such an extentthat oscillation takes place in the ab-sence of an injected signal. The in-vestigation is made in three sections,according to the frequency of thestray tone relative to the control fre-quency :-

(a) ws is sufficiently different toto, to allow the positive feedback atthe angular frequency co. to beneglected.

(b) co. is sufficiently near to cos,. tdmake the positive feedback important,but is not within the pull -in range ofthe oscillator.

(c) co. lies actually in the pull -in -range.2. The case when the positive feedback

at angular frequency w. may beneglected.

2.1. The effect of the amplitude of w.yn onthe amplification of co2

In this case the problem reducesto one of determining the amplifica-tion to a signal on the grid, E. sinco2t, in the presence of the lockedoscillation signal Egsyn sin coey2t. Theamplitude of the latter in the absenceof Es sin (..2.t is generally a knownquantity, and can in any case be de-termined approximately as discussedin Part I. We must know the valvecharacteristic relating output (anode)voltage to grid voltage; this is gen-erally of the formE. = aEg + PE: - 7E: . . . . etc. (I)Since Eg = Egsyn sin cu.,t+Es sin to.t,we have, considering only the firstthree terms,

Ea = Cl[Egm sin Osyat + Es sin cost] + P[Egsyn' sin' Wsynt + Es' sin' wst 2Eggy.

Es sin (2).y.t.sin (02t1 yEEg".3 sin' 24,2t + E.' sin' co.t 3Egsyn2 Es sin'wayst. sin co.t 3Egsyn E.' sin co,t. sin'

Now sin 0 = 4 sin e - 4 sin 30 and sin' e = a - 2 sin 20.Therefore the output of the two fundamental frequencies is given by[a y E.9 Eg.,n sin (.0.3.n/ + [a 7 Es' -312 y Egsyn'] Es sin 62.t.

In general, E.<< Eg.y., and theeffect of Es on the output of (.0.3, maybe neglected. But the second termshows that the effect of Egsys on the

co output of co. is considerable. We havethat the amplification to w. is

60S- a E.2 - 3/2 Eg.y.2 (2a)Almost always we may neglect 4 Es'

2 Fig. 2. The effect of Esyn. compared with 3/2 Egsys'; so the40 Es = 0.1 volt, fsyn = 8,000 amplification to wa becomesc/2, fs = 7,000 c/s, Q = 10.

a - 8/2 Y Egsys' (2b)It is sufficient for most practical

20 S' purposes to use this simple relation0 which neglects the terms in equation

(I) above the cube term. If, however,relatively large values of Eg.yn are in -

0 volved, appreciably greater accuracyI volt. is obtained if the 5th power term is

included. It should be noted that the

C Egsyn

6,000 asA

B 70005

-50 -40 -30 -20 -10Locking Voltage Esyn in db relative to



even powers do not influence theamplification of the fundamental fre-quency. One objection to takinghigher powers is the difficulty ofevaluating their coefficients frommeasured valve characteristics.2.2 Other non-linear effects-intermodulation

products and harmonics.A full analysis of the general prob-

lem of harmonic production and inter -modulation in amplifiers has beenpublished by Espley.2 For presentpurposes it will be sufficient to statethe products obtained assuming thatthe valve characteristic is sufficientlyrepresented by the cubic equation (i).

Second harmonic terms are213 E,,sy.2 sin 2co.yat+ /3E,' sin 253,1 (3a)Third harmonic terms are17Egsyns sin 3co.t+47E.3 sin pat (3b)Second order intermodulation productterms are :

Eg.y. E. cos (co., - co.) t

-13 Ems ES cos (Wsys Ws)t (3c)Third order intermodulation productterms are :

shows that if 4 E,2 is small comparedwith 3/2 E.."2 as is nearly always thecase, then the amplification of co, isindependent of the value of E,. Thatis to say, if Esy,, and consequentlyE..", is maintained constant, then theamplification of the stray signal islinear.3. The case where the positive feedback,

at angular frequency cu, may not beneglected, but co, does not lie in the' pull -in' range.

We have seen in the previous para-graph that the amplification of co, with-out positive feedback is linear owingto the fact that IE.' is small comparedwith 3/2 Ey.y.'. In this section we areconcerned with values of co, for whichthe positive feedback may not beneglected. We must, therefore intro-duce a new term Eg, to represent thegrid amplitude of 6), as distinct fromthe injected amplitude E,. The condi.tion for linear amplification of co, nowbecomes that lEg.2 is small comparedwith 3/2 Ey.y.2. Since, in practice,E. is never likely to exceed E." inthis range, and will generally be

47E gay.' E. cos (2Wsys - Ws)g si,7Egsyrk2 Es cos (2Wsys Ws)t

IYEgern E.2 cos (20). - EyOt - 17Egsyn E.' cos (20. + cosy.)t (3d)

The phases relative to the funda-mental have been neglected.2.3. Experimental results.

Fig. 2 shows the results of an ex-periment on the non-linear effect. Theoscillator used in all the experimentalwork described in this part had avalve type Mazda SP41 and 8o voltsH.T. The anode of the oscillatorvalve was coupled to the grid of anoutput valve by means of a very highratio potentiometer, and the voltageapplied to the second valve was sosmall that distortion in it may beneglected. The output millivoltsshown in the figures are the output ofthis buffer valve. In Fig. 2 the directmeasurements are shown plottedagainst E.", the voltage of injectedlocking signal, which is, of course, thedirect cause of the changes shown. Itwill be seen how rapidly the output ofco, falls as E.y, is increased.2.4. Results when (4.y. and (0o are not the same

The tests described above were car-ried out with the natural frequencyequal to the control frequency. Whenthese are not equal, the output of co,is increased owing to the smallervalue of Eg.,. Fig. 3 shows the re-sults of a test carried out under theidentical conditions of Fig. 2 with

= E. = 0.1 volt. The ratio ofoutput of co. to output of cos, is greatlyworsened (i.e., increased) as we,,,, de-parts from w,.2.5. The amplification of Ws is linear when

COsys is constant.

One other important relation is tobe noted in this section. Equation (2)

60D

`:2,40f

0Oco

circuit is evidently capable of freeoscillation at this frequency. Theseconditions are the same as those con-sidered in Appendix i of Part z, andlead correspondingly to the relation

Eg. + V(1 - x.2)2

E. x,)' (22(i x.82)2

(4)This gives the effective gain due to

positive feedback at a frequency de-fined by x, = .3.1w.. Apart from thisgain, the effects described in para-graph 2 apply equally to the presentcase.

In Fig. 4 curve (a) gives the gaincharacteristic calculated from equa-tion (4) for a Q value of 15. Curve (b)shows a measured characteristic of theoutput voltage of cos relative to theoutput of w,,.,, for the same Q value(note that co. = co., in this test), and itwill be seen that the agreement isquite close, considering the difficultyof determining exactly the effective Qof the tuned circuit under its operatingconditions. For comparison, theresponse of the tuned circuit itself isshown in curve (c), considered as aselective circuit in a constant -currentpath.

w2®0

E

Fig. 3. The effect of (wo - cosy).Esyn = Es =0.1 volt, fsyn =8,000 cis, fs = 7,000 c/s,

=- 10.

4.4,40

O0

I.20

X

>:

-120 -0.8 -0.4 0 +0.4 - +08 +12100 x (fern-;) A

much smaller, we may consider thiscondition to hold provided cob is out-side the pull -in range of the oscillator.

The use of a linear amplificationlaw greatly simplifies the analysis. Itenables us to neglect the presence ofthe locking signal provided this ismaintained constant, and the positivefeedback circuit may be worked out asthough co, were the only frequencypresent, although the loop gain at theresonant frequency is unity, since the

It can be seen from equation (4) thatif x, is very nearly unity, so thatQ2 (i - x.2)2<<i and (i - x.)z<<Q2 (i - x.2)2, then at a given value ofx.,

gain due to feedback cc i/Q (5)

4. The case where w, lies actually inthe pull -in ' range.

4.1. Analysis.

In this case co, is so close to w,,,, thatthe amplification of each is dependent


I16 Electronic Engineering August, 1943

on the amplitude of the other, and,consequently, no simplifications arejustifiable. The analysis becomes veryinvolved, and is not likely to be veryuseful in practice; therefore only anindication of how it can be effected isgiven here.

From paragraph 2.1 we have thatthe amplification of 64 isa - i7Eg.2 - '/2 7E..y.' and that theamplification of (...),, is a - Y Eg,,.'- '/2 7 Ego' . (The term Eg, has beensubstituted for E. as described in para-graph 3).

It is convenient to consider the co-efficients a and 7 as representing theloop gain characteristic, i.e., fromgrid back to the output of the gridcoil. Thus we obtain the relation-ships :Eg. = Es + (a + jb) La 7 I Eg.12 - 3127 I Egsyn 12] Eg.

andEgo,. = E.,. + (A + jB) [a - 17 I Egsy. 12 -'/'Y

IEg. 12] Eg.

+ jQ(i - x.2)where a + jb = x..

and A + jB = x.y.

I + Q' (s - x.2)2+ j Q(1 -

Q2( xsy.2)2

where x, = cusbas and x.y. = co.y./(0.(not necessarily unity).Also, Eg, is complex ; assume that

E.. = e., + je..Similarly Egsyn = 1'8201 + jesyna

If these expressions are substituted inequations (6a) and (6b), and in eachequation the real and imaginary termsare made into separate equations, thenwe evidently obtain four simultaneouscubic equations with the four variables

e,a, and e.y.2.and if all the other terms are known,these equations can theoretically be

4

Uc

e 8

:1 12

30

)343 16

3'420

0

024 08

-50 -40 -30Esyr, in db

-20 -10relative to I volt.

500

400

30(1,-

kr10

9)

020(

10000

0

0

Fig. 5. The effect ofvarying Esyn when fo =fsyn = 8,000 c/s and fs = 7,950 c/s, Es = 0.1 volt,

Q = 10.

... (6a)

(6b)

solved for these voltages. The moduliEg. I and I E,. I can then be ob-

tained, and also the phase angles, ifrequired. In practice, the solution isa matter of some complexity.4.2. Experimental results.

Some experiments were made to de-monstrate the behaviour of the oscil-lator under these conditions. The re-sults afford ample evidence of thephysical nature of synchronisation,i.e., that when a locking signal with-in a suitable frequency range is ap-plied, the free oscillation is sup-pressed due to the non-linear amplifi-cation of the circuit (see Appendix s

a

09)(= 'sAO

Fig. 4.-f Frequency response of locked ,oscillator ; (a) calculated, (b) measured, (c) response of tuned circuit alone.

Q = IS, Eg.syn = 0.7 volt, Esyn = Es = 0.1 volt.

0.94 098 10 r

16t2

12.9

0C

8 4,3,

a,

4-050

o0

600

so

of Part 2). If two locking signals areapplied (which is the case we are con-sidering here, since co and cu.,. bothlie within the locking range), thenthese both produce forced oscillationsat amplitudes depending on one an-other and on the relation of their fre-quencies to the resonant frequency ofthe oscillator tuned circuit.

In Fig. 5 is shown the variation inthe output of a tone of frequency7,950 c/s as the input level of a toneof frequency 8,000 c/s is varied. Thenatural frequency of the oscillator was8,000 c/s, and the input voltage of7,950 ,c/s was o.i volt. The Q of thetuned circuit was so. This low valuewas used in order that the lockingrange might be relatively large, andat the normal locking voltage of 0.1volt might allow the use of testingfrequencies sufficiently different to bemeasured separately on a waveanalyser, without error or undue diffi-culty. When Esy. was o.i volt (i.e.,- 20 db on the scale) the output of 4/.,was 52o mV. It will be seen that asE.,. is reduced, the output of 6). in-creases, and by the time E.,. is onlyabout o.oi volt, the output of w, hasreached its maximum value, and isnow independent of E".. In spite ofthe fact that Weyri = We, we see that Wsis now effectively the synchronisingtone, and w.,., behaves as a straysignal.

Fig. 6 shows the variation in out-put of the 7,950 c/s and 8,000 c/s tonesas the natural frequency of the oscil-lator is varied. E.,. and E. were bothmaintained constant at 0.1 volt. Whenthe natural frequency is roughly half

0

400

>1

1-300a.1-

0200

100

0

-0+

7950 c/s

8000 cis

-12 -0 8 -0 4 0 +0.4 +0 8 +1.2- 100 x fsyr7/0)/to

Fig. 6. The effect of (,,0 - yn) when fsyn 8,000 c/s andfs - 7,950 Esyn = Es = 0.1 volt, Q - 10.



way between 7,950 c/s and 8,000 c/s,the outputs of the two frequencies areequal.

It will be seen that the idea ofselectivity of the synchronised oscil-lator, suggested by the work of para-graph 3 and Fig. 4, can hardly be ap-plied in practice to the case where (...)lies within the locking range, sincevariations of natural frequency (whichare bound to occur in practice) over-ride all other considerations.5. The effect of taking the output from

the tuned circuit terminals insteadof from the anode circuit.

In Fig. 4, the frequency response ofthe oscillator was shown in terms ofthe amplification of an unwantedsignal injected into the grid circuit.The response of the oscillator tunedcircuit was also shown for comparison.From these curves it will be quiteevident that the effect of taking theoutput from the terminals of the tunedcircuit will not greatly modify the fre-quency response of the oscillator inthat region where the positive feed-back is effective. Over the rest of thefrequency band, the response will bethat of the tuned circuit, instead ofbeing flat. The effect of the valvenon -linearity is unchanged.

It will be seen that it is advantage-ous in practice to take the output fromthe tuned circuit in those cases whereinterference from frequencies remotefrom co., is to be expected. This is aless common problem, however; it isgenerally those frequencies near wwhich are found troublesome in prac-tice.

6. Sideband pull -in.An interesting effect that is of some

importance in radio work is knownas " sideband pull -in." If a tone ofangular frequency 63eyn ± C.3. is injectedinto an oscillator of natural angularfrequency 6.k, which is modulated byan angular frequency w,, then theoscillator can be synchronised to theangular frequency to.y. if (wan - wo) issufficiently small. The mechanism ofthis " sideband pull -in " is clearlysimilar to ordinary direct synchronisa-tion, and depends on the intermodula-tion terms (i.e., the even power terms)in the valve equation (i). A graphicaltreatment (without experimental evi-dence) has been published by Bab.'7. Conclusions.

The work described in this part hasshown that the analysis of the problemof unwanted signals mixed with thecontrol tone can be dealt with quitesimply by considering two factors :-(a) valve non -linearity and (b) the in-creasing positive feedback as the un-wanted frequency approaches thewanted frequency. These two factorsmay be considered quite independentlyover the whole frequency range ex-cept for that very small part lyingmore or less in the locking frequencyrange.

The main conclusions affecting thepractical design of synchronisingsystems are :-

(a) If the level of locking tone aloneis increased, the voltage ratio ofwanted to unwanted frequency in theoutput is increased.

(b) If the input levels of locit-ing and stray frequencies are bothraised by the same amount, the aboveratio may be increased or decreasedaccording to circumstances.

(c) Other things remaining constant,the output of unwanted frequency iftaken from the anode of the oscillatorvalve, is constant over most of the fre-quency range, but over a small range(the extent of which is greater forlower Q values in the oscillator tunedcircuit) the positive feedback becomeseffective, and an increased output isobtained depending on the smallnessof the difference between wanted andunwanted frequencies.

.(d) Within the locking frequencyrange the influence of the unwantedand wanted locking frequencies is ofthe same order relative to their inputlevels, and, because of drifting of thenatural frequency in practice, theratio of the two outputs is variable andnot easily computed.

BIBLIOGRAPHY1 S. Byard and W. H. Eccles, " The

Locked -In Oscillator-Its Applicationto Automatic Tuning and Measurementof Modulation," Wireless Engineer,January, 1941, p. 2.

2 D. C. Espley, " Harmonic Productionand Cross -Modulation in ThermionicValves with Resistive Loads," Proc.I.R.E., June, 1934, p. 781.

3 U. Bab, " Graphical Treatment ofPull -In Phenomena," Elehtrische Nach-richten Technik, May, 1934, p. 187.

Synthetic ReverberationBy D. W. ALDOUS

MANY methods have been de-veloped for adding syntheticreverberation, which can be

defined as a means of artificially pro-dAing any desired rate of sound de-cay, to recording material. Untilvery recently reverberation chambersand reverberation pipes, staggered oroffset tracks, and endless steel or filmtapes with a number of time -displacedreproducing heads, have been usedfor this purpose with considerablesuccess.

Now a device known as a " Rever-berstat " has been made available,designed for this purpose. Mr. J. K.Hilliard, of M.G.M. Studios inAmerica, recently gave members ofthe Society of Motion Picture Engin-eers some details of this new instru-ment.

It consists essentially of, a perma-nent magnet loudspeaker actuating arocker -arm to which springs are

INPUT

SPRINGSIMMERSEDIN OIL

P N

DRIVING UNITSPEECH COIL

DAMPERFELT

LOCKINGPLATE

LOCKINGBAR

LOCKINGPLATE

LOCKINGN. KNOB

CRYSTALCONTACT

MICROPHONEOUTPUT

attached, and these set into vibrationa piezo-electric crystal. The springsare surrounded by tubes of oil thatprovide the necessary damping. Thevibrations of the crystal produce anelectric current, which is then ampli-fied and combined with the' originalsignal. The time of reverberation iscontrolled by the length of thesprings and the oil damping aroundthe springs. The device is con-sVucted as a compact unit, withdimensions approximately' 4 ft. long,6 in. wide, and 3 in. deep. A cross-section of this unit is shown in theaccompanying figure.

It is apparent that it does notoccupy much space as compared withthe conventional acoustic chambersnecessary for most of the othermethods, and it is not susceptible toexternal noises to the same degree.As many as three such units are usedat one recording session to create thedesired reverberation in dialogue andmusic tracks, using different equal-isers, depending upon the type ofreverberation required.



Television After the WarA continuation of the discussion which took place at a meeting of the Wireless Section of the I.E.E.

part of which was given in the July issue.

Mr. T. E. Goldup (Mullard W. S. Co.).In considering the particular

aspect of the television problem raisedby Mr. Edwards in his opening re-marks, we must at the same time takeinto consideration many other rele-vant factors, such as the improve-ments in the xathode-ray tube,especially as regards spot size andscreen colour, the circuit design as awhole, and last but not least theeconomics of the manufacturingproblem.

During the war we have been ableto enlarge our experience and know-ledge with regard to the use of veryhigh frequencies, and when the timecomes for a television system to beinstalled at carrier frequencies of thevalue suggested by Mr. Edwards, weshall find that the valves and the com-ponents will be available, togetherwith accumulated practical experi-ence in their use.

If we are to progress in post-wartelevision on the lines indicated byMr. Edwards, there will have to beclose liaison between the circuitengineer and the valve engineer. Toooften there has been evidence of lackof this liaison which we valve peoplehave so much desired. We find oftenthat we design experimental valves togo into circuits, and when these cir-cuits are put into production receiversthey develop a number of defectswhich then have to be cleared up.These would not be present if thevalve engineer had been working withthe circuit engineer from the outset.

In his opening remarks, Mr.Edwards refers chiefly to television asan entertainment, but we must alsoconsider in the post-war period someof the possible commercial applica-tions of television. Those of us whoare thinking about this problem canname quite a number of successful ap-plications for television in industry,and we agree that a vast field of workand research lies before us.

I personally would like to see amore intensive interest by the Wire-less Section of the I.E.E. in the sub-ject of television generally, togetherwith more informal meetings of thischaracter dealing with other aspectsof television.Mr. D. A. Bell (A. C. Cossor) :

In considering the 'band -width re-quired for colour television, it shouldbe remembered that in monochromatictelevision the minimum frame fre-quency was fixed on grounds of flicker

rather than reproduction of rapidlymoving objects. The eye is moresensitive to absolute changes of in-tensity than to changes of colour, afact which is utilised in the flickerphotometer, so that it may not benecessary to increase the total numberof frames in the same ratio as thenumber of colours transmitted. Thereis, however, no doubt that a substan-tial increase in band -width is essen-tial for adequate colour television andwould therefore necessitate an in-crease in the carrier frequency abovethe values in use.Mr. J. Rhys-Jones (Plessey Co.)

I regret to note that the previousspeakers show a lack of a commercialmindedness which would have beenso evident at a meeting of this typeheld before the war.

I would suggest that the problemindustry will have to face, is to sup-ply the public with a service which isto be as good as possible at a pricewhich is as low as possible.

The solution of this problem ispurely one of economics, and theeconomic requirements can be con-sidered under two headings, namely,customer economics and supplyeconomics. The more important groupis, of course, that referring to thecustomer.

It is possible that cheaper receiverscan be supplied by not fitting facili-ties which a high definition transmis-sion makes possible, e.g., a high de-finition receiver requires a large num-ber of low gain stages of amplificationowing to the large band -width cover-age required. The time bases maybecome slightly involved owing to thelarge number of lines used togetherwith inter -lacing features, etc. Acheap receiver could, however, bebuilt using higher gain, smaller band-width amplifying stages, thus effect-ing economy in the receiver and per-haps still further effecting economyby not attempting to achieve an inter-laced picture.

Dr. R. C. G. Williams (Murphy Radio)In considering this matter of the

best choice of transmission constantsfor post-war television, we should becareful not to lose sight of the asso-ciated economic problem and it mightbe useful to review briefly the historyof television receiver prices up to theoutbreak of war.

When the Alexandra Palace servicefirst started, the various television

manufacturers marketed only a smallnumber of hand -made sets, selling atround about ,46o each. This was fol-lowed by an interim period of semi -tooling for about two years before thewar when what was perhaps the mostpopular model, the console typecabinet with a 9 in. cathode-ray tube,was being sold in fair quantities by anumber of manufacturers at about£30. Over both the initial develop-ment period and this interim periodlittle tooling was carried out and theselling prices were effectively sub-sidised in order to bring them withinreach of the public. The stage we hadreached immediately before the out-break of war was that nearly all theradio manufacturers had tooled andwere ready to go into, what was fortelevision, large scale production ona " bread and butter " televisionspecification selling at about £30. Ithink all companies were hoping thatwith the tooling and the larger quan-tities, these prices would make tee -vision manufacture self-supporting.The future then appeared to lie in anextension to the television servicewhich would increase the viewingpublic and a progressive improvementin manufacturing efficiency of sets,valves, and components, to get theprice of this " bread and butter "model as low as possible. It wasgenerally the experience of the indus-try that the bigger sales of radio setswere in the Zio to Liz category andwe had yet to find the correspondingoptimum price/specification compro-mise for television.

At this stage the war intervened andfurther work has been at a standstill.As I see it, wartime developments leadto the possibility of three lines ofaction :-

(a) Leaving the transmission stan-dards as they were pre-war andmaking use of all the manufac-turing improvements whichhave resulted from the war,particularly in the greater useof plastics and die castings toproduce sets more efficientlyand sell them to the public at alower price. This, combinedwith an extension to the tele-vision transmission services,would probably result in themost rapid immediate extensionof the industry.

(b) To make use of the improvedradio technique which has beendeveloped during the war to re-consider our transmission and


August, 1943 Electronic Engineering U9

reception standards and pos-sibly lay the foundations of aservice with improved picturequality in the years to come.The proposals made in Mr.Edward's opening remarks aredirected at one important aspectof this line of action.

(c) The possible political conse-quences of the war which shouldresult, and I think we all hopewill result, in a greater degreeof international co-operationand the possibilities of usingthe same picture standards, atany rate over much of the con-tinent of Europe.

I must apologise for broadening thediscussion well outside the scope ofthe title of the meeting, but I do thinkit is important to bear these mattersin mind as a background to the veryinteresting discussion which is takingplace. My own view is that the changeto 525 lines would provide a degree ofpicture improvement hardly sufficientto justify compromising the advant-ages of bending all our efforts toeconomical and rapid production un-less it were associated with interna-tional standardisation, bul this must,of course, remain as a purely personalopinion.

In conclusion, I would like to saythat my own view, which I believe isshared by a very great number of pre-war viewers, is that the picture stan-dard was of high entertainment value,and that I would want to considervery carefully the associated addedcost to weigh against the advantagesof any suggested improvement. Inshort-we might do a great deal worsethan revert to our pre-war standards.Mr. E. E. Shelton (Mullard)

Whatever the system and defini-tion decided upon, the cathode-raytube in the receiver has to be capableof reproducing the picture satis-factorily.

The cathode-ray tube designer istherefore called upon to produce aspot which will resolve the lines ofthe raster. If, then, the circuitengineer designs his circuits so that achequer board black and white patternof squares, with sides equal to thewidth of a line, is reproduced by onlya sinusoidal variation of brightness(i.e., the usual method of calculatingthe required frequency band), he is notdoing his part towards giving theviewer a picture with the resolutionof which the system is capable. Thedifference in resolution of detail in thevertical and horizontal directions wasreadily observable in certain com-mercial television receivers before thewar, but the effect was much reducedor absent in the " monitor " picturesat Alexandra Palace. This difference

is to be expected, for any failure inthe receiver to provide response overthe required frequency band reducesonly the definition along the lines, thevertical resolution is assured sincethe lines are bound to be discrete. Ifthe early contributions to this discus-sion mean that the circuit engineernow finds himself able to provide anincreased frequency band at the oldgain per stage, I suggest that thefirst step should be, not to increase thenumber of lines in the picture, but tomake full use of the possible defini-tion by increasing the resolution alongthe lines.Mr. 0. J. Russell (communicated)

In my view the whole question oftelevision has been overshadowed byan unconscious comparison with thecinema. This is very clearly indi-cated by the fact that the choice ofscreen shape has been dictated by theformat of the cinema screen. More-over, this obsession with the cinemais clearly indicated by the whole his-tory of articles and discussions upontelevision from the aspect of homeentertainment. Upon the beginningof the Alexandra Palace televisionservice, the comparisons of imageswas constantly referred to the cinema.

The position of television appearsto be exactly analogous to the earlydays of the cinema, when comparisonwith the legitimate stage pepperedevery article upon the future of thecinema. The cinema, however, hasby now largely outgrown this earlyinferiority complex, and it is clearfrom the writing of critics that the'function and technique of the cinemais by virtue of its technics inherentlydifferent, although allied to, the stage.It is time, therefore, for the realisa-tion that television is not merely acinema show produced by a rathermore clever technical process. Thepublic are not interested in technicalmiracles, they judge the productfinally upon a purely entertainmentbasis.

If television is to have a value andart of its own, rather than to bemerely a novel and inefficient form ofcinematograph, the balance of tech-nical and aesthetic and psychologicalfactors may have to be drasticallyaltered. Purely upon a technicalbasis the cinema is streets ahead ofanything that television can do whenimitating the cinema. Television, ifit is to become a vehicle for a newart form, must appreciate its limita-tions and capitalise upon its advan-tages.

The writer is in favour of boldlyabandoning the present picture for-mat, which in itself is . a miserablelegacy from the cinema. From the

point of view of presenting programmematerial of an intimate nature, andhence operating largely in closeup orsemi-closeup poses, the present pic-ture ratio is wasteful. For the trans-mission of the proposed material wecould use a picture aspect ratio inwhich the picture height is greaterthan the width in the ratio of 3 : 2. Alittle experiment will prove thatalmost any head and shoulders por-trait can be comfortably framed inthis picture ratio. Moreover, fromthe point of view of aesthetic satisfac-tion, which text -books on photographytake so much space in expounding,such a frame provides a neat and un-obtrusive surrounding for a face.

Practically all portraits are framedin a ratio approximating to this pro-jected 2 : 3 ratio, and the generaleffect is one of general satisfaction.No use of ratios analogous to thepresent cinema shaped screen for por-trait work occurs to me, and, in tact,such a use would in general be inar-tistic and inadmissible. Technically,the use of such a ratio is even moreimportant, for a little calculation willshow that if we are interested in in-creasing detail, the number of linescan be increased by about 4o per cent.without increasing the bandwidth,giving a worthwhile increase in de-finition, while in cases where the faceand expression of the speaker are ofmajor importance the face could bemade to fit the picture aperture ex-tremely closely, with a consequentfurther slight improvement in overalldefinition. Even if we decide to radiatea full colour picture we can do so on afour -hundred line basis without amaterially increased bandwidth. Infact,, for the same bandwidth as occu-pied by the Alexandra Palace station,a full colour picture may be radiatedusing the : 3 ratio picture with adefinition of approximately 390 lines.

However, it might well be objectedthat the subject matter radiated bythe television station of the futureshould not be tied down to a a : 3ratio frame, although this can beutilised for scenes involving morethan one performer. The writer isfirmly of the opinion that the present5 : 4 ratio should be scrapped. Thusa good case might be made out for asquare picture ratio, especially as thisenables the most efficient use to bemade of the round end of a cathode-ray tube. The increase in definitionthus obtained works out at about 12per cent. for the same band width.

- This picture ratio also reflects thetrend of modern camera design, wherethe at inch square negative representsa very effect compromise of many fac-tors, and efficiently utilises the cir-



BUT IN?WHATMODE

Some time ago we were approachedin connection with a steam pipewhich was continually being fracturedas a result of vibrations excited bythe flow of the steam. Simple pre-

cautions had not afforded a satis-

factory solution and we were askedwhether we could throw furtherlight on the problem.

We supplied a portable VibrationAnalyser which resolved the vibration

into its component parts and dis-closed an unsuspected mode of

vibration. An examination of thestructure of the pipe and its housingsquickly showed where this vibrationcould arise, and steps were taken todamp out this particular mode, withthe result that the trouble was cured.

This is just another example of theway in which electronic technique canbe brought to the aid of industry. If

you have a problem let us see whatwe can do. All we ask is your

patience if we take longer than weshould like, owing to the heavy

demands on our facilities just at

present.

*Il146011.1LABORATORIES LTD.

1130REHAMI WOODHERTS

TELEPHONE ELSTREE 1138

Bandwidth and Definition for Various Frame Ratios

Video Band Plain Stereo Full Colour Stereo/Full Colour Format

7.6 Mc/s.

1100 780 760 520 2 : 3

1000 710 690 480 4 : 5

896 640 620 430 SQUARE

800 570 550 380 5 : 4

3.2 Mc/s.

714 500 490 340 2 : 3

656 470 450 310 4 : 5

590 420 410 280 SQUARE

525 370 360 250 5 : 4

2.5 Mc/s.

632 450 440 300 2 : 3

592 420 410 280 4 : 5

520 370 360 250 SQUARE

465 330 320 220 5 : 4

1.9 Mc/s.

551 390 380 260 2 : 3

490 350 340 230 4 : 5

453 320 310 220 SQUARE

405 290 280 190 5 : 4

Note : Owing to uncertainty as to the exact factor, values for colour and stereopictures are calculated to the nearest ten lines).

cular field of view of the camera lens.However, bearing in view the personaland intimate aspect of television en-tertainment, a ratio that.has much tocommend it both for ability to covera large variety of subjects and effec-tive use of bandwidth might be a com-promise between the square pictureand the 2 : 3 format. The fact thatby using a new picture shape, the useof colour becomes in the realm ofpractical application without loss ofdetail is also a point that should beconsidered. To present these facts,the table given above shows the num-ber of lines required for black andwhite pictures, stereo -pictures, fullcolour pictures, and stereo -colour pic-tures. The figures for colour imagesare based on a factor derived fromthe fact that the frame frequency neednot be so great as expected,, owing tothe rarity of purely monochromaticsubject matter. Stereo figures arebased upon the transmission of twocomplete images for the normal framefrequency. The advantage ofcolour over a plain black and whitepicture would appear on these figuresto outweigh any considerations ofstereo images, and the introductionof colour may well prove to be oneof the factors that will really popu-larise television as a public entertain-ment.

Man-made Earthquakes(F rom The Daily Telegraph)

MR. PURBRICK, the white-haired bespectacled M.P. for

Walton, pursues with benign per_sistence his design of discomfitingthe enemy by induction of earth-quakes. He has already given theHouse of Commons a laugh by sug-gesting that this might be accom-plished by dropping a bomb down thecrater of Vesuvius.

Yesterday he gave it another by ask-ing the Government to investigate

" the application in America whereby aneutraliser man-made electrical disturbance morepowerful than the greatest storms of thunder andlightning can be reduced to a whisper," and to" consider the applicability of this method for theartificial promotion of seismic disturbances,volcanic eruptions, &c."

Mr. A, S. L. Young, a GovernmentWhip, solemnly replied that furtherinformation was being sought, thoughthe Government were advised that thedevice was unlikely to be of use as agenerator of seismic or volcanicdisturbances.

The following exchange thenensued :

Mr. Austin Hopkinson : " Can the Hon. Gentle-man explain the exact meaning of the phrase

neutraliser man-made electric disturbance ' ? "Mr. Young (apologetically) : " I am afraid that

is beyond me."

Don't worry, Mr. Young, its beyondus, too.



Frequency Modulation in Record ReproductionThe following account of the use of a frequency modulation system for reproducing gramophone recordsis taken from the paper by G. L. Beers and C. M. Sinnett in the Journal of the Society of Motion PictureEngineers (April 1943). The original paper contains a ,detailed analysis of the various factors in design

of reproducers which has had to be omitted in this abstract.

THE remarkable increase in thesale of phonograph records dur-ing the past few years is a de-

finite indication of the returning pub-lic interest in records as a medium ofhome entertainment. If the presentinterest in phonograph records is tobe maintained, on a permanent basis,it is essential that the reproduction ofsound from records be at least com-parable to or preferably better thanthat which be obtained from radiobroadcasting.

During the past few years, an in-vestigation was conducted to deter-mine the prospects of materially im-proving the overall performance ofrecord -reproducing systems. Onephase of the investigation wasdirected toward the possibility of re-producing frequencies up to io,000 or2,000 cycles from standard shellac

records without the introduction of ob-jectionable surface noise. In thecourse of this investigation, the pos-sibilities of producing a frequency -modulated signal by means of aspecial pick-up and associated cir-cuits was investigated. Fig. i showsin outline form the general construc-tion of an experimental frequencymodulation pick-up. A metal frameor mounting block is provided as asupport for an insulated plate whichis the high -potential side of the pick-up. To this mounting block is alsoattached a thin metal ribbon. Thei ibbon, which is mounted in a planeparallel to the insulated plate andspaced from it by a small air -gap, isplaced under tension in order to in-crease the natural resonance fre-

STEEL WIRE ANCHORED

INSULATED oo15 RIBBC.V

/N BLOCK MOUNTINGBLOCK

METAL PLATESTYLUS STEEL WIRE '

ATTACHED TO RIBBON

Fig. I. Experimental frequency modulationpick-up.

quency of the system. The stylus -supporting wire is anchored to themounting block at its upper end. Itis attached to the ribbon at approxi-mately the mid -point of its length andits free end is bent in a plane essen-tially parallel to the record groove.The sapphire which is used as a stylusis attached to the end of the wire. Theportion of the wire between the ribbonand the sapphire provides sufficientvertical compliance to minimisemechanical noise and to reduce dis-tortion due to pinch -effect. From thefigure it is apparent that displacementof the stylus laterally results in achange in the position of the ribbonwith respect to the fixed plate andthus produces a change in capacity.The overall length of the mountingblock shown in Fig. i is approxi-mately one-half inch. The normalspacing between the fixed plate andthe ribbon is approximately 0.004inch.

From a purely theoretical stand-point it is essential that in a frequency

Q

R5

DISC.SR.?.

Tc/0

+300.Y.

F.

Fig. 2. Oscillator and Frequency -discriminator -rectifier circuit.

20

30

- mum-1111111=11111I111111111111111111111111111111111EnumlinrM11111=111111

IIMEE11111V/11111111111111FM111111111111

INUM1111111111111111111MENEM1111101111111

modulation pick-up the change incapacity with displacement of thestylus be such as to produce a linearrelationship between frequencychange and motion of the stylus. Inother words, the variable capacitorformed by the elements of the pick-upshould, in radio terminology, be of thestraight-line frequency type. F rom apractical standpoint the distortion in-troduced by a pick-up constructedalong the lines indicated in Fig. i,when used with circuits to be des-cribed later, is sufficiently low as toto be substantially negligible.

Circuit ConsiderationsThe essential circuit considerations

which are involved in the design of afrequency -modulation record repro-ducing system may be stated asfollows :

(r) The carrier frequency to beemployed.

(2) A suitable oscillator circuit foruse with the pick-up.

(3) The type of frequency dis-criminator -rectifier combinationto employ.

A study of the question of theoperating frequency to use in a fre-quency modulation phonograph sys-tem leads to the conclusion that car-rier frequencies as low as those usedin the intermediate -frequency ampli-fiers of radio receivers and as high asthose employed for frequency modu-lation broadcasting will give satisfac-tory results. If the phonograph is tobe used in combination with a radioreceiver there may be some advantagein using a carrier frequency which

20000

20 50 100 200 500 ICCO C 5000

Fig. S. Calculated response characteristic of pick-up and arm.



-LI

ZL

I OnL23Tc2 C3T

permits the use of one or more of theintermediate -frequency amplifier cir-cuits as a frequency -discriminatingnetwork for converting the frequency -modulated signal into amplitudemodulation prior to detection. How-ever, if the phonograph is designed asa separate device it may be desirableto use a frequency in the neighbour-hood of 30 megacycles, particularly incase some frequency in this region isassigned by the F.C.C. for diathermymachines. If a carrier frequency isused in a band thus allocated by theF.C.C. no special shielding would berequired to prevent interference withother radio services. The signal levelprovided at the discriminator by thefrequency modulated oscillator canreadily be made quite high, so thereis no likelihood of diathermymachines or other electrical equip-ment causing interference with the

Since' the oscillator and frequencydiscriminator -rectifier circuits are toa considerable extent interdependent,they will be discussed together. Fig.2 is a schematic diagram of circuitswhich have given very satisfactory re-sults. The circuit problem in con-nexion with the oscillator is to pro-vide an arrangement which will havesufficient frequency stability from thestandpoint of line -voltage variations,temperature changes, etc., and at thesame time enable the pick-up capac-ity variations to produce the desiredfrequency change.

From the standpoint of obtainingthe maximum frequency change for agiven variation in capacity at thepick-up, it is desirable that the pick-.up be connected directly across theoscillator tuned circuit. This canofcourse, be accomplished by mountingthe oscillator tube and associated cir-cuit elements at the pick-up end of thetone arm.

This arrangement has not beenfound to be particularly desirable be-cause the tone arm is made undulylarge and the heat from the oscillatortube causes the end of the tone arm,

Figs. 3 and 4 (left), Equiva-lent circuits for high and low

frequencies.

Fig. 7 (right). Variation ofd and a with stylus radius.

Fig. 6 (below). Stylus seatedin record groove.

7

(aLtituCC

50

50 /4 40...%%N.N.,...ic

3 30r

1,:, THEORETICALLY GOES TO ZERO1, FOR ALL RADII BELOW 2 3 MIL.

2 20 r-IF GROOVE AND STYLUS WERE -PERFECTLY RIG/D

10 1

In el---- .., .

0 1 2 3 4 5 6STYLUS RADIUS - R - IN MILS.

7 8

which is handled by the user, to be-come uncomfortably hot. The sameresult, however, can be accomplishedby mounting the oscillator tube onthe main instrument chassis and con-necting it to the pick-up through aresonant transmission isused as the oscillator tuned circuit. Ithas been found that by connecting thepick-up previously described througha relatively low -capacity line to a con-ventional oscillator circuit as shownin the diagram a sufficient frequencyshift is obtained to give the desiredaudio -frequency output. In this casethe transmission line is treated as alumped capacity. The line is includedas an integral part of the tone arm.

It will be noted that the oscillatortube employed is of the 6SA7 type.This tube permits the use of electroniccoupling between the oscillator anddiscriminator circuits. The oscillatorfrequency is adjustable by means of

@,

LD /4 -012 -§f

-- qc

6-v42-

0

ro

/820

22

2426

30

34

TRACKING LOSS FORWAVELENGTH OF

5.3 Mils AT7000 Cycles.

1 2 3 4 5mi/. STYLUS RADIUS

TRACKING WEIGHTREQU/RED AT7000 Cycles

Fig. B. Tracking oss at17,000 cis. for variousradii of stylus.

an iron core which is associated withthe inductance L, shown in the dia-gram.

A simple resonant circuit is utilisedas the means for converting the oscil-lator frequency variations intochanges in the amplitude of the signalapplied to the diode portion of the6R7 tube. A powdered -iron core asso-ciated with inductance L, is used totune this circuit so that the meanoscillator frequency falls at approxi-mately the 70 per cent. response pointon one side of the selectivity charac-teristic. The rectification of the r -fsignal by the diode develops an audio -frequency potential across the resistorR,. This audio -frequency potential isthen amplified by the triode 'section ofthe 6R7. The output whichappears across resistor R. in the platecircuit of the 6R7 is applied to a suit-able audio -frequency amplifier andloud speaker.

The audio -frequency output of thecircuit shown in Fig. z is a functionof :-

(r) The oscillator voltage appliedto the discriminator.

(z) The frequency variations in thisvoltage which are produced bythe pick-up.The slope of the discriminatornetwork.The audio voltage gain obtainedfrom the 6R7.

An experimental pick-up employedin the circuit shown in Fig. 2 hasgiven an rms potential of 6 to 8 voltsacross resistor Rs when reproducinga 40o -cycle record cut at a grooveamplitude of o.00r inch:Response Characteristics of Pick Upandirone Arm :

Making use of the equivalent dia-grams in Figs. 3 and 4 the overallresponse characteristic of the systemcan be calculated. From these figuresit can be seen that current h repre-sents the velocity of the ribbon with

(3)

(4)



P.19

Last StrawAS the pace of production quickens, the care- laden manufacturer

must often feel like a camel contemplating the approach of thelast straw. Can his oft -revised schedule carry yet another complication ?Can he increase output still further without some impairment ofquality ?

The Simmonds products were designed to solve precisely thisproblem, and solving it they are, all over the country. Experienceabundantly proves that they save time, they save material and theysimplify assembly. They make it possible, in short, to quicken thetempo without detriment to the temper.

SIMMONDSIn high service to

AERONAUTICAL, INDUSTRIAL & MARINEConstruction

THE SIMMONDS NUT PINNACLE NUT SPIRE NUTSIMMONDS INSTRUMENTS, CONTROLS & ELECTRONIC PRODUCTS

FRAM OIL & ENGINE CLEANERSIMMONDS AEROCESSORIES LTD.

GREAT WEST ROAD, LONDONA COMPANY OF THE SIMMONDS GROUP

LONDON MELBOURNE MONTREAL PARIS NEW YORK



respect to the insulated plate and cur-rent i, represents the velocity of thestylus. The ratio of is to f, will pro-vide the response characteristic of thepick-up with respect to frequency.For high -frequencies this can be cal-culated from the following formulais \

i, C, + C, 1 - 2 771)2L Ca Ca )Ca + C3

For low frequencies, the responsecharacteristic may be obtained from

Ca

C, + Cs) (1 (277-1)2L,(C2+C,))

it will be noted that two peaks inresponse occur, one at tone -arm reson-ance and one at the high -frequencyresonance of the pick-up moving sys-tem. Fig. 5 shows the response char-acteristic as calculated from the aboveequations.

Tracking Weight Required to OvercomeVertical Force due to Lateral Velocity :

For proper tracking the stylus musthave sufficient vertical force exertedupon it to overcome the vertical com-ponent of force due to the lateralvelocity of the modulated recordgroove. Calculations have been madewhich show the vertical forces exertedupon styli of various radii whenseated in a standard groove having an88 -degree included angle, a'0.0023-incnradius cutting stylus and a groovewidth at the top of 0.0069 inch. Inaddition to the vertical forces, con-sideration has also been given to thevariations to be expected in pinch -effect with different sizes of reproduc-ing styli.

Fig. 6 illustrates a stylus seated in aecord groove of the above dimen-

sions. Two important factors whichchange the diameter of the stylus are :the tracking diameter (d) and the,wedging -angle (a). Tracking dia-meter d has a direct bearing uponboth pinch -effect and the high -fre-quency response and should be keptas small as possible. On the otherhand, the wedging -angle a, which de-termines the tendency of the stylus toclimb the groove wall should be madeas large as possible for specifiedgrooves. From this it is obvious that aa compromise must be made. Fig. 7shows the variations in d and a withstylus radius, and from observation itcan be seen that the stylus radiusshould not be less than 0.0025 inch orgreater than 0.0042 inch. Furthermore,since the curve for angle a is flat froma stylus radius of 0.0025 inch to 0.0042inch and the curve for diameterd is rising rapidly over this rangeit appears desirable, when recordgroove variations are considered,

to use a stylus radius of about0.003 inch

As the stylus radius is increased, itis apparent that for a given groovevelocity the output to be obtained athigh frequencies will decrease. Cal-culations have been made of the ex-pected loss at high frequencies, andFig. 8 shows the curve for this track-ing loss at 7,000 cycles for styli from(loots inch radius to 0.005 inch radius.It will again be noted that a stylusradius of 0.003 inch is indicated.

Overall Response CharacteristicsFig. 19, curve A shows the overall

response characteristic of the pick-up,tone arm, and discriminator asobtained from a frequency recordhaving a 50o -cycle crossover pointbetween constant amplitude and con-stant velocity. The rounded portion ofthis curve at the crossover frequencyis due to the limitations imposed bythe electrical network used to providethe recording characteristic. For thepurpose of comparison the calculatedresponse characteristic previouslyshown in Fig. 5 is included in thisfigure as curve B. The departurefrom linearity of this curve representsa distortion of approximately 2 per

Q. /30

.002 ool 0 .00l ,002

DISPLACEMENT OF STYLUS

Fig. 10. Diode current and stylus disp acement

2

0

2

4

6

cent. second harmonic and 0.1 percent. third harmonic. The change infrequency which corresponds to the

o.o0i5-inch displacement of thestylus is ± 15"o cycles.Change in Diode -Current with Stylus

DisplacementFig. 10 shows the overall linearity

existing between current in the dioderesistor and displacement of thestylus. This curve shows the com-bined effect on linearity of the follow-ing factors :

(1) Change in the capacity of thepick-up with displacement ofthe stylus.Change in frequency of theoscillator with change in capac-ity of the pick-up.Change in output of the fre-quency discriminator -rectifiercombination with change in fre-quency.

ConclusionAn experimental frequency -modula-

tion record -reproducing system, of thetype described, has been in use forsome time. All the evidence to dateindicates that the system is a practicalone and is not adversely affected bychanges in temperature, humidity, orline voltage.

The experimental frequency modu-lation pick-up meets the requirementsof a satisfactory pick-up to a degreewhich has not previously been attainedin a relatively inexpensive device. Thegeneral performance characteristics ofa pick-up of this type can be cal-culated within reasonable limits.

From the listener's standpoint, theexperimental frequency modulationphonograph system which has beendescribed makes it possible when usingconventional shellac records to extendthe frequency range of a record -repro-ducing system to ro,000 or 12,000cycles with surprising freedom fromsu -face noise, mechanical noise, and

distortion. F urtherreduction in surfacenoise can now be ob-tained with shellacrecords if they arerecorded with a high -frequency accentua-tion characteristicwhich is comparableto that used in tran-scriptions.

The writers wishto acknowledge thevaluable assistanceof Messrs. H. Belarand R. Snepvangersduring the develop-ment of the fre-quency - modulationrecord - reproducingsystem.

(2)

(3)

6

12

-14

18

100 CAS. 500 1000

Fig. 9. Overall Frequency response of F.M.pick-up and discriminator.



It will be news to most people thatmany vitally important inside parts ofa modern wireless set are of BakelitePlastics. Bakelite Laminated -amaterial made by compressing paperor fabric, impregnated with BakeliteSynthetic Resin, into a homogeneousmass-is used for these parts becauseof its special electrical insulationproperties, coupled with its tough-ness and the ease with which it canbe machined. This is a typical in-

stance of how Plastics serve the needsof modern industry.Most forms of Bakelite Plastics areto -day playing an important part inequipping our fighting forces and aretherefore not available to privateusers. The experience gained inthese new wartime fields will, how-ever, prove invaluable to manufac-turers in a great many industrieswhen we can once again turn ourminds to peacetime problems.

BAKELITE LIMITED, 18 GROSVENOR GARDENS, LONDON, S.W.I

TREFOIL.

BAKELITE PLASTICSPioneers in the Plastics World G13



BOOK REVIEWSThe Cathode Ray Oscillograph

in IndustryW. Wilson, D.Sc. 144 pp. 156 figs. (Chap-man & Hall, 12/6 net).

In his preface emphasising the ever -widening field of industrial applica-tion of the cathode-ray oscillograph,the author outlines his intention ofmeeting the need for guidance of thosewho could profitably employ theoscillograph, but who are not nor-mally workers in this field.

The book deals with both types oftube, metal and sealed -off glass, andafter describing their construction andthe various accessories, discusses thevarious measurements which can beundertaken with the tube,, including anumber of less usual ones.

Two novel additions to the contentsare a chapter on the Electron Micro-scope, and one on the care and main-tenance of the tube and its accessories.This is particularly useful for thosewho use the tube as an instrument andhave no previous experience of oscillo-graph practice.

Unfortunately, after reading thiswork, one cannot feel that the undeni-able need for a book dealing with theoscillograph from the user's point ofview has been really met. To succeedin this aim, a book must be explicitin the extreme, and as those for whomit caters are not likely to be able tocorrect errors and inconsistencies inthe text for themselves, these are tobe particularly avoided.

One is only too well aware of thedifficulties of the author of a technicalbook under war -time conditions, butit is disconcerting to find errors insuch abundance. For example, onp. 9 there is the peculiar physical con-cept that it is the vacuum and not theatmospheric pressure that holds 'ajoint together, whilst in the sameparagraph the term "high voltage"is used in mistake for "high vacuum."

Origin distortion is discussed onp. r r and p. 36, but the two referencesdo not appear consistent, nor do theyfully explain the effect. The treat-ment of aberrations generally seemsunsatisfactory as, apart from conspicu-ous omissions (such as the use of sym-metrical deflection not only to avoidtrapezium distortion, but also to mini-mise defocusing), the explanation onp. 38 for trapezium distortion takesinto account only the second ordereffect of electron velocity and neglectsthe more important refractive aspect.

The reference to this effect in thedescription of the Cossor double -beamoscillograph is consequently at vari-ance with the facts, whilst a littlelater in the description of this instru-ment the deflection coils are accusedof being in between the inner andouter mu -metal shields, a statementwhich is neither true nor technicallyacceptable.

In addition to these there are un-fortunately a great many more obvi-ous errors, such as a reference to theultimate vacuum of a rotary oil pumpas 0.5 mm. Hg., and a statement onp. zo that the vapour pressures of oiland mercury are Id' and to' mm. re-spectively. Lissajous' name is alsomis-spelt throughout.

In conclusion, one feels that inorder to serve the purpose of this bookbest the author would have beenbetter advised to include more detailedand accurate expressions of the funda-mentals of the cathode-ray oscillo-graph and to rely on a completebibliography to introduce workers inindividual fields to the best way ofapplying the technique to their par-ticular problems.

T. D. H.

Experimental ElectronicsR. m-Miiller, R. L. Garman and M. E.Droz. 322 pp. (Prentice Hall, Inc. N.Y.

n29/6 English Price).

A remarkable thing about this bookis that it is written by three professorsof Chemistry. Not that they may notbe fully qualified to write on such asubject, but there is the same feelingof surprise as if Professor G. W. 0.Howe had written a book on 'Experi-mental Chemistry.

The authors acknowledge their in-debtedness to standard works on elec-tronics and radio engineering, such asthose of Terman and Reich, and thereare references to technical literaturethroughout, 'including a few Britishjournals.

The introduction to the experimen-

Books reviewed on this pageor advertised in this Journal,

can be obtained from

H. K. LEWIS & Co. Ltd.136 Gower Street, W.C.I

If not in stock, they will be obtainedfrom the Publishers when available

tal work covers the usual elementarytheory, and the experiments are thenset out neatly with a preliminary notegiving the purpose of the experi-ment, materials required, and proce-dure., A list of supplementary read-ing and problems is given at the endof each section. The series is com-plete and includes nearly all the workon valves which would be done by athird -year telecommunications student.Some of the experiments need days tomake up, such as the three -stage in -vase feedback valve voltmeter, or abeat -frequency oscillator, in whichthe student is apparently expected tostart from scratch. This, of course,is all to the good, provided that thetime is available in the course, andone wonders how the students and re-search workers in chemistry, biologyand engineering at New York Univer-sity find time to do it all.

As a guide for instructors or "home_study" workers it is one of the bestbooks of its kind, and if all the ex-periments were diligently performedthere would not be many practicalapplications of vacuum tubes that thereader would hesitate to tackle.

G.P.

X -Rays in Research andIndustry

H. Hirst. 91 pp. 82 figs. (Tait Publish-ing Co. Pty., Melbourne, 7/6 English price),

A handy book which describes theproblems for which X-ray methodsare of use, and the practice and cal-culations of X-ray technique.

After a description of the produc-tion and properties of X-radiation,there are chapters on crystal structureand crystallographic examination, in-vestigation of alloys, castings, etc.The text is interspersed with numer-ous tables of data and the book iswell illustrated. There is also ashort bibliography. The whole workis a good summary of the applicationof X-rays to industry and is useful tohave for reference.

Electrical Technology for Tele-Communications

W H. Date (Longmans, Green & Co. 5s.)

In the review of this book whichappeared in last months' issue, weregret that the title was given in erroras " Electrical Technology forRadio Communications." The correcttitle is as given at the head of thisparagraph.



PRE-EMINENT PEACEINDISPENSABLE IN WAR

ADVERTISEMENT OF THE TELEGRAPH CONDENSER CO. LTD.GR 778S



NOTE SFROM THE INDUSTRY

R.S.G.B.New Headquarters

The Council of the IncorporatedRadio Society of Great Britain, an-nounces that new headquarters havebeen established at New RuskinHouse, Little Russell Street, London,W.C.i (Holborn 7373), at which ad-dress the General Secretary (Mr. JohnClarricoats) will be pleased to meetvisiting amateurs.

Since September, 1939, the member-ship of the Society has increased from3,50o to 5,5oo. Nearly 4,000 membersare on active service.

R. W. Paul's gift to ResearchIn his will the late R. W. Paul has

set aside a sum of over ,4loo,000 forthe endowment of a fund to pay forthe design, ,construction and mainten-ance of novel physical instrumentsand apparatus required by researchworkers.

The trustees are particularly in-structed to favour the construction ofapparatus which gives no prospect offinancial return.

The Committee entrusted with theadministration of the fund will con-sist of six members appointed by theRoyal Society, The Physical Society,The Institution of Electrical En-gineers, and The Institute of Physics.

CellophaneA Registered Trade Mark

DEAR SIR,-We have read thearticle, entitled "Safety with X -Rays-The Detection and Measurement ofRadiation," by A. G. Long, whichwas published on pages 52-54 of theJuly issue of ELECTRONIC ENGINEER-ING, and we were interested to notethe references to Cellophane, whichappear in the particulars relative toFigures 4, 6 and 7 of the article.

It seems to us, however, that inthose references the word Cellophanehas been used in such a manner asmight tend to create the impressionthat Cellophane is the name of amaterial.

One of the objects of this letter isto point out that Cellophane is notthe name of a material, but that theword "Cellophane" is our registeredtrade mark, and denotes, exclusivelyand distinctively, the brand of cellu-lose sheets and films manufacturedand supplied by us.

It is, of course, damaging to a trademark that it should be used as thename of a material, and we feel sure,therefore, that you will not disapproveour writing to you to explain the posi-tion.-Yours faithfully,

BRITISH CELLOPHANE, X.TD.

ABSTRACTS OFELECTRONIC LITERATURE

RADIOThe Determination of the Location andFrequency of Thunderstorms by a

Radio methodU. S. Forrest)

A method is described of continu-ously recording atmospherics in orderto obtain warning of the outbreak ofa thunderstorm and to determine thedistance of the storm from the record-ing site.

The apparatus consists essentiallyof a radio receiver tuned to approxi-mately 15o kc/s and connected to acontinuous chart output recordingmeter : a modulated oscillator is in-corporated in order to maintain con-stant the characteristics of the re-ceiver. The paper gives the resultsof three years' experience with thisrecording technique.

By correlating the output recorderdeflections with the known locationsof electric power system breakdownsdue to lightning, the relation betweenthe recorder output and the stormdistance has been determined. Fordistances up to 600 km. the equivalentfield strength of atmospherics at 15okc/s, has been found to be inverselyproportional to the square root of thedistance of the source.

-Jour. Roy. Met. Sec. Jan., 1943,page 33.

Voltage Regulated Power Supplies(A. B. Bereskin)

This paper discusses problems in-volved and develops an orderly pro-cedure for designing and constructingthese voltage regulated power sup-plies for specific applications. The cor-relation between design data and

tests on finished model is shown.-Proc. I.R.E., Vol. 31 (1943), p. 47.

Loop Antennas for Aircraft(G. F . Levy)

Characteristics, requirements anddesign considerations which are asso-

ciated uniquely with aircraft loopantennas operating in radio range orbeacon band extending from zoo -400kilocycles are discussed.

The " low -impedance " and the" high -impedance " types of air -coreaircraft loops are considered in detail.Both types are analysed mathematic-ally on the basis of their receiving effi-ciency and directive properties. -

Actual polar characteristic curvesare given for a number of loopantennas of both types. Iron -core loopantennas are considered sepa'ratelyand comparison is made with the morewidely used air -cored types.-Proc. I.R.E., Vol 31 (1943), p. 56.

I NDUSTRYThe Production of Fixed Carbon

Resistors(F. C. Carter)

The method of production of thevarious types of carbon resistor incommon use in radio and line com-munication equipment is described. Afeature is the employment of auto-matic machines producing large quan-tities of resistors of standard values.-P.O.E.E.J., 36 (1943), Pt. 1, p. 6.

Metallising Plastics(E. E. Halls)

Some of the wide applications ofmetallised plastics are described; it isemphasised that metal coatings nowhave specific uses and are not usedfor decoration alone. A summary ofthe methods of applying the films isgiven and certain types of films dis-cussed in detail, viz., films applied bymeans of metal powder in varnish orlacquer medium and cellulose lacquerfilms. Types of powders are dis-cussed together with the best form andmedia in which they may be applied.Moisture proofing with aluminium isconsidered in conjunction with theelectrical properties of organic bondedaluminium powder finishes.

-Plastics, June, 1943, p. 235.*Heating Wood with R. -F. Power

U. P. Taylor)Radio -frequency power (of the order

of 1-io Mc/s) may be used to provideheat for various wood processes, suchas seasoning, drying,, etc. Themethod may also be adapted for plas-tic plywood and impregnated mate-rials. A brief account of the theoryof radio -frequency heating is givenand the factors which determine itsapplicability discussed. Data for thecalculation of power required, timecycle and operating costs are given.-Trans. A.S.M.E., Ap.,, 1943, p. 201.*Resistance Welding Speeded and Im-

proved Tube control(G. W. Garman)

Two of the most important factorsin welding are duration of currentflow and the magnitude of the current.Details are given, of the applicationof electronic control to the regulationof these quantities and the beneficialeffects that have been obtained. Abrief sketch of the development ofa.c. electronic control is given fromthe first adoption of hot -cathode thyra-trons to the modern water-cooled sys-tems. Voltage adjustment and flexi-bility of the apparatus are describedand energy storage welding discussed.-Electronics, March, 5943, p. 117.*

Supplied by courtesy of Metropolitan -Vickers,Electric Co., Trafford Park.



MOULDINGS FORINSULATION

Aluminium Alloy shrunk onto a finished MYCALEXrod, making a perfect pointfor terminals, etc.

The fact that MYCALEX mouldings canbe integrated with metal parts affords manyopportunities for simplified design andgreater efficiency of insulation.In addition MYCALEX has excellent electricalqualities, resists heat up to 400° Centigradeand is impervious to weather conditionsinvolving heat, cold or pressure. It can bereadily machined to fine limits.

MYCALEX CUT PIECESDelivery from stock

Stock sizes of MYCALEX can be dispatchedwithin a few days. Price list will be sent on

. application.

MYCALEXCONDENSERS

For high duty work, high voltages and highfrequencies. Enquiries invited.

Good deliveries can now be effected.

MYCA.LEX LTD. CIRENCESTER, GLOS.

We have over 25 years' experience

in designing and manufacturing a very varied range ofSmall Electric Motors, Alternators, Generators and Electro-Mechanical apparatus.Our products are known throughout the world for reliabilityand stability under the most exacting conditions. In additionto producing special designs in quantity at competitiveprices, we are interested in your experimental needs. Assoon as they are released from the claims of war productionour research and design laboratory together with our manu-facturing resources will be at your disposal.

Write for particulars of any special type of apparatus that inter-ests you: we will forward details and literature when available

SMALL ELECTRICSMOTORS LTD.

BECKENHAM, KENTA subsidiary of

BROADCAST RELAY SERVICE LIMITED

TFLCOti,

AIM

TELCONCABLES

for

HIGHFREQUENCY

TRANSMISSIONand RECEPTION

Full particulars of all Telcon Products from 1

THE TELEGRAPH CONSTRUCTION& MAINTENANCE CO. LTD.Head Office: 22, Old Broad Street, London, E.C.2

Telephone! London Wall 3141


130 Electronic Engineering

A Note on the Puncture Strength of Porcelain, etc.By Dr. Ing E. ROSENTHAL

In connexion with a, recent articleby the author : "Dielectric Strengthof Porcelain and other CeramicMaterials,"* C. W. Marshall, ofthe Central Electricity Board, haspointed out that the value of the.graphs would be increased if indica-tions of the spread- of the individualobservations were made.

The following notes are thereforeappended for reference:

In order to obtain a reliable aver-age value of the puncture strengths ofa material, it is necessary to make aconsiderable number of tests. TheAmerican S.T.M. Standards onlyspecify for porcelain a number of five,but a greater number gives a morereliable average.

The spread varies (a) with the fre-quency, (b) with the temperature, (c)with the duration and rate of increaseof the voltage applied, (d) with thewave shape, and (e) with the electro-static field 'distribution.

The spread is smaller at high fre-quencies and larger at low frequen-cies, and it is smaller at elevatedtemperatures compared with roomtemperatures.

In carrying out impulse tests, oneobserves a greater spread of punc-* Electronic Engineering, March 1943.

& /0- 12 /4 /6 le

111111111111111111

EMPAIMISLIMII.1111111111110\1113 '111111111111111111MISS11111111111111=111111M

per Voltage Increaseof I KV.

1 Curves rare at Room Temp I5°CCurves if /50 °C

I

tures than at commercial frequencies.The punctures lie closer together

when the test arrangement excludesedge effects as far as possible. Edgeeffects tend to increase the spread ofthe observations.

It would, therefore, appear thatthere is a smaller spread in values inthe case of thermal breakdown than isthe case wheh the breakdown is pre-ponderantly disruptive.

August, 1943

At normal power frequency (5ocycles per second), the spread can beas much as 25 per cent. up or down,although if the rate of voltage in-crease prescribed by B.S.S. 137,namely, zo KV per second, is adheredto, the variation will only be of theorder of ± I2 per cent. In otherwords, the more slowly the voltage isincreased, the greater the spread ofobservations.

The graph given herewith was pre-pared by repeating twenty times testsat various rates of voltage increase.The horizontal ordinate indicates thenumber of seconds used for increasingthe voltage by i KV. The twentyreadings so obtained were added to-gether and divided by twenty in orderto obtain the average value. Thehighest figure above this average wasthen recorded above the horizontalordinate, and the lowest figure belowthe average was recorded below thehorizontal ordinate.

Curve (i) is for porcelain at roomtemperature (150 C.), and curve (2)is for porcelain at a temperature of15o° C. Although at first glance thespread of puncture values in the caseof porcelain seems to be rather con-siderable, it is smaller than in the caseof most insulating materials.

The NEW

11"'m " HYPERLOY "TRANSFORMERS AND CHOKES

1111111111111110111M

A range of high-performance, space -saving Com-

ponents designed to meet the exacting requirementsof modern Electronic and Communications equipments.

Small in size. Weighing only 2 ozs. Meeting the most rigid Tropical Specification. Easily mounted in any position. Manufactured in a variety of windings to

meet many diverse applications.

WRIGHT L WEAIRE LTD.HIGH ROAD, TOTTENHAM, N.I7

Telephone: TOTtenham 3847-8-9



To -day the products of industry conform to rigidspecification. In Radio, component and finalassembly alike are tested,andre-tested,their per-formance measured against exacting standards.It is the special function of Marconi Instrumentsto find the answers to testing problems ; toprovide the means for determining specific

R Cei

performance in communication equipments. Inthis specialised work the Marconi organisationbrings unrivalled resources to bear and a wealthof experience accumulated since the pioneerdays of wireless communication. New demandsare made and met with the traditional skill andcraftsmanship of Marconi creative engineers.

Al Instruments LtdST. ALBAN S HER TS TELEPHONE 4 3 2 3

WHAT PRODUCTIONMODIFICATIONS IN

SOLDERING PROCESSES ARE NECESSARY

WHEN USING WAR -TIME ALLOYS ')

This, and numerous other queries are answered in reference sheet 2 of "Technical Notes onSoldering," published by the manufacturers of Ersin Multicore-the A.I.D. approved solderwire with three cores of non -corrosive Ersin activated flux.Firms engaged on Government contracts are invited to write for a copy of this referencesheet and samples of ERSIN MULTICORE SOLDER wire.

The Solder Wire with 3 cores of Non -corrosive Ersin Flux

MULTICORE SOLDERS LTD., BUSH HOUSE, LONDON, W.C.2.TEM.IeBar5583 4


August, 1943132 Electronic Engineering

Classified AnnouncementsELECTRADIX BARGAINS

DYNAMOS, MOTORS, ROTARIESAs you know, we have many in stock for quick de-livery ; do any of these Interest you f Fine modernA.C. + HP Induction motors, self -start, 1,450 revs,as new. D.C. Motors, HP, 110 volts and 220volts, shunt, 1,750 revs. D.C. Motors, 1 HP, 230/250volts, shunt, 700 revs. L.H. D.C. 2 HP, 110 volts,2,000 revsW. Another D.C. 2 HP 250 volts, 1,050revs. N. 5 HP ditto, 230 volts, 2,100 revs. ; etc.,etc.ROTARIES FOR RADIO. E.D.C. and Crypto,etc., Various D.C. inputs and 50 cycle A.C. outputfor mains A.C. Receivers and Radiograms on D.C.CHARGING MOTOR GENS. D.C. Output8 volts 250 amps. coupled to 3 HP 220 volt D.C.motors. Another fine charger D.C. output 9 volts50 amps. for 220 v D.C. mains. Smaller output16 volts 5 amps. coupled to 220 volt motor, alsofor 110 volt motor. A.C. type charger for 50 cycle210/220 volt mains with generator, output 15 volts12 amps., 1,400 revs. ; another with 220 volt, 5 amps.D.C. output.GENERATORS. We can still supply small 6 voltand 12 volt, high speed dynamos ; 17/6 carriagepaid England and Wales.MOTOR CONTROL FLOOR FOOTSWITCHES. Ironclad 5 to 50 amps., 10/-. Forother switchgear, see last month's advertisement.METERS. We have some full size switchboardmeters, 4 in. and 6 in. dials, etc., A.C. and D.C. ;at low prices to callers.INDICATORS. Water level for tanks, withball -float geared to watch -dial panel gauge. Range9 in. rise or fall, 7/6. Battery Charge indicators" Mentor " thermal type, red light, 211- in. flushpanel case 6 or 12 volts, 5/-.PRESSURE GAUGES. Air or Oil, to 4 lbs, 2/6,to 50 lbs, 3/6, to 90 lbs, 4/-, to 120 atmospheres,10/6.LABORATORY GEAR. We can still supplyWheatstone Bridges, Sullivan and Tinsley MirrorGalvos, Scales and Stands ; Siemens high-speed Relays,Radlogoniometers, Wavemeters, Meggers, A.G. PanelVoltmeters, Rotaries and Alternators, 10.000 ohm.Relays, etc.

Note our new address. Visit our Showroom.ELECTRADIX RADIOS

214, Queenstown Road, Battersea, London, S.W.8Telephone : Macaulay 2159.

® -0--0- -0--0- 0 0 0 0 -0-o--0-

FACT0

In the near future our Officesand Works will be transferredto larger premises in PettyFrance, Westminster, S.W.I. Allcustomers will be notified indue course.

FICTIONBecause the name of Dr. N.Partridge has long been pre-eminent in connection with specialtransformers, individually de-signed and produced, there aresome who have the notion thatPARTRIDGE TRANSFORMERSare manufactured only in smallnumbers. This idea is very muchout of date.

If you are interested in largequantities-so are we.

Ph.D. B.Sc., M.I.E.E.Makers of Transformers and Chokes

King's Bldgs., Dean Stanley St.,LONDON

Telephone : VICtoria 5035

040-0-0-0-0-0-0-0-0- 0 a 0 0 0 0 0 0 0 0

S.W.I

The charge for miscellaneous advertisements on thispage Is 12 words or less 3/-, and 3d. for everyadditional word. Single -column loch rate displayed,El. All advertisements must be accompanied byremittance. Cheques and Postal Orders should bemade payable to Hutton Press, Ltd., and crossed, andshould reach this office, 43, Shoe Lane, London, E.C.4,not later than the 15th of the month previous to

date of Issue.

FOR SALEIN STOCK, Rectifiers, Accumulator Chargers,Rotary Converters, P.A. Amplifiers, Mikes, MainsTransformers, Speakers of most types, Test Meters,etc., Special Transformers quoted for.-UniversityRadio, Ltd., 238, Euston Road, London, N.W.I.Ger. 4447.

LOUDSPEAKERSLOUDSPEAKERS-We carryon. Sinclair Speakers,170, Copenhagen Street, N.I.

LOUDSPEAKER repairs, British, American, anymake, 24 -hour service; moderate prices.-SinclairSpeakers, r7o, Copenhagen Street, N.r.

MISCELLANEOUSWE WILL BUY at your price used radios, ampli-fiers, converters, test meters, motors, pick-ups,speakers, etc., radio and electrical accessories. Write,phone or call, University Radio Ltd., 238, EustonRoad, London, N.W.r. Ger. 4447.

WEBB'S Radio Map of the World enables you tolocate any station heard. Size 40' by 3e 2 colour heavyArt Paper, 4/6, post 6d. Limited supply on Linen, to/6,post 6d.-Webb's Radio, 14, Soho Street, London, W.1'Phone : GERrard 2089.

FULL range of Transmitting Keys, practice sets andother equipment for Morse training.-Webb's Radio,14, Soho Street, London, W.I. Phone : GERrard 2089.

ADVERTISER wishes to get into touch withPhysicists and Engineers (Radio or Electrical) havingdesigns or ideas for development in the followingfields : (r) Radio, Television, V.H.F., (2) Industrialand general electronic equipment, and (3) Electronictest equipment for all types of applications, particularlyas in No. r above. Assistance, financial or practical,would be available to those originating suitableprojects and any information given would be treatedin the strictest confidence. Write, giving fullestpossible details to Box 664, " Electronic Engineering."

SITUATIONS VACANTA.M.I.E.E., City and Guilds, etc., on " NO PASS -NO FEE" terms. Over 95% Successes. For fulldetails of modern courses in all branches of ElectricalTechnology send for our /12 -page handbook-FREEand post-free. B.I.E.T., (Dept. 337B), 17 StratfordPlace, London,

TECHNICIAN WANTED for research and develop-ment work in connection with Radio Condensermanufacture for Government. Also Works Managercapable of handling labour. Applicants need not haveactual Condenser manufacturing experience butelectrical knowledge essential. Box No. 662, "ElectronicEngineering."

WANTEDWE OFFER cash for good modern Communicationand all -wave Receivers.-A.C.S. Radio, 44, WidmoreRoad, Bromley.

HANK BUSHES and screws to your specifications(Repetition Work). Quick deliveries. D.T.Co.,' Electronic Engineering," Box No. 654.

FIRM of Electrical Engineers engaged on essentialwork in Earl's Court area require x Time and MotionStudy and Estimating Engineer, IlSenior Draughtsman(Chief) to take charge of Drawing Office and I Superin-tendent for Training School. Write with'-full details toBox 66o, " Electronic Engineering."

RADIO VALVE manufacturing facilities wanted byLondon Research firm. " Electronic Engineering,Box 659.

Makes 30 im-portant tests,

100 to 750 volts. A.C.

'iii, Ideal r RadioEngineers. Fromfo Wh ole-

salers or direct. Send for Leaflet L24.

RUNBAKENMANCHESTEM

GALPINS ELECTRICALSTORES

" Fairview" London Road, Wrotham, Kent,TERMS : Cash with order. No C.O.D.

(Eire and Northern Ireland orders cannot beaccepted.)

HEADPHONES, 120 ohm, Secondhand, completewith headband and cords, in perfect working order.Price 7/6 per pair, post free.INSTRUMENT METAL RECTIFIERS, by famousmakers, 10 M/A full load working. Price 15/. each,post free.TUNGSTEN CONTACTS, 3/16 In. dia., a pairmounted on spring blades also two high quality puresilver contacts, 3/16 ins. dia., also on spring blades, fitfor heavy duty, new and unused, there is enough baseto remove for other work. Price the set of fourContacts, 5/-, post free.MOVING COIL ampmeter, 2} in. dia., panelmounting, reading 0-20 amp., F.S.D. 15 M/A. Price30/- post free.ZENITH Vitreous resistances, size 5 in. x 1 in.,5,000 ohms. 100 and 150 M/A (two sizes). Price 4/ -each, post free.ELECTRIC LIGHT CHECK METERS, well-knownmakers, first-class condition, electrically guaranteed,for A.G. mains 200/250 volts 50-cy. I phase 5 amp. load10/- each ; 10 amp. load, 12/6, carriage 1/..I.K.W. FIRE ELEMENTS, mounted, size16 x If x 1 ins., for 220 volts A.C. or D.C., as new6/-, post free.ff WATT WIRE END RESISTANCES, new andunused, assorted sizes (our assortment), 6/6 per doz.,post free.VOLTMETERS, 2} in. dia., panel mounting, movingcoil, range 0-120 volts, F.S.D., very low, modernmeters by famous makers. Price, 32/6 post free.AMPMETERS, description as above, range 0.1iamps., Price, 25/- post free.KLAXON MOTORS, for 220 volts D.C., shuntwound, ball bearing, fitted reduction gear givingspeed of 700 r.p.m. High-grade job. Condition asnew. Price, 50/- carriage paid.D.C. MOTORS, shunt wound, ball bearing, * h.p.,high grade. Condition as new. Can be offered for110 volts or 220 volts. as required. Price eithervoltage, 40/- carriage paid.

THE BOOKS forI YOUEXPERIMENTAL RADIO ENGINEERING

By E. T. A. Rapson, A.C.G.I., D.I.C., etc. Assisted byE. G. Ackermann. This book sets out a number ofexperiments and methods of measurement suitable fora three or four years' course in radio engineering at aTechnical college. A few of them require ratherspecialised apparatus, but the majority may be carriedout with standard laboratory equipment. 8s. 6d. net.

PROBLEMS IN RADIO ENGINEERING

By E. T. A. Rapson, A.C.G.I., D.I.C., etc. A classifiedcollection of examination questions set from time totime by some of the more important examining bodiesin Radio Communication, together with some usefulnotes and formulae bearing on the different groups ofquestions, and answers to those questions which arecapable of a numerical solution. Fifth Edition. 5s. net.

WIRELESS TERMS EXPLAINEDBy " Decibel." An invaluable guide to the technicalterms used in books and articles on wireless, and inmanufacturers' catalogues. It explains the meaning ofevery term in the fullest and clearest manner, withnumerous illustrations, and gives additional informa-tion where this may prove useful. Second Edition3s. net.

Send for FREE Technical Cata-logue from Pitman's. It containsdetails of over thirty books onRadio, and will cure any techni-cal headache. Get one to -day.

39 PARKER STREET, KINGSWAY

PITMAN


August, 1943 Electronic Engineering

Wartime installationsshow more conclusivelythan ever that

you can

(kaCicSOUND Equip;,I0,42 V C eat.4

30 -watt Amplifier with Radio.There are TRIX amplifiers

from 5-500watts.

TRIX ELECTRICAL CO. LTD., 65, Bol s St.,London, W.I. 'Phone EUS 547t/2

'Grams : Tthadio, Wesdo, London.

LAMINATIONS & SCREENSRADIOMETAL PERMALLOY

SILICON ALLOYS

Electrical Sound & Television Patents Ltd.12 PEMBROKE ST., N.I

" SYSTEMATIC RADIO SERVICING "A practical method devised and employed by JBull. Also a catalogue of many Radio Service Aidsincluding " History of Faults," " Job Cards,"which almost repair the sets, " Valve Base DataCards," and perhaps, most important, a Rectifierwhich will replace any of the popular Universalvalves such as 12Z3, 25Z5, IDS, U30, 40SUA, etc.Price Is. 7d. post free.V.E.S. (A), Radio House, Melthorne Drive.

Ruislip.

*BOOKSELLERS TO THE WORLD M'Nearly 3,000,000 new and Second-hand Books on

Engineering and every other subject.Books Bought.

119-125 Charing Cross Road, London, W.C.2Tele : Gerrard 5660 (16 lines). Open 9-6 Inc. Sat.

nIERM=MS=MIIIIMISInesca

to customers' specifica-tions or in accordancewith standard list.

W. BRYAN SAVAGE LTD.Westmoreland Rood, London. N.W.9. Cohndale 7131

\REGISTERED TRADE MARK

BONDEDPAPER INSULATION

OF HIGH MECHANICALSTRENGTH

AND MOULDEDRESIN WITHOUT

FILLER.BOTH HAVE

EXCELLENTELECTRICAL

PROPERTIES.I

MICANITE & INSULATORSCOMPANY

WALTHAMSTOW

.010014.

M I C`41.410151,

Telephone: LARkswood 1044 (Pte Br. Etch)

LIMITEDLONDON E.I7

YOU can trust Ardux because others trusttheir lives to it. Ardux has been used

for joining stress -carrying aircraft structures. Arduxis, of course, officially approved for aircraft use.Here is an independent test report from a well-known aircraft firm :-

" Of the many adhesives on which we havecarried out tests of mechanical strength Ardux isto date the only one in which there was no failureof the adhesive layer. In addition Arduxproved equally good with either a smooth orrough surface of sheet, thus showing it to be anadhesive in the true sense. Fatigue tests suggestthat there is no weakening of the bond undervibration."

AERO RESEARCH LTD., DUXFORD, CAMBRIDGETelephone : Sawston 167-8

WAIT FOR IT !-and when normal conditions are re-stored, Reliance Potentiometers, incor-porating our many years of experience,will again be available.Until then National requirements mustcome first. if we can help you in thisconnection, we will. Therefore do nothesitate to write us.

RELIANCEManufacturing Co. (Southwark) Ltd.Sutherland Road, Higham Hill,Walthamstow. E. 17.

Telephone-Larkswood 3245

THIS series of Taylormeters represent thevery latest in multi -range measuring instrument

design and construction.

Write for complete specification to :-T AY L 0 R ELECTRICAL INSTRUMENTS LIMITED,

419-424 Montrose Avenue, SLOUGH, Bucks. Tel.: Slough 21381 (4 lines)

Greenwood


iv Electronic Engineering

THE SYMBOL\OF

RELI

We quote (and substanti to on test) figures giving the

sensitivity, selectivity a d general performance of

the " 358X " receiver. ut this is only half the story.

Service requirements di tate the highest reliability,

made possible in this receiver by many years'

experience in the d ign and production of

specialized radio com onents and apparatus.

The continuous reliab 'ty exemplified by the

" 358X " is the outco e of efficient over-all

design allied with ext me attention to elec-

trical and mechani details. Complete

technical details avail- e in 30 -page Instruc-

August, 1943

Communication Receiver

tional Booklet on " 58X " including all

circuit values. P 2,6, post free.

14, SOHO ST. OXFORD ST. LONDON W.I. Telephone GERRARD 2089

Printed in Great Britain by The Press at Coombelands, Ltd., Addlestone, Surrey, for the Proprietors and Publishers, Hulton Press, Ltd., 43-44 Shoe Lane London, E.C.4Sole Agents for Australia and New Zealand : Gordon and Gotch (Alsio), Ltd. South Africa : Central News Agency, Ltd.

Registered for Transmission by Canadian Magazine Post.


Documents

Engineering - World Radio History