t-1414vcidarld...good and bad picture areas limyl enses or rojection ome mechanicalin eceiver eli...

$: T-1414VCIdaRLD...GOOD AND BAD PICTURE AREAS LIMYL ENSES OR ROJECTION OME MECHANICALIN ECEIVER Eli ELEVISION SYSTEM SHORT WAVES T-1414VCIdaRLD JULY 1939 No. 137 Vol. XII. C\NVitkivikilittitit$
GOOD AND BAD PICTURE AREAS LIMYL

ENSESORROJECTION

OMEMECHANICALIN

ECEIVER

EliELEVISION

SYSTEM

SHORTWAVES

T-1414VCIdaRLDJULY 1939

No. 137 Vol. XII.

C\NVitkivikilittitit

E.M.I.

ositoSISISIA

014G-1STANCE BATTERY S. -W. RECEIVERUSH-PULL KT8 TRANSMITTER

,ONE -METRE OSCILLATORBERNARD JONES PUBLICATIONS LTD.CHANSITOR HOUSE. CHANCERY LANE

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-THE FIRST TELEVISION JOURNAL IN THE WORLD

ILLEVElfitlAND

SHORT-WAVE WORLD JULY, 1939

Seeshop-wherevergovernmentOf Ironmongers-inAskcompactWriteLeaflet

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works and by leading engineers and manufacturers.tins, 4d., Ed., 1/4 and VB.

see the FLUXITE SMALL -SPACE SOLDERING SET-but substantial-complete with full instructions, 7/6.

for Free Book on the art of " soft " soldering and ask foron CASE -HARDENING STEEL and TEMPERING TOOLS

with FLUXITE.To CYCLISTS ! Your wheels will NOT keep round and true unless the spokesore tied with fine wire at the crossings and SOLDERED. This makes a muchstronger wheel. It's simple-with FLUXITE-but IMPORTANT.

THE FLUXITE GUNIs always ready to put Fluxlte onthe soldering job Instantly. Alittle pressure places the right ell,111---- .

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11

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IN places as far distant as Taunton and Chelten-ham, Belling -Lee Television Aerial Installationsare giving consistently good results. AtBrighton-forty miles beyond the limits of theService Area-reception is reported excellent.Some of these achievements may not do justiceto television as an entertainment, but they showhow experts and enthusiasts rely on Belling -LeeTelevision Aerials both for experimentalpurpo es and for private amusement.

Four standard kits are available :No. 321K. Wall mounting di -pole without reflectorbut with stand-off arm and bracket, 65 ft. feeder cable,lightning arrestor and plug and socket for skirting

21 gns.No. 32ILK. As above but with chimney lashing(no mast) ... ... 3 gns.No. 323CK. Masthead di -pole and reflector, completewith 100 ft. balanced feeder cable, lightning arrestorand plug and socket for skirtingNo. 323LK. As above but with 16 -ft. mast and necessarygalvanised brackets and cables for lashing to chimneystack gns.

Prices do not apply to Eire

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'ingYISIOtiJULY, 1939

FLEXIBLE DRIVINGSHAFT.

For front panel control ofawkwardly placed com-ponents. Drives through90 degrees perfectly.Cable length 51 in. No.1096, 3,'6.

ANDSHORT-WAVE WORLD

RESULTSFOR BEST SHORT-WAVE

AAIw f USE EDDYSTONE COMPONENTSInsist on EddystoneYOURSELF and you'llquickly know why.Eddystone is attract-ing so many adherents.

NEW TYPEMICRODENSER

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1070.A full vision dual speed dialwith 20 I & 100 :1 speeds.Well graduated scale, readingincreasing as frequency in-creases. For 1 -in. panel andd -in. spindles. Ideal forH.F. tuning. Price 10,6.

The superiority of Eddy-stone Short -Wave Com-ponents is sending the salesleaping up each month.

AIR DIELECTRICTRIMMER.

DL -9 insulation, 3 to 65 mmfd.For all pre-set and trimming purposesand particularly for use with I.F.transformers. Cat. No. 978. Price3 6.

NEUTRALISING CONDENSER.Cat. No. 1088.

For H.F. circuits using low -capacitytriodes. Maximum voltage 2,000volts D.C. Capacity variation 1-8mmfd. Frequentite pillar insulatormounting, insulating adjusting knob.

Price 6,6.

ASK YOUR DEALER-OR POST COUPON for CATALOGUE ofManufacturer,.

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SHORT-WAVE COMPONENTS

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THE EDISON SWAN ELECTRIC CO. LTD. 155 (HARING (ROSS RD., LONDON, W.(.2

For full particulars write to Technical Service Department

386

No. 137 VOL XII JULY, 1939

and SHORT-WAVE WORLDSpecial Features

PAO&New G.E.C. Television Receiver ... 388E.M.I. Cinema Projector ... 389Lenses for Cathode-ray Projection 391

The Du Mont Television System ... 394The Oscillograph for Television

Receiver Servicing ... ... 397

Dipole Aerial with New Features ... 400

More Progress with Home Mechani-cal Receiver ... ... 404

Long-distance Battery S.W. Receiver 417

Beam Aerials and S.W. Programmes 420

Building a 1 -metre Oscillator ... 421

Push-pull liT8 Transmitter ... 423

5 -metre Crystal Exciter Unit ... 429Frame Aerial Receiver 430

TELEVISIONAND

SHORT-WAVE WORLDProprietors :

BERNARD JONES PUBLICATIONS, LTD.

Editor -in -Chief:BERNARD E. JONES.

Editor :H. CORBISHLEY, F.T.S.

Short -Wave Editor : KENNETH LOWERS

Editorial, Advertising and PublishingOffices:

Chansitor House, 38, Chancery Lane,London, W.C.2.

Telephones : Holborn 6158, 6:59.Telegrams : Beejapee, Holb., London.Subscription Rates : Post paid to anypart of the world -3 months, 3/6 ;

6 months, 7/- ; 12 months, 14/-.Published Monthly -1 /- net.

(On the first day of the month).Contributions are invited and will bepromptly considered. Correspondenceshould be addressed according to itsnature, to the Editor, the AdvertisementManager, or the Publisher, " Tele-vision and Short-wave World," ChansitorHouse, Chancery Lane, London, W.C.2.

IMPORTANT" Television and Short-wave World " is regis-tered at the General Post Office, London, fortransmission to Canada and Newfoundlandby Magazine Post. Entered as Second-classmail matter, Boston, Mass.

COMMENT OF THE MONTHUnreasonable Delay

QUITE a considerable number of interests are concerned about thedevelopment of television and several have sent deputations to the

Postmaster -General in order to make representations regarding its effectupon their own particular sphere of activities. These have included theradio manufacturers, radio retailers, the cinema industry and theatricalprofessions.

The answer in each case has been that the subject is under considera-tion by the Television Advisory Committee and that their subjectionswould receive sympathetic consideration when the time comes. In themeantime not the slightest indication of what is being done or whensomething will be done comes from the Committee. Manufacturers andtrade and professional interests are wholly in the dark despite the factthat immediate decisions in view of developments that are taking placein other countries are becoming of vital importance if we are to retainthe lead we now have.

Two of the matters of the most pressing importance are pronounce-ments on the erection of a transmitter in the Midlands and the positionof the cinema with regard to television. The delay has been ascribed tovarious reasons, foremost of which are the international situation andfinance. Nether of these, however, should be the concern of the AdvisoryCommittee which is of a semi -technical character; its immediate prob-lems are the technical possibilities of a station in the Midlands and theeconomic aspects of cinema television. The larger problems must ulti-mately be those of the Government.

The Popularity of Morse CodeDURING the past year or so there has been a gradual return to effi-cient morse code operating from the more simple and popular tele-

phony operating.The reasons for this change of heart by amateurs is not easy to dis-

cover for until last year speech was very rapidly taking the place ofmorse code. Amplifiers and all the equipment necessary for telephonyoperation are inexpensive.

Coincident with the crisis of last year, there was a sudden demandfor morse keys, and, ever since that time this demand has remainedquite steady. The change over might have been caused by very poorconditions on short waves making it more simple to communicate overlong distances with morse code than with telephony. Alternatively, itmay have been due to the demand of the Army; Navy and Air Forcefor proficient morse code operators.

At the present time the Three Services are training as many amateursas they can induce to join their ranks, so that operating on amateur fre-quencies is now of a higher standard than ever before. As these Service -trained operators are being taught a definite system of procedure, they aretaking a pride in operating, not only on Service frequencies, but also wheninter -communicating on amateur frequencies.

387

IELEYSIOilAND

SHORT-WAVE WORLD

The new G.E.C. BT.0124 combined televisionand all -wave auto -radiogram.

ANEW luxury addition has beenmade to the G.E.C. range oftelevision receivers. This is a

television and all -wave auto -radio-gram for A.C. mains at 72 guineas.The instrument is operated almostentirely by automatic press buttoncontrol, and gives the popular sizedpicture of to in. by 8 in.

Half of the cabinet face follows astraight vertical line behind whichthe screen of the cathode-ray tube isrecessed at an angle sloped for com-fortable viewing, thus providing acabinet overhang that shelters thepicture from unwanted light and re-flections. The other side of thecabinet slopes evenly back, so thatthe gramophone deck takes up thesmallest space necessary, and theradio tuning scale can be seen with-out stooping, with all the controls inthe simplest position for operating.

In addition to eight buttons forstation selection, there are sevenadditional buttons for purposes ofcontrol. The first button brings com-plete television entertainment; thesecond, television sound only for thespecial high fidelity sound broadcaststhat are transmitted daily by theB.B.C.; the third brings the gramo-phone equipment into operation ; andthe fourth, fifth and sixth cover theshort, medium and long sound broad-cast wavebands. No matter whichof these buttons is pressed first, itwill automatically switch on the set,leaving the seventh and last button toswitch it off.

The radio chassis incorporated

JULY, 1939

A NEW G.E.C. TELEVISIONRECEIVER

COMBINED TELEVISION AND ALL -WAVEAUTO -RADIOGRAM

employs a very advanced 5 -valvesuperheterodyne all -wave circuit, em-bodying A.V.C. and tone compensa-tion. Its range is almost unlimited,and in addition to the choice of anyeight favourite stations that the lis-tener can make by push-button, anyother programme can, of course, betuned in by hand. Incidentally, theselection of push-button stations canbe changed as often as the userwishes in a matter of a few seconds.

SimpleControl

The manually operated controls inthe front on the cabinet are few andextremely simple, combining a com-plete control of all the functions ofthe instrument. The first and secondvary the picture brightness and theblack -to -white contrast of the tele-vision picture. The third is a volumecontrol, and the fourth a tone con-trol, both being operative for tele-vision, radio and gramophone repro-duction.

The gramophone equipment is en-tirely automatic in operation and willplay batches of eight to in. or 12 in.records consecutively ; at the conclu-sion of the last, the mechanism isswitched off, and any record may berejected during playing.

The sensitivity of the 18 -valve tele-vision chassis is of a very high order,so that the instrument can be in-stalled in any part of the service area.

This instrument is the first of anew series of G.E.C. television re-ceivers to be released this season.It is actually the eighth successiveG.E.C. television receiver since tele-vision transmissions began. Themodel is known as the BT.o124.

Landmarks in TelevisionDevelopment

ALTHOUGH it is generallyassumed that television is aloth century development, its

basic principles were known anddemonstrated in the r880's ! Sil-houettes and crude outlines weretelevised, transmitted over wires for

short distances, and finally repro-duced.

For several decades thereafter,television was rather dormant. Itwas regarded as an interestinglaboratory subject of experiment butit appeared doubtful whether it couldever be perfected.

Progress was seriously hinderedby the lack of a satisfactory mediumfor transmitting, but in the period1914-1918, radio developed to suchan extent that shortly after it en-tered the home, and the old crystalsets gave way to valve receivers.

It was discovered that crude pic-tures could be sent through the airon radio waves, and experimentersamong whom was J. L. Baird,attacked the television problem anew.In America the Radio Corporation ofAmerica, was among the first toenter the field.

Of relevant importance are thefollowing dates and the discoveriesand progress made all have theirsignificance in development as weknow it to -day.

1676-Olaus Roemer discoveredthat light travels at finite velocity.

18I7-Berzelius discoveredselenium.

1830-Joseph N. Niepce and LouisDaguerre produced the first practi-cal system of photography.

1845-Faraday found that a ray oflight polarised in a certain plane canbe diverted by action of a magnet.

1857-Geissler produced the firstglass vacuum tube.

1873-Light-sensitive properties ofselenium discovered by a telegraphoperator named May, indicating thatlight values could be converted intoequivalent electrical values.

1878-Sir William Crookes in-vented the Crookes' tube, and demon-strated cathode rays.

1883-Edison discovered t h e" Edison effect," occurring in anincandescent lamp. An electric cur-rent was made to pass through spacefrom a burning filament to anadjacent metallic plate.

1884-Paul Nipkow patented thetelevision scanning disc.

(Continued on page 39o.)

388

JULY, 1939*r.11;IY1g*I0t1 _a....

ANDSHORT-WAVE WORLD

THE E.M.I. CINEMAPROJECTOR

As mentioned in last month's issue, Electrical and Musical Industries Limited havenow produced cinema television equipment which was first demonstrated privately

on Derby Day.

THE E.M.I. television equip-ment for cinemas is the thirdof this class which is now

available in this country, and thoughat the present time the field of use isextremely limited it is evident thatmanufacturers are preparing for thetime when cinema television be-comes general and equipment willbecome essential to every well-equipped cinema.

The E.M.I. television projectionequipment consists essentially of twoparts : (r) the actual projection ap-paratus used in the auditorium, and(2) the "driving" units which can besituated in a back -stage or other con-venient equipment room.

TheProjector

The actual projection apparatus ofwhich photographs are shown on thispage and the cover comprises scan-ning and modulation amplifiers, tube

A rear view of the E.M.I. Projector showing unit, lens system and control panels.the panels from which complete control of the The extreme compactness of the pro-

equipmentcan_be effected. jector makes it eminently suitable forinstallation in any theatre with little

alteration to the existing seatingarrangemeints, particular attentionhaving been given in this respect tothe design. The usual situation ofthis equipment would be at the frontof the auditorium, but it is of such anature that where the design of 'thetheatre will permit, it could alterna-tively be mounted on a lift on thefloor of the auditorium, in much thesame way as an organ console, andcould, therefore, be lowered out ofthe way when not required.

The angle of projection can bealtered so that, by suitable inclinationof the screen, the best viewing con-ditions can easily be obtained. Inorder to permit of this, the tube unitand lens system of the projector aremounted on a framework hinged atthe back, and with a simple raisingand lowering device at the front.Although, in general, the auditoriumwill probably be the most convenientlocation for the projector, the con-structional arrangements of certaincinemas may permit of alternativepositions. Where, for instance,the front line of the circle isabout so ft. or so from the screen,

389

.1.r.a.a;41 P/SLOtiAND

SHORT-WAVE WORLD

CONTROL PANEL

(MODULATIONAMPLIFIER

SCANNINGAMPLIFIER

TUBE UNIT

MICERIC MUSICAL iNOUTITIIS LTA.CINEMA TELEVISION EQUIPMENT

AERIAL

RADIORECEIVER

(UNMOORPANEL

POWERSUPPLY

the projector could, if preferred, beaccommodated there instead of in theauditorium. Back -projection is alsopossible. With the projector situatedapproximately so ft. in front of thecinema screen a picture i5 ft. by12 ft. 6 ins. is provided which is largeenough for satisfactory viewing evenin the largest cinemas.

Projection distance may be in-creased with a corresponding increasein size of pictures, still with sufficientillumination. The "drive" appara-tus is operated by remote controlfrom the projector and may, there-fore, be some distance away. Itcomprises vertical racks, a monitorand a compact and safe high-tensionunit. Included in this equipment arethe vision and sound receiver and thecontactor panel for remote operationof the equipment and power supplyunits. A special feature of the de-sign of the contactor panel is that thecircuits are interlocked in such a wayas to ensure perfect safety of theequipment.

An independent monitor is pro-vided for purposes of initial adjust-ment of the apparatus in the equip-ment room. High-tension supply forthe complete equipment is obtained

NMSIONuNir

t_ EQUIPMENT ROOM

nMONITOR

This is a schematicdiagram of thearrangement of theE.M.I. cinema tele-vision equipment.The projector is inthe auditorium andthe drive unit in aseparate room is

provided with remotecontrol.

from the extra hgh tension unitwhich is housed in the equipmentroom. This unit, which is of specialdesign, is particularly compact andis absolutely safe in use.

The installation includes provisionand erection of the aerial most suitedto the particular locality in which thegear is to be used.

" Landmarks in TelevisionDevelopments "

(Continued from page 3 8 8)

i888-Photoelectric cells werebuilt.

1890-C. Francis Jenkins beganexperimenting with apparatus thatcould be used with the Nipkow scan-ning`disc.

1906-Lee de Forest invented thethree -element vacuum tube with afilament, plate and grid.

1925-C. F. Jenkins demonstratedapparatus which showed far-off,moving objects, or " shadow -graphs."

" Television and Short-wave World "

circulates in all parts of the world.

JULY, 1939

1926-J. L. Baird, publicly demon-strated television transmission bywireless and wire by sending half-tone moving pictures from point topoint.

1928-First television drama, "TheQueen's Messenger," broadcast fromWGY's studios, Schenectady.

1929-Vladimir Zworykin, ofRCA, demonstrated a non -mechanicalreceiver using a special cathode-raytube called the " Kinescope."

1930-First showing of televisionin a theatre. The programme wasbroadcast from the General ElectricLaboratories to Proctor's Theatre,Schenectady.

1933-After io years of workZworykin announced success of his" Iconoscope," the modern tele-vision camera tube.

1934-New television camera tubedemonstrated by P. T. Farnsworth,in Philadelphia.

1935 --New type of wire line, thecoaxial cable, capable of transmittingtelevision signals, announced by BellTelephone Laboratories.

Back Issues WantedA correspondent, who wishes to

complete his volumes of TELEVISIONrequires the following issues whichare now out of print. If any readerhas copies of these for disposal weshall be glad to receive a postcardstating which are available.

1931. September, October.1932. April.1933. March, October, Novem-

ber, December.1934. January, April.1935. March, June, October.1936. January, February, March,

April, May, July.1937. April, December.1938. January.

Television InterferenceA new publication has recently been

issued by the British Standard Insti-tution devoted to radio interferencesuppression for automobiles andstationary internal combustion en-gines, which is the result of workcarried out with the co-operation ofthe Society of Motor Manufacturersand Traders, the B.B.C., the Elec-trical Research Association and theG. P .0.

This will be of interest to all whosuffer from interference not only withtheir television receivers, but also onshort -waves generally. The speci-fication (B.S. 833/1939) 15 priced2 S . 2d., post free.

390

JULY, 1939

TELEYISIMIAND

SHORT-WAVE WORLD

LENSES FOR CATHODE-RAYPROJECTION

THE FACTORS GOVERNING THEIR CHOICE AND USEBy Arthur Cox (Aldis Bros. Ltd.)

TO understand what type of lensshould be used in a given tele-vision layout involving the pro-

jection of a cathode-ray image, re-quires a knowledge of a few proper-ties of lenses.

Suppose that we have a parallelbeam of light incident on a lens, alongits axis, as shown in Fig. 1. In aperfectly corrected lens, free from

Axis

principal planes PP(I) and PP(2) andfocal points FP(I) and FP(2) asshown. The focal length is F. Thislens forms an image I of an object 0.If the distance of the object 0 fromthe first principal plane is U, find thedistance of the image from the secondprincipal plane is V, then there is arelation between U, V, and F. Thisrelation is :

AxiS Fig. 1. Diagramshowing the char-acteristics of a per-

fect lens.

all defects or aberrations, all the ray sof light would be refracted so as togo through the point FP. This is the" focal point." The distance BF,from the vertex of the rearmost lensto the focal point, is the " backfocus."

If the emegent rays are producedbackwards, so that each meets thecontinuation of the incident ray fromwhich it is derived, then the pointsof intersection are in a plane PP.This plane PP is a "principal plane."The distance PP to FP is the "equiv-alent focus," marked EF in thefigure. When a lens maker gives thefocal length, it is always understoodthat this refers to the equivalentfocus. ,The makers can supply, veryreadily as a rule, the back focus of alens, if this is required to ensure thecorrect design of the layout.

When the lens is turned round sothat the light traverses it in the oppo-site direction, we get another focalpoint, another back focus, and an-other principle plane, but the focallength is the same as before. Thus,for any lens we have two focal points,two principal planes and back foci,but only one focal length.

Suppose that we have a lens with

I I I

U V FThe image formed is upside downand as a rule is magnified. If themagnification is M we have :

VM = --

UThese two relations lead to the re-sults, that if we have a lens of focal

Fig. 2. Diagramshowing the lorma-tion of an image by

a perfect lens.

(I)

(2)

the separation of the principal planes,we get for the approximate overalllength from object to image :

LL=(M+2)F. F - (4)

M + 2

For example, if we have a lens of6 in. focal length, and require amagnification sufficient to bring a2 in. by 2 in. image on a cathode-raytube to a 2 ft. by 2 ft. image on ascreen-i.e., a magnification M =12-then the formula (4) gives an ap-proximate overall length of 7 ft.

The next consideration is theamount of light received and trans-mitted by the lens.

The f/number of a lens is the dia-meter of the effective part of thefront lens divided into the equiva-lent focus. By " effective " we meanthat part which will transmit all thelight incident, none being obstructedby stops and diaphragms inside thebody of the lens. The smaller thef/number, the more light is trans-mitted through the lens.

It is sufficiently accurate to takethe distance of the cathode-ray screenfrom the back of the lens as theback focus of the lens. This is true,as a rule, within a fraction of an inchfor fairly large magnifications.

We can also take, as a reasonable

length F, and requireM, then :

U= (t+-)F. V=(M+ (3)M

a magnification

Fand if we leave out of account - and

M

assumption, that the intensity of thelight emitted by an element of thetube screen is given by Lambert'sLaw. According to this the inten-sity I(x) in a direction making anangle X° with the perpendicular tothe surface is given by :

1(x) = I(o) Cosine x (5)

391

ILLEYISIOtiAND


ABERRATIONS IN LENSESThe fraction of the light emitted

by a small central spot E on thescreen, that is collected by the lens,is :

Fraction collected - ... (6)1+4Na

where N is the f/number of the lens.This result is rather interesting, as

it shows that it is of no advantage to

constructed that the image formed bythe blue rays is in the same positionand of the same size as that formedby the red rays. That is, " chroma-tic aberration " is to be eliminated.

(2) Rays of light that passthrough the edge of a lens are morestrongly bent than rays passingthrough the centre. This may resultin a point of light on the axis being

CATHODE RAYTUBE

LENS

Fig. 3. Diagram- showing the position

of lens and cathode-ray screen.

design a lens to bring the back focusdown; that is, as far as the centralbrightness of the image is con-cerned.

As the element of screen E movesaway from the centre, the fraction oflight collected becomes smaller. Atfirst it is a slow decrease, and thenit becomes more rapid. This may beleft out of consideration here. As arule a lens gives a sufficiently brightpicture over the whole region inwhich it gives good definition.

The formula (6) shows quite clearlythat to get the brightest image thef/number N has to be made as smallas possible. The trouble now arisesthat it is difficult to get a lens with asmall f/number and yet able to covera relatively large field.

The above theory was worked outon the assumption that the lens wasperfect. Actually there are six waysin which a lens may, and will, fallaway from perfection. Six ways, thatis, as a rough guide, but good enoughfor our purpose. These defects oraberrations are:-

(I) Chromatic aberration.(2) Spherical aberration.(3) Coma.(4) Astigmatism.(5) Curvature of field.(6) Distortion.

(I) The amount by which light isbent when crossing a glass surfacedepends both on the glass and on thecolour of the light. This may resultin the blue rays of light coming to ashorter focus, say, than the red rays,and the image formed by the bluelight may not only be in a differentplane, but if this is corrected, of dif-ferent size. The lens has so to be

reproduced in the image as a blurredcircular patch of light instead of abright point. This is " sphericalaberration."

(3) Some of the rays of light froma point off the axis, that should passthrough the margins of the compon-ent lenses, may be shut off by stopsand diaphragms. A possible resultof this is that an extra -axial point isreproduced as a bright spot of lightand a flair like the tail of a comet.This is " coma." When the tail oflight stretches away from the axiswe have " coma out " ; when itstretches inwards we have " comain."

(4) The rays of light, from a

is midway between the focal lines.In this position the image of thepoint of light is a small circular orelliptic patch, the " circle of leastconfusion."

(5) Even if all the rays from apoint of light emerge after refractionto come to a focus at a point, thereis no guarantee that all these imagepoints corresponding to object pointsin a plane will themselves be in aplane. They may be on a curvedsurface,, such as part of a sphere. Inthis case we have " curvature offield."

(6) Finally, even if a sharp focus,not spoilt by any of these five aber-rations, is obtained on a flat surface,there remains still the possibility of adistorted image. Straight lines maybe focused sharply on a screen ascurved lines. A grille of straightlines may be reproduced pincushion -or barrel -shaped, as shown in Fig. 4.

The aberrations (2)-(6) are the" Seidel " or " first order aberra-tions. With lenses of greater aper-ture and field there enter secondaryand higher aberrations, which be-come of increasing and preponderantimportance with the increase ofaperture.

The aberrations are corrected by askilful choice of radii for the lenscurves, of lens thicknesses, and oflens separations. The more compon-ent glasses used in the lens, the betterthe correction that can be obtained.

Fig. 4. Diagramshowing the effects oftwo types of coma

and distortion.

COMA OuT

x

AXIS

X

COMA IN AXIS

PINCUSHIONDISTORTION

BARRELDi STORTION

point away from the lens axis, mayemerge after refraction in a bundleof rays of such a form that each raygoes through a fine slit or line lj andthen through another line or slit 12.These are at right angles, and arethe first and second " focal lines."In this case we have " astigmatism."The best focus we can get, when alens suffers from astigmatism only,

The advantages of incorporating anumber of component glasses arecomparable to those derived fromusing a large number of stages in aradio circuit. Each stage or glasscan work better because too much isnot demanded of it. The disadvan-tage is the same-increased cost.

The attempts that have been madeto eliminate the Seidel aberrations,

392

IELVISIONJULY, 1939

and the others that are important atwide apertures, have led to variousmore or less standardised types oflenses. Naturally the type dependson the use to which it is to be put.

Two types of lenses are availablefor use in projecting cathode-rayimages. These are projection lensesand anastigmats.

The prototype of the projectionlens is the Petzval lens. Designed

CROWNGLASS

FLINTGLASS

Fig. 5. Petzval-type lens.

about 1845 it is still in vogue to -daywith certain modifications.

The Petzval lens consists of twopairs of lenses, each pair comprisinga crown glass and a flint glass. Thesepairs are mounted in a tube at a rela-tively large separation. The modifi-cations introduced consist mainly inchanging the order of crown andflint glasses, in cementing or leavingthem uncemented, and in usingglasses developed comparatively re-cently. This lens can be made withquite large apertures, F/2 and F/3being not unusual.

The construction is of a simpleform. The central definition is fre-quently superb. The aperture iswhat is needed to have a large light -gathering power. The defect of thistype of lens is that only a small fieldis covered.

An excellent example of the Petzvaltype is an Aldis lens designed forcinema projection work. This lenshas an aperture of F/2.2 and with afocal length of 4 in. gives superb pro-jection from a circle 1.2 in. in dia-meter. This result may be taken asa general rough guide. A projectionlens will give excellent projection, atthis aperture, from a circle of dia-meter not greater than one-third ofthe focal length. Naturally somelenses may have a larger coveringpower, but this result is true of thegeneral run.

An anastigmat lens can best bedescribed as comprising a number ofcomponent lenses packed togethercomparatively closely. The qualityof definition given by modern anastig-mats is astoundingly good over quitelarge fields even at large apertures.Designs have been patented for anas-tigmats working at about F/2, whichclaim to cover a field of diameterabout twice the focal length.

The more normal type tends to besimpler and cheaper in constructionthan wide-angle, wide -aperture anas-tigmats, and this factor may be ofconsiderable importance in the manu-facture of television sets for themillion.

An economical anastigmat is, forexample, the Aldis 2 in. F/3 lens.Fig. 6 shows the construction.

This lens will give excellent defini-tion over a circle of diameter aboutxi in. to 2 in. Again, this result maybe taken as typical of anastigmats,that are not specifically stated to bewide-angle lenses. A very good

ANDSHORT-WAVE WORLD

guide is to assume that an anastig-mat will give good projection froma field whose diameter is equal to thefocal length of the lens. The exactfield covered, after this guide hasindicated the approximate focallength of the lens required, may befound from the makers' catalogues.

The advantage of the anastigmatover the projection lens is that for agiven cathode-ray image and given

CROWN

A GLASS- _= - FLINT= GLASS

Fig. 6. 2 -in. F/3 anastigmat.

magnification, there is a muchsmaller overall length, since a smallerfocus lens may be used to cover thetube image. The disadvantage isthat to obtain a lens working at thesame aperture, and giving the samedefinition all over the field as a pro-jection lens, may necessitate a rathermore costly lens, such as those usedin miniature cameras.

Only the user can decide, in eachindividual case, whether for a givencost, the light -gathering power out-weighs the disadvantages of thelarger throw of a projection lens; orwhether, for a given light -gatheringpower, the increased cost of an anas-tigmat is justified. In most cases agood compromise would be to use anF/3 lens of the type shown by Fig. 6,which is not unduly costly and has areasonably large aperture.

Television Receivers areQuite Safe

ONE of the earliest criticisms ofthe cathode-ray receiver when itbecame known that voltages of

3,000-6,000 were employed was thepossibility of fatal accidents by shock.Voltages of this order were unknownin domestic use with the exceptionof certain apparatus of a quasi -medical nature which was known tobe harmless.

An initial problem of designerstherefore was to make the instru-ment quite safe in ordinary use andthis was quite easily accomplished bymaking the interior or any live partaccessible without first disconnectingfrom the mains. Of course, no pieceof apparatus can be made proof

against deliberate interference, butthe chances of shock to the ordinaryuser of a television receiver is cer-tainly much less than with a vacuumcleaner and the results would in allprobability be less dangerous.

Voltage is not the dangerous fac-tor. Frequencies and the amount ofcurrent available are of much greaterimportance, providing the voltage issufficient to force the current throughthe body. For example the voltagegenerated by the average car ignitionsystem is of the order of 15,000 volts,

Mention of " Television and Short-wave

World" when corresponding with

advertisers will ensure prompt attention.

and yet nobody regards such a systemas dangerous although it can give anunpleasant shock.

Comparatively low frequencies arethe most dangerous and with thesethe body will only tolerate a smallamount of current compared with ex-tremely high frequencies. For ex-ample 5o mA. at 5o to 200 cycles canbe dangerous, whereas 75o mA. at100,000 cycles can be tolerated with-out injurious results.

The real danger points are thesecondaries of the high -voltage powertransformers and it is probable thatit is only from these that any realharm would result except under ex-ceptional conditions. Condenser dis-charge, generally speaking, is notdangerous, but it is capable of givinga most unpleasant shock.

B 393

TELEYEJOhAND


THE DUMONT TELEVISION SYSTEMEMPLOYING TRANSMITTED SCANNING IMPULSES

REASONING that it is desirableto provide for extension to pic-tures of even higher definition

than are now accepted as standardwithout the necessity of renderingexisting apparatus obsolete either atthe transmitting or receiving end,the DuMont laboratories haveevolved a television system whichsolves many of the problems entailed.Conversely, it is claimed that high -definition apparatus of this type can

synchronising and sweep -frequencycontrols are therefore unnecessary.

At first it may appear that theaddition of these two sweep signalson two new channels seriouslycomplicates the methods, but advan-tages result therefrom which morethan offset the complication. Receivercontrol is simplified considerablyand the design will permit of recep-tion from numerous stations ofdiffering degrees of definition.

receiver and there simply amplifiedto utilise directly for the scanning.

In this way the receiver will followeven quite radical changes in thescanning raster. The problem ofmaintaining synchronism no longerexists as no synchronising pulses areutilised at the receiver and there isno need for the complicated systemof synchronising pulses with theirprovision for causing the interlaceof scanning.

Camera Tube

Video 0-2 Mc.

MM

WaveForm

Modifier

AudioMicro-phone

WaveForm

Modifier

Audio 0-10 Kc.

15 Kc.Osc.

Amp.

Modulo+.ing

Amp.

MixerModel.Amp.

57 Mc.OSc.

PowerAmp.

PowerAmp.

60 Mc.Osc

Mixer

Fig. 1. Double carrier transmitter for four independent signal;.

be used for a lower definition with-out radical alteration.

TransmittedScanning Impulses

The DuMont television system em-ploys the actual transmission of theentire scanning signals for bothhorizontal and vertical deflection inaddition to the conventional visionmodulating signals and the associa-ted audio -channel signals. The deflec-tion signals are generated exclu-sively at the transmitting station andsent by means of a suitably designedcarrier methods as independent sig-nals -to the receiver, thus simplifyingthe receiver considerably by makingit unnecessary to employ local sweeposcillators for each receiver. Local

Details of this system were given in a paper readbefore The Institute of Radio Engineers, NewYork, by Thomas L. Goldsmith. We are indebtedto " Communications," New York, for the in-formation.

R -FAmp.

56-62 Mc.

1stOct

I65 Mc.Osc.

VideoI -F

7-9 Mc.

F4.95-5.05 Mc.

2nd.Det.

VidenReceiving Tube

J

2 ridOct.

M41

Wave WaveForm Form

Modifier ModifierT.Filter 3 rd.44-16 Kc. Oct.

Filteril- 3rd.HAr

AvfoSignal241

Filter0 - f0 Kc.

AudioSpea ker.

Fig. 2. Double carrier receiver.

The complex equipment in anytransmission system rightly belongsto the transmitter, leaving thereceiver very simple to operate andfree from critical circuits whichmight require frequent attention. Itmay be seen presently how many ofthese advantages are possible whenutilising this new system.

In the DuMont system instead ofthe conventional practice of having aset of sweep -generating oscillatorsat the transmitter controlled by syn-chronising pulses, and having an-other set of sweep oscillators in eachreceiving unit, these synchronised bypulses sent out from the transmitterand filtered from the vision signals,one carefully controlled set of sweepgenerators is employed at the trans-mitting station. These sweep wave-form voltages are used to modulateauxiliary carriers in the transmissionsystem, enabling the actual sweepwave forms to be picked up at the

Two -to -one interlaced scanninghas been achieved quite acceptablywith the synchronising pulse methodalthough the receiving equipment isthereby complicated, but it is not verylikely that higher interlace ratios canbe employed by this method of re-mote control of oscillating circuits.

On the other hand, when the sweeposcillators of the master transmitterof this system have once beenadjusted to the proper frequencies,interlace ratios of four or six are en-tirely practical, as the deflection cir-cuits at the receiver are essentiallyconnected directly with the trans-mitter oscillators and automaticallyremain in step with whatever systemof scanning is being employed at thetransmitter.

FourSignal Channels

The receiver has four signal chan-nels, each of which is quite like

394

TELIVISJOilJULY, 1939

ordinary radio channels, thoughemploying unique frequency charac-teristics. These channels require noadjustment after installation otherthan proper tuning for satisfactoryaudio reception whereupon the re-maining signal channels are at oncein adjustment. There may, of course,be necessity for brilliance controlsassociated with the cathode-ray tube,but in general the set will not bemuch more complicated to operatethan the average broadcast receiver.

A primary advantage of thesystem is the practical possibility ofusing four -to -one or even six -to -oneinterlace, still maintaining sixtyfields or fractional scans per second

sinusoidal wave shapes and are thenmodified to the rather conventionalsaw -tooth signals by means of asimple filter network at the receiver,A cathode-ray tube is desirable em-ploying electrostatic deflection whichvery readily follows changes in thescanning system since electrostaticdeflection plates have practically nofrequency discriminating characteris-tics.

Fig. z shows a double -carrier trans-mitter for the necessary four inde-pendent signals. This systemutilises two separate ultra -high -fre-quency carriers to transmit thesignals.

The two carriers are in adjacent

ANDSHORT-WAVE WORLD

will be desirable to provide blacklevels on the picture signals to elimi-nate undesirable portions of thereturn traces, but these blankingpulses need not be of greater heightthan just sufficient to cause extinctionof the beam, for there is no need oftheir use for synchronising pulses,with the complex amplitude and fre-quency filtering at the receiver. Withsuch a vision signal it is feasible toutilise full hundred per cent. modula-tion of the ultra -high -frequencycarrier with efficient picture produc-ing signal. It is unnecessary tosacrifice 20 to as per Cent. of this verybroad channel for the purpose of syn-chronising pulses.

WaveForm

Modifier

Camera Tube

WoveForm

Modifier

L,$_. _1

LowSweep60-

HighSweep6615

ModulotingAmp.

AudioMicrophone

Audio 0- f0 Kc.

15 Kc.

Osc

Amp.

25 Kc.Osc.

Modul-ating Amp.Amp.

Amp. if

Amp.

Mixer Modul.Amp.

Mixerand

Modul-atingAmp.

Amp.

3 Mc.Osc.

PowerAmp.

57 McOsc.

R -FAmp.

-601.

1st.Oct.

65 Mc.Osc.

I -F6-10 At. --o

Filter0-2 Mc.

Receiving Tube

2nd.Oct.

video

I -F

iln AMA

WaveForm

Modifier

waveForm

Modifier

Filter 4th.14-16 Kc Det.

Al.11.

2.95- "it"3.0554c-J

3rd.Oct.

Filter"").- 1e-32

AutomaticSignalLevel

Control

Filter0-10 Kc.

4th.

AudioSpeaker

Fig. 3. Single carrier transmitter for four independent signals. Fig. 4. Single carrier receiver.

in order to insure absence of flicker,but utilising a correspondingly lowerframe or picture repetition frequency,by means of which a great reductionin signal band width is possible.Even including the extra bands re-quired for the transmission of the in-dependent sweep signals, the entireband necessary for a complete tele-vi-iem transmission is reduced to ohalf or less of the band width re-quired for 44r -line pictures utilisingthe two -to -one interlace of to -day withthe tentative line and field frequen-cies being used, because of the reduc-tion in the band width of videomodulating signals.

The general system may best beillustrated by a specific example. Inorder to maintain simple frequencydiscriminating circuits, the sweepsignals are transmitted in the form of

ultra -high -frequency channels to faci-litate dual handling at the receiver.One carrier is modulated by thevision signal alone, and the otherone is modulated by the three remain-ing signals, the sweeps and the audioin distinct narrow channels. Thesethree signals are kept distinct fromone another by the use of appropriatesubcarriers.

The camera tube for converting thepictures into the so-called visionsignals may assume several conven-tional forms, though very promisingresults have been obtained with theuse of a special type of photoelectricmosaic tube employing electrostaticdeflection. This type of deflectionis considerably more desirable whereit is planned to vary the style of scan-ning raster.

With certain types of scanning it

The sweep signal generators shownprovide sinusoidal wave shapes of 6ocycles per second and 6,615 cycles persecond respectively for the verticaland horizontal scanning. This typeof signal is rather easily handled inselective -filter circuits, and can bemodified by a simple resistance -capacity rectifier network into themore conventional saw -tooth wave-form which is very efficient in accom-plishing uniform coverage of thescreen area.

It is necessary to provide a suitableand simple means of transmitting thesweep signals and the audio voltagesindependently. The low sweep is used

to modulate the output of a 15 -kilo-cycle oscillator. The high sweep inturn is used to modulate the outputof a 25 -kilocycle oscillator.

The audio signals, generated in a

395

TELIYISIOtlAND

SHORT-WAVE WORLD

SMALLER t FREQUENCY BAND

JULY, 1939

conventional manner by microphone,supply the third channel which has afrequency band from o to io kilo-cycles. These three signals are com-bined and used to modulate the poweroutput of a 6o -megacycle carrier oscil-lator. The 57 -megacycle carrier andthe 6o -megacycle carrier are subse-quently fed to a radiating aerialsystem.

Fig. z shows the double -carrier re-ceiver for use with this transmittingsystem. It accepts the signals witha radio -frequency stage having aband pass of 56 to 62 megacycles.The first detector mixes this com-pound signal with the output of a local,65 -megacycle oscillator, and deliversthe signals to tuned intermediate -frequency circuits.

The vision second detector receivesonly those potentials intended tomodulate the grid of the cathode-raytube. The other selectively tunedintermediate -frequency stage is fol-lowed by a second detector which de-livers the three original signalsthrough tuned filters and third detec-tors in the cases of the sweeps anddirectly through a filter to the loud-speaker in the case of the sound sig-nals. Simple waveform modifyingnetworks deliver the deflecting volt-ages to the plates of the cathode-raytube.

SimplifiedControl

There are no critical local adjust-ments to be made to this receiver,after it is once lined up properly withregard to the filters. A single tuningcontrol is sufficient for both channels.The problem of satisfactory auto-matic signal level control is easilysolved since the output of the filterfor the high -frequency sweep remainsof constant strength and does notchange at all as the picture subjectmatter varies. A circuit can be pro-vided in the vision output to obtainbrightness regulation of the picturewith changes in the d -c backgroundlevel of the picture signal.

With these band-pass systems inthe receiver it can readily be seenthat small variations in the scanningsignals are immediately followed bythe beam in the receiving tube tomaintain faithful picture reproduc-tion.

With a somewhat wider channel ineach band, though keeping the samegeneral principles, receiving sets maybe produced having great flexibility

as to the types of scanning signalsthey may accept, and consequently ahigh-fidelity receiver can also be em-ployed without any change to observethe transmission from a low -definitionexperimental station so long as eachstation employs identical sub -carriersand maintains uniform separation be-tween its assigned carrier frequencies.

All the critical equipment is locatedat the transmitting station, leavingthe receiver simple to operate and in-expensive as compared with circuitscontaining complete sweep oscillatorswith their associated control features.

Fig. 3 shows an alternative methodof transmitting the four necessarysignals for this television system. Itemploys only one ultra -high -fre-quency carrier. The two sweep sig-nals have their subcarriers as beforeand a mixer combines the twomodulated subcarriers with the audio -channel signals. This compositesignal is used to modulate an inter-mediate subcarrier of three mega-cycles which can then be suitablycombined with the output of the visionchannel. Finally, the single ultra-high -frequency carrier is modulatedand radiated.

This method offers certain advan-tages regarding the ultra -high fre-quencies. Design of a single aerialsystem is simplified when it it notrequired to radiate two carriers as inthe first method, but merely to radiatethe one carrier with its somewhatbroader modulation. Only one ultra-high -frequency power amplifier isrequired.

The receiver for this single -carriersystem is shown in Fig. 4. It utilisesa conventional superheterodyne cir-cuit through the second detector, ex-cept for the use of the broad bandpass necessary for television recep-tion. At this point a low-pass filterisolates the vision signals andfeeds them to the cathode -ray -tubegrid. The band-pass intermediate -frequency stage selects the compositesignals still superimposed on thethree -megacycle subcarrier which isthen demodulated by the thirddetector.

The respective filters further isolatethe signals and deliver the sweep sig-nals through the fouth detectors andthe sound signals to the loudspeaker.

"Television and Short-wave World "circulates in all parts of the world.

Again the automatic signal -level con-trol is taken from the channel of thehigh sweep frequency.

AdvantagesIt will be of interest to consider the

important advantages of this systemover other contemporary systems. Ofmajor importance is the ability totransmit high -definition pictures witha reduced frequency band. Thissimplifies the requirements at boththe transmitter and the receiver. Itallows space for more televisionstations.

It makes it possible to transmitsignals on carrier frequencies withhundreds of miles range, though it iswell understood that fading andphase errors become more ominouswith increased transmission distance.With a six -megacycle peak -modulat-ing frequency it is essential to useultra -short-wave carriers which arenearly limited to the optical horizon,but with the video peak frequencieshalved, it is possible to utilise car-riers with increased rangc.

It is important to point out here justhow this video -frequency reduction isaccomplished in this system without asacrifice in definition. The systemmakes practical the use of interlaceratios as high as four and six. Withthe synchronising -pulse method ofcontrolling local oscillators at thereceiver, this is very difficult, if notabsolutely unreliable. With properequipment, the higher interlace pat-terns can be controlled at the trans-mitter, and the method described pro-vides the identical scanning systemat the receiving station.

Let us illustrate what is meant byan interlace ratio of four by a specificexample. To maintain freedom fromapparent flicker it is satisfactory toutilise fractional scanning at the rateof sixty vertical traverses or fields persecond. If the horizontal scanningfrequency is accurately enough con-trolled, the scanning can he made tooccur so that the entire system oflines is completed at a repetition rateof fifteen per second.

The frame frequency is fifteen persecond, providing fifteen completedpictures each second, yet the frac-tional scanning frequency is suffi-ciently high to maintain persistenceof vision, and the frame frequency offifteen is high enough to provide ade-quate continuity of motion of movingokkjects. By maintaining the field

(Continued on page 403)

396

Ts.! /10.11JULY, 1939

ANDSHORT-WAVE WORLD

THE OSCILLOGRAPH FOR TELEVISIONRECEIVER SERVICING

IT is becoming more generallyrealised that the cathode-rayoscillograph is the most compre-

hensive test instrument that has beendevised. In the past its use has beenconfined to laboratories, but of latethe instrument has been developedin such a manner as to render it suit -

11111111111 ouirt girt

Fig. 1. Waveform across D.C. restoration diodeload resistance. Time base frequency 2,531 c/s.

able for an almost unlimited numberof purposes and without requiringany very highly specialised know-ledge in its use. The Mullard Wire-less Service Co., Ltd., have appre-ciated this fact and have devotedconsiderable attention to the produc-tion of instruments of this class of aflexible and adaptable type. Two

moo

Fig. 2. Waveform across D.C. restoration diodeload resistance. Time base frequency 50 c/s.

models, the GM3152 and the GM3155have been developed primarily for theradio service engineer for visual cir-cuit alignment and radio and tele-vision receiver servicing.

It will be appreciated that the

mum Fos vom NMI ORD

Fig. 3. Waveform of " cross signal." Timebase frequency 3,375 c/s.

effect of each adjustment to areceiver shown visually by the res-ponse: curve on the screen of thecathode-ray tube is of the utmostvalue in the location of faults and thecauses of distortion.

Prior to the commercial develop-

ment of oscilloscopes the setting upof the necessary apparatus entailed alot of work and special knowledgewhich was out of the question underordinary circumstances. Such workis now eliminated by thoughtfuldesign of the instrument and thecathode-ray oscillograph is no moredifficult to use than the ordinary testinstruments. A certain amount ofknowledge in the operation of thecathode-ray oscilloscope is, of course,essential, but it is of a nature thatcan readily be acquired. In this con-nection the Mullard Company haveissued an instruction book entitled" Radio and Television ReceiverServicing with Cathode-ray Oscillo-graphs." It is quarto size, profuselyillustrated with photographs and dia-grams and the whole procedure ofservicing is fully explained in thetext. A nominal price of 2S. iod.(C.O.D.) (2s. 6d. and 4d. postage) ischarged for this book, and readersmay obtain copies on application tothe company at Century House,Shaftesbury Avenue, W.C.2.

As the text and photographs rela-ting to television receiver servicingare of particular interest to readers ofthis journal, we have obtained thepermission of the Mullard Companyto publish a portion. These extracts,it will be understood, only representa small fraction of the entire work,for in all the book contains close onseventy illustrations, and detailedinstructions for locating all radio andtelevision receiver faults.Testing SynchronisingSeparator Circuits

Owing to the complexity of the tele-vision waveform it is not practicalto use a signal generator for checkingthe operation of, the synchronisingcircuit, so that it is necessary tomake the tests on an actual transmis-sion from Alexandra Palace.

Examination of the waveformacross the D.C. restoration diode loadresistance (R2, Fig. 5o) shouldreveal a waveform similar to Fig. 1.This oscillogram was photographedwith a time base sweep frequency of10,125

- 2,531 c.p.s. Fig. 2 shows4

the waveform of a complete frame(time base frequency, 5o c/s). Theactual waveform of the vision part of

the signal will be dependent on the -picture detail at that moment beingtransmitted. The waveform of the" cross signal " which is radiatedbefore a transmission is very useful,for test purposes. It is shown in Fig.3. The time base frequency in this.

Fig. 4. Waveform of " cross signal " showingcurved leading edges due to attenuation of thehigher modulation frequencies. The ratio,of " synch." to modulation is also reducedoffing to a small input to the diode detector.

Time base frequency 5,062 c/s.

case was 3,375 c.p.s., i.e., one-third;of io,i25, which is the line frequency.If a satisfactory high frequency res-ponse is being obtained, the wave-form should be quite rectangular as -

Fig. 5. Oscillogram of line synchronisingimpulses showing the effect of the accentuationof the higher modulation frequencies. Time

base frequency 2,531 c/s.in the case of the synchronisingpulses. A curved leading edge wouldindicate a poor H.F. response (seeFig. 4). Also in this oscillogram theratio of the synchronising impulsesto the picture modulation is reducedowing to the diode detector being

Fig. 6. Oscillogram of line synchronisingpulses at the output from the separator valve.

Time base frequency 2,531 c/s.

operated with a small input voltap-e..This would not have an adverse ejecton the received picture.

A waveform which exhibits pro,-nounced oscillation may be due toaccentuation of the higher frequenciesor to a poorly designed correction

397

lagYisionAND

SHORT WAVE WORLD JULY, 1939

choke in the anode circuit of VI. Thiseffect is illustrated in the oscillogramof the line synchronising impulsesshown in Fig. 5. A fault in the D.C.restoration circuit may result in thehorizontal parts of the wave beingcurved. The waveform at the out-put from the synchronising separatorshould be substantially free fromvision content. If this is not the casethe circuits need adjustment. Fig.

Fig . 7. Frame synchronising impulse afterfilter network. Time base frequency 50 c,s.

6 shows the waveform from the linesynchronising output, and Fig. 7 theframe pulse after the filter circuit.Fig. 8 illustrates the effect of incor-rect filter network component values.

Magnetic deflection is becomingmore and more popular in televisionreceivers owing to the considerableadvantages the magnetic type of tubeoffers. For this reason more spacewill be devoted to the magnetic thanto the electrostatic deflection type.

Fig. 8. Frame synchronising impulse withinadequate filtering. Time base frequency

50 c/s.

In order that a satisfactory picturemay be received it is essential that thewaveform of the deflection current(or deflection voltage in the case ofelectrostatic deflection) should con-form to certain requirements. Thecurrent or voltage must rise (or fall)in a linear manner with respect totime. At the end of the frame scan-ning or forward stroke it must returnto its original value in 5 per cent. of

Fig. 9. Non-linear time base voltage.

the total frame period and 15 per cent.in the case of the line time base. Anon-linear or curved saw -toothvoltage as shown in Fig. 9 results in

the picture being compressed or ex-tended at one side of the picture orat the top or bottom according towhich time base is at fault.

An insufficiently rapid line timebase flyback will result in the left-hand side of the picture being foldedover. A similar fault in the frametime base would cause flyback linesto be visible at the top of the picture.

Magnetic DeflectionCircuits

Magnetic time bases usually con-sist of two valves for each time base(line and frame). The first valvewhich may be either a gas triode or ahard valve, provides a voltage ofsuitable waveform at the correct fre-quency for feeding the grid of thepower output valve. The deflectioncoils which are located round theneck of the cathode ray tube areusually of the low impedance type fedby a step-down output transformer.Some receivers, however, use highimpedance deflection coils for one oreven both deflection circuits. The fre-quency of the frame time base shouldbe 5o cycles per second and the linetime base 10,125 cycles per second.The time bases are kept accurately instep with the time base generators atthe transmitting station by means ofthe synchronising impulses alreadydescribed.

In the case of electrostatic deflec-tion the grids of the push-pull out-put valves are fed with a pure saw -tooth voltage, but for magnetic deflec-tion it is not practical to design thenecessary output transformer forfeeding the deflection coils which willhandle such a waveform without dis-tortion. It is therefore customary tofeed the grid of the output valve witha distorted waveform which will can-cel the distortion occurring in thetransformer. By suitable adjustmentof the circuit values it is possible toobtain a scan sufficiently linear for allpractical requirements. The oscillo-gram shown in Fig. 9 is of the voltagedeveloped across a small resistanceplaced in series with a high imped-ance frame deflection coil (equivalentto deflecton current). Considerablenon -linearity is apparent, which isdue to the capacity of the couplingcondenser between the anode and thedeflection coils being of too low avalue. Fig. so shows the waveformobtained when this capacity was in-creased to a suitable value. Oscillo-gram Fig. i t is of the voltage acrossthe frame deflection coils. The cir-cuit is highly damped by the anode

feed resistance of approximately 4,00oohms, so that the waveform of thevoltage retains its saw -tooth shape.

Fig. 12 shows the waveform of thevoltage appearing across the low im-pedance line deflection coils. Owingto the inductive output circuit thevoltage waveform bears little resem-blance to a saw -tooth. The currentwaveform should, however, be saw -

Fig. 10. Linear time base voltage.

tooth in shape, and may be observedby applying the oscillograph input toa resistance of, say, 25 ohms or lessconnected in series with the deflec-tion coils. The voltage across theprimary winding of the line outputtransformer reaches a very high valueduring the flyback period due to thesudden fall in anode current of thevalve. The voltage does, in certaincases, attain a value as high as 3,00o

Fig. 11. Voltage across high impedance framedeflection coils.

volts, so that an attempt should notbe made to observe the waveformacross this winding. Fig. 13 showsthe effect of the resistance in serieswith the charging condenser (gastriode time base circuit) having toohigh a value. Adjustment of this re-sistance within certain limits pro-vides a means of correction for a non-linear deflection current in the coils.

" Form " correction circuits may

Fig. 12. Voltage across low impedance linedeflection coils.

also be applied to the output trans-former (resistance and condenser in

378

JULY, 1939

fELEVISIgt)AND

SHORT-WAVE WORLD

series across secondary winding) orin the actual inter -valve coupling.

If either deflection circuit is not upto standard and the waveform appear-ing at the grid of the output valve issatisfactory, the fault will lie either in

Fig. 13. Distorted time base voltage due to" flyback " resistance having too hign a value.

the output stage, the output trans-former, or in the deflection coils t7tem-selves. The amount of distortion

age at the grids of the push-pull valveis of a suitable value for the directapplication to the deflection platesof the oscillograph. The voltagesappearing on the grids of these valvesshould, of course, be equal and showa phase displacement of 1800.

The operation of the output valvesis best ascertained by temporarily dis-connecting one deflection plate of thetelevision cathode ray tube and con-necting to the final anode, andmeasuring the amplitude of theraster. Now by reverting to theoriginal deflection plate connectionsthe amplitude of the raster should bedoubled (in vertical or horizontaldirection according to which timebase is under test). This measure -

TO E1LTVOLTAGE

SERIES RESISTANCESAPPROXIMATELY 50 MEGOHMS

TO CHASSIS OFRECEIVER

Fig. 15. Method of using cathode ray oscillographs GM.3152 or GM.3155 formeasurement of EHT voltages.

which may be tolerated in the outputvalve is much less than that whichpasses almost unnoticed in the case ofa radio receiver. It is therefore ofparamount importance that the valveis opet ating on the straight portion ofits characteristics and that there is nolimiting either by grid current or dueto the grid potential swinging near thecut off value. Before the anode volt-age of the line output valve may bechecked it will be necessary to putthe saw -tooth voltage generator tem-porarily out of operation (taking carethat the brightness on the televisionreceiver is turned down so that abright vertical line does not appearon the screen)c

Electrostatic Deflection'Circuits

It will not be possible to applythe deflection voltage directly to the-cathode-ray oscillograph as the spotwould be swept right off the screenand the centre portion of the wave-form only would be visible. The volt-

ment may be verified by disconnect-ing the other deflection plate andobserving whether the amplitude ofthe raster is similar to that obtainedwhen working with the other deflec-tion plate of the pair. A non -symmetrical deflection voltage willcause poor focus at the sides of thescreen; the shape of the raster willalso be distorted.

Measurement of E.H.T.voltages

The value of the final anode voltageof the television cathode ray tube willusually be of an order of 4,000 to6,000 volts, and owing to the limitedcurrent available in these circuits it isessential that the measuring deviceshould draw a negligible current orinaccurate readings will be obtained.The most suitable instrument is theelectrostatic voltmeter. This instru-ment is, however, quite expensiveand is of little use for ordinary radioreceivers, as its scale readings arerestricted to voltages of a high value.

Owing to the high input resistance ofthe deflection plate circuit of thecathode - ray oscillographs, typesGM.3152 and GM.3155 it is possibleto estimate with a reasonable degree

Fig. 14. Time base voltage with slow flybackstroke compared with Fig. 10.

of accuracy the E.H.T. voltages.The GM.3152 cathode ray oscillo-graph has an input resistance directto deflection plates of approximately2 megohms with the combinationswitch set to " external synchronis-ing " and approximately .5 megohmwhen set to internal synchronising.The input resistance of the GM.3155oscillograph is approximately 1.3megohms.

The following is the procedure forascertaining the H.T. voltage. Applythe input to the oscillograph, withswitch set to " direct to plates," tothe E.H.T. voltage via a series resis-tance of 5o megohms approximately(consisting of a number of carefullyspaced and insulated resistors), andmeasure the vertical displacement ofthe time base line (see Fig. 15). Ifthe deflection is excessive and resultsin the line being deflected right off thescreen the value of the series resist-ance should be increased: conversely,if the deflection is too small forreliable measurement the series resist-ance must be reduced. Disconnectthe input to the oscillograph andapply a voltage direct to the platesfrom an H.T. battery. Adjust thisvoltage by means of the tappingsuntil a similar deflection is produced.The E.H.T. voltage may now bereadily calculated by multiplying thisH.T. voltage from the battery by theratio of the potentiometer (RI + R2divided by R2). For example, sup-pose RI is 5o megohms and R2 is .5

Rimegohm, the ratio - + R2 = too

R2

approx. and if the H.T. voltage re-quired to deflect the time base line bya similar amount to that produced bythe E.H.T. voltage via the seriesresistance is 45 volts, the E.H.T.voltage will be 45 x too = 4,500volts.

399

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ALTHOUGH the dipole aerialwith reflector has become moreor less a standard article, ex-

perience has shown that unless dueattention is paid to the mechanicaldesign, it can be a source of troubleafter a period of use. It is, of course,exposed to winds, temperature varia-tions and atmospheric changes andthese factors necessitate it being rigidand capable of withstanding a certainamount of expansion without detri-ment to the mounting of the aerialand reflector members. A source oftrouble with early types in whichwood was used was the fracturing ofthe insulating supports owing to theexpansion and contraction of thewood.

Corrosion is another trouble and itis surprising to what extent this cantake place after the aerial has beenin an exposed position for some time.Also in the lightest breeze there isconstant vibration and any weaknessin the mountings soon leads to frac-ture.

A DIPOLE AERIALWITH

NEW FEATURES

Sketch of the Bullerdipole aerial and reflec-tor and some of thaconstructional details.

The desiderata for the dipole aerialare, therefore, freedom from possi-bility of corrosion, rigidity andability to withstand temperaturechanges. Bullers, Ltd., of 6 Law-rence Pountney Hill, E.C., who arecontractors for overhead electricsystems have kept these facts inmind in the design of a new dipolewhich they have recently put on themarket. As the sketches show thereare several novel features, some ofwhich we understand are the subjectsof patent applications. The aerialand reflector members are supportedon a galvanised tubular cross mem-ber which fits into sockets on the mastcap and a novel feature is introducedin this latter. This is in two halves,provided with clamping bolts whichnot only secure the cap to the top ofthe mast but also clamps the tubularmembers which can easily beadjusted to enable reflector and aerialto be exactly parallel. One half ofthe mast cap is provided with a lip atthe top which overlaps the other half

thus preventing the ingress of water.At the ends of the tubular cross

supports are two flat pieces of ironprovided with sockets and securelyriveted. On these are mounted theinsulator aerial and reflector sup-ports, four being provided for theaerial and two for the reflector. Atthe outer ends of the insulators splitbrass clamps are fitted to hold theaerial and reflector members.

The aerial and reflector consist ofheavy gauge brass tube heavilyR in.

coated with grey cellulose whichshould resist corrosion for a con-siderable time. Both aerial andreflector are in two pieces and a novelfeature of the former is a steatitedistance piece which fits into the endsof the tubes which are thus set at thecorrect distance apart for the properimpedance to match up the cable.One of the reflector members is pro-vided with a spigot which fits intothe end of the other and is securedwith a set screw.FixingMethod

Another noyel feature of thisaerial is the means provided for secur-ing it to a chimney stack withoutdrilling any holes or interfering inany way with the brickwork. Twogalvanised iron corner brackets arefitted with clamps to grip the pole.These brackets , are provided withhooked tensioning screws and a wirefrom each bracket is passed rightround the chimney stack and drawnup tight by means of the screws, thewire at each corner of the chimneypassing over metal plates provided

Method of fixing aerial to chimney stack.

with guides. Erection is thus asimple matter requiring no toolother than a spanner for tensioningthe wires and there is no possibilityof damaging the brickwork.

(Continued on page 403)

400

JULY, 1939

TELEYISIOAAND

SHORT WAVE WORLD

THE NEWSREELS

0 PPOSITION by cinema intereststo the televising of the news-reels is increasing, and at a

meeting of the Northern Branch ofthe Cinema Exhibitors' Association arecommendation to the General Coun-cil was passed that diffusion of thenewsreels concerned should not bepermitted.

TELEVISION AND LIGHT -GATES"Following the Roderick -Armstrong

fight for the world's welterweightchampionship at Harringay Arena,the question of allowing the televisingof boxing matches has been raisedagain. Less than 5,000 went to seethis fight, and according to Brig. -Gen. A. C. Critchley, the promoterslost about 8,000.

Opinion, however, among promo-ters differs and not all attribute thepoor attendance on that occasion tobroadcasting and televigion.

THE SCOPHONY BIG SCREENIt is stated that Odeon Theatres,

Ltd., have placed an order withScophony,' Ltd., for the equipment ofall Odeon cinemas with televisionreceiving apparatus. Sixty cinemasin London will be the first to beequipped, and it is understood thatthis will take from about r8 monthsto complete. There are about 300Odeon theatres but, of course, therewould be no point in equipping thoseuntil there was a local television ser-vice.

The chairman of Odeon Theatres,Ltd., Mr. Oscar Deutsch, is also adirector of Scophony, Ltd.

ACTORS AND VISIONAll members of the Actors' Equity

Association of America are now re-quired to submit offers and terms fortelevision appearances for approvalbefore appearing before the televisioncamera.

AMERICAN RESPONSEGeneral Electric (U.S.A.) television

engineers have been amazed at thepopular response to the television

demonstrations in the G.E. exhibitbuilding at the New York World'sFair.

The G.E. demonstration consists ofa small studio, into which visitors areinvited to be interviewed before a tele-vision camera, and a half a dozenreceivers in darkened booths acrossthe auditorium. People crowd inlines six deep in front of the gla,sswindow of the studio. Comments inthe booths of the television receiversreveal that when visitors see theirfriends televised they have an urge totalk back to them-as though theywere standing face to face.

PHONE LINES FOR TRANSMISSION

A telephone wire from MadisonSquare Garden, New York, wherebicycle races were in progress, to theN.B.C. studios in Radio City, a dis-tance of just over a mile, was experi-mented with by engineers of theNational Broadcasting Co. recentlyfor television transmission. It isstated that at this distance the resultsobtained were quite good. Use oftelephone lines for short distanceshas, of course, been made by theB.B.C.

YORKSHIRE CINEMA TELEVISION

Arrangements have been made forthe installation of television in anumber of cinemas in Yorkshire.

These include the Yorkshirekinemas of Gaumont-British. In allprobability, the New Victoria atBradford will be the first of the hallsowned by this. group to be fitted.

WIMBLEDON TENNISTOURNAMENT

improved camera positions shouldgive even better television picturesfrom the centre court at Wimbledonthis year than in 1938 and 1937.Formerly the " shots " have beenmade from an oblique angle, but thistime a "square on " view will beobtainable from a point opposite theRoyal Box. In previous years onecamera, used for occasional longshots, has been left unattended, butthis year all the cameras will be

manned and will be brought fre-quently into circuit with rapid changesof lenses.

Television from Wimbledon willbegin on July 1 and, as the all-important Finals Week proceeds,more and more play will be televised.On the last two days, July 7 and 8,cameras will be in continuous opera-tion from 2.3o to 5 p.m. The finalsto be televised will include the men'sand ladies' singles, and the men'sdoubles.

DEPUTATION TO P.M.G.Representations asking for the

limitation of the transmission of tele-vision programmes constituted ofdramatic, variety, music and singingitems to prevent big screen produc-tion in public establishments weremade to the Postmaster General lastmonth by a deputation representingstage interests. The plea was unfaircompetition generally detrimental tothe maintenance of the variety,theatrical and concert professions.

FILMS FOR A.P.According to the Motion Picture

Herald (U.S.A.) (May 20), the tele-vision director of the B.B.C. talkedwith various of the major distribu-tors' executives to obtain from thempermission to irse some of theirfeatures. He had sought arrange-ments through the. Motion PictureProducers And Distributors ofAmerica, which referred him toindividual executives of member com-panies. Progess, if any, was not dis-closed.

CROSLEY TELEVISION

The Crosley Corporation (U.S.A.)has leased the entire 48th floor ofCincinnati's Carew Tower for con-struction of television studios. CarewTower, 574 ft. high, will have anestimated service radius of 25 miles.The transmitter is rated at 1,000watts, and work is progressingrapidly.

EMPIRE TOWER FOR TELEVISION?

Tower of Empire -at BellahoustonPark, Glasgow, has been suggested

401

'11ELEVISIfit1AND

SHORT-WAVE WORLD

MORE SCANNINGSJULY, 1939

as a television station. Mr. C. 0.Stanley, chairman of the TelevisionDevelopment Committee, speaking atPeebles recently, however, said thatit would be to years or thereabout ifthe present attitude of the authoritiescontinued before Scotland had tele-vision. It was his personal opinionthat the obstruction to provincial tele-vision was coming from the PostOffice. He thought the Post Officehad contracted a new disease-" cablitis."

MISS RADIOLYMPIA, 1939A contest has been organised by

the Radio Manufacturers' Associa-tion to select the girl with the perfectradio and television personality toappear at Radiolympia-August 23to September 2, 1939. The heats ofthis contest are being conducted atthe leading seaside resorts, one nighteach week, from week commencingJuly to to week commencing August14. The girl will be chosen forappearance, personality and micro-phone voice.

At the completion of the localheats, semi-finals will be held in largecentres of population, such as Londonand Birmingham, to select twelvesemi-finalists who will appear inLondon for final judging. The semi-finals and finals will be judged by aCommittee of radio critics, film,stage and radio stars, and other well-known personalities.

DuMONT TELEVISIONTwo new DuMont television trans-

mitters are being finally tuned up totake the air shortly with experimentaltransmissions, while down in thespacious basement two televisionstudios and a control room arerapidly taking definite form so thatsuitable programme material may beavailable to the DuMont televisionstation, which was recently grantedan experimental licence to operatewithin the 42,000-56,000 kc. band.

One studio is being devoted todirect pick-up programmes, and thesecond film pick-ups.

Two transmitters are available forsimultaneous transmission within theallotted frequency band, permittingthe handling of vision and soundcomponents of a single programme,or the transmission of the same visionpick-up by the standard R.M.A.system and the DuMont system, fora direct comparison. Demonstrationswill be available shortly, so that the

relative merits of these two systemsmay be ascertained under actualoperating conditions. The DuMontsystem, which is described on anotherpage in this issue, eliminates the needfor sweep circuits at the receivingend.

The DuMont Laboratories, lastmonth, filed application for threeadditional television transmitters.No. i-A 50 -watt mobile transmitteron 6o-86 mc. ; No. 2-A i-kw. unitfor 515 Madison Avenue (top floor),N.Y.C., on 6o-86 mc. ; No. 3-a-kw. unit for the National Press

Buildings, Washington, D. C., on42-56 mc. and 6o-86 mc.

" HOME " TELEVISION ?The Milwaukee Journal has applied

to the Federal Communications Com-mission for permission to inauguratean experimental television service tothe public. The Journal Company'sapplication is the first -applicationfor the establishment of an experi-mental programme service for recep-tion in the home as distinct fromfundamental research or technicalexperiment. The Commission haspreviously issued a number oflicences for technical experimentonly.

NATIONAL SERVICE UNITS TO BETELEVISED

Television cameras will pay a re-turn visit to Hyde Park on July 2 forthe march past of National Serviceunits before His Majesty the King.The members of the parade will havecome from all parts of the BritishIsles and will include detachments ofthe Army, Navy, Air Force, A.R.P.services, the Auxiliary Police andNursing services. Incidentally, theparade will be His Majesty's firstimportant public engagement afterhis return from America.

MUSIC BEE FOR TELEVISION

A Musical Bee is planned for theevening television programme onJuly :co when two teams, part pro-fessional, part amateur, will bematched. With women rangedagainst the men, the contest will de-velop on the lines of a general musi-cal knowledge bee in which competi-tors will not only have to guess tunesbut identify strange instruments,translate 'obscure musical terms, re-cognise records played backwards,and solve other problems which

should not be too difficult to peoplewho have a little more than a noddingacquaintance with music. The wholeprogramme will be strongly visual inappeal, and even viewers who haveno knowledge of music will, it is be-lieved, extract a lot of enjoymentfrom this unusual programme.

TROOPING THE COLOURBROADCAST

Five London cinemas reproducedthe Trooping the Colour broadcast.The New Victoria, Marble Arch Pavi-lion and Tatler used Baird apparatus,and the Odeon, Leicester Square, andMonseigneur, Oxford Street, Sco-phony. All had audiences some-what larger than usually attend. Ithas been generally conceded that thequality of the reproduction was thebest ever on big screens, largely dueto ideal weather conditions.

FOOTBALL TELEVISIONAt the annual dinner of the Foot-

ball League Secretaries' and Man,-agers' Association Mr. Stanley R.Rous, secretary of the Football As-sociation, declared that it would be amistake for football people to standagainst television and broadcasting.This may be an indication that somearrangement will be made to televisematches next season.

SCHOOL LESSONS BY TELEVISIONAt Hurst House School, Staple-

hurst, Kent, the scholars are beinggiven lessons with the assistance of atelevision receiver. News reels andthe televising of events like "Troop-ing the Colour" and the departure ofthe King and Queen for Canada pro-vide the subject matter for generalknowledge teaching. These speciallessons have been started by theheadmaster, Mr. H. Farrington.

MR. GERALD COCK BACK FROMU.S.A.

Mr. Gerald Cock, 13.B.C. Directorof Television, who has returned fromthe U.S.A., where he has been in-specting the progress of television,addressing a gathering of the RadioManufacturers' Association on hisreturn, said : " England still leadsthe world in television, but Americaninterests are watching us. TheNational Broadcasting Company,Columbia, the Film Industry, theNew Deal itself, all these organisa-tions with their vast resources are

402

TELVISIOt1JULY, 1939 AND

SHORT-WAVE WORLD

AND MORE REFLECTIONSwaiting to take up television at thepoint to which we have brought it.

" It behoves this country to moveforward in the television field at sucha pace that we still continue to main-tain our lead. If only this countrywill go on developing television, therest of the world will come to us fortelevision equipment, not only forreceivers, but for transmission equip-ment itself. In every country of theworld, except England, television isin the experimental stage. In thiscountry it is already a practical pro-position. We know we have a threeyears' lead on the others. It is up tonations with the object of helpingus to maintain this lead while offeringthe results of our experience to otherthem to enjoy the facilities wealready possess."

SANDOWN PARKAt the moment there does not

appear to be any chance of theEclipse Stakes being televised fromSandown Park on July 14 aswas previously announced. TheJockey Club Stewards have refusedpermission for the race to be televiseddespite the fact that B.B.C. engineershad already surveyed the course andobtained permission from the San -down Park authorities to instal thenecessary equipment and cameras.

The attitude of the Jockey ClubStewards is to be deplored, as surelyit cannot have any effect on theattendance at the race meeting, whilefrom a technical aspect the transmis--sion would have been highly success-ful as the course is a short one andlends itself to a complete transmissionof the race without difficulty.

TELEVISION IN BLACKBURNPhilips' engineers at the new Black-

burn factory are very optimistic aboutreceiving television pictures there. Ifit is possible for them to erect anaerial 25o ft. above ground level andwith directors and reflectors they feelthere is a very good chance of satis-factory pictures being received. Theirresults are awaited with interest byreaders who live considerably beyondthe service area.

TELEVISION AT THE NEW YORKWORLD'S FAIR

American television was givenquite a boost by the transmission ofpictures of the King and Queen when

they visited the World's Fair.A commentator talking over one ofthe American short-wave stations wasvery optimistic regarding the possi-bilities of a rapid advance inAmerican television and was usingthe King and Queen's visit to provehow important it is that televisionshould be in every home in order thatthe ordinary viewer could be keptacquainted as to what was going oneven if they were not able to see theevents themselv,es.

LONG-DISTANCE AMERICANTELEVISION

Contrary to the theory that tele-vision programmes can only bereceived at a limited distance from thetransmitter, General Electric en-gineers in Schenectady using astandard console receiver picked thecomplete two-hour programme " tele-cast " by N.B.C. from the EmpireState Building. Both picture andsound were received exceptionallywell despite the fact that the distancefrom the transmitter was 13o milesand the receiver was located approxi-mately 8,000 ft. below " line ofsight." This is believed to be anAmerican record for reception of aregular broadcast television pro-gramme, although in this country andelsewhere, distances considerably inexcess of 13o miles have beenspanned. The test was made on May26 and a group of engineers erecteda temporary diamond directive aerialarray. It was suspended from fourmasts, with the plane of a diamondparallel to and about 40 ft. above theground. The aerial occupied a spaceon ground of about 30o by 600 ft.Tests were conducted close to thelocation chosen for the new high -power General Electric televisionstation which is being put up in theHelderberg mountains, 12 miles fromSchenectady.

GENERAL ELECTRIC U.S.A.RADIO -TELEVISION ACTIVITIES

A new department of the GeneralElectric Company which will con-solidate for the first time all radio,television, and related activities, hasbeen established with headquarters atBridgeport, Conn., effective immedi-ately. Dr. W. R. G. Baker, formany years associated with G.E.activities in the radio field and untilnow chairman of the radio manage-

ment committee, has been namedmanager of the new unit, to be knownas the radio and television depart-ment.

ANOTHER DEPUTATIONA deputation of radio dealers or-

ganised by the Radio and TelevisionTraders' Federation met the Post-master -General to explain the retail-ers' case for a new station at Bir-mingham and in other importantprovincial centres. It is hoped thatthe various deputations putting theirviews before the Postmaster -Generalwill ultimately have the desired effect.

" A Dipole Aerial with New Features "(continued from Page 400)

Except .for the aerial and reflectormembers and the insulators the en-tire construction is in heavily gal-vanised iron and the assembly shouldbe proof against weather conditionsfor a very long time. As clamps areused both for the mast supports andthe mast cap directional setting isquite an easy matter. The electricaldesign conforms to accepted stand-ards and the aerial may therefore berelied upon to be electrically efficient.As it is essential that the mast shouldfit the sockets this is included as partof the kit, its length being 12 ft.

" Du Mont Television System "(continued from Page 396)

frequency of sixty and reducing theframe frequency to fifteen instead ofthirty, as with the 441 -line two -to -oneinterlaced pictures, the video fre-quency band is halved without sacri-fice in either horizontal or verticaldefinition.

Use of single -side -band transmis-sion is, of course, possible with thissystem which will reduce the requiredfrequency band on the air to one -quarter of that of existing systems.

Another advantage is the assuranceof synchronism if signals are receivedat all. There is no local adjustmentof auxiliary controls. Furthermore,the receivers are capable of respond-ing to several scanning systems inturn from different transmittingstations.

It is realised that this system canonly stand on the merits of results ofextensive field trials which are underway. DuMont laboratory tests haveindicated that the system is entirelyfeasible.

403

72.1ir/E1011AND

SHORT-WAVE WORLD

MORE PROGRESS WITHTHE " HOME "

MECHANICAL RECEIVERBy J. H. JEFFREE

In preceding issues articles have appeared on the development of ahome mechanical receiver. Considerable success has been obtainedwith the apparatus described, most of which it is hoped shortly to

incorporate in a complete receiver.

pENDING the perfection of cir-cuits for synchronising thenewly -developed nine -ball motor -

scanner from the received picturesignals, a provisional circuit is givenherewithi which has been found towork, though it has the fault ofoccasionally letting the motor dropout of sync. if the controls are toosuddenly altered. As a driving cir-cuit for this motor, however, it willbe found quite efficient, and theabove defect appears to arise onlyfrom the swamping of the drivingoscillation too suddenly by the controlsignal; its cure, therefore, shouldonly be a matter of cleaning up thecircuit arrangements. We have notfound opportunity, unfortunately, tocomplete this in time for this month'sissue.

It might, also, be preferred to sub-stitute American type valves with 6.3volt heaters for the first two valves,to keep the heater voltage uniformthroughout the unit.

Points of interest in this circuit arethe cathode coupling of V2 to VI andthe feedback network from V3 to thegrid of Vz. Both arise from thenecessity of making an oscillator thatcan be varied from about 8uo tofo,000 c.p.s. in a simple manner.Using two valves for the purpose, ashere. there are several circuits thatwill achieve such a tuning range by

Driver unit for nine -ball high-speed scanner.

the variation of condensers and/orresistors, and that chosen is notclaimed to have any special merits ;most of them, however, have to berather carefully designed, if such arange is to be fully covered with alittle to spare. In the present cir-cuit, the main point was found to beensuring that the variable shuntcapacity from G2 to earth, which isthe main variable factor involved incovering the range, should be reduc-ible to as low a minimum value aspossible. Even a few extra micro-microfarads are enough to preventeasy tuning right up to fo,000 c.p.s.Therefore no additional couplings tothis grid were permitted, and thesync. signals were injected via thecathode resistor. For the samereason a screened grid type ischosen for this valve (V2) to reduceinput capacity.

The curious feedback network im-proves the oscillation range, and the

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JULY. 1939

variable resistor included in it is veryconvenient as a fine control of speed,as the main control, obtained by thecondenser, is fairly coarse. A stillfurther extension is obtainable by con-necting a small condenser, approxi-mately 20 micromicrofarads, inparallel with the 250,000 ohm resistorin this feed -back circuit.

Underside view of scanner drive unit.

404

lair/monJULY, 1939

DRIVING THE MOTOR

ANDSHORT-WAVE WORLD

Running theMotor

The motor has to be connected inthe plate circuit of the 6L6G directly,as the magnetisation produced by theD.C. flowing in its windings is essen-tial for its operation. The procedure

A photograph of the nine -ball scann3rand motor.

in starting and running up is asfollows : First, the oscillator controls(variable condenser and resistor) areboth set to maximum, when theoscillator note should be audible fromthe motor polepieces. The startingknob of the motor is twirled briskly(right-handed, for the presentarrangements) and the rotor shouldat once drop into rotation at a steadyspeed corresponding to the oscilla-tor frequency, The controls are thenturned towards minimum, graduallyenough for the motor to follow ; it isconvenient to turn out first the con-denser, which will take the speedfairly near to the desired 22,500r.p.m., and then bring it right up withthe resistor.

It was of interest to determine, inthe course of this work, whether themotor remained exactly in step withthe oscillator, as the speed was in-creased, or whether, as seemed pos-sible, it lagged behind somewhat, andonly caught up fully after the con-trols were fully set. To test this,signals from the driving oscillatorwere applied to the vision receiver,producing a vertical pattern on thescreen, and it was found that eventhe most drastic interference with themotor could not, even momentarily,disturb this pattern to any appreciableextent.

With this particular circuit, atleast, the oscillator and motor arelocked together, in running, almostas if they were a single entity, and

this doubtless is the reason why itis so easy to vary the speed withoutrisk of the motor dropping out. Withother circuits the interlocking is notso complete, and it may be neces-sary, in the interests of effective syn-chronism, to sacrifice a little of thisinterlocking by some modification ofcircuit values. The present circuit iscontrolled so effectively, one may say,by its interlocking with the motor,that it does not very readily acceptadditional control from the picturesignals; and it is thought that thismay be the source of the minor diffi-culty arising in this connection.

When the correct speed is reached,control impulses are applied throughthe variable condenser in the gridcircuit of Vt. There are two pointsin the vision receiver from whichsignal's may conveniently be drawn,via a condenser, for application tothis grid; from the plate of the V.F.amplifier valve V6 (or the grid V7,which is equivalent) or from the cir-cuits carrying the io me/s oscilla-tion that is fed to the light relay ;for instance, from the outer terminalof the preset condenser (C22) in com-partment 6. (See the May issue ofthis Journal, p. 275). From either ofthese points we get a signal in nega-tive sense (as simple V.F. or modu-lated a o me/s respectively) which canbe rectified at the grid of Vi in thepresent unit. If the amplitude of thissignal is sufficient, the picture modu-lation will then be pushed below thegrid base of this valve, and only thesync. impulses be passed on to Vz.

So far, we have had better resultswith the use of the io me/s oscilla-tion for this purpose, which has only

Photograph of slow -speed (frame) scan-ner and motor for

4 -in. picture.

the minor disadvantage, that care isdesirable, by the use of a short lead,and perhaps screening, to avoid let-ting this oscillation stray too muchinto the preceding stages of the visionreceiver. This is a matter for furtherexperiment, and perhaps anyone whoobtains one of these motors in thenear future will record his results.

In any case, if the control im-pulses are applied gradually byturning up the variable condenser, themotor usually locks in without muchtrouble. It seems better to have itrunning at a little above correctspeed, rather than below, beforeturning on the sync. impulses.

A photograph is shown of adriving unit to the circuit given, inwhich the two upper knobs are thespeed controls and the lower, thesync. admittance condenser. Bakelitedielectric reaction -type condensersare advisable on account of their lowminimum capacity.

HuntingAn important point in the design

of such a motor as this is the avoid-ance of hunting. When, as in thepresent case, it is run with a circuitthat locks itself to the motor, huntingis bound to be tied up with the be-haviour of the circuit also. So far,it has been found reasonably steady,with circuits like the one given, butdependent to a noticeable extent onthe circuit. Also, of course, imper-fect separation of the sync. impulsesfrotml the picture, which is in thepresent case a question of the ampli-tude of the applied impulses, givesrise to something like hunting. Ex-periments are being continued on thispoint.

405

ANDSHORT-WAVE WORLD

THE SLOW -SPEED SCANNER

JULY, 1939

The impression was unintentionallygiven, last month, that this motormight be home -constructed. Owingto the accuracy in certain details in-volved, and certain other technicalpoints, that is hardly feasible even forthe skilled amateur, without an un-reasonable amount of preliminarywork, and it is not proposed to giveany directions for such attempts.The author is arranging for the manu-facture og these motors, and theywill be available through H. E.Sanders and Co. as mentioned lastmonth. They are being supplied, forthe mechanical set, on a bracketmounting for fixing, by a single bolt,to the optical frame described in theJanuary, 1939, issue of this journal,in place of the mains -driven 67i ballscanner and motor there specified.

Slow -speedScanner

The slow scanner -motor is alsoillustrated with a four-sided plasticblock, scanner, of the, type describedin .previous issues, for producing a4 -in. 135 -line interlaced picture. Itis of very simple construction, butthe amateur worker is not likely towant to go to the trouble of fittingup the arrangements .for producingthe plastic block scanner. The motorpart, however, comprises a rotor con-sisting of an eight -tooth wheel, r in.in diameter, cut out of 1/16 in. thickiron sheet, and pole -pieces made bybending up a length of a in. by 3/32in. iron as shown in the picture, withwindings of No. 32 enamelled wire(for operation off the 8 volt 5o cyclesupply used to light the lamp).

There is only one point that isreally important for success with thismotor : there must be either a springcoupling of some sort between therotor and the scanner, or between,at least, some two parts of the rota-ting system as a whole, or else a partof some sort running free, with asuitable degree, of friction, on therotating system. This is necessaryto damp out disturbing impulses thatwould otherwise stimulate hunting oreven throw the scanner out of syn-chronism. This point was explainedin the August, 1938, issue of thisjournal. In the form now illus-trated there is a free running brassdisc, with a moment of inertia of thesame order as that of the scannerblock, which effectively keeps thesystem running smoothly.

Chance for SeriousExperiment

With the availability of these twoscanning units and the necessarylenses, the way has been opened forthe experimenter to work seriouslyon mechanical television reception.The author does not wish to give theimpression that he has offered herea finished and complete alternativeto the cathode-ray tube type ofreceiver; it is not feasible, with in-dividual work on an experimentalscale, to offer the certainty of trouble -free, perfect results that has beenachieved, with the cathode -may typeof receiver by years of research bymany big companies. It is assumed,therefore, that anyone who merelywants a trouble -free televisionreceiver will not bother with mechani-cal arrangements at all, until, if ever,the big companies have led the waywith cheap mechanical sets. Theexperimenter, however, is in a differ-ent class; he wants interestingdevelopments, and the chance to doa bit of research on his own, and ithas been that desire that has stimu-lated the author to suggest the pre-sent arrangements. He is fairly wellsatisfied that they are actually prac-tical means of receiving televisionprogrammes, and is going ahead todevelop them further.

It is hoped, in the course of thisdevelopment, to give shortly con-structional details for a set using thescanners now developed, and thevision receiver, lenses and optical

frame previously described, but withthe details of design cleaned up andthe overall size cut down. The pic-ture size of this set would be fourinches, and care would be taken toprovide for acceptable picture quality ;not merely, as so far, for the simplestarrangement that will do the job atall.

As has already been stated, this ideahas from the beginning been kept inmind, and the components describedare such that improvements inquality are possible with them byslight additions and modifications.The only big departure that wasnecessary from the original schemeoutlined a year ago has already beenmade, viz., the substitution of thenew nine -ball synchronised scannerfor the simple mains -driven type. Thereduction in over-all size of the set ismade possible by partly cutting theweb B (see previous articles) of theoptical bench, and bending this sothat the lamp is brought nearer inand nearer the front; a mirror is thenneeded to reflect the light round thisbend, to the light control, and in in-troducing this the opportunity will betaken to insert a small prismaticdevice for utilising the diffracted, in-stead of the direct beam, as hitherto,from the light relay, thus givingbetter contrast and gradation in thesimplest possible manner. At thesame time this will bring the picturecloser to the centre of the receiver,improving the appearance consider-ably. None of these alterations willbe difficult or expensive.

The Television ImageR. F. SCH RUETER, in discus-sing the acceptability of tele-vision pictures in Telefunken

Hausmitteillungen, from the points ofview of physics, physiology, andpsychology formulates the followingconclusions :

Psychologically and aestheticallyabsolute image size is not a decisivefactor in combined television andsound broadcast recepton.

Home television screen dimensions,for a 441 line interlaced image, shouldnot exceed 12.4 in. by 10.4 in.

With the present number of scan-ning lines, large images are of valueonly in large rooms and in connec-tion with proportionately extendedviewing distances.

The normal contrast range satisfiesall requirements, provided that straylight is excluded from the vicinity ofthe screen. Where stray light inter-feres, the brightness level in inter-laced images is limited by flicker.

In room; with interference fromthe lighting system the most satisfac-tory tone colour is produced byscreens which fluoresce with strongwhite and some blue.

Television calls for high fidelityacoustical reproduction to be accep-table, just as do sound motion pic-tures.

Television is significant primarilyfor extending ordinary optical limitsand thus enabling audiences to wit-ness distant events as they aretaking place.

406

JULY, 1939

Fig. 12. The power pack, output stage and loudspeaker.

EQUIPMENT to. provide thesound accompaniment to theprogrammes of the vision re-

ceivers described last month was de-signed for the same receiving con-ditions as the vision section. Anadequate sensitivity margin is pro-vided for reception at distances up to20 miles or so. The inclusion of re-generation renders reiteption, atslightly impaired quality, possible atgreater distances however. Again,as for the vision apparatus, the designis entirely conventional. In the firstplace this equipment consisted of aR.F. stage, a regenerative triodedetector and a high mutual conduct-ance output pentode. It transpired,however, that this arrangement hadnot quite the necessary gain and theregeneration control had to be ad-vanced considerably to provide therequisite volume. Despite this fact,however, it is considered that such anarrangement will provide excellentresults in the majority of cases up todistances of 20 miles.

IncreasingGain

It is a simple matter to amend thecircuit given to these conditionsshould it be desired to employ thissimpler arrangement. The valve V 17is omitted and the output terminalis connected directly to the o.t ittFd.condenser blocking the grid of theoutput valve Vr8. Should the gainsubsequently prove inadequate, it isa simple matter to include this addi-tional stage as shown by the circuitdiagram already referred to (Fig. so).To avoid any confusion, it is pointed

ANDSHORT-WAVE WORLD

ARECEIVER FORTELEVISION SOUND

Last month a complete design for a vision receiverfor local reception was given. This article describesthe sound unit, the whole providing a low-cost

efficient vision and sound combination

out that the photographs reproduced(Figs. 11-15) show the sound receiverin its original form, that is as a three -valve receiver. The additional L.F.stage later added, was accommodatedwith very slight alterations in theamplifier chasis, the valve holder forthis valve taking the place of the twoinput terminals shown in the photo-graph, Fig. 12, mounted adjacent tothe loudspeaker. These terminalswere then moved, forward. Adequatespace to accommodate the additionalcomponents exists beneath the chassisas is apparent from a glance at thephotograph, Fig. 13.

The increase in gain provided bythe additional stage is not fully re-quired, and advantage of this fact istaken by including negative feedbackto this stage, thereby overcoming theshortcomings of the pentode ouputvalve. Furthermore, due to the highefficiency of this output valve, theamount of L.F. gain that can usefullybe employed, unless somewhatelaborate decoupling is included to

Fig. 11. Interiorview of R.F. and

detector stages' of

sound receiver.

preclude the possibility of hum orL.F. oscillation, is restricted. Nega-tive feedback is thus rendered desir-able even when ignoring the questionof quality.

It will be seen that the apparatusconsists of two units. The small unitcomprising the R.F. and detectorstages, the larger unit the outputstage, and the L.F. coupling stagewhen this is employed. The powersupply arrangements for both chassisare also included in this unit. Thedimensions of these units are given inthe drawings, Fig. i5.

SimpleConstruction

This method of construction issimpler and also permits the signalreceiving section to be employed inconjunction with existing amplifiersor a normal broadcast receiving set.In the latter case it is only necessaryto connect the two output terminalsof the small unit to the pick-up ter -

407

TEJAYIS1OBAND

SHORT-WAVE WORLD

CIRCUIT OF SOUND RECEIVER

JULY, 1939

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minals of a broadcast receiver, theplate of the detector valve beingconnected through a blocking con-denser to the live pick-up terminal,i.e., to the terminal connecting to thegrid of the input valve. It is usuallysimple to determine which this is bytouching each in turn, the live ter-minal being that which, upon beingtouched, causes hum in the speaker.The volume control is preferablyturned well up, to increase the sensi- Fig. 13. Underside

tivity, during this test, view of power unitA conventional filter is included in and output stage.

the plate circuit of the output valveto reduce the treble response. Sucha filter will also mitigate harmonicdistortion and tends to level the loadcharacteristic. It is preferable whenemploying negative feedback toarrange for selective frequency dis-criminating circuits to be switchedinto the feedback circuit as an alter-native to the above. No details ofthese circuits are included, however,

Fig. 14.view of

detector

UndersideR.F. and

stage unit.

in view of the desirability of keepingthis description simple.

The speaker employed is a Celes-tion, but this item can be a matter forindividual choice. The optimum loadfor the Brimar type 7A3 valve is in theregion of 8,5..o ohms, and any suit-able Fpeaker can be employed.

The picture definition provided bythe vision unit is of a very high order,providing reasonable care is takenwith the adjustments, particularlythat of the condenser across the diodecoupling coil. The necessary adjust-ments to the time base are simplyeffected in accordance with conven-tional methods which have been fullyoutlined in previous articles.

408

JULY, 1939TELgYISIOil

ANDSHORT-WAVE WORLD

Tuning in the case of the soundreceiver is quite easily achieved. Atrimmer is fitted to permit the tuningcondenser to be ganged, but it is notreally necessary, as it is a simplematter when only a single station is tobe received to free the spindle coup-ling and adjust individually the twocondensers when the coupling can betightened. Should it not prove pos-sible to secure oscillation, the capa-city of the regeneration condenser

cerned, will largely depend upon theadjustment of the regeneration con-denser. Accordingly, no more feed-back than will provide sufficientvolume and discrimination againstthe vision channel should be em-ployed.

The circuit diagram of the visionunit power supply is given by Fig. 2b(May issue). It comprises a 25o voltH.T. supply for the vision and syn-chronising section. It will be obvious

-2 fi 2 j--- 24:.-..-oh-I/

rig. 15. Details of chassis construction.

can be increased. Again, for recep-tion of a fixed frequency station it isconvenient, should such a course benecessary, to parallel a small trimmeracross the regeneration condenser.It should be observed, however, thatthe quality of reproduction, as far asthe treble response at any rate is con -

that where an existing sound ampli-fier or a B.C.L. receiver is to be em-ployed, in conjunction with the smallsignal receiving unit, that the powersupply for this small unit can conve-niently be provided by this supplyunit an additional centre tappedL.T. winding for heater operation and

a separately smoothed tapping fromthe H.T. circuit being the only addi-tions necessary.

AerialIt is perfectly feasible to employ a

common aerial for sound and vision.The aerial terminals can be connectedin series or in parallel depending uponthe arrangement and layout of theunits. Alternatively, quarter -wavematching sections isolating the unitsfrom one another can be used. Thesesections can conveniently consist ofadjusted inductances if desired. As afurther alternative small transformerscan be employed. In general, suchadditional complications are unneces-sary, and it is entirely satisfactory toconnect the aerial terminals inseries. Also in the vision unit's cir-cuit diagram (p. 325, Fig. za) thereis shown a resistance between L7and the 7,5oo ohms resistance. Theinclusion of this item in the diagramis an error and no resistance is re-quired in this position.

CORRECTIONIt is regretted that a small error

occurred in last month's article inthis series. The terminal marked

mod ' in Fig. 6a should not bedirectly connected to the output ter-minal of the vision unit but should beisolated with a condenser of o.5 uFd.capacity connected in series.

A NEW STUDIOANEW system of television

studio lights has been installedin the N.B.C. Radio City tele-

vision studios which does away withthe necessity of using the heavy, heat -giving movie type " suns," " spots "and " broads." A complete pre-setsystem of lighting units, that formerlyrequired the service of three men forseveral hours, can now be acorn-plished by one man in less than tenminutes.

Basically, the new system consistsof many remotely controlled lightingunits, suspended from the ceiling ofthe television studio. Each unit, of abank of six lamps, may be raised andlowered, or tilted through a consider-able angle, and swung through nearlya complete circle. Light may thus befocused on any desired spot in thestudio. Remote control from thelighting engineer's desk at one end ofthe studio enables him to change thelighting set-up at any time during anactual broadcast without interferingwith camera movement.

LIGHTING SYSTEMThe new lighting units have

effected a reduction in electrical loadand a corresponding reduction instudio temperature.

One of the problems of studiolighting has been the supply of suffi-cient overall, illumination for thescenic sets used in a television show.Previously, television has followed amodified motion picture practice ofsetting individual light units in fixedoverhead positions.

ProvidesLight " Flow "

The resulting compromises in dis-tributing the available overall light-ing made this system inadequate fortelevision. Motion pictures are pro -

Ensure obtaining " Television and

Short-wave World " regularly by placing

an order with your newsagent.

duced piecemeal and the film asfinally released is assembled in thecutting room. A flexible lightingsystem is, therefore, not of greatimportance to the cinema industry.Television, however, follows stageand radio practice; the action flowscontinuously from beginning to endand the accompanying illuminationmust flow with it if acceptable photo-graphic effects are to be achieved.The new N.B.C. system provides thisnecessary " flow " in the light accom-paniment.

Light from the studio floor andfrom the sides of sets, used to" erase " undesirable shadows cre-ated by an overhead lighting system,is now supplied by lightweight andmovable floor units, each supportinga bank of inside silvered lamps. Asmall lighting " dolly," mounted onwheels and bearing several lamps,furnishes the flexible element in this" modeling " illumination. Lessthan two feet in height, this dollymay be moved to within a few feetof an actor without appearing in thepictures.

D409

IgLIYIS1011AND


RECENTTELEVISIONDEVELOPMENTS

A RECORDOF

PATENTS AND PROGRESSSpecially Compiled for this Journal

Standard Telephones and Cables Ltd. :: Telefunken Ges fur drahtlose Telegraphie m.b.hF. J. G. van den Bosch :: A. Carpmael and H. R. C. Van de Velde :: Baird Television Ltd.,

and E. G. 0. Anderson :: J. D. McGee :: W. D. WrightTransmitting Tubes(Patent No. 501,375.)

THE " mosaic -cell " screen of atelevision transmitter of thelconoscope type is replaced by a

photo -sensitive electrode consistingof a pair of thin metal sheets, placedback to back, with an interveninglayer of insulating material. Thesheets are perforated uniformly, oneside being coated with a photo -sensi-tive substance, and the other with alayer of highly -resistant material.

The electrode is placed midwayalong the length of a cathode-raytube, and the image to be televised isfocused on to the photo -sensitivesurface, which is then scanned by anelectron stream from one end .of thetube. The liberated electrons areprojected on to an electron -multiplierarrangement at the other end of thetube, where they are amplified bysecondary emission before passingout to the transmitter.-StandardTelephones and Cables, Ltd.

Television Cabinets(Patent No. 501,532.)

Relates to a cathode-ray televisionreceiver in which the picture on thefluorescent screen of the tube T isreflected by a mirror M so that it is

screen at the same time as the re- of the received picture. Mountedfleeted picture, since this would dis- next to the screen is a flat disc -liketract his attention. This, in turn, chamber, containing iron particlessets a limit to the height of the suspended in paraffin. The lightobserver's eyes when looking at the from a powerful lamp, mounted out -received picture. side the tube, is focused through the

According to the invention, the zinc sulphide screen on to the paraffincathode-ray tube, instead of being chamber.mounted vertically in the cabinet, is Normally the iron particles in the" set back " at the angle shown. paraffin set themselves " higgledy-For a cabinet of given height, this piggledy," so that they block outincreases the viewing -area or eleva- practically all the light from the lamp.tion D over which the picture can be But the static charges formed onseen in the mirror without interference the zinc sulphide by the action of thefrom the direct light of the fluorescent scanning -beam cause each of the ironscreen.-Telefunken Ges fur draht- particles to swing round and set them -lose Telegraphie m.b.h. selves " end on " so as to afford free

Transparent Screens passage for the light. In other wordsthe transparency of the paraffin cham-

(Patent No. 501,816.) ber is varied locally, according to theInstead of the usual fluorescent picture intensity. Light from the

screen a cathode-ray television re- lamp can therefore pass through andceiver is fitted with a screen of zinc project an image of the picture on tosulphide, on which the scanning -beam a large viewing -screen mounted out -acts to set up local charges corres- side the cathode-ray tube.-F. J. G.ponding to the light -and -shade values van den Bosch.

viewed indirectly. Although the in- Arrangement of tubePatentclination of the mirror can be varied, in cabinet.No.

501,532.it is normally kept at a fixed anglewhen the set is in operation. Theperson using the, set should not, ofcourse, be able to see the fluorescent

The information and illustrations on

0

Tj

7-

.4 73

75

4 T7

this page are given with permission of the Controller of H.M. Stationery Office.

410

Variable electronmultiplier. Patent

No. 502,686.

TLIVISIOtiJULY, 1939

Television in Colour(Patent No. 502,358.)

To produce television pictures incolour, the light from a powerful arclamp is passed through three different" light -valves," set side by side, andprovided with red, yellow and bluefilters respectively. Each cell is ofthe " supersonic " type in which apeizo-electric crystal creates high -frequency waves in a liquid, whichthen causes interference fringes to be

shown. In parallel with the leads Lis an amplifier A, which amplifies thelight picked up by a cell K arrangedto respond to the " background in-tensity " of the scene being televised.The effect of the auxiliary potential,so applied from the cell K to theelectrodes T5, T6, s automaticallyregulates the final output from themultiplier in the manner desired.-Baird Television, Ltd., and E. G. 0.Anderson.

Method of avoiding lossof focus. Patent No.

502,975

set up in the path of the ray of light.The three light cells are controlled

in turn, so as to give what is, ineffect, " interlaced " scanning foreach of the primary colours. For thispurpose a special type of a cathode-ray tube is used, in which the electronbeam is continually swept over threedifferent sections of a common anode.

Each of the three sections controlsau amplifier to which the incomingsignals ars applied, so that these arefed in rapid succession first to thered, next to the yellow, and then tothe blue " light valve." The differ-ent " scans " are finally reassembledon the viewing -screen by two rotat-ing mirror -drums set at right -anglesto each other.-A. Carpmael andH. R. C. Van de Velde.

" Variable " Electron - multiplier(Patent No. 502,686.)

The Figure shows an electron -multiplier arranged for amplifyingtelevision signals. More particularlyit allows the degree of amplificationto be. varied from time to time, inorder, for example, to follow any slowchanges that may occur in the aver-age light -intensity of the " back-ground " of the scene being televised.

Light from the picture is focusedon the photo -sensitive cathode C ofthe electron -multiplier, the resultingstream being amplified by secondaryemission from each of the " target "electrodes Ti . . . T8. Each of thesecarries a gradually -increasing positivevoltage which is tapped off from apotentiometer R. The voltage on thetwo electrodes T5, T6 is, however,reversed by means of the leads L as

Multiple -spot Scanning(Patent No. 502,796.)

A cathode-ray television receiver isarranged to produce several electron -streams, each separately controlled,so as to scan the screen in regularsequence, one after the other. Thecathode or " gun " of the tube con-sists of a number of separate andmutually insulated strips, each actingas the source of one stream. Thestrips are arranged along the outsideof a cylindrical heating -element witha filament running axially inside. Awire is connected to each stripthrough which separate control poten-tials are applied, to bring each intoaction in turn. Separate controlgrids may also be arranged in frontof each emitter, so as to ensure thatthe screen is scanned by each of thestreams in regular succession.-J. D.McGee.

Optical Focusing(Patent No. 502,975.)

In certain forms of television trans-mitter tubes the electron -emittingsurface is made curved, instead offlat, in order to avoid distortion ofthe image. In such cases the sensi-tised surface is usually transparent,and the optical image is projected onto its convex surface. The resultingelectron emission, of course, takesplace from the inner or convex sur-face.

This type of tube calls for an opticallens system of special design if thewhole image-and not merely theaxial rays-is to be truly focused.According to the invention, the

ANDSHORT-WAVE WORLD

optical system consists of a lens Lfor producing an image in the planeP, P, and a diverging lens Li placedin the plane P, so that the combina-tion produces an accurately -focusedimage on the convex surfaces whichcan then be placed directly in con-tact with the similarly -shaped surfaceof the photo -sensitive cathode.-W. D. Wright.

(Patent No. 501,966)Television system in which signals

from different scanning points can bemixed together.-A. I). Blumlein.

(Patent No. 502,696)Construction of stationary mirror -

ring, for scanning, in which all themirror, elements are held in positionby pressure applied to the two endmirrors.-E. Traub.

Patent No. 502,830)Circuit for producing saw-toothed

oscillations for use in scanning.-Marconi's Wireless Telegraph. Co.,Ltd.

(Patent No. 501,058)Clear-cut focusing of the electron

stream of a cathode-ray tube.-C. S.Bull.

(Patent No. 501,535)Cathode ray television receiver in

which a " flooding beam " of elec-trons is used in combination with theusual scanning-stream.-Baird. Tele-vision, Ltd., and T. C. Nuttall.

(Patent No. 501,741)Means for treating luminescent

screen material so as to increase itsresistance to burning. --M arc one sWireless Telegraph Co., Ltd.

(Patent No. 501,919)Electron -multiplier in which a

" mirror action " is used to producesuccessive impacts of the main dis-charge-stream.-H. G. Lubszynskiand W. S. Brown.

(Patent No. 501,931)Magnetic lens system for focusing

the electron stream in a cathode-raytube.-The British Thomson -HoustonCo., Ltd.

Patent No. 494,145.Cathode-ray receiver in which a

grid electrode is scanned by an elec-tron stream proportional to the in-tensity of the received signal, andcontrols the passage of a secondelectron stream on to a fluorescentsurface.-Radio-Akt. D. S. Loewe.

Patent No. 495,331.Method of offsetting the inherent

time -delay of circuits used in derivingsynchronising -impulses from A.C.mains.-Baird Television, Ltd., andV. A. Jones.

411

TEMISJOilAND

SHORT-WAVE WORLD

TelegossipTHOSE seven hundred viewers

who applied to the B.B.C. forinvitation to the free Television

Tea Party (which will have takenplace at Broadcasting House by thetime these words are read) may beinterested to hear how Mr. GeraldCock, the Television Director, chosethe 15o guests. He placed all theletters in a waste paper basket, hadthem well stirred and then picked atrandom.

One of the most interesting appli-cants was a man who declared thathe had been an invalid for thirteenyears and during that time had neverbeen able to go out to a cinema ortheatre. 'Television is a God -send tosuch unfortunates. He proposedgoing to Broadcasting House in hisinvalid chair.

20,000Receivers

There are now about 20,000 tele-vision set owners, according to semi-official estimates. So approximatelyone in thirty asked to go to theB.B.C. party, a very high proportion.The television audience is still to someextent a big family and viewers takea personal interest in the pro-grammes, the staff and the problemsof production. It was precisely thesame among pioneer listeners in the'twenties, but the broadcasting audi-ence quickly grew to unmanageableproportions, whereas television movesslowly.

Curioser and curioser grows thesituation regarding a Birminghamstation. Last month, writing on ex-cellent authority, I indicated that afavourable decision might be ex-pected soon Since then the Post-master -General, who was greatly im-pressed by the arguments put beforehim by the Radio Manufacturers' de-putation, has seen three other deputa-tions representing the theatrical andcinema industries, putting the casefor the opposition. It is reportedthat this has given him pause andthat there will be no provincial tele-vision station without suitable safe-guards for rival entertainments.

But I cannot believe that this isthe real cause for deferring a deci-sion. The Television Advisory Com-mittee exists to advance television notto raise difficulties. A prominentleader of the music hall industry toldme that every new entertainmentaffected theatre attendances at first,

but that eventually, when the noveltyhad worn off, people flowed back tothe music halls in increased numbers.Every new type of entertainmentseems to whet the appetite afresh andto stimulate the public demand to beamused. Mr. George Black, direc-tor of the General Theatre Corpora-tion, was for years a strongopponent of broadcasting. Now heis an enthusiastic believer in its pub-licity value.

I believe that the reasons for delayhave nothing to do with the clash ofinterests. The gear for the radiotelevision link experiments, orderedby the Post Office from E.M.I., hasnot yet been delivered, and, I under-stand, is not expected to be readybefore the end of the year. The factis that the Post Office has such a vastamount of work on hand for theDefence Forces and the A.R.P. or-ganisation that television has defin-itely taken a back seat. The RadioManufacturers' Association shouldnow press their campaign with re-newed vigour. Peace -time develop-ment cannot be entirely submergedby preparation for war. In the so-called bloodless "war of nerves"nebulous fears should not be allowedto produce that creeping paralysis ofthe nation's life which our enemieswould rejoice to see.

A.P.Staff

Nor has the financial difficultybeen properly resolved. The R.M.A."offer" to put up J,'roo,000 "if theprojected station were not a success"was couched in such vague terms asto be held valueless by official circles.The Advisory Committee, I believe,is much exercised over the possibilitythat Midland and Northern viewersmay not be satisfied to draw all theirprogrammes from London and maydemand separate studios and Regionalprogrammes. Now the staff ofAlexandra Palace was recently in-creased to 450. In other words, forthe present strictly limited serviceone -eighth of the total staff of theB.B.C. is employed. Roughly tentimes as many employees are requiredfor a television programme as for itsequivalent in sound.

But the service must be allowed togrow and a review of the difficultiesdoes not advance matters much.Officialdom must cease to boggle andact courageously and decisively.

JULY, 1939

A Causerie of Fact, Commentand Criticism

Meanwhile staff expansion goes on.The B.B.C. has just recruited fournew assistant studio managers andan outside broadcasting assistant.The assistant studio managers arePaul Chesterton, Peter Henschel,T. M. Jenkins, and Campbell Logan,and the new O.B. manager is G. dellStrother. All have had film and stage.experience. Mr. dell Strother wasan assistant director to AlexanderKorda for four years.

D. H. Munro, just returned fromNew York, where he has been advis-ing the Columbia television staff ontheir new service, is reticent abouthis visit because he says he does notwant to seem patronising or discour-teous to his late hosts. But the factis that, as always at the start, organi-sation was at a very primitive stage.Columbia had two cameras and twotelecine channels, but had omitted tomake any provision for sound ! How-ever, that was soon corrected, andMr. Munro produced one or twospecimen programmes on a closedcircuit. Regular programmes havenot yet been started by Columbia.

Big -screenDevelopments

One of my most interesting tele-vision experiences this month was thebig screen reproduction of Troopingthe Colour. This I saw at the NewVictoria which is only a short walkingdistance from the Horse GuardsParade. Some hundreds of people pre-ferred to watch the television versionat cinema prices rather than standin the crowd and endure the Juneheat. I imagined at one time thattelevision was playing tricks by mak-ing the long straight line of Guards-men into a crescent. But Mr. PhilipDorte vigorously defended his trans-mission and he must really have it outwith the Brigade of Guards, for Idecline to take sides.

I thought I was' used to big screenshows, but once again I was mostimpressed with this Baird achieve-ment. On entering the theatre I feltthat the most important improvementnecessary is more light, and then,from the back of the theatre it wouldto the eye be almost indistinguishablefrom a cinema picture.

I am told that even big screen de-velopment is held up by the AdvisoryCommittee's procrastination over aBirmingham station.

412

TELE YE1011JULY, 1939

NARROW BAND PICTURE TRANSMISSIONAMETHOD of transmission and

reproduction of line imageswhich do not necessitate great

detail has been the subject of experi-ment in the U.S.A. with the objectof using a comparatively narrow bandwidth. Tests have shown that adrawing of a woman's head could bereproduced in outline with an equiva-lent total band width of approxi-mately 2,60o cycles. This is madeup of two bands, each 1,300 cycleswide. Analysis of a more compleximage, such as that of an animatedcartoon shows that such materialcould be transmitted and reproducedby the method within a total bandwidth of To kc.

The illustrations shown by theauthor in explaining the system areeach in the form of a closed loop inwhich the spot on the cathode-raytube is made to traverse by applyingsimultaneously the proper voltagesto the horizontal and vertical deflect-ing plates. The voltages are, ofcourse, directly proportional to thex and y coordinates of the point ofthe drawing, taken along the path ofthe spot in the direction in which itmoves.

The system therefore essentiallyresolves itself into the problem ofmaking line drawings, determiningthe x and y coordinates for eachpoint on this line, generating deflec-tion voltages proportional to thex and y coordinates, and transmittingthe two voltages simultaneously.

At the receiver they are re-assembled in such a manner that xand y displacement voltages areapplied to the horizontal and verti-cal plates of the cathode-ray tube forthe reproduction of the image.

The primary advantage of thismethod is that it enables certaintypes of drawings to be reproducedwith much less band width than isnecessary at the present time with theusual scanning method of televisionoperation.

The two kinds of detail which willsuffer most are straight portions andsharp bends. The overall shape andForm of the image and the largerdetails are dependent on the lowerfrequencies which are present in thetransmission band, and these fre-quencies are therefore the most im-portant ones. If the bands includeenough harmonic to reproduce thesmall detail, even in approximate

form, the larger details of generalform will be reproduced with goodfidelity.

The total band width necessary forsatisfactory reproduction of a WaltDisney cartoon was judged to beto,000 cycles, this total being madeup of 5,000 cycles each for the x andy deflecting potentials.

A total band width of io,000 cycles

ANDSHORT-WAVE WORLD

is also adequate for about sevenwords of handwriting. The totalband width for script is proportionalto the total number of letters andspaces, or to the number of wordsof average length.

The type of images which arecapable of transmission by thismethod include drawings, diagramsand maps, either with or withoutanimation, animated cartoons, andscript.

TELEVISION STUDIOLessons of Seven Years' Experience in

IT has been found that real proper-ties invariably televise satisfac-torily, although suitable illumina-

tion may be required for emphasis.In painted properties, such as back-ground, windows and fireplaces, thedelineation of the object from thegeneral tone of the backgroundshould be sharp, and the width oflines comprising the structures bold.A certain amount of defocusing isusually obtained on the background,often for the purpose of centringattention on the principal characters,who are in sharp focus, as is utilisedin cinematography. The backgroundproperties are therefore televised insubdued tones as desired.

For multi -character scenes, thelong shot is often used with completesettings, such as a room, which mayassist in the story. If small itemsof interest are to be displayed, how-ever, the scene may be modified fromwhat would normally be a long shotto one showing only half or two-thirdsof the principals involved. One scenemay be changed into the other bymoving the camera, or by moving theprincipals. On many scenes, a ratherhigh camera is utilised, that is, thelens 4 or 5 feet from the floor.Changes from long shot to close-upmay be made once or twice during anepisode. Changes of scene areusually accomplished by panning,under which conditions, two sets areestablished on opposite sides of thegeneral stage area.

LightingThe technique of lighting for tele-

vision appears to be one of the mostfruitful in creating pleasing artisticeffects. So-called " flat lighting "will give television pictures, but oneswhich have little interest and sparklecompared to those televised withmore elaborate lighting. By flatlighting, of course, is meant thatnearly all the light to illuminate the

TECHNIQUEthe Don Lee Studios

scene comes from the front of the setand perhaps also from the top of theset at the front.

The advance technique appears tobe only limited by the number oflighting units available, and thepossibility of manoeuvring them asrequired for the changing conditionsbrought about by motion of the per-formers on the set. This problem iscomplicated by the fact that in tele-vision, illumination must be con-tinuous for the total duration of theact. In motion picture technique,each portion of action may be madeas a separate take and ample timeallowed for skilful placement of thelights.

In the Don Lee studio, a portableswitching panel is installed whichgives control of individual or limitedgroups of all the lights utilised. Withthis device the lighting supervisor canvary the lighting considerably with-out touching any unit. This controlis usually supplemented by changingdiffusers, changing the angle of theunit, and/or change of position ofmobile units by lighting assistants.A consderable number of the lightingunits are fixed in position near theceiling, each in the proper directionfor usual action as has been deter-mined by experiment. A few mobilefloor units are utilised.

Hard back lighting has been foundto be a very desirable component.This must be supplied by lens -reflec-tor .units. General lighting is pro-perly supplied by lampi in dull finishreflectors and modeling lights for theface must be diffused with one ormore diffusing screens.

The camera photo -electric tubesuffers a form of overload similar toover -exposure, if the illumination onthe subjects is too great. Thisusually occurs first on the faces ofthe performers and gives a " washed-out " effect, in which the sharpness of

413

IglAYS10,1AND


the features are lost. This condi-tion is eliminated by either reducingthe amount or hardness of the light,or stopping down the lens aperture.Make-up is also a factor in this effect,and lighting, camera aperture andmake-up must be correlated in orderto achieve desirable results. It hasfurther been found that the spectralcharacteristic of the light exercises animportant effect on the resultingimage. A pure white light is theideal.

Use ofModels

Cognisance is taken of the fact thatlarge and elaborate sets are beyondthe present scope of television econo-mically, if not otherwise, and thatphysically impossible actions mustnot be imposed upon the cast.Through the use of miniatures, how-ever, otherwise impossible action hasbeen televised. In a recent episode,a considerable portion of the actiontook place in close shot with thecharacters in an aeroplane. Run-ning out of petrol they go into a tailspin and crash on land. The firstscene was taken with the charactersand life-size properties. The nosedive was made by means of a minia-ture airplane, handled by wirei, andthe crash scene, previously set up onanother set, was occupied by thecharacters during the transitionthrough the miniature.

SoundPick-up

Two methods of microphoninghave been evolved, first, the boom ormoving microphone method, whereina comparatively light microphoneboom is utilised and moved to keepthe microphone reasonably close tothe performers. The usual micro-phone position is overhead and infront of the performers and as closeas possible without appearing in thepicture.

The second method utilises up tofour stationary microphones. Theseare arranged at strategic points onthe scene of action, and the electricalchange -over from one to another isaccomplished by fader operation bythe sound monitor supervisor. Thismethod does not require productionassistants for moving the microphoneboom.

Make-upMake-up is most important in long

shots. In close-ups, street make-upis sufficient, although accentuatedmake-up may be utilised by increasing

the light intensity on the subject.A base paint is utilised as a start.

Eyebrows are accentuated with blackor dark brown liner. Lipstick of abrownish -violet shade is applied.This colour has been found desirableafter considerable tests in perform-ance to the red lipstick, because thecamera tube exhibits increased sen-sitivity in the red region of the spec-trum, and because red light energyis particularly predominant in the in-candescent illumination utilised.

Overall supervision of all the pro-cesses of television operation and pro-duction can be exercised by a suitablytrained director, who observes theprogramme at a sight -sound tele-vision receiver located at a represen-tative point in the service area of the

television station. He talks by tele-phone to the televsion studio super-visor, television transmitter controloperator and possibly to other mem-bers of the operating staff. Defectsin lighting, camera technique, micro-phoning or television control ortransmitter adjustments are thus in-stantly apparent. Monitors are pro-vided in the studio and also at thetransmitter, the latter operating froman input which has been radiated.Following the complete broadcast, awritten report is prepared by thedirector. This includes tabulation ofvarious technical readings, the artis-tic observations on the merit of thecamera shots and lighting, and asummary of the merit of the broad-cast as a whole.

SPONSORED PROGRAMMES IN U.S.A.H ILE it is expected thattelevision will become anadvertising medium in the

U.S.A., the Federal CommunicationsCommssion has not yet licensed anytelevision broadcasting station tooperate commercially. The NationalBroadcasting Co. has not as yetplanned any immediate sale of itstime, but, of course, will expecteventually to make available certainhours of sponsored television pro-grammes. In the meantime, it isfollowing the policy of creating asmuch programme variety as possiblein order to build up a fund of experi-ence which will be of value to adver-tisers when the time comes for spon-sored programmes.

Programme material already triedhas included drama, variety andmusic and novelty, including ping-pong, fencing and animal acts. Full-length films, newsreels, and shortfilms were also tried. In the field ofeducation, programmes have been in-cluded embodying the microscopethrough which the " family life " ofminute organisms was watched by thetelevision audience and described byspecialists on the subject, traveloguesthrough various parts of the world,book reviews, dancing lessons, andscience demonstrations. Experimentshave been made with a mobile out -

Mention of " Television and Short-wave

World " when corresponding with

advertisers will ensure prompt attention.

door pick-up unit at various times todetermine what may be done in theway of providing broadcasts of cur-rent events and outdoor athleticcontests.

There has been collaboration withthose industries whose productsappear to lend themselves mostreadily to television exploitation. Ex-perimental programmes have beenworked out with advertisers in manyof the major industries, includingcars, fashions, jewelry, foods, steel,drugs, oil, tobacco and others.

Special observers have been em-ployed whose task it has been towatch and chart the development oftelevision in relation to its possibili-ties as an advertising medium. Thesemen have developed exhaustive filesof information on all phases of themedium and have explored its futurepossibilities from the economic andfrom the practical advertising stand-points, have made preliminary plansfor the maintenance of proper statis-tical records, the measurement ofreception conditions and a study ofthe psychological aspects of televisionadvertising. They are also care-fully studying the application of tele-vision programme technique to suchproblems as package design, com-mercial announcements, and drama-tisations of the uses of products.Analysis has been made of the typesof industries which may be expectedto be able to use television mosteffectively and the functions to be per-formed by all those concerned in theproduction of commercial televisionprogrammes have been studied.

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Using the 6L6G and APP4G ValvesTetrode and pentode valves have many advantages which make them suitable for amateur use.

Perhaps the main feature is the small amount of drive needed so that multi -band transmitterscan be made with the lowest number of stages.

TWO very .useful valves are nowbeing manufactured by theTungsram Co., the first of which

is a oL6G marketed by Webbs Radio,and the second the APP4G obtainablethrough all normal channels.

The special 6L6G has a ceramic baseand can be used as an R.F. power am-plifier, or oscillator as required. Toobtain optimum results the constantsadvised by the makers must be care-fully adhered to. To this end the fol-lowing data should be noted.

Constants for R.F. P.A. Class -BTelephony.

Carrier conditions per valve formaximum modulation factor of 1.

Anode voltage, 400 volts.Anode current, 75 mA.Anode dissipation, 3o watts.Anode input, 4o watts.Screen voltage, 25o volts.Screen resistance, 17,000 ohms.Screen current, 4 mA.Screen dissipation, I watt.D.C. grid current, 0.2 mA. approx.D.C. grid voltage, -25 volts.Peak R.F. grid voltage, 3o volts.Driving power (approx.)*, 0.25 watts.R.F. power output (approx.), 9 watts.

Additional output can be obtaineawhen the valve is used as a class -CR.F. amplifier and modulated. Theoperating conditions are then as fol-lows.

Carrier conditions per valve for usewith a maximum modulation factor of T.Anode voltage, 325 volts 400 volts.Anode current, 8o mA., 8o mA.Anode dissipation, 11 watts, r, watts.Anode input, 26 watts, 32 watts.Screen voltage, 225 volts, 225 volts.Screen resistor,t 10,000 ohms, 16,000

ohms.Screen current, 9 mA., 9 mA.Screen dissipation, 2.0 watts, 2.0 watts.D.C. grid current (approx.), 3 mA.,

mA.D.C. grid voltage, -45 volts, -50

volts.Peak R.F. grid voltage, 70 volts, 70

volts.Grid leak, 5,000 ohms, 10,000 ohms.Driving power (approx.), 0.2 watts,

0.13 watts.R.F. power output (approx.), 15 watts,

19 watts.

Maximum carrier power can, ofcourse, be obtained when the valve isoperated as a class -C amplifier for tele-graphy. In such circumstances the

At crest of A.F. cycle with modulation factor of x.t Connected to modulated anode voltage supply.

carrier power with only 400 volts H.1.is no less than 25 watts.

Key down conditions per valve with-out modulation.Anode voltage, 400 volts.Anode curernt (approx.), 95 mA.Anode dissipation, 13 watts.Anode input, 38 watts.Screen voltage, 250 volts.Screen resistance, 17,000 ohms.Screen current, 9 mA.Screen dissipation, 2.2 watts.D.C. grid current (approx.), 2.5 mA.D.C. grid voltage, -5o volts.Peak R.F. grid voltage, 8o voltsGrid leak, 20,000 ohms.Driving power (approx.), 0.18 watts.R.F. power output (approx.), 25 watts.

A valve of quite a different type is theAPP4G an ultra steep pentode with atop -cap grid connection and low inter -electrode capacities making it suitablefor U.H.F. tri-tet, or C.O. working.

The suppressor grid is brought out toa separate pin allowing the valve to beused for suppressor grid modulation.

Screen current, 4 mA.Grid bias voltage, -6 volts.Grid bias resistance, 150 ohms.Optimum load, 7,000 ohms.Power output at 5% harmonics,

watts.3.5

One of the most popular uses for theAPP4G is as a tritet crystal oscillatorin which the second harmonic output isapproximately 4 watts. Operating datafor the oscillator -doubler conditions areas follows.

Condition as Oscillator Doubler (Tritet)Anode voltage -25o, 400 volts.Anode current -25, 3o mA.Anode dissipation -4.25, 8 watts.Anode input -6.75, 12 watts.Screen voltage -25o, 200 volts.Screen current -4.5, 8.o mA.Screen dissipation (approx.)-l.o, 1.5

watts.Cathode resistance -20o, 200 ohms.Suppressor voltage (earthed)- -6.2,

-7.5 volts.Grid leak -30,000, 70,000 ohms.

General characteristics are as follows.Heater voltage I IndirectlyHeater current heated (A.C./D.C.Max. instantaneous peak anode voltageMax. anode voltsMax. anode dissipationMax. screen voltsMax. screen dissipationMax. heater cathode potential differenenceMutual conductance 1 taken atImpedance working point

4 volts A ±5%2 amps.55o volts400 volts9 watts205 volts1.5 watts

5o voltsTo mA./volts5o,oqo ohms.

The above data is merely to indicatethe limiting conditions for the operat-ing limits are as follows.Operating Conditions :-

Anode voltage, 25o volts.Anode current, 36 mA.

Screen voltage, 25o volts.

R.F. power output (approx.)-2-4watts (2nd harmonic).

Crystal current-negligible, negligible.As a fundamental oscillator II watts

of R.F. can be obtained from two valvesin push-pull with the following operat-ing conditions.

Condition as Fundamental OscillatorAnode voltageAnode currentAnode dissipationAnode inputScreen voltageScreen currentScreen dissipation (approx.)Suppressor voltageGrid leakR.F. power output

Capacitances:GI to all other electrodesGI to anodeG3 to all other electrodesAnode to all other electrodesGI to G3

Single valve.400

306

12

20051.00

50,0006

Push Pull.400 volts.70 mA. (per pair)17 watts (per pair)28 watts (per pair)

240 voltsio mA. (per pair)2.4 watts (per pair)o volts

50,000 ohms (each)II watts (per pair)

12.92 F.I.04/At/F.

10.5 iL/AF.

9.55 µµF.1.62 NuF

416

TELVISIOtiJULY, 1939

The loudspeaker has bean built in but provision has been made forphones to be switched into circuit.

FOR some considerable time therehas been an insistent demand fora sensitive and trouble -free bat-

tery -operated receiver which wouldprovide a good performance on amateurbands and at the same time be suitablefor reception of broadcast stations forthose who were restricted to the use ofone receiver.

There are many sets available at thepresent time for A.C. mains, but it doesappear that while there are many read-ers who are completely without mainsof any kind, they are rather ignoredwhen it comes to the design of goodbattery sets. Many readers are stillusing one and two -valve receivers. Thisis due to the desire for battery economy,lack of designs of more, ambitious sets,and to a lesser extent, total cost.

British0 ctals

Just recently, a range of valves hasbeen introduced under the trade nameof Mazda and these with octal basesand very low current heaters are idealfor amateur use. In addition, they areextremely economical and it is, there-fore, possible to build an excellent four -valve set with a total anode currentwell within the capabilities of a mediumtype battery.

Battery sets are also in demand bythose who participate in Field Days orwho wish to have a set that can betaken from point to point for checkingpurposes. All these features have beenborne in mind and I have built this setfeeling that the readers who have writ-ten to me about such a set will be welllooked after.

Although cost has been kept to aminimum the number of componentsand refinements have not been reducedso that the receiver does not do all thata good battery set should. Includedare band -spreading, with ganged band -set and band -spread condensers, a com-bination of capacity- and resistance -

ANDSHORT-WAVE WORLD

ALong-distance

Short-waveReceiver

This receiver has been designed by Kenneth Jowers toprovide a sensitive receiver for short-wave enthusiasts

who require a receiver for transportable use

controlled reaction so that maximumefficiency can be obtained on all bands,and an intermediate L.F. stage drivinga pentode valve in order to obtainmaximum volume on weak signals.Naturally the pentode valve will begreatly overloaded on strong signals,but this is fully taken care of by meansof a volume control in the grid circuitof the pentode.

The circuit of the receiver is shownon this page and all components havebeen keyed so as to line up with thevalues, etc., that are recommended.

The first coil is wound on a 4 -pinformer with a primary and secondary.One side of the primary is not earthedin the normal fashion so as to allowfor a doublet aerial connection. How-ever, when used with a Marconi aerial,the coupling coil can be earthed as in-dicated by the dotted connections.

The secondary of this coil is paralleltuned by two condensers. CI has acapacity of 16o mmfd. and is purelyfor band -setting; the second condenser

of the low -capacity type, actually s8mmfd., is for tuning purposes. It willcover all bands except 16o metres whichwill have to be tuned in two steps.

Condensers CI and Cz are gangedwith C5 and C6. This scheme, ofcourse, would only be satisfactoryshould the coils tuning these condensersbe of exactly the same inductance withthe same stray capacity in the circuit.This is practically impossible so thatC7 has also been included. This is asmall mica trimmer and is mounted in-side the coil former across the gridwinding. It is used merely to balancethe two circuits-aerial and detector -grid, so that condensers can be gangedwithout there being two tuning points.

Readers will appreciate that this,means C7 has to be duplicated for eachband as the condenser is made part ofthe coil, but once adjusted need not bere -trimmed.

SelectivityIn order to obtain maximum gain a

tuned transformer system is employed,which I have found to be more satisfac-tory than tuned grid which depends somuch on the anode choke for its effi-

Rio

+N.T

This theoretical circuit has the components marked with reference numbersare easily obtainable from the printed list.

`o LT

HT

o+1 -.T.

so that the values

417

TagYSIOtiAND


Low Battery Currentciency. In addition, the transformercan be obtained ready wound with re-action, primary and grid so making ithardly worth while to make coils espe-cially for the set. However, these re-marks do not apply to the aerial coil

TheDetector

Next comes the design of the detectorstage. Electron coupling causes com-plications such as a filament choke and

The left-hand control is reaction, in the centre tuner, to the right band -setting, while theswitch underneath the loudspeaker breaks the power supply. The two right-hand con-

trols are at the top screen voltage, underneath, audio gain.for it is a big advantage to be able touse just the right number of turns onthe primary in order to obtain the re-quired degree of selectivity in variousareas. Quite obviously if the receiverwere used in open country the degreeof selectivity required would be muchless than if the set were used in a townsuch as Coventry, for example, wherethere are so many active transmitters.In the latter circumstances the numberof turns on the primary can be reducedas the input circuit is reasonablyselective.

In the anode circuit of the first valveis slight decoupling made up of Rz, aresistance of r,000 ohms, and a by-pass

non-standard coils. Capacity couplingis unsatisfactory on the higher fre-quency bands unless very great care istaken. In any case it is not to be re-commended with a set of this kindwhich may be built by some readerswithout previous constructional know-ledge. Also, I did not wish to use atriode valve as so much more outputcan be obtained from the modern pen-tode with a fixed grid base.

For this reason a combination ofcapacity and resistance controlled re-action was included. On the lowerfrequency bands, the screen voltagecontrol R6 can be left set and reactioncontrolled by C16. But on the higher

This plan view shows the layout of all the components. Carefully readthe text to see how the circuit is wired.

condenser, C4, having a capacity of .01mfd. It will also be noticed that thescreen voltage is obtained by means ofa fixed resistance instead of a potentio-meter and if this resistance is tappedinto the anode circuit on the low -voltageside of R2 rather than directly to theH.T.supply.

frequency bands, C16 should be set ina position slightly below oscillationpoint and regeneration then controlledby R6. This provides extremelysmooth control. On amateur bandswhich cover only a limited wavelengthC16 need only be adjusted once for eachband, provided the 'R.F. choke in the

detector -anode circuit is the one speci-fied.

While V2 normally 11, ould providesufficient output fully to l Dad the L.F.pentode, on some of the weaker signalsthere might not be sufficient gain toload the loudspeaker, so to take care ofthis possibility an intermediate triodeamplifier has been included and it reallydoes repay for the slight extra expense.V3 is resistance -capacity coupled in thenormal way and arranged so as not toprovide maximum gain but rather com-plete stability. It is then transformercoupled to the pentode valve with thevolume control across the secondary ofthe transformer so as to limit the inputto V4. A small loudspeaker has beenbuilt in, not because the average ama-teur likes a loudspeaker, but because aspreviously many readers will use thisset for the reception of short-wave pro-grammes. Also the Colonial readerhas to be remembered for the receiverwill work quite nicely on medium waveswhen selectivity is not of primaryimportance.

For ham use headphones are gener-ally needed and to prevent D.C. cur-rent flowing through the windings ofthe headphones a choke -filter circuit hasbeen included. Switch Sz is one of therotary radiogramophone switches whichenables headphones or loudspeaker tobe switched into circuit as required.This switch and the jack for the head-phones is mounted on the rear lip of thechassis.

H.T.Current

As regards the valves used the total

This is the simple R.F. stage. The knob shown controls tone correc-tion circuit.

current consumption is rzo volts H.T.and is only very slightly over 9 mA.,which is extremely good for a receiverof this kind with two audio stages. Thefirst valve is a variable mu -pentode,type VP23, which has a slope of a littleover r milliamp. per volt. In the de-tector position is an SP22 with a slope

418

JULY, 1939

lailYIS/Ot1AND

SHORT-WAVE WORLD

Covers Ham Bands and Broadcastof .9 mA. per volt followed by an HL23low -current triode having a high am-plification factor of 25, and finally, aneconomy pentode, type PEN25. This

last valve provides approximately 400milliwatts, ample for general use.

Panel andChassis

As regards construction the panel isof aluminium finished black and cut soas to fit a standard 1034 Eddystonecabinet. Actually, the panel is 17 in.wide by 91 in. high. A 5 in. hole iscut for the loudspeaker and this shouldbe arranged so as to allow 21 in. be-tween the edge of the speaker and theedge of the panel to accommodate theaudio volume control and the screenvoltage control.

The final variable potentiometer ismounted on the screen which dividesthe detector from the' R.F. portion.

On the extreme left-hand side of thepanel comes reaction condenser C16,with the main tuner in the centre driv-ing C2 and C6 and the band -settingcontrol almost in the centre. Althoughthe receiver is extremely compact nodifficulty will be experienced in theconstruction providing this is done inthe correct order. Of course, the con-densers have to be mounted as shownin the illustration before any wiring canbe put on. After which the aerial con-densers and the screen on which theyare mounted have to be temporarily re-moved, then it will be quite easy to wireup the detector and audio stages. Thegrid condenser C8 and grid leak R3 aremounted in the wiring, as can also beseen from the plan view.

In order to overcome the cutting of

large holes where they are rather un-necessary, the aerial coil and H.F.transformers are mounted on baseboardtype holders. This does not affect the

Metal shields for the first threevalves have fixing holes ratherlarger than the valve sockets on towhich they are supposed to mount.To overcome this the fixing holesfor the valve holder and the fixingholes for the valve shields should beat right angles. Do not attemptto make one set of holes do for bothvalve holder and shield. It is alsoquite unnecessary to use a sub -chassis coil holder for the R.F.transformer. By mounting thisholder on top of the chassis con-struction is simplified while thewiring is, if anything, kept shorterthan if the contacts were below thechassis. Both the R.F. stage, de-tector R.F. transformer and tuningarrangements can (quite clearly be

seen from thislillustration.

wiring in any way which can still bekept reasonably short.

The valve screens do not quite fit thevalve holders as regards the mountingholes, so unfortunately, two holes can-not be used for both screen and valve

holder, so care must be taken in thefittings of these two components sothat the screen holes are at right anglesto the valve holder holes. The inter -valve transformer Ti mounted on topof the chassis underneath the loud-speaker, with a filter choke close to theoutput pentode.

The under baseboard wiring is quitesimple but will look rather untidy un-less the battery leads are terminated ina small terminal block. Actually, Iadvise constructors to mount fourdouble -ended soldering tags on a smalllength of bakelite and to mount thisoff the chassis on a Raymart SP pillar.L.T. and H.T. can then be terminatedto these soldering tags and in turn to aBulgin battery board.

After the receiver has been wired andchecked, I advised constructors to re-move the two connections to the prim-ary of the H.F. transformer and to con-nect the aerial to this primary. Thenadjust the detector and audio stagesuntil maximum results are obtained.After this has been done to satisfaction,the primary can be reconnected intothe circuit and the entire receiver used.

Condenser C7 must be most carefullyadjusted for each waveband otherwisedouble hump tuning will result and alack of overall gain. Normally, thereceiver has been designed to coverfrom 15 metres up to 200 metres,

(Continued on page 44o)

TTERY S.W. RECEIVERJACK.1-Type JI (Bulgin).PLUG.1-Type P15 (Bulgin).RESISTANCES, FIXED AND VARIABLE.I-2oo,000 ohm type f watt (Rx) (Dubiier).I-x,000 ohm watt (R2) (Bulgin).x-3 megohm type 1 watt (R3) (Bulgin)1-75,000 ohm type f watt (R4) (Bulgin)1-25,000 ohm type f watt (R5) (Bulgin).x -5o,000 variable potentiometer type B (R6)

(Dubilier)./-25,000 ohm type x watt (R7) (Dubilier).I-.25 megohm type* watt (R8) (Bulgin).i-5,000 ohm type x watt (R9) (Dubilier).1-5oo,000 ohm variable potentiometer type B

(Rio) (Dubilier).I-Io,000 ohm vanable potentiometer type B

(12I/) (Dubilier).SWITCHES.x-S88 (Sx) (Bulgin).I-S92 (S2) (Bulgin).SUNDRIES.3-Knobs type xo86 (Eddystone).2-Type ioo9 couplers (Eddystone).1-Dial light type D9 (Bulgin).1 -4 -way battery cable type BC2 (Bulgin).I-A-E socket type X383 (Clix).3-Valve screens type VS (Raymart).2-Anode connectors (Bulgin).Loudspeaker Gauze (Peto-Scott).TRANSFORMER.1-Type LF33 (Tx) (Bulgin).

ACCESSORIESACCUMULATOR.I-Sx5o (Ever Ready).BATTERY, H.T.x-Super power (Siemens).BATTERY G.B.x- 9 volt Winner (Ever Ready).VALVES.x-VP23 met. (Vi) (Mazda).x-2,2 met. (V2) (Mazda).x- 23 met. (V3) (Mazda).r-PEN25 clear (V4) (Mazda).

AA LONG DISTANCE BCHASSIS, PANEL, CABINET.1-Aluminium panel 17 X 91 finished black

(Peto-Scott).1-Aluminium chassis to specification finished

black (Peto-Scott).1-Screen to Specification (Peto-Scott).r-Steel cabinet finished black type 1034 (Eddy-

stone).COILS.1-Set type 959 (Eddystone).COIL FORMS.3-Type CF4 (Raymart).2-Type CT4 (Raymart).CHOKE, R.F.x-Typp CHN (Raymart).CHOKE, L.F.1-Type LF4o (Bulgin).CONDENSERS, FIXED AND VARIABLE.i-x6o mmfd. type 1131 (CI) (Eddystone).1-/8 mfd. type 1094 (C2) (Eddystone).I-.ox mid. type 46oris (C3) (Dubiller).t-.or mid. type 46or/s (C4) (Dubilier).1-x6o mmfd. type 1/31 (C5) (Eddystone).1-18 mfd. type 1094 (C6) (Eddystone).1-3.30 mmfd. type SW95 (C7 (Bulgin)x-.000x mid. type mica (C8) (Raymart).I -1.o mfd. type 4609/s (C9) (Dubilier).1-.ox mfd. type 4601/s (Cxo) (Dubilier).

mfd. type 69oW (Cr') (Dubilier).mfd. type 69IW (Cx2) (Dubilier).mfd. type 4609/s (Cr3)

I-z-o mid. type 4609/s (Cx4) Dubilier).mfd. type 4601/s (CI5) Dubilier).

1-.0002 mid. type 957 (Cr6) (Eddystone).DIAL.1-Type xo7o (Eddystone).i-Type 1097 (Eddystone).EXTENSION OUTFITS.2-Type ioo8 (Eddystone).HEADPHONES.x-Pair type A (S.G. Brown).HOLDERS, COIL1-Type 969 (Eddystone).r-Type SWet (Bulgin).HOLDERS, VALVE.4-Octal type VH56 (Bulgin).

419

TELF.YIS101AND

SHORT-WAVE WORLD

Beam AerialsJULY. 939

andS.W. Programmes

This article is part of a talk given over W2XAD and W2XAF by Boyd W. Bullockof the General Electric Co., New York, on the new G.E.C.S.W. stations. It will interestreaders who may not realise why beam aerials are needed or how " SktP" affects S.W.

transmissions

0 NE of the vital considerations ininternational short wave broad-casting is the problem of provid-

ing the intended foreign audience witha signal which is sufficiently good toenable consistent and satisfactory re-ception of programmes.

In the first place, radio waves exhi-bit the characteristic of jumping oft

into space from the transmitting an-tenna and not returning to earth untilconsiderable distance has been tra-versed. This behaviour becomes morepronounced and the effective distancegreater as the frequency is increased,until, in the short-wave broadcast re-gions, " Skip distance," as it is called,becomes a very important factor.

Now, if " skip distance " for a givenfrequency remained constant, the prob-lem of picking a frequency to reach agiven area would be relatively simple.But " skip distance " varies widely fora given frequency-being affected bydaylight and darkness, by the seasons,by such remote phenomena as sunspots,and by the direction (geographicalbearing) of the line between transmitterand receiver. The general situation isthat daylight decreases skip distance-and therefore effective range. A fre-quency such as 15,330 kc. (ig metres)band is good for broadcasting service toSouth America from Schenectady, N.Y.,in the daytime-afternoon especially-but is not very suitable after dark. Atnight, frequencies in the 9,000 kc. (31metres) band are much more effective.In the morning, the 21,000 kc. (13metres) band is best.

Moreover, the portions of the dayduring which the above frequencies are

most suitable vary with the seasons ofthe year, since with the changing sea-sons, not only do the hours of sunriseand sunset change, but also the angleat which sunlight passes through theatmosphere.

Both the Convention at Berne andthe F.C.C. maintain engineering sec-tions which continually study the com-

W6XBE which hasbeen erected at Treas-ure Island, San Fran-cisco, uses a 100 Kwamplifier and one ofthe new Alexander -son beam arrays. Itis used to provideprogrammes forlisteners in the Orient.

plex and changing problem of fre-quency (and power) assignments-thepurpose being to permit as many sta-tions as possible to operate within therelatively limited bounds of the radiospectrum-without undue interferencewith each other.

Many stations, of course, may be as-signed the same frequency-but in sucha case it has been deemed that geo-graphical separation and limited power(and perhaps restrictions on the hoursof operation) are sufficient to preventinterference and confusion harmful tothe services of the individual station.

From the fact that the higher fre-quencies-those falling within the so-called short-wave region (1,600 kc. anoup) and particularly those above 4,000kc.-exhibit remarkable distance-covei -ing ability, it is apparent that the prob-lem of interference prevention become,world-wide in scope.

In February and September of 1925,W2XAF and W2XAD were firstlicensed to the General Electric Com-pany as experimental short-wave broad-cast stations. Ever since that time,both stations have transmitted pro-grammes for the benefit of listeners inother countries. During this period,their schedules have grown heavier, andmore and more programme features

have been presented which were speci-fically designed for particular foreignaudiences.

In 1928, the assigned frequency otW2XAF was raised slightly to 9,53o kc.,its present frequency. In 5929, jW2XADwas dropped from 15,340 kc. to 15,330kc. and at the latter figure its frequencyhas remained.

During recent years, W2XAF hasoperated with a power output of 25kilowatts, while about a year ago,W2XAD went to 20 kilowatts.

Until the latter part of 1936, thebroadcasting from W2XAF andW2XAD brought constant evidence ofstrong, consistently received signals inCentral and South America. Then re-ports began to come in of interferenceby a growing number of other short-wave broadcast stations. Some, of thesewere local Latin-American stations,while others were European.

The most consistently complained otwas DJ N, a station in Berlin, operat-ing on 9,45o kc.-io kc. higher thanW2XAF.

The nature of this interference was" side -band " interference-a form oftrouble which occurs when two power-ful signals are received which, althoughthey may be working so kc. apart onadjacent channels, still become mixed.This effect occurs because the modulat-ing or voice frequency which is super -

(Continued on page 447).

The Alexanderson beam array now used bymany G.E.C. stations.

420

TELEYSICH1JULY, 1939

The ultra -high fre-quency transmitterdescribed in this

article is very simple

to construct andwas designed in thefirst place in thelaboratories ofHeintz and Kauf-

The layout of the valves and tuning lines are clearly shown in this illustration.

ANDSHORT-WAVE WORLD

man, Limited, of

San Francisco.They have supplied

us with this informa-

tion for the benefit

of British Amateurs

who are keen on

U.H.F. working.

Building.A One -Metre Oscillator

AMATEURS who are licensed tooperate on the real ultra -highfrequencies can undertake a con-

siderable amount of interesting experi-mental work with quite low cost.

Most valve and component makersare now in a position to supply the

resistance. The wavelength is chosenby adjusting the position of the shortingbar on the anode bar tuning line. Thecloser this bar is brought to the valvethe shorter becomes the wavelength towhich the transmitter is tuned.

The limiting wavetength occurs

/Ow

This theoretical cir-cuit indicates theextreme simplicity ofthe U.H.F. trans-mitter and the limitednumber of compo-

nents.

specialised gear needed although thisgenerally means valves only.

The Heintz -Kaufman Co., of SanFrancisco, have produced an excellentU.H.F. valve in the HIC-24 low -C tri-ode which sells in this country for 24s.Two of these valves in push-pull on

metres will provide a power outputof 25 watts with an anode voltage of800. The transmitter is very simpleand can be built without difficulty bythe amateur who has not had any ex-perience of U.H.F. working. All thesnags have been ironed out in the HKLaboratories while all the componentsneeded are available in this country.

At the top of this page is an illustra-tion of the transmitter showing the lay-out of the components and the tunedlines in the anode circuits. A woodenboard is required for losses are takencare of by means of stand-off insulators.

TuningMethod

For wavelengths of between r -itmetres the connections from grid to grid

must be a very heavy shorting bar of lowwhen the shorting bar is placed directlyacross the anode terminals of thevalves. With this adjustment the oscil-lator will operate at approximately o.8metre.

It will be seen that a second shortingbar is shown on the anode line. Thepurpose of this shorting bar is to de -tune the unused line and so preventcoupling of power into this portion ofthe circuit.

Excitation is controlled by the ad-justment of the shorting bars on thefilament line indicated in the sketchof the circuit. Proper adjustment canbe observed by noting the grid currentwhich varies directly with the excita-tion. The two shorting bars on eachof the two filament lines should be keptapproximately the same distance fromthe valves for obtaining optimumperformance.

Radio -frequency power should pz+e-ferabljt be taken by coupling to theanode lines. It is important that thisbe done in such a manner as to maintaina balance between the valves to theearth plane and to the load. If poweris to be delivered to an electric lightbulb or some type of dummy load itmay be placed directly across the lineson the valve side of the shorting barand very close to it. Loading can beincreased by sliding the dummy loadtowards the valves.

If it is desired to deliver the R.F.power to a transmission line the load-ing may be varied by a degree of coup-ling to a loop or hairpin. Normal in-creases in loading will be accompaniedby increased power outputs, increasedanode currents, and decreased grid cur-rents, while abnormal loading willcause decreases in power output andefficiency.

1 412

76 E A6y.-1'1'17All the dimen-sions must becarefully ad-hered to andthose of im-portance aregiven in this

sketch.

421

TEUYISIOhAND

SHORT-WAVE WORLD

When coupling with a loop at theend of the transmission line to deliverpower to the aerial, care must be takento see that the loop does not come indirect contact with the anode line asthis will apply the high anode voltageto the aerial and transmission linecircuit.

If proper care is taken a quarter -waveaerial may be directly coupled to theoscillator itself. It should be remem-bered, however, that this aerial willcarry anode voltage and proper insu-lation should 1:4 provided. Anotherscheme is to isolate the feed line withlow -capacity condensers of the airspaced type.

The quarter -wave aerial may betapped directly on to the circuit near tothe shorting bars on any of the linecircuits. Heavier loading will be ob-tained as the point of contact on thequarter -wave radiator is moved closerto the valves.

A quarter -wave radiator becomes avery sensitive voltage indicating devicewhen used in this way and will showdue to the loading on the circuit muchsmaller voltages than the usual neonindicator.

In ultra -high frequency oscillatorsof this kind it is of the utmost import-ance to avoid radiation from the circuitsthemselves. As each portion of the cir-cuit is an appreciable percentage of theradiated wavelength, it is possible thatthey may be subtracting R.F. power and

radiating on their own. Proper pre-cautions must be taken to prevent suchstray radiation. Stray radiation isbest avoided by the balancing on allcircuits to earth and by neutralisingpush-pull operation.

This means that each portion of thepush-pull circuit must be equally bal-anced in their stray capacities with allother components. If this is not donethe circuit will radiate power sensiblyin proportion to the degree of un-balancing.

PowerSupplies

For this reason the power suppliesto the anode grid and filament are care-fully located at mid -point because ofthe jumpers of their tuning line. Dueto the physical arrangement of the twosets of filament tuned lines as shownin the illustration, it is difficult to bal-ance them to the earth plane and toeach other simultaneously. A goodbalance is accomplished by the use ofsmall tabs, fastened to the outer mem-bers of each of the filament tuninglines. These tabs add capacity to themetal base or earth plane and serve toequalise the stray capacities of the oppo-site members to the adjoining filamenttuning circuits.

The capacity of these tabs to the baseshould be adjusted for maximum R.F.output-at a given power input, so real-ising maximum efficiency

JULY, 1939

1-1 MetreOperation

For the most efficient operation onthese wavelengths, it is necessary to adda tuning line from grid to grid at thevalve socket terminals. Such a linereally exists under the previously des-cribed 1 -metre conditions but it liesentirely within the valve and socketleads.

To control excitation, with a grid -tuning line added, both adjustments ofthe grid tuning line and the filamentmust be consistent. The results ofthese adjustments are observed by not-ing the grid current which varies insympathy with changes in excitation.Adjustments are made for the propervalue of grid current while other con-siderations in the adjustment of theoscillator are the same as for I -metreoperation.

The characteristics of the HK24 valveare as follows :-

Filament voltage 6.3.Anode current (2 valves) 175 mA.Anode voltage Boo.Grid current (2 valves) 18 mA.Grid resistor 2,500 ohms fo watts.Power output 25 watts.Power output is critical to anode

voltage and grid current. Valuesgiven are optimum and using valueshigher or lower than those specified willresult in lower power output anddecreased efficiency.

SNOWDON 56 Mc TESTSIN view of the success of the 56 mc.

transmissions of GW6AA from Snow -ion last September, a more ambi-

tious series of tests has been arrangedto take place in July, covering theweek -end of the R.S.G.B. 56 mc. FieldDay.

All transmissions will be crystal con-trolled, mainly C.W., and receivers forall types of transmissions will be used,although it is hoped that crystal con-trolled transmissions will predominate.A small petrol driven generator will beused to solve the problem of supplyinglight and power for operating the sta-tion over a period of several days.

The following aerial systems will bein operation :1. A horizontally polarised fixed direc-

tional array beamed on London.2. A vertically polarised rotatable

beam array.3. A wave -and -a -half vertical Frank-

lin Uniform aerial.4- A horizontal half -wave aerial run-

ning North -South.Two days are to be set aside for the

erection of the apparatus and aerialsystems on the summit, but it shouldbe understood that the success of thetests is largely dependent upon theweather conditions prevailing at thetime. Even in summer, winds exceed-ing gale force are often experienced on

the summit of Snowdon, and squalls ofrain and hail with terrific wind veloci-ties occur without notice.

The operators will be on the summitfrom July 5 to July xo, but scheduledtransmissions will not commence until19.0o B.S.T., on Friday, the 7th. Auto-matic C.W. test calls of ten minutes'duration will be made at the followingtimes: (all B.S.T.).

Friday, July 7-19.00, 20.00, 21.00.Saturday, July 8-14.0o, 16.00, 18.00,

20.00, 22.00.Sunday, July 9-10.0o, 12.00, 14.00,

16.00, 18.00, 2 I . 00, 22.00.Reports of stations heard, and other

details of general interest concerningthe tests, will be given at the followingtimes, telephony being used :-

Friday, 7th -22.0o.Saturday, 8th -17.00.Sunday, 9th-o9.45, 20.00.

Call -signs of distant stations whichhave been heard, but not contacted,will be given in C.W. after each ofthese transmissions.

The main object of these tests is toinvestigate the radiation diagrams ofthe various aerial systems used, tocompare with the theoretical, and withthis object in mind, schedules are de-sired with stations equipped with fieldstrength measuring apparatus (includ-ing receivers fitted with S meters, as

comparative figures only are required).The aerial system in use at thatmoment will be given out in each trans-mission, code groups being used for theC.W. transmissions, and these shouldbe given in all reception reports, wherepossible. All such reports will beacknowledged, and will be muchappreciated.

Schedules with C.W. over 150 milesfrom Snowdon are also desired, andanyone wishing to make schedules forthese, or any tests they may wish tocarry out during the period July 7-9,should write as soon as possible toDavid S. Mitchell, The Flagstaff, Col-wyn Bay, North Wales.

Dollis Hill Radio CommunicationSociety

The Hon. Secretary of this society isE. Eldridge, 79 Oxgate Gardens,Cricklewood, N.W.2, and he has sentus the following information on thesociety's activities. The last meetingof this society was on June zo andnormal meetings will recommence inSeptember next. A portable trans-mitter was in operation on June 9 withboth phone and C.W. on 14. Mc. withthe call sign of the President-G6SKP.

Arrangements are being undertakenmy G6SK, G6OV and G6KQ. Trans-port difficulties are not anticipated, asthe site, to be determined, will be closeto a coach service.

422

TELEYISIORJULY, 1939

The transmitter ready for the untidy flexible wires. Notice thecomparatively few components.

WE take great pleasure in des-cribing a simple but efficienttransmitter using British com-

ponents throughout in which the per-formance is better than if any of thecomponents, particularly valves, wereof American design.

This transmitter was built in the firstinstance around the recently producedvalves by G.E.C., the KT8 tetrodeswhich are somewhat similar to theAmerican 807. Apparently, the originalidea was to produce a valve dir6ctlyinterchangeable with the 807, butevents have proved that the BritishKT8, while still being interchangeable,is distinctly better as regardsmechanical design, R.F. output andwhat is very important to amateurs,price.

First of all, the data on the KT8valve. It is an R.F. transmitting typetetrode with an indirectly heated chan-nel, aligned grids which producedirected electron beams resulting in avery low screen current. The valve issuitable for use as an oscillator, fre-quency multiplier and power amplifier.The anode is brought out to a top cap,while the anode -grid capacity has beenkept to the commendable low figure ofo. 12 mmfd. Consequently, with carefuldesign it is not necessary to neutralisethese valves.

A 6.3 volt, 1.27 ampere heater is used,while the maximum anode voltage is600 and the maximum screen voltage300.

As used in this circuit, for Class Ctelegraphy, the anode current shouldnot peak to more than 95 mA. andunder these conditions an output of ap-proximately 38 watts per valve is ob-tainable, resulting in an overall effi-ciency of 73 per cent.

If modulated, the anode voltageshould be reduced to 475 volts and 25ovolts to the screen. Provision must alsobe made to modulate both screen andanode simultaneously and at 14 mega -

ANDSHORT-WAVE WORLD

An All -British Tx.A Push -Pull

KTSTransmitter

This transmitter has been designed to provide anoutput of 75 watts on the 3.5 megacycle channel.The basic circuit, however, can be used on anyamateur band and down to an output of approxi-mately 25 watts. It is suitable for 4 -band operationowing to the low amount of drive required by the

KT8 valve.

cycles the R.F. output is approximately3o watts per valve when working underClass C conditions.

In the first stage of the transmitter isa KT66, another Osram tetrode primar-ily designed for use in audio amplifiers,but which lends itself for inclusion incrystal -oscillator circuits in place orvalves of the 6L6G type.

The KT66 is directly interchange-able with the 6L6G the only noticeablevariation being a slightly higher heatercurrent resulting in a greater totalemission.

The circuit of the transmitter isshown on this page and it is extremelysimple despite the fact that it will pro-vide about 75 watts of carrier undernormal conditions. The total amountof drive required is only about ri wattsso that the regenerative oscillator pro-vides ample output even if the finalstage were to operate on frequencies farremoved from the fundamental of thecrystal.

4 -BandWorking

Our tests indicate that with an 8o -metre crystal the final stage will operateon 8o, 40, zo and even to metres. Onthe later band, however, the crystal -oscillator is admittedly operating atmaximum R.F. output, but not to suchan extent that it causes excess crystalcurrent.

It will be noticed that in the cathodecircuit of the crystal -oscillator has beenincluded an R.F. choke. This withoutits more conventional parallel con-denser causes the oscillator to beslightly regenerative which gives a dis-tinct increase in output on harmonicsand at the same time reduces the crystalcurrent.

As the output from the crystal -oscil-lator circuit can be as high as 15 wattscapacity coupling between stages is notfeasible. In addition, this type of coup-ling is not to be recommended particu-larly when a single ended circuit iscoupled to a split circuit. For thisreason, link coupling is absolutelyessential for it does enable the amount

C

R3

J IV3 7

Complete theoretical circuit. Meters are recommended but are not essential.

423

7 '111i/slot'AND

SHORT-WAVE WORLD

Low Drive High OutputJULY, 1939

of drive to the KT8's to be reduced tothe required value.

Constructors who have not had pre-vious experience of tetrodes of this kindshould be warned that over drive causeslack of efficiency and that should re-

sults in the first instance not be satis-factory do not endeavour to increasethe drive for this only makes mattersworse.

A fixed total grid current to the finalstage of between to and 7 mA. shouldbe obtained, which is the optimumworking figure.

Owing to the low grid bias requiredthere is no need to make use of a biasbattery or bias pack. The grid bias isobtained by means of the total currentflow across R5, a resistor having a valueof too ohms, and the grid current acrossR4, a resistor of to,000 ohms.

The resistor R5 is merely to preventhigh anode current when drive is notapplied, and is quite a precautionarymeasure.

The KT8 valves are very dicile tohandle in the correct circuit, but theycannot be used in a circuit in which thelayout does not lend itself to high effi-ciency. It must be remembered thatKT8's have a slope of 6 milliamps pervolt so that liberties cannot be takenwith the circuit. Do not, however, ob-tain the idea that the KT8 valve is diffi-cult to handle. With the circuit recom-mended they are as simple to use asslope triodes. Notice for example, theinclusion of resistors R7, R8, R9 andRio. These are most important andshould in no circumstances be omitted.

Resistors R7 and 8 and the grid of theKT8 have a value of 5o ohms, and theresistors R9 and to in the screens 500ohms. The by-pass condenser C7 isconventional and has a capacity of.002 mfd., while condenser C t, an in -

This side view of thechasis shows the cry-stal -oscillator circuitwith the KT66 valvemounted in a holderon stand-off insula-

tors.

novation, has a capacity of .001 mfd.Both the heaters of the KT8's and the

KT66's are run from the same voltagesource and have one side by-passed tochassis by means of C9, a condenser of.01 mfd.

CoilData

Next comes coil data; Lt and L2 arewound on ti in. formers of a conven-tional type, while L3 is wound on a2- in. former and mounted on Raymartinsulating pillars. 20 gauge enamelledcover wire is used on Lt and L2 and 16gauge enamelled covered wire on L3.The windings are as follows : 8o metresfor Lt,38 turns close wound; L2 42turns close wound and centre tapped;L3 56 turns close wound for 28 turns,half -inch gap and close wound for afurther 28 turns. A single turn link isrecommended around the centre of thiscoil for coupling to a remote aerial coil.On 4o metres 21 turns for Li, 30 turnsfor L2, zo turns for L3 wound in twohalves with a gap of half an inchbetween the centre turns.

As regards construction, owing to thefact that the chassis is of rather heavygauge steel all the major componentsare mounted either on stand-off insula-tors or on top of the chassis so there isno need to cut large holes. The splitstator tank condenser is mounteddirectly on to the chassis and the re-maining two variable condensers arealigned up with it to provide a sym-metrical panel layout.

Condenser C5 is raised off the chassisapproximately half an inch, while C4is mounted on,an Eddystone adjustablebracket. Notice also the crystal holder.This is of the Q.C.C. type with anAmerican base, but used in the circuitis an adaptor so that British or Ameri-can crystal holders can be used at will.

A power unit providing Soo volts at200 mA. is recommended with 2 fila-ment windings.

A PUSH PULL KT8 TRANSMITTERCHASSIS AND PANEL.2-Type x109 (Eddystone).2-Type II2 number 6 (Eddystone).2-Pans type rim (Eddystone).COIL FORM.1-Type CF4 (Raymart).COILS.2-Specially wound to frequency (Li and L3)

(Peto-Scott).CONDENSERS, FIXED.r-.00x mid. type 69oW (Cx) (Dubilier).1-.002 mfd. type tubular r,000 v. (C2) (Dubilier)1-.002 mid. type tubular x,000 V. (C3) (Dubilier)1-.00016 mfd. type TROx6T (C4 (Premier)x-Type 1087 (G5) (Eddystone).1-.002 mfd. type 4601/s (C6) (Dubilier).1-.002 mfd. type 4601/s (C7) (Dubilier).1-108o (C8) (Eddystone).

mfd. type 4601/s (C9) (Dubilier).2-4 mfd. type LEG 65o v. (Cro) (Dubilier).CRYSTAL.1-Standard type with enclosed holder type

U (Q.C.C.).CHOKES, R.F.r-Type CHN (RFCx) (Raymart)r-Type SW68 (RFC2) (Bulgin).r-type Pie -wound (RFC3) (Premier).CHOKES, L.F.x -Type 25o mA. 4o H. (Premier).DIALS.3-Standard indigraph (Peto-Scott).DIAL LIGHT.x-Type D9 (Bulgin).EXTENSION OUTFIT.1-Type roo8 (Eddystone).

HOLDERS, VALVE AND COIL.r-Type SW2 x (Bulgin).x-Ceramic octal type X248 (Clix).2-Ceramic 5 -pin type X147 (Clix).r -4 -pin type Xxxx (Clix).JACK AND PLUG.1-I-Type J2 (Bulgin).I-Type P15 (Bulgin).KEY.r-Bar type (Webb's Radio).METERS.

-o-roo mA (Premier).1-o -to mA (Premier).1-o-r5o mA. (Premier).PLUGS, SOCKETS., ETC.12-Insulating pillars type SP (Raymart).RESISTANCES, FIXED.1-5o,000 ohm type x watt (RI) (Dubilier)1-20,000 ohm type PR 38 with extra clip (R2

(Bulgin).x-2,000 ohm type - watt (R3) (Premier).I--io,000 ohm type 4 watt (R4) (Premier).r-xoo ohm zo watt (R5) (Bulgin).r-ro,000 ohm type 8 watt (R6) (Premier)2 -5o -ohm type watt (R7 and R8) (Dubilier).2-5oo-ohm type x -watt (R9 and to) (Dubilier).SUNDRIES.3-Terminal saddles type 1046 (Eddystone).SWITCHES.3-Type S8OT (Sr, S2 and S4) (Bulgin).I -Type S88 (S3) (Bulgin).TRANSFORNMR.1-Type SP5o3 (Premier).VALVES.r-KT-66 (VI) (Osram).2-KT8 (V2 and V3) (Osram).1-5Z3 (V4) (Hamrad).

424

TELEVISIONJULY, 1939

One of the Hamrad R.F. relays whichoperates from A.C. mains.

IT is rather surprising that with somany low-cost amplifiers availableand the ease with which the average

transmitter can be modulated to pro-vide high -quality, that so much interestis devoted to C.W. It did appear atone time as if the number of amateursoperating purely, on C.W. would slowlydecrease, but on the contrary many sta-tions which have in the past used tele-phony have now changed over to C.W.Consequently manufacturers and agentsin this country are now handling alarge amount of interesting gear forC.W. operators.

RelaysRelays for keying purposes are avail-

able from Hamrad Wholesale, varyingin price from 13s. upwards. These re-lays sold under the trade name of" Guardian " are for R.F. make -and -break aerial change -over, etc., and rundirectly from an A.C. source. Theyare reliable with good contacts andwill pass far more R.F. than is likely tobe encountered in the average amateurstation. An illustration of one of theserelays is shown at the top of this page.

Webbs Radio also have a completerange of relays varying from simpletypes costing as little as 6s. 9d. up tothe large Gordon heavy duty R.F. re-lays at 52s. This type of relay has adouble -pole double -throw contact, runsfrom A.C. mains, and has the low powerfactor of .04 showing negligible lossat frequencies as high as too mega-cycles.

In the Ward -Leonard range, is asingle -pole single -throw double break

The McElroy audio oscillator.

ANDSHORT-WAVE WORLD

Interesting New Equipmentfor

Short- waveExperimenters

type for iio volts A.C., priced at 23s.Also at Webbs Radio are a completerange of keys, etc., specially built foramateurs. The Junior Bug is nowdown in price to 17s. 6d. with a stan-dard Bug at 37s. 6d. and the supermodel at 45s.

Those who are keen to learn C.W.should invest in one of the Mac practicesets which are complete at 19s. 6d., in-cluding a t,000 -cycle mechanical oscil-lator. This produces an excellent notevery similar to C.W. picked up by areceiver and is ideal for code teaching.

This automatic sender can be purchasedoutright or_hired for training purposes.

In addition, there is an audio oscilla-tor mounted and housed in a bakelitecase, and arranged for 2,00o -ohm out-put or a zoo -ohm connection for a low -impedance input to a modulator. Anynumber of components can be used withthis oscillator and complete with twovalves, ballast valve and line cord isonly 32s. 6d. It will operate on A.C.or D.C. at any voltage between ito and25o.

The McElroy automatic telegraphicequipment is probably the only gear ofits kind in this country at the presenttime. There is an automatic sender,which is tested at too p.w.m. andguaranteed for 75 p.w.m. A lightfrom an exciter lamp on to a photo-electric cell is interrupted by inkeddots and dashes on ordinary recordedtape. The impulse is amplified toactuate a sensitive relay which deliversa keying output to work a local oscilla-tor or transmitter. It is ideal fortraining operators for high-speed work-ing and the equipment can be hired foras little as 7s. 6d. per week. Forchecking purposes there is the Mac re-

corder which is the same price as theMac Auto, that is £8. It is designedfor direct coupling to, the output of anyradio receiver and is complete with in-put transformer, and rectifier. It pro-duces the conventional inked tape asused by telegraph companies.

It is possible to record efficiently upto too w.p.m. while tests have beenmade as high as 300 w.p.m. Designedto work with the Auto recorder is thetape puller .at 7s. 6d., in which isbuilt a heavy A.C. inductance motorwhich will not, of course, cause anyinterference.

There is no need to use large un-gainly condensers in the average ama-teur low -power transmitter. Eddystonewith their new range of miniature con-densers, not to be confused with theoriginal micro-densers, have produceda range of components which are suit-able for use in transmitters or receivers.They vary from the model 1094, havinga maximum capacity of 18 mmfd. upto the model 1131, having a maximumcapacity of 16o mmfd.

Readers will be interested to noticethat the low -capacity condenser has aminimum of 3 mmfd. and the high -capacity condenser a minimum of 4.75mfd. The model 1094 has a D.C. flash-over voltage of 3,500 and is priced at3s. 9d.

The well-known air dielectric trimmer,model 978, has been modified so that itcan be panel controlled by means ofknob and dial. This condenser can beused to advantage in ultra -high fre-quency transmitters and in its modifiedform has the type number 1013. Theminimum capacity is 3 mfd. and themaximum capacity 65 mfd.

Mounted on this McElroy key is a 1,000cycle mechanical oscillator.

425

ELLIVISIMAND

SHORT-WAVE WORLD

A Good Key Band Switching JULY, 1939

ResistorsThere is also the model 1132 which

has a minimum capacity of 2 mfd. verywide spacing between plates and amaximum capacity of only 12 mmfd.It is priced at 4s., complete with knoband dial.

Improvingthe C.O.

By connecting a high -frequencychoke in series with the cathode of theaverage pentode or tetrode oscillator abig increase in R.F. output can be ob-tained. However, the choke must beof the correct inductance otherwise thecircuit will oscillate without the crystalin use. A suitable choke for this pur-pose we have found is the Eddystoneio66 which has a self capacity of 2.4mmfd. and an inductance of 17.9 milli -henries. It is fitted with fixing termin-als and takes up very little space inthe chassis. Those who are botheredwith insufficient output from the C.O.are advised to try this idea and to useone of these chokes which only costs as.

These Eminent resistances carry very high -currents but are extremely cheap.

A NewKey

One of the nicest keys we have triedfor a long time is the new Hamrad jobwhich is priced at us. 8d., an odd sortof price, but all the same the key is avery good one. It is hand -made withpolished silver contacts, but the mainpoint about it is that it has tensionsprings on either side of the centrepivot. In this way, tension can be ac-curately adjusted and it is no overstate-ment to say that the average operatorwill find his sending speed increasedwith this key. It is possible to send morequickly than usual without difficulty orerror.

Operators who are not too pleasedwith their sending and who are in-clined to make errors in keying shouldtry one of these new Hamrad keys forit will certainly bring about animprovement.

As crystals vary in size it is alwaysadvisable to use a holder which willtake large square or round crystals.The Hamrad ceramic holder with hand

lapped plates will take crystals up toin. square. These holders are priced

at 7s. 6d. each and will fit ordinary

The main feature of this key is the double ten-sion spring on either side of the centre pivot.

sockets or valve holders. Alternativepins are supplied with the holder.

Webbs'Switches

Band switching is coming intofashion becaase so many operators re-cognise that with present conditionsseveral frequencies must be available.In order to do this correctly, the switchembodied must have the very minimumamount of loss. For this purposeWebbs Radio are supplying an Ohmiteswitch. It is made of porcelain ofvitreous enamel and is excellent forhigh voltages and high -frequency use.Each switch has Ahree contacts so thatthree bands can be covered with one setof coils. Two or more switches can beganged for tuning or control While theycan be mounted on insulated bracketsin order to reduce the capacity betweenswitch and chassis. Complete withknob and mounting they are priced atios. 6d. and are suitable for power am-plifiers and output circuits up to i kilo-watt rating.

A complete transmitter, air tested,and providing an input of Jo watts isavailable from Premier Supply Stores.This transmitter is suitable for A.C. orD.C. mains. operation, and on the 7megacycle band is supplied with crys-tal and inductance.

Accessories have not been omitted in

The Eddystone condenser on the left is mainlyfor trimming but can also be obtained completewith knob and dial. On the right is one of thenew Eddystone mierodensers having a maximum

capacity of 18-mmfd.

view of the low price for an o-ioo mA.meter is included and keying is ar-ranged in the cathode of the oscillator.This transmitter can be modulated anda suitable amplifier is available whichwill also operate on A.C. or D.C. mains.A kit of parts is only £2, or wired andtested .42 15s. od.

To go wits this amplifier there is amicrophone of the Res pattern pricedat £r, which has a low noise level anda frequency range of 45 to 7,500 cyclesplus or minus 2 db.

KT8It is quite a simple matter to make

a transmitter covering several wave-bands with only two valves, that is pro-viding the right valves are used. TheGeneral Electric Co. are now in a posi-tion to supply the KT8 transmittingtetrode, a valve which does not nor-mally require neutralising and whichwill provide a carrier power in the re-gion of 4o watts. This valve has a 6.3volt 1.27 ampere heater and is designed

For band switching the best low -lossswitches are the Ohmite type available

from Webbs Radio.for a maximum voltage of 600 on theanode and 300 on the screen. Theamount of drive required is very smallindeed, being in the region of .5 to .75watts. Consequently a single tri-tetoscillator would drive this valve onfour wavebands from a single crystal.As a frequency multiplier on 14 mega-cycles, the output is in excess of 12watts. It is priced at 22s. 6d. and isprobably one of the best valves of itskind available to amateurs at the pre-sent time.

When using valves of the high -slopetetrode class it is important that the .

screen voltage be accurately obtainedand be dependable. Resistances forthis work are available from Hamrad,which vary from the 8 -watt type at 1 id.up to the too -watt type at 3s. Anothertype is rated at 67 watts and in valuesof 25o ohms to 3,000 ohms is priced atis. 9d. This particular resistance iswound on a porcelain former so that itis extremely cheap at the price asked.

426

IELEAS10t1

II

JULY, 1939

A Special Transformer

ANDSHORT-WAVE WORLD

In our June issue we made brief re-ference on page 384 to the new Ham-rad model 140 receiver which is nowin full production. An illustration isshown on this page. It uses 12 valvesexcluding the rectifier, which are an1851, 6J8, 6F6, two 6K7, two 6C5, two

6F5, two 6H6, 6L6, 6J7 .and 5Z4.Electrical band -spreading is includedand the coverage is 9 to boo metres, infive bands with an, efficient high -frequency stage on all bands.

There are two intermediate -frequencystages at 465 kc. and variable selec-tivity. Variable delayed A.V.C., withseparate valve amplifying the D.C.components. A special feature is anundelayed amplified R meter calibratedin R points which will read with orwithout A.V.C. on both phone andC.W.

Frequency drift is negligible due to alarge extent to the use of a separateoscillator and frequency changer, whilethe crystal filter is arranged so that itcan be used for telephony operation.There are two stages of audio, the finalproviding 6+ watts while high and loimpedance outputs of 2,000, 15, 71 andI; ohms are included. This receivercan be demonstrated by any of theHamrad agents, and the price is£27 los. od. with hire purchase ifrequired.

Service engineers and those inter-ested in public-address equipmentshould bear in mind the fact that SoundSales, of Marlborough Road, London,N.19, manufacture excellent outputtransformers which solve a multitudeof problems. It is always rather diffi-cult quickly to erect a number of loud-speakers at a distance from the mainamplifier, but by using the Sound Salesline transformer with a Soo -ohm primary and tapped secondary this problemis overcome. It is suggested that theoutput transformer in the amplifier

This is the Sound Sales line transformerwhich has so many uses as explained

in the text.

have a Soo -ohm secondary feeding intoa 50o -ohm line. This line is then ter-minated in the special Sound Salestransformer having a 50o -ohm primary.The secondary can be tapped, as theone in the illustration, for 15 or 3oohms so that loudspeakers can be con -

The new Hamrad 140receiver which has a totalof 13 valves and manyunusual refinements. Ithas a particularly effec-tive R meter which oper-ates on both phone and

C.W.

nected in series, parallel or series -parallel.

Another interesting transformer madeby this company is type E../US.. Thistransformer provides an output of 6.3volts with a 4 -volt input, so that inter-national octals or American valves canbe used in receivers normally requiringBritish 4 -volt valves. Alternatively,the voltage can be stepped down soallowing British valves to be used inAmerican' receivers.

As the maximum output is 3 amperes,amateurs using transmitting equip-ment with British valves can change

over to 6.3 valves with the minimumamount of trouble. These transform-ers are priced at 7s. 6d. each and fulfilquite a long -felt want.

Apparatus Described inRecent Issues

ANUMBER of our back issues arebeing repeatedly asked for byconstructors. We have collated

these requests and the more popularissues with the receivers, etc., to whichthey refer are listed below. Any ofthe issues can be obtained from ourBack Number Department, price 2s.,plus postage.Flat Tap Beam Antennas-Feb., 1938.5 and io metre Transmitter-Feb. 1938.2 -valve Receiver for io metres-March,

1938.A EIL6G Speech Amplifier-July, 1938.Cheap Battery Charger-July, 1938.15 -watt Transmitter-July, 1938.Beginner's 2 -valve Receivet-Septem-

ber, 1938.C.W.R. Transmitter-October, 1938. ,5-8 metre Receiver-October, 1938.Single valve Transmitter-October,

1938.Battery -operated Transmitter-Novem-

ber, 1938.Building a Rotary Beam-December,

1938.A 6L6G-8oi Transmitter-December,

1938.An A.C. 3 -valve Receiver-December,

1938.A.C. Frequency Meter-January, 1938.Regenerative Pre-selector-February,

1939.5 -metre C.C. Tx.-March, 1939.Two -valve A.C. Short-waver-April,

1939.8 -valve Communication Receiver-May,

1939.

The Lawrence Thaw Trans-asiaticExpedition

Very complete radio equipment isbeing taken by this expedition whichhas been manufactured especially for,hem by the General Electric Co., Ltd.,of America. It consists of two truckshousing four ultra -high frequency trans-mitters and communication type receiv-ers, similar to police radio installations.Two medium high -frequency transmit-' ers and receivers have also been in--tailed, the whole being powered in-lirectly from car batteries. The an-ennas for ultra -high frequency use are

of the quarter wave fish -pole type allow-ing for communication between fourcars in motion. A 128 ft. antenna on3o ft. collapsible poles is to be used forThe medium high -frequency transmit-ters.

427

TilEYSLOtiAND

SHORT-WAVE WORLD

ALTHOUGH the Goddess of DX(whoever she might be) did notunduly shower her gifts upon

N.F.D. participants, the anti -cyclonicsunshine made up for this and helpedconsiderably to liven up those operatorssuffering from aching wrists and" can't -keep -open " eye -lids.

A brief account of what was seen ona e8o-mile tour covering most of thestations in districts 12, 13 and 14 mayinterest other participants.

District 13 bit upon the novel idea ofarranging a 56 mc. link between theirstations at Westerham, Kent; Warling-ham, Surrey; and Dulwich Hamlet,S.E. Unfortunately the life of the linkwas short-lived as the :onverter at their1.75 mc. station died on them and thenatural thing to do was to grab the onefrom the 5 -metre link station. BestDX worked by G2RCP, the 14 mc. sta-tion, was SU5AAP, CX2AJ, VX3QZand W4FDJ. Both GzRCP andG3ZJP (the top band station) weresituated in the same field, being but 5oyards away from each other at a loca-tion 690 ft. above sea level. DX waslacking at the 3.5 mc. station at War-lingham, but they did hear two or threeW's and a VO. A different tale camefrom Dulwich Hamlet F.C. Ground,

JULY, 1939

THE It.S.G.B.National

Field DayThis information on N.F.D. has been compiled by F. L. Post-lethwaite, G5KA, who next month will resume his very popular

feature " Long Skip."

GM2SP and GM3GGoperating theSeottish" D " 7 -megacycle

station.

where the crew at G2JBP accounted forW3, PY, CT2 and six HB portables on7 mc.

From G6ZOP, Mill Hill, N4VV.7, wecame away with ideas of how DXshould be worked. They accounted forW6DWW, VU2FOP, VU2AN, LU2DGand SU5AAP. This district's 3.5 mc.station claimed to be a really portableone ! It was whispered to us that itcould be assembled in 2 minutes, andhad in fact been done in this time. Thesecret was a liberal supply of plugs andsockets ! No DX had been workedhere, but a contact had been made withall Scottish portables barring station" D." This remark came from a lotof the other 8o and 16o metre stations,and for those who don't already know,these two Scottish stations were not on.It took 2 hours to find the 7 mc. sta-tion of district 12. They were hiddenaway on the opposite bank of the RiverLea, which necessitated a somewhatperilous boat crossing. How they gottheir gear across without gettingdrowned is still a source of wonder tous ! The lack of DX by this stationwas probably accounted for by the lowangle of radiation owing to the ex-tremely marshy site they occupied.

GsRVP, the Essex 14 mc. station,

G4BZ, G8AB and G2CD who were behind the key at G8ABP nearHarlow, Essex.

was situated near Danbury Common,the highest point in the country. PoorDX conditions were blamed for the lowtotal of 19 contacts made. Perhapsthey spent too much time eating those12 eggs, i8 sausages and quantities offried bread ? A bright spot from their7 mc. station at Thundcrsley was theirsystem of having two receivers workingwith an ingenious push-button inter-communicating device to warn thetransmitting operator when a suitablesignal had been heard.

In a letter from GW6AA, we gatherthat they fully expect to run off withthe top -band certificate. As it isagainst the wishes of the R.S.G.B. weare refraining from publishing theirtotal score. GW6AA and G6GL eachput in 16 hours of continuous operatingat this station. Superhuman work wasdone at their 14 mc. station by G3YL(yes, she is a YL) who, apart fromworking some startling DX, did all thecooking, showed the OM's how to putup a tent, completely erected a mastwith the aid of only one male, andclimbed a tree to put up the receivingantenna. She didn't get a wink ofsleep over the whole operating period,either ! DX worked by this station in-cluded VU2, VE3, VK2, VK5, KAI andnumerous W's. Refinements at thecamp included a petrol generatingplant for lighting and accumulatorcharging, and a double -pole double -throw R.F. relay to put the TX on toeither of two antennas.

Although several of the stationsvisited could not be called "portable,"simplicity was the keynote throughout.

The Scottish " D " 7 -megacycle station with (left to right)GM4HB, GM6SR, GM6LS and GM4FT.

428

JULY, 1939AND

SHORT-WAVE WORLD

The VK2NO5 -metre Crystal -exciter Unit

This 5 -metre exciter is very simple and inexpensive to build and hasproved most effective in Australia where it was designed by VK2NO.

ONE of the most prominent ultra -short wave workers, who hasachieved some very fine results

during the last few years, is Don B.Knock, VK2NO, known to our readersas the radio editor of the Australianpublication, The Bulletin. In thatjournal he has published the data onhis latest crystal -controlled exciter unitand in view of the fact that he uses thisto drive his comparatively low -powerfinal stage, the signal from which hasbeen heard in this country, we feel sureit will interest our readers who are keenon U.H.F. experimental work.

The exciter can be used also as aphone or C.W. transmitter and providesa healthy carrier output of around 20-25 watts. There is no need to use com-paratively fragile and expensive ro-metre crystals for with the recommendedcircuit and a 7 -megacycle crystal it isquite possible to over drive the final807.

Because the exciter has so much R.F.output to spare, it can be used to drivea medium power final push-pull stageusing valves of the 35T or HK24 type.The circuit is shown in which a 42 oscil-lator is capacity -coupled' to a 6L6Gquadrupler in the usual way througha roo mmfd. mica condenser. The anodecoils are arranged end to end for induc-tive coupling. Where previously asmall flash -lamp indicator in a ro-metreabsorption meter showed only a slightglow the amplification of the ro-metreharmonic by reinforcing in this manneris such that the lamp burnt out as the6L6G tank circuit was tuned to reson-ance.

An important point is that the R.F.choke in the anode feed to the oscillatorand quadrupler must not be omitted or

the scheme is most unsatisfactory. An807 was used in the final but in its placethe new Osram KT8 will be found mostsatisfactory. It is capacity -coupled tothe 6L6G quadrupler. As a seriestuned doubler to 56 mc. the output isup to 25 watts with Soo volts H.T.

With the exception of the coil dataall resistor and capacity values areshown in the circuit. Tuning conden-sers must have ceramic or high insula-tion and the same remarks, of course,apply to valve holders.

Coil data is approximately as fol-lows : Li (oscillator -anode), 20 turns14 gauge enamelled copper wire closewound r in. internal diameter. L2(quadrupler anode), 6 turns 14 gaugeenamelled copper wire, r in. internaldiameter wound to a length of ri in.L3 (the series tuned doubler -anode), roturns of 12 s.w.g. enamelled copperwire close wound and I in. diameter.All coils are wound on air and are maderigid by cementing strips of celluloidalong the winding, after completion.Suitable coils ready wound are obtain-able from Denco, of Clapton

As the 25 mmfd. tuning condenser inthe L3 circuit has the rotor at earthpotential it can be of the close spacedvariety although one of the most suit-able condensers for English amateursis the Eddystone model 1094. The zoommfd. condenser tuning the oscillatoris obtainable from Raymart, while thequadrupler condenser is again anEddystone 1094.

Series tuning in the 807 circuit hasproved to be highly satisfactory, parti-cularly as it enables such a high valueof inductance to be used in the circuit.The exciter can be used with high effi-ciency on ro metres by using the 807

LI La

100

as a buffer, or by doubling in the 6L6Gstage and doubling to ro metres in thefinal stage. The later method has thebig advantage that the 807 as a doublerwill not, of course, require any neu-tralising.

Although provision is !made for ameter in the anode circuit of each valve,there is no reason why these metersshould not be in a cathode in the moreusual manner. This system has theadvantage that there is less likelihoodof damage resulting to these metersthrough mis-tuning when they are inthe cathode circuit.

All R.F. chokes are of the Eddystone1022 type, while the power supply pro-vides Soo volts using a straightforward83V rectifier. The anode current of the42 oscillator is only 35 mA. and the fre-quency remains very steady owing tothe fact that the screen voltage to the42 is kept low by using a roo,000 ohmseries resistor.

If complete stability is to be obtained,it is important that the crystal -oscilla-tor is not driven too hard. Later typesin valves, such as the 6F6 can be usedin place of the 42 but there is verylittle, if any, decrease in R.F. output.

The author suggests that his ownarrangement in the final stage shouldbe considered. He uses the exciter todrive a pair of 8oi's in push-pull, whileif further output is required the 8orcan in turn drive a pair of 35T's.

An efficient exciter of this kind wouldbe completely wasted unless it is usedin an efficient radiating system. It hasbeen found both by experimenters inthis country and by VK2NO that thetwo -section W8JK beam is the mostsatisfactory and compact 5 -metre array.

L3

0-150 MA

01-1T+500v.

Only three stages are used in the exciter while the output is sufficient from the 807 to use the arrangement as a complete transmitter.A 6F6 can be substituted for the 42 if required.

429

TELEYISIOtlAND

SHORT-WAVE WORLD

A selection of Tungsram 1.4 volt valves.

THE latest type of 1.4 volt valvesare particularly useful when em-bodied in battery -operated low

consumption receivers and amateurswould be well advised to consider thisrange of valves.

A small superheterodyne using fourvalves and a frame aerial will give asurprisingly good performance onamateur bands and can be built in sucha way that it is truly portable and wellworth carrying round on field days orfor checking purposes.

A circuit of a suitable receiver isshown on this page. The first valve isa 1A7G pentagrid convertor with a 1.4volt heater and a current of only 5omA. The conversion conductance isapproximately 25o while the maximumanode -screen and anode -grid voltage is9o. In fact this voltage will power theentire receiver. Total cathode currentof the 1A7G is 2.4 mA. which is notexcessive for a valve of this class.

The frame aerial is connected acrossthe control grid -earth circuit of thefirst detector. In the control grid cir-cuit of the -oscillator is a parallel tunedgrid coil and an air cored primarylightly coupled. Tuning is carried outby means of a too mmfd. condenser,but as it is practically impossible foramateurs accurately to track both theoscillator coil and the frame aerial con-densers, it is essential to use additionalpadding.

In the case of the oscillator this canbe a small condenser of the postagestamp type, but a condenser across thecoil should preferably be a variableplate, an integral part of the aerialtuning condenser and adjustable fromthe front panel.

For normal frequencies the I.F. trans-formers should be 400/500 kc. the ac-tual frequency being a matter of per-sonal taste.

The second valve is an intermediate -frequency amplifier designated 1N5G,a straightforward pentode which re-quires 90 volts on both anode and

JULY, 1939

Using 1.4 -volt Valvesin a

Frame AerialReceiverDuring the next few months there will be considerable outdoor activity anda portable receiver for ham bands will be useful for the average amateurs.How the new 1.4 volt midget valves can be used to advantage is

explained in this article.

screen, has an amplification factor of1,160, and a total current of 1.5 mA.This type of valve enables high gainto be obtained in the I.F. stage so thatthere is plenty of latitude if extra selec-tivity is needed.

Following ' the I.F. amplifier is adiode -triode used as a second detector,A.V.C., and audio amplifier. This iscoupled in a conventional manner andthe valve, a ,H5G, has an exception-ally low current of .14 mA. Thetriode section of this is capacity coupledto an output pentode type 1C5G withan anode current of 9.1 mA. for anoutput of 240 milliwatts.

It will be seen from this that thetotal consumption from the power ofthe receiver is only 13.14 mA. at 90volts, with a total filament current of.2 ampere. The filament current canquite safely be taken from a dry cellof ti volts rating, but although notgenerally used it is an advantage toinclude a small series resistor to reducethe excess with volt supplied by thebattery.

The frame aerial can be woundaround a small chassis and need not bemore than 1 ft. square for this willleave ample space for the receiver. Thevalves are of the midget type with a

maximum overall length of about 4 in.The single coil is of the plug-in typewhile special miniature I.F. trans-formers with iron cored coils are avail-able for this circuit from Peto-Scott.

Of the controls, these merely consistof tuning condensers, audio gain inte-gral with which is the two -pole on/offswitch. With a little ingenuity theplug-in coil could be fitted to the sideof the cabinet to facilitate easy wave-band coverage.

By virtue of the large parallel tun-ing condensers three wavebands can begenerally covered without coil changesso that if built for amateur use the re-ceiver would cover 20, 4o and 8ometres, or with a little care 4o, 8o and16o metres. It is not recommended forto -metre work as the frame aerialwould not provide sufficient pick-up.Also parallel condensers have too highminimum capacity Tor efficient work onthis wavelength.

The too mmfd. condensers are of thebroadcast type and for convenienceganged together. A small loudspeakerabout 5 in. in diameter is required andbuilt in. No difficulty will be experi-enced with this as the valves are en-tirely free from microphony even whenmounted close to the loudspeaker.

AINTENIVA

/476

a2 rf,C600 v

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ay.

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820 IONINS

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1M

This complete circuit gives all values required but the coil and framebe wound to the frequency required by the user.

x

aerial have to

430

JULY, 1939

tansionAND

SHORT-WAVE WORLD

The Short-wave Radio WorldA CATHODE-RAY AERIAL

PHASEMETERIN the April issue of the American

publication Electrpnics appeared afull description of cathode-ray equip-

ment for the true phasing of aerialarrays.

This particular phasemeter has beendesigned for monitoring the operationof directional arrays and up to sixelements can be accommodated.. In

A Review of the Most Impor-tant Features of the World's

Short-wave DevelopmentsIf a phase shifting device is con-

nected in series with one voltage leadthe phase of this voltage can be ad-justed until a straight line trace isobtained. The phase shift introducedis then equal to the phase difference inquestion. In Fig. i can be seen the

1617

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fff utffit [DT

1617

af69

323

956 1617

T

69

T

IF

913

T11^

i.a

Fig. 1. The theoretical circuit of the C.R. phase meter.

addition, a V.T. voltmeter can also beused to check up the amplitude ofaerial currents.

The meter issimple to use for thephase adjustment has only to be rotateduntil the straight line trace is obtained,after which the phase difference canbe read off directly. Should two direc-tional elements be in service the phaseshifter can be left in position as it isonly necessary to switch on the moni-tor and to observe the shape of thepattern.

The designer, John P. Taylor, statesthat with directive arrays the phasingnetwork can be checked before erection,if the line impedance is known. Thisis done by feeding R.F. to one end ofthe network and using the phasemeterto read the phase difference betweenthe input voltage and the voltage atthe output of the network. As themeter has an input impedance of 8oohms it can be used with standard co-axial lines. With this arrangement thecathode-ray tube is used in quite astraightforward manner. It is wellknown that when voltage is applied tothe two pairs of plates having the samefrequency and are in phase a straightline trace appears on the face of thetube. For small phase differences, tracebecomes an ellipse enlarging to a circlefor a 9o -degree difference.

theoretical circuit of the apparatusneeded while in Fig. 2 is a practicaldiagram showing the application.

THE 1852 AS A MIXERThe new 1852 pentode valve although

designed for R.F. and I.F. work isparticularly suitable for use in mixercircuits. The circuit showing thechanges necessary to instal the 1852 inan average communication receiver are

aPickupcoils /4

Concentrich nes

I

shown in Fig. 3. Only minor changesare required such as condenser, C5,being connected between the oscillator -anode and the mixer grid instead ofbetween the oscillator -grid and the6L7 normally used. The screen resis-tor R8 should also be changed tooo,000 ohms while additional by-pass

condenser C is connected between cath-ode and earth. The suppressor gridof the 1852 is earthed and not connectedto cathode which helps to better theimage ratio.

A good R.F. oscillator is the 6J5triode which is an evolution of the 6C5,

L3

pL,

:

C3

Ls0

Li

7'T"o Ice

Fig. 3. An 1852 pentode can be used toadvantage in mixer circuits.

1

c

8

6JS

but has a much lower input capacity.The values in the circuit are as fol-lows :-C 002 mmfd., C5 mica trim-mer, C6 and 7 .r mfd., C1r .2 mfd., Cr2.005 mfd., C14 roo mmfd., Ri 300 hms,R2 1,000 ohms, R7 iso,000 ohms, R8roo,000 ohms, Rr5 15,000 ohms.

We can thoroughly recommend ama-teurs who wish to improve the perform-ance of their communication receiversto modify the 5852 in the manner sug-gested in place of a 6L7.

BIAS FOR AUTOMATICMODULATION CONTROL

A simplified arrangement for obtain-ing bias for automatic modulation con-trol is shown in Fig. 4 and is a schemedeveloped by Frank C. Jones, W6AJF,and described in detail in the Juneissue of Radio.

Phasesh I fter

1 R. F.amp.

R.F.amp.

C.R.± tube

0 Fl

IFig. 2. The practical application can be appreciated from this diagram.

431

IriELEYSIMIAND


A 5 -metre Tx. :: One -valve Tx.Automatic modulation control will

undoubtedly before long be used inevery amateur phone transmitter for itis realised that over modulation cancause havoc in the crowded telephonybands. Automatic modulation controlis a system whereby a diode rectifierdelivers automatic volume control to avalve in a speech amplifier in order to

should be adjusted for very exact neu-tralising. The complete scheme isshown in Fig. 5, but readers are re-ferred to the original article whichgives full data.

A CHEAP 1 -VALVETRANSMITTER

The newcomer will appreciate the

6L 7

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PICID. TAM11-

DR/veRs AND CLASS 8.14X,

+23-0. v.

To Cuss C FINAL

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1000-0 1

/10 i(A.0

Fig. 4. Automaticmodulation controlis a very necessaryrefinement in orderto prevent over mod-ulation on crowded

phone bands.

keep the gain constant. It is suggestedby the designer that a valve of the 866class be used in the diode circuit, hav-ing the anode connected via an R.F.filter into the suppressor or injectiongrid of a low level amplifier valve.

In this scheme no current flowsthrough the diode at any time unlessthe cathode becomes more negativethan the anode. When this occurs theclass C stage is over modulated, sincefor ioo per cent, modulation the nega-tive voltage audio peaks should equalpositive D.C. voltage. When thediode cathode becomes more negativethan the cathode current is low throughthe anode resistor to earth.

AN INEXPENSIVE 5 -METRECRYSTAL CONTROL

A suppressor modulated transmitterusing receiving type valves has beendesigned by N. W. Mix, WIIGL, andappears in the June issue of "Q.S.T."It uses a type 89 electron -coupled oscil-lator with the grid on 28 megacyclesand the anode on 56 megacycles driv-ing two 89's as push-pull 56 megacycleamplifiers. A carrier of 4 watts is ob-tainable and ioo per cent. modulationcan be used without frequency modula-tion. The audio section consists of ahigh -gain single button microphonefeeding into 6C6 and is R.F. coupledto a type 37 triode, the output fromthis being fed into the grid of the 89's.Neutralising of the 89's is essential asthe grid -anode tuning is not sufficientto prevent oscillation. This neutralis-ing is done by strips of copper aroundthe outside of the valve and cross con-necting the strips to the grids. Theyare held in place by a rubber band and

simplicity of a single valve transmitterpublished in the June Radio, whichembodies one T-21 tetrode valve. Itis for C.W. operation and covers the8o 'and 4o metre bands, although thehigher frequencies can also be used.The maximum output is 15 watts on 8ometres and approximately 12 watts on4o metres so suiting recently licensedamateurs. The bulk of the compon-

IZ/

42

.89

5$-3a243oa 4

63.v "14.024,-s

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8

/2

ents are of the standard broadcast typewhile the power pack has to deliver375 volts at go mA.

The single coil in the anode circuitconsists of 41 turns close wound on a

in. diameter former or for 4o metres21 turns spaced to a length of 2 in. ona ti in. former. The tank condenser isa 5o mmfd. midget and the fundamen-tal crystal is always advisable. Com-plete circuit is shown in Fig. 6.

/3

C3

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C

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ona-o\el - 80 Aferrq

1/0/41,ok_

COILSOCKETS

X X

T2/g //FL-.

csT

3) - +57g v,Fig. 6. A simple 1 -valve beginner's

transmitter.

37

Fig. 5. Receiving type components are used throughout in this 5 -metretransmitter which provides a carrier power of 4 watts.

5

432

JULY, 1939

TELVISIMAND

SHORT-WAVE WORLD.

g's

All the controls are clearly marked while full electrical band -spreading is included.

AN interesting addition has justbeen made to the P.S.E.I.range of Trophy receivers, in the

new Trophy 6, an inexpensive com-munication receiver which has beendesigned specifically for communicationuse amongst amateurs.

As the name indicates it is a 6-valverhaving four wavebands giving contin-uous coverage from 6.5 to 545 metres.A separate dial is provided to give elec-trical band -spreading which actuateson to a separate set of band -spreadingcondensers. The. main dial is directlycalibrated in frequencies and so ar-ranged that each individual wavebandis quite separate from its neighbour.

Amongst the refinements includedare switchable automatic volume con-trol, switchable beat -frequency oscilla-tor, a B.F.O. pitch control, send -receive switch, built-in loudspeaker,phone jack and provision for a doubletor Marconi aerial.

The first valve in the receiver is a6TH8 triode-hexode designed specifi-cally for short-wave working. Thisis followed by a 6K7 intermediate -frequency amplifier, a 6Q7 double -diode triode detector A.V.C. controland first -audio amplifier, and in theoutput stage a 6V6 tetrode, a smalledition of the 6E6, which provides ap-proximately 2 watts. The beat -fre-quency oscillator, a 6C6, has an iron -cored coil with the pitch control actu-ally being a movable iron core.

The first coil in the I.F. amplifier isalso iron cored, the transformers beingtuned to a frequency of 456 kc. and ad-justed to give a maximum band widthof 7 kc. This provides quite a highdegree of selectivity and as much ascan be expected with a small receiverof this kind.

Despite the high selectivity he aver-age gain is excellent. Average sensi-tivity figure over all wavelengths isapproximately 20 microvolts per metrewith a peak on the To -metre ham bandof 15 microvolts per metre. A figurewhich compares very favourably withsets of a higher price.

On the lowest wavelength band, theoscillator circuit is highly efficient,

The P.S.E.I.Trophy 6Communication

Receivermade so by the use of a tuned reactionwinding to ensure even oscillation overthe entire band. Consequently, ama-teurs will find that the band coveringapproximately 17-46 megacycles is un-usually senstive and that the televisiontransmission can be received at longdistances from the transmitter.

Noise level is particularly low, andeven with the B.F.O. in circuit the risein noise is barely worth mentioning;however, to adjust the amount of coup-ling between the B.F.O. and the in-coming signal, one can merely reducethe value of the coupling condenser.This condenser is made up of twoparallel wires which can be pulledapart to reduce coupling. However,this little modification is not reallynecessary unless the user is likely toconcentrate on the reception of veryweak signals.

Band number one practically covers14.5 to 47 megacycles, so allowing aslight tolerance at either end of theband over the official figures. Bandtwo covers 5 mc. to amc., band three1.6 mc. to 5.5 mc., and band four .5 mc.to 1.75 mc.

The band -spread control with itsseparate dial is calibrated in single de-grees from zero to too and on all ama-teur bands except 16o metres gives com-plete coverage without having to. re-adjust the band -set condenser.

As can be seen from the illustration,

the number of controls have been kepteat minimum and all these are carefullymarked to show their exact use.

We have tested this instrument andifound it highly satisfactory. OmC.W. it provides an extremely stablenote free from wobble or drift. Thecabinet and chassis are of heavy gaugesteel, so that on the 14 megacycle band,for example, the receiver can actuallybe moved about a bench without thesignal beginning to wobble.

The base of the receiver comes offvery simply exposing all the trimmers.to view. The model tested was very ac-curately aligned, but there are alwaysamaturs who feel they can improve onthe manufacturer's setting. They willappreciate the ease with which the" works " can be seen.

On all amateur bands a representa-tive selection of stations were obtainedand even on the higher -frequency bandswhen conditions were bad signals werereceived. The instrument is excellenton the commercial channels of 13, 16,19 metres, etc., while the gain appears.to be rather peaked on the now popu-lar C.W.R. and Service channels.

The cabinet size is 171 by 9 by inand at gi gns. it is really excellentvalue for money. Full information on,this receiver can be obtained from theP. S. E.I., Ltd., Pilot House, Stoke -Newington Church Street, N.I6, men-tioning this journal.

The back of thereceiver comes awayvery easily exposingthe main componentsto view. As can beseen a special band -spreading condenser

is Included.

433

la.EvsionAND


Making the most of the8 -valve Amateur -band Receiver

This receiver was first described in the May issu3, but as many readers have asked for additional dataon the operation, this short article has been prepared.

CONSIDERABLE number ofreaders have asked for furtherdetails regarding this receiver so

as to obtain the best possible results.As so many of these questions are ofa. similar type I hope to be able to dealwith them in this short article.

A slight increase in gain can be ob-tained by altering the primary windingson the R.F. and mixer coils. This isa matter for experiment, but generallyspeaking the R.F. coil on zo metres willstand a primary coil of four completeturns. On to metres the number ofturns should be three or even four itthe aerial in use is a short one. For themixer coil try a primary winding of fiveturns on 20 metres and four turns onto metres.

GainControls

Some readers find that the gain con-trol in both R.F. and I.F. stages are alittle rough in operation. If thisshould be the case the variable resist-ances specified can be changed to io,000ohms each both having logarithmicpatterns.

It is also possible to find two oscilla-tor beats and the correct one to use isthat having the lowest frequency. Hereagain a change can be made for it willsometimes be found that the' high fre-quency beat will provide a better signalon the to and zo-metre bands. This,however, will tend to restrict the band -spreading. To overcome this one platecan be removed from each condenserallowing for a t7o-degree coverage onthe zo-metre amateur band.

All of these suggested alterations arequite unimportant but the additiveeffect is very considerable. It is alsohelpful to use a tuned aerial on eachband. Those who are restricted to theuse of one aerial should employ somesort of aerial coupling device for whenthe aerial is roughly tuned to the bandin use the gain in signal strength canbe as much as two R points. Thetransmitting amateur will probablyhave such a tuner already in operationin the transmitter so arrangements caneasily be made to couple this tuner tothe receiver.

A gain in the I.F. stages can be ob-tained by using as an I.F. amplifier theMullard TSP4 pentode valve. Caremust be taken in the wiring otherwisethe stage may become unstable whileat the same time the bias resistancemust be altered to makers' require-ments.

If the I.F. stage is made controllablyunstable this also helps on weak sta-tions. To do this remove some of thescreened wire from the anode lead ofthe valve. Generally if about 2 in.of the covering is stripped off the stagewill start to oscillate when the gaincontrol is at maximum. In this waythe last fraction of gain can be used.

The receiver will work down to 5 -

metres and put up a good performanceon the television and amateur channels.However, it is important that the oscil-lator volts should be correct.

On zo and to metres an oscillatorvoltage of I 2 can be obtained withoutany trouble, but on 7 metres this willdrop to about 7 volts and at 5 metresto 6 volts. However, it has beennoticed that on the television bandthe performance is still good with theoscillator voltage down to 3 volts.

Very rarely does an amateur use allbands with the same degree of consist-

ency. There are always one or twobands which are more popular. For thisreason I suggest that the receiver belined up for the most popular bands, forexample, if the high -frequency bandsare to be used arrange for the couplingcondenser in the I.F stage to be at mini-mum capacity for this will increase theselectivity without causing any decreasein overall gain. However, if the con-denser is left set in the same positionon the i6o-metre band the signalstrength will not be so great as if thecoupling were tighter.

One of the advantages of a homebuilt set is this versatility so the best

results can always be obtained on eachband. It would be possible to arrangefor one setting on the controls, butthis would give average results on allbands without that peaking on indivi-dual bands which is now possible withthis set.

The advantages of the three I.F.transformers was explained in the Mayissue. However, these transformersmust be trimmed correctly and if pos-sible with an oscillator and outputmeter. If test gear is not available,however, pick on a weak station andadjust the trimmers until the strongestsignal is obtained. The trimmersshould be adjusted in the correct orderstarting with VC13 and working backto VC7.

The B.F.O.When listening to C.W. the output

from the B.F.O. is hardly sufficient tobeat up a very strong signal. This was

Most of the smallcondensers arefixed under thechassis includingthe band setting

condensers.

done in order to keep the noise level toa low level. Readers, however, who areprepared to put up with the increase innoise can make the B.F.O. more healthyby taking the lead from the anode ofthe B.F.O. valve direct to the diodeanode in V4 blocking the D.C. voltageby means of a .00005-mfd. condenser inseries with the lead. It should bepointed out. however. that strong sig-nals can be heterodyned by merely re-ducing the R.F. gain.

If there are any points which I havenot covered I shall be pleased to answerany letters if a stamped addressed en-velope is sent with the letter.-J.T.R.

434

TELEY1.510t1AND

JULY, 1939 SHORT-WAVE WORLD

OS RAMKT 8

BEAM TETRODE

Type KT8

PRICE 22/6 EACH

Type KT66 price 15,'- each

A New Transmitting Valveof outstanding interest

for AmateursThe Osram Valve type KT8 is a Radio Frequency TransmittingTetrode having an indirectly heated cathode. It has alignedgrids which produce directed electron beams resulting in a verylow screen current. Thus the limit normally set by screendissipation is largely removed. The valve is suitable for use asan Oscillator, Radio -frequency Amplifier or Frequency Multi-plier for frequencies up to 6o Mc S.

CHARACTERISTICS :

Heater voltage .. 6.3

Heater current 1.27 amp. approx.Anode voltage 600 max.

Screen voltage 30o max.Anode current *95 mA. max.Screen current 12 mA.

Anode dissipation 25 watts max.Screen dissipation 3.5 watts max.Anode input 57 watts max.Grid driving power 0.5 to 1.5 wattsMutual conductance 6.o mA./volt

(measured at Ea = 25o, Es = 25o, Ia = 72 mA)

* Under efficient Class C conditions.

Anode connected to top cap ; British 5 -Pin Base.

For Modulator, use OSRAM KT66. Output in Class ABipush pull, 32 watts audio ; octal base.

Write for leaflets giving full technical and operative data to the Osram Valve Dept. of :

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

1/et. of The General Electric Co. Ltd., Magnet Kingsway, London, W.C.2

435

TELEYSIMAND

SHORT-WAVE WORLD

Radio Society ActivitiesWill Hon. Secretaries of Radio Societies who wish for news to appear in

this column please send the information before the 15th of the month.Slade Radio

THIS society was perhaps one of thefirst in this country to organiseDirection Finding Contests for

amateur experimenters. They are nowin the middle of a new series of contestswhich are being well attended. Test arebeing conducted on a scientific basis,using a formula to award points. Atrophy is being presented to the win-ning team, which has been given to theclub by the founder, Dr. C. H. Har-court, M.B. The new hon. secretaryis L. A. Griffiths, Esq., 47 WelwyndaleRoad, Erdington, Birmingham, whowill be glad to send all details of thesociety to any interested reader livingin the district.Tonyrefail and District Radio

SocietyThe hon. recretary of this society has

now obtained his full transmitting callsign, GW3QB, and he is very keen toincrease the number of members whoare able to take part in field days andcontests. Information can be obtaineafrom E. Powell, Esq., 44 PritchardStreet, Tonyrefail, Glam. At the an-nual general meeting 2FRK, GW3QB,and GW3CR were elected chairman,secretary and treasurer respectively. Ithas been decided to hold the main FieldDay on July 23, and members are nowconstructing apparatus and arrangingduties. This contest is open to allmembers so that there is still time forintending members to join.Eastbourne and District Radio

SocietyRecent lectures have dealt with radio

from all angles including 5 -metreaerials and equipment, short-wavesuperhet receivers, commercial trans-mitters, and quality amplifiers. Thehon. secretary of this society is T. G. R.Dowsett, 48 Grove Road, Eastbourne,Sussex, who can supply all data to in-tending members. Field days and out-door contests have been arranged forthe next few weeks and it is hoped thatthese will, as usual, be well attended.Thames Valley Amateur Radio

and Television SocietyThe T.V.A.R.T.S., whose headquar-

ters are at the Albany Hotel, StationYard, Twickenham, Middlesex, havefound it necessary to effect a change inpolicy. Through lack of enthusiasmthe old club was dissolved, but by ap-proaching recently licensed amateurs anew club has been formed. This has alimited membership for those holdingfull radiating licences, artificial aeriallicences and B.R.S. members of theR.S.G.B. ' The new club will still beknown by the old name to avoid con-fusion. The main function of the

T.V.A.R.T.S. is to cater for those in-terested in short-wave transmission andto help as many members as possibleobtain a radiating licence. A 3.5 mc.station was operated during theR.S.G.B. National Field Day for thethird year in succession. The officersfor the year are : President, G. H. Bil-lison, G6GB ; secretary, D. R. Spew -l-ing, G3JG; treasurer, A. Mears, G8SM,assisted by G2NN, G5LC, G2G,K, andG3GQ.

Wolverhampton S.W. RadioSociety

During the past few weeks interesthas been concentrated on 5 -metre workwith great success. Large numbers of

amateurs have attended each 5 -metrefield day so that a special one has beenorganised for July i6. On these fielddays distances of up to 20 miles havebeen covered with reports from listen-ing stations up to 35 miles. There arenow four 5 -metre stations active inWolverhampton so that the next con-test should be of particular interest.Full details can be obtained from theHon. Secretary, W. H. Hill, G8BP, atthe headquarters, 76 Darlington Street,Wolverhampton.Wirrall Amateur Transmitting

and Short-wave ClubMeetings of members and interested

amateurs are held on the last Wednes-day of each month at 7.30 p.m. Mem-bership at the moment is in excess of45 including two full licences andseveral AA calls. Amateurs in the'Wirrall district are advised to get intouch with the secretary for this societyhas an interesting programme arrangedincluding Morse classes and field days.A club magazine is also published. Thehon. secretary is J. R. Williamson, 13Harrow Grove, Bromborough, who wiltsupply all details as to membership.

JULY, 1939

North Manchester Radio SocietyMembers of this society come from

all parts of Manchester, for the head-quarters are only two minutes fromPrestwich Railway Station. Member-ship fee is 5s. per year plus a supple-mentary charge of 3d. at each officialmeeting attended. Club headquartersare open on Sunday afternoons formeetings, while a selection of radiomagazines are available for the use ofmembers which can be borrowed if re-quared. Modern communication re-ceivers are being demonstrated fromtime to time, while conducted tours andoutdoor events have been scheduled.Headquarters are at 14 Fairfax Road,Prestwich, and the hon. secretary is R.Lawton, Esq., so Dalton Avenue,Thatch Leech Lane, Whitefield, Man-chester.

G5DR operating oneof the R.S.G B.National Field Daystations put up bythe Cambridgegroup of amateurs.

The Woolwich and North KentAmateur Transmitting ClubThis society has just been formed

and members are required. Any readerliving in this area who is interested inamateur radio should get in touch withthe hon. secretary, 33 Westergate Road,.Upper Abbey Wood, S.E.2.Southend and District Radio and

Scientific SocietyThe next Field Day to be run under

the auspices of the various societieswhose names have previously been an-nounced, is to take place on Sunday,July 9, and on this occasion will beorganised by the Murphy Radio Clubin the Welwyn district.

The last di: ection finding field dayorganised by the Romford Society wasenjoyed by all. The organisers are tobe congratulated on their choice of loca-tion, which introduced many unexpecteddifficulties. Enthusiasm is so great forthese events that when one competitorwas unable to find motor transport hedug an old bicycle out and during theday must have cycled over 50 mileswith his equipment strapped on hisback.

436

1";:i P/NIOMJULY, 1939

ANDSHORT-WAVE WORLD

4:01 gvials

WITH the NEW

The NEWBuilt-in MONITOR

Jlere s whal 1.1 means to you A self-contained frequency meter is built into this receiver which

allows the exact frequency measurement of your own transmitter. It allows checking of the exact frequency of an incoming signal. It makes possible the location of the amateur bands with absolute

accuracy.

It makes it possible to re -set the dial to an exact pre -determined fre-quency so that you may be positive to return to any station which youhave already worked.

Allows you to set the dial on the exact frequency of a station which youwish to work.

Accuracy is controlled by beating against an expensive broadcaststation frequency equipment.

Other features :-Ten tubes, noise limiter, moving coil " R " meter, 340 degreesof electrical band -spread, ceramic coil forms on high frequencybands, high frequency insulation on both tuning condensers,pre -selection on all hands from 43 m rcto 540 kfc, iron -coredI.F.'s, crystal filter, with iron -cored coupling transformer.

RADIOMARTBRITISH HOWARD DISTRIBUTORS

4cienfifically

HOWARD 460COMMUNICATION RECEIVER

wtfll Attilt=1.1/

FREQUENCY MONITOR ANDNOISE LIMITER

MODEL 460, with Frequency Monitor and 8 -inchDynamic Speaker in cabinet to match Receiver

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437

TagYISIOt1AND


The Nursery WavelengthsBy G6

This provocative article has been written by a professional wireless engineer who holds a transmittinglicence. He has been "off the air " for about ten years and, on returning, finds conditions so different

that he puts forward suggestions for improvement.

ISUPPOSE that there is no Club,Lodge, Association, Society, orother group of men in existence that

can, for sheer camaraderie equal thenow large body of transmittingamateurs at home and abroad. Theywill go to no end of trouble, and oftenpersonal inconvenience, to help a trans-mitting friend.

But-I now prepare to duck-forsheer thoughtlessness and selfishnesswhen on the air, some of the 'phone en-thusiasts deserve to be put away intocorrective institutions to be taught theelements of social conduct andrestraint.

After about ten years' absence fromthe ether I come back and on theamateur bands I find that I have to tryto inject my own modest attempts intunothing short of pandemonium.

Generally, the 'phone amateur ignoresentirely what other people are doing.He scrambles for the desired contactamong other scramblers in an uncon-trolled din.

Another thing, if some of them couldonly realise that their voices are beingreproduced at full strength not only inliterally thousands of lounges, livingrooms, and drawing rooms, but also inthe laboratories of professional wirelessengineers, they would blush with con-fusion and embarrassment.

To -day, nearly all wireless manufac-turers offer all -wave sets and the voiceof the amateur, like the broadcastartiste, can get into millions of homes.

There is the gentleman who talksabout his school and his motor -car in ablasé old -school -tie style; the manwhose domestic troubles have beenbrought to an end by divorce, and thecream of sententiousness in the voice ofa gentleman who could, if you werethere, prove to you by mathematics anda slide rule why his argument is soundthough he is unable to put it into simplewords.

The loudspeaker on which the latterwas heard was damaged, I'm afraid, bybooks, transformers, a variable con-denser, and a stool that were thrown atit by several professional wirelessengineers whose feelings boiled abovethe cold atmosphere of the laboratoryin which they were working.

Some amateurs on 'phone are enter-taining; most of us have enjoyed, forexample, the American lady, and theboys in Greece, but for every one giftedwith a merry prattle there are dozenswhose flat -voiced platitudes bring forthhowls of derision from intelligentlisteners.

I wonder how many transmittingamateurs know about the new familygame called " Old Man Percentage." ?This is useful on wet nights whenordinary broadcasting is a. bit dull. TheBookie is selected, and he tunes in, onzo, 40, or 160 metres, to locate the sixor seven most affectionate amateurs onthe air. After a test period of listening,he states his prices and bets are laid bythe family. One person takes down thetransmissions completely. If he or sheknows shorthand, so much the better,but they are usually laboured enoughfor longhand. The rest of the partymeantime checks off each " old man "as it comes over. You know the sortof thing : " Thanks old man for yourreport. Yes, old man, I have gone upin frequency a bit old man, but I mustsay, old man, you are right outside theband. Yes, old man, no, old man, allright, old man . . . ." and so on. Thenwe work out the percentage of admans to the total words and the Bookiepays out on win and place bets.

I hate to spoil a good game, butreally ! . . .

A psychologist would say that thesevoluble radio telephonists reveal the ex-istence of a. repressed ego. Failing,perhaps, to find a means of self-expres-sion in their daily lives, they comehome at night and pour their troublesand their triumphs into the ether-sothey think-for one man to hear, butunfortunately it comes back again witha shout where they least expect it. Agreat deal of it is as remote from theneeds of experimental wireless as anoffice boy's usefulness is to the businesssuccess of his firm.

You may say, " Don't listen to it,then," and there's the rub. One hasto, sometimes, if one wants to use theether as well.

Ignoring altogether the subjectmatter of the transmissions, these vol-uble amateurs occupy too much etherand for far too long. As there is muchmore in fishing than catching fish, sothere is far more in transmitting thanmaking contacts.

Surely it should be the duty of eachamateur to listen first upon and aroundthe frequency he proposes to use. If itis being occupied by C.W. or telephonythen he should refrain from transmit.ting until the others have finished. Ifthe others should commit the crime ofpersistent occupation then they deserveto be jambed until things arestraightened out.

" Ah ! " says the ruthless DX seekerwho is not limited by money or time," if I were to wait until my channelwere clear I should never do anything."So he applies for permission (some-times) to use increased power and, insteps, reaches the maximum to shouteverybody else down. Thus things getworse instead of better and it is nocause for surprise to learn that the PostOffice comes down quickly on thosewho wander, with their infernal din,outside the band.

Behind all this sit, in dignity andskill, the C.W. amateurs. These gentle-men of the ether usually occupy nomore than their allotted frequency, witha note pure and steady by crystal con-trol (often an example to commercialand official stations), and for the mini-mum transmitting time. They do notleave a carrier whistling away whilethey think out the next thing to say, andtheir transmissions are rarely heard,and certainly not understood, by thelistening public.

How ,often 4o we hear a clear, cleannote coming er in unblemished Morseto the correct international procedure,suddenly blotted out by the familiar" Boo. . ." of the telephony carrier,dropping slightly in pitch as it settlesdown, and then the wash of modulationelbowing its way through the crowd.

It can be argued, of course, that thisstate of affairs stimulates progress indesign; that here we have the reasonfor the highly selective communicationsreceiver, but would it not be better, nowthat so many occupy the amateur bands,to adopt an Ether Code.

There is now a " First -Class Opera-tors' Club " (F.O.C.) whose object is" To encourage and maintain a highstandard of operating techniqueamongst British Radio Amateurs "from which it is obvious that membersof the Club propose to adopt a gentle-manly code of behaviour in the use ofthe ether; a step in the right direction.

Applicants for membership of thegroup are invited to make suggestionswhich I have already done, and if asubstantial backing is obtained, theManager and Committee have promisedtheir full support in putting the schemeinto operation.

My suggestion is that we shouldadopt a semi -commercial procedure.We must start somewhere and thelogical thing to do is to start withthose who are most advanced. TheC.W. amateur is more than half -way to

438

1P.LEVISIOhJULY, 1939

ANDSHORT-WAVE WORLD

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I

439

ANDSHORT WAVE WORLD

the desired goal and since most of themwill be in sympathy with this plan,there is good reason to believe that thestart will be a good one.

What we are going to do about thetelephonists, especially those who com-pletely blot us out for half -an -hour at astretch with multi-plex, I do not knowfor the moment, but it will all come outin the wash, and those with commercialexperience on that side will help, Ifeel sure.

On the C.W. side then, it is suggestedthat each member of the club shoulduse a printed telegraph form in pads,roughly, as follows :-

of keeping always to the right, steppinginto the road at a Belisha crossing toindicate intention to cross, waiting for,say, six cars to pass, and then proceed-ing with hand uplifted.

With other minds to work on this tosettle details something good shouldcome of it, and surely we should getassistance from the Post Office onborderline points if any. Once in opera-tion there are all sorts of things thatcould be done to bring the amateurbands out of the nursery where they aregetting a bit too old to stay.

To relieve pressure on the presentmanager of the F.O.C., the Editor has

FIRST-CLASS OPERATORS' CLUB.

Date 1 Time sent 1 Words 1 Time recd. Band

To :via

Where contact is desired the stationoriginating the message calls in thecommercial fashion :

GIAA de GIZZ. F.O.C. MSGthe call signs being sent three timeseach. If no reply is forthcoming thecall is repeated at a fixed period later.

When the station transmitting isheard, the station called replies : GIZZde GIAA. K, and the message is sentin the usual way. Matters of QRM,QRN, and words missed are overcomein the commercial fashion until therecipient is able to give his R.

That contact is then completed asthough a third person had written outthe message. The channel becomes freefor others, while the recipient writesout his reply with telegraphic brevity.In the meantime either the sender or re-ceiver may accept or transmit messagesfrom others in like form.

When the reply is ready the recipientof the first message now becomes thesender and, after calling and receivingK, sends his message in the same way.The form is ripped from the pad andimpaled upon a spike file for reference,P.O. check, and agreement with thelog -book is required.

I see nothing in this that runs counterto the Post Office requirements anymore than Police regulations could bedisregarded by the actions of a pedes-trians' club, the members of whichadopted a rigid and polished procedure

kindly given his permission for lettersand postcards of approval and criticismto be addressed to me as follows :

" Semi -commercial,"c/o Television and Short-wave World.

Each one will be acknowledgedbriefly by card, the letter analysed andsubmitted to the F.O.C.

Do you agree ?

"A Long DistanceShort -Wave Receiver"

(Continued from page 41[9)

but recent tests have shown that it willprovide quite reasonable gain on theto -metre band provided the band -set-ting condensers are omitted. Thismerely means releasing two wires, onefrom each condenser. Actually, whathappens is that the added capacity ofC1, C2, C5, C6 and C7 is rather toohigh to allow of satisfactory to -metreoperation. For this reason, CI and C5are omitted on that band only.

During the past few weeks the to -metre band has not been particularlylively, but signals have beef receivedand when compared with reception onother receivers, this band appears to bequite satisfactory.

It is not advisable to consider thisset suitable for medium wave broadcastreception except by Colonial users.

JULY, 1939

Active 5 -metre StationsMax. Buckwell, G5UK, whose QRA

is Leigh -on -Sea, is now very active on5 metres. The transmitter uses an 8o8in the final, runs with an input of gowatts, while his receiver is a superhetbuilt especially for the 5 -metre band,with acorn valves, and a signal strengthmeter. During the past few weeks hehas worked and heard a large numberof 5 -metre stations and has supplied thefollowing information for amateursactive on this band and also listenerswho wish to check their receivers.

The following are the crystal fre-quencies of some of the better knownshort-wave stations.

kc. kc.56,020 G5ZT 56,952 G6NU56,020 G6TL 57,000 G5UK56,070 G3CU 57,000 G5ZT56,088 G6QC 57,084 G6TL56,120 G2KI 57,200 G8KD56,170 G6FL 57,240 G211CI56,180 G5MA 57,300 G2MV56,336 F8CT 57,400 G2OD56,340 G6QZ 57,470 G8OS56,360 G6PG 57,60o G6CW56,400 G5AA 57,68o G5CD56,400 G8MU 58,000 G2NH56,520 G§QC 58,000 G8JV56,704 GJKI 58,828 G8'LY

The following stations have beenheard but no frequencies are available,G5TX, G6VX, G5BY, G6F0.

In addition the following six stationshave been worked but frequencies notobtained : G6DH, G6NC, G2AW,G2ZV, G60T, G2iLC.

G5UK operates every evening on 56mc. immediately after the finish of theB.B.C. television programme. In ad-dition he has a regular schedule at 7.30B.S.T. and uses on all transmissions anautomatic sender. He mentioned thatat the present time 5 -metre stations arebest received between 22.000 and 23.15B. S. T.

While on the topic of short-waveactivities we should like to mentionthat G5TZ, in the Isle of Wight, isreceiving Belgian and Dutch stations,but so far has not been able to workthem. Signals, howevier, are reason-ably consistent.

Edgware Short-wave SocietyArrangements are now well in hand

for a 5 -metre Field Day to be held bythis society on July 2. Ten entrantsare competing and G2QYP will be incharge of the transmitter to radiateeach hour for five minutes. This sta-tion is also working on July 9 duringthe R.S.G.B. 5 -metre Field Day.

Future meetings include a discussionon 5 -metre Field Day apparatus.

440

JULY, 1939

TELIYISIOhAND

SHORT-WAVE WORLD

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441

ANDSHORT-WAVE WORLD JULY, 1939

With the AmateursBeam aerials, some hot news about new receivers, and new countries

to work are discussed in this article by G5ZJ.

BEAM aerials are at last cominginto their own in this country,probably due to the very bad con-

ditions which make it essential thatamateurs either greatly increase theirpower or the efficiency of the radiating

The rotary beam at G2FB.

systems. As a power increase of anyimportance is now impossible the onlyway of working DX particularly ontelephony is by using high -gain narrow -angle rotary or fixed beams.

G2FBA recently licensed station G2FB at

Welwyn, Herts, is doing extremely wellon 2o -metre phone with an extremelylow input. Many may think the stationuses a " Californian kilowatt " orsomething like that for the DX workedby G2FB is really exceptional. How-ever, I decided to go along and look atthis station and found that the inputreally was low and that the explanationwas to certain extent location butprimarily the excellent results are dueto antenna systems pure and simple.

A lattice mast has been erected and isused as a focal point for all antennasystems. In use at the present time area fixed W8JK beam which is hung upwell in the clear and does provide agood gain on 14 megacycles. Two half -waves in phase are also available andfinally a rotating beam with closespaced reflector.

The tower on which the rotatingbeam is mounted is not very high butas the roof of the building is compara-tively flat and is 70 ft. above ground theaerial is really in an advantageous posi-tion. By using the main lattice mast asa fixture for various aerial systemsG2FB is able to erect simple aerials inpractically almost any position he re-quires, for around the house are a largenumber of 70-8o ft. trees to which the

free end of the antenna systems couldbe connected.

I spent a most enjoyable evening withG5UMP at Mardley Hill, near Welwyn,where the 1.7 Mc. N.F.D. station wasbeing operated. G5UMP did extremelywell particularly in view of the factthat the input was only 7-8 watts, powerbeing obtained from a vibrator con-vertor. However, some really slickoperating by G8DR and GUM soonpiled up, the points. This location isideal for 1.7 operation as a near -by treeis approximately 140 ft. away from thesite selected for the station so that132 ft. aerial could be used withouttx ouble.

G5DR of Cambridge also had a goodportable station for N.F.D. and hadplenty of help both with the operatingand the catering, the latter point beingvery much appreciated.

A general topic of conversation at re-cent ham meetings has been DX on 5metres and all sorts of amateurs whonormally keep to the L.F. bands arenow considering what they can do abouta transmitter for 5 metres. The Thorn-ton Heath short-wave society are ar-ranging a contest for 5 -metre directionfinding on July 9 and stations who areparticipating include G2DP, G2RD andG3FP.

It is very likely that these transmis-sions will be heard over fairly wide dis-tances so that readers with suitable re-ceivers are invited to listen. The secre-tary G2RD of 4 Nutfield Road, Thorn-ton Heath, Surrey, will supply furtherdata on this event.A NewZone

vE5Aiiu is located 28 miles from theArctic circle and is not just anotherVE5 station to be worked, for he tells

me that he is in zone one and for mostEuropean amateurs this would probablybe a new zone to add to the list.

VYIAQ is very keen to work G sta-tions and promises to QSL one hundredper cent. He uses a pair of TZ4o's inClass C with 120 watts input, Class B

One of the operators at G5UMP wasG8DR, here at the key.

modulated by RK is's and uses amatched impedance Y antenna. Thereceiver is a Hallicrafter SX16.

A NewHallicrafter

While talking about Hallicrafters,here is something that is really news.A receiver which is going to completelyshake up the market as regards hamcommunication receivers. This set isthe new Hallicrafter SX24, a ninevalver that has everything. It covers8 -wave bands, from 8 to 550 metres,has a crystal filter, built-in frequencymonitor with a calibrated band -spread

National Field Day withthe Cambridge groupof amateurs under thedirection of G5DR.Laurie Jones, G5J0, isalso taking an active

part in this station.

442

Tr 'JISIJ,`1AND

SHORT-WAVE WORLDJULY, 1939

Principles and Practiceof

RADIO SERVICINGBy H. J. HICKS

305 pages, 9 x 6, 212 illustrations. 18/- netT'HIS book approaches radio servicing from the angle ofI showing how and why various circuits operate. The

fundamental principles underlying amplifiers, detectors,power supplies, and other component parts of radio sets arecarefully explained and the application of each point to setoperation and set troubles discussed. Here is informationthat goes beyond rule -of -thumb methods-familiarises youwith the engineering principles underlying the constructionand function of radio parts and circuits, so that you canhandle not just a few, but all kinds of troubles that may arise.

Theory and Applicationsof

ELECTRON TUBESBy HERBERT J. REICH

670 pages, 9 x 6, illustrated. 30/- net

THE purpose of this important new book is to give thereader a sufficiently thorough grounding in the funda-

mental principles of electron tubes and associated circuits toenable him to apply electron tubes to the solution of newproblems. The author has not attempted to discuss allapplications of tubes to special problems but rather to coverbasic principles and typical applications. At the same time,the book is exceptionally complete, including a wealth ofmaterial assembled and co-ordinated in a single volume.

Principles ofELECTRICITY

and

ELECTROMAGNETISMBy GAYLORD P. HARNWELL

619 pages, 9 x 6 illustrated. 30. net

EMPHASISING the experimental and scientific ratherthan the mathematical or engineering aspects of the

subject, this important new book is intended for advancedundergraduate or graduate courses in electricity andmagnetism. In addition to the fundamental classical pheno-mena, elementary discussions of electronics and gas dischargeshave been included. It is assumed that the student isfamiliar with the elements of the subject of electricity andwith the fundamental mechanical concepts of force andenergy. A knowledge of the differential and integral calculustechniques is also pre -supposed.

McGRAW-H I LLAldwych House, London, W.C.2

HuR RIn addition to our range of new Communication Receivers we have a very fine selection ofshop-soiled and second-hand receivers and transmitters. We fully guarantee every item andwe make a point of checking carefully the alignment, sensitivity and controls of every piece ofapparatus before sale. We list below a small selection of receivers and transmitters, but suggestthat you send for our free catalogue giving technical data on the entire range.

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Telephone:HOLBORN 9894.5

WHERE THE HECK9DO THEY ALL GO

NOW READ THISThis advertisementappeared in the JULY1938 issue of this

journal. The positionis the same to -day.

The majority of Radio and Television Amateurs wouldbe surprised to know the number of Transformers,Chokes, etc., that we produce during the year. If youmade umpteen guesses it would be very difficult, even ifyou did arrive at the approximate number, to find thereason for such a large quantity and the ultimate destina-tion of all these products.

Firstly, it would take pages and pages of " Televisionand Short -Wave World " to fully describe all thedifferent types, but it is not so difficult to accountfor the quantity when you realise that we have a specialsection devoted to the design and production of Trans-formers, Chokes, etc., of all types which are suppliedto Government Departments, Laboratories, Institutions,and a very large number of Amateurs and Radioenthusiasts throughout this country and abroad.

In view of the number of similar products it mayseem to you a miracle that our sales are so high andthat we keep it up all the year round-the answer-" ASK ANY OWNER OF A SOUND SALESPRODUCT."

In any case, why not let us send YOU our latestcatalogue and Technical manual. PRICE 6d.

Specified by

SOUND!MARLBOROUGH RD., -.sifting (Contractors to theUPPER HOLLOWAY, G.P.O., etc.)

LONDON, N.19. LIMITED Tel.: Archway 1661/2/3

443

TELEYS1011AND


New Tx Condensersdial, a built-in noise limitor and is areceiver built entirely for A.C. mains.The price is only £21, so bringing itdown to the low -price range. A fullspecification can be found on the backpage of the cover.

G8DR and G5UM himself at the NFD stationG5UMP.

Another item of news regardingHallicrafters is a frequency meter thatcan be used to calibrate incoming oroutgoing signals and crystals. It is ex-tremely accurate, completely self-con-tained and is A.C. operated. The price,complete, Z9.

Many amateurs have used the popu-lar G.E.C. Home Broadcaster micro-phone, in fact on 4o metres every otherstation at some time or other seems tohave invested in one of these littlemicrophones. In view of its remarkable

success a new model has been producedproviding an even better performancewith low noise and is mounted in abakelite case. It is provided with abase containing the battery and volumecontrol and is supplied complete with25 ft. of screened cable. The price re-mains unchanged at r gn.G2JH

I listened to an interesting QSO on40 metres between two stations, one ofwhich is using the call sign G5ZJ, myown. This QSO went on for quite along time and after it had completed,I called the pirate G5ZJ, but unfortu-nately there was no reply. There seemsto be quite a lot of this pirating about,for J. K. Hankinson, G2JH, who onlyworks on the ultra -high frequencies, isreceiving a lot of cards regarding hissupposed transmissions on 3.5 Mc. Anyamateur who can supply information re-garding the pirating of G2JH shouldsend it to the real holder of this callsign at the address in the call book.

W2JKQ, W. P. Schweitzer, who is sowell known to British amateurs via his20 -metre telephony, sailed on June 29in the President Wilson with theU.S.A. Rifle Team which will be tak-ing part in contests at Petersham thisyear. He is staying in London andhopes to contact some of the Britishamateurs he has worked over the air.

A very strong signal is being receivedin this country from VU2FA operatedby Major Atkinson from Kasauli. Thesignal is actually R9 on the meter witha frequency of 14,092 Kc. and the QRAwhich is not in the call book is TheMilitary Food Laboratories, Kasauli,Punjab, India. A new batch of crystalshave just been sent out to VU2Fa, soin addition to 54092 he will be using14016, 14024, 54044, 14060 and 54092with a rhombic antenna.

A most consistent station fromGeorgetown, British Guiana wasVP3LF, ex VP3AA. He is now off theair until next September, but who willbe operating from various VP6 stations,as he is on holiday in Barbados.

ZD2B whom many amateurs think isa pirate station is actually fullylicensed and can be heard on telephonyat the L.F. end of the zo metre band. Heis using an electron -coupled oscillatorand the station is actually operated bysome engineers of the Royal Corps ofSignals at Gibraltar. ZD2B will prob-ably be a new country for Britishamateurs.

One of the new Raymart wide -gap condenserswhich are mentioned in the text.

I have just been trying some ofRaymarts new transmitting condensers.They are certainly very robust andeasy to mount. They are available infixed Stator er single types in all theusual capacities from 5o mmfd. eachstation to zoo mmfd. each section andcosting 17s. 6d. or 22s. 6d. They areof the 3,500 peak voltage type and aminimum spacing of .087 in. The singletype of too, zoo or 300 mmfd. are pricedat 16s. 6d., 22S. 6d. and 27s. 6d.respectively, being of the ro,000 peakvoltage type and with a plate spacing of.590 in.

liorbewi e"AND HERE'S TO THE HOUSEWIFE THAT'S THRIFTY

HANDY, BRIGHT andSAVES YOU MONEY !

100 PAGES, 33 ARTICLES

AND FEATURES

6D MONTHLY

Housewife is the first pocket-size magazine dedicated exclusively to the woman of the home. It caters for every aspect

of the housewife's interest-her house, her children, her kitchen, her hobbies, her appearance, her social activities. No

other monthly magazine of feminine appeal includes such a variety of subject matter treated from an essentially practical

point of view and presented in such a highly condensed, yet readable form.

JULY ISSUE NOW ON SALE AT ALL NEWSAGENTSPUBLISHED BY THE PROPRIETORS OF "TELEVISION & SHORT-WAVE WORLD"

444

JULY, 1939

VAN HOLDERS

The CLIX valveholder rangecovers patterns to accept allthe recognised English and Ameri-can valves including the Midgetand Acorn types.As an alternative to the usualPaxolin Models there is a serieswith Frequentite CERAMIC platesspecially suited for Television,Short-wave and other high -efficiency work." CLIX " specified by the designerof the KT8 TRANSMITTER described

in this issue.

I Ceramic octal type X248 1/3

2 Ceramic 5 -pin type X147Ild. ea.

I Lam -plastic base, 4 -pin typeXI I I 5d.

All contact -tubes are of the CLIXRESILIENT type, machined fromthe solid (not stampings) and,by a process involving helicalslotting, are given a stout re-silience which guarantees perfectcontact irrespective of the valve -pin construction.

CLIX Radio and ElectricalCatalogue Free.

CONNECT WITH CLIX

British Mechanical Productions, Co., Ltd.,

79a, Rochester Row, London, S.W. I .

Hoddesdon and District RadioSociety

During the last i6o-metre Field Dayorganised by this Society stations workedincluded G8TM, G8TL, G8SK, GzWT,G61.3 T, and many others. The trans-mitter consisted of a crystal -oscillatorand a power amplifier using a P.M.22Abattery -operated valve on 1,940 Kc.

G5H0 'and 2SUU have been experi-menting with kite aerials while on holi-day in Ventnor. No London stationswere heard on 16o m. in I.O.W., but aWeymouth station, G2XQ, was well re-ceived. Full information on thissociety can be obtained from the hon.secretary at Caxton House, High Street,Hoddesdon, Herts.

The Bromley and DistrictShort-wave Society

The Bromley and District short-wavesociety is now well on its feet under thepresidency of Mr. Miles, G2NK, so wellknown to the amateur radio fraternity.At the moment some 25 members havejoined the society, giving a nucleus onwhich to build a more ambitious scale.The great demand for morse classes hasbeen met by instruction under G8KV,and it is anticipated thus to help theAA members to a speedy full licence.At a recent meeting an interesting des-cription of his special TRF receiverwas given by 2FWV, followed by apractical demonstration of its capabili-ties on the amateur bands.

Weekly discussionary meetings areheld at the clubrooms at 191 HighStreet, Bromley. All interested inshort wvae radio in the district are in-vited to attend. Particulars of member-ship can be obtained on application tothe Secretary, Mr. H. N. Holbrook, 191High Street, Bromley, Kent.

CANDLER

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All desiring to become proficientin Code work should fill in theCoupon below.

Candler Code Courseshave helped thousands to passtheir full tests for securinglicences, and have also helpednumerous operators to greatlyincrease the w.p.m. speeds.

1 hree Famous CoursesJunior Scientific Code Course for beginners.Teacher all the necessary code fundamentals scientifi-callyAdvance High Speed Telegraphing for operatorswho want to increase their w.p.m. speed and improvetheir technique.Telegraph Touch-type Writing for those who wantto become expert in the use of the typewriter.

Terms : Cash or monthly paymentsFill in the coupon for FREE copy of the " BOOK OFFACTS "ii. men um IC43tipcbN

NAME

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Post coupon in fd. unsealed envelope to LondonManager. (Room 55B),

121, KINGSWAY, LONDON, W.C.ICANDLER SYSTEM CO.Candler System Co., Ashville, North Carolina, U.S.A.

ANDSHORT-WAVE WORLD

TROPHY Short WaveCOMMUNICATION

Type Receivers

All -British TROPHY Receivers satisfy a long -feltwant. We believe (and the large number of TROPHYsnow in regular use proves) that TROPHY Performanceand Value feature combination, is definitely unbeatable.The scientific interest, listening thrills and entertainmentprovided by the short -waves make a reasonable demand-the use of a specially designed TROPHY. The8 -valve TROPHY A.C. Communication model (illus-trated) has a continuous wave -range of 7 to 550 metreswith R.F. on all 5 bands. Bandspreading is continuousand refinements include AVC and BFO switches separateOscillator, Pitch control, Stand-by switch (for trans-mitters) and headphone jack. The TROPHY 8 is

designed for use with a separate P.M. speaker. Cashprice 12 gns. Terms : 15/6 deposit and 18 monthlypayments of 1516. Guaranteed, 12 months includingvalves. Matched Cabinet Speaker 2 Gns. extra.

TROPHY models from £5 15s.See page 417 for special review on TROPHY 6 by

Mr. Kenneth Jowers, SI W Editor. Demonstrationsarranged at both branches below. Complete lists avail-able post free.

PETO SCOTT CO. LTD.,77 (T15) City Road, London, E.C.1. Tel. Clissold 987541 (T15) High Holborn, London, W.C.1.

Tel. Holborn 3248

Universal Electrical Co.221, CITY ROAD,

LONDON, E.C.I.Telephone : CLERK 7030

Photo Electric Cells, 15/. each.Mercury Relay Valves (American) for use with above valves if

necessary, 10/- each.

Champion Valves most types, 2/6 each.

Transformers 110 to 230 volts, 12 volts input, 15/- each 240volts input, 6 volts output, 6/- each, suitable for trains andmodels.

Claude -General Neon Transformers input 200/240, output3,000 volts, .1 K.V.A., 10/. each.

D.C. Electric Drills, 230 volts, 30/- each.Sliding resistances, 400 and 800 ohms, 7/6 each.

Sets of " G.E.C." Filters, 5/- each.Anti -Interference Units, pair of H.F. Chokes and pair of

.1 T.M.C. Condensers, 2/6 the set.

New 30th H.P. Universal Motor, 200/250 volts, 27/6 each.American " Weston " Set Analyser, A.C./D.C., 1,000 ohms

Per volt, 2 Meters, 14/10/..

" Ferranti " Line Transformers, new, 6/- each.

" Foster " Double Wound Transformers :110 to 230 volts 500 watts, 50/-.110 to 230 volts 1,000 watts, 80/-.110 to 230 volts 2,000 watts, 100/-.110 to 230 volts 3,000 watts, 130/-.110 to 230 volts 5,000 watts, 190/,

Weston Milliamp Meters, 0-200, 15/. each.0-250 15/.

Ammeters 0-30 15/.D.C. Meters 0-2,50015/

I

445

lagY1S1011AND


Building

TeleRec

A Simple &

PracticalHandbook

APRACTICAL

HOME - CONSTRUCTORHANDBOOK

FOR EVERYBODY

For the

AmateurHome

Constructor

Building Television Receivers at Home',Is a practical handbook giving precise instructions that will enable any amateur to build a Television Receiverguaranteed to produce pictures of present-day standards both as regards definition and brightness. Three

designs are provided with a wide range of picture size and the constructional information and illustrationsare in such simple detail that they can be understood and carried out quite easily by the average wirelessamateur. Results are assured.

CONTENTS INCLUDE :How a Television Receiver worksReceiver giving pictures up to 12 inchesThe Time Base, Cathode -Ray Tube network and

Receiver Power UnitAdjusting the Vision Receiver, the Tube and Time

Base Power UnitAdjusting the Time BaseAdding refinements

100 ILLUSTRATIONS

2/6 netFROM ALL BOOKSELLERS

OR

Small -picture ReceiversReceiver giving a 4 -inch picture. The simplest

Home -Built TelevisorTime Base for 4 -inch Tube ReceiverThe Power Units of the 4-inch,Tube ReceiverLong Distance ReceptionSimplified Receiver using a 1 -inch Cathode -Ray

Tube

112 PAGES

2/9 post paidFROM THE PUBLISHERS

BERNARD JONES PUBLICATIONS LIMITED,CHANSITOR HOUSE, CHANCERY LANE, LONDON, W.C.2

(Proprietors of " TELEVISION AND SHORT-WAVE WORLD ")

446

IREYSJOt1JULY, 1939

" Beam Aerials and S.W.Programmes."

(Continued from page 420)

imposed on the carrier frequency tendsto widen out the carrier by an amountplus and minus the modulating fre-quency. Technically, a modulated car-rier wave can be resolved into threecomponent frequencies -one the funda-mental carrier frequency, one the funda-mental minus the modulating fre-quency, and the third the fundamentalplus the modulating frequency.

It can be seen readily that whenmodulating frequencies go above 5,000cycles (5 kc.), carriers separated byonly to kc. will cross up. Modernhigh-fidelity modulation involves fre-quencies at least as high as 8 or 9 kc.

Because of the difference in direction,DJN could cover South America effec-tively by using a narrow beam -only15 degrees wide. Right away, the DJNsignal was powerful because most of itsenergy appeared to be crowded into thisnarrow beam.

As for the broadcasts from Schenec-tady, a much wider beam had to be usedto properly spread out and cover theSouth American continent -with, corre-sponding loss in signal strength eventhough higher power might be used inthe antenna.

After a careful study of the situationand of the frequencies still available,

General Electric applied to the F.C.C.for certain new authorisations.

One of these was a power increase totoo kilowatts for both fW2XAF andW2XAD. Another was for the use byW2XAD of two additional frequencies,9,55o kc. and 21,5oo kc. Still a thirdwas for permission to build an inter-national broadcast station, TreasureIsland at the Golden Gate Expositionin San Francisco, California, using callletters W6XBE.

W6XBE is completed, while the newtoo -kilowatt amplifier at Schenectadywill be ready in a short time. Thisamplifier, available to either W2XAFor W2XAD, utilises a newly developedtube particularly suited to high powerat high frequencies.

While directive antennas, of theAlexanderson panel type, have beenused for many years by W2XAF andW2XAD-particularly by the latter -the new plan contemplates the hegularuse of such antennas for all transmis-sions to particular countries or areas.

For instance, on the evening scheduleto South America, a 3o -degree beamfrom W2XAD on 9,55o kc. is centred onRio de Janeiro, while W2XAF sendsout a second such beam, on 9,53o kc.,and adjacent to the 9,55o beam on thewest. W2XAD thus specialises to thepredominantly Portuguese half ofSouth America.

A directive antenna at W6XBE en

ANDSHORT-WAVE WORLD

ables the new California station to servethe Orient effectively. Such transmis-sion from this station encounteres a far'more favourable daylight -darknesssituation on the Far Eastern circuitthan could be possible from Schenec-tady.

)FREQUENCYCONTROL UNITS

Ground to within 5 kc. of yourspecified frequency In the7 mc. amateur band, andsupplied complete with officialcalibration certificate to anaccuracy of 0.025%.

Specified for the10-811

TRANSMITTER

described in this issue.

Q.C.C. Type 55.The Standard X CutCrystal. Temp. Co-efficient 23 cycles perMc. Max. R.F. crystalcurrent 100 m/A.

PRICES :

Type S5 unit ... 20/ -Type S5 Crystal,

unmounted 15/ -

Send 14d. stamp forour full price list ofall types of quartzcrystals and radiotransmission com-

ponents.

Type U Mount. A plug-in Mount (f In. centres).Fitted with stainless steel electrodes and a smart nickeland black enamel cover plate 6/.THE QUARTZ CRYSTAL CO., LTD.

Kingston Road, NEW MALDEN, Surrey.Telephone : MALDEN 0334

GALPINS ELECTRICAL STORES75, LEE HIGH ROAD, LEWISHAM, LONDON S.E.I3 Telephone:I LEE GREEN 5240TERMS Cash with Order I

or C.O.D. Charges extra

ERNEST TURNER & WESTON 2 -in. dial moving coil milliampmeters, B.S. 1stgrade 0 to 5 and 0 to 50,10/6 each.TELEGRAPH. Morse inker complete with tapping key and sounder, fitted platinumcontacts in first-class condition, £3 10s. Ditto, less tapping key, 50/-. C/F. (Theformer is of later pattern.)WESTINGHOUSE RECTIFIERS. L.T. 6 volt 2 amps. D.C. output, input 11 volts,in new condition, 10/. each." NEWTON " MOTOR GENERATORS, input 220 or 100 volt D.C. output. 500/750volts 200 m/A. D.C. output, 30/.. C/F. Ditto, input 16 volts, 8 amps, output 35/- each.C/F.D.C. MOTORS approx. , h.p., 50 volts shunt wound, 7/6, post 1/-.DYNAMOS, all shunt wound and fully guaranteed, 220 volts 15 amps., £610s. ; 220volt, 10 amps., 13 ; 100 volt, 20 amps., £6 10s. ; 80/90 volt 10 amps., £2155. ; 25 volt.8 amps., 32/6.SWITCHBOARD VOLTMETERS, Everett Edgcumbe, etc., 6 -in. dial, moving coil,0 to 300 volts, 15/. : 0 to 500 volts, 17/6 ; A.C. 0 to 250 volts, 15/-.EX.R.A.F DOUBLE WOUND GENERATORS, giving two outputs, 1,200 volts100 m/A., and 10 volts 4 amps., 15/- each, post 1/6." EPOCH " SUPER CINEMA MOVING COIL SPEAKERS, 6 -volt field (lesscone), 15/, C/F." STANDARD " TELEPHONE COPPER SCREENED 23 S.W.G. TELEPHONEWIRE, 100 yd. coils, 4/.. All new.ZENITH WIRE WOUND RESISTANCES (Vitreous) 5,000 ohm carry 170 m/A.,10,000 ohm 50 m/A., 2,500 ohm 170 m/A., 750 ohm 300 m/A., 255 ohm 500 m/A., 1/. eachPost 4d.SILVERTOWN GALVANOMETERS, jewelled movement, very sensitive. 5/. each."SULLIVAN" TRANSMITTING CONDENSERS, variable, in glass tank,.0005 mf., and 001 mf., 7/6 each, post 1/-.INSTRUMENT WIRE, 4 lb. reels of 20 G enamel, 6/-, P/F. ; 15 lb. of 16 gauge enamel.15/-, post V- ; 7 lb. of 18 gauge D.C.C., 8/8, post 6d. ; 7 lb. of 10 gauge D.C.C.,P/F. All new wire.A.C. INDUCTION MOTORS,allfully guaranteed,/ h.p. 2,800 r.p.m. with starter, 80/.1 h.p. Double Spindle 1,450 without starter, 50/. ; 2 h.p. Double Spindle 1,450 r.p.m.,complete with starter, O. All for 200/250 volts 50 cy. 1 phase." MACKIE " ROTARY CONVERTORS, 80/120 volts D.C. input at 11 amps. Output80/120 volts 64 amps. 1,000 cycles, £4 10s. each. C/Forward.LARGE SCALE MOVING COIL MRLIAMP METERS, 0 to 10 and 100 m/A..7 in. dial, 25/. ; 0 to 12 m/A., 10 in. dial, 25/- ; 0 to 15 m/A., 4 in. dial 15/. ; 0 to 10m/A., 6 in. dial, 17/6 ; 0 to 18 m/A., 5 in. 15/. ; 0 to 3,000 m/A., hot wire in. dial, 22/6 ;a Marconi Moving Coil, 250 to 1,500 voltmeter, 7 in. dial, 25/.. All first grade meters," PHILIPS " MAINS TRANSFORMERS, 200/240 volts input, 2,000/0/2,000 volt200 m/A. output, with two L.T.'s, 22/6 each. C/Forward.SMALL SPOT WELDING TRANSFORMERS, 200/230 volts input, 3-41 and 71volts at 150/300 amps. output, 17/6. C/Forward.NEON TRANSFORMERS, input 200/250 volts 50 cycles 1 -phase output, 10,000 volts10 m/A., 12/6 each. post 1/.. Ditto, 7,000 volts 8 m/A., 101-, post If-. Ditto. 5,000 volts5 m/A., 7/6, post 1/-. :All brand new.)THE " RACON " MOVING COIL HORN SPEAKER UNITS. 15 -ohm SpeechCoil 6 volt, fitted handle, 15 watts, 15'. each, post 1/6.

3,000 -WATT AUTO TRANSFORMERS, 0 to 220 volts in steps of 10 volts. Usefulas small arc welders. Fully guaranteed, 65/- each. C/F.PHILIPS 10 -WATT PRE -STAGE AMPLIFIERS, less valves (in good condition),10/6 each. Post 1/6.EX -NAVAL 1.VALVE BUZZER WAVEMETERS, 200/24,000 metres. Completein solid teak case. Size : 15 x 10 X 8 (less valve). Turner unit enclosed in coppertank (Sullivan high note buzzer). Price, 7/6 each. C/F. Not sent C.O.D.EVERSHED EX.R.A.F. HAND DRIVEN GENERATORS, with 2 outputs 800 volts30 m/A. and 6 volts 2 amps., 25/-, post 1/6.VOLTAGE CHANGER AUTO TRANSFORMERS, 100/120 volts to 200/240 voltsor vice versa, 250 watts, 17/6 ; 500 watts, 25/- ; 1,000 watts, 37/6 ; 1,500 watts, 42/6 eachC.F. All fully guaranteed.MOVING COIL METER MOVEMENTS for recalibrating into muhirange meters.Low m/A. deflection. 21 -in. dial, 5/. each ; 4 -in. and 6 -in. dial, 6/. each. Post II-.(Note : All these meters are by good makers -Elliott, E. Edgcumbe, etc.)ELECTRIC LIGHT CHECK METERS, 200/250 volts. 50 cy., I phase, 5 and 10 amps.,6/- each. P.F.X.RAY TRANSFORMERS, by well-known makers, all fully guaranteed. 50 cyclemains, 40,000 volts, 10 m/A., £5. 68,000 volts, 20 m/A., £710s. 100,000 volts, 30 m/A.,£10 10s. All carriage forward.A.C. MAINS RELAYS, 230 volts, trip at 1 amp. A few also at 400 volts, 7/8 each.Post 9d.EX.R.A.F. ROTARY CONVERTORS. D.C. to D.C. 12 volts input, 500 volts75/100 m/A. output, brand new, 25/-, post 1/- ; S.H. condition, 20/-, post II-. Also afew with damaged brush, gear windings O.K., 10/. each, post 11-.SPOT WELDING TRANSFORMERS, 220/240 volts, 50 cy. 1 phase inputf to 5 voltsat If kilowatts. Makers, Foster. 45/-. C/F.EX.G.P.O. CI ASS TOP RELAYS, Typ B. Useful as Keying Relays, 5/. each, post6d. Also a few only that need points, which are easily fitted. 2/6 each. P/F.MAINS SMOOTHING CONDENSERS. Philips I mf., 3,000 volt working, 5/- each,post free. Siemens, 4 mf., 1,500 v. test, 2/6 each. T.C.C. 4 mf. 300 v. A.C. wkg., 2/.each. Standard Telephone I mf., 400 v. wkg., 3 for 1/-, post 4d., or in lots of 100.12/6, post 1/6. T.C.C. 2,000 mf., 12 v. wkg., 3/. each.ROTARY CONVERTOR, 220 D.C. to 150 volt A.C. 50 cy. 1 ph. 600 watts, with starterand step-up transformer to 200/240 volt , £4 10s. C/F. Another 100 volt D.C. input70 volts A.C. 50 cy. I ph. output at 250 watts, 40/0. C/F.FERRANTI SPEAKER OUTPUT TRANSFORMERS, Type " A," ratio 74 to I .

pri. D.C. resist. 900 ohms, impd. 12,500 to 30,000. Type " B," ratio 24.9 to 1,pri. D.C.resist. 14,000 to 20,000 ohm., impd., over 111,000. Sec. D.C. resist., 13 ohms on bothtypes. In new condition, 4/. each, post free.P1 STANDARD TELEPHONE push -back connecting wire (new), 220 -yard coils,12/6. post 1/-." SAVAGE " MAINS TRANSFORMERS, 200/250 volts input 50 volt 8 amp. output,12/6 each.STANDARD TELEPHONE MAINS TRANSFORMERS, input 200/250 volts,output 250/0/250 volts 200 m/A., 3 x 4 volt windings and a 50 -volt winding, 12/6 each.EVERETT.EDGCUMI3E Thermo Coupled R.F. Meters, 21 -in. dial, 0 to 250 m/A.,25/-. 0 to 3 amp., 20/. each.A few only Everett-Edgcumbe Thermo Meters with Thermo burnt out, but movingcoil reads approx. I m/A. A first -grade movement, 10/- each.

447

Tidl:UYISeigt1SHORT-WAVE WORLD

Two New Cossor ReceiversTwo very interesting receivers have

just been released by A. C. Cossor, Ltd.,of Highbury Grove, N.5, and are nowavailable through all their usualchannels.

'The first is a battery -operated super -het, including an ingenious system ofpress button tuning. Any one of 6medium or long -wave stations can in-stantly be selected by pressing theappropriate button, while the pointer onthe dial rotates to the correct wave-length. Buttons can be adjusted tocover any required station from thefront of the receiver, so should at anytime there be a change in station wave-lengths the user of the receiver can re-adjust his own press buttons.

Four valves are included, a triode-heptode frequency -changer, designed togive high gain on short waves, a vari-able Mu pentode I.F. amplifier, double -diode -triode detector, audio amplifierand A.V.C. valve, and finally, a high -output economy pentode. The tuningrange is 16.4 to so metres; 190 to 55ometres, and 82o to 2,200 metres. Someof the features include permeability ironcored I.F. transformer; iron cored pre -selector coils on medium and longwavelengths; automatic volume con-trol ; high " Q " coils ; automatic gridbias and full vision dial calibrated with

over 4o station names. The price is 9guineas, or .4t0 4s. 3d. complete withbattery and accumulator. Hire pur-chase terms are available for this modelnumber 33 receiver.

A larger receiver is the model 62, afive valve all -waver in console cabinetfor A.C. mains. Vale sequence issimilar to the previously mentionedbattery set, except that the first valveis a triode-hexode frequency changerand the output valve is a triode de-signed to give extremely high quality.There is also, of course, the usual indir-ectly heated rectifying valve.

The console cabinet in walnut is 33iin. high by 181 in. wide and II in. deep.It has been acoustically designed inconjunction with an 8 in. high fidelitymoving coil loudspeaker.

A switch plug for an extension loud-speaker and sockets for a gramophonepick-up are also included. There arethree wavebands with this receiver tocover 16 to 2,150 metres, so that the receiver will tune in most of the impor

Ensure obtaining " Television and

Short-wave World " regularly by placing

an order with your newsagent,

JULY, 1939

tant short-wave channels as well as allmedium and long -wave broadcaststations.

Selectivity is extremely high, a com-mendable feature in view of the con-gestion in medium waves at the presenttime. This selectivity is obtained par-tially to permeability tuned I.F. trans-formers, plus a large number of tunedcircuits. Readers interested in a reallygood short-wave reception will bepleased with the performance of this re-ceiver for it has extremely low noiselevel and is provided with a good slow-motion dial free from back -lash.

The receiver complete and ready foroperation is priced at i i guineas, or onhire-purchase terms.

The Sky -Pilot AerialReaders who are not able to erect a

conventional horizontal aerial or whoare troubled with interference shouldwrite to Messrs. Pilot Radio, of 31-33Park Royal Road, London, N.W.io, forinformation on their new Sky -Pilot, anaerial of the vertical type which can befitted to a pole or window frame. It isapproximately x x ft. long and is madeup of four sections. The total weight isonly ti lb. despite the fact that theaerial is made of tapering steel tubingcadmium plated. These aerials arevery effective, and at the price asked,2IS., good. value for money.

A FreeQSL SERVICE

AMONG the many privileges offered to members of theRadio Society of Great[Britain, none is more appreciatedthan the free QSL Service instituted by the Society some

15 years ago.Non -transmitting members are granted a B.R.S. (British Re-ceiving Station) number on election which enables them to sendand receive cards through the Bureau without giving directreference to their names and addresses.Full details of this exclusive R.S.G.B. Service will be forwarded onrequest.

The T & R BULLETINSINCE 1925 this Journalghas brought to members of the

R.S.G.B. the latest news of short wave interest. With theappearance of the July number, members will receive details

of the Society's 14th Annual Convention to be held in Londonin September. In addition they will read many full length tech-nical articles contributed by prominent members, whilst theDX Fraternity will find a new feature introduced under thetitle " Up and Down the Ham Bands."

A copy of this issue, together with details of member-ship, will be sent to any interested reader sendingP.O. for 1,- to,-

The Secretary -Editor,

R.S.G.B.,73, Victoria Street, London, S .W.I

TELEVISIONDEVELOPMENTSAre you keeping abreast of modern televisiondevelopments ? Whether amateur or professionalyou must be in touch with the latest trend ofresearch.The Television Society enables you to meetfellow workers in the field of television, both inthis country and abroad.Founded some io years ago The TelevisionSociety provides a scientific and non-partisanplatform for discussion on all aspects of the subject.Meetings are held monthly during the session(October -June) and are reported in full in theSociety's Journal which is sent free to all members.The Society's activities are shortly being enlargedto meet the growing interest in the subject andmembers will have a unique opportunity of further-ing their knowledge by contact with well-knowntelevision engineers.

Full particulars of membership qualifications may be had from the Hon.General Secretary :-J. J. Denton, 17, Anerley Station Road, London,

S.E.20.

THE TELEVISION SOCIETY(Founded 1927)

President : Sir AMBROSE FLEMING, M.A., D.Sc., F.R.S.

448

JULY. 1939

1 YISIDt1AND

SHORT-WAVE WORLD

BUSINESS EQUIPMENTThe charge for miscellaneous advertisements on this page is 12 words or less 2/-, and 2d. for every additional word. Single -column inch rate

displayed, 12/6. All advertisements must be accompanied by remittance. Cheques and Postal Orders should be made payable to Bernard JonesPublications Ltd., and crossed, and should reach,this office not later than the 15th of the month previous to date of issue.

OPPORTUNITIES SECTIONMISCELLANEOUS

WIRELESS LICENCES

According to preliminary figuresissued by the Post Office there was anincrease of paid licences during Mayof 2 I , 143. A total of 450,830licences were issued while 459,687 ex-pired. Free licences to the Blindtotalled 4,344, while 3,933 expired. Itwould be interesting to know whythere was a drop in licence figuresduring April, but in any case it issatisfactory that this drop in licenceshas been arrested and the figures nowshow a slight increase.

The total number of licences inforce at the present time is nearly 9million, the official figure being8,984,250.

NEW TELEVISION ANNOUNCER

Miss Olga Edwardes has been re-engaged by the B.B.C. as a tem-porary announcer from the periodJuly 31 to September 2 to take theplace of Miss Jasmine Bligh who willbe on holiday during that time.

Eastbourne and District RadioSociety.-Full information on the acti-vities of this society can be obtainedfrom the Hon. Sec., T. G. R. Dowsett,48 Grove Road, Eastbourne, Sussex.The annual subscription is only 55. anda wide selection of subjects are being

k dealt with by lectures in the- comingseason. We advise readers in that areato gat in touch with the secretary

EMPLOYMENT

MECHANICAL - OPTICAL - TELEVISIONTHE "JEFFREE " HIGH SPEED MOTOR

Valve Driven, Synchronised by Vision Signal,Speeds at 22,500 Revs. Per/min.

DETAILS AND PRICES AVAILABLEOscillators for Motor or Light Modulation

Cells can be Supplied to Order.Send Your Requirements to

H. E. SANDERS & CO. Tele.4 Grays Inn Rd., London, W.C.1 Chancery 8778

INDEX TO ADVERTISERSPAGE

A.C.S., Ltd. .. 443Automatic Coil Winder &

Equipment Co., Ltd. ..Belling & Lee, Ltd. ..British Institute of Eng. TechnologyBritish Mechanical Productions, Ltd.Candler System Co...Clix .

Electrical.. 385.. Cover il

Coveriii445445445

Edison Swan Electric Co., Ltd. 386Fluxite, Ltd. Cover ifFoyles, Ltd. . CoveriiiGalpins . 447General Electric Co., Ltd. 435G5KA CoveriiiHintrad Wholesale, Ltd. 441McGraw-Hill Publishing Co. . 443Marconi's Wireless Telegraph Co., Ltd. Cover liPeto-Scott Co., Ltd. 445Premier Supply Stores 439Quartz Crystal Co., Ltd. 447Radiomart . .. 448Radio Society of Great Britain CoveriiiSanders, H. E., & Co. CoveriiiSound Sales, Ltd. .. 443Stratton & Co., Ltd. 385Television Society, The 448Universal Electrical co. .. 445Webb's Radio .. . Coveriv

FOYLES FOR RADIO BOOKSSpecial Radio Deportment. New and secondhand bookson radio and every other subject. Stock of nearly3 000,000 volumes. Send for free catalogues.

* FOYLES *113.125, CHARING CROSS RD., LONDON, W.C.2

Telephone: G d5660 (16 lines)

A HANDY REFERENCE LIBRARYof books pertaining to his hobby is necessary to every " ham."Those listed bel...w will start you with your library :-RADIO AMATEUR'S HANDBOOK 1939 edition contains 560pages and 189 illustrations. Will solve all your transmittingand receiving problems. Price 5/6d. post free." RADIO " HANDBOOK 1939 edition, 600 pages, 7/- post free.RADIO ANTENNA HANDBOOK 3/6d. post free.RADIO TELEPHONY HANDBOOK 3/6d. post free.HINTS AND KINKS 2/6d. post free." RADIO " ZONE MAPS I/2d. post free.RADIO PHYSICS COURSE 17/6d. post free.CALLBOOKS. June issue. now on sale. Price 6/- post free.

G5KA, 41 Kinfauns Road, Goodmayes, Ilford, Esse3eDept. T7

MISCELLANEOUS

ALL TYPES of Rotary Converters, electric motors,battery chargers, petrol electric generator seta, etc.,in stock, new and second -band.

A.C.-D.C. Conversion Units for Operating D.C.Receivers from A C. Mains, too watts output, fa. to;150 watts output, f3. 10.

WARD, 46, Farringdon St., Londcn, E.C.4. Tel.Holborn 9703.

LOUDSPEAKER repairs, British, American, anymake, 24 -hour service; moderate prices.-SinclairSpeakers, Alma Grove, Copenhagen Street, Ka.

WANTED - Baird Neon, 20" Disc, Kerr Cell,Drum, Etc. Box 26.

BOOKS

ALL WIRELESS and radio engineering booksavailable on new terms as low as 25. 6d. monthly.Write a card for details from, Phoenix, Chandos PlaceW.C.2.

ELECTRICAL SERVICE

CONVERTERS wanted and for sale, E.D.C.C,approximately 200 watts. Easco, 18, Brixton Road,S.W.9.

LOUDSPEAKERS

3,000 SPEAKERS P.M. and energised 4' to 147including several Epoch Sinclair Speakers, AlmaGrove, Copenhagen Street, N.:

PATENT AND TRADEMARK AGENTS

GEE & CO., patents and trade marks throughout theworld (H. T. P. Gee, Mem.R.S.G.B., A.M.I.R.E.,etc.), Estab. 1905. 51-62, Chancery Lane. London,W.C.2 (2 doors from Government Patent Office).'Phone: Holborn 4547 and 4548. Handbook free.

KINGS PATENT AGENCY LTD. (B. T. King,A.I.Mech.E. (2 BKT) Patent Agent) 146a, QueenVictoria Street, London, E.C.4. ADVICE, Handbookand Consultations tree. 'Phone City 616r.

TELEVISION.A NEW COURSE OF INSTRUCTION.

We have pleasure In announcing that our new " Television " Coursehas met with remarkable success. The enormous demand for theCourse has shown, beyond anyshadow of doubt, that It fills that long -felt need which we anticipateJ when we went to such trouble andexpense in Its preparation.We shall be happy to send full details of this special " Television "Course on request. Particulars are also available of other CoursesIn all branches of Wireless, Television, Talking Picture Engineering,etc., and of the easiest way In which to prepare for the A.M.I.E.E.,A.M.I.W.T., etc., Examinations.

We teach by correspondence, and guarantee " NOPASS-NO FEE." Our Technical Consultant is

Professor A. M. Low.end for full particulars to -day. Free and without obligation.

THE BRITISH INSTITUTE OF ENGINEERING TECHNOLOGY337, SHAKESPEARE HOUSE, 17119, STRATFORD PLACE

LONDON W.I.

III

TELEYSIONAND

HORT-WAVE WORLD JULY, 1939

THE NEW HALLICRAFTERSKYRIDER DEFIANT

MODEL SX24

NINE VALVES

COMPLETE INSTRUMENT

£21 : 0 : 0HIRE PURCHASE FACILITIES

AVAILABLE

It is not too difficult for an able radio engineer to create a receiver with outstanding performance-but tobuild this receiver and sell it at the low price of the Skyrider DEFIANT, that requires the kind of genius thatseems to be found only in the Hallicrafters Laboratories.The Skyrider DEFIANT offers performance that can be favourably compared to any receiver regardless ofprice. It has new features, like Built-in Frequency Meter Tuning, that are absolutely new. And in additionit has all the desirable features and qualities that are needed for outstanding amateur reception.

FREQUENCY METRE TUNING. The Band Spread Dial is accuratelycalibrated throughout the amateur bands, and, when once set, main-tains a high degree of accuracy throughout the band, bringing insignals on their frequencies as indicated on the dial.

BUILT-IN NOISE LIMITER. The noise -limiting circuit is of recentdevelopment, highly efficient in reducing noise level on the ultrahigh frequencies. All leads are short and close to the noise -limitertube for greater efficiency.

VARIABLE SELECTIVITY. A six position Variable Selectivity Switchis provided, offering a degree of variability suitable to all practicalrequirements for CW and phone. Selectivity positions are asfollows : AVC off-Sharp Crystal, AVC off-Broad Crystal, AVCoff-Sharp IF, AVC on-Broad Crystal, AVC on-Sharp IF, AVCon-Broad IF.

FREQUENCY STABILITY. By means of an especially developedcircuit, variations in line voltage cause only a barely discerniblechange in oscillator frequency.

BATTERY OPERATION. In addition to the AC Power Supply, apower plug is provided at the rear of the chassis for the connectionof a source of filament and high tension DC voltage supply formobile or emergency operations.

BREAK-IN RELAY OPERATION. Terminals are provided on therear panel for stand-by relay operation.

CRYSTAL FILTER. A Bliley Resonator Crystal in a new Hallicrafterslow capacity crystal holder with a double balance bridge circuitallows a high degree of rejection of unwanted signal even wheninterfering signal is closely adjacent.

GENERAL COVERAGE -43.5 to .54 MC4 BAND POSITIONS

Band 1- .54 to 1.73 MC Band 3- 5.0 to 15.7Band 2-1.7 to 5.1 MC Band 4-15.2 to 43.5

BAND SPREAD CALIBRATION80 Metre Amateur Band 20 Metre Amateur Band40 Metre Amateur Band 10 Metre Amateur Band

9 TUBES6SK7 r.f. amplifier6K8 first detector and oscil-

lator.6SK7 first i.f. amplifier6SK7 second i.f. amplier

MC

6SQ7 diode detector. AVCand first a.f. amplifier

6F6G power amplifier76 beat frequency oscillator76 rectifier6H6 noise limiter

5 METER calibrated in S units and DB.CONTROLS

I-RF Gain 8-Bandspread Tuning2-Band Switch Control3-Selectivity Switch 9-Tone Control Switch4-Crystal Phasing 10-Automatic Noise Limiter5-Audio-Gain Switch6-Pitch Control I I-Send-Receive Switch7-Main Tuning Control 12-BFO Switch

MAIN TUNING DIAL. Directly Calibrated, Translucent IlluminatedDial.

ELECTRICAL BAND SPREAD. Directly Calibrated, TranslucentIlluminated.CABINET DIMENSIONS. 191 ins. wide, 91 ins. high, 10A ins. deep.

WEBB'S RADIO, 14, Soho Street, London, W 1PHONE: GERRARD 2089

SOLE DISTRIBUTORS FOR BRITISH ISLES OF HALLICRAFTER EQUIPMENT

Printed in Great Britain for the Proprietors and Publishers, BERNARD JONES PUBLICATIONS, LTD., Chansitor House, Chancery Lane, London, W,C.,9, byTug PRESS AT COOMBELANDS LTD., Addlestone, Surrey. Sole Agents for South Africa: CENTRAL NEWS AGENCY, LTD. Sole Agents for Australia and Nei

Zealand : GORDON AND GOTCH (AUSTRALASIA), LTD.

t-1414vcidarld...good and bad picture areas limyl enses or rojection ome mechanicalin eceiver eli...

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