325th Consecutive Issue-Seventh Year A SHORT WAVE … · 325th Consecutive Issue-Seventh Year A...

JUNE 161928

AUTOMATIC SYNCHRONY IN TELEVISION IclEN5Ts

A DYNAMIC SPEAKER

REG. U.S. PAT. OFF

The First and Only National Radio Weekly325th Consecutive Issue-Seventh Year

IMPROVE YOUR AERIAL

ARE WAVES BROAD?

ONE METER FOR AC AND DC

A SHORT WAVE ADAPTER FOR AC SETS

Any AC Set Will Reproduce Short Waves (15 to 133 Meters) With the Aid of This SimpleAdapter Requiring No Extra Tubes.-See Page 3

RADIO WORLD June 9, 1928

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plete Two -in -One (AC and DC) scientific trouble -shooting test set, con-sisting of one No. 215 and one No. 346, for which I will pay the ]postman $13.50, plus a few cents extra for postage.

3 If 0-500 v. high resistance voltmeter No. 347 is preferred, put cross 1in square and pay $14.50, plus postage, instead of $13.50, plus postage. I

0 One No. 215 alone $10.00.

NAME .,

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JUNE 161928

AUTOMATIC SYNCHRONY IN TELEVISION IclEN5Ts

REG. U.S. PAT. OFF.

The First and Only National Radio Weekly325th Consecutive Issue-Seventh Year

A DYNAMIC SPEAKER

IMPROVE YOUR AERIAL

ARE WAVES BROAD?

ONE METER FOR AC AND DC

A SHORT WAVE ADAPTER FOR AC SETS

Any AC Set Will Reproduce Short Waves (15 to 133 Meters) With the Aid of This SimpleAdapter Requiring No Extra Tubes.-See

15-130METERS$1250

RADIO WORLD

AIR -KING' //

N e\11/

PATENTS PENDING

97% AIR

DIELECTRICGENUINEBAKELITE

4

SHORT WAVE PLUG-IN COILSThe new Air -King Short Wave Kit consists

of three plug-in coils, ranging from 15 to130 meters (when tuned with a .00014 mfd.condenser), and a plug-in base, with variableprimary, which is soldered with phosphorbronze flexible connections to permanent an-tenna -ground binding posts on the base. Eachcoil is accurately space -wound on a bakelitesquirrel cage form, with ribs threaded to lockeach turn in place.

Friction holds the variable primary in anyposition it is put in. Double contact betweencoil prongs and the jacks in the base assureperfect connection at all times, from the mo-ment of inserting coils.

The Air -King Short Wave Kit is speci-fied by Herbert E. Hayden for his A.C.Short Wave Adapter, described in thisissue.

If Your Dealer Can't Supply You, Order Direct

MFo. by AIR -KING PRODUCTS CO.2 22-2 26 GRAND ST. BROOK LYN,N.Y, U.S.A:

Guaranteed resistorsresistors are non -Inductive and non-eapacitative.ARTHUR H. LYNCH. Inc.

1775 Broadway N. Y. C.

SendforBook

NEXT WEEKJust the portable you've been looking

for-light in weight, only four tubes,sensitive and moderately loud. Also ashielded two -stage AC audio amplifier,with filament transformer, built into aHammarlund shield. How to build aC eliminator is another interesting ar-ticle in next week's issue, dated June 23.

GetsEverything but Static

Brings in Far -Away StationsLoud and Clear Regardless

of Static ConditionsFans everywhere are replacing their

troublesome and static gathering up -in -the -air aerials with the marvelous newGROUND ANTENNA-Aer-O-Liminator.Radio engineers and hundreds of users

I testify that Aer-O-Liminator gets betterlong distance reception, almost unbeliev-able freedom from outside noises, fargreater selectivity and marvelously true,clear, sweet tone quality.

John E. Christenson, Radio Engineer,Chicago, writes : "I have tested and thor-oughly approve the Aer-O-Liminator. Ifind it increases selectivity and volumewithout distortion, practically eliminatesstatic, gives good, clear tones, both onlocal and distant stations. I would recom-mend the use of the Aer-O-Liminator toevery radio owner to get the best recep-tion from his set."

RushrhisImportant Coupon,CURTAN MFG. CO.,154 E. Erie St., Dept. 830-G,Chicago, Ill.

Please send me at once complete descrip-tion of Aer-O-Liminator, with details ofguarantee, Scientific Proof, and FREETRIAL OFFER.NameAddressCity

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EASY TOINSTALL

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FREE TRIALMake this thrilling test at our risk!Install an Aer-O-Liminator (Ground Antenna). Leaveyour old overhead aerial up. Try out on a night whenstatic is bad. If you do not get a wonderful improve-ment in freedom from static, greater selectivity andclear, sweet tone without interfering noises, if you can'tget good reception on stations that are drowned out bystatic on your old aerial, you need not pay us a redcent for this test. Send coupon at once for scientificexplanation of Aer-O-Liminator (Ground Antenna) proofof performance and our conclusive iron-bound guaranteeand remarkable Free Trial Offer. Mail Coupon TODAY!

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une 16, 1928

BE SURE TOBUY or SPECIFY

GENUINE

PARTSin building the AC SHORTWAVE ADAPTER describedin this issue by Herbert E.

Hayden.

If your dealer does not stockKaras Parts, send your orderdirect to us and we will seethat you are supplied.

Karas Electric Co.4039-FC. N. ROCKWELL ST.

CHICAGO

ForNOTICE

hest results use genuine patented non-magnetic

44 VACSHIELD"on your Shield Grid Tubes.infringements. Look for nameon each shield.

At your Dealer's orORANGE RESEARCH

247 McKinley Avenue

Beware of imitations aadand patent No. 1,564,654

by mail, $1.00.LABORATORIES

East Orange, N. J.

VICTOREENSuper CoilsSend for Folder

Geo. W. Walker Co.2825 Chester Avenue

Dept. B Cleveland, 0.

Make any Good ReceiverBETTER

ct, oc,TUBES

C.E.TIF43. CO.Providence

R.I.

DYNATONEELECTROMAGNETICPOWER SPEAKER UNITOperates on6 -Volt "A"battery orTrickleCharger.Draws four -tenths of anAmpere.For Cones,Balsa Wood,AirplaneCloth, etc.

Proper Impedance forModern Tubes

Approved by Radio World, Radio News andother Prominent Acoustical Laboratories.

Sent C.O.D. under 10 -day money -backguarantee. Write for literature.

UNIT ONLY, weight 4 lbs $12.50UNIT and 12" CONE $15.00UNIT, CONE and BAFFLE,

size 13" x 13" x 10" deep $18.50 -

Fanspeaker Radio Company74 DEY STREET NEW YORK CITY

aft on MD 11101.11..0

JUNE 16, 1928Vol. XIII, No. 13. Whole No. 325

15c per Copy.[Entered as second-class matter, March,1922, at the post office at New York,

N. Y., under Act of March, 1879.]

-UNINTERRUPTED READER INTERESEVERY WEEK EVERY YEAR

RADIO WORLD

Technical Accuracy Second to None A Weekly Paper published by HentaessyRadio Publications Corporatio*, fromPublication Office, 145 West 45th Street,

New York, N. Y.(Just East of Broadway)

Phone: BRYant 9558 and 9559

An AC Mbe Adapterfor Short Waves

MANY short wave receivers, andadapters for receiving short waves on

broadcast receivers, have been described.These have been for DC operation. Buthere is an adapter which will convert anyAC operated broadcast receiver into ashort wave set, provided that the detectorin that receiver is of the -27 type, as itnearly always is.

Fig. 1 shows the circuit diagram of theadapter. It is the conventional short wavereceiver which has proved to be the mostpopular for all short wave purposes. Withthis circuit the new Air -King short wavekit works excellently.

The antenna coil Ll is of fixed induct-ance and is used for all the coils that maybe plugged into the circuit. It is mountedon hinges so that the coupling between itand the secondary may be adjusted to anydesired value. This adjustable primarycoil can be seen- in Figs. 2 and 3 in frontof the tuning condenser.

L2, the secondary, and L3, the ticklerwinding, are wound on the same form forany one of the radio frequency transform-ers in the plug-in set. The secondary iswound with heavy enameled wire on arugged, squirrel -cage bakelite formhaving six lateral ribs. These ribs aregrooved for the wire so that the turnscannot shift about. Thus the inductanceof any given coil remains fixed in value.

The tickler winding is placed inside thesecondary in a peripheral groove cut inthe lateral ribs and it is cemented so thatit cannot work loose. Fine wire is usedfor this coil so as to minimize capacitybetween the windings. The wide air spacebetween the tickler and the secondarywindings also reduces the capacity greatly.

Prong Terminals UsedThe four terminals on the plug-in coil

are brought to four long prongs similar tophone tip terminals and are rigidly securedto the coil frame. The terminals arespaced so that they can be inserted intothe coil receptacle in only one way, thuspreventing short circuit.

There are three coils in a set, as shownin Fig. 4. The approximate wavelengthrange of each coil when tuned with a.00014 mfd. condenser is stamped on eachcoil. Thus the largest has a range of 57to 133 meters, the intermediate a range of31.5 to 68 and the smallest a range of 15to 33.5 meters.

The largest coil has 19 turns on the(Continued on next page)

By Herbert E. Hayden

FIG. 1

P

THE CIRCUIT DIAGRAM OF AN ADAPTER WHICH CONVERTS ANY ACOPERATED BROADCAST RECEIVER INTO A SHORT WAVE RECEIVER.

LIST OFLl, L2, L3-One set of Air -King short

wave coils with receptacle, with three coils15-33.5, 31.5-68 and 57-133 meters.

L4-One National RF choke coil.Cl-One Sangamo .00025 mfd. grid con-

denser with resistor clips.C2-One Karas .00014 mfd. straight line

frequency condenser.C3-One Karas .00025 mfd. straight line

frequency condenser.

PARTS111-One Lynch 2 megohm grid leak.One Benjamin Y type socket (five

spring).Two Karas Micrometric dials.Two American Hardware aluminum

sub -panel brackets 7x1 inches.One Formica front panel, 7x14 inches.One Formica sub -panel, 7x13 inches.One four lead cable, 27 inches long, with

five prong plug.

4 RADIO WORLD June 16, 1928

FIG. 2CLOSE-UP VIEW OF THE COIL ANDRECEPTACLE OF THE AIR -KING ACSHORT WAVE ADAPTER. NOTETHE GRID PRONG IS INSERTEDFIRST AS, A GUIDE FOR THEOTHERS. NO MISTAKE CAN BEMADE IN INSERTING THE COILS,BECAUSE THE PRONGS FIT IN

ONLY ONE WAY.(Continued from preceding page)

secondary and 6 turns on the tickler. Theintermediate coil has 8 turns on the sec-ondary and 4 on the tickler. The smallestcoil has 3 turns on the secondary and 2turns on the tickler.

The antenna coil has 10 turns.The coil receptacle or base is provided

with terminal sockets so shaped that thecoils may be inserted with greatest ease.Each receptacle jack is provided with twostiff springs which will make two wipingcontacts on each terminal when a coil isinserted. Terminal soldering lugs are alsoprovided, and these are integral parts ofthe spring detail. This eliminates fourpossibilities of poor contact.

The antenna coil is connected with twoflexible leads to two binding posts mountedon the coil receptacle.

Straight Line Frequency CondensersThe tuning condenser C2 is a Karas

.00014 mfd. straight line frequency con-denser, which is controlled with a KarasMicrometric dial. Thus accurate andmicrometric control of the tuning ispossible over the entire tuning range ofany coil.

The tickler control condenser C3 is asimilar instrument, of .00025 mfd. maxi-mum capacity. It also is controlled witha Micrometric dial, which enables closeadjustment and control of the regenera-tion. The rotor of this condenser shouldbe connected to the cathode K.

The grid condenser Cl is a Sangamo.00025 mfd. unit which is provided withclips for the 2 megohm metalized gridleak Rl.

A radio frequency choke coil L4 is putin the plate circuit of the tube. Withoutthis coil the regeneration will not bedefinite at some settings of the ticklercondenser and for some of the coils. Alsothis choke coil must be wound so that itwill be a choke for all frequencies in thetuning ranges of the three coils. It shouldbe wound in slots which are separated bya short distance in order that the dis-tributed capacity be as low as possible.If there is considerable capacity in thecoil the choke coil will not be effectiveat the shorter waves to which the adaptermay be tuned. A choke coil of 60 milli -henrys is suggested, but other values may

REARFIGS 3 AND 4

VIEW OF THE AC SHORTWAVE ADAPTER AND A VIEW OFTHE THREE COILS IN THE AIR -KING KIT.

be used provided that the distributedcapacity of any coil chosen is low. Theone shown on the front cover is a NationalRF choke coil, which fits into a Lynchsingle mounting.

Heater Tube UsedSince the adapter is intended for use in

conjunction with an AC receiver in whichthe detector is a -27 type heater tube, aY type, five prong socket is employed.The one used was a Benjamin springcushion type.

For plugging into the socket in thebroadcast receiver a four lead cable ter-minating in a five prong plug is used. Thegrid prong on the plug is not used. Theproper connection between the plug andthe adapter tube is shown in the circuitdiagram Fig. 1. This plug may be thebase of a burnt -out -27 tube, into theprongs of which four flexible insulatedleads are soldered.

To make the adaptation the -27 typedetector tube is taken from the broadcastreceiver and the adapter plug is insertedin its place. Then the tube is insertedin the socket in the adapter. When thepower is turned on the broadcast receiverthe short wave receiver is ready to oper-ate.

The panel is of hard rubber and is 7x14inches. The sub -panel is of the samematerial and is 7x13 inches.

Regeneration PointersThe characteristics of a short wave re-

ceiver are such that the wavelength tuningdial may be calibrated, with not muchdanger of variation from day to day, butthe regeneration control can not be cali-brated, because it depends on a series ofcumulative effects.

In every instance the degree of couplingbetween the antenna coil and the second-ary is influential on regeneration. Whilethe feedback is caused by the regenerationcondenser, the antenna resistance effect iscontrolled by the degree of inductivecoupling. The looser the coupling, the

less the effect of the antenna reactanceupon the secondary, and the greater theregenerative possibilities. Hence, with agiven setting of the regeneration con-denser, and a given degree of antenna coilcoupling, a point just under oscillation,which is the most sensitive point, may bereached. Then, by increasing the induc-tive coupling, the capacity feedback wouldhave to be increased, for regenerationmay have been lost, and the addedcapacity brings it back. A reciprocal re-lationship exists.

Also, the condition of the B supply hassome effect. If batteries were used thismight prove serious as the voltage of thebatteries approached the cutoff limit, butwith an AC operated B supply, where theline delivery is utilized in rectified form,only the variations in line voltage wouldhave any effect. This is a negligible itemas influencing regeneration.

How to Insure RegenerationTherefore it is well to keep a record of

the stations heard, by noting the dial set-ting of the left-hand condenser, whichcontrols wavelength. No need to try tocalibrate the regeneration condenser, be-cause you simply swing that until regen-eration sets in, increasing or reducing re-generation as needed. If no regenerationis obtained, loosen the antenna coil coup-ling simply by pushing the antenna coila little farther from the secondary. Thisis done in an eye's twinkling.

The long outdoor antenna used forbroadcast reception works well on shortwaves, for the antenna picks up waves ofall radio frequencies. But often improvedresults on short waves are obtainable byreducing the electrical size of the antenna.This may be done by physical reduction orby retaining the regular outdoor antenna,and using a small fixed condenser in serieswith it.

One side of this series condenser wouldgo to the antenna binding post, which isbuilt into the coil form, and the other(Continued on Page 23)

June 16, 1928 RADIO WORLD

How to Connect Any Set's Outputfor Television Reception

TUNE, listen and look for televisionpictures broadcast three times a

week by WGY, from Schenectady, N. Y.,1:30 to 2 p.m. Eastern Daylight SavingsTime-Tuesdays, Thursdays and Fridays.

Tuning for television is done the sameas for radio broadcast sound, and it isdone with the same apparatus. Listeningto the characteristic 18 cycle per secondflutter of television is done with the aid ofa headset or loudspeaker in the ordinaryway. Listening to the reception is notessential. It is merely a convenient wayof telling when the receiver is tuned inon the desired carrier wave.

The final object of a television receiveris to give the fan a picture to look at.He gets it by looking at a flickering neonor Kino lamp through tiny holes in thescanning disc which rotates in synchron-ism with the corresponding disc of thetransmitter. The speed of the motordriving the local disc is controlled manu-ally with a rheostat.

The only change in the broadcast re-ceiver to adapt it to television receptionis confined to the output side of the lasttube. There are several circuit arrange-ments which may be used, the choice de-pending on the type of output circuit al-ready in the power tube of the receiver.Fig. A shows one hook-up.

Arrangement of Output CircuitTwo 30 henry choke coils connected in

series are put between the plate of thetube and the positive terminal of the platevoltage supply. The total effective in-ductance of these coils is 60 henrys. Suchhigh inductance is used in order that thechoking effect be high at the low fre-quency fluctuations which may be con-tained in the visual signal.

The neon glow lamp is connected inshunt with the two chokes and the platevoltage supply. In addition to the lamp avariable resistance and a 67 volt batteryare connected in the shunt circuit. The67 volt battery is so connected with refer-ence to the B voltage source that thevoltages add up in the circuit containing-the neon lamp. Thus if the voltage ap-plied to the plate is 180 volts and thevoltage in the shunt circuit is 67 voltsthe total voltage in the neon lamp -chokecoil circuit is 247 volts. It takes some-thing over 200 volts to cause some neonlamps to glow.

As soon as the glow appears, a currentflows in the neon tube circuit. The in-tensity of this current depends on thevoltage and- the resistance effective inthat circuit. If the current is excessivethe neon lamp will glow too brightly andits life will be shortened. For that rea-son it is advisable to insert a variableresistance in series with the lamp to limitthe current to the value recommended bythe makers of the tube. Serious damageto the lamp is likely to result if the seriesresistance is omitted.

Why Lamp FluttersWhen a single voltage is impressed on

the grid of the power tube the plate re-sistance of that tube varies. The signalcurrent through the neon lamp varies inthe same manner and thus the light flick-ers with the incoming signal.

As an aid in tuning in the headset orloudspeaker can be connected across theneon tube. When doing this it is nec-essary to connect a condenser in serieswith the speaker to prevent heavy directcurrent from flowing through its wind-ings. This current would probably burn

By Neal Fitzalan

(Fia.

5W 171FD

B+ria.e)

AT THE LEFT IS THE CIRCUIT DIAGRAM OF THE OUTPUT TUBE OF ARADIO RECEIVER, TO WHICH A NEON GLOW LAMP HAS BEEN CON-NECTED FOR TELEVISION RECEPTION. AT RIGHT IS A DIAGRAM FORAID IN TUNING IN A TELEVISION CARRIER. A LOUDSPEAKER OR HEAD-SET MAY BE CONNECTED ACROSS THE NEON LAMP FOR LISTENING TO

THE CHARACTERISTIC FLUTTER,

out the coils in the speaker. The con-denser may have any convenient capacitywhich will pass enough of the 18 cyclecurrent to be heard, for example, 1 or 2mfd.

The telephone shunt circuit across thelamp is shown in Fig. B. A switch Sw isalso put in series with the telephone sothat the shunt circuit may be openedwhen the set has been tuned in. Whenthe switch is open none of the visioncarrying current passes through the shuntand all is forced through the lamp, thusmaking contrasts between the lights andshades greater and the reproduced picturemore clearly visible.

The resistance in series with the neonlamp should consist of two sections, one a

1,000 ohm fixed resistor and another a0-4,000 ohm variable resistor. The cur-rent carrying capacity of both should bewell over 20 milliamperes.

The object of using two resistors, one1,000 ohms fixed value and another ofadjustable value with a range of 0-4,000ohms, is to make the circuit foolproof byinsuring that there will always be 1,000ohms in the circuit.

The lamp used should have been de-signed especially for television reception.Lamps made foi. night lights and signsdo not as a rule have a luminous platelarge enough to cover the image, andmost of them have no plate at all butsimply two luminous points.

World Experts AgreeOn Sun Spot Effects

Washington.A definite connection exists between

solar activity and radio transmission whenobservations are averaged over long per-iods according to Dr. L. W. Austin, ofthe Bureau of Standards, in a reportmade public by the Department of Com-merce. The full text of the Department'sstatement follows:

"Dr. Austin has just submitted the re-port to the Committee on Solar andTerrestrial Relationships of the Interna-tional Research Council in Brussels forits approval. It gives a summary of theconclusions which may be drawn fromthe work of Espenschied, Anderson andDailey, and C. N. Anderson of the Amer-ican Telephone and Telegraph Company,

of G. W. Pickard, of the WirelessSpecialty Apparatus Company, and ofDr. Austin on the relationship of radiotransmission to solar activity.

"Year by year, and probably month bymonth, the daylight signals in the me-dium and long wave ranges rise and fallwith the sunspot numbers in the chang-ing sunspot cycle, while the night signalsappear to change in the inverse sense,the report reveals. There is evidence ofchanges in reception in the period of thesun's roation (27 days)."

"It also appears that the daylight staticis less in years when sunspots are nu-merous and greater when sunspots arefew, according to the report."

This confirms previous beliefs.


Automatic TelevisionBy Paul L. Clark

THE apparatus hereinafter describedcomprises a conventional type of

scanning elements geared together andrun by a constant speed motor. The basicrequirement of television transmission issynchronization of the apparatuses atboth the sending and receiving stations,and, even the slightest variation fromsynchronism causes displacement of thepicture signals on the receiving screenrelative to corresponding signals derivedfrom the image to be transmitted.

Tolerable Variation

For precise results the deviation shouldbe zero; but a slight variation, say, thewidth of a single picture point (area) ispermissible. A greater variation causesthe received images to flicker and con -

[One of the most important problems in connection with television is that of schronization of .the receiver scanning element with that of the transmitter. Presynchronization is absolutely necessary or the received picture will not be distinct.

Various schemes for synchronization have been proposed. In one method the receiviis maintained in synchronous speed with the transmitter by a manually operate.d rheastqThe operator of the receiver continually manipulates the rheostat so as to keep the imaireceived as clear as possible. This method is akin to maintaining a camera in focus o

an object when the distance between the object and the camera is subject to continuchanges, either because of motion of the camera or of the object, or both.

While manual synchronization is not exceedingly difficult it distracts the operatoattention from the contents of the picture and concentrates it on its mechanical feature

sequently produces inaccurate delineationand blurred pictures.

The object of the present system istwo -fold: (a) to synchronize constantlyand synchronously with the transmissionof each visual signal, and (b) to hold thereceiver motor and scanning elements

FIG. 1THE TRANSMITTING APPARATUS IN PAUL L. CLARK'S1 SYSTEM OFTELEVISION, SHOWING THE LIGHT CHOPPER T WHICH IS AN ESSEN-

TIAL FEATURE OF THE AUTOMATIC SYNCHRONIZATION.

FIG 2THE RECEIVING APPARATUS OF MR. CLARK'S SYSTEM OF TELEVISION,SHOWING THE LIGHT MODULATOR MJN, THE RECEIVER LIGHT CHOP-PER R AND THE TWO PHOTO -ELECTRIC CELLS IN THE ARMS OF AWHEATSTONE BRIDGE THAT IS USED FOR CONTROLLING THE SPEED

OF THE SCANNING MOTOR.

rigidly keyed -in to corresponding ele-ments of the transmitting apparatus, sothat the departure from synchronism can-not vary more than the fraction of thewidth of a single picture point.

Similar Light Choppers UsedTo accomplish this result, similar light

choppers T Fig. 1, and R Fig. 2, are usedboth in the transmitter and the receiver,so that with the apparatuses in syn-chronism, the beam of light Al from theilluminated image to be transmitted, andwhich passes through the second apertureof the chopper T, must register with thebeam R of the receiver, and beam R

.must pass through corresponding aperturenumber two of the receiver chopper R.

As long as synchronism prevails, suc-cessive light beams pass through succes-sive apertures of the chopper as shownat R1, Fig. 3; but if the receiver motorspeeds up, a non -registration occurs, asshown at the upper part of Fig. 3, pro-ducing an interception of the successivelight beams and consequently varying theamount of light on photoelectric cell Flproportional to the instantaneous out -of -phasing of the receiver.

As will be seen by reference to thefollowing detailed description, this inter-ception of light by the chopper R is usedto control the speed of the motor whichdrives the optical scanning elements ofthe receiver.

Constant Speed MotorBy referring to Fig. 1, the transmitter

is seen to comprise a familiar type ofscanning elements A, B, which are gearedtogether so that the high-speed polygonalmirror B, revolves much faster than themirror A, and these mirrors are drivenby a constant -speed motor (not shown).

As these mirrors revolve at the requiredspeed, successive points of the illuminatedimage C are translated by the photo-electric cell F into electrical signals ofequal and short duration but of valuesvariable in accordance with correspondinglight or dark points on the picture, theprinciple employed in most forms of tele-vision transmission.

The use of a light chopper was firstdisclosed by Rosing (Patent No. 1,161,734,Nov. 23, 1915) and is used by several ex-perimenters to break up the direct anduneven pulsations of a picture into separ-ate impulses of equal length, say, onehundred -thousandth of a second, therebyproducing substantially an alternatingcurrent comparable to a radio frequencyof 100,000. The chopper of Rosing is,however, used only in his transmitter,whereas the writer uses a correspondingchopper in his receiver for the purpose ofregulating the motor speed, and obtain-ing synchronizing precision within narrowlimits.

Action of TransformerThe electrical impulses or signals pro-

duced in the cell F are transformed intothe required form by, the transformer G,and transmitted to the transformer H, at

June 16, 1928 RADIO WORLD

ynchronizing Apparatuspractically excludes the operator from enjoying the picture, although other spectatorsenjoy it unless the operator forgets the mechanical features. This is not unlike

wing, where the driver must keep his eyes on the road if the passengers are to enjoycenery in comfort and safety.The ideal arrangement of the synchronizing elements is such that the transmitterhe receiver are maintained at the same speed automatically. This can be broughtby making a part of the visual signal control the speed of the receiver. A very

ous method of automatic synchronization has been devised by Paul L. Clark, ofklyn, N. Y. In this method the picture modulated signal itself is used to retardcelerate the receiver to synchronize its speed with that of the transmitter.

-EDITOR]

the receiving station, employed to controlthe deflection of an oscillograph mirror J.and thereby produce a beam of light ofintensity proportional to the strength ofthe corresponding electrical signal.

New Light ValveThe light valve devised by the writer

consists of a source of light L, a lens Kwhich focuses the light upon the oscillo-graph mirror J and a lens P which receivesthe light from the mirror J and directsthe light to fall upon the scanning ele-ments B and A. Adjacent each lens isa grid comprising a plurality of equi-spaced bars, the function of the valvebeing to produce by means of the oscil-lograph mirror J, an optical image ofthe grid M through variable degrees ofregistration with the grid N, so that amaximum deviation of the mirror J per-mits a maximum amount of light to passthrough the grid N.

The chief advantage of this arrange-ment is that high frequencies are obtain-able because a complete valving isaccomplished with an almost infinitesimalmirror deflection.

The beam of light from the lens Pfalls upon the rotating mirror B, and isreflected thereby to the rotating mirrorA, thence to traverse the viewing screenU and produce thereupon a picture cor-responding to that of the illuminatedimage in the transmitter.

Thus far the description. is chalracterie-tic of 'previously used television appar-atus.

Photo -Electric Cells UsedIn the beam from the mirror P is

placed a small fixed mirror Q, whichreflects a certain part of the light derivedfrom the light valve, to fall upon a photo-electric cell F2. A second fixed mirrorS, is placed to intercept a certain partof the light which is reflected by thehighspeed mirror B, and rapidly deflectthe light so intercepted in the form of abeam R, to rapidly traverse the chopperR, pass therethrough, and be directed bythe lens V, to fall upon a photelectriccell Fl.

Thq cells Fl and F2 are connectedtogether in a suitable Wheatstone bridgecircuit and to an amplifier (occupyingthe place of the usual galvanometer).

To the output side of this amplifier isconnected a small auxiliary field windingW, placed preferably on the pole -tips ofthe small driving motor of the receiver.As long as synchronous conditions per-sist, the current supplied to the amplifierby the cells Fl, and F2 will be zero; buta displacement of the beam R ifrom exactregistration with the chopper aperturecorresponding to that of the chopper ofthe transmitter will initiate a flow ofelectric current into the amplifier, tendingto weaken or strengthen the coil W andthus control the motor speed.

Manually Controlled MotorThe motor must be manually controlled

close to synchronism, preferably slightly

above synchronous speed, using theautomatic control merely to check thespeed, and restrict the angle of "hunting."

By referring to Fig. 3 it is seen thatthe light signals are continuously pro-jected upon the photoelectric cell, butin variable ratios, depending upon theaccuracy of registration, and that theexciting current of the auxiliary fieldcoil is varied in accordance with the regis-tration of the high -frequency light beamsR on the chopper R.

Instantaneous Response

The response of the photo -electric cellsto different amounts of light is practicallyinstantaneous, so that the regulation maybe considered instantaneous, except forthe time lag due to the hysteresis of themotor pole -tips.

'5ER/17"R" PROGRESSIVE1 REGISTRATION ( /A/fleet/R/9TE)

EFFECTIVEPHOTO- ELECTR/C

CURVE

fe. ACCURATE REGISTRATION14/ /TM SYNCHRONISM

FIG. 3

A CLOSE-UP OF THE LIGHT CHOPPER R, SHOWING EXACT REGISTRA=TION AND SYNCHRONISM (LOWER) AND FAULTY REGISTRATION(ABOVE). THE WHEATSTONE BRIDGE IS BALANCED WHEN LOWERCONDITIONS PREVAIL WHEN UPPER CONDITIONS PREVAIL IT ISUNBALANCED AND RETARDING OR ACELERATING CURRENT FLOWS

IN THE OUTPUT COIL.

FIG. 4

SIMPLIFIED DRAWING OF THE WHEATSTONE BRIDGE, SHOWING THETWO PHOTO -ELECTRIC CELLS Fl AND F2 IN TWO ARMS, RESISTORSR, R IN THE OPPOSITE ARMS, AND AN AMPLIFIER IN THE BRIDGE

CIRCUIT, B.


CarrierHasNoWidthHow Is Wave Broad?

By J. E. AndersonTechnical Editor

AT LEFT ARE THREE DIFFERENT RESONANCE CURVES, INDICATINGTHREE DEGREES OF SELECTIVITY. THE HIGHEST IS THE MOSTSELECTIVE. THE DOTTED CURVE INDICATES THE LIMITED RESPONSEDUE TO DETECTOR OVERLOADING. AT RIGHT IS REPRESENTED ADAMPED WAVE PRODUCED BY THE DISCHARGE OF A CONDENSER INA TUNED CIRCUIT. SUCH A WAVE WILL INDUCE OSCILLATION IN ATUNED CIRCUIT EVEN IF THAT CIRCUIT HAS NOT THE SAME RESONANT

FREQUENCY AS THE WAVE.

\ VHAT is a broad wave? We oftenhear that the carrier wave of a cer-

tain station is broad. Complaints aresent in to authorities that a wave is sobroad that it interferes with the receptionof other stations.

Just what does the broadness of a wavemean, if anything?

If a wave is broad it must mean that itcontains many frequencies close together.Otherwise it would have no "width" atall. It would all be at one point in thefrequency spectrum. If the wave is broadand it has many frequencies close to-gether that fact should be evident whenan oscillating receiver is tuned in. Thereshould not be one series of squeals, start-ing at a high pitch, going down to zeroand then rising to a very high and super -audible pitch again as the tuning con-denser is turned, but there should bemany such series of squeals, and theyshould coincide so that at any point onthe tuning condenser within the squealingrange there should be squeals of allpitches.

But that never occurs.There is only one series of squeals for

each broadcast station and there is onlyone pitch squeal at each setting of thetuning condenser within the squealingrange of the carrier. That is, the broad-cast wave, so far as the carrier is con-cerned, has no width!

The carrier is located at a point in thefrequency spectrum. Hence saying thata broadcast wave is broad is meaningless.

Spark Wave May Be BroadWhile a broadcast and continuous wave

may not have any broadness, a wave emit-ted by a spark transmitter may be widein effect, because it induces resonant fre-quency currents in any circuit by shockexcitation.

But the complaints are not so muchagainst broad spark waves as againstbroad broadcast waves. The complaints

are directed against waves which have nobroadness, waves which are fixed in fre-quency.

There may be conditions in broadcasttransmission under which the harmonicfrequencies of the fundamental carrierare radiated with considerable intensity.That station does not then send out onebroad wave but it sends out several waves,but none of them has any width.

Harmonics are sent out by a stationwhen the antenna is coupled too closelyto the oscillating system and when noprovision has been made for eliminatingharmonics from the antenna current.Cases in which considerable power is radi-ated on the harmonics of a station carrierare so rare that the subject may be dis-missed.

Modulated Wave Has WidthA modulated broadcast wave has some

width, for with the carrier frequency maybe associated side frequencies of lowerpower which differ in frequency by notmore than 10,000 cycles above or belowthe carrier frequency. Thus the modu-lated broadcast wave may have a widthof 20,000 cycles or less. But these widthsare transient. They only occur momen-tarily and occasionally. At other timesthe width is only 2,000 cycles, 200 or per-haps only 60 cycles wide. Whenever thesignal carries a frequency of F cycles,the width of the wave is 2F cycles. Whenit eqrries no signal it has no width.

When a radio fan complains that thewave of a broadcast station is broad it isnot the width due to the modulation whichis in question. It is the apparent widthdue to the power of the station.

And when the fan complains of broad-ness of the wave he simply confesses thathis receiver is not selective. It is the re-ceiver which is broad and not the waveof the station.

His receiver does not have the power todiscriminate among frequencies. It re-

sponds to several frequencies with almostthe same readiness. It may be tuned nom-inally to 750 kc but it accepts 550 and 950kc with practically the same volume.

Every receiver, no matter how selective,accepts all frequencies to some extent.

11,..n a rece'ver is tuned to one frequencyit accepts that frequency much betterthan others. In fact, so strong is the sig-nal received on the resonant frequency incomparison with signals accepted on non -resonant frequencies that it seems thatthey are absent. But they are there andcan be brought up by amplification.

Selectivity of ReceiverThe relative values of the resonant and

non -resonant accepted signals depend onthe selectivity of the tuned circuit, whichin turn depends on the resistance in thatcircuit. If the resistance is low the selec-tivity is high and the accepted signals onnon -resonant frequencies are very small incomparison with the accepted signal onthe resonant frequency. If the resistanceis high the selectivity is low and there isrelatively little difference between theaccepted signals at resonant and non -resonant frequencies.

The individually tuned circuit in abroadcast receiver may be quite selective,yet the receiver as a whole may not beany more selective, although it may haveseveral tuned circuits in tandem. In fact,the overall selectivity may be lower thanthe selectivity of any one of the tunedcircuits.

There are many reasons for this condi-tion. First, the several circuits may notbe tuned to the same frequency; second,the accepted signal may not pass throughthe tuned circuits ; third, the detector tubemay become overloaded long before theresonant point is reached.

Lack of precise tuning of all the tunedcircuits in the receiver is a common sourceof lack of selectivity, especially whenseveral condensers are controlled from asingle shaft, without trimmers. This con-dition may be remedied by trimmers onthe individual circuits, or by readjustingthe capacities and inductances in thetuned circuits.

Signal Skips the TunersThe second cause for broadness men-

tioned above was that the signal does notpass through the tuners but reaches thedetector directly. The only tuner effectivein that case is the one preceding the de-tector, and even that may not be as ef-fective as if the signal had entered solelyby the antenna. This case is exemplifiedwhen the tuning coils are exposed andmounted so that they act as antennas.

The battery leads also aid this condition.The remedy is shielding of the entire re-ceiver, except the antenna, and alsoshielding the different tuners from eachother. It is only local and powerful sta-tions which will come in strong withoutfirst passing through the proper selectivechannel.

The third cause of broadness in a re-ceiver containing two or more selective,tuned circuits is that the detector becomes

(Continued on page 20)

June 16, 1928 RADIO WORLD 9

Meters That MeasureBoth AC and DC

F /a. / F/G, 2

By Reginald Forrester

F/G.3 F/G. 4

ATTRACTION AND REPULSION AS SHOWN IN FIGS. 1 AND 2 ARE USEDIN THE CONSTRUCTION OF METERS. IN FIG. 1, TWO PARALLEL WIRESHAVE A CURRENT THROUGH THEM BY VIRTUE OF THE VOLTAGE ANDCURRENT SUPPLIED BY THE BATTERY AT TOP. ATTRACTION TAKESPLACE. HOWEVER, WHEN SERIES CONNECTION IS RESORTED TO,REPULSION RESULTS. IN FIG. 3 THE WIRE IS COILED, AND PARALLELCONNECTION RESORTED TO, AS IN THE CASE OF THE STRAIGHT WIREIN FIG. 1. THE RESULT IS THE SAME-ATTRACTION OF ONE COIL TOTHE OTHER. ONE COIL IS MADE MOVABLE. IN FIG. 4 EXEMPLIFIEDTHE SERIES COIL CONNECTION. NOTE THAT THE CURRENT CAN FLOWIN THE SAME DIRECTION EVEN THEN. THE REPULSION TYPE OFMETER IS POPULAR JUST NOW FOR A UNIVERSAL DC AND AC FILA-MENT VOLTAGE TEST METER, WHERE A SINGLE METER SERVES FOR

BOTH TYPES OF CURRENT

THE need for meters capable of meas-uring alternating currents and vol-

tages is incresing daily in proportion tothe number of AC receivers put into ser-vice. Ordinary meters adapted for directcurrent installations are useless for thispurpose.

'There are many types of meters suitablefor AC measurements. One type makesuse of a thermo-couple made of twodissimilar metals. The alternating cur-rent to be measured is made to heat oneof the junctions of two metals. Theheat generated will set up an electro-motive force which will send a smalldirect current through the circuit andthis current is measured with a sensitivedirect current meter such as a 0-1milliameter or a microammeter. Thethermo-couple can be used to measureboth direct and alternating currents.

Another type of AC meter makes useof the expansibility of a wire when it isheated. The current to be measured issent through the wire, heating it. The,expansion is measured by means of scaleand pointer. This meter also measuresboth alternating and direct current.

The Repulsion TypeA third type of AC meter makes use

of the mechanical force exerted by oneconductor upon an adjacent conductorcarrying current. rt is, known as therepulsion type meter because the forcesare so adjusted that one conductor re-pels the other. We, shall discuss theprinciple of this meter in greater detail.

Suppose two wires A and B in Fig. 1

are mounted close to and parallel toeach other and subjected to some tension.If the two wires are connected in seriesand a current is caused to flow throughthem in opposite directions the wires willattract each other, as shown in Fig. 1.Now, if the two wires are connected in

parallel, as in Fig. 2, the currents in bothwill flow in the same direction and thetwo wires will repel each other. Thewires will bulge outward as shown.

These two cases come under the generalrule that two bodies charged oppositelyattract each other and that two bodiescharged in the same sense repel eachother, or that two unlike magnetic polesattract and two like pole repel.

Coils RepelFig. 2 contains the principle of the

repulsion type of meter, as well as theprinciple of the repulsion type of motor.

Suppose two coils are mounted so thatone is inside the other and in the sameplane. The turns in the two coils willthen be parallel. Let one of the coilsbe rigidly mounted and one so that itcan turn easily about a pivot. Connectthe two in parallel as in Fig. 3. Thisconnection is the same as in Fig. 2, theonly difference being the coiling of thewires. Connect the terminals across abattery. Current will flow in both coilsand at every point the two currents willflow in the same direction.

Thus one coil will repel the other. Sinceone coil is fixed and the other is pivotedthe moveable coil will turn. This turningis resisted by a spring. The angle throughwhich the coil turns will depend on thestiffness of the spring and on the in-tensity of the current flowing in the coils.It also depends on the number of turnsin the two coils. Hence to make a sen-stive repulsion type meter a large numberof turns and a weak spring should beused.

If the battery supplying the current isreversed the current will be reversed inboth coils and the direction of the turningwill remain the same. Therefore, thistype of meter will measure alternating

currents as well as direct. In otherwords, the meter is a universal motor.

Connected in SeriesIt is clear that the two coils can be

connected in series and still have thecurrent in the two coils flow in the samedirection. This is shown in Fig. 4. Avoltmeter built on this principle shouldbe connected in series while an ammetermight better be connected in parallel. Inuniversal motors the stator and the rotorcoils are either connected in series orin parallel,( just as as they can be inmeters.

The repUlsion principle is invoked inseveral popular meters today, particularlymeters used for measuring the voltageof AC tube filaments. This is important,because some of these tubes, like the -27,are short-lived when over-voltaged. Onemay introduce a resistance at the inputto the filament transformer (in the pri-mary circuit) and, by watching the meterin the filament circuit, testing a singletube while the other tubes in the set arestill working, can make sure the voltageat the filament of the -27 does not exceed(2.25 volts. In fact, many experienced setbuilders prefer the slightly lesser gainobtained at 2 volts, because of the muchlonger life of the tube and the conse-quently reduced need of replacement,even though 2.5 volts are regarded as"safe."

Such a replusion type of AC -DC meterwhere one instrument serves both pur-poses, is employed in the Universal AC -DC Scientific Set Tester and TroubleShooter. It is well to use a high resist-ance voltmeter, to determine plate volt-age, in addition to the replusion meterand the double reading DC milliammeterincorporated in the foundation unit.

Kennedy Is AppointedJensen Representative

James A. Kennedy, formerly vice-pres-ident and field executive of Arthur H.Lynch, Inc., has severed his connectionwith that concern to become the metro-politan representative of the Jensenelectro-dynamic speaker. The JensenRadio Mfg. Co., is located in Oakland,Calif., and Mr. Kennedy's office is at1775 Broadway, New York City (GeneralMotors Building). Telephone, Circle 7571.

Mr. Kennedy was congratulated by hisfriends on obtaining this attractive line,to which he is devoting all his time, asit was a tribute to his sales ability andpopularity. One of the heartiest hand-shakes came from Arthur H. Lynch him-self, who also handles a loud speaker, theDecatur, also William H. Beardsley,treasurer of the Lynch organization, con-gratulated Mr. Kennedy and induced himto have his office in the same building, sothat the three of them would not loseconstant touch with one aonther.

Mr. Kennedy was reluctant to leave theLynch organization, but the Jensen Com-pany wanted an exclusive office to takecare of the sales volume. The Jensenspeaker is taking the country by storm.


A Good Antenna Is BestA- /97- TOP FLAT TOP

4

IY TENNA

E2

FL/9T TOP

A---VER 77 CAL

GROUND ROUNDLEADLE -17D 111P

COC/NTER PO/SE

FOUR DIFFERENT ANTENNA CIRCUITS. AT THE LEFT A REGULAR ANTENNA AND COUNTERPOISE ARESHOWN. THIS IS PARTICULARLY SUITABLE FOR SHORT WAVES AND WHERE A GOOD GROUND IS NOT AVAIL-ABLE. LEFT CENTER SHOWS THE REGULAR ANTENNA AND GROUND CIRCUIT. RIGHT CENTER THE SAMECONNECTION IS USED EXCEPT THAT A CONDENSER C IS INSERTED IN THE LEADIN TO MAKE THE CIRCUITEFFICIENT ON SHORT BROADCAST WAVES. AT THE RIGHT THE SAME ANTENNA IS SHOWN WITH A LOAD-

ING COIL L IN THE LEADIN TO ADAPT CIRCUIT TO LONGER WAVES.

PL..9T TOP

--VERr/cRL

By James

\VERr/cRL.

4 -----GROUND ---GROUNDLEAD LE AD

0 NE of the most important factors con-ducive to good radio reception is the

one that is most frequently overlooked inbuilding and installing the set. And that is,the means of picking the signals out of theair, whether outdoor or indoor antenna, loop,light -socket pickup, etc.

The greatest magician (radio, electric orof the stage) cannot reproduce a signal thatis not picked up.

A conservative estimate would be that not25% of all the antennas in the country thatfeed the 12,000,000 receivers in use through-out the nation are 100% efficient. A setis purchased by the layman (we are not nowspeaking of the experienced fan or setbuilder), and a makeshift aerial is hastilyput up, either on the roof or indoors; theset performs seemingly beautifully but, alas,it is by no means working with 100%efficiency. If it does one-half of what aproperly calculated and rightly installed an-tenna system would do, it is performingmiraculously.

Twisting and TwirlingThe locals probably come in with good

volume and occasionally, through somefortuitous accident, some distant station, butpoor John Layman sits many a night throughtwisting, twirling, thumbing and perchancekicking at the unfortunate dials, but nothingelse seems to be on tap. The desired sta-tions are there for the "asking," but hisantenna does not "ask." The set ownerhears his more advanced friends crowingabout distant stations they bring in regu-larly and he naturally blames his lack ofDX on his set, and yet, the set may becapable of outdoing even the records of hisfriends.

Almost any one of the present-day re-ceivers will bring in good results if the lo-cation is fairly good, if the set is properlyhandled, and if fed by a good antenna sys-tem.

The Constants of an AerialWith the coming of summer, the present

is a good time to consider the aerial, clean-ing it, revamping it, as it were, or installinga new one complete from end to end with aneye to the utmost in efficiency.

The first step to this end is the con-sideration of its constants. Whether your

antenna is an excellent, poor or mediumpickup of the radio waves depends mainlyupon its constants. These are its electricalproperties which can be determined by exactmeasurements, or computed to a fair enoughdegree for ordinary requirements by anotherof its properties, namely, its effective height.

The term constant is not a fixed one byany means, because some of these electricalproperties of the antenna vary greatly withthe length of the radio waves to which theantenna is attuned. But at any particularwavelength, the constants of an aerial whenused with a ground, will remain practicallythe same.

Accumulations of dirt, snow and ice willaffect the constants of the antenna. However,these changes and variation will not affectthe aerial of the home receiver to any, seriousextent. They are only serious in the casesof laboratory experimental equipment withwhich we are not at present concerned.

Importance of Electrical PropertiesUsing the term constants to cover the elec-

trical properties of our proposed antenna, wefind them to be inductance, capacity,resistance and the resulting fundamentalwavelength. Antenna inductance is an in-herent electrical inertia which retards thechanges in the rapidly reversing current in-duced in the antenna by the incoming radiowave.

The antenna capacity is a property whichenables it to hold a certain electrical charge,afterwards to discharge this in the form ofelectrical energy through the receiver intothe earth. This capacity is expressed inmicrofarads.

The aerial's resistance is the oppositionwhich it offers to the flow of the high -frequency currents induced in it. High -frequency, or radio frequency, currents flowonly on the surface of a conductor. Itfollows, then, that if the surface resistanceis increased the efficiency will be reduced.

Functions of Antenna ConstantsThis antenna resistance is a complex

quality, but it may readily be expressed inohms. The length of the wave to whichthe antenna will respond when it is con-nected directly to earth is the fundamentalwavelength of the antenna. Thus, if anantenna has a fundamental wavelength of

710 kilocycles, strong electrical vibrationsor oscillations will be set up in the receivingantenna by a transmitting station that issending out signals on 710 kilocycles.

If the inductance and capacity of your an-tenna are increased its fundamental wave-length is also increased. However, the ca-pacity is more easily changed than the in-ductance. The resistance has little effect onthe fundamental wavelength, but if theresistance is increased the current inducedby the radio wave is decreased.

Thus we may connect a variable con-denser across the terminals of our tuningcoil to vary the capacity and thereby increasethe wavelength to which the complete an-tenna system will respond. This gives usa remedy for many tuning troubles in vari-ous types of receivers.

These facts are important to rememberto get the most out of our antenna installa-tion. The smaller the dimensions of ourcomplete antenna system, the less the energyit will pick up, ergo, less volume on localsand weaker signals on distant stations, butthe greater the selectivity. Extraneousnoises, like static, nearby and local electricalinterferences and discharges, however, willbe loud enough to annoy the most insensitiveear.

This small antenna must be kept perfectlyclear of all objects that will have a shieldingeffect to insure functioning with even smallefficiency.

Do not get the impression from this thata small aerial is useless, for in many casesa short aerial is the only available one, andit can be highly efficient.

Other Contributing FactorsMany factors should be considered in set-

ting up your antenna. Avoid freak installa-tions, hoops, triangles, balloon, umbrella andother unusual forms. Usually, the straight,single wire is best, with the lead-in takenoff from the end pointing toward the stationsfrom which you favor reception. If theantenna slopes, the high end should be fav-ored for lead-in.

Continuing the antenna throughout for thelead-in, right to the binding post, avoidslosses from improper connections as it is notalways possible to solder the joint perfectly.

Considering the constants and meeting ,

them as nearly as possible in the antenna


Aid to DX and VolumeCarroll

will give the best results.With a two -wire antenna you will have a

higher fundamental wavelength which isdue to higher capacity and inductance ascompared with a single wire.

In figuring out your antenna constants itis not possible to.be exact unless you havethe equipment. It is merely our purpose toenable you to get better results than thoseordinarily obtained. Figuring on first yourlocation, the swing allowable and the di-rection to be favored, the constants may nowbe figured with an eye to the length andheight. However, as to height, the higherthat one is able to erect the antenna, thebetter.

Installing the Antenna SystemBear in mind, before proceeding with your

installation, that a high antenna not onlymeans lower capacity-i. e., the electricalcapacity existing between the aerial andground-but it also means a longer lead-in wire which is part of the aerial system,and the value of which must be consideredin calculations of wavelength. The naturalwavelength of your antenna should never begreater than the lowest wavelength to bereceived. A rough approximation of wave-length in meters is obtained by multiplyingthe linear length by three.

Keep the antenna and lead in as rigid aspossible in order to avoid swaying whichresults in fading effects upon reception.Keep the lead-in away from and clear ofall obstructions. After the wire has beenbrought into the room, it should not betacked to the wall.

Many sizes of wire are used, insulatedin many forms, but number 14 copper wireis large enough for efficient reception in allaverage installations. The larger, or strandedwire is better only insofar as it is mechanic-ally stronger. The resistance is lower on agreater surface area, but there are so manyother features of resistance involved in prac-tice that a larger conductor than this isnot necessary for our purpose. The wireused may be bare or insulated and enameledwire is good as it offers better resistance todirt and .oxidization.

Importance of Proper GroundAs we have pointed out before, all con-

nections should be soldered, if possible thusinsuring permanently low resistance. Thewater pipe makes the best ground and theradiator pipe is next, if the former is notavailable. Never use a gas pipe or anelectrical wire conduit for this purpose. Theground connection can best be made with aclamp, being sure that all contact surfacesare absolutely clean and insuring this by aliberal use of sand or emery paper. Makethe ground wire as short as possible.

If the location should be so unfortunatelysituated that any form of natural ground isnot available, an iron pipe driven deep intomoist soil or a copper plate buried in theearth may be used. As a last resort, acounterpoise, which is simply another aerialsuspended near the surface of the earthunder the working antenna may answer thepurpose. This counterpoise may consist ofseveral wires paralleled.

A high antenna should be supported bymasts, preferably of wood, well braced.Lower antennas may be supported fromchimneys, dumbwaiter tops, adjoining higherroofs, etc., but in every case should be wellinsulated and kept free and clear from allobjects and other aerials.

Get Yours HighestIn the case of a multiplicity of aerials, run

yours above the highest and at right anglesto the nearest. Good insulators are now to

be had everywhere but glazed porcelain is bestfor this purpose.

In case the fundamental wavelength of theantenna proves to be above 250 meters, acondenser connected in series with the lead-inwill adjust it. If a fixed condenser is used,its capacity should be around 0.0003 micro -farads. A variable condenser connected inseries with the coil or shunted across theterminals will allow for a wider tuningrange. If trouble is experienced in takingthe lead-in from either end of the antennait may -be taken off from the center. Al-though the single wire antenna is most effi-cient, if space is limited, a two, three orfour wire cage antenna will answer, figuringthe fundamental wavelength as of the singlewire originally intended.

If the reciver is of the tuned radio fre-quency type or has a regenerative tuner, it isnot necessary to install a high antenna.However, if the receiver utilizes but onestage of radio frequency amplification witha non -regenerative detector, it is well tohave the antenna as high as possible remem-bering to keep it clear of all obstructions.

Connecting the receiver in the ground lead,close to the ground, will increase the effec-tive working height of the antenna and im-prove reception. There are many opinionsand ideas of improving reception by unortho-dox installations, but the foregoing facts arebased on sound principles and should givebest results. No means of picking up sig-nals is better than a good aerial system.properly installed.

How to Get Long LifeFrom Your AC Tubes

Ask the first AC set owner you meetjust what the value of line voltage is in hishome. The answer will undoubtedly be:"Why, 110 volts, of course !" He may evenappear offended that one should question hisknowledge of so fundamental a radio andelectrical matter.

His answer may be correct-and thenagain it may not be.

The true value of voltage at the con-venience outlet or lamp socket actually maybe anywhere from ten to twenty-five voltshigher. One prominent manufacturer ofAC sets states that the value of voltage usedin New York City for radio operation iscloser to 130 volts in most cases than to 110volts.

No one can tell the exact AC voltagevalue in his home if he has not checked itwith an accurate AC voltmeter. Failure todo this very thing has resulted in no littletrouble and needless expense to thousands ofowners of AC sets, because tubes in the re-ceiver, exposed to excess voltage, have beenblown out or their life reduced. AC tubescost anywhere from $3 to $6 apiece, de-pending upon the type. One set of tubesruined, or even the useful life cut in half,involves an expenditure far greater than thecost of checking up on line voltage and mak-ing the addition of a resistor to cut downvoltage to the correct value.

Filament DelicateThe filament of a vacuum tube, and par-

ticularly that of the AC heater type, is adelicate thing. It will not stand muchabuse. It is made to operate at a definitevoltage and current rating. Naturally, ifthe actual values exceed those for which itis designed, a shortening of useful life, orcomplete destruction of the filament maytubes will have a life practically equal tothat of the five -volt, general purpose type,or approximately 1,000 hours.

A point overlooked frequently, is thatAC sets are usually designed to operate at afixed line voltage. Provided the incomingvoltage does not rise above the limit takenby the manufacturer in designing the set,the tubes will give long and efficient service.

Tips to Users of AC TubesHowever, a majority of commercial re-

ceivers using AC tubes has no provision forcompensating for line voltage increases abovethe point of safety.

Where the line voltage exceeds the arbi-trary value assumed by the manufacturer,immediate damage to tubes may occur, orcertainly a very marked shortening of usefullife, unless some means is taken to reducethe incoming line voltage to safe limits.

The man who has already experiencedtrouble with short tube life will be quickto profit by suggestion and immediatelycheck up on the value of line voltage inhis home. He will make certain that hisreceiver is operating within the correctlimits. For those who have recently in-stalled AC sets or are about to build or buyone, the suggestion that line voltage bechecked is certainly worth while.

Trouble with excess voltage can be fore-stalled at slight cost, and uninterrupted en-joyment of the new receiver is assured.Gambling and guessing in the matter ofline voltage can only mean that one standsan excellent chance of having the annualtube budget much higher than it should be.

Check UpIf the value of line voltage is found after

a careful reading to be above that of thearbitrary figure assumed by the manufac-turer, there is only one sensible and econom-ical thing for the wise man to do.

The work of checking line voltage is notdifficult, and can be done by any set ownerby one simple measurement and a fewequally simple computations. An AC volt-meter with range from 0 to 150 volts is usedto measure the incoming line. If the voltageis found excessive for radio operation ofAC tubes, a screw driver, and about twodollars worth of equipment will remedy thetrouble once for all. Fifteen minutes work,another check with the AC voltmeter, and itwill be found that the voltage across thetransformer primary is down to or slightlybelow the maximum figure for safe opera-tion of tubes.

For ease of handling and ready mounting,Ward Leonard Resistors of the EB type(equipped with Edison screw base) havebeen found satisfactory. They have highcurrent and watts rating.

* * *

[A table showing how to select the properresistor to eliminate the excess live voltagehas been prepared by Ward Leonard Elec-tric Co., 31 South Street, Mt. Vernon, N. Y.,and will be sent free on request to the com-pany. Mention RADIO WORLD.]


Electrical Recording

Nml

10 100 1000FreqUer1C7

FIG.1CURVES ILLUSTRATING THE PROCESS OF EQUALIZATION OF TRANSMIS-SION IN THE EQUIPMENT FOR BROADCASTING ELECTRIC PHONOGRAPH

RECORDING AND IN HIGH QUALITY AUDIO AMPLIFIERS.IT electrically recorded? Every buyer

1 of phonograph records asks that question.If the record in question is not electricallyrecorded the prospective buyer will not haveit, because he knows that quality reproduc-tion is not possible with it.

What makes the electrically recorded pho-nograph record so superior to the old me-chanically produced record?

The answer lies in equalization. And whatis equalization? There is where our storybegins.

In the process of recording there are manymoving parts which are actuated by thesound to be recorded. These moving partsMust move in exactly the same manner asthe sound waves impinging on the dia-phragm. If they do not, the record willnot be the equivalent of the sound, and thereproduction will be distorted.

Moving Parts in ReproducerThere are also moving parts in the repro-

ducer. The record must make these partsmove in the same manner as the undula-tions in the groove. If they do not, thesound reproduced will not correspond withthe sound recorded.

Thus there are at least two sources of dis-tortion in mechanical recording and repro-duction. One is the possibility that the re-cording mechanism does not follow theoriginal sound accurately and the other isthe possibility that the reproducing mechan-ism does not follow faithfully the recordas it exists.

There is of course the possibility thatone of these sources of distortion counter-acts the other, but that possibility is veryremote. The two sources of distortion areboth of the same type, that is mechanical,and hence they are additive, so that the netdistortion may be very great. That they areadditive no one will dispute who has playedthe same composition with the mechanicallyand the electrically produced records.

Mechanical ImpendancesSound is a vibratory phenomenon. There-

fore the record will be undulating or waveshaped, the complexity of the wave depend-ing on the complexity of the sound. To

10000

produce this undulating groove the recordingand the reproducing mechanisms must vi-brate. But all the moving parts havemechanical impedance, that is, they resistrapid changes in position. And this im-pedance varies with the frequency of thevibration.

A heavy mechanism will resist rapidvibrations more than slow. Therefore thehigh notes will neither be recorded nor re-produced accurately. The low notes willfare much better. Thus the fidelity of thereproduction would be better the lower thepitch, if there were no other factors.

But there is also resilience in both therecording and the reproducing mechanisms,that is there is spring action. The two dia-phragms are the main sources of resilience.

Spring action is just opposite to mass ac-tion. Whereas mass retards the high notes,spring action retards the low. A spring orother resilient mechanism offers very littleimpedance to high frequencies and verymuch to low. Therefore the diaphragms andother springs involved in the processes ofrecording and reproduction suppress the lowpitch sounds and brings out the high.

Resonance EffectsIt would seem then that neither high nor

low notes would be recorded or reproduced,looking at the problem from one point ofview. Or it would seem from another pointof view that both the high and low are re-corded and reproduced equally well. Butthere are many more effects which causewide differences between the original andthe reproduction.

Resonance perhaps is the greatest of theseeffects. At one or more frequencies theretarding effect of resilience will just neu-tralize the retarding effect of massivity. Atthis frequency there will be very little im-pedance in the moving parts. A sound ofthat frequency will exaggerate the undula-tions in the record and the reproducedsound.

At frequencies near the resonance fre-quency there will be some exaggerationbut less than at the exact frequency ofresonance. This exaggeration usually fallsin the middle registers. Hence the middle

By Sebastiannotes will be reproduced enormously louderthan either the lowest or the highest.

The resonance frequency of the recordermay be different from that of the repro-ducer.' In that case there will be at leasttwo frequencies which will be exaggerated,but much less than if the two resonancepoints occurred very close together.

Even when there are two resonance pointsthe high and the low notes will not bebrought out as well as those in the middleregisters, and the reproduction will not begood. However, one resonance may fall ata very high audio frequency, in which casethe high notes would fare well.

More Than Two Resonance PointEven when we confine ourselves to the two

diaphragms there will be more than tworesonance frequencies. In fact there willbe many for each diaphragm. Every oneintroduces distortion to some extent.

But all the distortion possible is not con-fined to the moving parts. Some of it isintroduced by the horn sound collector ofthe recorder and of the sound distributorof the reproducer. Any horn of reasonablelength usually `cuts out the low notes, andit is in the two horns perhaps that mostof the distortion enters. Most of the oldphonograph reproduction was painfully weakon the low notes.

Resonance in the horns also contributes tothe distortion. Both the recorder and thereproducer horns have several resonance fre-quencies which are both recorded and re-produced too loudly in comparison withother frequencies.

Electrical RecordingElectrical recording presents a different

picture. The sound collector is a micro-phone such as is used in broadcasting. Alltroubles introduced by the horn are elim-inated at once. The microphone is so con-structed that it is almost equi-sensitive forall frequencies. To be sure, the diaphragmhas resonance points, but they can be dampedout to any desired extent. And they are.Low volume of output is of no consequence,for it can be amplified. In mechanical re-cording all the volume possible must bepreserved, for it cannot be amplified. Vol-ume by resonance is depended on largely.

The microphone is subject to one diffi-culty. The very high notes are picked upwith about twice normal strength. But thatis only a momentary difficulty.

The output of the microphone then is afaithful electrical copy of the sound thatfell on the diaphragm. But it is weak. Itis necessary to amplify it, and for that ahigh quality audio amplifier is used. Theconstruction of an audio amplifier whichwill preserve the relative, intensities of thehigh, the middle and the low notes is simple.This is not one of the problems of electricalrecording.

The RecordingBut the output of the audio amplifiermust actuate the recorder. This contains

moving parts, 'which contain mass andresilience. Thus it will take more powerto record the low and the high notes thanthe middle. And resonance is possible. Asin the microphone, resonance peaks can beleveled down by damping and it is onlynecessary to increase the amplification tobring the output up to the required value.Thus the record will be a faithful copy inwax of the original sound, provided thatthe lows and the highs are up to normal.More leveling is necesary to bring them upif required.

EqualizationAt this point equalization enters the pic-ture. If the record will not be a faithful

June 16, 1928 RADIO .WORLD 13

ffects EqualizationGroot

copy of the origitial sound when the elec-trical system is faithful, there is no reasonwhy the electrical system should be keptfaithful. After all, it is only a link betweenthe original and the reproduced sounds.Distortion can be introduced into the elec-trical system, provided it is of the rightkind and amount, to make the undulations inthe record an exact copy of the originalsound. That is what is done. And theprocess of introducing the right amount ofdistortion, of proper frequency distribution,to make the record faithful to the original,is called equalization.

Filters and NetworksEqualization is accomplished by means of

suitable electrical networks or filters com-posed of inductance, capacity and resistance.The distortion in the record without theequalizer is measured and then the audioamplifier and filter are designed so as justto effect equalization.

When that amplifier is used for recordingthe undulations in the record will correspondfaithfully to the original sound.

Now suppose we have a record which inevery respect is true to the original sound.Will the reproduced sound from every pho-nograph also be faithful? It will not. Butit will be improved to a marked extent.If it is true that the horn of the reproduceris the main cause of distortion in the re-production the low notes will be weak evenif the record is true.

Intentional ExaggerationThis weakness in the reproduction of low

notes in the average phonograph can becorrected in the recording by so designingthe electrical equalizer as to over -exaggeratethe low notes.

What constitutes proper over amplifica-tion and recording of the low notes woulddepend on the length of the horn on the re-producer. No two types of phonographshave the same length of horn. Hence ifthe over amplification is made correct forone horn it will not be sufficient for ashorter horn and it will be too much for thelonger horn. The reproduction from themachine with the shorter horn will lackdepth, that from the machine with the longerhorn will be boomy.

Electrical Reproduction

When the record is played mechano-elec-tricallv another problem enters. When agood pick-up unit and a high quality audioamplifier and loudspeaker are used the re-production will be true to the undulations inthe record. If the record has been exag-gerated on the low notes the output of theloudspeaker will be boomy, comparable withthat from the best phonographs with longexponential horns.

The reproduced sound will not be faith-ful to the original but somewhat exaggeratedon the base notes.

Big Power All RightBut this is not a weakness of the electrical

system of playing, for it is better to have agreat deal of power on the low notes than tohave them weak and almost inaudible. Ifthey are too strong to suit the individualit is a simple matter to suppress them tothe desired extent. The simplest methodperhaps would be to connect a condenserin series with the speaker. The smaller thiscondenser is the more the low notes willbe depressed. It is much easier and lessexpensive to depress the volume on lownotes, than to build it up if it is weak.

PICKUP

(Fia. 13)

LOUDSPEAKER

0RECORDER

O

PHOIslOaRRPH(FIG. C)

FIG. 2

A. THIS SHOWS A POSSIBLE ARRANGEMENT FOR EQUALIZING PHONO-GRAPH RECORDING. THE MICROPHONE IS FOLLOWED BY A HIGHQUALITY AMPLIFIER, WHICH IS FOLLOWED BY THE EQUALIZER NET-WORK. FINALLY THE EQUALIZED SIGNAL IS DELIVERED TO THE RE,CORDING MECHANISM. B. THE ESSENTIAL STEPS IN ELECTRIC REPRO-DUCTION OF PHONOGRAPH RECORDED SOUND. C. THE ESSENTIALS OF

MECHANICAL PLAYING OF A RECORD.

Audio EqualizationAnd Its Workings

The principles of equalization are shownin the curves in Fig. 1. A shows a char-acteristic in which both the high andthe low notes are suppressed while themiddle are transmitted too strongly. Thehump indicates either regeneration or re-sonance, or both. B shows a characteris-tic which is almost the reverse of A.There is a sharp depression in the middleregisters. If a circuit having the char-acteristic of B is combined with an am-plifier having the characteristic of A thehump in the middle is leveled.

B is produced by a condenser and an in-ductance coil in series connected acrossthe line, for example across the loud-speaker leads or across a coupling resis-tor or a transformer winding. This con-denser and inductance circuit is tuned tothe frequency of the hump in curve A.The sharpness of the dip in curve B mustbe the same as sharpness of the hump incurve A. This is effected by using moreor less resistance in series with the con-denser and the inductance.

But the combination of curves A andB is not enough to equalize the deficien-cies in A. Both the high and the lownotes must be brought up. Curve C showsa characteristic which has a high trans-mission on the low notes and a negligibletransmission on the high. This is a char-acteristic of a low pass filter of a certaindesign. It can be designed so that whencombined with A and B the low note

transmission is just brought up to thedesired level.

High Notes AmplifiedThe high note transmission is still defi-

cient because the slight rise in B is notsufficient to compensate for the drop incurves A and C. Therefore a high passfilter of suitable design must be put intothe line. D is a characteristic of such afilter. The curve is practically the re-verse of curve C. The rapid rise in thetransmission of the highs compensate forthe drops in curves A and C.

The ideal curve toward which the de-signer of the equalizing network worksis shown by curve E. It is a perfectlystraight line from the highest to the low-est frequencies. This curve should bethe overall transmission characteristicfrom the original sound to the repro-duced.

Of course it is not practical to makethe overall transmission curve straight.but any deviation from rectilinearity canbe made as small as is desired.

COLUMBIA ANNOUNCES SETThe Columbia Phonograph Company is

going into radio. A set, to 'be knownas the Columbia, will he ready early nextseason. This set will be manufacturedthrough special arrangement with theKolster Radio Corporation.


A DC -AC Electric Set,And One of the

AN77

anha

-2 2 I

s

Cho 7C/317

060ooll'

Rh2

C

Tq

J7

-27

Ca

7 / A

C12

Ci

Chi

4001

2

C

1

BOTH AC TUBES AND DC TUBES ARE USED IN THIS ELECTRIC SET

C OMPLETE electrification of receiversis now possible without the use of so-

called AC tubes throughout. Relays whichoften get out of order are dispensed with.Trickle charges to throw on and off arenot used as such. Storage batteries arebanished from the set. Only one switchis used in the set and that may be installedin the 110 volt power line. That switchcontrols the entire power for the set.

Complete electrification means that allthe voltages, A, B and C, are derived fromthe power line. How is it done withoutthe use of AC tubes throughout? Thatquestion will be answered in the descrip-tion of a four -tube all -electric receiver.

Screen Grid Tube for SensitivityTo insure the highest possible sensitiv-

ity in a four -tube receiver the first tubeshould be a screen grid tube, and this tubemust be properly operated. Another fea-ture necessary for high sensitivity is re-generation in the detector circuit. Hencea three circuit tuner is used in conjunc-tion with a standard -01A tube as de-tector.

Hum elimination demands that the fila-ments of these two DC model tubes, thatis of the screen grid and the detector, beheated with direct and steady current.How this is accomplished without the useof batteries will be taken up later.

Hum elimination also requires that thefirst audio tube be of the heater type. Thistube is ordinarily used for detection, butas it is an excellent amplifier as well as adetector it is used in the first stage ofaudio.

The power tube, which may be a -71Atube, can be heated directly from a 5 -voltwinding on the filament transformer with-

out the introduction of appreciable hum.Therefore this is done. The two ACheated tubes, the -27 and the -71A,are heated by two secondaries on thesame transformer T3 in Fig. 1.

A Battery Eliminator UsedThe steady direct current for the fila-

ments of the first two tubes in the circuitis derived from an A battery eliminator.This is made of a rectifier and a filtercircuit capable of delivering at least .382ampere. There are many trickle chargersavailable which can be operated with anoutput as high as .75 ampere. An outputof .5 ampere is considered as a low rate.Hence one of these can be used to de-liver a current of .382 ampere for an in-definite time without any danger of over-taxing the charger.

There are several types of charger cap-able of delivering a current up to .75ampere. Some are dry and operate oncrystal rectifier principle. Others aredry on the exterior but contain an activepaste which constitutes the electrolyte.Still others work on the principle of un-directional gas conduction. All of these aresuitable for the purpose of a low currentdrain A battery eliminator, and all can beobtained in radio stores.

The main element in the filter is a highcapacity electrolytic condenser. Severalmanufacturers make these condensersnow in capacities from 1,000 to 4,000 mfd.They are dry on the exterior and containthe electrolyte in paste form. They aresealed like dry cell batteries.

Choke Coils NecessaryA high capacity condenser is not suf-

ficient to take out the ripple in the out -

3

By N.

V

ff

put of the rectifier. One or two chokecoils must be used in addition. Theseneed not have a high inductance if thecapacity of the condenser is high. Neithercan chokes for this be made of high in-ductance without making them too largefor practical use.

The inductance required depends on thecurrent drain as well as on the capacityof the condenser. For a capacity of 3,600mfd. and a current drain less than 2 am-peres two chokes of .01 henry each can beused. For a current drain as low as .382ampere each choke may have an in-ductance of as high as .25 henry.

Ready made filters having two electroly-tic condensers of a total capacity of 3,600mfd. and two choke coils of .01 henry eachcan be purchased in most radio stores.The rectifier and filter of the A batteryeliminator are shown in the lower leftsection of Fig. 1. T4 is the step-downtransformer which feeds the rectifier.This transformer comes with the charger.The electrolytic condensers are labeledC13a and C13b, and the chokes Ch4 andCh5. The chokes and the condensersmay be obtained in one unit.

Voltage AdjustorA rheostat Rh2 of about 20 ohms is put

in the negative lead of the output of thefilter for adjusting the voltage applied tothe filaments. This should be set so thatthe voltage across the filament bindingposts is 6 volts. The rest of the filamentadjutment is made by an arnperite lA forthe detector and by R1, R2 and Rhl forthe screen grid tube. R1 should be afixd rsistor of 10 ohms, which is put inthe negative lead for giving a small nega-tive bias to the grid of the tube. R2 is a


with Trickle Chargerew A -Filters

C. Fellish

a

List of PartsLoLl-One radio frequency transformer

for .0005 mfd. condenser.L3L4L5-One three circuit tuner for

screen grid tube and .0005 mfd. condenser.Chl, Ch2-Two 85 mh radio frequency

chokes.Ch3-One 30 henry audio frequency

choke.Ti, T2-Two audio frequency trans-

formers.T3-One filament transformer having

one 21/2 and one 5 volt windings.R1-One fixed 10 ohm resistanceR2-One fixed 5 ohm resistor.R3-One 2 megohm grid leak.R4-One 1,200 ohm fixed resistor.R5-One 2,000 ohm fixed resistor.Rhl, Rh2-Two 20 ohm clarostats.1A-One No. 1A aznperite.Cl, C4-Two .0005 mfd. tuning con-

densers.C2, C5-Two fixed .01 mfd. condensers.C3-One .00025 mfd. grid condensers

with clips.C6-One fixed .0005 mfd. condenser.C7, C8-Two 1 mfd. by-pass condensers.

C9, C10-Two 2mfd. by-pass condensers.C11, C12-Two 4 mfd. by-pass conden-

sers.Three X Type sockets.One Y type socket (five prong).Four binding posts.Two aluminum shields.One Vac -shield for screen grid tube.Two Micrometric dials.One B battery eliminator.One trickle charger giving at least .5

ampere.One Tobe A filter.One three socket block.One 7x21 panel.One 10x20 baseboard.

5 ohm fixed resistor. This is put in thepositive to enable the grounding of therotor plates of condenser Cl. It is usedto prevent excessive filament current whenthe rheostat is turned down. The rheo-stat should have a maximum resistance of20 ohms, and it may be used for controllingthe volume.

Two separate tuning condensers Cl andC4 are used because it is considered thatseparate tuning controls are preferable toa ganged control and trimmers. Each ofthese condensers should have a capacityof .0005 mfd. The secondary coils Ll andL4 should be wound for this capacity.

The first RF transformer LOLL may beany standard coil of good make, designedfor .0005 mfd. tuning. The three circuittuner must be of special design. Theprimary L3 must have many turns on it.In a regular three circuit tuner providedwith a neutralizing winding equal to theprimary winding the entire winding maybe used for the primary with the screengrid tube. There are many three circuittuning coils on the market now whichhave been recommended. But the firstcondition is designed especially for thescreen grid tube. One of these is thatthe number of turns on the primary wind-ing be from 50 to 90 per cent of the num-

ber used on the secondary L4. If anordinary three circuit tuner is adapted forthis purpose by a ding turns to the prim-ary, it may be necessary also to add 25per cent more turns to the tickler wind-ing L5.

Sorting the WavesA radio frequency choke coil Chi of

about 85 millihenrys should be put in the45 volt lead running to the screen grid.This is for the purpose of preventingsignal current in the screen grid circuit ofthe tube from getting into the high volt-age source. To make this filtering moreeffective a .01 mfd. condenser C2 is con-nected from the screen grid to the minusA line. Another condenser C3 of the samecapacity is connected from the B plusside of L3 to the filament to preventsignal current in the plate circuit fromgetting into the high voltage source.

A choke coil Ch2 of not more than 85millihenrys is put tickler return and theplate binding post of the first audio trans-former. It prevents the transmission ofhigh frequency currents into the audioamolifier. A by-pass condenser C6 of.0005 mfd. is connected as indicatedmake detection and regeneration efficient.

The grid condenser C3 and the grid leakR3 have the usual values of .00025 mfd.and 2 megohms, respectively.

Audio Transformers UsedThe receiver is transformer coupled,

and two good audio, transformers T1 andT2 should be selected for it. The qualityof the output depends largely on thechoice of these. There are many goodones to choose from.

The output of the power tube is filteredby means of a chok ecoil Ch3 and a con-denser C12. The coil should have an in-ductance of at least 30 henrys when acurrent of 20 to 30 milliamperes flow. Thecondenser should be about 4 mfd. Itmay be larger but the use of smallervalues depresses the amplification on thelow notes.

Grid Bias Automatically Obtained

The grid bias for the heater tube is ob-tained with the aid of a fixed resistor R4placed in the cathode lead. Its valueshould be 1,200 ohms. This resistor is by-passed with a condenser C8 of 1 mfd.A by-pass condenser C9 of 2 mfd. is alsoput in the plate circuit between the B plusbinding post on the transformer T2 andthe cathode. This condenser is oftenplaced in the B battery eliminator, but itis more effective if placed where indicated.

The bias on the power tube is also ob-tained with a resistance R5. This shouldhave a value of 2,000 ohms for a -71Atype tube. It is put in the lead to themid -tap on the heating transformer. Itis by-passed with a condenser C10 of 2mfd. A by-pass condenser C11 is also con-nected between the B plus side of thechoke coil Ch3 and the mid -tap on the5 volt winding. This condenser also isoften placed in the B battery eliminator.It is more effective when connected asin Fig. 1. Note that C10, C11 and theloudspeaker all are connected to the mid -tap. This connection gives the best re -

sults when a receiver is operated by aB battery eliminator.

Any good standard eliminator giving amaximum output voltage of 220 volts at40 milliampere drain may be used. Manyof the by-pass condensers shown in Fig.1 will be contained in the eliminator andit is then not necessary to use all, or itis not necessary to use as large values.For example, C16' may have a value of 4mfd. If it has it will not be necessary tomake C11 more than 2 mfd., but withoutC16 the capacity of C11 should be at least4 mfd. If the eliminator is assembledC16 should be, omitted and put in the C11position. C17 is in the B battery elimin-ator. It is not necessary when C8 and C9are used.

Voltages UsedThe screen grid, the plate of the de-

tector, and the mid -tap on the heaterwinding for the -27 tube are all con-nected to the 45 volt tap on the voltagedivider. The connection of the mid -tap onthe 2% volt winding to plus 45 reduceshum to a great extent. The plate on thescreen grid tube is returned to the 135volt tap on the voltage divider and thereturn of the plate circuit of the powertube is to the top of the voltage divider.

For best results the detector with itsinput coil should be enclosed in a me-tallic shield at least 1/16 inch thick, andthis should be grounded. In answer tothe question "Is it really necessary to usethe shield?" which is often asked, it mustbe stated that it is necessary for bestresults. The screen grid tube with itsinput circuit should be enclosed within asimilar shield. The dotted lines showwhere the shields should be placed, thatis in reference to the plate of a tubeand the tuning coils.

There are three plugs in the circuit forplugging into a 110 volt AC source. Itis suggested that a three socket blockbe made a part of the circuit and thatthe line switch be placed between thisblock and the outlet socket in the wall.If this is done the single switch can beused for turning on and off the receiver.

A Screen Grid ProblemThe screen grid tube is a high ampli-

fier, consequently by using a given num-ber of standard tubes and comparingthem with screen grid tubes, altering thecircuit to provide high plate load im-pedances, for screen grid plates, one findsthe screen grid tubes give much moreamplification. They have been called thegreatest advance in radio tubes in fiveyears.

Operating in the other direction, onemay reduce the size of the antenna veryconsiderably, when using the screen gridtubes, even down to five feet of wiredangling behind the receiver. The vol-ume may be as great as it was when along, high outdoor antenna was usedwith other tubes. Therefore, if one re-duces the size of his aerial, and gets thesame volume, some wonder whether theextra cost of the screen grid tubes doesany more than enable one to reduceantenna size-an extra cost of severaldollars, compared with a saving of anold stretch of wire.


The Dynamic SpeakerDYNAMIC means forceful, in onesense of the word. And when that

word is applied to the electro-dynamictype of speaker it aptly characterizesthat speaker, for it is the embodimentof force. It radiates power most effec-tively.

There are many advantages in prin-ciple of the electro-dynamic speaker oversome other types. One is that there isno hysteresis loss in the iron armature,for it has no iron armature, unlike mostother types of speaker. There is practi-cally no hysteresis loss in the magneticcircuit, for the magnetic flux in the cir-cuit is constant and unvarying. It isonly variations in the flux in the mag-netic circuit which causes hysteresis loss.Since in the dynamic unit these lossesare absent the sensitivity of the instru-ment is greater, that is for a given inputof electrical energy there will be a greateroutput of sound energy. The energy or-dinarily lost in hysteresis is convertedinto sound energy.

No Rigidity

Another noteworthy advantage in theelectro-dynamic speaker is that thearmature coil is not ciiidly supported.It is free to move *ithout restraintsfrom the supports. Thus wide swings,such as will occur at the low notes, arenot impeded. Full low note sensitivityis thus insured. The flexibility of thesupport also prevents resonance effects inthis section of the unit. Thus there willbe no frequencies which will be broughtout more strongly than non -resonantfrequencies. This has a great deal todo with the naturalness of the reproduc-tion.

Of course the unit is not the entirespeaker. It is possible that the soundradiator is so constructed that resonanceeffects will enter. But there is no reasonwhy the sound radiator, a cone for ex-ample, should be mounted rigidly. Ifthis also is mounted on flexible supportsresonance effects are avoided and theradiation of sound will be uniform overthe whole frequency range, provided thatthe size of the radiator permits it.

Hemstreet Adams BrookmanThe flexibility of the supports of the

sound radiator and the armature coilinsures low note reproduction, but nothigh note reproduction. If the movingparts are heavy the rapid vibrations ofthe high notes will be impeded. Thusa necessary condition for high note re-production is that all the moving partsshall be as light as possible. This re-quires a light weight form for thearmature winding, light wire and a lightcone structure.

The coil form can be made of a lightpaper cylinder treated with shellac togive it some rigidity. The coil can bemade of fine copper wire, or better still,aluminum wire. The insulation on thewire may be enamel, for this gives theleast bulk and at the same time it isthe lightest.

The number of turns on the coil woulddepend on the diameter of the coil formas well as on the desired impedance. Asto the choice there is much latitude forthe output transformer which must beused can be made to match any powertube to any desired armature winding.

There is one important limitation. Ifthe number of turns be small a high ratiostep down transformer must be used. Thismeans that a heavy signal current willflow in the armature, which requiresheavy wire. This in turn increases theweight of the armature. The wire usedshould be finer than that which would1Se used if the coil were stationary, andthe heat generated can be dissipated bymaking the diameter of the coil largerand using fewer layers on the coil.

A small, light paper cone may be usedas the main radiating surface, and thearmature coil should be mounted directlyon this cone. This will eliminate thecoupling rod and the lateral vibrationsin this which sometimes mar the purityof the output.

As a means of forcing the cone to"take hold" of the air in front of it andof preventing the sound wave producedby the vibration from returning to theback of the unit a rather large baffleshould be used around the front of thecone. This may be made of wood or

stratched fabric. The larger this baffleis the more effective will the speaker be.

One point on which the electro-dynamicunit is superior to other types is thatthere are no pole pieces to stop thevibration of the armature coil. Thuseven on the loudest passages and thelowest tones the upit will not chatter.

The armature coil moves in a strongmagnetic field. The motion is such thatthe wire on the coil cuts the lines ofmagnetic force at right angles. Forfidelity of reproduction the turns of thecoil should always be in a constantmagnetic field. Thus the region of uni-formity of the field should be a littlelonger than the length of the coil. Ifthe turns on the coil should move intoa weaker region of the field in eitherdirection the force actuating the cone willdecrease towards the peaks of the signalwave. This would introduce harmonicsinto the reproduced sound.

Electro-Magnet Sets Up Field

The motion of the coil is very smallas compared to its dimensions and thoseof the pole faces of the magnet andtherefore the dimensions of the pole facesdo not need to be very much largerthan the coil to insure that the coil re-main in a constant field. This is particu-larly so when the coil is mounted sym-metrically with the pole faces, for thenwhen some of the turns move into aweaker field others move into a stronger.Thus the effects of non -uniformity ofthe field are cancelled nearly out.

The field in an electro-dynamic speakeris produced by a magnetizing coil carry-ing direct current. The coil may be de-signed for either low voltage or highvoltage operation. For example, it maybe wound so that when it is conenctedacross the 6 volt storage battery theproper strength of magnetic field is pro-duced. Or it may be designed so thatit may be connected to a tap on the Bbattery eliminator. It may also be woundso that the magnetizing coil can be usedas one of the filter coils in the filtercircuit.

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IN SOME SUPER -HETERODYNES A LOW PASS FILTER IS USED IN THE PLATE CIRCUIT OF THE FIRST DE-TECTOR AS WELL AS IN THE PLATE CIRCUIT OF TH E SECOND DETECTOR. SUCH A FILTER IS USED INTHE PLATE CIRCUITS OF NEARLY ALL ORDINARY RECEIVERS FO RTHE PURPOSE OF ELIMINATING THERADIO FREQUENCY CURRENTS FROM THE AUDIO FREQUENCY AMPLIFIER. IF THE LOW PASS FILTERIN THE PLATE CIRCUIT OF THE FIRST DETECTOR HAS THE SAME ELECTRICAL DIMENSIONS AS THOSEUSED IN THE SECOND DETECTOR THE INTERMEDIATE FREQUENCY CURRENTS ARE PREVENTED FROMPASSING INTO THE INTERMEDIATE AMPLIFIER AND THE RECEIVER WOULD LOOSE ITS SENSITIVITY. FORTHIS REASON IF A FILTER IS USED AT ALL IN THE PLATE CIRCUIT OF THE FIRST DETECTOR IT MUSTBE DIMENSIONED TO FIT THE INTERMEDIATE FREQUENCY. IT MUST PASS THE INTERMEDIATE FRE-QUENCY SIGNAL WITH MINIMUM ATTENUATION AND IT SHOULD SUPPRESS AS MUCH AS POSSIBLE THEBROADCAST FREQUENCY CURRENTS. A SMALL BY-PASS CONDENSER AND A LOW VALUE INDUCTANCE

CHOKE SHOULD BE USED.


Build a Dynamic OutfitBy J. W. Fitzpatrick, Jr.

13"

THE trend of public favor is towardthe dynamic speaker. Under every

possible test the dynamic unit truly faith-fully reproduces the entire musical scalerange, bringing out the basses with theutmost realism, and stand high plate volt-ages. The radio constructor, includingthe custom set builder, will be able tobuild a modern type of speaker of thiskind at moderate cost.

A practical and resultful speaker of thistype is the one illustrated, using a smallcone mounted in a baffle box, or the soundchamber of your phonograph or radioconsole. This practically the resultsof the large -sized diaphragm of linen orpaper and yet a neat, small speaker, easyto mount anywhere, handy where space islimited. It also gets away from the un-gainly effect of the large box and papercone speakers. Wide experimentationwith various sized surfaces of differentmaterials, with varying depths for unitmounting, has proven the deep baffle boxthe best means to house the dynamic unitfor finest reproduction.

Making the Baffle BoxThe baffle box may easily be made at

home, or the neighborhood carpenter willput it together for a small fee, or theseboxes may be procured already made.

Your baffle box should be constructedout of a good grade of wood, whichshould beat least three -eighths of an inchthick. The front should have an eleveninch circular opening to accommodate thetwelve -inch cone. The back of the boxshould be left open and a three-inch stripof hard wood screwed across the exactcenter for the support of the unit: Theedge of the cone should be covered withfelt to prevent rattling against the coverof the box. The edge is merely pressedsecurely against the front of the box, ex-actly behind the opening, and is held inplace by the pressure of the unit.

The cone should be twelve inches, andto accommodate this cone, the box shouldmeasure at least 13x13x10 inches deep in-side. Bear in mind that the larger thebox, the lower the frequency "cut off"point at the lower end of the scale.

The job is very simple and quickly doneif one ;c pro- with tools. The illustrationsshow clearly the details of assembling thebox, mounting the cone and attaching theunit. Any cone about this size may beused or a very fine cone for this purposemay be procured all ready to use.

Considerations in Choosing UnitThe unit must be of rugged construc-

tion to handle the full load of the new

Fanspeaker Radio Co.

Diagram of bafflebox construction,showing front andside views withexact measure-ments (at left).

power tubes without blasting. It shouldgive good volume which may be toneddown for home use, at the same time giv-ing true and natural reproduction of thefull orchestra, either turned on full ortuned low. A unit of this type is illus-trated and has given full satisfaction.

Designed primarily for this purpose, theFanspeaker electro-dynamic unit fullyanswers the purpose and helps us to buildthe complete dynamic speaker at a veryreasonable price, complete. The out-standing feature of this unit and one inwhich it differs from all others is in theuse of an electro-magnet instead of a per-manent magnet for polarization.

The advantage of the use of an electro-magnet for a power speaker will bereadily apparent to the reader when it isconsidered that an average stock modelof the unit illustrated picked up a weightof eighty-five pounds-nearly twenty-fivetimes its own weight-whereas a perma-nent magnet is considered good if it liftsfour or five times its weight. And theelectro magnet used less than one-halfampere when connected to the 6 -voltstorage battery.

Prevents ChatteringAnother advantage is that while the

sensitivity is net greatly increased, thepowerful magnetic strength allows theuse of longer air gaps without decreasingsensitivity, thereby allowing greater roomand freedom for the armature to vibratewithout striking the pole tips and chat-tering.

To get the true fundamental bass notesfrom a speaker these vibrations must bepresent in the unit and it is the low fre-

LAST AUDIOSTAGE IN SET

THE RUGGED AND POWERFULELECTRO-MAGNETIC UNIT USEDliN BUILDING THE ELECTRODY-

NAMIC SPEAKER.

quency vibrations that produce the great-est amplitude of movement in the arma-ture, so that to produce them faithfullythe unit must be low pitched and this re-quires long airgaps between the armatureand pole tips, otherwise chattering isbound to occur, not to speak of variousother forms of distortion.

If an A battery is not used with the set,for instance, if you have an AC set, or ifit is not convenient to use the A batteryof the set, a trickle charger connected tothe 110 volt AC line may be used to sup-ply the low voltage direct current re-quired. No filter is necessary between thetrickle charger and the speaker unit.

The diagram clearly shows the methodof connecting the unit for operation fromthe storage A battery.

Method of ConnectionConnecting the unit is a very simplematter. It is only necessary to connect

four wires to the completed speaker-two for the regular speaker terminals onthe set and two for connection to the Abattery or trickle charger for supplyingthe direct current to the electro-magnet

(Continued on page 22)

OUTPUT TRANS. ORCHOKE COIL AND COND.

FIL SWITCHON SET

TO 6V. A. BATT

SPEAKERTERMINALSON UNIT

'A- BATTERYTERMINALSON UN IT

The method ofconnecting the Abattery to theunit. If a tricklecharger is used,the A batteryterminals on theunit are connectedto the charger in-stead of to the setswitch.


A THOUGHT FOR THE WEEKF you want to do something big, build a

.1 television receiver, invite two hundredradio manufacturers to a demonstration ofreception, and DEMONSTRATE!

The First and Only National Radio Weekly

ladle World'. Slogan: "A radio set far every Wane."

TELEPHONES: BRYANT 0558. 0559PUBLISHED EVERY WEDNESDAY

(Dated Satarday of lame week)FROM PUBLICATION OFFICE

HESTNESSY RADIO inIBLICATIONlil CORPORATION145 WEST 45TH STREET, NEW YORK. N. Y.

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EDITOR. Roland Burke HennessyMANAGING EDITOR. Herman BernardTECHNICAL EDITOR, J. E. Andersen

ART EDITOR, Anthony SedanCONTRIBUTING EDITORS:

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ADVERTISING RATESGeneral Advertising

$ 410100..0.801 Page, T "sill" 442 Ihms34 Pim T ":7583" -. .... 211 VMSla Page. 4 ''' D. CI. 4141 Hsu 100.00sA Page. d " rk a 111 limas 15.00% Page, 4 " S. a lames IT.1101 Column, 2%"idl" 104 lines 100.001 Inch 10.00

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enter. Business Opportunities, 10 cents per word. $1.00minimum.

ETwtered as seeend-class matter March 23, 1931, atNth Post Office at New York, N. Y., under the Act etwrap 8, 1879.

Holland Clearly HearsIndia, 11,160 Miles

Cologne.A direct radio telephone service be-

tween Holland and the Dutch East Indieswas opened here at the international pressexhibition. The first message was sentby Dr. J. R. Sloetemaker, Dutch Ministerof Labor, in the presence of MayerAdenauer of Cologne and a number ofhigh German and Dutch Governmentofficials. Connection was established withthe Governor of the Dutch East Indies atBandoeng. The radio link was betweenKootwijk and Rantja Ekek.

Replies came from Malabar, India, toMeyendal, Holland. The conversation wasastonishingly clear and easy to follow,although the distance traveled by theradio waves was more than 11,160 miles.

WGY Narrow on Tele-vision

EXPERIMENTAL interest in televi-sion is running abnormally high for

a field of endeavor so far removed fromeasy development and comprehension,and so hampered in its ability to copewith the extensive interest.

So far the reception of waves modu-lated with moving vision has not been asuccess with independent experimenters,although the transmitting agencies, likethe General Electric Company and theBell Laboratories, have been able tomake commendable demonstration overshort distances.

For the time being, in the East at least,interest focusses on WGY broadcasts onits regular wave, 380 meters. Threeafternoons a week - Tuesday, Thursdayand Friday, 1:30 to 2 P. M., Eastern.Daylight Saving Time - television isbroadcast by this station.

What with the necessity of a receiverbringing in the wave, of the constructionof a scanning disc with staggered aper-tures 3S one -thousandths of an inch indiameter, of the operation of a motor inperfect synchrony with that at the trans-mitter, and of the faultless functioningof a neon or Kino lamp, all in an effortto bring in a picture 1 1/2 inches square,the difficulties are severe enough. Butif WGY is to remain the chief goal itshould transmit television at hours some-what more accommodating.

The present attitude of the GeneralElectric Company is merely to tolerate,but not encourage, independent televisionexperimenting. Martin P. Rice, managerfor broadcasting of the General ElectricCompany, recently approved a publicityrelease from his institution which setforth :

"The schedule is adopted to assistElectric Company engi-

neers in the development of a systemof television transmission and recep-tion and, while the public is welcometo experiment with the signals, itshould be understood that the planis purely experimental and subject tochange at any time. To offer circuitsor plans for a television receiver, Mr.Rice states, would be unfair, as itmight imply that the station will con-tinue indefinitely the transmission ofsignals suitable for the type of re-ceiver described."

And this from "the Father of Broad-casting !"

It is not to be expected, of course,that the General Electric Company willpublish hookups, for indeed the systemnow used may be discarded just as un-expectedly as was the one that Dr. E.F. W. Alexanderson, chief consultingengineer of the same company, describedbefore the Institute of Radio Engineerslast year. And the company no doubtis besieged by inquirers, most of whomdo not understand what television is allabout, hence the company must do some-thing to discourage the motley descent ofquestioners. But it is one thing to fortifyoneself against undesired interrogationand dodge the encouragement of televisorconstruction of short-lived utility, andanother thing to pretend to be toleratingindependent angling for the televisedwave, while actually discouraging it.

The meagre half hour three days aweek, at a very awkward period of theday, and likewise at a time when it ishard to bring in WGY at all throughoutmuch of the East, to say nothing ofpoints farther away, might well be sup-planted by television broadcasts nightly,after the program broadcasts .of the sta-tion. That would give independent ex-perimenters a fairer show, and perhapsfrom their efforts something worth -whilewould develop.

That the assistance of outside exper-_

imenters is not wholly distasteful to thecompany was proved by the short wavetests of recent memory, likewise the testsof increased power on the 380 meter wave.From all over the world reports wererequested, and these were expertly di-gested and compiled, until they lookedas important as a statistical report ofthe Department of Commerce. And theGeneral Electric Company was pleasednot only to disseminate the digested re-sults of this volunteer reporting, but sendforth its public thanks, as well. Whythe same spirit can not prevail as totelevision is hard to understand, par-ticularly as it must be assumed the com-pany is more deeply interested in thedevelopment of the art than in theadoption of any particular system oftelevision that may be developed in thesacred precincts of Schenectady, N. Y.

The company's good intentions are wellestablished even in the television field.Dr. Alexanderson two years ago wrote aspecial article, which the company dis-tributed, in which the theory and appli-cation of television were treated, withspecial emphasis on the difficulties to besolved. The distinguished engineer'slecture before the Institute, and thecompany's virtually public demonstrationof transmission and reception of televisionin Schenectady, made only a few monthsago, command public confidence. Buta more considerate and co-operativemood in the company's councils inrespect to transmission of television, sothat this great, fascinating field may notseem to be too strictly and dubiouslyconfined, would do the company noharm, and perhaps do the world at largea lot of good.

Freed's Great PatentNEARLY everybody should be sur-

prised to learn that a patent has beengranted to Joseph D. R. Freed, presidentof the Freed-Eisemann Radio Corpora-tion, on the use of by-pass condensersat radio frequencies, particularly as Mr.Freed's publicity release on the subjectsets forth that he discovered this fetch-ing use for a condenser in 1924. Someradioists remember such use respectablyprevalent in 1920, while others, of ripermemory, may go back still farther.

Nevertheless Mr. Freed is to be con-gratulated on his invention. It showsenterprise extraordinary. It puts him ina class with Fleming, deForest, Fessen-den, Armstrong and Alexanderson. Itgives him a new right to be banquetedby his many admirers. It fixes at lastthe identity of that individual to whomthe radio public owes so much. Scarcelya set user in this land, or anywhere elsein the world, for a fact, who does notappreciate the deep significance of theby-pass condenser, enemy of commonimpedance, eradicator of stray noises,killer of self -oscillation, friend of richand poor alike!

By the grant of the Patent Office (No.1,671,959) doth Mr. Freed become en-titled to the excited admiration of thepopulace. May all the blessings that suchastuteness deserves descend upon him inquantity production, and if there are anyother things that he fancies, may thegenerous gods oblige him!

'PHONE TO UNITE AMERICASThe American Telephone & Telegraph

Company is formulating plans for con-necting North and South America with asystem of radio telephone, according toa statement by Frank B. Jewett, vice-president. The proposal is first to effectan intercontinental short-wave radiophoneservice between Buenos Aires, Argentina,and New York, for which transmittingand receiving apparatus is already beingconstructed.

AC TUBE HINTOperate the -27 type tube at 2 to 2/

volts on the filament ; no more.


10 PER CENT

STATION CUT

HELD ENOUGHA "house-cleaning" on not more than

10 per cent of the wave channels in thiscountry should make the general broad-casting structure ideal from the view-point of the listener, said Paul W.Morency, field representative of theNational Association of Broadcasters,after completing a six -week tour of theMiddle West and South.

There is no apparent need, accordingto Mr. Morency, of a complete jugglingof the radio system to get the best con-ditions for the listeners. He said thatthe changes made in the wave assign-ments by the Federal Radio Commissionhad resulted in vastly improved receptionthrough the states of Texas, Kentucky,Oklahoma, Louisiana, Kansas and otherstates in the region.

Tells of "Vast Improvement""The general improvement has resulted

from reductions in power where neededand a few shifts in the waves of severaloffending stations throughout the UnitedStates," said Mr. Morency.

"If such a vast improvement as hasbeen indicated by reports from listenersin the territory mentioned has resultedfrom such comparatively few changes,it is reasonable to suppose that the com-plete picture can be clarified with com-paratively few more shifts, intelligentlymade.

"Many persons believe that the broad-cast structure must be entirely upset andrebuilt to gain radio perfection, but ap-parently this will not be necessary."

Fewer Stations NeededMr. Morency believed the number of

broadcast stations in the United Statesmust be reduced somewhat to bring theservice to the average listener up to ahigh level.

He pointed out that because of the longSummer season in the Southern andSouthwestern states listeners in thoseregions needed high powered transmitterto enable them to get clear receptionthrough atmospherics.

Shorthand MessageSent by Photoradio

A photograph of a greeting written inshorthand was transmitted by the RadioCorporation to a conference of educatorsand shorthand experts attending abanquet at Liverpool commemorating thefortieth anniversary of Gregg shorthand.

This was the first time that a messagein shorthand had ever been transmittedby photoradio and according to R. C. A.engineers, opens up new possibilities forcondensing lengthy messages and state-ments into smaller spaces with a conse-quent reduction in cost of the picturetransmitted.

The received photoradiogram wasclearly legible and even the experts as-sembled could read the message withoutthe aid of a stenographer.

WOO DISCONTINUEDPhiladelphia.

WOO, Philadelphia, owned by the JohnWanamaker store, signed off indefinitely,having decided that the station did notbenefit the store in proportion to the ex-pense.

Freed Gets a Patenton Bypass Condenser

There was Marius Latour, of France,with his claims that nearly everythinginfringed his patents.

There was the Radio Corporation ofAmerica, with its patents that requiredset manufacturers to be licensees witha lease of life or infringers doomed todissolution.

There was Lektophone in the speakerfield.

There were others.And now comes Joseph D. R. Freed,

president of the Freed -Eiseman RadioCorporation, with a patent that his com-pany says "causes almost every receiverused to be an infringement."

And the patent is on nothing less thanthe use of a bypass condenser at radiofrequencies. Conception date in 1924.Patent No. 1,671,959, granted recently.

Mr. Joseph D. R. Freed's Opinion"In my opinion," said Mr. Freed, "every

tuned radio frequency set now in use em-bodies the invention contained in theabove patent. Because of the universaluse of this principle, most engineers andmanufacturers have assumed that it wasold. However, it has proven to be an orig-inal conception of the utmost importanceand I am now being -granted a patent onthe basic rights to this invention."

Mr. Freed stated that he discoveredearly in 1924 that the only way to preventreactive coupling in the amplifier circuitsand loads common to all stages was touse the by-pass condenser method whichis the subject of the patent. Now thatthe patent is granted, Mr. Freed hasdetermined to get after the set manu-facturers and collect!

Technically, the patent is granted for"means for eliminating reactive couplingin radio circuits."

Lists SpecificationsIn his specification to the Patent Office

Mr. Freed stated :"It is well known that in tuned multi-

stage radio frequency amplifiers it isessential to eliminate all couplings be-tween successive stages. This couplingmay be either magnetic, capacitative, orreactive, or it may be due to all threekinds of coupling.

"The magnetic coupling, as is known,can be eliminated for, for instance byplacing the inductance coils contained inthe several circuits in proper geometricalrelation to each other to prevent linkageby stray flux.

"The capacitative coupling, such forinstance as may be due to the internalcapacities of the thermionic tubes em-ployed in the circuit, can be avoided, asis also known, by properly neutralizingor balancing these capacitative effects so

that capacitative coupling between stagesis avoided.

"A reactive coupling commonly occursin these circuits due to the fact that thedifferent stages of the amplifier circuithave certain leads in common. Sincehigh frequency currents flow in some ofthese common leads, and since these leadshave a certain amount of inductance, re-actance voltages are set up therein. Theeffect of these voltages is that for in-stance the reactive voltage set up by thecurrent flowing in one stage, would effectthe current which tends to flow normallyfrom the other stage through the sameconductor, thereby modulating it undulyand bringing about an undesired coup-ling between the two stages.

"Such reactive coupling arises particu-larly in the unavoidable leads between theamplifier circuits and the batteries, whichfor practical reasons are usually commonto all stages. Since these leads are ofappreciable length, they have an appre-ciable inductance, which may represent aconsiderable I.( actance at high frequen-cies, and thus bring about a substantialcoupling between the several radio fre-quency stages. This coupling may besufficient to produce undesired oscilla-tions, notwithstanding the fact that allother coupling may have been eliminatedby suitable provisions known in the art."

The Claims Freed MadeMr. Freed's claims were phrased thus :"1.-A radio circuit comprising a plu-

rality of radio frequency amplifier stageshaving thermionic tubes arranged in cas-cade with a portion of their outputcircuits in common and a condenser shunt-ing substantially all of the commonportion of their output circuits and ofsufficient capacity to keep the reactancevoltage, tending to occur in the commonportions of the output circuits, below thevalue at which it may cause self -oscilla-tion.

"2.-In a multi -stage radio frequencyamplifier circuit a plurality of thermionicamplifier tubes, each having a filament,a grid and plate, each tube having itsoutput side coupled with the input sideof the succeeding tube, the filaments ofall of said tubes having a common,grounded filament lead, a source of directcurrent connected into the output circuitsof all of said amplifier tubes and havinga lead in common with all of said out-put circuits, and a condenser connectedbetween the junction point of said leadwith said output circuits and saidgrounded filament lead, to shunt the re-actance voltage tending to develop insaid common output circuit lead."

In applying for the patent Mr. Freedsubmitted blueprints and everything!

WEBC Power HigherSo Coolidge Can Hear

Washington.Increase in broadcasting power for the

radio station situated nearest PresidentCoolidge's summer camp on the BruleRiver, in Wisconsin, was announced bythe Federal Radio Commission. The fulltext of the announcement follows:

"To make sure that the President mayhave radio reception from the outsideworld, the Federal Radio Commission hasdecided temporarily to increase the powerof station WEBC, at Superior, Wis., from

250 to 1,000 watts for evening broadcast-ing during the summer months. WEBCis operated by the Head of the LakesBroadcasting Company.

"While the Commission is standingfirmly behind its policy of not changingfrequencies or increasing power pendingits new regulation to conform to recentlegislation by Congress, it deemed thisexception necessary in the case of WEBCout of deference to the President of theUnited States."

20 RADIO WORLD June 16,'1928

tastunitiL

*I A Strong, Rugged Loud UnitThat Drives Any Cone Speaker and Reproduces

Fine Tone at Great Volume!This unit has a full floating armature,

which means that armature is mounted sothat it acts like a plunger between two setsof magnets or pole pieces. As the magnet-ization of the armature changes under theinfluence of the signal it plunges first towardone pair of pole pieces and then toward theother.

The large field magnet used insures astrong and permanent polarizing flux, whichprotects against loss of sensitivity from self-demagnetization to which some loudspeaker

o o units are subject.The cone driving pin is directly coupled

to the full floating armature at that pointon the armature where the force is greatest.This insures against loss of power throughcomplicated levers.

The sturdy construction and heavy weightof the assembled unit prevent motion of theunit itself and insure that all the power istransformed into sound.

The armature is adjustable from an exposed knobin the back.

Apex, chuck and thumbscrew supplied with ach unit!This unit stands 150 volts unfiltered. r- - -

WM filtered output the unit has stood up GUARANTY RADIO GOODS CO.,,to 550 plate volts continuously without 145 West 45th St., New York City.damage.

Please send me one cone speaker unit (Cat.1098), as advertised, with apex. I will paypostman $3.75, plus few cents extra for post-age. Your 5 -day money -back guaranty is

I accepted.

Each unit is supplied with an, apex, con-sisting of two metal plates, so that any typeof airplane cloth or cone speaker may bebuilt; also with each apex are supplied athreaded chuck and thumbnut for engagingthe pin. The screw firmly grips the pin.Besides, a 60 -inch cord with tips, is alsosupplied with each unit.The Pewertune Giant Unit, complete withapex, chuck, screw and 60" cord; total Iweight, 3 lbs. (Cat No. 1093) 33.75

SEND NO MONEY!

I Name

Address

I City State5 -DAY MONEY -BACK GUARANTEE!

KARAS SHORT WAVE SET, three tubes. 13to 750 meters, described in the March 31, April7, 14, 21 and 28 issues. Send 60 cents for thesefive issues and get blueprint free. RADIOWORLD, 145 W. 45th St., N. Y. City.

EVERY FRIDAY at 5.40 P. M. (Eastern Day-light Time) Herman Bernard, managing editor ofRadio World, broadcasts from WGBS, the GimbelBros. station in New York, discussing radio topics.

THE NATIONAL SCREEN GRID 5, describedby James Millen in April 14th, 21st and 28th issues.Fully illustrated, including picture diagrams ofwiring. Uses screen grid tube for the single RFstage, four other tubes standard. Send 45c forthese three copies and get blueprints free. RADIOWORLD, 145 West 45th St., New York City.

Take Your Choice of 5.Other PublicationsFor NEW RADIO WORLD Subscribers Ordering NOWRadio World has made arrangements-To offer a year's subscription for any one of the following publications with one year'ssubscription for RADIO WORLD-RADIO NEWS or SCIENCE and INVENTION or BOYS' LIFE or RADIO DEALER orRADIO (San Francisco).

This is the way to get two publications-for the price of one:-Send $6.00 today for RADIO WORLD-for one year (regular price-for 52 numbers)-and select any one of the other-six publications for twelve months.

-Add $1.00 a year extra for-Canadian or Foreign Postage-Present RADIO WORLD subscribers-can take advantage of this offer by-extending subscriptions one year-if they send renewals NOW?

Radio World's Special Two -for -Price -of -One Subscription BlankRADIO WORLD, 145 West 45th Street, New York City.Enclosed find $6.00 for which send me RADIO WORLD for twelve months (52 numbers),beginning and also without additional cost,Radio News, or Science and Invention, or Radio Dealer, or Radio (San Francisco), orBoys' Life (or $10.00 for a two-year subscription to one address), thereby getting RADIOWORLD and the other selected magazine, BOTH for two years. No other premium withthis offer.

Indicate if renewal.Offer Good Until

July 10, 1928.

Name

Street Address

City and State

Broadness isNot In

(Continued

overloaded long before the resonant fre-quency is reached. The output of the de-tector is proportional to the square of theinput voltage as long as the input volt-age is low. As the voltage is increasedthe output is no longer proportional tothe square of the input. Indeed, the out-put may not increase at all as the inputvoltage is increased beyond a certainvalue.

It is conceivable therefore that in tuningin a strong broadcast station the over-loading point will be reached long beforeall the tuned circuits are in resonance.For example, two of three tuned circuits

5000 -Watt StationCosts $90,000 a Year

In an article in "The N. A. B. News,"organ of the National Association ofBroadcasters, Adelaide L. Fitch gives atabulated expense list of a typical 5,000watt station, with a total expenditure of$90,000 for one year. The article follows :

$90,000 was spent by a representative5,000 watt station last year. The distri-bution of costs is shown below, and wethink the amount spent on each depart-ment shows careful thought and planning.Perhaps the Program Department spenta little too much in comparison with theCommercial Department, but this can beremedied, if necessary, this year.Commercial Dept.

(Two people) 5% $ 4,500Program Dept.

(Five people, includingannouncers) 35% 31,500

Engineering Dept.(Six -men) 25% 22,500

Publicity Dept.(One man) 3% 2,700

Office Service & Supplies(Two people) 7% 6,300

General Overhead(This includes taxes,insurance, rent, depre-ciation and othercharges 25% 22,500

100% $90,000

forBetter Radio

It's out at last-"The Gatewayto Better Radio"! And it's fullyworth waiting for-a big, 36 -pagemanual, with 88 illustrations and20,000 wards of practical radioinformation. Only 25 cents per

copy, either from your dealer or by remittingstamps or coin toAmerican Mechanical Laboratories, Inc.

Specialists in Variable Resistors285 N. SIXTH ST. BROOKLYN, N. Y.

C 1 ARMTAT-.1140sy pst. O '

Radio World'sTRADE SHOW NUMBER

Published last week. Dated June 9th.Six solid pages of the new things at theChicago Radio Show. 15 cents a copy,postpaid. Radio World, 145 W. 45th st.,New York City.-(Advt.)

NO OTHER PREMIUM OF ANY KIND WITH THIS OFFER RECENT ISSUES of Radio World, 15c each.Be sure to give date of issue when writing. RadioWorld, 145 West 45th Street, New York City.


in Set,Transm issionom page 8)

in a receiver may appear sharp but thethird has no apparent effect on the volume.The detector is then overloaded, or nearlyso, for all settings of the third condenser.

The remedy is to limit the input to thecircuit so that the detector will not beoverloaded at any time, even when all thetune*i circuits are in exact resonancewith the desired signal. This remedy mayrequire shielding of the set, as in the sec-ond case discussed above, and also theinsertion of some volume control in theantenna circuit.

A spark signal may come in at all set-tings of the tuning condensers even whenthe receiver is very selective.

Even for Low PowerPower Tube Helps

Some persons, even grandparents, preferlow volume. They never use enoughvolume to require a power tube. How-ever, that is no reason why they shouldnot use a power tube. True, they canget along well enough without one, butif they do use one they will improvequality.

The power tube is likely to have animpedance with which the speaker im-pedance works better, particularly if anup-to-date speaker is used., as is frequentlythe case.

Bakelite Front and Aluminum Subpanelfor the

4 -Tube Screen GridDIAMOND OF THE AIR

Five -Day Money -Back Guaranty

ON

$5.00

ft5View of the Completed Receiver, using Drilled Front Panel and Aluminum Subpanel

Finest eye appeal results from construction of the 4 --tube Screen Grid Diamondof the Air when you use the official panels. The front panel is bakelite, alreadydrilled. The subpanel is aluminum, with sockets built-in, and is self -bracketing.Likewise it has holes drilled in it to introduce the wiring, so nearly all of it isconcealed underneath set. Make your set look like a factory job.

Front panel alone, bakelite, drilled $2.35Aluminum subpanel alone, drilled, with sockets built-in 3.00

Screws, nuts and insulating washers supplied with each subpanel.

GUARANTY RADIO GOODS CO.145 WEST 45TH STREET NEW YORK, N. Y.

[A few doors east of Broadway]

RADIO WORLD SEVEN WEEKS, $1.004 -TUBE SHIELD GRID DIAMOND OF THE AIR BLUEPRINT FREE WITH EACH SUCH SUBSCRIPTION!At 15c per copy, each week for seven weeks, Radio World costs you following the blue print, can build a distance -getting and voluminous

$1.05, but if you subscribe for seven weeks at $1.00 you will also get the set, the parts for which list remarkably low.official blueprint of this circuit FREEI The blueprint was designed by The new shielded grid tube is used as the radio frequency amplifier.H. B. Herman from the original laboratory receiver. Size of blueprint, That is why the amplification finally ,is boosted forty times over and27 x 27 inches. All connections, leads, parts, etc., shown actual size, above what it would be if an -01A tube were used instead.Very simple to follow. Such simplicity of construction marks the receiver that it can be

Home constructors of radio receivers, and custom set builders, by completely wired, skillfully and painstakingly, in two and a half hours.DISTANCE JUST ROLLS IN THOUGH SET IS EASY TO TUNE!

All you have to do is to follow the official blueprint, and lot a new Great stability! No neutralization required! No shielding necessary!world of radio achievement is before you! Distant stations that four -tube You'll be overjoyed. But you should place every part in exactlysets otherwise miss come in, and come in strong. No tuning difficulty the right position. Stick to the constants given, and, above all, wireis occasioned by the introduction of this new, extra powerful, startling according to the blueprint!tube, but, in fact, the tuning is simplified, because the signal strength When you work from this blueprint you find that every part isis so much greater. shown in correct position; and every wire is shown going to its correctThe circuit consists of one shield grid stage, detector and two trans - destination by the ACTUAL ROUTE taken in the practical wiring itself.former audio stages, with 112A in the last stage.

When you work from the official wiring diagram you find everything Mr. Herman's personal set was used as the model. This is a matter-of-sofact blueprint, with solid black lines showing wiring that is above thedelightfully simple that you marvel at the speed at which you get the subpanel, and dotted lines that show how some of the wiring is doneentire receiver masterfully finished. And then when you tune in-more underneath.marvels! 'Way, 'way up, somewhere around the clouds, instead of onlyroof hi h, willzat find the amplification! Everything is actual size.

EVEN A NOVICE CAN BUILD THIS CIRCUIT SUCCESSFULLY!RADIO WORLD. 145 West 45th St., N. Y. City.Enclosed please find:

than you ever expected you could get on four tubes-and the parts areNAME I well within the range of anybody's purse.ADDRESS I Complete official list of parts given on each blueprint; also theschematic wiring diagram (besides the picture diagram of the wiring.)CITY STATE

I SEND YOUR ORDER TODAY!

Not only is the actual size of the panel holes and instruments given,0 MOO, for which enter my name on your list of mail subscribers for seven but the dimensions are given numerically. Besides, it is one of thoseweeks and send me FREE at once one official blueprint of the Four -Tube Shielded delightful blueprints that novice and professional admire so much-oneGrid Diamond of the Air, as designed by H. B. Herman, and described by him of those oh -so -clear and can't -go -wrong blueprints.in the February 4th, 11th and 18th issues of Radio World. No other premiumthis offer. 0 45c extra for Feb. 4th, llth and 18th issues. Be one of the first to send for this new blueprint, by all means, andRenewal 0 Present subscribers may renew for seven weeks under this offer. I build yourself this outstanding four -tube receiver, with its easy control,Put a cross next to word "Renewal."

i, fine volume, tone quality, selectivity and utter economy. It gives more

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NEW SHIELDED GRID TUBES for Dia-mond, S -M Six or Laboratory Super, Tyrman 70.Price $5 each. Philip Cohen, 236 Varet St.,Brooklyn, N. Y.

CHARGE Radio 'A' and 'B' Batteries at Home.Bulb type charger, 21/2 ampere. $6.50 complete.Silent operation. High efficiency. Satisfactionguaranteed. Shipping weight 9 lbs. UniversalRectifier Co., 106 2nd St., N.E., Charlottesville,Va.

RADIO-Fastest growing business is the treat&Arc you sharing the profits? Let as show raghow. No selling. Free booklet. Co-OperotheRadio Doctors Dept. W, 131 Eases St., BalmMass.

"CALIFORNIA STATIONS" Three in onenight, 3 tube Foreign Circuit Blueprints 50c.A. R. S., Box 18, White Plains, N. Y. 6-30.28

GUARANTEED 'Safety Razor, with strop, is mat,strong carrying ease, 25 cents. First-class. new.Send coin, hI 0. or stamps.-P. Cohen, 236 VaretStreet, Brooklyn, N. Y.


"DOUBLE R"METERS

Our Complete Cotalogueof Meters is Contained

in This AdvertisementPOCKET AMMETER

No. 1 -For testing dry cells, 0-40 ampereDC scale pocket meter $1.50

POCKET AND PORTABLEVOLTMETERS

No. 8 -For testing A batteries, dry or stet-age, 0-8 volts DC scale $1.65

No. 10 -For testing A batteries, dry or st-age, 0-10 volts DC scale 1.65

No. 13 -For testing A batteries, dry or stor-age, 0-16 volts DC scale 1.66

No. 50 -For testing B batteries, dry or stor-age, but sot for B eliminators, 0-50 voltsDC scale J.65

No. 39 -For testing B batteries, dry or stor-age, but not for B eliminators, 0-100 voltsDC scale

No. 40 -For testing A and B batteries, dryor storage, but not for B eliminators i donreading, 0-3 volts and 0-100 volts DC scale.. 2.25

No. 42 -For testing B batteries, dry or stor-age, but sot for B eliminators; 0.160 voltsDC scale 2.00

No. 346 --For testing B voltages, includingeliminators. High ressitance water 0-300volts DC scale 4.50

No. 347 -Same as No. 346, except that scaleis 0.500 volts 5.50

No. 348 -For testing AC current supply line,portable, 0-150 volts 4.50

VOLTAMMETERSNo. 18 -For testing amperage of dry cell A

batteries and voltage of dry or storage Abatteries, double reading, 0-8 volts, and0-40 amperes DC $1.8f

No. 35 -For testing amperage of dry cell Abatteries and voltage of B batteries (not Beliminators); double reading, 0-50 volts, 0-40amperes DC 2.00

PANEL VOLTMETERSNo. 335 -For reading DC voltages, 0-8 volts $1.65No. 310 -For reading DC voltages, 0-10 volts 1.65No. 316 -For reading DC voltages, 0-16 volts 1.65No. 326 -For reading DC voltages, 0-6 volts 1.65No. 337 -For reading DC voltages, 0-50 volts 1.65No. 339 -For reading DC voltages, 0-100 volts 1.75No. 342 -For reading DC voltages, 0-150 volts 1.75No. 340 -For reading DC voltages, double read-

ing, 0.8 volts, 0-100 volts 2.25(Panel meters take 2-5/64" hale)

PANEL AC VOLTMETERSNo. 351 -For reading 0-15 volts AC $2.25No. 352 -For reading 0-10 volts AC 2.25No. 353 -For reading 0-6 volts AC 2.25

(See No. 348 under "Pocket and PortableVoltmeters.")

PANEL MILLIAMMETERSNo. 311 -For reading 0-10 milliamperes DC.41.95No. 325 -For reading 0-25 milliamperes DC LISNo. 350 -For reading 0-50 milliamperes DC 1.65No. 390 -For reading 0-100 milliamperes DC 1.65No. 399 -For reading 0-300 milliamperes DC 1.65No. 394 -For reading 0-400 milliamperes DC 1.65

DC PIN JACK VOLTMETERSNo. 306 -For Radiolas No. 25 and 28, 0-6 volts

DCNo. 308 -For No. 20 Radiola, 0-6 volts DC 2.90No. 307 -Desk type voltmeter with cord, 0.6

volts DC 2.50

6 -VOLT A BATTERYCHARGE TESTER

No. 23 -For showing when 6 -volt A batteryneeds charging and when to stop charging;shows condition of battery at all times...41.85

PANEL AMMETERNo. 338 -For reading amperage, 0.10 amperes

DC $1.65

SEND NO MONEY!GUARANTY RADIO GOODS CO.,145 W. 45th St., N. Y. City.

Please send at once your meters, cataloguenumbers:

for which I will pay postman advertised priceplus few cents postage.

Name

Address

City State RW-128ALL METERS SOLD ON FIVE-DAY

MONEY -BACK GUARANTY

A Dynamic SpeakerEasily Constructed

(Continued from page 17)

FRONT AND BACK VIEWS OF THE COMPLETED SPEAKER,SHOWING METHOD OF MOUNTING UNIT AND CONE. NOTE

DEPTH OF BOX.

windings of the unit. Four terminals areprovided on the unit for these wires.

In operation, you can feed it the fullpower of your set, whether 90 voltsor 550volts, and it will withstand the voltagewithout choking or blasting, rendering thefinest of reproduction. No speaker filteris needed, but one may be used if desired.

If the completed speaker has been

Blueprintof

Screen Grid Diamond4 -Tube Model Using

Space Charge DetectionAs Designed by H. B. HERMAN

$1.25This circuit uses TWO screen grid

tubes. One is the RF amplifier, the otherthe detector. The RF tube is used inregular screen grid fashion. The detectoroperates on the space charge method, asexplained in February 18th issue. Audioconsists of one resistance coupled and onetransformer coupled stage. Copy of thisissue, 15 cents extra.

RADIO WORLD145 West 45th Street

NEW YORK CITY(Just East of Broadway)

Telephones: Bryant 0551, 05:50

RADIO WORLD, 145 W. 45th St., N. Y. City.Please send me following at once:

One blueprint, V a 27 inches, clearly showingevery oon.nection for the 4 -tube SG Diamond.using spaoe charge detector. $1.25 enclosed.

1:1 One copy of February 18th issue of RADIOWORLD, 15 cents extra.

NAME

ADDRESS

CITY STATI

properly constructed according to direc-tions and the unit rightly mounted asshown, the builder will have one of thefinest speakers obtainable, up-to-date inevery respect.

The writer has long experimented withall types of speakers, specializing forsome time past on the dynamic having dis-carded all others in favor of this type. Hewill be glad to help out fans, custom setbuilders and all in search of quality inradio reproduction. Address J. W. Fitz-patrick, Jr., care of RADIO WORLD, 145West 45th Street, New York City.

Short Waves Awardedfor Commercial Use

Washington.The Federal Radio Commission has al-

located seventy-four short-wave channelsfor commercial transoceanic service andissued operating licenses for fifty-twochannels.

The Mackay Company were issuedtwenty-three operating licenses on con-struction permits previously issued fortransoceanic public service communica-tion. The Radio Corporation of Americareceived twenty-nine operating licenseson construction permits previouslygranted.

Subscribers: Look at the

Expiration Date on

Your WrapperWe do not like to take your name from

our subscription list without specific in-struction to do so because many of ourreaders wish to keep a complete file of th*paper.

Please, therefore, look at the subscrip-tion date stamped on your last wrapper,and if that date is earlier than the Issuecontained in the wrapper, please sendcheck to cover your renewal.

In this way you will get your copieswithout interruption.

Subscription Dept., RADIO WORLD,145 West 45th Street, New York aty.

June 16, 1928 RAL)I0 WORLD!

Short Wave Adapterfor Any AC Circuit

' (Continued from page 4)

FIG. 5. FRONT PANEL VIEW AS IDEALIZED BY AN ARTIST

would go to the antenna. What size thiscondenser should be is best determinedexperimentally, but in any event not morethan .00025 mfd. should be used, and oftenas small a capacity as .00005 has givengood results, particularly when the lowestof the three short wave range coils isused.

Where Short Antenna HelpsOnly this smallest coil ever presents

any problems in regeneration. If the chokecoil that assists regeneration is of toohigh inductance, it may have too high adistributed capacity, and at the very highfrequencies such capacity might bypassthe radio frequencies around the chokecoil, preventing the necessary chokingeffect. If regeneration fails for this coil,resort to a short antenna, say 10 to 25feet of wire in the room, or the seriescondenser. Always decrease the antennacoil coupling very materially for thesehigher frequencies.

It is lots of fun to listen in to shortwaves. In last week's issue, dated June9; was published on page 16 a list of shortwave stations in the United States, manyof which send regular programs, and allof which are well worth fishing for.

When to ComplainWith the aid of the wavelength ranges

given on the Air King coils, and with theassurance of correct capacity, as whenusing, the Karas straight line frequency.00014 mfd. short wave condenser, onecan determine on what wavelength thestation is being received.

This is extremely helpful, because some

r" WAVE TRAP, $1.50GenuineMoulded Bake-lite Casing,panel or sub -panel mount-ing option, orplacement atopof cabinet,mark this newmodel wavetrap that cutso u t interfer-ence. S n dcheck, P. 0.money ordersor postagestamps.

Five-day mousy -back guarantyGuaranty Radio Goods Co.

1 145 Walt 45th St., N. Y. City

stations have variable short waves, someof the most interesting ones use two shortwaves simultaneously, and all too oftenshort wave reception is obtained from ad-ditional transmission of a regular broad-cast program, without the announcer everstating the short wave call letters or theshort wavelength.

When you run across such objection-able and annoying tactics, you shouldwrite to the broadcast station, complain-ing about this neglect of the listener'swelfare.

But there's little enough to complainabout, and much to rave about, on theshort waves, even the reception of pro-grams, while somewhere in the promisingfuture lurks the possibility that the shortwaves will carry television, hence we mustfamiliarize ourselves with short wave re-ception.

(Other illustration on front cover).

BLUEPRINTand Instruction Sheet

for the Silver -MarshallShielded Grid Six

The New ReceiverUtilizing the New reShielded Grid

CentsTubes with TheirPowerful Kick.

Guaranty Radio Goods Co.145 WEST 45TH STREET

NEW YORK CITY

tone fidelity, clarity, sensitivity - by auto..matically keeping tube filament voltageconstant, despite "A" battery variations.

PERITERED V 6 PAT OFF

ghe "SELF-ADJUSTING"Rheastafeliminates band rheostats. Simplifieswlftun4einicaEngr;

only Amperite. $1.10 mounted (U.S.A.)FREE -"AmperiteBook" of latest circuitsand construction data.Write Dept. R.W. U.

RADIALL CO.50FranklinSt.,NewYork

36" GIANT CONE $6.00KIT

(Pedestal FREE with allorders received before June

I 5.)

Kit consists of onePowertone Unit, onedesigned front sheet ofFonotex, one plainPhonotex back sheet,two metal rings, onemetal bracket, o n eapex, thumbscrew andchuck; one tube ofcement; hardware; in-struction sheet. Tri-foot pedestal. FREEif you order. NOW!SEND NO MONEY!

We Ship C. 0. D.GUARANTY RADIO GOODS CO.

145 West 45th Street New York, N. Y.FIVE-DAY MONEY -BACK GUARANTY!

THE DIAMONDOF THE AIR

Using General Purpose Tubes

4 TubeSet uses three type A

c tubes and one 112 type;w has TRF stage, regen-

erative detector and two stages of trans-former coupled audio. (This is not ShieldedGrid Diamond.)

5 TubeSame RF and detector

Sas the other, but hasone transformer and

two resistance coupled audio. Especiallysuitable for B battery operation. (NotShielded Grid Diamond.)

lomom anima

Guaranty Radio Goods Co.,145 West 45th Street, New York City.Please send me one newly printed official blue-

print of the-o 5 -tube Diamond of the AirEi 4 -tube Diamond of the Air

(Check off one you want.)and the textual data giving full directions for con-struction.

Enclosed please fled 25 cents to defray all ex-pense.

NAME

ADDRESS

CITY STATE(These are not Shielded Grid Diamonds.)

Let Radio World Follow You on Your VacationIf you are a subscriber and are going away this summer, send usyour name and change of address and we will see that the paperreaches you every week.

If you are not already a subscriber, send us one dollar and yourname will be placed on our subscription list from now until LaborDay and your address will be changed as often as you desire.Such change should reach subscription office two weeks in advanceof date of publication.

Subscription Dept., RADIO WORLD, 145 West 45th Street, New York City

325th Consecutive Issue-Seventh Year A SHORT WAVE … · 325th Consecutive Issue-Seventh Year A...

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