RADIO BROADCAST ADVERTISERThe <strong>Radio</strong> <strong>Broadcast</strong>Dubiliercondenser blockTYPE: PL-381as specified byRADIO BROADCASTType PL-38i condenser unit has beenselected by <strong>Radio</strong> <strong>Broadcast</strong> becauseof its long life and general adaptability.It is the ideal eliminator condenserbecause of the improved dielectricmaterial used. Each unit mustwithstand severe tests in order to passour rigid inspection standards. Dubiliernigh quality workmanship andreputation protect your investmentand eliminate trouble.Note the Flexible, Rubber -Covered Leadsand convenient mounting tabs. Metallic containersprotect condenser element from moistureand mechanical injury.Capacities 2,2,4,4,1, 1 mfd. operating voltageand nowDUBILIERBUFFERCondensersFor satisfactoryservice using theRaytheon rectifiertube, the newDubilier buffercondenser is absolutely essential. Made of two.1 mfd. condensers electrostatically shielded fromeach other and from external capacity effects.Flexible rubber-covered leads. Metallic containerswith mounting tabs. Two types: PL-91for 400 volts D.C.; PL-340 for 600 D.C. volts.At all DealersWrite For Booklet(^4 new booklet "17 Ways to Improve yourSet" will be mailed on receipt of ten cents.Tells how to use fixed condensers and givescircuit details. Be sure to get your copy.)DubilierCONDENSER CORPORATION4377 BRONX BLV'D NEW YORK, N.Y.SHEETSTNQUIRIES sent to the Questions and Answers department of RADIO BROADCAST were at one time* answered either by letter or in " The Grid." The latter department has been discontinued, and allquestions addressed to our technical service department are now answered by mail. In place of " TheGrid," appears this series of Laboratory Information Sheets. These sheets contain much the same typeof information ax formerly appeared in " The Grid," but we believe that the change in the method of presentationand the wider scope of the information in the sheets, will make this section of RADIO BROADCASTof much greater interest to our readers.The Laboratory Information Sheets cover a wide range of information of valu-e to the experimenter, andthey are so arranged that they may be cut from the magazine and preserved for constant reference. Wesuggest that the series of Sheets appearing in each issue be cut out with a rajor blade and pasUd on 4" by 6"filing cards, or in a notebook. The cards should be arranged in numerical order. Several times during theyear an index to all sheets previously printed will appear in this department. The first index appearedin November.Those who wish to avail themselves of the service formerly supplied by " The Grid," are requested to sendtheir questions to the Technical Information Service of the Laboratory, using the coupon which appearson page 60 of this issue. Some of the former issues of RADIO BROADCAST, in which appeared the firstsets of Laboratory Sheets, may still be obtained from the Subscription Department of Doubleday, Page &Company at Garden City, New York.No. 89 RADIO BROADCAST Laboratory Information Sheet<strong>May</strong>, <strong>1927</strong>Short-Wave CoilsSOME DATA ON THEIR RESISTANCE'THIERE are, at present, a great many excellent* coils on the market for use in short-wave receivers.They are generallyof the "plug-in" typeso that different coils are used to obtain the variousranges required.These coils should have as low a radio-frequencyresistance as is possible, consistent with a constructionsufficiently rugged to prevent their being damagedif they are handled somewhat roughly. Itwould be preferable if the coils could be wound onsome solid form but the question then arises whetheror not a form can be used without increasing theresistance of the coil to a considerable extent.The General <strong>Radio</strong> Company has conductedsome experiments along this line to determine justhow much the form used affects the coil's resistanceand also to determine what size wire is bestto use. Tests were made using a standard bakeliteform having a diameter of 2J". The curve given onthis Sheet indicates how the radio-frequency resistanceof the coil varies with the size of the wireused. Evidently, from the curve, the wire size is notespecially critical but best results are obtained witha wire size of about No. 12 or 14 gauge.It was found that the use of good binders to holdthe turns in place has no appreciable effect upon theresistance. A coil was wound in such a manner thata form could be slipped in and out of it withoutdisturbing the wire. Measurements on the coil withand without the form indicated that the differencein efficiency was negligible.Tests were also made with regard to shieldingNo. 90SOME OF THEIR ADVANTAGESoperation of a transformer is usually ex-* plained by saying that the current flowing inthe primary sets up an alternating magnetic fieldwhich in turn causes a current to flow in the secondary.This is also the simplest way to explain theoperation of a loop antenna, the only differencebeing that the alternating magnetic field thatcauses the current to flow in the loop is in the formof radio waves.The number of volts induced in a loop by the passageof radio waves is:2 TC f n A H x 10-swhere H is the amplitude of the wave, f the frequency,n the number of turns in the loop, and A thearea of the loop. The voltage calculated from thisformula is only correct when the plane of the loopis vertical and perpendicular to the direction of themagnetic field. That is, the loop must be pointingtoward the transmitting station. If rotated abouta vertical axis only a quarter of a turn, no voltagewill be induced.This feature is the most important advantage ofa loop, for two stations using exactly the same wavelengthmay often satisfactorily be separated (providedthey do not lie in the same or exactly oppositedirections) by simply turning the loop at rightRADIO BROADCAST Laboratory Information Sheetand it was found that the shielding could be placedvery near the coil and have no appreciable effect.The result of the tests may be summed up as follows:When designing a coil for use on the 40-meter2.01.5J.flLoop Antennas14 16 18 20 22B&S WIRE GAUGE(7500-kc.) short-wave band (all these tests weremade at this frequency), it is well to (1.) use aboutNo. 12 to 14 wire; (2.) use a coil form if desired;(3.) use any good dope as a binder; (4.) use anyreasonable amount of shielding where advantageous;(5.) keep the form factor (diameter dividedby length) around 1 to 2. 5.These data are taken from the February, <strong>1927</strong>,issue of the General <strong>Radio</strong> Experimenter.<strong>May</strong>, <strong>1927</strong>angles to the interfering station. Loops are cominginto greater use as transmitting stations becomemore powerful, and they will probably ultimatelybe used almost exclusively on account ofthe small space required, ease of installation, portability,lack of necessity to safeguard against lightning,and the improvement of the ratio of signalstrength to interfering noises, due to their directionalproperties.If a loop is compared in size to an antenna of theordinary type it would appear that the amount ofenergy intercepted by the loop would be exceedinglysmall indeed. The fact is, however, that a goodloop antenna, tuned with a condenser having lowinsulation losses, will pick up signals much betterthan might be expected from a comparison of itssize to that of an outdoor antenna. This is due tothe fact that the loop has a very much lower resistancethan an elevated antenna.The loop type antenna has been used most frequentlyin conjunction with super-heterodynes because,with this type of receiver, it is easy to obtaina large amount of radio-frequency amplification.During the last year, however, several receivers ofthe neutrodyne type have been placed on the marketdesigned for use with a loop. These receiversare generally completely shielded so as to preventinteraction between the loop and the coils in thereceiver.
RADIO BROADCAST ADVERTISER 53Model AC-97-Tube, 2-Dial, Battery lessThis two-dial control set ts designedespecially for AC power, for use with theAmrad A B & C Power Unit. Easilyoperated, marvelous selectivity. Furnishedwith Power Unit but without tubes.142Console Model 192Model S-7337-Tube, 2-Dial, Battery TypeOwners of this Amrad Neutrodyne reportcomplete satisfaction. High ratio verniercontrols simplify tuning. Volume Is controlledby a single adjustment. Beautifullydesigned cabinet finished in twotonedmahogany. Without accessories.#77Console Model 1271 tube 'Neutrody ^ties a^yAMRADNeutrodynes are built with the greatestskill and precision. Each set must pass certainhigh standard tests before it leaves the factory.The great skill and engineering feats of the AmradLaboratories are manifest in thecircuit as well as in the beautifully designedcabinets.Produced tinder mass productionmethods influenced by Powel Crosley,Jr., combined with Amrad's engineeringskill, these genuine neutrodynes arethe greatest values on the market.The console model AC-g-C is an unusualvalue. It is a 7-tube set withtwo-dial control. All the necessarypower is furnished by the Amrad A Band& C Power Unit, an efficient power sup-tested under actual home conditionsply"B" ELIMINATOR"Will furnish B current voltages22%, 30 or 4 5. 69. 90, 135 or 180.Maximum volts. 180 at 50 mils.Unit is housed In a metal cabinetand finished in black enamel.#35'Precisionfor more than a year and operating from AC current.100-120 volts, 60 cycle. No trickle charger is concealedin this unit. No more power supply troubles.Just snap the switch and set is in full operation. Thecabinet is of beautiful two-toned mahoganyfinish, with the genuine Crosleymusicone built in. This is a wonderfulvalue at $192, with the powerunit,but without the tubes.Write Dept. 2E? for descriptive literatureand information.AMRAD CORPORATIONMedford Hillside, Mass.'Efficienl ^iube genuineltyutrodynes, unsurpassedin /he radio market anywhere at this price /60 125Model S-5225-Tube, 3-Dial, Battery TypeAmnd quality is again exemplified inthis beautifully made and proportionedset. The simple, yet elegant lines ofthis set are pleasing to the eye. Actualreports of performance are remarkable.Simple to tune and easy to operate. Alsomade in console model at $110.Model AC-55-Tube, 3-Dial, Battery lessA compact, rllli ictit si-t delivering theutmost in radio enjoyment at the lowestpossible cost. No batteries to fuss with.Operates direct from light current. Unusualselectivity, volume, and tone mattethis the greatest neutrndyne value on themarket. Ctusric Mrtel 1175.
- Page 1 and 2: RADIO BROADCASTVOLUME XIMAY, 1927,
- Page 3 and 4: INDEX.ContinuedPAGEThreshold of Hea
- Page 5 and 6: RADIO BROADCAST ADVERTISERALUMINUMB
- Page 7 and 8: RADIO BROADCAST ADVERTISERfIA REALA
- Page 9 and 10: :RADIO BROADCASTVOLUME XI NUMBER 1M
- Page 11 and 12: MAY, 1927WITH MACMILLAN TO THE ARCT
- Page 13: THE MARCHInterpretation of Current
- Page 16 and 17: 18volved the law in precarious lega
- Page 18 and 19: The ElectricalA Non-Technical Expla
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- Page 22 and 23: A Balanced Short-Wave ReceiverA Des
- Page 24 and 25: What About the A BatteryThe Importa
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- Page 34 and 35: AS THE BROADCASTER SEES ITDrawings
- Page 36 and 37: 38 RADIO BROADCAST MAY, 1927Interes
- Page 38 and 39: Some Facts About Coil DesignThe Osc
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- Page 44 and 45: ''Measuring TubeCharacteristicsA Pa
- Page 46 and 47: 48 RADIO BROADCAST MAY, 1927MUTUAL
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