Radio Broadcast (Nov 1926-Apr 1927)

432 RADIO BROADCAST ADVERTISER "It's working voltage* that counts" ami] the world The amazing results obtained with power amplifiers is the radio sensation of the year. Perfect tone quality and the capacity to handle the full volume of a brass band without distortion, has made power amplification the "last word" in radio. You, too, can enjoy all these advantages even with your old set, and at a minimum cost, by building a power amplifier with Dubilier Condensers. Dubilier Condenser Type 903, illustrated, is designed to withstand the high voltage surges which often occur in the filter circuits of power amplifiers. In fact all Dubilier Condensers are built with this high margin of safety, and with an indicated working voltage* that insures a long life in continuous operation. Send 10c for our booklet "Seventeen Ways to Improve Your Set." It gives the most recent information on power amplifiers, filters and battery eliminators. *Working voltage means more than "test voltage.7' It is the voltage at which a condenser may be safely used in continuous operation. Dubilier CONDENSER CORPORATION 4J77 BRONX BLVD. NEW YORK, N. Y. R213. Harmonic Methods of Frequency Harmonic Measurements. Amplifier Bureau of Standards Paper No. 5^0. "Establishment of Radio Standards of Frequency by the Use of a Harmonic Amplifier," C. B. Jolliffe and Grace Hazen. A harmonic amplifier is described, together with its application in establishing radio standards of frequency from an audio-frequency source. The results of one-frequency meter standardization are summarized briefly. A sonometer, an auxiliary pitch-measuring device, is described, and the method of using the harmonic amplifier with this auxiliary for the standardization of piezo oscillators and comparison of audio frequencies is given. The work has shown that radio-frequency meters may be standardized with high precision and ease from a fundamental audio frequency by use of a harmonic amplifier. The accuracy of the standardization is limited only by the accuracy of the fundamental frequency source and the precision and accuracy of the frequency meter. The harmonic amplifier is simple and rapid in operation. Fixed frequency generators, such as piezo oscillators and electron-tube driven tuning forks, may also be accurately and rapidly standardized by the use of the harmonic amplifier and the auxiliary sonometer. R351. Simple Oscillators. Oscillator Burgess Engineering Circular No. 12. Part'l. or Driver. "A High Frequency Driver," W. H. Hoffman. A vacuum-tube radio frequency oscillator, also called a driver, is described, with detailed constructional information given. It is designed to cover frequencies from 375 kc. (800 meters) to 25,000 kc. (12 meters) for purposes of radio measurements. The indicating instrument used is a milliammeter connected in the grid circuit of the vacuum tube. Five coils cover the frequencies used. R384.I. Wavemeters. Wavemeters, Burgess Engineering Circular No. 12, Part II. Short-Wave. "Short-Wave Wavemeters," F. H. Schnell. Two wavemeters, one calibrated in kilocycles and the other in meters, each having a range of 30,000 kc. (10 meters) to 3000 kc. (i 00 meters), are described. The instruments serve many uses, as outlined. Curves showing the relation between dial settings and either wavelength or frequency readings for Karas and Cardwell condensers in connection with various sizes of coils, are appended. R8oo(62i.353). Batteries, Primary. Batteries, Burgess Engineering Circular No. II. Primary. "Estimating B Battery Service Life," W. B. Schulte. The paper presents a method of testing B batteries and shows the shelf life, discharge, and capacity characteristics of B, or plate, batteries, classified according to battery weight in pounds. Examples are given showing how approximate service-hours may be computed for all standard combinations of tubes and batteries. Tube plate currents with various grid bias voltages are shown by curves. The effects of the number of tubes, the grid bias voltage, the size of B batteries, and the type of tubes, are clearly shown as a help for the user to figure his own requirements. R 1 7 1 . Interference. Interference. Proc. I. R. E., Oct., 1926. Pp. 575-603 "Reduction of Interference in Broadcast Reception," A. N. Goldsmith. The factors in station interference with broadcast reception, namely signal field strength, receiver selectivity, and psychological reactions of the listeners, are analyzed. Statistical data correlating these factors with interference complaints from listeners in the vicinity of the 50-kilowatt broadcasting transmitter at Bound Brook, New Jersey (wjz), are then presented, these data being the results of a survey by a .pecial interference reduction staff. The clearing up of the complaints by this service, using simple methods which are described, indicates the feasibility of high-power broadcasting stations, as well as the necessity for them because of the requirement of reliable broadcasting service over large areas. In the appendix, the construction of a series wave trap is outlined. R113.7. Transmission Formulas. Transmission Proc. I. R. E., Oct. 1926. Pp. 613-647 (Short-Wave) "Some Measurements of Short-Wave Principles of. Transmission," R. A. Heising, J. C. Schelleng, G. C. Southworth. Quantitative data on field strength and telephonic intelligibility are given for transmission at frequencies between 2.7 m gacycles(iii meters) and 18 megacycles (16 meters), and for distances up to 1000 miles, with some data for distances up to 3400 miles. The data are presented in the form of curves and surfaces, the variables being time of day, frequency, and distance. Comparisons are made between transmission over land and over water, between night effects and day effects, and between transmission from horizontal and from vertical antennas. Fading, speech quality, and noise are discussed. The results are briefly interpreted in terms of current short-wave theories. A Circuit Diagram Correction AN ERROR crept into the diagram, Fig. 8. on page 288 of the January, 1927, issue. This drawing is a schematic diagram of the power-supply device described by James Millen. A connection between the minus A and the center tap of the transformer filament winding supplying the power tube was shown. This is incorrect. The lead should, instead, be connected from minus A to the center tap of the transformer high-voltage secondary. The ground connection should also be transferred from filament winding to the negative A terminal. The picture diagram given on page 286 is absolutely correct. DESJ1MUTLASI r<Md ^tora^e A Batteigr Two -Year 1 Guarantee 1 Bond in Writing Famous the world over for reliable, enduringperformance. Solid Rubber Case lasting protection against acid or leakage. Approved and Listed as Standard by Leading Authorities including Radio News Laboratories, Popular Sci. Inst. Standards, Pop. Radio Laboratories, Radio Broadcast Laboratories, Radio in the Home and Lefax, Inc. Send No Money Just state number wanted and we will ship same day order is received, by express CO. D. Pay expressman after examining batteries. 5% discount for cash with order. Remember, you save 60% on World Buiteries— so send your order today. WORLD BATTERY COMPANY Dept. 24 1219 S.Wabash Ave., Chicago, III. NEW LOW PRICES Solid Rubber Case Radio Batteries 6 Volt, 100Amperes $10.00 6-Volt. 120Amperes $12.00 6-Volt, 140-Amperes $13.00 6-Volt, 11 -Plate $10.00 6 Volt, 13 Plate $12.00 12 -Volt, 7 -Plate $14.50 Set your radio dial? at 288.3 meters for the World Storage Battery Station WSBC. Variety — new talent — always Interesting. Jerry Sullivan, Dir. and Announcer "Chl-CAW-eo" BIG NEW 1927 CATALOG-FREE Dealers, Agents, Set Builders— set embig 1927 Catalog — 225 nationally advertised lines. Lowest prices in America! Largest, most complete stock. Radio's latest developments. It's FREE — send for your copy now. AMERICAN AUTO & RADIO MFC. CO., Inc. 1437. McCee Street, Wansas City, Mo. Improve Your Set 100% FeriIo-IossCtls / SHIELDED TUNED RADIO TRANSFORMERS [ SELECTIVITY 1 DISTANCE J $5 00 Per Set SPACEDAIRWOUND TUNED RADIO TRANSFORMERS Feri Lo-Loss Coils. Low distributed capacity, low dielectric losses and many other features insure unequaled results. Wiring Diagram and instructions supplied with each set of three. Send for Descriptive Literature on other Feri Products FERI RADIO MFG. CO. 1167-A Bedford Ave. Brooklyn, N. Y.