Radio Broadcast (Nov 1926-Apr 1927)

428 RADIO BROADCAST ADVERTISER THOUSANDS OF RADIO ImSET OWNERS need these improvements 1 THE U. S. Navy the Signal Corps and 69 makers of leading standard sets use the variable resistance controls made by Central Radio Laboratories. These improved controls should be used on your set if you want the last word in quality for fine reception. Yet, owing to our huge output the cost is no more than for many inferior devices. Modernize Your Old Set with , Central at) ModiTpluG Tone volume is, as you know, the one big improvement in this year's best sets. You can enjoy this improvement with your present receiver for only S2.50. Modu-Plug is especially for that purpose. It provides full tone volume control from a whisper to maximum, simply by adjusting the small knob on the plug. Matches the speaker impedance to the set. Attaches instantly without tools. Standard type Modu-Plug replaces present speaker plug. Cord type fits sets not equipped with jacks. Either type, at dealer's, or mailed di $o 50 rect RCen4,ralat» » g adiohM With "A" Battery Switch Here is the variable resistance guaranteed always smooth, noiseless and permanent in adjustment. Tapered to control oscillation and volume, it also has a positive, quick acting "A" battery (switch. One knob replaces two. Turning knob to. right lights tubes, then increases volume. To left decreases volume, then cuts off batteries. Resistance is 0 to 500,000 ohms. You cannot imagine the great improvement until you try it. Adapted to all circui ts. At dealer's, or mailed SO ^0 direct A T» CentraJatJ Jvlieostatd Where your old design rheostat overloads, heats up and quickly becomes noisy ou new style tubes using increased current, Centralab Ribbon -type Rheostats will operate smoothly and permanently quiet. Insulated metal discs hold rigid a smooth flat resistance surface instead of wires, insuring even regulation and no dead spots. Every set using this rheostat is improved. 2 resistances for 5tol0tubes,atdealer's, $1.25 or mailed direct. . . . We make variable resistances for both the U.S. Navy and Signal Corps and for (*£k makers of leading standard sets SEND NO MONEY— If your dealer isn't supplied, order direct from us. Send no money. Simply pay postman on delivery, plus few cents postage. Install and test for 10 days. Then if you are not more than pleased and delighted with the wonderful results, return the goods to us and your money will be refunded. 10 DAYS' FREE TRIAL! CENTRAL RADIO LABORATORIES 22 Keefe Avenue Milwaukee, Wis. Rin. Electromagnetic Theory. Ether Popular Radio. Nov., 1926. Pp. 63 5ff. Waves. "Are There ' Ether Waves' After All?" E. E. Free. Experiments conducted by Prof. D. C. Miller, of Cleveland, Ohio, on the problems of the existence of the ether have received considerable attention, due to the claims put forth that a slight ether drift has been detected. The Michelson-Morley experiment showed no ether drift, and Einstein's Theory was based on this evidence. Dr. Miller's experiment consisted in measuring the interference fringes of light passing in different directions. He obtains a variation of speed of light parallel to the axis of the sun of about 6 miles per second, and believes that the whole solar system is falling through space at an actual speed of about 120 miles per second. This coincides remarkably well with astronomical observations. R120. Antennas. Antennas. Proc. I. R. £. Oct., 1926. Pp. 67.5-688 Principles of, " Field Distribution and Radiation Resistance of a Straight Vertical Unloaded Antenna Radiating at One of Its Harmonics," S. A. Levin and C. J. Young. The operation at the harmonics of the grounded antenna, and of an ungrounded antenna at any distance above ground, has been considered as far as current, voltage and power distribution, electromagnetic field, and radiation resistance, are concerned. The antenna is always assumed to be a straight vertical wire and unloaded. The ground is supposed to be a perfect conductor. R140. Radio Circuits. Radio Circuits, Proc. I. R. E. Oct., 1926. Pp. 689-693. Calculation of. "A Method for Maximization in Circuit Calculation," W. Van B. Roberts. Having found the expression for a current (or voltage, or power, etc.) in terms of complex quantities representing the constants of a circuit, it is often desired to determine what value of some one of these complexes makes the absolute magnitude of the current (or voltage, etc.) a maximum or a minimum. Rather than reduce the expression to its absolute value first, and then maximize in the usual way, it is often much less tedious to differentiate the expression while in the complex form. The condition for which the absolute value is an extremum is then not that the derivative is equal to zero, but that the derivative multiplied by a small increment of the independent variable gives to the dependent variable an increment which is at right angles to the vector representing the dependent variable itself. The condition of maximum obtained by this method is often in a form that is more compact and that has obvious physical significance. Two examples of the use of the method are given. R134. Super-Heterodyne. Super-Heterodyne. Proc. I. R. E. Oct., 1926. Pp. 695-698. Origin of. "On the Origin of the Super-Heterodyne Method," W. Schottky. ....... In this discussion theauthorpointsout how, in his opinion the super-heterodyne method of ether wave reception was first conceived by himself and others while doing research work in the Siemens Laboratory, Germany, during the war period. This idea was patented in 1917, and another in June, 1918. These are said to be older than the original Armstrong patent, pertaining to the same methods of reception. R113.4. Heaviside Layer. Heaviside Wireless World (London). Layer. Sept. 8, 1926. Pp. 359-360 "Conditions Under Which Short Waves Penetrate the Heaviside Layer," E. V. Appleton. The writer discusses the changes that transmitted wireless waves of various wavelengths undergo when meeting the Heaviside Layer. On the longer waves, it is said, the conductivity of the upper atmosphere is equivalent to that of a sheet of copper one meter in thickness. However, the penetrating powers of the shorter waves, their peculiarities as made manifest by the skipped distances, makes it probable that energy penetrates the Heaviside Layer. Somewhere between one and ten meters all of the transmitted rays are said to leave the earth and escape. R610. Station Descriptions. Station, Wireless World (London). Sept. 22, 1926. Pp. KDKA. 413-416. "KDKA. 309.1 Meter Transmitter." A description of station kdka, East Pittsburgh, is given. Details relating to construction and the constants of the antenna system, the oscillator, modulator, and amplifier units, the power supply, and the control system, are discussed. Photographs and drawings accompany the article. The station is said to operate at an efficiency of 67 per cent. R344.5. Alternating Current Supply. Rectifier, Wireless World (London). Sept. 22, 1926. Pp. Ruben. 423-424 "The Ruben Rectifier," A. Dinsdale. A solutionless electrolytic rectifier, developed by an American named Ruben, and known as the Elkon rectifier, is described. It is composed of two discs between which a film is formed when connected to the circuit. The principle of operation is not disclosed. R320. Antennas. Antennas, Wireless World (London). Sept. 29, 1926. Resonance. Pp. 45t-453 "Frame Aerial Crystal Reception," W. H. F. Griffiths. The effects produced when tuning a distant antenna to resonance with a broadcast station are outlined. If the currents induced in this way are appreciable, the receiving antenna will radiate and thus increase the signal strength for a neighboring receiving set, which is also tuned to the same wave. A loop antenna was used to obtain the results outlined and graphed. R343. Electron-Tube Receiving Set. Receiver, Radio Broadcast. Dec. 1926. New "Universal." Pp. 154-158. "The New 'Universal' Receiver," H. E. Rhodes. This receiver is a revised model of the R.B. "Universal" described in Radio Broadcast for Jan., 1926, pp. 331-336, and uses the Roberts system of neutralization, condenser control of regeneration, and a two-stage transformercoupled audio frequency amplifier. The article presents the diagrams, the assembly information, and data on construction and testing. GEORGE ELECTRIC COMPANY "B POWER UNIT" TYPE "M" Complete with Tube $29.50 Our patented filter circuit is most efficient, delivering absolutely pure direct current, free from any hum or distortion. The Type M Unit is sturdily constructed, and will last as long as the best receiving set. Variable resistances permit the selection of voltages to make your set work efficiently at all times. You can bring in distant stations with more volume, and your locals with purer tone. This unit operates on 1 10 volt, 60 cycle A. C. It will deliver 180 volts, with plenty of current for a ten tube set or sets equipped with power tubes. FULLY GUARANTEED Our dealer will be glad to give you a demonstration. Write for further information. GEORGE ELECTRIC COMPANY 751 Carleton Ave. St. Paul, Minn. Dealers and Agents! — Write today for attractive agency proposition LONG This is a good time to subscribe for RADIO BROADCAST Through your dealer or direct, by the year only $4.00 IMPORTANT MM .Ml th& k-f TUBE I Itself Amperite alone can supply automatically, the self-adjusting filament control your tubes require for perfect rheostat regulation under all varying conditions. Insistupon Amperite.and accept nothing else. Simplifies wiring. Eliminates hand rheostats. Specified by leading engineers in every popular circuit. Types for all tubes. Price SI. 10 mounted (in U.S.A.) At all dealers. 0^gg-(f;aff QptttpCttty SO FRANKLIN ST.. NEW YORK FREE Write for 1 look-Lips to Dept. R.B -2 Jhe "S ELF -AD J US T ING " Rfieostat