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346
Radio Broadcast
FIG. 2
Several other minor changes have been made. The variable condenser has been shifted to the antenna side of the coupler primary, by which maneuver, control of the set is apparently facilitated, owing to a possible stabilizing effect of the ground on the directly coupled grid. A grid leak, quite an important item, has been added, and a condenser placed across the phones or primary of the first transformer, as the case may be. For convenience, the receivers have been shifted nearer to the plate. If, when constructing the set, the experimenter does not fancy the immediate expense of amplifiers, the auxiliary apparatus is merely eliminated on the diagram, along with the extra B batteries, and the phones connected in place of the first jack.
A slight variation in the fundamental circuit, which has proved remarkably popular where introduced, is shown in Fig. 2. The tuning elements, exclusive of the variable condenser, are three home-made variometers, which may be constructed for less than fifty cents apiece. The variometers are wound on cardboard statofs and rotors (the stationary and revolving parts) three and a half and three inches in diameter respectively. The stators are wound with 18 turns of No. 22 or No. 24 single cotton-covered wire, and the rotors with 22 turns of the same. The variometers may be panel mounted by bushings as described in the Grid in Radio Broadcast for December. The connection between the stator and rotor of variometer number two is broken in order to permit the hooking-in of the detector "B" battery. C2 is a .0015 mfd. telephone shunt condenser.
The set is slightly more difficult to tune than Mr. Parker's circuit, but the semi-regenerative function of the third variometer is soon comprehended with surprising results. Variometer number one, in conjunction with the variable condenser (which should be provided with a shorting device for waves in the neighborhood of six hundred meters) varies the wavelength. The middle variometer controls feedback or regeneration.
The set has no taps, all tuning elements being continuously variable by the variometers and condenser. As a result, it is remarkably selective, with tuning possibilities that, used appreciatively, rival the best inductively coupled outfits.
SUPPLEMENTAL LIST OF BROADCASTING STATIONS IN THE UNITED STATES FROM NOVEMBER 23
TO DECEMBER 24 INCLUSIVE
CALL SIGNAL
OPERATED AND CONTROLLED BY
KFCL Los Angeles Union Stock Yards Los Angeles, Calif.
KFCQ Motor Service Station Casper, Wyoming
KFDB Mercantile Trust Company of California San Francisco, Calif.
KFDC Radio Supply Co Spokane, Wash.
KFDF Wyoming Radio Corp Casper, Wyoming
KFDH University of Arizona Tucson, Arizona
KFDJ Oregon Agricultural College Corvallis, Oregon
KFDL Knight-Campbell Music Co Denver, Colorado
KFEJ Guy Greason Tacoma, Washington
KFEP Radio Equipment Co Denver, Colorado
KFGG Astoria Bridget • . Astoria, Oregon
KFGH Leland Stanford Jr. Univ Stanford University, Calif.
KFHJ . Fallen Company Santa Barbara, Calif.
KGW Portland Oregonian Portland, Oregon
WLAG Cutting & Washington Radio Corporation Minneapolis, Minn.