Radio broadcast .. (1922-30)

In the R. B. Lab 237 Variotransformer is used. former having a range from 200 to 600 meters, suggested this instrument as the solution to the problem. This transformer has both primary and secondary continuously variable by turning a single knob, and both windings are always tuned to the same wavelength, i. e., in resonance with each other! Fig. i shows the set as made up under the supervision of the R. B. Lab and in which our theory was maintained beautifully in practice. The circuit is identical with that shown on page 14 of the November RADIO BROADCAST, except that the Ballantine Variotransformer is substituted for T2, and, of course, the variable condenser across the secondary of T2 is not used. WHAT THIS SET WILL DO ON THE single tube shown in the photograph and on the diagram, it will bring in signals more loudly and clearly than a one-tube, single-circuit regenerative set. Reception is generally superior to that achieved with the set described by Mr. Harkness in the November RADIO BROADCAST. With one exterior stage of audio amplification, it will bring in local broadcasts so as to fill a large room (the single tube itself will actuate a good loudspeaker) giving a volume exceeding that of the average regenerative set with two stages of audio amplification. It gives signals of remarkable clarity, with freedom from crackling sounds (excepting static, of course) and other extraneous sounds. It will tune sharply with a minimum of effort, and with greater ease than any single-circuit regenerator. WHAT THIS SET HAS DONE (The following four paragraphs, by the Editor of this magazine, indicate what he, personally, has done with the receiver under discussion.) WE HAVE tried this one-tube reflex with all kinds of tubes in all kinds of places. In every case it has proven to be a "knock-out." On Long Island, 23 miles from New York, we have heard two stations in Chicago on a loud-speaker, using a 6o-foot antenna and a single UV199 tube with about 80 volts on the plate. The music was not loud enough to dance to or keep the neighbors awake, but it could be heard in a room of moderate size. Speech was perfectly understandable, and several of our friends who witnessed the performance were as amazed as FIG. I Showing the one-tube reflex circuit made up by the R. B. Lab. The Ballantine We reprint the original circuit diagram on page 218 we were. Truly, we did not expect such results. To date, we have heard (from Garden City, L. I.) KDKA, WGY, WJAZ, and WDAP on a loudspeaker, with the equipment described above, which is not too bad. The local stations can be heard on a loud-speaker either night or day and many other longdistance stations have been heard on the phones. During the radio show in New York, some of our out-of-town friends were anything but polite in letting us know that our enthusiastic statements regarding this one-tube reflex were taken with a grain of salt. One went so far as to say, " Radio and golf will surely make liars of us all." That was the last straw. We took a train for Long Island, grabbed our little set from the living room table, amid shouts of objection from an erstwhile happy family, and returned to New York. We made directly for the room of our friend, our pockets jammed with dry cells, B batteries, a pair of phones, and a coil of annunciator wire. Under one arm we carried the receiver; under the other a loud speaker. In a few minutes all the connections were made. A cuspidor-weighted wire swung from a window on the twenty-first floor of an exclusive New York hotel. We were less than two blocks (or squares) from the powerful broadcasting station of the Radio Corporation at Aeolian Hall. We had no trouble in tuning out that station and bringing in other New York stations on the loud speaker — which does not speak badly for the selectivity of the receiver! WHAT THIS SET WILL NOT DO THE set will not oscillate, or "spill over," to your own annoyance and that of your neighboring enthusiasts (except as described above). It is apparently immune to body capacity effects, shielding being quite unnecessary.