Radio broadcast .. (1922-30)

5io Radio Broadcast SOME POINTS ON CONSTRUCTING AND TUNING FROM SEVERAL NIGHT-OWLS THE HOOK-UP THAT WON THE CONTEST THE circuit diagram used by Russell Sheehy, winner of the one-tube contest, is here reprinted from the February issue, together with some information which he has supplied on the construction and operation of his set. " My entire outfit is home-made," he says, "including the vario-coupler, which is wound with 35 turns on the stator and 35 on the rotor. No switch points or taps are used. The only trouble I had with this circuit was in the paper condensers, and I strongly advise the use of mica condensers and tubular leaks in the grid circuit. The .001 mfd. variable condenser across the phones and batteries may be substituted by a .002 mfd. fixed condenser or sometimes on near-by stations by a .005 mfd. fixed condenser. In the last instance, the signal strength is very materially increased. The entire circuit is quite simple of operation and most of the tuning is done with the condenser in the aerial circuit and the tickler control. ... I operate my filament on 4.4 volts and very rarely have to change it. With most of the detector tubes I have tried, the best B battery voltage is 18. . . . I have MR. SHEEHY S EFFICIENT HOOK-UP 1 Variable condenser of .001 mfd. capacity. 2 Any variocoupler of standard make, range 1 50 to 600 meters. ^ i -megohm grid leak. 4 Grid condenser of .0005 mfd. capacity. 5 Variable condenser of .001 mfd. capacity. 6 aoo-ohm potentiometer. 7 2OO-ohm potentiometer. 8 B battery, i6£ to 22 volts for UV2oo tube. 9 Antenna 125 feet long, 40 feet high, 7/22 stranded. 10 Counterpoise ground. Single wire 125 feet long, buried one foot deep, under the antenna. found that two potentiometers are quite an asset when long-distance signals are desired. . . . The potentiometer with the slider grounded at the correct position of the tickler may cause the tube to oscillate, by moving it toward the negative side, and it is just before this point of oscillation that signals are clearest and loudest. The set is operating at its best when you find that moving the condenser either way produces no oscillation, but there is a sort of "purr" on each side of your signal. . . . Don't turn your filament right off. Turn it off a little at a time. . . . Keep your aerial well insulated at both ends. . . . Don't run No. 24 wire to your A battery; use No. 14 at least." Mr. Sheehy 's complete description of his set, and his aerial and ground system, is found in RADIO BROADCAST for February (pp. 336 and 337). A statement including a complete list of stations heard up to January 3ist, was sworn to before a notary public and forwarded to RADIO BROADCAST. The total mileage for the 159 stations is 111,240, the most distant station being KHJ, Los Angeles — 2,610 miles from Mr. Sheehy's New Hampshire home. J. Kelly Johnson of Oskaloosa, Iowa who has piled up an aggregate of 81,145 miles, is a strong advocate of soldered connections throughout his set. Those who have been bothered with crackling noises in the phones which they have reason to believe is not static, or who have had to stop and readjust a poor contact in the middle of an effort to bring in some long-distance station, will do well to take Mr. Johnson's advice to heart. He says: "The current supplied to a radio set from an antenna is extremely minute. A very slight resistance in the circuit very materially decreases the amount of current. So the first consideration is electrically perfect joints. The most satisfactory method of securing these is by means of soldering. All connections in the efficient radio sets are soldered. Granted that some sets are successful when no solder has been used, how long will their efficiency lastr For a short time only. Such joints oxidize or pull apart and are bound to weaken signal strength, cause disturbing noises, and make increasing annoyance." Here is some further sound advice about making home-made coils: " If you make your own coils, here is another important consideration. Take care that the