Radio Broadcast (May 1923-Oct 1923)

The "How Far Have You Heard?" Contest 235 of more than 600 meters, as the R. F. transformers will not handle waves over that length. Separate B batteries are used for the radio and audio frequency, but a single 6-volt A battery is used foi both. Jacks for the detector and each stage of audio frequency are supplied for use on signals from stations close enough not to require the full power of the set. This saves the batteries and tubes a little. The tuning is controlled by two condensers — a 43-plate variable in the primary circuit and a 23-plate variable and vernier in the secondary circuit — and two potentiometers, one used as a stabilizer. A word about condensers, both fixed and variable. From my experimenting with different kinds and makes of both types of condensers, I have discovered that those whose movable and stationary plates are very close to each other are not as practical as those having the plates a little farther apart because of the fact that dust particles are floating in the air at all times, and some of these settle on the plates of the condensers. In time, enough of these particles may collect so as to cause some of them to touch each other as the plates are moved, thus causing a discharge between the plates of the condenser, the dust particles acting as a high resistance conductor. If this should happen, the set would become very noisy and would cut its efficiency very materially; so, for this reason, encased condensers are best. Due to the fact that there are no spring contacts to come loose or to wear out, variable condensers whose plates are balanced have been found to be more efficient for longevity and hard use. Another important thing is the selection of fixed condensers. Paperinsulated fixed condensers are liable to puncture if high B battery voltages are being used, and when this happens it sounds as if all the arc lights and X-Ray machines in the community were inside the set! From some few experiences like the above, I have found that micainsulated fixed condensers are more satisfactory. The tubes are mounted in cascade, back of and about two inches away from the panel. They are placed behind their respective rheostats so as to keep the leads from the latter as THE RECEIVER BUILT BY MR. HARRINGTON Whose success in transcontinental reception can be attributed, in large measure, to soldered connections throughout his set short as possible, and all the connections are soldered. Too much stress cannot be laid upon the importance of soldered connections. All joints and connections, leads to transformer and socket binding posts, battery binding posts, etc., should be soldered. There will be no " rockcrushers" or "stamp mills" in a set so connected. In order to keep their leads as short as possible, the transformers are set directly behind the tubes, and have their cores at right angles to each other. The transformers are separately shielded and the shields grounded. A C battery is used to impress a heavier negative charge on the grids of the amplifier tubes in the audio frequency, and this tends to cut out distortion and also to increase the volume of the signals. The voltage used here is varied to get the best results, sometimes being as low as 1 \ volts but never over 7! volts. 90 volts on the plates of the R. F. tubes, 18-23 on 'the detector, and 90 on the A. F. amplifiers bring the best results. Two outside aerials are available for use. One, a 5-wire inverted L, 44 feet long and 65 feet high with a fan shaped counterpoise containing 350 feet of wire is very efficient on the more distant stations. The other, a single wire 165 feet long, 65 feet high at one end and 50 feet at the other, works very well on the local and near distant stations. The leads in are taken from the higher end and are as short as possible. For reception up to 500 miles, where great strength of signals is not desired, a loop aerial is used. With it the set becomes ultra-sensitive. Music from stations 300 miles away using a reasonable amount of power output in their aerial, comes in strong enough to operate the Baldwin phone and be heard over the entire room. Cunningham 301A tubes are used throughout the set, and I