Radio Broadcast (May 1928-Apr 1929)

M 'ANY listeners a. 2 turning away from the narrow confines of the broadcast band, in which too often musical excellence and technical perfection are stifled under the never-ending flood of politics and sectionalism. Naturally enough, the recent trend has been toward the short waves. It would be useless to claim that there are more interesting things above the broadcast band than below it, but much of the real pleasure of radio lies in a broad interest rather than a narrow one, in standing aloof from the fads, in being somewhat original. And an exploration of the waves between 550 and 2500 meters will not prove entirely what Carl Dreher calls "chocolate-and-pineapple" originality. In the July issue of Radio Broadcast a short-wave adapter for the R. B. Lab. receiver was described. This article continues the completion of the Lab. receiver, but the adapter here described may be used with practically any set having one or more stages of audio-frequency amplification. As the adapter contains a detector circuit, only the audio circuits of the receiver are used. The adapter's phone broadcast reception possibilities, in America at least, are slight. Most of the signals within its range are in code. But the adapter makes a good code practice set for those who wish to broaden their radio knowledge in this direction. GENERAL DESIGN The adapter, whose circuit is shown in Fig. 1, consists essentially of a tuned detector circuit which can be made to regenerate or oscillate. For economy and compactness the regeneration condenser is quite small. The antenna coupling is inductive and variable. The detector output terminates in a tube base which plugs into the detector socket of a standard broadcast set. The adapter detector (with its high tuning range) in this way temporarily replaces the set detector. Two Silver-Marshall plug-in coils Li, L2, and L3 — the 111-D and the 111-E — are THE long-wave adapter described here was designed in conjunction with the short-wave adapter described in the July number of Radio Broadcast, to extend the receiving range of the R. B. Lab receiver, so as to include all the wave-bands between 20 and 2500 meters. However, the unit may be used with any receiver that embodies one or more stages of audio. By substituting a 0.0005-mfd. tuning condenser for the 0.00035mfd. condenser illustrated the tuning range may be extended so as to receive NAA, at 2677 meters, and other stations above 2500 meters. Also a plain dial may he substituted for the more expensive vernier dial mentioned in the list of parts, since long-wave stations will remain tuned-in over several dial degrees. — The Editor. used. With the 0.0003 5-mfd. tuning condenser, Q, the respective tuning ranges of these coils are 6001400 meters and 1 100-2500 meters. The calibration chart in Fig. 2 will probably hold quite Ant. A A+ B + FIG. I. THE CIRCUIT DIAGRAM 275 approximately for any adapter, as on long waves circuit changes do not have a very great effect. A 0.0005-mfd. tuning condenser would extend the tuning ranges slightly, and would be desirable for those who wish to copy the naa time, weather, and press broadcasts on 2677 meters. For effective reception at higher wavelengths the antenna should be rather long. It is true that many stations can be heard on the usual 100foot broadcast antenna, but signals are louder with a longer one. The writer used a 250-foot single wire in tests, and 750 to 1000 feet would not "be too long. Even on short waves a long, low single wire seems to improve the signalnoise ratio upon which satisfactory reception depends. Where the lighting wires are overhead rather than underground, a light socket antenna plug offers possibilities. constructional details HP HE construction is plainly apparent from A the diagrams and photographs. The unit is so simple that none should have trouble with it. The arrangement of parts and wiring can, of course, be varied to suit individual requirements. The wiring is done with solid Acme Celatsite. As explained in the short-wave adapter article, the a.c. tube is not a good oscillating detector. For this reason a d.c. tube is always used in the adapter; it may be almost anything from a ux1 12A to a ux-199. The ux-i 12A, UX-200A and Ceco H are more sensitive than others. If a ux-199 is used with a 6-volt battery the rheostat, R2, should be 50 ohms. The plug connections are clearly shown in Fig. 4. If the receiver power is direct current, the adapter requires no additional battery. If the receiver power is alternating current, the adapter requires an A-battery. For intermittent use with a storage battery tube four or eight dry cells should do; a ux-199 tube will run even on a 45-volt C-battery. A list of the parts used in this particular set is given below.