Radio Broadcast (May 1928-Apr 1929)

40 RADIO BROADCAST NOVEMBER, 1928 FIG. 5. SCHEMATIC DIAGRAM OF MODULATOR in the phones of the pick-up receiver. The assistant must enunciate decently as otherwise he is worse than useless. He also must hold the mike in the proper position and at the correct distance. With these conditions as a good start one may now adjust the gain control, microphone voltage and bias of the modulator tube. The bias may be set at 10 per cent, of the modulator plate voltage at the beginning, and varied from this point. In general a large bias has an advantage in keeping the tube cool. If one has meters available it will be found good practice to adjust the currents to modulator and amplifier tubes so that they are of nearly equal value. Having once found a good setting one may watch the antenna meter thereafter, judging from its movements the degree to which things remain the same. A better way of doing this is to put a d.c. milliammeter in the modulator plate lead — and leave it there. If an assistant is not available one may place the "mike" before a good loud speaker running at a moderate level on some decent input — not a jazz band. The listening is then done as before. It is scarcely necessary to say that all adjustments of this sort should be made with the antenna cut off. The beginner will find himself confused when trying to determine the difference between good and bad speech from his own set. He is able to find some help from the fact that a bad phone makes no difference between the letters F and S, and very little between P, B, D and T. In addition to this it very probably will " blast " on some notes and on some of the vowel letters, especially O. Repeating alphabet and the groups of letters just mentioned, together with reading and counting are all good tests. One entirely useless test is to get on the air and work someone. The truth does not lie in that quarter — or perhaps I lack faith through being neither a "brasspounder" nor very much of a "ragchewer," but mainly an occasional transmitting experimenter. One very important point to remember is that the best of phones will not compensate for C6(Plug in) RFC. V.QMiL' 0+ Amplifier O High Voltags FIG. 8a. This circuit is utilized when a 210-type r.f. tube is used with a plate potential in the order of 400 volts from a not-too-good sloppy handling of the "mike." One must keep at a fixed distance and speak in an even tone of voice. Looking around the room does not help, nor does a cigarette or cigar between the lips. Consider the good care taken in broadcast announcements as compared to the ignorant use of the same equipment by a new speaker on his first broadcast station. AND AS FOR THE KEY \A/ t^le one may ^° rnany things in* " correctly. The best rule is to send little and listen much until one learns the manner in which not to do things. This is easily done for tained. Warning — the antenna meter is easily burned out if kept off-scale long. If it runs off — detune or pull the switch instantly. Then shunt the meter with a length of wire — 6 inches at a guess — and try again. If it still runs off shorten the shunt until it does not. The process takes some practice and should be done for all the bands after which we will be ready to — but that's next month s story. AMATEUR WAVELENGTHS THAT there be no confusion regarding who may transmit, and what frequencies are available for amateur operations, the following quotation from "Revised Amateur Regulations" dated March 6, 1928, and signed by W. D. Terrell, Chief, Radio Division of the Department of Commerce, gives all the necessary information. "An amateur station is a station operated by a person interested in radio technique solely with a personal aim and without a pecuniary interest. Amateur licenses will not be issued to stations of other classes. "Amateur radio stations are authorized for communication only with similarly licensed stations, except as indicated below, and on wavelengths or frequencies within the following bands: FIG. 6. PICK-UP RECEIVER USING A 199 TUBE the average performance is not perfect and the air is still cluttered up with tireless "CQ" callers who make the most imperfect phone seem holy and pure. When one does call — let it be at a speed where the sending will be readable for "It isn't the words per minute but the messages per hour that count" — and again — "What profiteth speed when but used to repeat what was sent badlyr " Of the set itself little need be said when operating for radio-telegraph transmission only. The Kilocycles Meter s 401,000 to 400,000 0.7477 to 0.7496 64,000 to 56,000 4.69 to 5.35 30,000 to 28,000 9.99 to 10.71 16,000 to 14,000 18.7 to 21.4 8,000 to 7,000 37.5 to 42.8 4,000 to 3,500 75.0 to 85.7 2,000 to 1 ,500 150.0 to 200.0 and at all times unless interference is caused with other radio services, in which event a silent period must be observed between the hours of 8:00 p. m. and 10:30 p. m., local time, and on Sundays during local church services. Sw. \ 1 A.KEYS-6 FIG. connections are explained in the diagrams; the standard practices are too lengthy to be put down here. The Radio Manual by Sterling at this moment seems alone to contain the new regulations. One comment with regard to the set can be made. If for any reason it is desired to use C bias on the r.f. amplifier tube in place of the unorthodox resistance bias shown in the October paper this may be done by feeding the C battery to the clips of the cartridge-resistance-mounting. The oscillator-amplifier set-up has been so laid out that the C battery can be placed behind it and leads run in without difficulty. If, as in my case, the intention is to use the setup portably the clips themsevles should not be disturbed. Perhaps I have been wrong in the assumption that tuning the oscillator-amplifier is self-evident. The procedure is to set the oscillator with the aid of the wavemeter, then to place the little lamp-loop near the amplifier plate-coil (Aero Coil L2) and tune that circuit for greatest brightness, finally to revolve the antenna condenser until the greatest antenna meter reading is ob B.-KEYS R.F.CCt. C KEYS BOTH -B & R.F 7. CONTROL CIRCUITS Amateur radio telephone operation will be permitted only in the following bands: Kilocycles 64,000 to 56,000 3,550 to 3,500 2,000 to 1,715 Meters 4.69 to 5.35 84.5 to 85.7 150.0 to 175.0 RFC. R-F.C. O+B ■ O-B A z FIG. 8b This arrangement must be employed if the condensers will not stand the high amplifier plate voltages