Radio Broadcast (May 1928-Apr 1929)

124 RADIO BROADCAST DECEMBER, 1928 A variable-speed motor with a highly developed speed control is used in this televisor tions a 2000-cycle current was generated by the motor turning the transmitter disc. This current was carried by a pair of wires, or a separate radiowave channel, to the receiver where it was amplified and fed into a 2000-cycle synchronous motor. This motor was aided in driving the receiving disc by a larger motor adjusted quite closely to the right speed. Rumors have it that the Baird system scrambles a synchronizing signal in with the picture frequencies and thus needs only a single pair of wires or wave band for the whole television operation. If so, and it is simple, it is a great step in the right direction. Then we have many semi-successful speed regulators for variable-speed motors. Some are highly developed mechanical governors similar to the one shown in the picture. It is an interesting diversion to put a slip of paper under the edge of a phonograph record on the turntable and try adjusting the speed to, say, 75 revolutions per minute. After several minutes of timing and readjustment notice if the slip of paper crosses the starting position at the end of every minute. Electrical equivalents often include a resistor that may be short circuited periodically with a button or key manipulated by the operator who must pay close attention to the direction the picture is slipping, bring it back quickly, and not overdo it. The exact speed adjustment may be found finally with any of these devices, but at that moment the disc may be part of a turn around from where it should be, so exact synchronism in every respect is not easy. It is quite a ways from throwing a switch and sitting in the big arm chair for an evening's entertainment as we now do with audible programs (or until some advertising program gets so nauseating we tune in another station) So far it might appear that a synchronous motor connected to the homelighting current is the final answer, as 60 cycles is the standard frequency supplied about 98 per cent., of the homes in this country having public electric service. Indeed, many believe this is the only satisfactory answer, and in most any radio store one can get into heated argument on either side of the question. The only tangible evidence seems to be that a brand of clock, known as a "Telechron," which has a miniature synchronous motor geared down to the hands, seem reasonably accurate when operated on a 60-cycle circuit. The arguments then proceed along lines of how much deviation from 60.0000 cycles is permissible for television, and if the clocks gain or loose a few seconds per day how many times in so many minutes will the pictures be null and void or worse. Also, if the error accumulating during the 24 hours of the day is corrected in the space of an hour by a worse error in the opposite direction what will be the effect? The writer, being of an experimental turn of mind, and thoroughly fed up on such arguments which get nowhere, decided to find out for himself how the various so-called 60-cycle currents in different parts of the country compare, which data forms the "meat" of this article. If anyone else knew the answer, based on measurements instead of hearsay or guess, he has certainly kept it a close secret. A few oscillographs costing a few thousand dollars connected to a few leased long-distance telephone lines and an army of engineers putting local lighting current on the end of these lines suggested itself as the first solution. It never got further than a suggestion, however, as every radio amateur has a reputation to uphold, namely, being able to get any result desired from the stuff in his boxes of junk. (That wasn't the only reason, but it may get by.) Now it so happens that when a neon bulb (costing 55c) held in the hand is moved parallel with an antenna lead of an amateur transmitter it lights bright and dim in spots if a poor filter is used in the transmitter plate-supply system. If no filter is used at all there are spaces between the bright spots that are dark, especially if a single oscillator tube is used in a transmitter operating on one half of the a.c. cycle. This lamp acts the same way if connected through a transformer to the output of several stages of audio-frequency Table L Comparisons of Lighting Frequencies amplification after an ordinary short-wave tuner has been adjusted to similar signals from other amateur stations. Now it was only necessary to compare these flashes produced by the distant station with those caused by the local lighting current to measure their difference in frequency. Here at last was found one desirable feature of the class of transmitter which is most cursed by broadcast listeners in its immediate vicinity! The first measurements were made by passing enough of the local house current through the neon lamp to light it to about half brilliancy or about the same intensity as the signal which was passed through the same lamp. When the incoming signal was in step with the local power the *Time Call Location Sec. per Rev. Direction Frequency 8:21 3br Toronto, Ont. 2.2 Same 59.546 8:22 3als Richmond, Va. 5 2 Same 59.615 8:27 3als Richmond, Va. 17 0 Same 59.882 8:37 Tampa, Fla. 75 Against 62.666 8:39 3ajd Catonsville, Md. 1 0 Same 58.000 8:42 9beu St. John's Sta., Mo. 3 Same 59.333 8:45 8dvm Not Listed ? ** 60.000 8:49 WIZ New Brunswick, N. J. 24 7 Same 59.927 9:00 WIZ New Brunswick, N. J. 23 7 Against 60.084 9:02 2bgz Jamaica, L. I., N. Y. 60.000 9:04 3apq Quakertown, Pa. 5 Against 60.400 9:06 2bkh Bloomfield. N. J. 30 Same 59.933 9.09 4AAR Elkin, N. C. 5 3 Against ** 60.378 9:11 2wi Westfield. N. J. y 60.000 9:13 CQ (Unknown) 5 7 Against 60.351 9:14 nu (Unknown) 6. 5 Against 60.308 9:15 3a VL Not listed 7 3 Against 60. 274 9:16 3avl Not listed 5 Against 60.400 9:17 3avl Not listed 6 2 Against ** 60. 323 9:19 2wi Westfield, N. J. ? 60.000 9:22 4AHO Not listed 240. Against 60.008 9:25 WYE Mt. Clemens, Mich. 120. Same *** 59.984 9:30 9e\vq Richmond, Ind. 7 Against *** 60.286 9:32 3cgf Phoebus, Va. 17. 2 Same 59.884 9:35 8dbg East Liberty, Pa. ? 60.000 9:40 2blx White Plains, N. Y. ? 60.000 9:43 1CTP West Haven, Conn. 20 Against 60. 100 9:46 8bfr Jeanette, Pa. 20.4 Against 60. 098 9:50 3apq Quakertown, Pa. 10 Against 60.200 9:53 ICRS Not listed 28 Same 59. 929 9:57 4ab Raleigh, N. C. 5. 8 Against ** 60.385 9:59 8dnj Bay City, Mich. 7 60.000 10:00 9erh Chicago, 111. 21 Against 60.096 10:05 9ejo Geneva, 111. 30 Same 59.933 9 A.M. WGT San Juan, Porto Rico 1 Against 62.000 Time p. M. (Eastern Daylight Saving) unless indicated otherwise. "Exact synchronism or very close to this. "Peculiar modulation producing additional "spokes." FIG. I Diagram A shows the essential parts of a simple television transmitter and receiver. Diagram B indicates the si%e and position of the reproduced image. lamp became bright, and when it slipped behind a half cycle, or gained a half cycle, so it was 180 degrees out of phase the lamp went out or became dim. This would have been entirely satisfactory except for four things: It was hard to time or count the pulsations when the station was keying; it was slow and discouraging trying to call and instruct the right amateur stations to hold their keys down for a few minutes; there was no way of knowing which frequency was the faster, and atmospheric fading, quite rapid at this time of the year, made the results very confusing. Experimental research at this point gave way to plain "monkeying." Engineers seldom use this undignified expression but their "cut and try" is much the same. An old quarter horse power induction motor with a white cardboard disc on the shaft and a black diameter line inked across the disc was illuminated with the neon lamp connected on the local lighting current. With this arrangement it was noticed that the motor ran so near synchronous (1800 r. p. m.) that the black line looked like a four-spoke wheel slowly turning backward (like old time movies of buggy carriages). A hack saw and cold chisel on the rotor soon made a synchronous motor and the "spokes'" thereafter stood still. But when the neon lamp was lighted by the amplified signals of distant "raw-a.c." amateur stations the spokes revolved, sometimes fast, sometimes slow, sometimes backward, and sometimes forward, and therein hangs this tale.