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SIXTY-EIGHT STATIONS INSTALL GENERAL RADIO COMPANY MONITOR
The General Radio Company, of Cambridge, Mass. , has already equipped 68 stations with its new frequency monitor which will enable these broadcasters to meet the rigid requirements of General Order No. 116 which goes into effect June, 1932. The General Radio Monitor indicates directly the deviation from channel frequency on a large pointer-type meter in the operating room.
"This equipment is simple and is easily installed and maintained by the station operating personnel. Its guaranteed accuracy, although set at a conservative figure, is well in excess of that demanded by the Commission, and with careful operation an even better accuracy can be obtained", according to H. B. Richmond, of the General Radio Company.
"The essential element in the new monitor is a highly stable piezo-electric frequency standard which operates at a frequency differing from the assigned channel by exactly 1000 cycles per second (usually on the high-frequency side). Voltages from this standard and from the unmodulated master oscillator of the transmitter are supplied to a new type of audio-frequency meter which indicates directly and continuously the deviation of the resulting audio-frequency beat tone from 1000 cycles per second.
"For example, if the transmitter is off-channel by 40 cycles per second on the high side, the beat-tone frequency is 960 cycles per second; if off-channel 40 cycles per second on the low side, the beat-tone frequency is 1040 cycles per second. Actually, the large meter dial is marked in Cycles per second so that it reads *40 cycles high* or ’do cycles low1, as the case may be. No calculations are required; the device is direct reading.
"The crystal oscillator utilizes an entirely new circuit which minimizes the effect of temperature variations on the quartz plate and makes the resulting frequency more nearly independent of the circuit constants than has heretofore been possible. The result is a system of very great stability in which the checking of calibrations is made considerably easier. For instance, crystals may be recalibrated at the end of the one-year guarantee period, or, in case of accidental damage to the plate, a new one maybe ordered without returning the oscillator.
"Our development work on the frequency deviation meter has been in progress for several years. Experience has proved conclusively that an indicator type of instrument which shows the direction as well as the magnitude of a frequency drift is the only satisfactory scheme.
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