Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

176 FREQUENCY MODULATION, Volume Iwhich there is little or no resistance to slow rotation of the motor shaft.This motor responds on application of voltage to frequencies up to 1000cycles.In order to make tuning and performance checking of the frequencycontrol simple and rapid, the necessary test equipment is built into theexciter. A cathode-ray oscilloscope, with the required switching mechanism,is provided. By selecting the proper switch position it is possibleto check the division in each divider and also the tuning andmultiplication of the tripler stages, by means of Lissajous figures.The accuracy of the frequency control is so exact that it is limitedby the heat cycle of the crystal oven. During test, this effect producedBeBP» urQ»0.Fig. 13a regular variation of ± 40 cycles at 100 megacycles as the thermostatof the crystal oven went on and off. The control action is smooth andrapid. There are no critical adjustments. The range of control can beas high as ± 1000 cycles at 20 kilocycles—that is, ± 5 per cent. At100 megacycles this amounts to ± five megacycles. In case of failure ofthe frequency control during a program, operation can be continuedwith manual frequency control by locking the motor shaft and adjustingthe frequency with a vernier tuning control located on the masteroscillator tank coil.