Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

266 FREQUENCY MODULATION, Volume IFig. 11—Matching the discriminator to the oscillator.bias is approximately equal to the peak amplitude of the applied signalvoltage, the lock-in range will be as shown by Figure 12.For small applied voltages the lock-in range increases rapidly fromzero with increasing signal voltage until it reaches a maximum, andit then decreases slowly with further increase in voltage as shown bythe dashed line.In practice, the screen and plate resistors can be chosen to correctthis falling off of the lock-in range with increased input. This compensationwill give the constant lock-in range beyond the knee of thecurve as shown by the solid line.Effect of Tube ConstantsThe lock-in range depends upon the amount of quadrature currentthat can be developed by the tube.This means that the tube shouldhave a fairly high zero-bias plate current and a fairly high mutualconductance from the No. 1 grid to plate. This assures large pulsesof plate current which produce the required reactive current. TheAPPLIED VOLTAGEFig. 12—Effect of signal voltage on lock-in range.