(under subclass 606) Subject matter in which the system includes a reference signal of the same frequency as the carrier frequency which is used with means to compare it with the modulated signal to obtain the modulating wave.
SEE OR SEARCH THIS CLASS, SUBCLASS:
684, for servo systems in which the novelty lies in the detector which may be an F M detector. Also subclass 318, for motor speed control by electrical frequency difference type detector.
SEE OR SEARCH CLASS
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems,
42, for miscellaneous frequency comparison between a fixed frequency signal and a variable frequency signal. 329, Demodulators,
103, and 110+ for frequency demodulation, per se.
340, Communications: Electrical,
825.71+, for frequency responsive remote control systems.
