Abstract: A frequency shift keying signal in analog form alternatively includes a mark frequency, f.sub.m, and a space frequency, f.sub.s. Demodulation of the frequency shift keying signal is achieved in a digital circuit utilizing a clock and first and second counters. Each counter may have a count N. The clock produces pulses with a frequency of 2Nf.sub.c ; where N is the count of the counters, and f.sub.c is a frequency intermediate the mark frequency, f.sub.m, and the space frequency, f.sub.s. Associated digital circuitry permits the first counter to produce an output indicative of the presence of the mark frequency only when the first counter has continuously counted N clock pulses. Further digital circuitry permits the second counter to count only intermittently, and a reset circuit resets the second counter before it can produce a high output signal when the mark frequency is present in the frequency.

Abstract: A signal control circuit for a burst signal transmission system has a comparator for receiving a burst control signal from a burst control signal generator and an output signal from an envelope detector and for generating a difference signal therebetween. The difference signal is supplied to an attenuator, a preamplifier or a nonlinear power amplifier for receiving a modulated carrier wave so as to control attenuation of the attenuator or gain of the preamplifier or nonlinear power amplifier whereby a waveform of the output signal from the nonlinear amplifier is made analogous to that of the burst control signal from the burst control signal generator.