Periodic signal detector

A periodic signal detector is disclosed that may be incorporated in a voice actuated communication system. It comprises a series connected low pass filter, limiter, and bistable multivibrator, the outputs of the latter of which are connected to a pair of sweep generators. A differential comparator detects the difference in the outputs from said pair of sweep generators and uses said differences as a signal to trigger a first monostable multivibrator. A second monostable multivibrator is triggered by one of the outputs of the aforesaid bistable multivibrator. An AND gate detects the simultaneous occurrence of the outputs from said first and second monostable multivibrators and produces an output in response thereto. An averaging integrator averages the output signal from said AND gate to a more useful level before it is, in turn, used to effectively key a transmitter or some other utilization apparatus. An input utilization apparatus, such as a receiving transducer, provides the complex frequency input signal to the subject periodic signal detector, from which a predetermined frequency periodicy is to be detected thereby.