Abstract: A pulse repetition frequency (PRF) detection system is provided for indicating the existence of pulse trains having predetermined repetition frequencies in a composite signal containing pulse trains of different pulse repetition frequencies. The system includes a plurality of independent sorters to which the composite signal is sequentially applied. Each of the sorters is operable to detect a pulse train having a predetermined pulse repetition frequency, to indicate the detection, and to produce pulses for inhibiting or blocking the application of the corresponding pulses of the composite signal on a pulse-by-pulse basis. The sorters may be arranged and interconnected in a decreasing order of frequency detection whereby the signal applied to each successive sorter has all higher frequency detected pulse trains removed therefrom.

Abstract: A circuit for detecting the occurrence of incoming pulses at a predetermined repetition rate while remaining unresponsive to pulses occurring at an even harmonic of such rate, the circuit including a clock pulse generator and resettable counter arranged to count the pulses produced by the generator and to produce an output representing its current count, resetting means for resetting the counter to its "0" count state when an incoming pulse arrives at a time after the arrival of a preceding pulse which started the clock pulse generator which is equal to or greater than the time between pulses occurring at the repetition frequency to be detected, signal producing means for producing an output signal only when the time of arrival between such incoming pulses is equal to the time between pulses at the repetition frequency to be detected, and output signal suppressing means arranged to prevent the production of an output signal when an incoming pulse arrives at a time after the arrival of an incoming pulse which