Abstract: A communication system comprising one or more communication units (transceivers) in which the transmitter includes means for modulating the carrier wave in such manner that the carrier amplitude is not varied by signal information but nevertheless signal information content can be extracted by conventional amplitude-modulation detection at the receiver. The signal power spectrum is varied along the frequency axis due to angle or phase modulation. The main components of each unit includes a transceiver, antenna and a phase-reversal modulator-correlator module between the antenna and the transceiver. The modulator-correlator module is bidirectional in operation and therefore it further modulates a spectrum of any signals from the transceiver which are radiated from the antenna and likewise modulates the spectrum of any electromagnetic wave signals received by the antenna.

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