Transceivers

Abstract

According to the present invention a common channel duplex a.m. transceiver comprises a pair of multiplicative mixers arranged to receive signals from two sources, receiver aerial means constituting one of the sources and arranged to feed received signals to the multiplicative mixers, transmitter aerial means, and oscillator/modulator means constituting the other of the sources and arranged to feed signals for transmission to the transmitter aerial means and to provide for the mixers of the pair, local oscillator signals which are at the same frequency as the carrier frequency for transmission and wherein it is arranged that the carrier frequency for transmission and the carrier frequency of the received signal are common to a single channel of the transceiver, phase quadrature means connected to provide a phase quadrature relationship between two signals fed to the mixers of the pair from one of the said sources, a pair of signal combiners fed one from each mixer, a pair of low-pass filters fed one from each combiner, a pair of correlator arrangements each having first and second input ports and an output port, the first input port of each correlator arrangement being fed one from each low-pass filter, detector means via which signals from the oscillator/modulator means are fed to respective second input ports of the correlators, the correlator arrangements being operative to correlate signals derived from the low-pass filters with detected signals from the oscillator/modulator means thereby to provide at the said output ports feedback signals which are fed one from each correlator to respective combiners, and an a.m. demodulator responsive to signals fed from the low-pass filters for providing a.m. output signals corresponding a.m. modulation carried by the received signals.