Demodulator for signals hybrid modulated by more and less significant

Abstract

A demodulator for demodulating a received quadrature amplitude modulated signal includes a generator for generating a local carrier signal, a synchronous detector responsive to the local carrier signal for deriving in phase and quadrature phase base bank components from the modulated signal, means responsive to the received signal for deriving timing pulses, a first sampler responsive to the timing pulses for producing samples of the in phase base band components, and a second sampler responsive to the timing pulses for producing samples of the quadrature phase base band components. First delay means for delaying the in phase component samples, second delay means for delaying the quadrature phase component samples, a correlation circuit responsive to the undelayed and delayed, in phase and quadrature phase, component samples for producing a correlation signal. A synchronous pulse generator responsive to the timing pulses and the correlation signal produces synchronizing pulses. A phase control circuit responsive to the synchronizing pulses and the undelayed and delayed, in phase and quadrature phase, component samples produces a control signal. The control signal is supplied to the local carrier generator to control the phase of the local carrier signal relative to the received signal.