Derangement detector in a receiver of a system for data transmission by

Abstract

A receiver of a system for data transmission by means of p-phase modulation comprises a digital phase discriminator with a calculating unit which calculates in a first interval of each sampling period the in-phase and quadrature components of a signal derived from a passband signal at sampling instant jT by a phase rotation over an angle equal and opposite to the phase of a reference carrier at instant (j-1)T. A simple derangement detector is obtained by means of a sign detector for a component supplied by the calculating unit during a second interval of each sampling period, the phase of the reference carrier then having been subjected to a phase rotation equal to the phase variation of the transmitted carrier, and by means of a calculated circuit which calculates the quantity .vertline.x.sub.3 .vertline.-kx.sub.3, where k<tan (.pi./p) and x.sub.3, x.sub.3 are the in-phase and quadrature components supplied by the calculating unit during a third interval of each sampling period, the phase of the reference carrier then having been subjected to an additional phase rotation equal to +(.pi./p) or -(.pi./p) depending on the sign determined by the sign detector. Alarm pulses are supplied at a negative sign of the quantity calculated by the calculating circuit.