Abstract: A four stage phase displacement modulator has a numerical signal generator with four outputs, which respectively deliver four signals, each signal having a frequency which is equal to the carrier frequency. The respective phases of the four stages are 0, .pi./2, .pi., and 3 .pi./2, which respectively appear at four inputs of a encoding device. In addition, the encoding device has two governing inputs which respectively receive two successions of impulses which constitute the modulating signal. The output of the encoding device is connected to the input of a band-pass filter, the output of which delivers the four phase modulated signal. The encoding device has a validation input to which is coupled the output of a monostable flip-flop driven by a clock signal at the rhythm of pairs of binary bits applied to the encoding device. Variable capacitors adjust the dephasings between the delivered signals.