Abstract: Intermediate frequency signals are produced by mixing with an oscillator voltage and subsequently filtered and demodulated. The oscillator voltage or the resonance frequency of the filter or filters are followed up by a control voltage derived from the demodulated signal corresponding to the intermediate frequency. The perturbatory phase modulator occurring as a result of the control lag is compensated by opposite-phase phase-modulation which is superimposed on the intermediate frequency. In this, the phase modulation is achieved by a phase modulator which is connected with the output of a demodulator by a matching circuit. Another possibility for achieving phase modulation of the intermeidate frequency is to modulate the oscillator of the mixing stage.