Abstract: A phase lock loop having an instruction input to which is applied the output signal of the frequency-modulated variable frequency oscillator. The pass band of the loop is regulated in order to obtain at its output, a frequency-filtered signal corresponding to the frequency-modulated signal applied to the instruction input. A phase demodulator having inputs coupled to the instruction input of the loop and to the output of the loop supplies a signal corresponding to the modulation index of the signal supplied by the oscillator. This signal is compared with a reference signal by a comparator circuit, which supplies a control signal to means for adjusting the amplitude of the modulating signal applied to the input of the oscillator, in order to permanently adjust the modulation index of the frequency-modulated signal, produced at the output of the oscillator, to the value of the desired modulation index corresponding to the reference signal.

Abstract: A satellite telecommunications system having peripheral stations and a central station which communicate with each other via a satellite. The central station transmits a reference frequency to the peripheral stations via the satellite. The central station receives the reference frequency, determines the frequency drift and transmits a controlling signal to the satellite. The reference frequency transmitted by the satellite is controlled by the controlling signal so as to be stable in time.