Abstract: The device for recovery of the clock frequency of a digital signal comprises a rectifier, a filter having a very narrow bandwidth coupled to the first input of a phase comparator of analog type, a controlled oscillator, the output of which delivers the recovered clock signal and is coupled to the second input of the phase comparator via a low-pass filter. The output of the phase comparator is connected to the input of a loop filter, the output of which is connected to the control input of the oscillator.

Abstract: A clock-frequency recovery device applicable to digital transmission systems for radiocommunications by tropospheric or ionospheric propagation as well as from moving vehicles includes a rectification circuit, a filter circuit, a switching circuit and an output circuit comprising a delay line controlled by a phase-locked oscillator. The input of the output circuit is connected to the output of the filter circuit when the noise level of the transmission is below a predetermined threshold value. The input of the output circuit is connected to its own output when the noise level of the transmission is higher than said threshold value.

Abstract: The invention relates to a multicarrier signal receiver protected against unwanted signals. Between the high frequency circuit and the intermediate frequency circuit, it has a frequency-selective attenuation and preselection circuit, while a circuit for detecting the disturbed channels is coupled to the demodulation circuit and supplies control signals characteristic of the appearance and disappearance of the unwanted signals. The receiver also comprises a control circuit eliminating the disturbed channel for processing demodulated signals and for the automatic control of the intermediate frequency amplifier circuit, and controlling the attenuation of the disturbed channel in the selective attenuation circuit.

Abstract: In a system for frequency-diversity transmission, separate and distinct frequency carriers are obtained from the frequency modulation of an oscillator by a pure frequency with an index such that a certain number of Bessel lines thus obtained constitute a corresponding number of separate carriers. All the carriers are subsequently modulated by the information, then power-amplified in a single amplifier having a peak power equal to that of a single signal whose effective power would be the sum of those of the separate carriers. By means of this system, equipment for radio communication by tropospheric or ionospheric scatter propagation can be constructed in a simple manner and at low cost, with a high diversity order.