Abstract: System for the secret transmission of audio signals having at one end a coding arrangement comprising an input low-pass filter which selects the secret audio signals to be transmitted, two parallel signal paths at the output of this filter, each path having a modulator of the phase-inverting type and a further low-pass filter, a stage for generating two modulation signals of the frequencies F.sub.1 and F.sub.2 and a first change-over switch which alternately switches through the output of the two paths in dependence of the state of a binary quasi-random signal, the encoded audio signals to be transmitted being available at the output of the change-over switch, and in which at the other end there is a decoding arrangement comprising a stage for regenerating the modulation signals of the said frequencies F.sub.1 and F.sub.

Abstract: A substantially digital circuit for correcting phase deviation which comprises a phase comparison stage and a synchronizing control stage. The phase comparison stage includes a reference oscillator, a frequency divider connected to the output of the oscillator and whose output signals constitute the useful line deflection drive signals, as well as a phase comparator comprising a logic circuit and a counter. The logic circuit receives the output signals of the frequency divider and the line synchronizing signals and the counter, which is connected to the output of the oscillator produces a signal which is representative of the phase deviation detected in control stage, the latter comprising a state detector for detecting the synchronized state, in which the phase deviation detected is below a limit value or the unsynchronized state and a correction signal generator for controlling the division ratio of the frequency divider.