Abstract: The invention relates to information transmission systems in which the band is spread at the transmitting end by means of a pseudo-noise sequence and is returned to normal at the receiving end by a similar sequence. In such systems it is essential that the frequency of the various oscillators used for the frequency conversions should be kept constant, or alternatively that the oscillators at the receiving end should be synchronized with the oscillators at the transmitting end. In accordance with the present invention the oscillators at the transmitting end are synchronized by the clock frequency of the code generator and at the receiving end this clock frequency is extracted from the received signal and used to synchronize the oscillators in the various conversions. One of the oscillators at the receiving end may be a Gunn oscillator which is synchronized by applying the output of the pulse generator to its synchronizing input terminal through a frequency multiplier.

Abstract: A phase regulating circuit operating in accordance with the delay lock loop principle DLL for synchronizing the phase of a pseudo-random generator at the receiving end which is controlled by a pulse train oscillator and having two identical signal channels and wherein the inputs to the signal channels from the pseudo-random generator is rapidly switched between the two input mixers and wherein the output of the mixing networks is rapidly switched to a difference forming device so as to provide an output for the frequency control circuit of the pseudo-random generator.