| 摘要 |
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. In another arrangement the frequency of the Gunn oscillator is controlled by comparing the phase of the output with the phase of the output of a frequency multiplier supplied by the pulse generator. In yet another arrangement the outputs of the Gunn oscillator and the frequency multiplier are mixed to form a difference signal which is compared in phase with the outputs of a low frequency reference oscillator.
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