GB1257319A - - Google Patents

Abstract

1,257,319. Phase controlled systems; secret transmission. GENERAL ELECTRIC CO. Ltd. 20 Feb., 1970 [20 Nov., 1968], No. 55172/68. Headings H3A and H4R. A circuit for determining, or providing a response dependent upon a time displacement T u between two signals having the same random or quasi-random waveform, comprises an arrangement e.g. Hilbert Transform network 8, for imposing quadrature phase shifts between discrete components of the same frequency in a frequency band in the two signals without introducing any gain variation with frequency and a correlator 4 e.g. of a quadrant multiplier 5 and a low-pass filter 6, to provide a correlation signal having a characteristic which is an odd function of time displacement. The circuit also includes a timing network 3 controlled in dependence of said output signal to produce a time delay equal to that of a test network 2. The test network may correspond to the delay involved in a signal utilization path such as target receiver path delay in a radar, or a portion of the system loop in a complex processing plant. The two signals may be derived from a single analogue random generator 1 or from a single or two identical digital quasi-random generators 10, 11 as shown in Fig. 6 connected to band-pass filters 14, 15. The two generators 10, 11, may be used in a voice communication system comprising a unit 20 supplying a transmitter 21 with speech at a constant power level i.e. eliminating variations at a syllabic rate, the speech being superposed on the quasi-random analogue signal. The signal path between the filter 14 and the Hilbert transform network 17 constitutes the unknown time delay and the P output of 17 and Q output of 18 are applied to a correlator 19 to produce a signal to be applied to circuitry (not shown) to control clock generator 11 so that the time delay in signal path 13, 15, 18 equals the above unknown time delay. The Generator 13 is synchronized to the generator 12 and subtraction of the noise output from 15 at S yields a pure speech signal restored to its original power level by unit 22. The system may be used as part of an analogue or digital communication link with a digital link inserted between generator 12 and band-pass filter 14 and an analogue link inserted between separate parts of the band-pass filter 14.