| 摘要 |
971,109. Cross correlation detectors. GENERAL ELECTRIC CO. Jan. 30,1961 [Feb. 8, 1960(2)], No. 3437/61. Heading G1U. [Also in Divisions H3 and H4] A system for distinguishing recurring signals from random noise comprises a delay line 1 to which an input containing a signal to be recognised is fed. Time spaced amplitude values of the input signal derived from spaced tappings on the delay line are initially stored in a unit 2 and are each - compared with subsequent values of the input signal amplitudes at the respective tappings in a correlator 3. If the correlation between input and stored signals is above a certain level a threshold detector 4 provides an output to an arithmetic unit 5 which revises (weights) the stored values according to the subsequent input values. This process is repeated. The threshold of detector 4 varies automatically with the time interval between successive operations and becomes higher as this interval lessens. Thus with successive revisions the stored values gradually become free of noise and enable the recurring signal to be detected. In Fig. 2 the input signal values at tappings 12, 13.... 14 of the delay line 10 are continuously sampled by capacitors 15, and also multiplied at 16 by the corresponding stored signals on the capacitors 19, via cathode followers 20. The multiplier outputs are fed over summing resistors 21 to an amplifier 22, the output e in of which is thus indicative of the cross-correlation between the stored and input signals. The amplifier output e in is fed to a threshold detector 23 which in turn provides an input pulse to a pulse generator 24 each time the correlation function e in reaches a peak greater than the previous peak of e in that is e in / max stored on a capacitor 27. Any output from the pulse generator 24 energizes thyratron controlled relays 37 each associated with a respective delay line tap 12, 13. . ., so that each sampling capacitor 15 is momentarily disconnected from its associated tap and connected across the corresponding storage capacitor 19 to bring the stored voltage thereon nearer to the sampled voltage on capacitor 15. In this way, as the number of these operations increase, the voltages stored approach more closely to the required recurring signal. A resistance 40 in parallel with each capacitor 19 determines its discharge rate and hence the rate at which any charge corresponding to a signal which does not recur for a long time, disappears. The recurring signals stored on the capacitors 19, are read by a commutator 41. A number of systems may be interconnected, Fig. 5, (not shown) to recognise a number of different signals. |
