GB1518006A - Frequency-selective signal receiver - Google Patents

Abstract

1518006 Frequency selective receiver INTERNATIONAL STANDARD ELECTRIC CORP 6 April 1976 [10 April 1975] 13865/76 Heading G4H [Also in Division H4] A frequency-selective signal receiver comprises one or more correlator units A1, ...., H 4 each producing two outputs U, V which are squared SQ and added ADD and then applied to a circuit CC which produces an output only when the adder output exceeds a threshold value S, the input signal X being split into two channels in each correlator unit and multiplied therein with a reference signal and with the signal phase displaced by 90 degrees respectively, then integrated. As described, the receiver recognizes a signal X consisting of one out of four high frequencies f 1 -f 4 and one out of four low frequencies f 5 -f 8 . The receiver comprises eight correlation circuits A-H each receiving a respective frequency as reference signal and each containing four correlator units, e.g. A1-A4, whose operation is time-displaced by a fixed amount. The outputs U, V from A1-H1, then A2-H2, &c., are applied in turn to gates U1-U16 connected to the squaring circuit SQ; U<SP>2</SP>, V<SP>2</SP> are applied via gates U17, U18 and stores ZR1, ZR2 to ADD and CC, and the two outputs (one from A-D and one from E-H) from CC are applied via gates U19-U26 to register R decoder K and register AR to provide a signal A which indicates the received signal frequency combination. The integrators in each correlator unit may be digital counters VRZ, Fig. 5 (not shown).