GB1393071A - Circuit arrangement for a selective signal receiver - Google Patents

Abstract

1393071 Frequency analysis INTERNATIONAL STANDARD ELECTRIC CORP 4 Jan 1973 [11 Jan 1972] 559/73 Heading G4H Apparatus for the analysis of a compound A.C. signal at an input E1 consisting of several different frequencies comprises a modulator, preferably a ring modulator M, being supplied at a second input E2 with a cyclically swept frequency search signal, a plurality of storage devices S1-S8, preferably flip-flops or capacitors connected to the output of the modulator M via respective fixed contacts of a switch W so that the storage means may be cyclically connected one at a time to the output of the modulator and during the same time interval in each cycle of the sweep of the search signal. The storage devices F1-F8 each comprise an R-C integrator circuit followed by a trigger shaper circuit as input to the capacitor or flipflop. The switch W is controlled by a counter Z and the swept frequency signal is derived from generator G controlled by a saw-tooth waveform generator GS. In one embodiment, a shift register is controlled by a clock oscillator to move a "1" output through each of its 9 stages, the first eight of which are connected to operate switch W through its range of positions, and the ninth to reset an integrator which has been integrating a constant voltage source to provide the increasing ramp signal. The shift register is replaced in a second embodiment by a binary counter and binary to decimal converter. When the search frequency corresponds to one contained at the input E1, the modulator provides a D.C. output which is integrated and held as a "1" signal in the corresponding storage device. In all other events an A.C. signal of the difference frequency is provided. If only one frequency present is required, the search signal may be a single frequency and be cyclically phase swept.