GB632374A - Improvements in discriminators and detector circuits for angle-modulated waves - Google Patents

Abstract

632,374. Frequency and phase modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 6, 1946, No. 26788. Convention date, Sept. 6, 1945. [Class 40 (v)] A discriminator-detector circuit for anglemodulated waves comprises a pair of series circuits 15, 14 and 16, 17 in parallel from the unlike but equal reactances 14, 17 of which at the carrier unmodulated frequency, a pair of rectifiers 20, 21 are fed developing variable opposed voltages across load resistances 30, 31, depending on the variation of the reactances with frequency. The circuits 15, 14 and 16, 17 may be series resonant at the unmodul.ated carrier frequency or, if not, the reactances 15, 16 and 14, 17 are made approximately equal to form a resonant tank circuit 8 tunable by one condenser 16, to which the other condenser 14 is ganged to maintain the output reactances 14, 17, equal at the unmodulated frequency. Alternatively the circuits 15, 14 and 16, 17 may each be series resonant at slightly different frequencies on opposite sides of the centre frequency. The inputs to the diodes are applied by way of condensers 23, 25 and vary in accordance with variation of the reactances 14, 17 with frequency. The input valve 1 may be an amplifier and/or limiter, feeding the discriminator by way of a D.C. blocking condenser 19 or, Fig. 2 (not shown), the tank circuit 8 may be atÀhigh D.C. potential and connected to earth by a condenser, a parallel resistance providing a non-inductive lead to the limiter valve anode and broadening the discriminator timing. With phase-modulated waves a de-emphasis correcting network follows the detector.