GB611335A - Improvements relating to receivers for angle-modulated carrier waves - Google Patents

Abstract

611,335. Frequency modulation. RADIO CORPORATION OF AMERICA. April 27, 1946, No. 12732. Convention date, April 27, 1945. [Class 40 (v)] A receiver for angle-modulated waves is muted unless correcting tuned, and the muting is removed by rectifying the oscillatory voltage set up in a sharply-resonant network tuned to the desired mean frequency. As shown, the output of a limiter valve 16, preceded by the usual superheterodyne stages, is fed through a coupling-condenser 63 to a sharply-tuned circuit 59, 62, across which is connected a diode rectifier 57 and load resistor 56. The negative voltage arising at the lower end of this resistor is applied to the grid of a valve 50. When no signal is being received, the valve 50 passes current through the cathode resistor 39 and drives the cathode of the audio-amplifier 37 positive so as to mute the receiver. As the set is brought into tune, the I.F. wave approaches resonance with the circuit 59, 62, and the negative voltage on the grid of the valve 50 rises, thus reducing its space current, and diminishing the prohibitive bias on the audio-amplifier cathode. The limiter valve 16 feeds a discriminator-rectifier circuit which may be of the phasing type described in Specification 489,094, the detected audio output being fed to the grid of the amplifier 37. The negative voltages at the lower end of the rectifier load 56 may control a tuning indicator 70 of the magic eye type.