GB570772A - Improvements in and relating to radio receiving circuits - Google Patents

Abstract

570,772. Valve circuits for wireless reception ; frequency modulation. MULLARD RADIO VALVE CO., Ltd., and RICHARDS, C. L. July 30, 1943, No. 12406. [Class 40 (v)] The audio-frequency stages of a radio receiver are arranged to be switched for the alternative reception of amplitude-modulated waves, frequency-modulated waves, or continuous-wave telegraphy. The incoming waves are fed from preceding stages into the grid circuit of a valve V1, the grid-cathode space acting as a rectifier and giving a signal voltage representative of amplitude modulation across a resistance R1 in the grid circuit, which voltage is led to the contact AM of the three-position switch S. Frequency modulation is detected by a phasing discriminator comprising coil Lp, tuned circuit Ls, Cs, and rectifier R2 arranged as described in Specification 567,813, the switch contact FM being connected to one end of the load resistance R3. For the reception of CW telegraphy, an oscillator valve V2 is energized by a switch H ganged with the switch S, and supplies local oscillations to the anode of the valve V1 to produce audio beat voltages at the contact CW which is connected to the resistance R3. A resistance and blocking condenser may be interposed between the anodes of valves V1, V2, Fig. -2 (not shown). This resistance may assist in providing necessary damping for the circuit Ls, Cs. In a further modification, Fig. 3 (not shown), the local oscillation from V2 is fed to the grid of the valve V1 and CW as well as AM signals are taken across the resistance R1. AVC voltage is derived in part as shown in Fig. 1, but arrangements are provided by which during CW reception another AVC voltage is derived from the slider of an output potentiometer.