GB423194A - Noise suppression in radio receivers - Google Patents

Abstract

423,194. Valve amplifying circuits. MURPHY RADIO, Ltd., ELLIS, H. D., and BAKER, G. B., 62, Brook Street, Hanover Square, London. Aug. 8, 1933, Nos. 22192/33 and 22089 /34. [Class 40 (v)] A method of suppressing noise in radio receivers having automatic volume control consists in positively biassing to a condition of low stage gain an amplifying-valve of the receiver, and superimposing a negative bias derived from rectification of the amplified signal. In the Figure an amplified high frequency signal is applied to circuit 38 of the rectifying diode 39, the resulting potential across the resistance 40 being applied to the control grid of triode 42 whose anode circuit includes resistance 43. When the received signals are below a certain intensity level, the grids of the high frequency amplifiers 23, 24 are positively biassed by the voltage drop across part 47 of the supply potentiometer, the control diode 44 being inoperative since the potential of point 48 is positive with respect to 49. As signal strength increases, 48 becomes negative with respect to 49, the diode 44 passes current and the resulting voltage drop across resistance 45 opposes that due to 47 thus reducing the positive bias on 23, 24 and increasing the gain; the effect is thus cumulative. The voltage determining the signal level at which the receiver becomes active is the difference between the potentials across part 46 of the potentiometer and resistance 43 with no signal.