GB681630A - Improvements in and relating to noise limiters for use in radio receivers - Google Patents

Abstract

681,630. Automatic noise suppression. BRITISH COMMUNICATIONS CORPORATION, Ltd., and HEFTMAN, T. S. June 19, 1951 [June 19, 1950], No. 15319/50. Class 40 (v). In a noise-limiting circuit employing a rectifier automatically biased by a voltage dependent upon the amplitude of the received signals, a further fixed bias is employed in opposition to the variable bias so that, in the absence of a received signal, all noise voltages and weak signals below a level determined by the fixed bias are prevented from passing the limiter. The series diode 17 is biased from the demodulator stage 11 over resistor 16 and capacitor 15 having a time constant such that the voltage across capacitor 15 varies with the audio signal, but is unaffected by short noise pulses. The series diode 17 thus passes the audio signals, but noise pulses render it non-conducting. Any negative-going pulses that pass this diode cause the shunt diode 20 to conduct and are thereby suppressed. The addition of resistor 21 connected to a positive potential causes diode 20 to conduct and 17 to cut off so that no signals are passed until the demodulator output is sufficiently great to remove the paralysing bias.