GB649074A - Improvements in noise limiting circuit arrangements for radio receivers - Google Patents

Abstract

649,074. Radio interference suppression circuits. FITTON, Ltd., R. N., and BEAUMONT, F. H. Dec. 15, 1948, No. 32442. [Class 40 (v)] A noise limiting arrangement for radio receivers comprises a first diode and a load circuit, and a second diode, the cathodes being connected together and the second diode being negatively biassed by the output of the first, so that it conducts only during noise impulses to attenuate the demodulated output. In Fig. 1, carrier frequency is applied to tuned circuit 1 and detected by diode 4, 5 to provide a demodulated output from load circuit 2, 3. A second diode 7, 5 which is biassed by the output from load circuit 2, 3 smoothing being effected by a large condenser 10, is also fed with carrier frequency by means of a coil 8 which is coupled to tuned circuit 1. When the percentage modulation exceeds a predetermined value, depending on the degree of coupling of coil 8, diode 7, 5 becomes conducting, and the resultant heavy loading of tuned circuit 1 reduces the demodulated output from the first diode. In a modification, a further coil is introduced which is in series with coil 8 and is coupled to the primary of an input transformer, the secondary of which is constituted by the tuned circuit 1 coupled to coil 8. Fig. 3 shows an alternative arrangement in which the first diode 14, 15 is effectively in shunt with the tuned circuit, and the second diode 20, 15 is fed from a tapping on the tuned circuit 1.