GB530256A - Improvements in or relating to systems for eliminating static interference in radio receiving systems - Google Patents

Abstract

530,256. Wireless receiving systems. ZUCCARELLO, W. E. June 2, 1939, No. 16313. Convention date, Nov. 15, 1938. [Class 40 (v)] In an interference preventing system of the type which comprises the steps of amplifying combined signal-modulated carrier and static impulses in one receiving circuit, while amplifying only static impulses of a greater strength than the carrier in a second receiving circuit, and balancing the output currents of one circuit against the output currents of the other circuit to cause the static to be eliminated, the second circuit is caused to respond only to static impulses of greater amplitude than the carrier by the provision in the second circuit of a feedback circuit for audio-frequency energy. An aerial 1 feeds two similar parallel circuits A, D comprising H.F. amplifiers 4, 4b, mixers 22, 22b, I.F. amplifiers 50, 50b and detectors 61, 61 b. The output from the detectors pass respectively to grids 79, 80 of a mixer 77 which feeds the audio-frequency amplifier 94. A feed-back conductor 98 is taken to each of the first three stages of circuit A while a feed-back conductor 102 is taken through a R.F. choke 103 to the corresponding points of circuit D. By this means it is arranged that circuit A responds to modulated carrier and static interference while circuit D is made to respond only to static above a certain intensity level. These two signals acting on grids 79, 80 serve to neutralize the static, since leads 70, 84 are taken from opposite ends of condenser-resistance networks 68, 68b. Thus the current fed to the input of valve 94 is free from static of greater intensity than the carrier.