GB381784A - Improved means for eliminating interference in electric signalling systems - Google Patents

Abstract

381,784. Wireless and wired wireless receiving systems ; code telegraphy. FUCHS, J., 5, Jasomirgottstrasse, Vienna. Dec. 19, 1931, No. 35190. Convention date, Dec. 19, 1930. [Classes 40 (iii) and 40 (v).] In a wireless, wired wireless, or audio frequency signalling system, interference is eliminated by combining the received signal with two or more local frequencies so as to produce two beat frequencies, one audible and the other supersonic, the two beat frequencies being subsequently rectified and recombined in such a way that interference is balanced out. As shown in Fig. 2, a circuit F tuned to the incoming frequency is influenced by two local oscillators U1, U2 and the resulting beats, one audible and the other supersonic, are separated in the tuned output circuits H1, H2 of a detector M. Each of the circuits H1, H2 is coupled to the grid circuit of further detectors G1, G2, the plate circuits of which act oppositely on the output transformer T. In a modification, a further heterodyne is introduced in one or both of the circuits H1, H2, Fig. 3 (not shown). In receiving audio-frequency telegraph signals, these are first stepped up to a supersonic frequency and then treated as described above.