GB219987A - Improvements in secret signalling systems - Google Patents

Abstract

219,987. Western Electric Co., Ltd., (Assignees of Fletcher, H.). July 31, 1923, [Convention date]. Secret signalling systems; thermionic modulating systems.-In a secret signalling system, the waves to be transmitted are divided into subbands which are variously treated, e.g. by inversion or transposition, before transmission, and means are provided to vary the treatment. Fig. 1 shows a telephone system in which speech waves are divided into four sub-bands by filters Fa - - F<d>, any of which may be cirectly transmitted or treated by modulating circuits M<1> - - M<4> according to the position of switches 1 - - 4. The modulating circuits are of the balanced-valve type shown in Fig. 4 in which an oscillator 52 superposes a modulating wave on the speech subba.nd, and one of the side bands is selected by the filter F<c> and transmitted through the hybrid coil 55. In the modulating circuits M<1> - - M<4> various frequencies may be superposed according to the position of the switches 11 - - 16, 21 - - 26, 31 - - 36, and 41 - - 46, and one or other of the resultant side bands selected bv the filters F<a> - - Fd according to the position of the switches 101 - - 103, 201 - - 203, 301 - - 303, 401 - - 403, which arrangement gives various combinations 126 of which are highly selective in a wireless transmission system in which only a single side band is transmitted. Applications of the arrangement to a two-way two-station telephone system, and to a two-way wireless terminal station in which the signals are superposed on a carrier wave which is suppressed, are described in the Specification.