GB179016A - Inverted voice current transmission - Google Patents

Abstract

179,016. Western Electric Co., Ltd., (Western Electric Co., Inc.). Feb. 25, 1921. Telephone systems.-Speech is transmitted in an unintelligible form by inverting the speech frequencies, that is to say, if S is the speech frequency at a given moment a frequency K-S is transmitted, where K is a frequency such as 2200 above the limit of what is essential for clear articulation. This is effected by using the speech currents to modulate a current of frequency K, thus obtaining currents of frequencies K + S and F - S, and suppressing the currents K + S by means of a filter. At the receiving station the inverted currents are re-inverted and rendered intelligible by similar means. Current of frequency K from a source 8, Fig. 1, is modu. lated by speech currents in a modulator 5 of the two-valve kind described in Specification 151,928, [Class 40 (v), Wireless signalling &c.], (which gives pure modulated currents K + S and K - S free from currents K or S), and the lower band of modulated currents K - S is passed,through a filter 16, of the kind described in Specification 142,115, into the line L. Incoming currents from the line L are amplified by a valve 18 and modulate current from the source 8 in a modulator 24, the lower band of modulated currents being passed through a filter 26 to the receiver 27. The invention is applicable to wireless systems.