GB644608A - Improvements in pulse switching systems - Google Patents

Abstract

644,608. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 26, 1947, No. 26138. Convention date, Sept. 26, 1946. [Class 40 (iv)] [Also in Group XL (c)] In an automatic exchange system of the type described in Specification 644,571, in which speech signals are transmitted in both directions simultaneously over the same distributer and wherein the outgoing signal consequently appears as an unwanted signal on the incoming lead, a portion of the outgoing signal is fed directly to the incoming lead and so phased as to neutralize the unwanted signal. As shown outgoing amplitude-modulated signal pulses S(s) are directed to appropriate subscribers connected to secondary emission electrodes e by grid modulation of the beam of the distributer D. Incoming signals from the subscribers modulate the secondary emission from the electrodes e to produce pulses W (a) in the incoming lead, wherein variation of the secondary emission due to the outgoing signal S(s) also produces an unwanted pulse component W(ks). A portion of the outgoing signal is fed to the valve V in opposition to the unwanted component so that its output contains the incoming signal pulses Z(a) only. Should the unwanted signal bear a non-linear relationship to the outgoing signal a network of compensating non-linear resistances may be included in the connection between the outgoing lead and the valve V.