GB710600A - Improvements in or relating to voice frequency signalling system - Google Patents

Abstract

710,600. Voice-frequency signal receivers. STANDARD TELEPHONE & CABLES, Ltd. June 6, 1952 [July 10, 1951], No. 14314/52. Class 40 (4) A receiver for two voice-frequency signals has a separate receiving circuit for each signal, the unwanted signal in each circuit being suppressed by the frequency-selective negative feedback of an amplifying valve which has cathode circuit tuned to the unwanted frequency. In the arrangement described the receiver descriminates between pure signals and signals occurring simultaneously with other frequencies. As shown, incoming signals at a transformer T1 are applied over a buffer amplifier V1 and. a transformer T2 to a fourwire terminating set or a two-wire line. Signals from transformer T1 are also applied to valve V2 which has its cathode circuit tuned by a rejector circuit L1, C1 so that one signal frequency and any spurious frequencies are fully amplified and supplied to a signal receiving circuit over a transformer T3. The unwanted signal frequency suppressed by valve V2 is obtained from the rejector circuit L1, C1 and energizes a further valve V3 which is tuned by L2, C2 in its cathode circuit and suppresses only the signal frequency acceptable to valve V2. The output of V3 consists primarily of a single signal frequency and is applied to a second receiving circuit over a transformer T4. In the receiving circuits the two signal frequencies each control a biased relay X1, X2 over an acceptor circuit C3, L3 or C4, L4 and a rectifier W1 or W2. Spurious frequencies present in the output of valve V2 are rectified at W3 and energize guard windings a2, b2 on the two relays, the signal frequency being eliminated by a rejector circuit C5, L5. The valves V2 and V3 have high mutual conductances and function as-limiters, the resultant harmonic distortion being filtered off by shunt condensers C6 and C7 respectively.