GB826727A - Improvements in and relating to signal detectors - Google Patents

Abstract

826,727. Automatic exchange systems. TELEPHONE MANUFACTURING CO. Ltd. Feb. 22, 1956 [March 3, 1955], No. 9447/55. Class 40 (4). [Also in Group XL (c)] In a circuit for repeating either A.C. or D.C. impulses, a triode V1 controlling an impulsing relay P is biased back by the leading edge transient to compensate for the tendency of impulses to be longer when derived from high level signals. Fig. 1 illustrates the relay operating times for low and high level impulses f, #1, x being the operating current of the relay. In one arrangement, Fig. 5, audio-frequency signals from an amplifier VIA are rectified at W to produce a control potential across resistor R. In response only to transients, a transformer TR1 and a half-wave rectifier V1B produce a biasing potential across elements R2, C2, The transient biasing potential across R2, C2 is opposed to the signalling potential across R and has the effect of delaying the operation of relay P. Rectifier V1B may be replaced by a fullwave rectifier so that the release of relay P is accelerated by the trailing edge transient. In relay P polarizing winding w is used to balance the standing anode current of V1. Resistor R1 and capacitor C1 in the grid circuit of V1 are also effective to delay operation of P and advance release of P. The transient bias voltage is adjusted by means of resistor R4 which also controls the polarizing winding w of relay P. The arrangement may be used for " tone-on " signals as well as for " tone-off " signals.