GB566602A - Improvements in telephone or like systems - Google Patents

Abstract

566,602. Exchange systems; two-way transmission. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and BEALE, C. E. July 1, 1943, No. 10679. [Class 40 (iv)] In a system employing voice-frequency signalling over repeatered junctions, a circuit associated with the voice-frequency receiver at each end of the junction prevents the transmission of outgoing signals as long as voice-frequency currents are arriving over the junction and for a period thereafter at least equal to the hang-over time of the echo-suppressors. The arrangement obviates the need for the use of signals that are repeated until acknowledged from the receiving end. As applied to a system of the kind described in Specification 559,016, the outgoing relay set ORS and v.f. receiver OVR, including the detecting circuit ODE, are connected by way of a hybrid transformer ORH to a link leading to the hybrid transformer OLH of a 4-wire junction 10, 11, the arrangement at the distant end of the junction being similar. Instead of using the hybrid transformer ORH, it may be arranged that the receiver OVR is disconnected while signals are being transmitted. The detecting circuit comprises a pair of high-speed relays OSA, OSB controlled from the receiver OVR through a thermionic valve OVI, and a slow-release relay OSHT dependent thereon. These relays when energized disconnect the signal source from the line transformer T1 and open lead 12 to restrain the operation of the signal timing switch, this condition being maintained after the junction becomes clear during the release period of relay OSHT. In order to deal with simultaneous signals from both ends of the junction, relay OSHT and the corresponding relay at the distant end are given different release periods. Specification 559,016 is referred to.