GB550344A - Improvements relating to telephone systems - Google Patents

Abstract

550,344. Automatic exchange systems. SIEMENS BROS., & CO., Ltd., and CLAY, D. L. Aug. 8, 1941, No. 10110. [Class 40 (iv)] It is usual when impulses are repeated over junctions for the arrival at the repeater of the first impulse of each train to bring about a circuit change which improves the condition of the outgoing circuit as regards impulsing. According to the invention, this change is effected by a prefix signal which precedes each impulse train. The prefix may talk the form of an unbalancing of the loop or of a very short break which can be detected by a high-speed relay. When voice-frequency impulsing is employed, the prefix may serve to connect up a receiver in readiness for the reception of impulses. The repeater shown in Fig. 1 generates and transmits a prefix before each impulse train whether it receives a prefix or not, a delay being imposed on the repeated impulses in the latter case. Upon seizure, line relay AT connects up AB, AC and release relay B connects up HA to complete the outgoing loop through relay D. If a prefix, which consists of a brief earth connection to one wire of the loop, is received, differential relay AS responds and relays PS, PT energize in succession to repeat the signal. Relays CO, COA, COB also energize in succession, transferring the incoming loop to relay AA and putting the outgoing loop under the direct control of that relay for the repetition of impulses. The continu- - ance of this condition is dependent on the operation of dialling relay C, so that at the end of the train the circuits are restored to their condition before the prefix was received. If no prefix is received, the relapse of AT at the first impulse, besides connecting up dialling relay U, causes the successive operation of PS, PT to send the prefix. The control of the outgoing loop through relays AB, AC in this case delays the repeated impulses to allow for 'the insertion of the prefix. Relays PS, PT, restore at the end of the train. The modification shown in Fig. 2 employs two single-winding line relays, AST being released by a prefix while AT is held. Relay CO is disconnected by PT to prevent its being flicked during the impulsing when no prefix is received. It is to be noted that the prefix produces no 'effect at an incoming selector which has only the usual .two-winding line relay. In the repeater shown in Fig. 4, in 'which the repeated impulses are of voice-frequency, the receipt of the prefix causes the successive operation of relays PS, PU, PT, with the result that the outgoing loop is bridged through resistance R and a prefix is sent until relay AA energizes, this relay being connected to the incoming loop, as in Fig. 1, for the repetition of impulses. In a modification, Fig. 3 (not shown), the repeater receives a prefix but does not transmit one.