Improvements in or relating to telephone systems

674,243. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 23, 1950 [July 22, 1949], No. 19389/49. Class 40 (iv). In a system using a single voice frequency for the setting up and supervision of connections and having arrangements for end-toend signalling over a plurality of trunks, the incoming end of each trunk in a connection is released by a single pulse signal from the outgoing end of the connection and the outgoing end of each trunk is released by a single pulse signal from the incoming end of the associated trunk due to the initiation of release thereat. The outgoing equipment may be seized from an operator's position or by transit selectors. The incoming equipment gives access to selectors. A signalling frequency of 2520 c.p.s. is used. Outgoing call, Figs. 1, 2. When the operator plugs into the jack OJ, battery over the sleeve wire connects up S which busies the relay set to the selector levels SM. Relays SS, SR, FLS operate in turn, FLS actuating contacts to indicate the next idle junction. Relay SS brings up R for the operating period of AX to transmit a 40-60 m.s. seize signal. When the operator throws her dialling key, low resistance battery connected over the tip conductor energizes RR, which completes a circuit for DT to operate R, A and to shunt down RR. Relays A, RR when operated short circuit the signalling source. In response to dialling, relay A sends impulses of the signalling fre-' quency. Restoration of the dialling key momentarily connects battery to the. sleeve wire to bring up LR. Relays DT, R fall back respectively lighting the supervisor lamp and disconnecting the signalling source. Setting up a connection through a tandem exchange. Receipt of the seize signal by the incoming relay set, Figs. 3, 4, causes VFA to operate E and C. At the end of the signal, VFA, C release, G busies forward and AA, AB and AD switch through. The dialled impulses are repeated by AA to extend the connection to a further junction, whereupon earth from the associated outgoing relay set, Figs. 1, 2, operates TRA, which locks up relays AA, AB, AD, disconnects a resistor YFA and the bridge comprising D and I from across the speaking circuit and earths a lead PS to operate a pad switching relay if required. In the seized outgoing relay set TR is operated to switch through the talking connection, disconnect relay VF, earth a pad switching lead PS and to connect up R. R, AX interact to transmit the seize signal. Relay RG energizes follow