Patent GB-523517-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1939-01-10
Abstract: 523,517. Manual exchange systems. SIEMENS BROS. & CO.,.Ltd., PETERS, C. L., HUMPHRIES, H. E., and HENSLER, B. A. Jan. 10, 1939, No. 850. Addition to 499,832. [Class 40 (iv)] In a system as described in the parent Specification in which junctions or trunks of various transmission losses are adapted to be connected in tandem and in which modification of the transmission in terminal equipment of a trunk, when required, is effected by a relay individual thereto and operated and held over a through wire to the other trunk terminal, the relay is polarized or associated with a rectifier to enable a different signal to be given over the same wire. As described, a pad-control relay PC in series with a rectifier is operated when required by negative battery on the wire and a calling or rering relay RR is operated by positive battery. The Specification describes a manual system in which a terminal, Fig. 1, of a high or low loss four-wire trunk repeatered at the exchange, or a high or low loss two-wire non- repeatered trunk terminal may be connected to either of the similar terminals shown in Figs. 3 and 4. Both-way working may be used but the detail description relates to one-way working. The four-wire connections are such that all wires are used for both directions of speech as described in the parent Specification. Connections between two four-wire terminals. The operator answers the call by inserting plug LAP of the cord-circuit, Fig. 6, into jack ILJ and as an outgoing four-wire connection is required she plugs LCP, Fig. 6, into jack OLJ, Fig. 3, and also plugs the additional cord-circuit, Fig. 5, into the corresponding jacks INJ, ONJ of. the other pair of line wires. In the completed connection, sleeve relays FW in'the additional line circuits are operated to switch through and remove the normal terminating networks YC, QT, a terminal network YT, QX in the cord circuit which serves as a safeguard against an unterminated line being removed by shunt field relay C or a differential relay may be used for this purpose. When the operator is actually on the line, the speak-key operates relays SK, SL (shown as contacts only), and the latter unbalances differential relays DS, DR in the sleeve circuits of the main line pairs to release the relays FW in the additional line circuits. The pad-control relays PC (ii) in the terminals of the two trunk circuits are effective or provided only in the case of a high-loss trunk, such a relay being operated by battery over coil RC in the additional cord-circuit. The ring or ring-back key RCK, RAK in the main cord-circuit applies positive battery to the tip wire to operate RR over rectifier UA which sends the appropriate signal assumed to be voice-frequency in Fig. 1 and ringing current in Fig. 3. Connection between four-wire and two-wire terminals. If the call incoming over the fourwire terminal, Fig. 1, is such that a two-wire outgoing trunk is required, the operator inserts plug LCP of the main cord circuit into jack OLJ, Fig. 4, the auxiliary cord circuit being unused so that the additional pair of wires in Fig. 1 remain terminated by YC. QT. The pads in Fig. 1 are removed only if the trunk terminated in Fig. 4 is of high loss and for this purpose it is arranged that a relay CB, (not shown) operated when the trunk is in use, connects negative battery to the tip wire to operate PC (i), Fig. 1, over rectifier UA. Similar control of the padcontrol relay occurs in the case of a call incoming to the terminal of Fig 2 and outgoing over the four-wire terminal, Fig. 3, the negative battery signal being given by a relay BA in Fig. 2.