Patent GB-439970-A (GB)
Title: Improvements in or relating to combined telegraph and telephone exchange systems
IPC: H04M11/06
Filed: 1934-06-18
Abstract: 439,970. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and JACOBSEN, B. B., 63, Aldwych, London. June 18, 1934, No. 18048. [Class 40 (iv)] A telephone system providing telegraphic facilities for subscribers has the following features : (1) change over from telephony to telegraphy or vice-versa in an established connection is dependent respectively on replacement or removal of the receiver ; (2) if standstill conditions arise during telegraph transmission, the connection releases automatically and therefore, due to (1), the substations are in condition to receive telephone calls; (3) a substation telegraph equipment releases more quickly when released by a signal from a distant sub-station than when release is initiated at the sub-station itself; (4) an operator may break down a telegraphic connection, Specification 378,064 is referred to and features described therein may be utilized in the present arrangements. The telephone set 2 is normally connected across line L1, L2, and after a call has been set up over an automatic exchange, the subscribers agree to go over to teleprinting and each momentarily operates a non-locking key P, the operations at both sub-stations being identical. Relay M pulls up in a circuit including the teleprinter motor 6 which does not start up, M locks up, connects the line to transformer 4 of the voice-frequency teleprinter equipment I and operates relay W, but leaves relay R connected across the line in series with telephone set 2. Assuming the telephone receiver is off the hook, R pulls up. The circuits of relays T, S are now open, and in order to complete the teleprinter connection, the subscribers replace their receivers, R falls back, and T pulls up to complete a low resistance circuit over M (upper) for the motor 6 which starts up. Relay W and teleprinter magnet 10 are now supplied from a low tension battery eliminator in 1. Teleprinting may now take place, signals transmitted at tc being converted into voice-frequencies at 1, the received signals being converted to divert current impulses in 1 to operate magnet 10. After teleprinting ceases, three possibilities arise: (1) The subscribers may desire to resume telephony, in which case they merely lift their receivers. Relay R operates and short circuits M which relapses, opens the supply circuit from 5, whereupon W and T (slow) fall back. The telephone set 2 is now directly across the line and R falls back so that the circuits are ready for telephony ; (2) The connection may be cleared down by one or both parties pressing key C until the motor 6 stops as indicated by lamp 12. Assuming one party presses key C, contacts c1 cause the transmission of a long signal which is received at both sub-stations and causes the operating current through W and 10 to cease. The relapse of W operates S slowly (half a second at the distant sub-station since key contacts c2 are closed, and one second at the initiating substation since c2 are open). Relay S at each station disconnects the motor 6 and releases M which disconnects the supply so that S and T fall back slowly. The circuits are now normal with the telephone set connected directly across the line ; (3) The circuits are left at a standstill. The motor 6 is automatically disconnected at x in known manner, and the circuits clear down as in (2). Unattended teleprinter reception. The subscriber on leaving his substation throws locking key AU to make the u contacts. Relay R is thus connected across the line in series with condenser 15, vibrates in response to ringing current, and operates M which locks up and connects the voice-frequency unit 1 across the line to trip the ringing whereupon R falls back. As key contacts a3 are open and T is unoperated, the unit 1 sends back a tone signal to the calling party to indicate teleprinter operation. At the unattended sub-station, W also pulls up, remains held over 1, and T energizes slowly when R falls back, stops the tone and connects up the low resistance circuit for M and motor 6 which starts up. The calling party switches over to teleprinter operation as previously described and checks the connection by using the " answer back " device. Release of connection to an unattended substation by exchange operators ; toll break-in. The connection may be released, as previously described, if the release tone signal is sent by an operator, or, if resistance 9 is replaced by a high impedance to ringing current, the operator may energize R by ringing and so release M to break down the connection. Calling party automatically brings into operation teleprinter at called sub-station. The telephone bell is arranged in a purely local circuit and is rung only after a delay in which teleprinter signals are not received. Ringing current prepares the connection of the teleprinter which is completed on receipt of a special teleprinter code.