Patent GB-854611-A (GB)
Title: Improvements relating to telephone systems
Inventor: STALLWORTHY FRANK ALLEN
IPC: H04Q1/446
Filed: 1956-04-19
Abstract: 854,611. Automatic exchange systems. SIEMENS EDISON SWAN Ltd. April 9, 1957 [April 19, 1956], No. 11983/56. Class 40 (4). A voice - frequency ring forward signal (2280 c/s.) made by an operator over a bothway junction in the face of an interrupted tone signal is automatically delayed so long as a test indicates the presence of tone on the line. The signal is a short pulse of only 170 to 250 millisecs. which is easily distinguished from a 2 sees. clear forward signal and falls within the interruption period, 750 millisecs., of the tone signal. The signal may be made in the face of busy tone to offer a trunk call to a busy subscriber or in the face of N.U. tone to transfer the call to an enquiry desk. The transmission of the signal is made dependent upon the operation of the voice-frequency receiver at the effective outgoing circuit of the junction. As in the outgoing line circuit described in Specification 827,174, non-linear resistors are used to prevent sparking at relay contacts and a rectifier is used to guard a relay against operation by reversed potential. A cold cathode discharge tube is used in a capacitative timing circuit. An alarm is given if the circuit is busy 10 sees. after the caller clears, the circuit being indicated by a lamp. General arrangement.-An outgoing line circuit, Figs. 1A, 1B, 1C, is connected to a manual board or to a selector at terminals 1, 2, 3 on the left and to a bothway junction at terminals, 5, 6 on the right. The circuit operates in substantially the same way as the outgoing circuit described in the Specification referred to, corresponding parts of the two circuits bearing the same references. The voice-frequency receiver, which is not shown, is common to both the outgoing circuit and to an incoming circuit (not shown) at the same end of the junction and is connected to line 23, 24 through transformer TR1 in compartment GH1. Leads 26, 31 to 42 give access to the incoming circuit, relays SA, SB being provided to connect the outgoing circuit to the junction. The relays pull up in the order A, AB, SB, B, SR, SA on seizure of the circuit. A relay X winding, not shown, in the receiver is normally up and falls back in response only to pure voice-frequency signals, contacts x1 x2 in compartments GH2, GH3 being shown back. Pick-up signals, dialled impulses, reply, clearance and acknowledgement signals are all transmitted as described in the Specification referred to, accompanied as necessary by line splitting. Ring forward.-Windings I and II of relay OC oppose each other in the loop circuit over wires 21, 22 and the relay remains on its back contacts when A is up in the loop. When the operator presses the ring-forward key, ground is applied to wire 22, relay OC pulls up and A remains up. Signal timing relay RR follows and short circuits its own winding I to delay release. When the key is released, OC falls back, testing relay TT pulls up, dialling relay CD being back, RR is held and signalling current is applied to the line 23, 24 through a pad AU9. After attenuation by AU9, the signal is just sufficient to release X in the receiver but it is not effective until the tone current in the line is interrupted. Relay TRR then pulls up over front contacts of bl, sb5, sb6, tt6 and back contacts of xl. Relay TT falls back and is followed slowly by RR, signalling current being applied to the junction in full strength by relay TX during the delay period. Relays BB, CF, CR, D, DB, DD, SP and the timing circuit comprising condenser C2, C18, resistor R12 and discharge tube CT1 operate substantially as described in the Specification referred to. When the caller clears and B falls back relay DB comes up one complete circuit through a lamp L to an alarm connected to lead 9. The alarm operates after 10 seconds if SB is still up.