Patent GB-626982-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1946-11-29
Abstract: 626,982. Exchange systems. SIEMENS BROS. & CO., Ltd., YATES, K. R., and HENSLER, B. A. Nov. 29, 1946, No. 35514. [Class 40 (iv)] In a system involving voice-frequency signalling for the operation of a two-way trunk on a manual outgoing and automatic and manual incoming basis, the incoming end being switched from an incoming selector to a manual board in response to a ring forward signal, the arrangement is such that on a call set up automatically the reply of the called subscriber prevents subsequent transmission of the ring forward signal. Upon seizure of the trunk, a restraint signal is sent from the incoming end until the incoming selector is ready to receive setting impulses. Two frequencies X, Y are used for signalling and are sent by the operation of relay SP and relay TX or TY, the incoming VF receiver being disconnected. Outgoing call. When the operator plugs in, sleeve relay S energizes, followed by GS, ZR, SP, CB. Relay MB connects the trunk to the jack, and TX energizes during the operating time of GT to send an X frequency seizing signal. Relay GT connects up GR. An X frequency signal returned over the trunk operates BB, which locks, and when the signal ceases Z pulls up and applies dialling tone through relay DL. If the operator throws the dialling key, DL responds and completes an impulsing loop to relay A which repeats X pulses over the trunk. The return of the dialling key unbalances differential relay DF which operates and connects up LR, causing the release of DL, SP, A, DF. The operator may now hear supervisory tones received over the trunk. If, on hearing dialling tone, the operator rings forward, relay RF responds and connects up LF, LR, and SP, TY are operated by earth. pulses on wire WEA to send Y pulses over the trunk. An X frequency acknowledge signal operates G which disconnects Z, ZR and connects up RK to terminate the ring forward signal; RK restores unless the operator is still holding the ringing key. The condition is now the same as if the operator had dialled except that LF is up, and in consequence further operation of ring forward relay RF is independent of supervisory relay AR. The reply signal consists of Y pulses repeated until effective. Relay G responds and connects up AK, AR, dimming the supervisory lamp, and at the end of the pulse AS(i) energizes in series with AR(i), while AK falls back slowly and controls the sending of an X frequency acknowledge signal which stops the reply signal. Relay AR opens the original circuit of RF if LF is not up. The clear back signal is similar to the reply signal and results in the energization of AR(ii),  AS(ii) ; relay AR falls back since its windings are in opposition and lights the supervisory lamp, and AS goes back at the end of the pulse. An acknowledge signal is sent as before. When the operator clears down, relays S, GS, LR, LF (if operated), MB relapse and a clear forward signal of Y frequency is sent under the control of a stepping switch M, and is acknowledged by a long Y pulse which effects the release of GR, CB. Incoming call. Relay B responds to the seizing signal, locks and connects up CB, while at the end of the signal BB, BR energize and present a calling condition to the incoming selector. Relays SP, TX operate to earth on wire TE and send the restraint signal. If the operator dials, the received impulses are repeated over wire TF, and the reply of the called party operates relay D, whereupon SP, TY are controlled by earth pulses on wire WEB to send the reply signal. The acknowledge signal energizes AR(i), AS(i). A similar signal is sent when the called party clears and the acknowledge signal energizes AR(ii), AS(ii), causing the release of both these relays. The clear forward signal unlocks B which disconnects BR, BB to restore the incoming selector, and relays AK, H, RL operate temporarily to send the backward release signal. If the operator rings forward when the called subscriber is not on the line, the receipt of Y pulses operates AK which connects up MB to direct the trunk to the manual board and LF, and at the end of the operating pulse AK falls back slowly, sending the acknowledge signal. The calling lamp CL lights and ringing tone is sent back from wires WIR. When the operator replies to the call, sleeve relay S disconnects LF and the operation of supervisory relay D sends the reply signal.