Patent GB-503761-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1937-10-06
Abstract: 503,761. Semi - automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., McCLEW, J. W., and RICHARDS, I. T. Oct. 6, 1937, No. 27140. [Class 40 (iv)] In a system, in which all connections in and between two small exchanges called R.C.Xs. are set up by a main exchange operator over a single junction leading to one of them, there being also a single junction between the R.C.Xs, each R.C.X. is provided with one finder-connector link and an auxiliary half-link comprising a connector only which serves to extend incoming calls when the ordinary link is in use. The single controlling junction may extend to the main exchange through a tandem satellite exchange. The figures show the apparatus at the tandem R.C.X. Specification 502,545 is referred to. Call from subscriber connected to tandem R.C.X. Line relay R, which is provided with alternative connections for magneto and common battery lines, locks in series with start relay FS, and the finder advances under the control of stepping relay GF to the calling line, when switching relay FF energizes over test wiper LF1. Meanwhile relays RA, RB operate in turn and the former falls back slowly, sending a pulse of ringing current over the, junction, the ringing generator having been started by FS. The ringing pulse may be repeated at a tandem satellite exchange after selection of a main exchange junction thereat. Start relay FS remains locked, and busy tone relay BT is connected to start wire 20 so that a subscriber initiating a call while the link is in use receives busy tone. The call, however, is stored and is extended when the link becomes idle. When the operator plugs in, relay A energizes followed by sluggish relays B, BA, and the battery charging circuit through resistance YJ is opened. In the case of a calling line directly connected to the tandem R.C.X., RS energizes and supplies battery feed through relay FI, which energizes provided the subscriber is on the line and connects up DD, DR to give a batteryreversal signal. If this signal is not received, the operator throws a key to unbalance differential relay OC which operates and connects up RF to ring the calling subscriber. To establish the call, the operator dials over the junction, impulses being repeated by A to set the connector CS. Dialling relay C connects up E, ER and off-normal relay VN pulls up. Assuming the wanted subscriber is connected to the tandem R.C.X, the line is tested when C falls back, and if it is idle, switching relay H operates and the wanted subscriber is rung, first continuously until ER relapses and then intermittently. Ring-trip relay F connects up feed relay CI since CR is operated over wiper CS5, and DD, DR reoperate to give a reply signal. 'On withdrawal of the operator, A, B fall back and BA holds under the control FI and maintains FS, H. F, CR. When release occurs, the connector restores under the control of stepping relay GC. If the wanted line tests busy, BY operates on the relapse of E and sends back busy tone to the operator, who informs the calling subscriber. If the call to a party-line, PR operates over wiper CS5 when C falls back and connects up CR, F to delay ringing.. Relay H now connects up ED, which closes a circuit for repeating leg impulses over wiper CS2 to equipment such as that described in Specification 462,038 for selecting the wanted party. After this digit ED, F fall back and ringing takes place. The contacts of banks LF5, CS4 representing party-lines are cross-connected, so that in the case of a revertive call, PRR operates and connects up H on the relapse of C in spite of the busy condition of the line. If the wanted subscriber is connected to the terminal R.C.X., the connector is set on the junction thereto and HS operates over wiper CS5 and connects up HSR, F. A loop is now completed through CI, CD to the terminal R.C.X. and the next digit is repeated to set up the connection therein. Upon reply, CD is operated by battery reversal and connects up DD, DR to repeat the signal. Call from subscriber connected to terminal R.C.X. The contact of bank LF6 corresponding to the junction to the terminal R.C.X. is. wired to terminal J, so that on an incoming call, HS operates but not HSR. If the wanted subscriber is on the terminal R.C.X., busy tone is not applied when the connector CS is set on the junction, and the relapse of ID allows the next digit to be repeated back over the loop through FI, FD to set the connector at the terminal R.C.X. Upon reply, FD is operated by battery reversal and repeats the signal. When the operator withdraws, the relapse of A frees the junction to the terminal R.C.X. and the relapse of BA restores the connector CS. Checking calling subscriber's number. This may be done for metering purposes before the desired connection is established. If the subscriber is on the tandem R.C.X., the connector CS is set on his line and busy tone is received. A talking connection may be established by unbalancing relay OC as described later. The checking connection is released by application of a high voltage pulse to operate TO in series with neon tube NL, whereupon BR disconnects B, BA to restore the connector. If the subscriber is on the terminal R.C.X., the connector CS is set on the junction and the next digit is repeated back through FI, FD as described in the preceding paragraph. The receipt of busy tone from the terminal R.C.X. is regarded as a sufficient check. Since RS is back, the opera. tion of TO now connects up SRA instead of BR, extending a metallic circuit to allow the high voltage pulse to pass to the terminal R.C.X. Incoming call from main exchange. This is established over the connector CS as already described. To offer a trunk call to a busy subscriber, differential relay OC is unbalanced to apply a distinctive ringing signal to the junction. Testing subscribers' lines. After setting the connector CS the test clerk applies a high voltage pulse of reversed polarity to operate TC which connects up TS, SW to cut out the feed bridges and complete a through metallic connection to the desired line. A similar signal at the conclusion of testing restores the original connection. Relay SRB allows the trans. mission of the high voltage pulses to the terminal R.C.X. Ringing and tone generators, Fig.' 11. Ground on start wire 13 connects up RC and momentarily and operates to connect up RC, HR. The last relay locks, completes a talking connection and connects up BP. If the call is accepted, the subscribers are asked to hang up, and the operator again throws her key, whereupon RC connects ground to test wiper CS3 to ensure elease of the existing connection. Relay H energizes and ringing takes place in the normal manner. If the runk call goes to the terminal R.C.X., HS is up and the operation of RC, HR repeats the unbalance ignal. Since in this case BA is up vhile FS is back, OE energizes and onnects up BT to busy the link to calling subscribers. A half - link comprising a connector 1CS is provided for setting up incoming calls vhen the ordinary link is in use for a local call, the switch-over of the junction being effected by CA, CB, ;C when this is the case. Coin - box subscribers. A relay operated over an additional wiper of the finder LF may be used causes RT to operate intermittently, its windings being in opposition, producing ringing tone in transformer T2. Vibrating relay RV generates alternating ringing current in transformer T3, while relay IR operates intermittently under the control of condenser QG and low resistance YP and through IRA connects interrupted ringing supply to wires 12, 16. Ground on start wire 10 causes intermittent operation of BZ to produce busy tone in transformer T1, while XB, ZB interact to interrupt the supply over wire 11. In response to a test number, retard TT trips the ringing, and TN starts the generators and connects back continuous busy tone. If a fuse has blown, FA is operated and the operator receives ringing tone with the ordinary on and off periods reversed. Faulty finder. If the finder LF fails to find the calling line, thermal relay TH operates and opens the initial circuit of start relay FS. The operator on plugging in finds no one on the line and is unable to ring. The removal of the plug releases FS, but the call will then come in again in the case of a common battery subscriber, and the operator will realise the existence of the fault.