Patent GB-503343-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1937-10-06
Abstract: 503,343. Semi - automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and BAKER, G. T. Oct. 6, 1937, No. 27139. [Class 40 (iv)] In a system in which all connections in a small office called an R.C.X. are set up by a distant operator, the speaking connection to the called party in a local call is initially set up over one path and is then transferred to another path so as to leave the former path free for the establishment of an incoming call. In the R.C.X. described there is only one local link but several can be provided. This link comprises relay connecting arrangements at both ends and is associated laterally with the junction and with a relay counting chain which acts as a,register marker for local calls and as a final selector for incoming calls. Calling operator from R.C.X. No. 6 subscriber's line relay 6R, energized by looping the line or by operating the magneto according to the type of instrument used, locks in series with common start relay ST. If the link is idle, RO pulls up sluggishly energizing SW which energizes B and applying continuous ringing current to the junction from lead 10, FA being permanently operated. Relays AJ, AP of the relay finder pull up since the calling subscriber is No. 6 and these relays lock up energizing cut off relay 6K releasing RO and extending the calling line to the junction. 6R, ST fall back. If ST is operated by another subscriber the latter hears busy tone induced from the upper winding of ST, but his line relay remains locked up if he hangs up. Checking calling number and establishing local call. When the operator plugs in, AA pulls up, but not OC which is differentially wound, followed by BB, E, and, if the subscriber is still on the line, as indicated by the condition of A, DD which reverses the current in the junction to give a signal. If the subscriber called when the link was busy and has hung up, the operator re-calls him by unbalancing the junction to energize OC which operates RF to apply ringing current to the line. To check the number given by the calling party as his own, the operator dials it into the junction and AA repeats it to the counting chain BJ, DJ to BP, DP and relay C in parallel. C energizes ER. Assuming six impulses are received, BJ, DJ, BP, DP are operated and line 6 is selected. On the relapse of C, test relay H is connected to the test wire P6 and since No. 6 is calling, H is not operated and the operator receives busy tone on the relapse of E which follows that of C owing to the operation of ER. As a further check the operator may extend a talking connection over the counting chain by unbalancing the junction to energize OC which energizes F. On the relapse of OC, HR is operated in series with F. A talking circuit is thus made to the selected line. The connecting side of the link is then released by connecting a voltage to the junction high enough to break down a neon tube NT and of a polarity such that TO operates and releases the counting chain relays and relays HR, F whereupon E pulls up again. The operator now dials the wanted number and this line is tested. If it is idle, H operates in series with the wanted cut-off relay, locks and energizes HR which releases E, ER. Before the relapse of ER, steady ringing current from 10 goes out over the wanted line and afterwards intermittent ringing current from 11 is applied to the line over ring trip relay F. On the relapse of E, ring-back tone is connected up for the benefit of the operator. On the called party's reply, F completes a temporary talking connection and remains held in series with HR. DD is energized over the loop and reverses the connection of the junction line relay AA to signal the operator. F also energizes the appropriate one or more of a group of connecting relays CJ to CP which complete an alternative talking circuit to the called line. The operator then clears, releasing AA, BB, HR, F, H, the counting relays and SW are released and release-control is transferred to the calling party. Outgoing calls. These are established in the same way as local calls up to the clearing of the verification connection. The operator extends the junction in the usual way to the wanted party. Incoming calls; breaking in. When the operator takes the junction into use, AA, BB and the counting relays are operated and the line is rung as in the case of local calls but, since SW is not operated, the talking connection over contacts of the counting relays is maintained until the end of the connection. A call of this kind can thus be established even if the link is busy. If the wanted party is busy the operator can break in as in the case of the checking connection. If the call is' accepted, the existing connection is broken down by re-operating OC to extend ground to the junction point of the wanted party's cut - off relay and the connector or finder relay involved in the local connection. The latter is shunted out and when the releasing earth is removed, the cut-off relay holds in series with H whieh connects up DD to provide the called side feed. Testing and fault alarm arrangements. A test clerk selects a line to be tested in the same way as an operator and applies a high voltage to the junction in such a direction as to operate TC. TS pulls up, followed, when the high voltage is removed, by TR. A metallic connection is thus made from the junction to the selected line and AA, OC are disconnected from the junction, AA being held locally. To restore the impulse relay, TC is operated again, and this time releases TS and holds TR. At the end of the pulse, TR is released also. Relay FA, Fig. 5, is permanently operated except when the battery fails. It then extends the junction to a particular telephone on the system. Current supply equipment. Fig. 5. When ringing current is required, earth is connected to wire 16 and RT, RC operate in series. RT removes a shunt from its de-energizing winding and then falls replacing the shunt. Intermittent operation of RT generates a tone current in transformer T1. Ringing current is generated in transformer T2 by a vibrator RV and ringing current and ringing tone are applied intermittently to lines 11, 13 respectivelyby a slow interrupter constituted by relays IR, IRA and a large electrolytic condenser QF. Steady ringing current is applied to lead 10 over a current-limiting lamp RR. Busy tone is generated by relay BZ when ground is applied to lead 15 and is intermittently connected to wire 14 by an interrupter constituted by relays XB, ZB. Specification 502,545 is referred to.