Patent GB-540132-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1940-04-04
Abstract: 540,132. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., COMYN, F. E., and FRYDMAN, E. April 4, 1940, No. 6073. [Class 40 (iv)] In a system in which certain subscribers are provided with keys for setting up frequently wanted calls over a feed circuit individual to the subscriber, a single wire extending from each key serves both for selecting a particular wanted subscriber and for signalling an incoming call from that subscriber. The key-calling subscribers may be provided with keys for calling certain subscribers who are not themselves given such facilities. Connection between two key-calling subscribers.-It is assumed that the circuits shown are individual to subscriber No. 2, and that he wishes to call subscriber No. 1. Upon operation of key KL1, relay SW pulls up and connects the line to the individual feed circuit in which line relay LN energizes. A circuit now exists from key KL1 over terminals MR, K for relay D, and this relay connects up the appropriate switching relay 14, which locks independently of D. Each feed circuit is provided with a set of terminals +, -, PN, L and a corresponding switching relay for each other subscriber who may be called by the key operation, the terminals +, -, L being jumpered together to allow for all the possible connections, and the terminals PN connected up bv similar relays such as IH being multipled to the private wire of the corresponding subscriber. Relay IH closes a calling circuit over relay RT, terminals L to lamp LP2 and relay A at No. 1 substation, the lamp being flashed and a buzzer BZ being operated from E2 when RT pulls up. At the same time, KC energizes over terminals H, KC, and SR extends the feed circuit to the + and - terminals. The calling circuit is made whether the wanted party is idle or busy, but if he is idle, battery over his cut-off relay energizes PT, and K pulls up to mark the line busy and extend flashing ground from E1 to the calling party's lamp LPS. The called party answers by operating key KL2, which brings about operations similar to those described above to connect his feed circuit to that of the calling party. The circuit between the two feed bridges is supplied with current over relay SR which is connected up by W. It is to be noted that the flashing ground applied at E2 to the calling circuit shortcircuits the relays D intermittently so as to prevent the possible operation of a relay H owing to the called party having just pressed a selecting key. Lamp LPS remains alight if a subscriber leaves any selecting key operated after hanging up. Connection to subscriber not provided with key-calling facilities.-In this case, terminals MR, H are strapped respectively to terminals X, EC, so that relav EC energizes instead of KC. Relays PT, K operate as before if the called party is idle, but since SR is not up, ringing current is applied over relay F, which upon reply connects up SR to complete the talking connection, the latter relay acting as a feed relay. Ringing current is withheld if the called party is busy, but breaking-in may be provided by a strap between terminals DS, DA to make an immediate circuit for SR. Alternatively, a strap between terminals RA, RB allows a faint ringing tone to be applied to the busy connection. Conference calls &c.-A call involving several key-calling subscribers may be set up by the operation of the appropriate keys by the calling subscriber. An attempt to call both a keycalling subscriber and a non-key-calling subscriber, however, results in the application of NU tone on account of the simultaneous operation of KC, EC. Relay SW may be released by means of key KH to enable an ordinary call to be made by dialling while holding an existing key-controlled connection.