Patent GB-475874-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1936-05-26
Abstract: 475,874. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., (in Liquidation), and COMYN, F. E. May 26, 1936, No. 14880. [Class 40 (iv)] A small system in which ordinary stations are interconnected through a common link CL under the control of a marking switch which responds to dialled impulses includes also a master station MS having a direct line to each ordinary station. Calls from the master station are established by key-operation, an existing call being broken down if necessary, while calls to the master station are set up with the assistance of the marking switch. On the initiation of a call at an ordinary station, start relay ST and line relay L energize, and the latter extends the line to feed relay A which connects up release relay B. Relay E energizes and connects dial tone relay DT to relay A. Dialled impulses are repeated by A to set the marking switch, relay C being operated during the train and E being held thereby, and test relay H is connected to wiper C1 between the successive relapse of C and E. If the wanted line is busy, H is inoperative, and the relapse of E connects up busy tone relay BT. If the wanted line is idle, H operates and connects earth to wiper C1 to operate L, which connects the called line to feed relay A. Dial tone is again sent to the calling party while a circuit is closed over wiper C2 for the wanted party's buzzer RSB. On reply the buzzer is cut out and C reoperates. Conversation takes place over wires S, which are both connected to feed relay A. Upon release, relays A, B, C, ST, H fall back and relay E acts as a stepping relay to home the marking switch. A call to the master station proceeds in the same manner to the point where the wanted line is tested. Relay H connects up line relay LM (not shown), which lights a lamp individual to the calling party in series with AL,.which operates a buzzer MSB. The master station replies by operating the appropriate key KL which takes into use the direct line to the calling station and connects up MM, disconnecting LM. On operation of speak key KS, relay M energizes, disconnecting L and A, so that the link CL is available for further use. The handset MST, MSR or the loudspeaker LS and microphone MSM are used alternatively, and in either case relay R connects the local battery to parallel talking circuits, one over wires R, S and the other over wire R with earth return. The master station makes a call by operating the appropriate key KL and speak key KS, whereupon a circuit is closed for the buzzer RSB of the wanted station. Upon relay, R energizes and completes the talking circuits. The master station may listen to an existing call by operation of the key KL only, and break down the call by means of speak key KS, which brings about the release of line relay L. If the listening feature is not desired, the functions of the key KS may be taken over by the keys KL. If the link CL is engaged when an ordinary call is initiated, a small current through the receiver via resistance YB informs the calling party that the apparatus is not ready to receive impulses.