Patent GB-535453-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M9/00
Filed: 1940-02-13
Abstract: 535,453. Direct-call systems ; manual exchange systems. GRAHAM & CO., Ltd., A., and VAUGHAN, C. H. Feb. 13, 1940, Nos. 2707 and 9213. [Class 40 (iv)] Two stations connected by a two-wire line are provided one with a battery and the other with a metal rectifier, and calling is effected by reversing the line connections at either station to allow current to flow over the line and through the rectifier. The arrangement is applicable to exchange systems, each substation being provided with a rectifier, and the talking connections being made at a switchboard through a condenser or transformer coupling. Direct-call system, Fig. 1.-The line is looped at station A through the battery and buzzer BZ and at station B through the buzzer BZ and rectifier MR which normally prevents current flow. It is convenient to fit the rectifier in each set and to short-circuit it by a link RU at station A. Similarly the battery terminals at station B are bridged by a link BU. Upon temporary actuation of the calling key CK at either station, the line connections at that station are reversed and the resulting line current operates the buzzer BZ at the called station, causing the receiver R to emit a note at the buzzer frequency through the medium of a condenser K. A lamp S is also lighted. The buzzer at the calling station is shortcircuited by the calling key. The talking circuit is completed at each station over switchhook or handset contacts W. In modifications, Figs. 2, 3 (not shown), no separate calling key is employed, and the reversing and other movable contacts are controlled by the switchhook. The line connections at both stations are thus reversed when the talking circuit is set up. In all these arrangements, further stations B may be connected to the line and code ringing by station A may be used. Two stations B, however, can communicate only through the agency of station A. Exchange system, Fig. 4. The substation circuits are similar to those of station B in Fig. 1, while the switchboard circuits follow the lines of station A. Answering jacks OJ are provided for the connection of the operator's set HMT, and jacks CJ serve for setting up connections by means of single-wire cords CPC. When a calling key CK is actuated, line current operates the buzzer BZX, causing a common receiver CRX to emit a calling note, and an individual lamp SX lights. The operator by plugging her set HMT into the jack OJ disconnects the buzzer and lamp and completes a talking circuit to the calling party. Line relay LR energizes in this circuit and lights an engaged lamp EL. If another party is wanted, the operator actuates the corresponding calling key CKX and sets up the connection by bridging the appropriate jacks CJ by a cord CPC, thus coupling together the circuits of the two parties through a pair of condensers KKX. The operator's set HMT may be removed, clearing signals being given by the extinction of the lamps EL. Interconnected exchange systems, Fig. 5. The substation circuits are again similar to those of station B in Fig. 1, and talking connections are set up by means of individual speaking keys SKX at the switchboard. A common buzzer BZ and calling lamp SX are controlled by relays PR in parallel with individual indicators I. For calling between the two switchboards, the calling circuit over wires LX1, 2 includes the battery at C1 and a rectifier MRX at C2, so that current flows when the connections are reversed at the key CKX at either end. The talking circuit between the switchboards includes one wire LX3 and a condenser KKX at C2 and is completed over the keys SKX at each end, and this circuit serves to interconnect substations connected respectively to the two switchboards.