Patent GB-615504-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q5/00
Filed: 1945-12-15
Abstract: 615,504. Automatic exchange systems. TENCH, F. (Automatique Electrique Soc. Anon.). Dec. 15, 1945, No. 451/48. Divided out of 615,448. [Clase 40 (iv)] Party lines, for use particularly in large private systems of the type described in Specification 615,448, extend between two exchanges, from either of which access may be had to the lines. Party line subscribers may initiate calls over either exchange, the party lines being employed exclusively for the traffic of the party line stations. On local battery lines, means are provided at each station for transmitting positive or negative pulsating direct current, derived from the ringing current, for calling the different end exchanges, normal ring- ing current being employed for calls between stations on the party line. In the case of fully automatic working, the dialling of different exchange codes by a calling party at a station on the party line enables a connection to be set up to one or other of the terminating exchanges. The exchange network (Fig. 1) is identical with that described in Specification 615,488, but in addition to the normal interexchange junctions, party lines, e.g. PL1, PL2, PL3 follow the railroad tracks of a railway network and serve the branch stations thereon. These party lines are characterised by a prefix beginning with the digit 7, code ringing being employed for calling on local battery lines, and numerical selection on fully automatic lines. Specification 615,505 also is referred to. Local battery operation. As shown in Fig.. 4, a local battery party line extends between two exchanges AUT1, AUT2, the former being that at which the terminating equipment of Figs. 5 and 6 is located. Exchange AUT2 is similar except that the line connections to 3A and 3APA are reversed. A connection to another party line subscriber is set up by code ringing with KS1 unoperated. This also brings up 3AP and 3APA, but the operators are not signalled since the longest pulse is shorter than the operate time of VI and TI. To call AUT1, KS1 is thrown up so that positive pulsating D.C. is applied to line from the generator, bringing up 3AP only. Switch KS1 is thrown down to give negative calling current to call AUT2. Outgoing calls. The terminating circuit (Figs. 5, 6) is seized by an A.C. pulse (191, 192 and 193, 194 strapped); relays 3AP, VI, TI and S1 all pull up, the last relay holding to transmit a 16 c.p.s. tone from 200 to the calling party, and light the lamps PL2 and PL3 in the operator's position equipment (Figs. 7, 8). Operation of 7KB (Fig. 7) brings up OM and 10M to connect the operator to the calling party while 7KC operates 2R, 6HS hunting under control of 3I until 2CNA pulls up to an idle first group selector. The operator sets up the required connection and then restores 7KB, releasing OM and 10M. Incoming calls. On seizure over a party line selector, 7A (Fig. 5) pulls up followed by 2HA, 2HB, IS and SP. The party line subscriber is selected by coded ringing in the morse code, 3 being dialled for a dash and 1 for a dot. Relay 7A releases on the first impulse and brings up 1RP and ICD which holds under control of 3I for the duration of the train, and connects 16 c.p.s. ringing current to the line. The operator may set up a general call to all subscribers on all the party lines by suitable manipulation of 7KE which brings up the 1CD relays in all the terminating circuits. Operation of key 7KL brings up DR which starts a graduated howler and applies its output to the party line. Emergency calls. Emergency calls may be set up throughout the network from any point on the railroad, portable local battery sets being provided which may be hooked on to a pair of wires following the railroad, e.g. the wires forming the party line. Automatic operation. A detailed description of automatic party line working is given in Specification 615,505. The terminating circuit of Fig. 2 (not shown) is taken into use on all calls. The party lines are divided into sections and on calls originated on the party line, discrimination is effected so that the terminating circuit is retained in use only if the call is for the exchange associated with it, or originates on the. section adjacent to it.