Patent GB-711522-A (GB)
Title: Improvements relating to party line telephone systems
Inventor: BARROW NORMAN
IPC: H04Q5/06
Filed: 1952-04-02
Abstract: 711,522. Party-line systems. SIEMENS BROS., & CO., Ltd. Jan. 30, 1953 [April 2, 1952], No. 8430/52. Class 40 (4) Each substation on a party line has a plurality of electromagnetic switching devices responsive to a party-selecting code comprising a like plurality of successively applied elements, each element having at least two different characteristics, and all the devices at any one substation are successively operated only on receipt of the code signal appropriate to that substation, the successive operation of all the devices at that substation being effective to complete a circuit for the operation of the bell at that substation. Substation circuits, Fig. 1.-Each substation on a party line comprises a telephone set T and two relays X and Y, each relay being connected to one or other of the line wires a and b in series with a rectifier and a gas discharge tube T1 or T2. The party-selecting code has two elements, each consisting of a positive or negative potential of 130 volts applied to wire a or wire b at the associated exchange or switching centre. The first code element operates the tubes T1 and relays X at three of the substations, and a circuit is thereby prepared at each of these substations for the tube T2 and relay Y. The second code element then operates the tube T2 and relay Y at one of these substations. This connects the bell AB at the selected substation to that line wire over which the second code element was not transmitted and to which ringing current is now applied. The called subscriber answers by lifting his receiver and closing key contacts BK to loop the line and trip the ringing and code transmission, whereupon relays X and Y fall back and the bell is disconnected. Key contacts BK must be closed also in making a call. In the case of a revertive call, contacts BK are opened on the reception of busy tone and closed again when the called subscriber answers. The tubes T2 may be omitted at substations called by a code of which the two elements are applied to different line wires, the circuit then including the connection shown as a dotted line at substation 1. The number of parties on a line may be doubled by the use of polarized bells and unidirectional ringing current. Final selector, Fig. 2, and associated relay set and code selecting switch, Fig. 3.-.The final selector has the usual impulse receiving relay AA, dialling relay AC, answering supervisory relay AD, ring tripping relay AF, and release control relay BB. Relays AA and BB are normally operated during a call, and AC is energized during reception of the impulse trains representing the tens and units digits: At the end of the tens impulses a wiperswitching relay operates, closing a contact in the circuit for relay ST, and at the end of the units impulses relay AC is released, bringing up ST followed by relays DC and CA. The party-selecting impulse trains are now received and are repeated by AA to magnet DSM which steps wipers DS1-8 accordingly. The first train consists of either 2 or 8 impulses and at its conclusion DC releases, bringing up relay AX to energize relay AY and re-operate DC Relay AX releases at the first break period of the second train, which consists of from 1 to 6 impulses. At the end of the second train DC and CA release, applying earth to wiper DS4 and completing a circuit for slow-operating relay CO. The two elements of the partyselecting code, each consisting of a positive or negative potential of 130 volts, are now applied in succession to the called line a, b. The first element is applied over wiper DS7, and the second over wiper DS8 after the operation of relay CO. The selection of the particular line wire a or b for the transmission of each code element is effected by relays CC and RB, whose operation depends upon the position of wiper DS4. During the transmission of the first code element over one line wire, earth is connected to the other wire via wiper DS3. The operation of relay CO releases relay AY to remove this earth and connect ringing current from lead RI to that line wire which is not carrying the second code element. The wanted party is rung as described above. When he answers, relay FA is energized and brings up relays FF and AF to disconnect the code and ringing circuits and complete *the talking connection. Relay AD is energized, and ST and CO are released, and a homing circuit is completed over wiper DS1 for the code-selecting switch DS. Revertive calls.-A special dialled digit indicative of a revertive call sets a group selector to a group of contacts connected to relay sets similar to that shown in Figs. 2 and 3 and is followed by the two party-selecting digits. Busy tone is sent to the caller who opens the loop by means of key contacts BK as described above so that code transmission and ringing may proceed. The caller closes the loop again when the called party answers. According to the Provisional Specification, a revertive call mav be effected with normal dialling by arranging for the final selector to camp on the line. Automatic group switching centre, Figs. 4-7.- The centre shown caters for nine 12-party lines and three junctions to a parent exchange, and comprises four finder-connector links. Each of these links is the first choice for a different group of three incoming lines, three of the four groups including a junction. The four links are connected in a chain circuit, as indicated by the dotted line 41, Fig. 4. An incoming call operates line relay L which connects earth to the chain circuit and marking battery to the relevant contact in line finder bank FD3. Assuming that 'the link circuit shown is the first choice of the calling line and is free, magnet FDM steps the line finder FD until it is stopped on the calling line by the operation of test relay RT in series with cut-off relay K. Relays A, PG, B, CD, BA, and E are energized, and L and RT fall back. Dialling tone is supplied by a relaxation oscillator DT, and the chain circuit is extended to the next link. Call to party-line subscriber.-A train of from 1 to 9 impulses corresponding to the wanted line is received and is repeated by relay A to magnet CNM which steps the connector CN accordingly. At the end of the train, CD releases and brings up relay PA, which switches the impulsing circuit from CNM to magnet RSM and also re-operates CD. One or two further dialled digits indicative of the wanted party are received and set wipers RS1-8. If two party-selecting digits are required, the first is 1 and causes wiper RS2 to complete a circuit for relay SD which operates when CD releases after the impulse. A circuit is thereby completed over wiper RS2 for magnet RSM to step its wipers to contacts 11. Relay SD then releases, and relays RS and CD are operated. The second party-selecting digit is 1, 2, or 3, and wipers BS1-8 are set to contacts 12, 1, or 2. If only a single party-selecting digit is required, a train of from 2 to 10 impulses sets the switch to a position in the range 3 to 11. In either case, the release of relay CD at' the end of the party-selecting impulses brings up relay TA which initiates the delayed release of relay E. If the wanted line is engaged, the release of E connects busy tone from lead BT. If the line is free, however, test relay H is energized and brings up relay F before E. releases. The first code element is applied over one of the wipers RS 5-8 to line wire a or b while earth is'applied to the other line wire over wiper RS3. The release of E energizes slow-operating relay P which changes over the connections of the code-selecting wipers RS 5-8 so that the second code element is applied to one. line wire while ringing current produced by the oscillation of relay RR is applied over wiper RS4 to the other. The oscillator DT supplies ringing tone via contacts irt. When the called party answers, relay RT operates to release F which switches through. Relay D operates.in the feed-bridge circuit, and relays PA, RS, and TA fall back, the circuit being now ready for conversation. Revertive call.-On receiving busy tone the caller opens the loop by means of his key contacts BK as described above. Relays A and B are released, removing earth from the line finder test wiper FD3. Corresponding contacts on the connector bank CN4 and the line finder bank FD4 are connected, and earth is extended over the relevant one of these connections to the test relay H which operates in series with cut-off relay K, bringing up relay F so that code transmission and ringing proceed as described above. The caller recloses the loop when he hears the called party answer, and the call proceeds in the normal way. If the called party fails to answer, the connection is forcibly released after a predetermined interval by means of two thermal relays TH and THA. Call to parent exchange. The caller dials "O" so that the connector CN is set to contacts 11 connected to the first choice junction, the second and third choice junctions being connected to contacts 12 and 1 respectively. In bank CN3, contact 11 is connected to terminal p in the line circuit. Terminals p and pp are strapped together in each line circuit except that of the first choice junction. The release of CD at the end of the impulse train brings up relay MB which starts relay RR oscillating and applies earth to the test relay H. Either a dry loop or battery feed may be presented to the outgoing side of the bridge by the use of strap Ul or straps U2 and U3 respectively. If the junction is free, H operates in series with K and extends earth over connector wiper CN3 to busy the junction and to operate relay JG in series with the cut-off relay K in the second choice junction. The caller receives ringing tone as previously described and the call proceeds in normal fashion. If ringing current is to be applied to the junction, strap PE (Fig. 6) is placed in position, so that relays F and P are energized and E is released, ringing current being supplied via wipers RS4 and RS5. I