Patent GB-448651-A (GB)
Title: Improvements in or relating to party-line circuits for telephone systems
IPC: H04Q5/20
Filed: 1935-03-15
Abstract: 448,651. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London. March 15, 1935, No. 8160. Convention date, Oct. 31, 1934. [Class 40 (iv)] A party line subscriber's transmitter and receiver are normally entirely disconnected from the line by contacts of a relay which is differently connected at different sub-stations on the line and can be operated only in response to a discriminator at the exchange by which the calling or called sub-station is determined. A part of the line circuit equipment, including the discriminator, is common to a number of party lines, but individual line relays and a meter for each party are provided. Parties associated with the same common circuit cannot call each other. Sub-station circuits. Two-party lines are described, differentiated by references X and Y, the circuit for an X station being shown in Fig. 1. Relay PX is connected to the negative wire (the corresponding relay of the other party is connected to the positive wire) and when a call is made or answered, operates over switchhook SW in response to battery connected by the discriminator to the negative wire. PX connects up the telephone set, remains held over the loop, is slow-to-release so that it holds during impulsing, and is shunted for speech currents by the series bell condenser QA. Exchange circuits, Fig. 2. When a call is made, ground at the sub-station operates individual line relay L, which locks in series with common relay FX. Relay L at l3 opens the locking circuit of a second line relay L<1> and so on to prevent simultaneous seizure of the common circuit. Relay PX at the substation does not yet operate owing to the high resistance of L. The line is now connected to relays LL and J of which J is the discriminator. If the X party (ground on negative), calls, LL operates alone, whereas if Y (ground on positive) calls, J pulls up, locks over its right hand winding and reverses the line connections so that LL also operates, PX still remaining inert. Relay LL loops the outgoing line (chaindotted circuit) to start a line switch or starts a call finder over the circuit marked with crosses. K and F also operate. If the " call is a flick of the switch-hook, LL does not operate so that FR pulls up to shunt the locking winding of L. The parties have separate appearances in the connectors, but the private wires of the X and Y parties are separately multipled and busied by K so that no party associated with the common circuit can be called. When the outgoing third wire is grounded at the line switch or call finder, Q operates in a circuit over which K also holds, switches t rough, and releases LL and FX. Battery feed from the group selector now operates sub-station relay PX. If the Y station had called, J would be operated to reverse the connections and operate the corresponding relay at that station. Metering and release. When the called party replies, metering potential on lead M (which is connected to P in case of call finders) operates the correct meter XM or YM over f5, j4 to ground or battery according to the type of metering signal used, and MT pulls up in parallel and locks. When the connection is released, K falls back, Q remains held over its lower winding to maintain a busy ground in the connector banks and to hold K. Relays F and MT release slowly in succession, ground, battery or booster being applied over mt4 to operate the meter a second time. On the relapse of MT, Q falls back and permits FX to re-operate and maintain the busy condition at the connectors, FR pulls up and short-circuits L, whereupon. FX, FR fall back and the circuits are normal. In ground or booster metering where the meter is held operated during conversation, the dashed line circuit over contacts of F and K is provided so that the meter is released on the relapse of K prior to re-operation as above described. Incoming calls. The speaking leads + XY, -XY from the connectors for the two parties on a line are multipled together, separate + XY leads are used for each line associated with the common circuit, but all the -XY leads are connected in multiple. As previously stated, the positive and negative private wires are multipled in X and Y groups. When the common circuit is seized by a connector, Q operates alone for a call to an X party and in series with J for Y parties. Q opens the circuit over which the L relays are operated on outgoing calls and prepares the speaking path. The L relay of the called line is operated by the usual battery on the ringing circuit over XY, locks up and connects XY to relay FX which also operates and ringing current passes over F (right hand) to the positive or negative wire of the party line as determined by the operation or non-operation of J. When the party replies, F pulls up, trips the ringing at the connector whereupon battery feed, the direction of which is determined by J, will operate the correct relay PX or PY at the sub-station. On release of the connector, Q falls back and FX (right hand winding) pulls up followed by FR which releases L and the circuit restores to normal. Repeater, Fig. 3 ; recall ringing. A repeater is used between the common circuit, Fig. 2, and the finders or line switches in cases where current reversals occur at the exchange since these would interfere with party line operation. Relay A is the feed and impulse relay for the calling party, B and C the usual release and dialling relays, whereas RG responds to recall ringing and repeats the signal from RL to the party who made the call.