Patent GB-763145-A (GB)
Title: A telephone system with two-party connections
IPC: H04Q5/00
Filed: 1954-03-19
Abstract: 763,145. Automatic exchange systems. LICENTIA PATENT - VERWALTUNGS. GES. March 19, 1954 [March 24, 1953], No. 8102/54. Class 40 (4). In a two-party satellite exchange, connected by a single pair to a main exchange, and in which initiation of a call causes ground to be applied to one or other of the legs depending upon which subscriber is calling, the line circuit at the main exchange contains at least one relay which ensures that the calling earth is always transmitted forward over the same wire for the purpose of starting line-finder or preselector action. First embodiment, Fig. 1. When subscriber number 1 calls earth is received over line wire La to bring up line relay R1. This relay switches through the speaking wires to place the relay R(VW) in the preselector VW in parallel with R1. The consequent lowering of the resistance of the circuit over the wire La brings up the subscriber's branching relay which is of the retentivity type, as described in Specification 749,120, so closing the speaking loop for subscriber number 1 and disconnecting subscriber number 2. The preselector started by the operation of R(VW) now operates in the normal manner, and when the first step is taken relay T hitherto unoperated due to differential action, now operates and disconnects the line relay R1 from the wire La. R1, however, holds locally, and connects up the appropriate meter Z1. A call from subscriber member 2 proceeds similarly, it being noted that the line relay always connects the calling wire (in this case Lb to the a wire of the preselector). At the end of the conversation (reverting to the case of subscriber No. 1) when the calling subscriber hangs up the preselector homes, thereby releasing the cut-off relay T by differential action. Relay T releases R1 which is then reconnected to wire La. Further, relay T connects - potential to line wire Lb (over coil 5/6 of R2), so replacing earth on that wire from wire b of the preselector. This potential reversal provides releasing current for the release coil of the subscriber's branching retentivity relay. In the case of a call to one of the subscribers, relay T is operated over c1 or c2 from the final selector LW, so disconnecting R1 and R2, and ringing current is transmitted over a1 or a2 to La or Lb. Disabling arrangements for the subscribers are provided as described. Second embodiment, Fig. 2. Only one line relay R1 is provided which operates only in the case of subscriber number 2. In the case of subscriber number 1 calling, earth over the line wire La and resistance WT seizes the line-finder AS which commences hunting. When the line is found T operates over the c-wire, and disconnects the other subscribers line relay R1 from the b-wire which is now extended to the line-finder. Relay T also cuts out the resistance WT from the a-wire. If subscriber number 2 calls by earthing the wire Lb, relay R1 operates thereby extending the calling earth to the a-bank of the line-finder which then hunts as before. When the line is found T operates to switch through the speaking wires and R1 holds in series with T. Release takes place when,T is de-energized as described for the first embodiment. If service to subscriber number 1 is to be discontinued strap 5, 6 is removed and a strap is provided between points 6 and 7 to provide release potential for subscriber number 2. To disable subscriber number 2 strap 4, 8 is removed and points 7 and 8 are strapped. Removal of straps 1, 2 or 2, 3 bars calls to the respective subscribers. Third embodiment. In this case the line relays R1, R2 are retentivity relays. Calling earth on line wire La operates R1 over its coil 1/2, this relay then disconnecting itself from the wire La and connecting itself to the condenser C. When the preselector starts to operate - potential is removed from wire c and the condenser C charges over Wi, the charging current being in such a direction as to hold R1. When the connection is released wire c is again connected to - potential and the discharge current of the condenser releases R1.