Patent GB-724852-A (GB)
Title: Improvements in or relating to party line telephone systems
IPC: H04Q5/00
Filed: 1953-05-01
Abstract: 724,852. Party line systems. WESTERN ELECTRIC CO., Inc. May 1, 1953 [May 3, 1952], No, 12120/63. Class 40 (4). The subscribers connected to a party line are provided with an additional private communication channel to which a calling or called subscriber is automatically transferred if the channel is idle, or if it becomes idle during the course of the call. The private channel may be a separate line as shown, or a carrier channel on the party line in the range 10-20 kc. A single private line may be provided for two party lines. In Fig. 1, transfer from the party line 13 to the private line 12 is effected by a slow-release polarized relay 23 located near the subscriber's set. The lines 12, 13 are normally connected at the exchange to switch terminals 27, 28. Assuming that the private line 12 is idle and that subscriber 10 calls or is called over line 13, relay 29 energizes followed by W which (1) connects line 12 to terminals 28 and (2) reverses the current in line 13 to operate transfer relay 23. The current in line 12 holds 23 and operates 30 which shunts out 29 and allows Z to pull up while W remains held. The party line 13 is thus switched to terminals 27 and its connections are such that a second calling or called subscriber remains on that line. But if the call on the private line 12 ends first, the relapse of 30 allows 29 to reoperate and shunt out W, whereupon the second call is transferred to line 12. The second operation of 30 releases Z and restores the line connections to normal. Should the exchange seize line 13 over terminals 27 while there is a call on line 12 over terminals 28, W and Z are held over sleeve 42 in case the existing call is released before the called subscriber in the new call replies. In the case of a revertive call, if the group is idle the caller is at once transferred to line 12 and gets a finder over terminals 28. He dials appropriate digits, and the connector finding terminals 28 busy seizes line 13 over terminals 27 and rings. Upon reply, the line current is reversed in the connector and the called subscriber is transferred to line 12, the call being held by the finder. If an existing call on line 12, terminals 28 is released while the revertive caller is dialling, he is transferred to line 12, terminals 27. The connector therefore seizes line 13 over terminals 28 and rings, the called subscriber being transferred to line 12 upon reply as before. If the connector finds both lines busy on account of a second call in the group, the revertive call can be set up by standard revertive procedure, both subscribers being run when the caller hangs up subscribers being rung when the caller hangs up after hearing busy tone. But if the revertive caller is using the private line, when he hangs up the existing call on the party line is transferred to the private line, and the revertive call is set up on the party line. In a modification, Fig. 2 (not shown), the transfer relay 23 is provided with a holding winding which becomes bridged across the private line 12. It is released by the opening of line 12 by means of a pair of relays (replacing 30) which operate and restore in succession. The line reversing contacts may be controlled directly by relays 29, 30. It is suggested that a community of 250 subscribers might be accommodated on a 100-line exchange having 50 individual lines and 25 two-line groups of the kind described each serving 8 subscribers with selective ringing.