Improvements to the devices ensuring the secret telephone conversations, applicable to rural lines and rows are grouped in sets

摘要

243,791. Sherman, H. B. Sept. 2, 1924. Party-line exchange systems ; automatic exchange systems.-When a subscriber on a partyline, C. D lifts his receiver 19 to initiate or answer a call, a relay 1 is energized over its high and low resistance windings 2, 3 in series with a relay 5 at the exchange and removes a short-circuit from the receiver, at the same time shortcircuiting its high-resistance winding 2 to prevent the energization of the corresponding relay of any other subscriber on the line, so that secrecy is ensured. Operation of the relays 1, 5 and of the substation bell Band magnets F and exchange indicator 31, 30 takes place over the two party-line wires in parallel. In the case of a call for another subscriber on the same line, the calling subscriber rings the code call without lifting his receiver, so that relay 5 is not energized and the call does not reach the exchange indicator 31, 30. He then lifts his receiver, energizing relays 1, 5, and when he hears the called subscriber take down his receiver he momentarily presses a key 11 to remove the short-circuit from the high-resistance winding 2 to permitenergization of the relay 1 of the called subscriber. If the exchange is automatic the subscribers' dial is connected as shown in Fig. 3. Non-operation of the relay 1 when the receiver is lifted serves as an indication that the party-line is busy.