GB610790A - Improvements in telephone systems - Google Patents

Abstract

610,790. Exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. April 16, 1946, No. 11724. Convention date, April 19, 1945. [Class 40 (iv)] Signals are transmitted over a telephone line by the application thereto of alternating current by either of two relays which connect the line wires to the terminals of the source in opposite senses so that the initial current goes to line in one direction or the other. The receiver comprises an arrangement of relays and rectifiers arranged to respond differently to these two initial current directions and thereafter to remain operated, in the position taken up in response to the initial current, for the duration of the A.C. signal. As shown in Fig. 1, the transmitter comprises three relays of which R3 generates the A.C. and R1 or R2 connects the source to the line La, Lb. Operation of R1 or R2 completes a D.C. circuit through the primary of T and connects the secondary to the line wires in one of the two senses. Simultaneously, R3 operates, changes the current direction in T and interrupts its operating circuit, whereupon it continues to reverse the current in T as long as R1 or R2 is operated. The receiver shown in Fig. 4 comprises a double-winding polarized relay. A current impulse from La to Lb energizes the lower winding and results in the actuation of the lower spring-sets so that the lower winding remains energized independent of the subsequent reversals of current in the line, contact 106 repeating the signal. Similarly, an initial impulse in the opposite direction energizes the upper winding, contact 101 repeating the signal. In a modified receiver, Fig. 5 (not shown), two normal relays replace the polarized relay, while in a modified transmitter a separate A.C. source is employed after R3 has transmitted the initial signal.