ELECTRONIC LINE EQUIPMENT WITH TWO-WIRE-FOUR-WIRE CONVERSION CIRCUIT FOR TELEPHONE EXCHANGE

摘要

Equipment without telephone transformer or amplifier. It is connected to the subscriber by terminals (1, 2) and to the telephone exchange by terminals (3, 4, 5, 6). It comprises a d.c. voltage source (8), four transistors (10, 12, 14, 16) and three pairs of equal resistors (9-11, 13-15 and 17-18). Sidetone is eliminated by the circuit (18-16-17). Of use in telephone exchanges of all kinds.