Subscriber's electronic line equipment comprising a two-wire-four-wire conversion circuit for a telephone exchange

A subscriber's electronic line equipment comprising a two-wire-four-wire conversion circuit for a telephone exchange, characterized in that it comprises:

• a d.c. voltage source (8) having its positive terminal connected to a chassis,
• a first transistor (10) having its base connected to the transmission output (4) of the telephone exchange (7), its emitter connected to said chassis by a first resistor (11) and its collector connected to the negative terminal of a d.c. voltage source (8) by a second resistor (9) having a resistance equal to the resistance of said first resistor (11),
• a second transistor (12) having its base connected to the emitter of the first transistor (10), its collector connected to said chassis and its emitter connected to a first wire (1) of the subscriber's line by a third resistor (13),
• a third transistor (14) having its base connected to the collector of the first transistor (10), its collector connected to the negative terminal of the voltage source (8) and its emitter connected to a second wire (2) of the subscriber's line by a fourth resistor (15) having a resistance equal to the resistance of said third resistor and equal to half the total impedance of the line and the subscriber's set, the second transistor (12) being of the opposite polarity-type from the third transistor (14),
• a fourth transistor (16) having its base connected to the second wire (2) of the subscriber's set, its emitter connected to the emitter of the third transistor (14) by a fifth resistor (17) and its collector connected (a) to the first wire (1) of the subscriber's line by a sixth resistor (18) having a resistance equal to the resistance of said fifth resistor, and (b) to the receiving input (3) of the telephone exchange (7).