A New Type of VF Repeater for Two-Wire Transmission Loops

Power loss at voice frequencies in two-wire telephone lines is presently overcome by employing electronic repeaters which produce bidirectional amplification without undue interaction between the outgoing and incoming paths. This isolation between the directional gain elements is achieved by employing balanced transformer windings or negative impedance transformations. Both methods rely heavily on complex line matching circuits to minimize the chance of instability or "singing." This paper describes a simple repeater that achieves bidirectional amplification while using conventional 1:1 line transformers. The obtainable return loss against fixed terminal impedances is only limited by the quality of these transformers. The new device reproduces the action of a hybrid transformer using very simple electronic circuitry and has a potentially wide application both in two-wire systems and in two to four wire conversions.