| 摘要 |
Transmission and signaling range of a telephone transmission line is extended by controllably inserting boost potentials into the line to series aid an applied central office battery. Insertion of the potentials is realized by sensing the direction of current flow in the line and switching a corresponding potential into the line. Optical couplers, each including a light emitting diode and an associated phototransistor, are employed as the line current sensing elements and switching elements. |
