| 摘要 |
<p>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 isolators, each including a light emitting diode and phototransistor, are advantageously employed as line current sensors and switching elements. Insertion of boost potential into the line is controllably delayed in response to changes in the direction of current flow caused by apparent reversals in the polarity of the applied central office battery.</p> |
