Telephone connection control circuit - has line encoder whose control potential initiates supply signal of opposite polarity to subscriber terminal voice line

摘要

The control circuit, for a telephone connection with voice coders, is improved by allowing each subscriber to check before or during connection whether the coder is available for his terminal. The first control potential in the coding device that connects to the lines, applies a supply signal to the subscriber terminal's voice line of opposite polarity to the exchange supply. This supply signal is applied when the voice coder is able to be engaged. A rectifier is connected between the voice lines in the subscriber terminal via an indicator and forms a D.C. circuit carrying the reversed polarity.