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.