GB893561A - Improvements in or relating to circuit arrangements for receiving audio frequency control signals provided with audio prefix signals, for use in telecommunications systems - Google Patents

Abstract

893,561. Automatic-exchange systems. SIEMENS & HALSKE A.G. March 18, 1959 [March 18, 1958], No. 9468/59. Class 40 (4). In an arrangement for receiving VF signals the receipt of a prefix signal of sufficient duration brings about the association with the signal path of common apparatus for receiving and dealing with the ensuing control signals. As shown, an incoming line L is coupled inductively to switching apparatus VF and is bridged by a resonant circuit RK tuned to the frequency of the prefix signal. The presence of this frequency on the line therefore charges two condensers C1, C2, the latter being located in common apparatus. If the signal endures for 50 mins., say, the charge on C2 is such that transistor Tr2 is effective to operate start relay An which causes a finder S to hunt for the line L, the charge on C1 being detected by transistor Tr3. Although the finder is shown as a wiper-switch it may be a relay switch, an electronic switch or a crossed-coil switch. Relay P energizes and a voice-immune receiver VSE is connected up to receive the remainder of the prefix signal, relay VE being operated, followed by V. At the end of this signal VE falls back and D is operative during the release time of V to connect up a receiver TSE for the ensuing control signal, which is transferred in D.C. form to a register ZS. Relay T energizes and biases a diode TD to block the line. The receiver TSE sends a signal to a marker M and if necessary controls a transmitter ZD to send forward VF signals. If, however, the received signal is a backward one, relay W is energized as well as T and the transmitter ZD sends VF signals over the incoming line L. The system may be one employing carrier working.