REPLY SIGNAL SENDING SYSTEM

PURPOSE:To eliminate the influence of a sent out carrier wave, to be exerted on transmission and reception of a reply signal by inhibiting close of communication channel between a modulating and demodulating device and an exchange network until the completion of transmission and reception of the reply signal in a junction line of in-band frequency signal after sending out the reply signal from a network controlling device to the exchange network. CONSTITUTION:A time limit circuit TM is provided in the energizing circuit of TrQ1 of a network controlling device NCU'. A ready signal ER is transmitted to the NCU' as a circuit switchover signal CML, and makes TrQ2 conductive and starts a time limit circuit TM. The TrQ2 operates a relay S, and forms a DC loop circuit for an exchange SW' and sends out a reply signal. On the other hand, a modulating and demodulating device MD' does not transmit carrier wave to an exchange SW' while the contact cm of a relay CM is in open state. When a started time limit circuit TM detects the lapse of time set longer than the time required for detection of stopping of signal from the device IR' by an in- band frequency signal device IR, makes the TrQ1 the state of conduction, and operates the relay CM to close communication channel between the device MD' and exchange SW'.