| 摘要 |
PURPOSE:To detect assuredly only a signal sould be detected that is sent from the remote side by breaking the actuation of a detecting circuit for reception signal when a signal component similar to the reception signal is detected by a signal detecting circuit set at the transmission side. CONSTITUTION:When a PIS (procedure interruption) signal is supplied from a device of the remote side, the PIS signal appears at a port B of a hybrid circuit 1 and is supplied to a comparator 7 through a BPF6. The output of the comparator 7 is converted into a direct current by a smoothing circuit 8 and supplied to the input at one side of an AND circuit 10. While a small amount of output appears also at a port A of the circuit 1. However it is impossible for this small amount of output to actuate a comparator 4, and the output of a smoothing circuit 5 is set at ''0''. Therefore, the output of an inverter 9 is set at a prescribed level of voltage, and the circuit 10 is opened. If the transmission signal contains a large amount of the frequency component equal to the PIS signal, the output of the circuit 5 is set at a prescribed level of the circuit 5. Then the circuit 10 is closed.
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