| 摘要 |
PROBLEM TO BE SOLVED: To prevent service interruption state due to off-hook at the time of no-speech communication by having a speech communication detecting means and providing a circuit which avoids no-speech communication state with a receiver picked up. SOLUTION: A speech communication detection circuit 5 operates a DET relay when it recognizes voice on a general speech communication level. The DET relay of the circuit 5 operates during speech communication with off-hook, no-speech communication detection relay 9 does not operate and also it does not operate even when there is no speech communication for a short time because it is saved by a timer circuit 11. However, when there is no speech communication with a receiver picked up for a long time, the DET relay of the circuit 5 is recovered and the relay 9 through the circuit 11 operates. An idle state is shown to a station exchange 1 side when an operation relay switch 12' disconnects a direct current loop circuit between L1 and L2, a switch 12" recovers a calling circuit at the time of a call from others to enable an incoming call from the exchange 1 even with the receiver off.
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