| 摘要 |
PURPOSE:To keep the quality of reception to a desired quality level by providing a switch circuit causing interruption of a microphone circuit depending on an output signal representing the non-transmission state from a state recognizing means. CONSTITUTION:A voice signal and a control signal are fed to a hand free telephone set 30 via a subscriber circuit 15 connected to a subscriber circuit 14. When a call of a speaker 22 is caused in the telephone set 30, speaker call information is sent to an exchange 10, where dial tone connection is caused, speaker-on information is sent to the telephone set 30 to set a switch circuit 20 and the listening of the dial tone is attained via the speaker 22. When a called party hooks on after the end of talking, a switch circuit 21 is turned off and the microphone 22 is turned off, a busy tone is generated and given to a caller. When the caller enters hooking on, the interruption information is given to the exchange 10 to turn off the switch circuit 21 of the speaker 22.
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