| 摘要 |
PURPOSE:To avoid trouble of interrupting talking by providing a sound and silence detection circuit and switching the frequency for interception prevention only when a voice signal is changed from a sound state into a silence state. CONSTITUTION:A voice signal from a speech line L is inputted to a sound and silence detection circuit 17 via a speech circuit 101, in which detects whether the voice signal is in the sound state or the silence state and the result is outputted to a control section 108. The control section 18 detects it that a detection result signal from the circuit 17 changes from the sound state into the silence state and sends a switching command signal with a voice information channel frequency while using a control information channel to a slave set 2 at this point of time. The slave set 2 receiving the switching command signal from the master set 1 switches the voice information channel frequency for transmission reception and sends the notice signal representing the frequency switching end to the master set 1 through the use of the control information channel. The master set 1 receiving the signal switches the channel frequency to modulate the voice signal from a telephone line L based on the frequency and sends the result to the slave set 2. |
