| 摘要 |
PURPOSE:To install many interphone sets to a communication line by providing a switch through which control information and voice information are sent in separate band and disconnecting a voice circuit at standby. CONSTITUTION:A frequency band of a line using a communication as a carrier line is divided into a base band and other frequency band, a control information signal such as a device number of a caller interphone set and a called interphone set is sent while using the base band and a carrier subject to frequency modulation by a call tone or a voice signal is sent while using the frequency band other than the base band. That is, a caller interphone set 20 generates a call tone and a modulated wave is sent to a communication line 21 from a switch 22 after frequency modulation. The modulated wave is demodulated by a demodulation circuit through a switch of the called interphone set and a band pass filter to energize a reception speaker. In hooking on a hook switch at the called party, a control circuit sends the information to the caller side. Then a control circuit 37 turns off a call tone generating circuit 26 other caller side and talking is performed between the caller side and the called party.
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