| 摘要 |
PROBLEM TO BE SOLVED: To provide a doorphone master set in which a connection burden is reduced. SOLUTION: In the doorphone master set A, a control signal transmitting circuit 42 and a control signal receiving circuit 41 are connected to a connection point P on control signal routes R1-R4, and band-pass filters F1-F4 for allowing only the frequency band of a control signal to pass to prevent power supply from a slave set power supply section 5 to an additional master set C and transmitting the control signal separately from an audio signal and a video signal between a slave set connection terminal T1 and an additional connection terminal T2 are respectively provided between the connection point P on the control signal routes R1-R4 and the slave set connection terminal T1 and between the connection point P and the additional connection terminal T2. COPYRIGHT: (C)2008,JPO&INPIT
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