| 摘要 |
PURPOSE:To obtain a callout circuit reduced in the number of compoenents by commonly using a squeltch circuit and a muting circuit. CONSTITUTION:When a handset of a wireless interphone A is hooked off, a transmission switch SWa1 is made on and a switch SWa2 is changed over from a terminal (a) at waiting side to (b) side, then an inaudible frequency signal generation circuit 1a is operated, a signal in 30kHz is transmitted to an output circuit 4a via a modulation circuit 2a, FM modulation is made to the carrier of a carrier generation circuit 3a and transmission is made from an antenna 5a to an opposing station B. On the other hand, the station B detects the transmitted inaudible signal at the inaudible frequency detection circuit 16b to make an inverter 162 to a low level. Thus, a transistor TR1 turns off, an informing circuit 10b is operated and a callout tone is produced from a speaker 11b. At the same time, a low frequency amplifying circuit 17b is operated by turning off the TR1 and muting is turned off. When a handset at the station B is hooked on, a transmission switch Wb1 turns on and a switch SWb2 is selected to the terminal (b), and the inaudible frequency signal is transmitted from the station B to the said station A. |
