| 摘要 |
PROBLEM TO BE SOLVED: To surely hear the voice (receiving signal) from an intercom slave unit at the side of a master unit even when the indoor noise level is relatively higher than the outdoor noise level. SOLUTION: A master unit A comprises a microphone 1, a speaker 2, a call switching circuit 5 which compares the level of a transmitting signal with that of a receiving signal and passes the signal with the relatively higher level to switch over the transmitting mode and the receiving mode, and a microcomputer 13. In the master unit A, the microcomputer 13 forces the switching circuit 5 to switch to the receiving mode for a specified time T1 after the end of the transmitting mode forced by a press-to-talk function. Thus, one can surely hear the voice (receiving signal) from an intercom slave unit C at the master unit A side even when the indoor noise level is relatively high. COPYRIGHT: (C)2005,JPO&NCIPI
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