| 摘要 |
a fixed device having a first controller for outputting a control signal for multichannel monitor to enlarge empty channel information and controlling a channel change operation using the empty channel information, a first frequency synthesizer for synthesizing the control signal with a local frequency corresponding to the frequency of the channel to be checked, a first mixer for mixing the local frequency signal with a channel frequency signal applied from a first duplexer to output an intermediate frequency signal of the channel to be checked, and a first multichannel monitoring device including a first channel state detector for demodulating the intermediate frequency signal to detect whether a voice signal or a noise exists; and a portable device having a second controller for outputting a control signal for multichannel monitor to enlarge empty channel information and controlling a channel change operation using the empty channel information, a second frequency synthesizer for synthesizing the control signal with a local frequency corresponding to the frequency of the channel to be checked, a second mixer for mixing the local frequency signal with a channel frequency signal applied from a second duplexer to output an intermediate frequency signal of the channel to be checked, and a second multichannel monitoring device including a second channel state detector for demodulating the intermediate frequency signal to detect whether a voice signal or a noise exists.
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