| 摘要 |
PROBLEM TO BE SOLVED: To provide a gap filler for preventing surely a case in which only a noise factor is amplified and transmitted when there is no input signal, and for recognizing easily that there is not received signal. SOLUTION: A first coupler 8a for detecting a received signal level, a second coupler 8b for detecting a retransmission signal level, and an alarming means 14, are provided. An input level reference value for comparing a detected received signal level, and an output level reference value for comparing a detected retransmission signal level, are set by program. When the detected input signal level is lower than the input level reference value, and the detected retransmission signal level does not agree with the approximate output level reference value even through the gain of a variable amplifying circuit 4b is made changed; the CPU of a control unit 3 is so programmed that the gain of the variable amplifying circuit 4b becomes a minimum and the alarm means 14 starts the alarm operation. COPYRIGHT: (C)2005,JPO&NCIPI
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