| 摘要 |
PROBLEM TO BE SOLVED: To back up transmission by one transmission line even if a fault occurs in another transmission line and to improve the stability of transmission by comparing the respective levels of the transmission signal received through a radio wave and the transmission signal received through an infrared ray and setting the pertinent transmission signal of the high level to be a normal reception signal. SOLUTION: When the transmission state of the radio wave is normal and the communication fault occurs owing to the crossing of the transmission line of the infrared ray IR by a man, the first peak value (infrared ray IR) of the first reception signal SR1 is smaller than the peak value (radio wave R) of the second reception signal SR2 . In such a case, a comparison circuit 25 outputs a second switch signal SK2 to a switch 29 so as to adopt the radio wave R whose signal level is higher than the infrared ray IR. Thus, the moving piece 29d of the switch 29 is connected to an input terminal 29b-side and a modulation signal Sm is inputted to a demodulation circuit 30 through the switch 29. The demodulation circuit 30 demodulates it and outputs a video signal S1 and a sound signal S2 to an output terminal 31. |
