| 摘要 |
PURPOSE:To output a backup signal at the time when a demodulating signal does not reach a prescribed level by switching to a main signal and a backup signal in accordance with a demodulating signal level by an output of an amplifier. CONSTITUTION:In the case an optical signal is not inputted, a signal is not outputted either from a photodiode 9, therefore, a voltage level after passing through a detector 21 becomes an L level. Accordingly, a comparator 17 detects abnormality, transistor 18 is turned on, and a relay 11 is energized. As a result, from the signal output 15, a backup signal inputted from a coaxial signal input 19 is outputted. In the case there is no input to an optical transmitter 6 due to a fact that an input cable is detached, etc., although a optical signal is inputted, and even in the case of a fault of a high frequency signal amplifier 14, a voltage level of an output of the detector becomes L, and finally, the relay 11 is energized and the backup signal is outputted automatically from the output 15. In such a way, a stagnant wave caused by a fault, etc., can also be backed up as a system. |
