| 摘要 |
PURPOSE:To discriminate any abnormal state occuring to a modulating circuit correctly by detecting plural narrow-band signals and monitoring the spectrum state of a modulated signal. CONSTITUTION:A signal from an input terminal 1 is modulated by a modulating circuit 2 and then outputted from an output terminal 3 as a modulated carrier. A part of the modulated carrier is led to three narrow-band-pass filters 11-1- 11-3 having different center frequencies to be band-limited respectively, and then inputted to signal detecting circuits 12-1-12-3. The spectra after the band limitation at the center frequencies f1-f3 are detected by the detecting circuits 12-1-12-3 and sent to a discriminating circuit 13 with levels V1-V3 corresponding to the respective spectra. The circuit 13 compares them to discriminate the occurrence of an abnormal state accurately. |
