| 摘要 |
PURPOSE:To obtain a monitoring device for phase modulator with simple constitution, by using a characteristic in which a mixer is operated as a phase detector. CONSTITUTION:The outputs of an original oscillator 10 and a phase modulator 11 are respectively applied to a mixer 4 and a signal in a frequency difference between the frequency of a phase-modulated signal and a carrier from the oscillator 10 is obtained at an output terminal of said mixer, and the low frequency component corresponds to a modulated input signal. Thus, a signal applied to one of a comparator 8 via a low-pass filter 9 and an amplifier 7 is a modulated input signal component via the phase modulator 11 and since a signal applied another input terminal of the comparator 8 is the original modulation input signal, if the phase modulator has any failure, both of them are not coincident, and a failure signal is obtained at a terminal 14. |
