APPARATUS C/N MEASUREMENT

摘要

PURPOSE:To control the waveform distortion generated in a phase synchronous loop and to decrease measuring error, by selecting the frequency of an intermediate frequency signal given on a phase difference detector sufficiently larger than that of the intermediate frequency signal given on a branching filter. CONSTITUTION:The external input signal is applied to a freqnency mixer 9 together with the output of a variable local oscillator 5 and an intermediate fre quency signal f1 is outputted. The phase comparison of this signal f1 with the output of a stadard oscillator 10 is carried out by a phase difference detector 11 and the difference output is fed back to the oscillaor 5 through a wave filter 12 and the phase synchroniaation is carried out. On the one hand, the signal f1 is applied to a frequency mixer 14 together with the output of a local oscillator 13 and is converted into a smaller intermediate frequency signal f2 than the signal f1. This signal f2 is applied to a branching filter 15 and separated into a carrier component fc and a noise component fN, then C/N of the external input signal is detected by a level ratio detector 7. Hereby, measuring error can be decreased not subjecting to the influence of noise level even if the waveform distortion is produced.