| 摘要 |
PURPOSE:To prevent a loop from being disturbance due to a disturbing radio wave by exercising control over the center frequency of a tracking filter to follow up an input signal by making a phase comparison between the input signal and output signal of a tracking filter. CONSTITUTION:An input signal is supplied via adder 42 to tracking filter 43, the output of which is added to the input signal via attenuator 44. Further, the output of filter 43 is supplied to phase comparator 47 by way of phase shifter 45 and limiter 46 and through limiter 48, the output of adder 42 is supplied to phase comparator 47, whose output is supplied to filter 43 as a control voltage for its center frequency by way of loop filter 49 and loop antenna 50. As a result, the center frequency of tracking filter 43 follows up the instantaneous frequency of the input signal, so that disturbance of the loop due to high-frequency and low-frequency disturbing signals and noises in the input signals can be removed.
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