| 摘要 |
PURPOSE:To prevent a squelch output from generating even when a sweeping signal is inputted while keeping a quick response by providing a pulse detecting part and a logic part at the output side of a comparing part. CONSTITUTION:When the sweeping width of a sweeping signal exceeds the band of a narrow-band filtering part 1, the output of the narrow-band filter 1 is changed, therefore, the output of a detecting part 2 is as shown in Fig. (a). As the result, the output of a comparing part 3 comes to be like (b), the period is shorter than a time constant tau of a pulse detecting part 4, therefore, the output of the pulse detecting part 4 (mono-stable multivibrator) does not return to the original condition, the pulse width is extended rapidly like (c), and after the sweeping signal is eliminated, the output returns to the original condition. Consequently, the output of a logic part 5 is seen like (d). A little delay (about tau) occurs when the sweeping signal is turned off until the output of the logic part 5 is changed, and this can be evaded by making the sweeping width narrower than the band of the narrow-band filtering part 1 and turning off the sweeping signal when the sweeping signal is turned off. Thus, the response speed is hastened and the S/N deterioration can be prevented.
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