| 摘要 |
PURPOSE:To perform automatic tuning correctly under a little frequency of fluctuations of ambient temperature and a secular change, by controlling the oscillation frequency of a variable local oscillator to that of a fixed local oscillator through counting and comparison. CONSTITUTION:The output of a fixed local oscillator 18 and that of a variable local oscillator 15 are supplied to a frequency counting comparator 26 to count and compare both the oscillation frequencies. On the basis of the comparison result, a motor 24 is controlled to equalize the oscillation frequencies of the oscillators 15 and 18 to each other. In this case, only when a changeover switch 19 is placed on the side of the oscillator 18, namely, when the oscillator 18 is connected to a frequency converter 14, the frequency counting comparator 26 is put in operation. Consequently, the comparator 26 performs digital processing to nearly eliminate the influence of temperature fluctuations and a secular change, and when plural fixed local oscillators 18 are provided, or when a frequency synthesizer is used as the fixed local oscillator, automatic tuning to the frequency of either case is performed correctly. |
