| 摘要 |
A variable-frequency main oscillator of digitally tunable high output frequency fA is controlled by the integrated output voltage of a phase discriminator receiving on the one hand a relatively low comparison frequency and on the other hand a matching feedback frequency stepped down from output frequency fA by frequency division or by heterodyning with an auxiliary frequency fH of the same order of magnitude from an ancillary oscillator, a difference frequency fD=fA-fH is fed to a frequency discriminator delivering a corrective voltage, independent of that emitted by the phase discriminator through a filter network, to the control input of the main oscillator. A pair of frequency selectors varying the feedback frequency and/or the comparison frequency enable the output frequency fA to be adjusted in coarse and fine tuning steps, the coarse adjustments being also applied to the auxiliary frequency fH to limit the excursions of the difference frequency fD. In order to minimize shifts in the corrective voltage due to changes in the setting of the fine-tuning selector, a digital command generated by that selector is converted into an analog compensating voltage subtracted from the output voltage of the frequency discriminator.
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