Fast cavity auto-tuning systems for hydrogen masers

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Abstract
An auto-tuning system for the microwave cavity of hydrogen masers is considered. It is shown that it can be applied to oscillating masers. A tight control of the cavity resonant frequency is insured, with a short time constant. This is favourable to the improvement of the long term frequency stability of this frequency standard. Operating conditions exist which do not perturb the ultimately achievable long term frequency stability of the standard. It is shown that the microwave cavity resonant frequency can be easily adjusted so that the spin exchange frequency shift is eliminated as well as with known other cavity tuning methods