Experimental frequency and phase stability of the hydrogen maser standard output as affected by cavity auto-tuning

An atomic hydrogen maser cavity autotuner system and the effect of autotuning on the time and frequency domain stability are described. Measurements of very-long-term stability and drift of the masers were made at several international standards laboratories. Time and frequency domain measurements made at STSC are discussed. The data show that the spectral purity of the maser output signal and the time domain stability are not significantly degraded by cavity frequency-switching; the autotuned maser retains the exceptional short- and medium-term stability of the classical active oscillator maser. Cavity pulling is under precise control, and the exceptional long-term stability capability of the maser can be attained with a single, field operable standard