Experimental Study of the Frequency Stability of a Maser Oscillator Operated with an External Feedback Loop

In this paper, we report the results of an experimental study of the short-and mid-term frequency stability for both a hydrogen maser and a rubidium maser operated with an external feedback loop to modify the cavity quality factor. A revised version of the theoretical expression of the frequency stability for this type of maser is given and a numerical solution for various maser parameters is calculated. The predicted frequency stability exhibits an optimum when the cavity Q is varied. The experimental results presented in this study agree with this conclusion.