Ammonia Masers

Operating characteristics of ammonia masers on the 3,2 line of N14H3and on the 3,3 line of N15H3are described. Experimental and theoretical results on the stability, resettability and mutual consistency of ammonia masers are discussed. A method of manual tuning of the cavity by the magnetic perturbation of about 2 oersteds on the 3,2 line of N14H3ensures a resettability of the frequency within a few parts in 1011. A system of automatic cavity tuning for a pair of masers has been accomplished which allows higher accuracy. Various types of frequency shifts and fluctuations are considered and methods of reducing them are discussed. Numerical evaluations of the stability and reproducibility of the ammonia maser are compared with the hydrogen maser.