Ammonia Masers

Operating characteristics of ammonia masers on the 3,2 line of N¹⁴H3 and on the 3,3 line of N¹⁵ H3 are 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 N¹⁴H3 ensures 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.