Improvement of a digital automatic cavity tuning system in the active hydrogen maser CH1-75

Possibilities of the active hydrogen maser CH1-75 frequency stability improvement for time intervals 1 h-1 d due to a digital automatic cavity tuning system are discussed. This system uses a hydrogen atom spectral line quality modulation method and a reversible counter measuring two masers beat period for the time interval T at two spectral line quality significances. Two hydrogen masers with frequency instability at T=100 and 1000 s and at different modulation methods (beam density, inhomogeneous magnetic field in storage bulb and mixed method) were investigated. The results were used to change the CH1-75 specification and to fix frequency stability