Characteristics and performance of miniature NBS passive hydrogen masers

The design and performance of the miniature NBS passive hydrogen (MPH) maser are examined. The maser is 26.7-cm high, 66-cm deep, 45.5-cm wide, and weighs 30 kg. The components and functions of the maser's physics package, and the hydrogen and cavity servosystems are described. The effects of changes in the second-order Doppler effect, cavity pulling, wall shift, spin exchange frequency shift, magnetic field changes, microwave power, and phase modulation drive on the output frequency of the maser are analyzed. The frequency stability and timekeeping ability of the MPH maser are evaluated. The data reveal that frequency stability is affected by the environment and the frequency stability in a benign environment is (1.5 x 10 to the -12th tau exp -1/2)sq + (5 x 10 to the -15th)sq, tau = 1-500,000 s. It is observed that the MPH maser is capable of excellent timekeeping performance and the timekeeping uncertainty is about 0.4 ns/day and 4.0 ns/week