Performance of Soviet and U.S. Hydrogen Masers

The frequencies of Soviet- and U.S.-built hydrogen masers located at the Smithsonian Astrophysical Observatory and at the United States Naval Observatory (USNO) were compared with each other and, via GPS common-view measurements, with three primary frequency-reference scales. The best masers were found to have fractional frequency stabilities as low as 6x10(-16) for averaging times of approximately 10(4) s. Members of the USNO maser ensemble provided frequency prediction better than 1x10(-14) for periods up to a few weeks. The frequency residuals of these masers, after removal of frequency drift and rate of change of drift, had stabilities of a few parts in 10(-15), with several masers achieving residual stabilities well below 1x10(-15) for intervals from 10(5)s to 2x10(6)s. The fractional frequency drifts of the 13 masers studied, relative to the primary reference standards, ranged from -0.2x10(-15)/day to +9.6 x 10(-15)/day. See also ADA239372. Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd) held in Vienna, VA on 4-6 December 1990. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd), p509-524, December 1990.