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A Clock Ensemble Using Only Active Hydrogen Masers



Thomas E. Parker, Stefania Romisch


The current real-time timescale at NIST, AT1, as well as the post-processed scale TP162, both contain hydrogen masers and commercial cesium frequency standards. The cesium standards are much nosier in the short term than the hydrogen masers and consequently have very little short-term weight. However, they may have better long-term stability than the masers and therefore contribute to some extent to the long-term performance of the scales. Nevertheless, the cesium standards are expensive to maintain and require attention from the staff. A test has been performed using the post-processed AT1 timescale algorithm for two cases to investigate the impact of commercial cesium frequency standards on the clock ensemble at NIST. In the first case both hydrogen masers and cesium standards were used, and in the second case only hydrogen masers were used. The ensemble using both masers and cesium standards is identified as TP162, and the ensemble using only hydrogen masers is identified as TP165. Over the 500-day test interval the number of hydrogen masers in TP162 and TP165 was exactly the same. Over the test interval the two scales diverged by only 6.3 ns, with an average fractional frequency difference of 1.6x10-16. Allan deviation plots of the two scales relative to TAI are nearly identical.
Proceedings Title
Proceedings of the 48th Annual Precise Time and Time Interval Systems and Applications Meeting
Conference Dates
January 30-February 2, 2017
Conference Location
Monterey, CA
Conference Title
Precise Time and Time Interval Meeting (PTTI)


Cesium Standard, Hydrogen Maser, Time Scale


Parker, T. and Romisch, S. (2017), A Clock Ensemble Using Only Active Hydrogen Masers, Proceedings of the 48th Annual Precise Time and Time Interval Systems and Applications Meeting, Monterey, CA (Accessed June 24, 2024)


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Created January 31, 2017, Updated July 3, 2017