Appendix A: The Impact of the HP 5071A on International Atomlc Time

David W. Allan, Alex Lepek, Len Cutler, Robin Giffard, Jack Kusters

Abstract:	The international clock ensemble, which contributes to the generation of International Atomic The (TAI and UTC), has improved dramatically over the last few years. The main change has been the introduction of a significant number of HP 5071A clocks. Of the 313 clocks contributing to TAI/UTC during 1994, 94 of these were HP 5071As. The environmental insensitivity of the HP 5071A clocks is more than an order of magnitude better than that of previous contributing clocks. This environmental insensitivity translates to outstanding long-term stability - with a typical flicker floor of a few x10^-15. In addition, there are now several hydrogen masers with cavity tuning contributing to TAI/UTC. These not only have outstanding short-term stability, but comparatively low frequency drift and excellent intermediate-term frequency stability. By analyzing the data available from the international ensemble, we have obtained two important results. First, the frequency stability obtainable with an optimum algorithm is about 10^-15 or both the intermediate and long-term regions. It could be as good in the short-term if time transfer measurement instabilities were reduced sufficiently. Second, with cooperation, this performance can be made available on an international basis in near real time. The recent enhancements in the contributing clocks are already providing a significant improvement in the accuracy with which UTC is made available to the world from several of the national timing centers, such as NIST and USNO.
Published in:	Proceedings of the 27th Annual Precise Time and Time Interval Systems and Applications Meeting November 29 - 1, 1995 The Doubletree Hotel at Horton Plaza San Diego, California
Pages:	235 - 256
Cite this article:	Allan, David W., Lepek, Alex, Cutler, Len, Giffard, Robin, Kusters, Jack, "Appendix A: The Impact of the HP 5071A on International Atomlc Time," Proceedings of the 27th Annual Precise Time and Time Interval Systems and Applications Meeting, San Diego, California, November 1995, pp. 235-256.
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