A STUDY OF LONG-TERM STABILITY OF ATOMIC CLOCKS

David W. Allan

Abstract:	The importance of long-term frequency stability has increased significantly in recent years because of the discovery of the millisecond pulsar, PSR 1937+21. In addition, long-term stability is extremely useful not only in evaluating primary frequency standards and the performance of national timing centers, but also in addressing questions regarding autonomy for the Global Positioning System (GPS) and syntonization for Jet Propulsion Laboratory's (JPL) Deep Space Tracking Network. Over the last year, NBS has carried out several studies addressing questions regarding the long-term frequency stability of different kinds of atomic clocks as well as of principal timing centers. These analyses cover commercial and primary cesiumbeam frequency standards; active hydrogen maser frequency standards and the new commercial mercury-ion frequency standards at United States Naval Observatory (USNO). The support and cooperation of the timing centers involved have, along with the GPS common-view measurement technique, made these analyses possible. Fortunately, the measurement noise was significantly less than the clock noise for the longterm stability regions studied. Fractional frequency stabilities, olt), of parte in 1014 down to parte in 1015 were observed for various of these standards. It is believed that frequency stabilities on the order of a part in 1015 will be necessary to measure the effects of gravity waves on frequency stability between millisecond pulsars and atomic clocks on or near the earth.
Published in:	Proceedings of the 19th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 3, 1989 Sheraton Hotel Redondo Beach, California
Pages:	375 - 380
Cite this article:	Allan, David W., "A STUDY OF LONG-TERM STABILITY OF ATOMIC CLOCKS," Proceedings of the 19th Annual Precise Time and Time Interval Systems and Applications Meeting, Redondo Beach, California, December 1987, pp. 375-380.
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