A Study of Long-Term Stability of Atomic Clocks
NATIONAL BUREAU OF STANDARDS BOULDER CO TIME AND FREQUENCY DIV
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The importance of long-term frequency stability has increased significantly in recent years because of the discovery of the millisecond pulsar, PSR 193721. 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 Laboratorys 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 cesium-beam 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, sigmay tau, of parts in 1014 down to parts 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.
- Test Facilities, Equipment and Methods