MAINTAINING HIGHLY ACCURATE GLOBAL SYNTONIZATION USING THE HYDROGEN LINE

Samuel C. Ward

Abstract:	The NASA-JPL Deep Space Network (DSN) supports spacecraft navigation requirements through the use of ensembles of atomic frequency standards located in Australia, California, and Spain. The synchronization of these widely separated reference frequency standards is maintained over long periods, >6 months, through use of a technique that exploits the phenomena that: the magnitude of the offset of the output frequency of a particular hydrogen maser (H2M) from the hydrogen line is constant throughout the life of the H2M. The magnitude of an H2M's frequency offset (F,) from the hydrogen line is a function of ?CF, ?Fr, ?Ft, ?Fw, where m is the ambient magnetic field in the bulb, r is cavity mistuning, t is thermal motion of hydrogen atoms in the bulb and w is wall collision caused shifts. Of these four, ?Fr is the major contributor to drift of the output frequency. Subsequent to a careful cavity tuning operation any residual frequency offset is due to the other three error sources (?F, ?Ft and ?Fw). This residual Fo is largely a function of the manufacturer's design and the maser's geographic orientation. .Thus this residual Fo, for a particular H2M at a fixed location, will be constant throughout the life of the H2M. In August-September 1980 the Fo of three Smithsonian Institution Astrophysical Observatory (SAO) model VLG-1 OB hydrogen masers at widely separate locations were measured against a "calibrated" model 5061A cesium beam frequency standard. In April -May 1981 after the three H2M's were returned to the hydrogen line, the Fo values returned to within [formula] of the original "calibrated" values. Since the "calibrated" 5061A was calibrated against UTC (NBS), then the synchronization between H2M's and to UTC (NBS) was maintained within a few parts in 10^13th over a period of >8.5 months. More accurate synchronization may be obtained if the returning is performed more frequently.
Published in:	Proceedings of the 13th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 3, 1981 Naval Research Laboratory Washington, DC
Pages:	503 - 504
Cite this article:	Ward, Samuel C., "MAINTAINING HIGHLY ACCURATE GLOBAL SYNTONIZATION USING THE HYDROGEN LINE," Proceedings of the 13th Annual Precise Time and Time Interval Systems and Applications Meeting, Washington, DC, December 1981, pp. 503-504.
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