Rubidium Clock Lamplight Variations and Long-Term Frequency Instability: First Analyses of Multiyear GPS Data

James Camparo, Ilaria Sesia, Valerio Formichella, Giovanna Signorile, Lorenzo Galleani, Patrizia Tavella

Abstract:	In the rubidium atomic frequency standard (RAFS), an rfdischarge lamp produces the device’s atomic signal. As a consequence of the light-shift effect, variations in the lamplight’s intensity result in variations in the RAFS’ output frequency. While the basic physics of the light-shift is reasonably well understood, its operational implications for global navigation satellite system (GNSS) performance is only beginning to be fully appreciated. Here, we describe first results examining decade-long histories of on-orbit GPS RAFS lamplight variations and GPS RAFS frequency variations. Our preliminary analyses have focused on one space vehicle’s RAFS, and our conclusions are tempered by that present limitation. Nevertheless, our analyses suggest that a RAFS’ long-term frequency stability (i.e., ? ~ 106 sec) is likely lower-bounded by the lamp’s intensity fluctuations. Moreover, considering the light-shift coefficient for this one particular RAFS over 12 years, we find that the data do not support Camparo’s hypothesis regarding RAFS frequency aging and a timevarying light-shift coefficient.
Published in:	Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting January 25 - 28, 2016 Hyatt Regency Monterey Monterey, California
Pages:	150 - 156
Cite this article:	Camparo, James, Sesia, Ilaria, Formichella, Valerio, Signorile, Giovanna, Galleani, Lorenzo, Tavella, Patrizia, "Rubidium Clock Lamplight Variations and Long-Term Frequency Instability: First Analyses of Multiyear GPS Data," Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting, Monterey, California, January 2016, pp. 150-156. https://doi.org/10.33012/2016.13136
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