Common-View Comparison Using Two Iridium STL (Satellite Time and Location) Receivers at National Laboratories with a Very Long Baseline

Andrew N. Novick, Shinn-Yan Lin

Abstract:	We compare the outputs of two Satellite Time and Location (STL) low Earth orbit (LEO) receivers in common-view with a very long baseline. By comparing the STL pulse per second (PPS) output to national laboratory timescales at distant locations, we can determine how well clocks or timescales can be compared. Values of Coordinated Universal Time (UTC) from the Bureau International des Poids et Mesures (BIPM) Circular-T data are used as the reference comparison of the timescales of the two laboratories. The baseline between Boulder, Colorado in the United States and Taoyuan City in Taiwan is greater than 11,000 km. Also, the Iridium satellites are at a low altitude of 780 km, which largely limits the possibility of making common-view comparisons using LEO satellites. We are constrained to using the all-in-view technique (Johnson et al., 2023), where the composite output of a receiver is used for the comparisons and not individual satellites, as in traditional common-view techniques. Comparisons of a commercially-available STL receiver compared to UTC(NIST) show one-day averages within a range of < 6 ns over several days, an Allan Deviation (ADEV) of 7.75 × 10-14 at one day of averaging and Time Deviation (TDEV) of < 4 ns at one day of averaging. These results show that it could be possible to compare time scales at long baselines, as well as clocks at commercial institutions, when global navigation satellite system (GNSS) signals may not be available.
Published in:	Proceedings of the 57th Annual Precise Time and Time Interval Systems and Applications Meeting January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	21 - 27
Cite this article:	Novick, Andrew N., Lin, Shinn-Yan, "Common-View Comparison Using Two Iridium STL (Satellite Time and Location) Receivers at National Laboratories with a Very Long Baseline," Proceedings of the 57th Annual Precise Time and Time Interval Systems and Applications Meeting, Anaheim, California, January 2026, pp. 21-27. https://doi.org/10.33012/2026.20484
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