NIST and OP GPS receiver calibrations spanning twenty years: 1983 – 2003

We present results from two calibrations performed in 2003 between the Global Positioning System (GPS) common-view receivers located at the National Institute of Standards and Technology (NIST) and at the Bureau National de metrologie - systemes de reference temps espace (BNM- SYRTE) of the observatoire de paris (OP) in the context of calibrations performed over 20 years, 1983-2003. We also present several years of continuous comparisons between receivers located at each of the two labs: NIST and OP. These results show that the best GPS receivers in use have delay variations with peak differences of under 5 ns over a year. This contributes to defining the current practical limits of GPS common-view time transfer. Since GPS common-view time transfer is still used for the majority of links between laboratories contributing to international atomic time (TAI), the noise and uncertainties in common-view affect the short-term performance of TAI, for averaging times from 5 to 30 days.