GPS time transfer using carrier-phase and P-code measurements

Previous studies have already shown the potential of carrier-phase and P-code measurements from geodetic GPS receivers for the comparison of internal receiver references with an improved performance. Several experiments on time and frequency transfer based on phase and P-code measurements are related in this paper: a zero baseline comparison at the BIPM using data from two AOA TTR4-P receivers connected to a HP 5071A clock, and short baseline comparisons (of several hundreds of kilometres) using data from TTR4-P units in operation at the BIPM and from AOA Turbo Rogue receivers in operation at the ORB, Brussels, and the IFAG, Wettzell, both connected to a hydrogen maser. Preliminary results show encouraging results for frequency transfer carried out with Turbo Rogue phase measurements. However, noise as high as 250 ps on 30 s phase measurements, and thus larger than expected, superimposed on unexplained excursions up to 0,5 ns for 1-2 hours periods, has been detected in results from experiments involving the TTR4-P unit belonging to the BIPM