ABSTRACT This paper describes the software and equipment used at the Laboratoire primaire du temps et des fréquences du Bureau national de métrologie (BNM-LPTF), Paris, France. Two H-masers in short baseline, one located at the BNM-LPTF and the other at the Laboratoire de l'horloge atomique du Centre national de la recherche scientifique (CNRS-LHA), Orsay, France, were computed in parallel with the BNM-LPTF software and with the BERNESE V4.1 software. The comparison of the results issued from both computations shows an agreement within 100 ps (1σ). In addition, comparisons with the BNM-LPTF software were made over 10 days with the H-masers located at the Physikalisch- Technische Bundesanstalt (PTB), Braunschweig, Germany, and another at the National Physical Laboratory (NPL), Teddington, United Kingdom. The data collected show that a modulation with an amplitude of 50 ps and a period of 700-800 ps affects the equipment of the NPL. In addition, these comparisons show that the noise of the instruments together with the environmental conditions at the PTB was higher than that of the NPL and the BNM-LPTF during the observation period. The best relative frequency stability obtained, in the BNM-LPTF/NPL comparison, is about 3 x 10-15 for averaging periods between 6 x 104 s and 3 x 105 s. This result is in good agreement with the expected stability of H-masers. It demonstrates that the noise brought by the GPS carrier phase measurements can be averaged out at this level.
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