The BNM-LPTF software for the frequency comparison of atomic clocks by thecarrier phase of the GPS signal

This paper describes the software and equipment used at the Laboratoire pri maire du temps et des frequences du Bureau national de metrologie (BNM-LPTF ), Paris, France. Two H-masers in short baseline, one located at the BNM-LP TF and the other at the Laboratoire de I'horloge atomique du Centre nationa l 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 (1 sigma). In addition, comparisons with the BNM-LPTF softwa re were made over 10 days with the H-masers located at the Physikalisch- Te chnische Bundesanstalt (PTB), Braunschweig, Germany, and another at the Nat ional Physical Laboratory (NPL), Teddington, United Kingdom. The data colle cted 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 sho w that the noise of the instruments together with the environmental conditi ons 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 10(4) s and 3 X 10(5) s. This result is in good agreement with the exp ected stability of H-masers. It demonstrates that the noise brought by the GPS carrier phase measurements can be averaged out at this level.