The LNE-SYRTE has developed a two-way station for ground atomic clocks comparison using microwave links through Intelsat. This high performance technique allows us to compare remote clocks - the geostationary satellite is used as a microwave relay- without any intermediate clock unlike the GPSsystem. The goal is twofold: to give a better contribution of the French atomic clocks to the international atomic time TAI calculated by the BIPM and to have an accurate system to compare primary frequency standards which are disseminated among the European and American laboratories. Two performances are reached today: 1.5 ns uncertainty for UTC-UTC (OP) and 1.10^-15 frequency stability at 1 day for the two-way link. Our laboratory is also developing a satellite simulator for the improvement of the station time accuracy, with high performance in terms of noise, below 20 ps at 1 s. In order to establish microwave links with Asia through PanAmSat, the installation of a 2nd two-way station is in progress.

Picture: TWSTFT station of LNE-SYRTE, driven by UTC(OP), equipped with a SATRE mode and a satellite transmitting/receiving device through Intelsat.