Development of a two way satellite time and frequency transfer station at BNM-SYRTE

The national metrology institute BNM-SYRTE has developed an earth station for satellite communications in order to compare, by using radiofrequency link with other earth stations installed in Europe and USA, atomic clocks disseminated in the time laboratories. The goal of BNM-SYRTE is to contribute in the realization of international atomic time (TAI) calculated by the BIPM, by using an alternative technique to GPS, denoted TWSTFT (two way satellite time and frequency transfer). With this particular technique, atomic clocks are compared through a geostationary satellite using microwave links between ground clocks and the satellite, in the frequency bands 13,75-14,50 GHz (up-link) and 10,95-12,75 GHz (down-link). Such comparisons are made using the spread spectrum method with a 70 MHz intermediate frequency (IF) carrier modulated by a pseudo-noise (PN) code sequence, at 2,5 MChips/s, generated by a SATRE (satellite time and ranging equipment) modem.