The use of single or dual frequency timing receivers allows us to compare remote atomic clocks with high precision. We have developed measurement methods which are applied either, historically, to the C/A code of the L1 carrier signal, or, more recently, to the precise codes P1 and P2, of the L1 and L2 carrier signals, which are combined linearly giving the P3 code. The use of P3 code instead of C/A code in the long distance clock comparison strongly reduces the noise level due to the ionosphere compensation. We also contribute to the development of calibration methods and data processing of the new generation GPS receivers. The best stability reached in the laboratory is about 170 ps at 1 day on one GPS P3 link in common view. The calibrated link OP-PTB by GPS P3 is used by the BIPM as a back-up link in the French contribution to TAI. LNE-SYRTE is registered as an IGS station, through one of its dual frequency GPS receivers and is a member of the IGN permanent GPS network RGP.

Picture: different single and dual frequency GPS antennas installed on the site of the Observatoire de Paris.