Comparison of remote cesium fountains using GPS P3 and TWSTFT links

The cesium fountain primary frequency standards FO2 and FOM of BNM-S RTE (Bureau National de Metrologie Systeme de Reference Temps Espace) and CSF1 of PTB (Physikalisch-Technische Bundesanstalt) have been compared using two different time transfer links: GPS P3 CV (Global Positioning System Precise Code, Common View) and TWSTFT (two-way satellite time and frequency transfer) during 10 days of almost continuous fountain operation. The resulting relative frequency differences between the remote fountains amount to several 10^-15 , whereas the total uncertainty of each clock (including statistical and systematic uncertainty) was = 10^-15 for the 10-days comparison. An experimental investigation of the noise on the two links between PTB and BNM-S RTE was performed later during two months. This allows us to deduce a link noise for a 10-day period of about 2times10^-15.