Tung Thanh Thai, Ilaria Sesia, Istituto Nazionale di Ricerca Metrologica, Italy; Joseph Achkar, Baptiste Chupin, Giovanni Daniele Rovera, LNE-SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, France; Dirk Piester, Physikalisch-Technische Bundesanstalt, Germany; Miho Fujieda, Tadahiro Gotoh, Ryo Tabuchi, National Institute of Information and Communications Technology, Japan

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TWSTFT has been one of the most popular techniques used for comparison of remote atomic clocks. It typically employs the code-phase of a signal modulated by a pseudorandom noise (PN) code sent and received by microwave link via a geostationary telecommunications satellite [1]. The National Institute of Information and Communications Technology (NICT) has developed a Two-Way Carrier-Phase (TWCP) satellite frequency transfer technique [2] and successfully integrated it with PN code-phase for time transfer in a new modem called Software Ranging System (SRS) [3]. Three SRS modems have been deployed to Istituto Nazionale di Ricerca Metrologica (INRiM / IT), LNE-SYRTE (OP) and Physikalisch-Technische Bundesanstalt (PTB) for experimentation in comparison of local realization of Coordinated Universal Time (UTC(k), where k is the laboratory responsible for the generation of the time scale). We will present preliminary code-phase-based and carrier-phase-based results for the links between UTC(IT), UTC(OP) and UTC(PTB). A comparison with other satellite time and frequency transfer techniques currently available at all sides is carried out, i.e. TWSTFT link using SATRE modems and using Software-Defined Radio (SDR) receivers [4]. We find that TWSTFT with SRS modems achieve promising results of about 3e-15 at 1-day averaging time using code-phase measurements. [1] “The operational use of two-way satellite time and frequency transfer employing pseudorandom noise codes”, Recommendation ITU-R TF.1153-4 (08/2015) [2] “Carrier-phase two-way satellite frequency transfer over a very long baseline”, M Fujieda et al 2014 Metrologia 51 253 [3] “Development of a new digital TWSTFT modem”, Miho Fujieda, Ryo Tabuchi and Tadahiro Gotoh, International Journal of Electrical Engineering, Vol.27, No.4 pp.141-145 (2020) [4] “Use of software-defined radio receivers in two-way satellite time and frequency transfers for UTC computation”, Zhiheng Jiang et al 2018 Metrologia 55 685