Ryo Tabuchi

Carrier-phase-based two-way satellite time and frequency transfer

We performed measurements of carrier-phase-based two-way satellite time and frequency transfer (TWST-FT) with an A/D sampler and conventional TWSTFT system. We found that an instability resulting from a local signal at the satellite transponder was negligible. The short-term stability of 4 × 10-13 at 1 s was achieved in a short-baseline measurement. The results showed good agreement with the GPS carrier phase.

The New Generation System of Japan Standard Time at NICT

NICT has completed a new generation system for the realization of Japan standard time. There are various renewals in this system. One of the big changes is the introduction of hydrogen masers as signal sources for UTC(NICT) instead of Cs atomic clocks. This greatly improves the short-term stability of UTC (NICT). Another big change is the introduction of a newly developed 24ch dual-mixer-time-difference system (DMTD) as the main tool for measurements. The reliability of the system is also improved by enhanced redundancy and monitoring systems. The new JST system is in regular operation since February 2006.

Carrier-phase TWSTFT experiments using the ETS-VIII satellite

The National Institute of Information and Communications Technology (NICT) has developed and tested carrier-phase two-way satellite time and frequency transfer (TWSTFT) as a next-generation technique applicable to greater distances and resulting in higher precision. A method different from that used for code-based TWSTFT is required for carrier-phase TWSTFT. We propose a new method based on variations of carrier phases for the propagation of signals.Using the ETS-VIII satellite launched by the Japan Aerospace Exploration Agency (JAXA) and the Time Comparison Equipment (TCE) system developed by NICT, carrier-phase TWSTFT experiments were carried out between two ground-based hydrogen masers separated by a baseline of 110 km. Our tests showed that the frequency difference between two hydrogen masers can be measured for averaging times larger than 1000 s and the precision of carrier-phase TWSTFT is about 100 times better than that of code-based TWSTFT.

Error correction of precise time transfer experiment between ground and ETS-VIII

The Engineering Test Satellite-VIII (ETS-VIII) is a Japanese geostationary satellite. Its missions include basic satellite positioning experiments using onboard atomic clocks. The National Institute of Information and Communications Technology (NICT) developed special equipment for this time transfer link. This link makes precise time transfer between the onboard atomic clock and a ground reference clock using two way time transfer method and carrier phase measurement for the first time in the world. We have corrected ionosphere error by two received downlink measurement data and compared to obtain a precision as better than 3ps between both clocks.

Precise time transfer activities in singapore

Precise time transfer is one of the essential works for time-keeping laboratories in maintaining the standards of time and frequency. At the National Metrology Centre (NMC) in Singapore, we have been seeking to improve the time scale performance and time transfer capability by employing different time transfer techniques. Currently, three different time transfer systems are used in the laboratory, namely, GPS code observation by a single frequency multi channel receiver and a dual frequency multi channel receiver; GPS carrier phase observation by geodetic receiver; Two Way Satellite Time and Frequency Transfer (TWSTFT). In this paper, the results of time links between NMC and other Asian and European laboratories are presented, using GPS C/A and TWSTFT techniques.

Time management system of the QZSS and time comparison experiments

National Institute of Information and Communications Technology, Japan (NICT) developed the time management system of the first Quasi-Zenith Satellite (QZS-1), which consisted of on-board time transfer subsystem (TTS) and related ground systems such as time management stations (TMS). TTS can measure the time differences between an on-board Rb clock and an atomic clock of the TMS. TTS can also measure the time differences between the on-board Rb clocks and the satellite reference clock, moreover between the L-band signals and the satellite reference clock. This paper describes about the time management system and shows results of a time comparison experiment between the QZS-1 and the ground TMSs using TTS.