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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.

We have developed a new VLBI system based on the conventional K-4 system, whose data-acquisition mode includes VLBA and VSOP data modes. In developing the new VLBI data-acquisition system, multi-bit quantization sampling, high-speed (wide-bandwidth) data sampling, and the data acquisition mode were taken into consideration. The new acquisition system has one-bit and two-bit quantization sampling modes for VLBI, and four-bit and eight-bit sampling modes for general-purpose use. The total data rate is up to 256 Mbps, and up to 16 video channels can be selected. Anti-aliasing filtering is carried out in analog (32 MHz), and after sampling, the 16-MHz, 8-MHz, etc. filterings are carried out in the digital filter. The digital filter is used because it results in good phase characteristics. This system is specially designed for the Key Stone Project, and an input interface unit is incorporated in the VSOP.

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