Development and performance of the terminal system for VLBI space observatory programme (VSOP)

The VSOP terminal is a new data-acquisition system for the Very-Long-Baseli ne Interferometry (VLBI). This terminal was primarily designed for ground t elescopes in the VLBI Space Observatory Programme (VSOP). New technologies; higher-order sampling and digital filtering techniques, were introduced in the development. A cassette cart was also introduced, which supports 24-ho ur unattended operations at the maximum data rate of 256 Mbps. The higher-o rder sampling and digital filtering techniques achieve hat and constant pha se response over bandwidth of 32 MHz without using expensive wide base-band converters. The digital filtering technique also enables a variety of obse rving modes defined on the VSOP terminal, even with a fixed sampling freque ncy in an A/D converter. The new terminals are installed at Nobeyama, Kashi ma, Usuda, Mizusawa, and Kagoshima radio observatories in Japan, and are be ing used in VSOP and other domestic VLBI observations. In this paper the ke y features of the VSOP terminal focusing on these advanced technologies are presented, and the results of performance tests are shown.