Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
In 1980's, VLBI observations were conducted using Mark-II, Mark-III VLBI terminal, or the VLBI terminal which is completely compatible with Mark-III type. Therefore, the VLBI terminal is unified by Mark-III type in 1980's. In 1990's, many types of VLBI terminal have been developed.
First is K4 VLBI terminal which was developed by CRL(Communications Research Laboratory) in Japan. This recording system is a cassette type and it uses a rotating recording head. The tape running is very stable, and there is no bit shift and the parity error is very small. The recording modes of 64 Mbps, 128 Mbps and 256 Mbps are available now. The recording duration of each K4 tape is 50 minutes in the rate of 256 Mbps, and 200 minutes in the rate of 64 Mbps. The automatic tape changer for 24 tapes is also available. Therefore, any operator for the tape change is not necessary in normal VLBI experiment during 24 hours in the rate of 256 Mbps mode, and during about one week in the rate of 64 Mbps. We have also developed the video converter and formatter. The size of K4 VLBI terminal is compact (1/3 of Mark-III type) and the weight is light (1/4). The K4 system is used in the domestic VLBI experiments in Japan, KSP system and mobile experiments. Recently, NAO (National Astronomy Observatory) set K4 system at Urumqi station. VSOP terminal had been developed based on K4 system. Recorder and formatter is the almost same as K4 system for KSP system. However, it needs the time control units. Japan has five correlation system for K4 system; 1)KSP correlater (6 baselines), 2) Kashima correlater (one baseline), 3)GSI correlater, 4)NAO mizusawa correlater, 5)VSOP correlater.
S2 VLBI terminal developed by Canada. It combines a few home video decks, and the price is cheap. The maximum recording rate is 128 Mbps. It is used in AT(Australia Telescope) VLBI network and in many countries. The correlation for S2 system is available in Canada, and at ATNF in Australia. VLBA terminal whose maximum recording rate is 256 Mbps is used worldwide. Mark-IV which will be available for 2 Gbps mode is developed in USA and the correlation center has been established in JIVE and other country. Mark-IV is upper compatible with VLBA. These two systems use open reel tapes. In Japan, we have developed the new VLBI terminal which is available for 1 Gbps mode and uses cassette tapes.
There are many types of VLBI terminal in the Asia and Pacific VLBI network. Australian VLBI network is unified by S2 system. Japanese VLBI network is unified by K4 system (or VSOP system). However, the global VLBI experiments were conducted by Mark-III, and in future Mark-IV will be used. JIVE adopted Mark-IV system. VLBA system is most popular now, and it is the standard type in VSOP project. It is very complex situation to conduct the collaborated VLBI experiment in Asia and Pacific network. VSOP group in Japan has the copy equipments among VSOP K4, S2, VLBA system, and some institutes in Japan have plans to make a copy equipment. It is necessary to make an standard method how to conduct the joint experiment using copy equipment and to establish the standard format of the future VLBI terminal.
In this December, the technical workshop for APT and APSG will be held at Kashima, CRL in Japan. These themes were discussed in this workshop.