The Next Generation Giga-bit VLBI Terminal

Junichi Nakajima
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan

Hitoshi Kiuchi
Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan

Sachiko Okumura, Kazuyoshi Sunada
National Astronomical Observatory

Hideyuki Kobayashi
Institute of Space and Aeronautic Science

Yoshihiro Chikada, Noriyuki Kawaguchi
National Astronomical Observatory

Joint Japanese group (NRO, ISAS and CRL) have started to develop new VLBI terminals. This system will standardize surprisingly high speed aquisition (1024M-bits per second) in the near future. To establish high sensitivity in VLBI observations, which enables observations of the weak distant QSO, we must make better use of the receiver bandwidth. Ground based VLBI is limited by the radio telescope aperture size and the integration time due to the atmosphere. Development of both the High Speed Sampler and the High Speed Data Storage has started. This equipment will be employed as the next Japanese VLBI standard terminal (Fig.1). We will name the system brand new "J-1" or something which indicate the difference from the K-4 series.

Figure 1. 1024Mbps VLBI terminal.

The High Speed Sampler is designed to sample the data rate of 1024/512/256MHz 1/2/4ch 1/2bit selection. The baseband signal is supplied from the NRO wide-band video converter which receive 5 to 7GHz IF optical transmission. The sampler is equipped with the external time code input. When the correlation system needs the time code, it can insert a user programmable one. We will use the DSO (Digital Storage Oscilloscope) AD-aquisition module for the sampler. The continuous sampling DSO provides the function of selection of various rates and channels. Hence we are using the DSO, this sampler can monitor the input signals directly. This is convenient to adjust the signal level. The sampler applications to the interferometer and the digital spectrometer components are possible.

The High Speed Storage System will reach the 1024Mbits/sec recording. To achieve the first ever performance in VLBI, we are modifying the HDTV-VCR (High Definition TV Video Cassette Recorder). This recorder is designed for multi-HDTV-formats. VLBI raw data is recorded as the part of HDTV frame data. Error rate is better than 10^10. The recorder time sequence is controlled by the newly designed VLBI interface. The interface is arranged to record the data without time code. Playback speeds of 1/2 to 1/32 are possible for the low-data rate correlation system. Some of the initial specifications of the VCR did not reach our targets, and we are trying to increase the performance.

Updated on November 2, 1995.
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