Plan for a High-rate Data Recorder and a New Data Acquisition Terminal
Hitoshi Kiuchi
(kiuchi(AT)nict.go.jp),
Michito Imae, Shin'ichi Hama, and
Mizuhiko Hosokawa
Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan
Abstract
At the Communications Research Laboratory (CRL), we have been developing VLBI
data acquisition terminals (K series) for mainly geodetic purpose. The latest
one is the K-4 system, which has a maximum recording rate of 256 Mbps.
The high-end version of the K-4 system, which has fully automatic operation
is utilized in the Key Stone Project and formal error of a few millimeter
over 100 km baselines is performed in daily observation, which is published on
the WWW (http://ksp.nict.go.jp). Recently CRL has been developing a new
VLBI recording system using a GBR recorder for a near-future system which is
based on a data recorder that has a maimum recording rate of 1 Gps, which is
the state of the art. Besides the development of the GBR system, CRL, as the
IERS-VLBI Technical Development Center, is planning to construct a
next-generation VLBI system which will have a maximum recording and data
processing rate of 2048 Mbps in order to achieve highly sensitive and accurate
VLBI. This system will be applicable to various fields of VLBI observation,
such as the micro-arcsecond-order radio astrometry to investigate the whole
image of our Galaxy using the apparent positional movement of quasars due to
gravitational lensing effects [Hosokawa et al., 1997].
Concept of new system
The aim of this plan was not to develop a low-price system but to develop a
pioneering technology system in order to comprehend the whole image of the Galaxy
by detecting dark matter. A low-price system will be developed in another plan.
We are starting the design of the new system for discussion as follows;
Phase and delay calibration system
TDB,
Video signal converter
multi-channel and wide video bandwidth
(32 MHz/ch * 32ch or 64 MHz/ch * 16ch),
Input interface (or formatter)
Using high-speed A/D converters which have maximum sampling rate of
more than 150 Msps and 8-bit sampling in each channel.
Using digital filtering to minimize the phase flatness,
Data recorder
Target maximum recording rate of 2048 Mbps, helical scan recording
head (for long-term continuous integration), cassette tape, low bit
error rate (better than 10-10), etc.
Output interface
Having modes comaptible with other VLBI acquisition systems,
Correlation processor
64 MHz clock 32 channels, using ASIC technology for
flexibility, etc.
We welcome suggestions and comments about this development project from a
wide range of VLBI users, especially concerning;
high rate data recorder
interface specifications, recording time per volume, bit error rate, etc.
accurate instrumental delay calibration method for bandwidth
synthesis method,
input interface
number of sampling bits, specifications of digital filter,
sampling frequency, etc.
compatibility with Mark-III, IV, VLBA, S-2, K-4, etc.
We are planning that the output interface will have an output mode
for all or several of the ones of the present VLBI acquisition systems.
Suggestions for applications and science targets of the new VLBI
acquisition system are also requested.
Reference
Hosokawa, M., K. Ohnishi, and T. Fukushima, Fluctuation of extra galactic
reference frame due to gravitational lensing in our Galaxy,
to be published in the Astronomical Journal, 1997.
