The Facility of Tsukuba 32-m VLBI Station

Kazuhiro Takashima1( takasima(AT)gsi-mc.go.jp), Yoshihiro Fukuzaki1, Keizou Nemoto1, Kousei Shiba1, Shinobu Kurihara1, Michiko Onogaki1, Kouhei Miyagawa1, Kyoko Kobayashi1, and Shigeru Matsuzaka2

1 Geodetic Department,Geographical Survey Institute, Ministry of Construction
Kitasato 1, Tsukuba, Ibaraki 305-0811, Japan
2 Geography and Crustal Dynamics Research Center
Geographical Survey Institute, Ministry of Construction
Kitasato 1, Tsukuba, Ibaraki 305-0811, Japan

Introduction

This report summarizes the specification of Tsukuba 32m VLBI station at the Geographical Survey Institute (GSI). We present our history of VLBI activities and the status. First of all, GSI developed three mobile VLBI systems and had repeated observations with CRL. In 1998, GSI constructed a domestic VLBI network with five permanent stations. A main station of the network is Tsukuba 32-m VLBI station (Fig. 1). It also becomes a key station in the international VLBI networks, especially in Asia.


Figure 1. Tsukuba 32m VLBI antenna.

Antenna

Tsukuba station has a 32 m cassegrain parabolic antenna, which is made by NEC Co. All of components are painted white color to protect the deformation by the imbalance of temperature from sunshade. The main reflector is covered with thermal insulator panels, then its temperature is kept between +/-3 degrees by using a ventilation system in the back structures. The antenna structures have covers to avoid direct sunlight. Table 1 shows the specification of the antenna, such as the slewing speedand limit angles.

Table 1. The specification of antenna
Year of Construction 1998
Radio Telescope cassegrain
Mount Az-El
Diameter of Main ref. 32 m
Surface Contour of ref. +/-0.5 mm
Azimuth Velocity 3 deg/s
Elevation Velocity 3 deg/s
Azimuth Limit 10 - 710
Elevation Limit 5 - 88
Table 2. Station Configuration
8 letter TSUKUB32
2 letter Ts
DOMES 21730S007
CDP 7345
Approx. Pos
X (m) -3957408.8
Y (m) 3310229.3
Z (m) 3737494.8
Lat (deg.) 36.1031
Lon (deg.) 140.0887
Hight (m) 44.7

X-Band Tsys 50 K
S-Band Tsys 75 K
X-Band SEFD 300 Jy
S-Band SEFD 360 Jy

Azimuth angle of the antenna is controlled by a wheel and track system. The original azimuth rails, which weigh 73 kg per meter and are 10 cm wide, was cracked because the stress between wheel and rail was larger than our assumption. In April 1999, the rails have been replaced with larger ones (Fig.2).


Figure 2. The replaced rail (Left: before, Right: current).

For the moment, the significant problem of the rail has not happened again. On the top of antenna, which is above subreflector, a GPS antenna (Fig.3) is attached for the purpose of tie survey and collocation.


Figure 3. The replaced rail (Left: before, Right: current).

Table 3 shows front-end frequencies of Tsukuba 32m antenna. A cooled HEMT receiver which was made by Nitsuki Co. was installed in X-band. First local PLOs, which were made by CTI LTD., were installed. However, the phase of the PLOs were unstable worse than a thousand degree per day due to change the temperature variation in the front-end room. We installed a cover rack for PLOs, and the PLOs are now always cooled by Peltier cooling system to minimize effects by the temperature variations of the outside air. Three intermediate frequencies (IF) at X-band were installed there.

Table 3. The front-end frequencies at Tsukuba station
Input (MHz)S band X1 band X2 band X3 band
2100-2500
2120-2360 (BPF)		 7780-8280 8180-8680 8580-8980
PLO1 (MHz) 1600 7280 7680 8080
PLO2 (MHz) 2000 7680 8080 8480

Back-end

From front-end to back-end, signals are transmitted by optical fibers to avoid the power loss. But we have troubles with the optical fibers since they often fails to operate recently. We are now investigating the cause of the troubles. Mark IV and K-4 systems have been installed there. We can record with both systems simultaneously.


Figure 4. Back-end equipment.

Others

Two control systems have been installed in the station. One is the Field System version 9 (FS9) developed by NASA GSFC. It is used for international experiments with the Mark IV system. Another is the workstation GAOS (WS-GAOS) developed by CRL and GSI. It is used for domestic experiments with the K-4 system. Recently, we can also use the FS9 for domestic experiments because it now supports K-4 systems by a cooperation with CRL Kashima and NASA GSFC.

Since 1999, a copy system, which can copy data from K-4 tapes to Mark-IV tapes, has been installed to translate the data recorded at the stations only with the K-4 system.


Figure 4. The diagram of copy machine (from K-4 to Mark-IV).


Updated on June 2, 2000. Return to CONTENTS