C

VL

T
D

BI

C R L

COMMUNICATIONS RESEARCH LABORATORY

Serial No. 21

November 2002

CONTENTS
The 2nd CRL TDC Symposium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Proceedings of the 2nd CRL TDC Symposium (Kashima, September 20,
2002)
An evaluation of positioning error estimated by the mesoscale non-hydrostatic . . . . . . 2
model – Preliminary report –Ryuichi Ichikawa, Hiromu Seko, and Michael Bevis
Holographic measurement of Kashima 34-m radio telescope surface accuracy . . . . . . 3– Preliminary report –Hiroshi Ohkubo, Tetsuro Kondo, Ikuto Yonezawa, and Hiro Osaki
Dependence of correlation dimension of QSO radio wave intensity time series . . . . . . 5
on red shift
Md. M. R. Khan and N. Tanizuka
S-band RFI problems at Kashima 34-m antenna and a passive filter for mit- . . . . . . 9
igationEiji Kawai, Hiroshi Ohkubo, Junichi Nakajima, and Jun Amagai
Measurements of harmful interferences in the HF-UHF bands caused by ex- . . . . . 12
tension of power line communication bandwidth
Fuminori Tsuchiya, Hiroaki Misawa, Tomoyuki Nakajo, Ichiro Tomizawa, Junichi
Nakajima, Masatoshi Ohishi, Takayuki Ono, and Akira Morioka
Advancement of Versatile Scientific Sampling Processor (VSSP). . . . . 16

Hiro Osaki
VLBI observations using IP-VLBI system for orbit determination of deep . . . . . 18
space spacecraft – Group delay measurements of GEOTAIL and NOZOMI
telemetry signals –Testuro Kondo (kondo@crl.go.jp), Ryuichi Ichikawa, Yasuhiro Koyama, Mamoru
Sekido, and Hiro Osaki(continued on inside front cover)International e-VLBI experiments. . . . . 23
Yasuhiro Koyama, Tetsuro Kondo, Junichi Nakajima, Moritaka Kimura, Hisao
Uose, and Sotetsu Iwamura
Yamaguchi 32m radio telescope and an on-line observation system. . . . . 27

Kenta Fujisawa
Development of compact VLBI system. . . . . 29
Ikuto Yonezawa, Junichi Nakajima, Hiroshi Ohkubo, Masato Tsuboi, and Takashi
KasugaThe implementation of the PC based Giga bit VLBI system. . . . . 31

Moritaka Kimura and Junichi Nakajima
VLBI development merge into to PC commodity. . . . . 34
Junichi Nakajima, Moritaka Kimura, Yasuhiro Koyama, Hiro Osaki, and Tetsuro
Kondo
Current status of the VERA

. . . . . 36

Osamu Kameya, Hideyuki Kobayashi, and the VERA team
VSOP-2, a next generation space-VLBI mission. . . . . 38

Yasuhiro Murata, Hisashi Hirabayashi, and members of Space VLBI WG- News - News - News - News Farewell ceremony of Kashima 26-m antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

November 2002

1

The 2nd CRL TDC Symposium about the application of the e-VLBI to determine

Yasuhiro Koyama (koyama@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, JapanAs a Technology Development Center (TDC)of the IVS, Communications Research Laboratory(CRL) had held IVS Technology Development Center Meeting twice every year until March 2001.
The laboratory has executed a transition from anagency belonging to the Japanese government to
Independent Administrative Institution on April 1,
2001. After the transition, the IVS Technology Development Center Meeting was reformed to make ita symposium and we started to call for contributed
papers from broader community. Originally, thesecond symposium was to be held in March 2002,
but was postponed until this time because there
was the Second IVS General Meeting in February
2002. The second IVS Technology Development
Center Symposium was then held on September
20, 2002 at the large conference hall of the main
research building in the Kashima Space ResearchCenter. At the symposium, 17 oral presentations
and 4 poster presentations were given and during
the day.
On the same day, the farewell ceremony of the
26m antenna in the Kashima Space Research Center was held since it will close its history soon. The
antenna had been a symbol of the geodetic VLBI
research in Japan. Motions of the plates around
Japan and inter-plate deformations were actively
investigated by using the antenna. The positionof the reference point of the antenna based on
the International Terrestrial Reference Frame wasused as the essential reference to establish Geodetic Coordinates 2000 which was oﬃcially adopted
as a national coordinate system of Japan. Contrastively, the importance of the geodetic VLBI has
been gradually changing from positioning capability to the unique ability to determine Earth’s orientation independently from any other space geodetic techniques. Reﬂecting this fact, many presentations given in the symposium were relatedwith the developments of the e-VLBI systems andPC based observation/correlation systems which
are expected to improve the current turn aroundtime of the geodetic VLBI data processing to determine Earth Orientation Parameters, especially
UT1-UTC. There were also many presentations

precise orbit of planetary space-crafts in near realtime.
The symposium was coincidently held just when
the old symbolic antenna is closing its history (seepage 41 for details), but it certainly opened a new
window for future directions of the geodetic VLBI
research and developments.

Pictures taking on the second CRL Technology Development Center symposium held on September
20, 2002. The picture at the top is at the auralsession. At the middle, symposium participants,
and the bottom, at the poster presentations.

IVS CRL-TDC News No.21

2

An Evaluation of Positioning
Error Estimated by the
Mesoscale Non-Hydrostatic
Model –Preliminarily report–cm

1

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
Meteorological Research Institute3
University of Hawaii

35°N

5cm
0

km

50

Zenith Wet Delay

ICHIKAWA Ryuichi1 (richi@crl.go.jp),
SEKO Hiromu2 , and Michael BEVIS3

12.0
11.5
11.0
10.5
10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0

139°E

We are now evaluating atmospheric parameters(equivalent zenith wet delay and linear horizontal
delay gradients) derived from slant path delays obtained by ray-tracing through the non-hydrostatic
numerical weather prediction model (NHM) with
1.5 km horizontal resolution. Our ultimate purpose is to establish a new method for reducing atmospheric eﬀects on geodetic positioning. We ﬁrst
seek to establish the level of positioning error due
to intense mesoscale phenomena such as the passing of cold fronts, heavy rainfall events, and severe
storms. The NMH provides temperature, humidity
and pressure values at the surface and at 38 heightlevels (which vary between several tens meters andabout 35 km), for each node in a 1.5 km by 1.5 km
grid that covers Izu peninsula of the central Japanand surrounding ocean.
We performed ray tracing experiments for theentire grid of the NHM at one epoch of the 1200
UT 3/7/1997. For each station we invert the simulated data set, consisting of 52 slant delays, using
an isotropic and an anistropic delay model. The
isotropic model has only one parameter – the zenith
wet delay (ZWD). The anisotropic delay model ofChen and Herring (1997) has two additional lateral
gradient parameters. We compare the ‘true’ ZWD,
computed by directly integrating the wet refractivity ﬁeld of NHM, with the ZWD estimated byleast squares inversion of the ‘observed’ slant delays obtained by ray tracing. We did this using theisotropic and the anistropic delay models.
Figure 1 shows the zenith wet delays (ZWDs)
computed using ray tracing based on the vertical
proﬁle of the NHM. Gradient vectors estimated using least squares inversion of ray-traced slant delays
are also indicated (white allows). A characteristic
ZWD pattern caused by the mountain lee waves
is presented in this ﬁgure. At the east of the Izu
peninsula ZWDs are lying in a north-south band
about 10km in width and about 50km in length.
This ZWD pattern is consistent with the observed

Figure 1. Zenith wet delay retrieved by the 1.5km
NHM at the 1200UT of March 7, 1997. Arrows
indicate gradient vectors estimated by the best-ﬁt
anisotropic model to the slant delays using ray tracing through the NHM.
GMS cloud image [Shimada et al., 2002]. Large
gradient vectors are perpendicular to the northsouth ZWD band. In addition the biggest gradients
occur at the northern part of the peninsula where
topographic variations produce a much more complex distribution of water vapor.
We are now numerically examining positioning
errors calculated from the slant delays through the
NHM, assuming realistic GPS and VLBI positioning. In the another paper we will present the behavior of the positioning errors under the atmospheric disturbance in local scale, the relation between the ZWD errors and the vertical positioning errors, and the eﬃciency of the reduction of
the azimuthal anisotropy of the atmosphere using
the anisotropic mapping function [e.g. MacMillan,
1995; Chen and Herring, 1997].
References
Chen, G. and T. A. Herring, Eﬀects of atmospheric azimuthal asymmetry on the analysis of space geodetic
data, Geophys, Res. Lett., 102, 20489-20502, 1997.
MacMillan, D.S., Atmospheric gradients from very long
baseline interferometry observations, Geophys, Res.
Lett., 22, 1041-1044, 1995.
Shimada, S., H. Seko, H. Nakamura, K. Aonashi, andThomas A. Herring, The impact of atmosphericmountain lee waves on systematic geodetic errors observed using the Global Positioning System, Earth
Planets Space, 54, 425-430, 2002.

November 2002

3

Holographic measurement of
Kashima 34-m radio telescope
surface accuracy –Preliminary
report–Hiroshi Ohkubo1 (okubo@crl.go.jp),
Tetsuro Kondo1 , Ikuto Yonezawa2 ,and Hiro Osaki1
1Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
Ibaraki University
2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
1.

Figure 1. Near-ﬁeld(Left) and Far-ﬁeld (Right)
phase pattern.

Introduction

We have planned to measure surface accuracyof Kashima 34-m antenna using a microwave holographic technique. It had been diﬃcult to carryout holographic measurement, because there wasno reference antenna exists near Kashima 34-m antenna site. To realize a holographic measurement
we adopted CARAVAN 0.65-m antenna [Yonezawa
et al., 2002] as a reference antenna. A geostationary satellite, N-star b, was used as a reference radiosource in a far-ﬁeld region.
Only a few satellites are matched with a frequency and AZ/EL position requirement of ourmeasurement system. We are working on data
analysis and have not reached result yet. In this Figure 2. Kashima 34-m antenna and CARAVAN
report, we will introduce a measurement system 0.65-m antenna are used to receive the geostationand a result of experimental observation brieﬂy.
ary sattelite N-star b.
2.

Measurement

2.1

TheoryA microwave holography is technique to measurea far-ﬁeld pattern of test antenna using a reference
antenna. Then applying the Fourier Transform tofar ﬁeld pattern to get aperture distribution of amplitude and phase of test antenna. Aperture distribution of phase error is considered to represent
surface error of reﬂector. Figure 1 shows relationship between near-ﬁeld aperture phase distribution
pattern and far-ﬁeld phase pattern.
2.2

Measurement system

During measurements, the Kashima 34-m andthe CARAVAN 0.65-m antennas observe signal
from the geostationary satellite N-star b (see Figure 2). Elevation of satellite from Kashima site is
48.02 deg.
Figure 3 shows a diagram of holographic measurement data acquisition system. RF signals at
Kashima 34-m and CARAVAN 0.65-m station are
fed to down converters and each 0-2GHz IF signal are fed to video converter. Outputs of video
converters, 2 channel 2MHz video signals, are ﬁnally fed to the VSSP (Versatile Scientiﬁc Sampling Processor) [Osaki et al., 2002], then sampled

Figure 3. Microwave holographic measurement
data acquisition system.

and stored on HDD. Sampling rate is 4MHz 4bit
1ch for each station. Data are stored in HDD, thenprocessed by software correlator.
2.3

Antenna maneuverOn the ﬁrst attempt of our measurement, we acquired data at each 1024 (32×32) points. After

IVS CRL-TDC News No.21

4

4.

Conclusion

The holographic measurement of the Kashima
34-m antenna is in progress. Antenna scan pattern was improved but estimated phase error of
the system is still large. Main reason comes fromdue to a local oscillator phase error of the reference
telescope. Now we are improving the system andwe will present the results of holographic measurements to improve system.
References
Figure 4. Antenna maneuver.

Osaki, H., T. Kondo, and M. Kimura, CRL IVS TDC
news No. 20, pp. 7-9, 2002.
Yonezawa, I., J. Nakajima, H. Ohkubo, M. Tsuboi, and
T. Kasuga, CRL IVS TDC news No. 21 (this issue),pp. 29-30, 2002.

Figure 5. Phase ﬂuctuation of measurement system.

data processed, we found that phase connectivity
between each observation is not good. Thus in thesecond attempt, we changed antenna scan pattern.
Using radial and raster scan (Figure 4), data was
acquired continuously during a scanning process.
Radial scan is thought to be shorter observation
time because beam center is measured at each scan.
Although raster scan consumes observation time,the data processing will be easier. At this moment
we took data of both scan pattern.
3.

System error estimation

Figure 5 shows correlated phase during experimental observation. During this observation test
antenna received signal from the satellite in center of beam. From this result, phase stability ofthe system is measured to 0.028 degree/sec. Thisantenna scanning process takes about 16 minutes.
Hence phase ﬂuctuation of measurement system
will contribute measurement error of 1.1 mm. Previously we estimated that local oscillator phase error contributed as large as 0.85 mm.

November 2002

5

Dependence of Correlation Di- “result” list.
mension of QSO Radio Wave list1 = {A, B, C, D, E}
Intensity Time Series on Red list2 = {a, b, c, d, e, f, g, h, i, j, k, l, m, n}
result = { (Aa + Bb + Cc + Dd + Ee), (Ab + Bc
Shift
+ Cd + De + Ef), (Ac + Bd + Ce + Df + Eg),
Md. M. R. Khan1(mostaﬁz@mi.cias.osakafu-u.ac.jp)
and N. Tanizuka1,2(tanizuka@mi.cias.osakafu-u.ac.jp)
1

Graduate School of Science
Osaka Prefecture University
1-1 Gakuen-cho, Sakai, 599-8531 Japan
2
College of Integrated Arts and Sciences
Osaka Prefecture University
1-1 Gakuen-cho, Sakai, 599-8531 Japan
Summary: The variation of the radio wave intensity with time from the quasars (QSOs) at cosmological distance are unpredictable because of unknown dynamical structures of the radio sources
and the external factors eﬀected on the path ofwave propagation. In this paper, the preliminary analysis results of the time series data of thequasars of S band (2 GHz) and X band (8 GHz)
are presented.
The purpose of our study is to calculate the degree to which the presumed dimension of the dynamical system are limited from the GrassbergerProcaccia (GP) method by correlation integration.
1.

Introduction

In our previous study, time series data of QSO
radio wave ﬂux density were analyzed on the standpoint of Higuchi’s fractal dimension, Hurst exponent, power spectrum etc. Khan et al. [1]. The
calculated results were plotted and compared withrespect to red shift. In that results, we did not
get any information about the eﬀect of external
noise. In the present analysis, a convolution timeseries has been calculated from the original radio
wave time series. Then the correlation dimensions
for both time series have been calculated and plotted with respect to red shift. In these results, a
new notion has been probed that inevitable external noise may be accumulated on the original radio
wave at the time of the wave passing through thespace from the cosmological distance.

(Ad + Be + Cf + Dg + Eh), (Ae + Bf + Cg + Dh
+ Ei), (Af + Bg + Ch + Di + Ej), (Ag + Bh + Ci
+ Dj + Ek), (Ah + Bi + Cj + Dk + El), (Ai + Bj
+ Ck + Dl + Em), (Aj + Bk + Cl + Dm + En) }If the length of original data is x and the lengthof kernel is y, then the length of convolution data
will be (x - y + 1). For example, here the lengthsof “list2” is 14 and length of “list1” is 5. So, thelength of “result” is (14 - 5 + 1) = 10.
In our analysis, we have used the kernel values,
Wolfarm [2] as follows
1n2√ Exp(−)
100
6.1 2π(1)where n = - 10 to 10, which gives us the folloing
list of kernel values.
kernel = {0.0240595,
0.0456283, 0.0509339,
0.0647496, 0.0654004,
0.0557305, 0.0509339,
0.0290939, 0.0240595}

and

2.2

0.0290939,
0.0557305,
0.0647496,
0.0456283,

0.0344851, 0.040066,
0.0597714, 0.062836,
0.062836, 0.0597714,
0.040066, 0.0344851,

(kernel) = 1(2)

Correlation Dimension and Multidimensional Embedding Spaces

We have used the Grassberger-Procaccia (GP)method to calculate correlation dimension for
multi-dimensions, Hilborn [3]. We have calculated
the correlation sum by
C (m) (r) =

1
N2

N


θ(r− | xi − xj |)(3)

i,j=1&i=jwhere θ(t) is the Heavicide step function and θ(t)= 0 if t < 0 and θ(t) = 1 if t ≥ 0, and m denotes thedimensions. m-dimensional vector is the collectionof m components
xi = (xi , xi+τ , xi+2τ , ..., , xi+(m−1)τ )(4)

here τ is the time lag and it represents the timeinterval between the successively data values that
we have used to construct the vector xi .
2.1 Convolution Time Series
The “length” of the diﬀerence between the two
To calculate the convolution time series, we have vectors is usually taken to be the “Euclidean
processed the convolution operation on the mi- length”
crowave time series data with some kernel values.
m−1
For example, let us consider, “list1” is the kernel
√ 
|

x
−

x
|=
(
{xi+kτ − xj+kτ }2 )(5)ijvalues, “list2” is the time series data, then the rek=0
sulted values of convolution operation is shown in2.

Analysis Methods

IVS CRL-TDC News No.21

6

Finally, we have calculated the correlation diFig. 7 shows the relationship between red shiftmension from the following equation for some range and correlation dimension and Table 1 shows theof r values which is called the scaling region.
values of correlation dimensions of KSP observation. In this case, we have used about 1000 day’s
C (m) (r) = kr−Dc (m)(6) data on daily basis and for most of the sources wegot 50% or more missing values. On observation,some portions of data are observed on daily ba2.3 Embedding Theorem
sis and other portions are observed on every after
Given a dynamical system with a m-dimensional one day basis. If we take the data on every after
solution space is x(t) = fs (x(t)). Let, y(t) be some one day basis, the data range is about 500 or less,observation and y(t) = g(x(t)), and v(x) = (g(x), which is very few data to get eﬀective result. In thisg(fs (x)), ..., g(fsm−1 (x))) be the lag vector.
analysis, about 50% data are compensated by the
The embedding theorem states that if the system average of neighbour values. As a result, for mostproduces orbits in the original state space that lie of the sources we got the correlation dimensions lie
on a geometric object of dimension Dc (which need between 3 to 5.
not be integer), then the object can be seen without
any spurious intersections of the orbit in another 4. Conclusion
space of integer dimension m and
The diﬀerence between the correlation dim > 2Dc(7) mension of the original time series and the convolution time series increases as the red shift increases
that is also known as Fractal time delay embedding(as shown in Fig. 6). The diﬀerence of their deprevalent theorem, Abarbanel [4].
pendence on the red shift might be concluded alternatively as follows:
3. Result and Discussion
1. The original time series data is superimposed
The original time series, after primary noise elimby external noise on passing through the wave
ination and compensating missing values, is shown
propagation media. The result of the convoin Fig. 1, Khan et al. [1] and the convolution timelution may reﬂect the source dynamics in aseries is shown in Fig. 2 of source 0336-019 at 2
higher manner.
GHz of GBI observation. Fig. 3 and 4 show thethree dimensional state space map for original and2. The original time series data reﬂects directly
convolution time series respectively at time lag 5
the source dynamics, if there is negligible eﬀect
days.
on the wave through its propagation.
Table 1 shows the list of sources observed by Key
Stone Project (KSP), Koyama et al. [5], [6]. Ta- Referencesble 2 shows the list of sources observed by GreenBank Interferometer (GBI) [7]. Column 1 through [1] Md. M. R. Khan, N. Tanizuka, ”Comparative
Time Series Analysis of Radio Wave Intensity of
4 show IAU source designation, red shift, correlathe QSOs observed by VLBI (KSP) and GBI”,
tion dimension (S & X band) and % of missing
Proceedings of the First CRL TDC Symposium,
value (S & X band).
(Kashima, Japan, Sept. 19, 2001) pp. 4-7, IVS CRLFig. 5 shows the relationship between correlaTDC News No. 19. Technology Development Center News, Communication Research Laboratory, Serialtion exponents and phase space dimension for origNo. 19, November 2001. Web: http://www2. crl.go.
inal and convolution time series. In this ﬁgure, thejp/ka/radioastro/tdc/news 19/pdf/news19 index.pdf pp.
correlation dimensions (about 2.5) for convolution
4 ・7.
time series clearly satisfy the embedding theorem(equ. 7). But for original time series, the corre- [2] Wolfarm, S., The Mathematica book, Mathematica Version 4, Cambridge University Press, 904 - 908.
lation dimension (about 5 - 6) do not satisfy theembedding theorem all time.
[3] Hilborn, Robert C., Chaos and Nonlinear Dynamics,
Fig. 6 shows the relationship between redshift
Oxford University Press, 367 - 485, New York, 1994.
thand correlation exponents at 10 dimension, which
we deﬁned here the correlation dimensions of the [4] Abarbanel, Henry D. I., Analysis of Observed Chaotic
Data, Springer, 11 - 23 and 39 - 67, New York, 1996.
systems’ dynamics, of GBI observation. This ﬁgureshows us an important information that, for the [5] Y.Koyama, T.Kondo: Microwave flux density variations
case of original data, the correlation dimensionsof compact radio sources monitored by real-time Very
have apparent dependence on redshift except theLong Baseline Interferometry, Radio Science, Vol. 36,
squired one1 ; in case of convolution data, it seems
No.2, pp.223-235, Mar./Apr. 2001. (also in Web site [6])there is less dependence of correlation dimensions[6] http://ksp.crl.go.jp/index-j.html
on red shift.
[7] http://www.gb.nrao.edu/fgdocs/gbi/gbint.html 2
1 Most of the sources, we have analyzed about 1000 days

2 The Green Bank Interferometer is a facility of the Na-

data. But for the squired source as shown in Fig. 6, we haveanalyzed only 300 days data which we can ignore.

tional Science Foundation operated by the NRAO in supportof NASA High Energy Astrophysics programs.

November 2002

7

2.8

2.6

2.6

2.4

2.4

Jy

Jy

2.8

2.2

2.2
2
2
1.8
1.8

1.6
44000

44500

45000

45500

46000

46500

47000

44000

44500

45000

Day

45500

46000

46500

47000

Day

Figure 1. Original time series.

Figure 2. Convolution time series.

Figure 3. 3D phase space map for original timeseries.

Figure 4. 3D phase space map for convolution
time series.

SourceName0059+581
0727-115
0316+413
1226+023
1921-293
1253-055
1334-127
1641+399
0923+392
2251+158
1730-1300420-014
2145+067
1308+326
2134+004
0552+398

Red
shift
...
...
0.017
0.16
0.35
0.54
0.54
0.59
0.70
0.86
0.90
0.92
0.99
1
1.93
2.37

Table 1. KSP Observational Data
Correlation dimensions % of Missing
S BandX BandS Band
2.741
2.843
53.12
2.603
3.915
51.27
3.966
5.512
50.39
3.970
4.965
50.78
3.841
3.010
51.56
3.230
4.848
51.56
4.618
3.880
51.76
3.736
3.508
50.68
4.444
4.135
50.59
3.365
3.057
50.29
1.882
2.180
79.98
3.963
5.311
50.78
4.816
4.792
50.39
4.780
5.483
50.78
7.217
7.181
50.39
4.531
3.657
60.74

valuesX Band
59.18
52.73
51.37
51.86
53.32
52.64
52.83
51.17
51.66
51.07
82.42
52.05
50.88
52.25
50.98
62.01

IVS CRL-TDC News No.21

8

SourceName
0300+470
0133+476
0235+1640333+321
0202+319
0215+015
0237-234

Red
shift
z
0.475
0.86
0.94
1.26
1.47
1.715
2.225

Table 2. GBI Observational Data
Correlation dimensions
Origina
Data
Convolution
Data
2 GHz
8 GHz
2 GHz
8 GHz
2.33
5.60
1.14
1.14
3.50
4.15
2.20
2.15
3.85
2.24
1.69
1.65
3.87
2.62
2.69
1.40
2.56
4.52
1.30
2.71
4.85
6.82
2.55
2.04
7.20
8.55
3.15
2.48

Figure 5. Correlation exponents vs phase spacedimension of 0336-019 at 2 GHz of GBI observation.

% of Missing

values

2 GHz
2.66
21.96
7.52
18.33
21.50
13.90
16.68

8 GHz
2.66
17.38
7.52
17.70
20.24
14.36
16.68

Figure 6. Relationship between red shift andcorrelation dimensions for GBI observational
Data, in legend, Org for original time series
and Con for convolution time series.

Figure 7. Relationship between red shift and correlation dimensions for KSP observational Data

November 2002

9

S-band RFI problems at
Kashima 34-m antenna anda passive filter for mitigation
Eiji Kawai1 (kawa@crl.go.jp),
Hiroshi Ohkubo1 , Junichi Nakajima1 ,and Jun Amagai2
1

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
Yokosuka Radio Communications ResearchCenterCommunications Research Laboratory
3-4, Hikarino-oka, Yokosuka-shi, Kanagawa
239-0847, Japan
1.

Figure 1. An example of RFI spectrum at the Sband IF of Kashima 34-m antenna. Frequency of
O Hz corresponds to 2020 MHz in the sky.

Introduction

Severe RFI at an S-band due to a thirdgeneration mobile phone system (IMT-2000)1 occurred at Kashima 34-m antenna in December
2001. KSP-VLBI observations had been interferedat Koganei since July, 2001 due to a nearby transmitting station [Amagai et al., 2001]. Fortunately
we could mitigate RFI by inserting a passive ﬁlter
to an LNA output in both Koganei and Kashimacases. However the third-generation system is theworldwide standard, so that geodetic VLBI receiving dual S and X bands may be seriously aﬀectedby this system in near future.
2.

RFI due to IMT-2000

Figure 1 shows an example of spectra at the Sband IF signals of Kashima 34-m antenna after the
IMT-2000 service started. An IF ampliﬁer was saturated due to strong signals transmitted from an
IMT-2000 base station located several kilometersapart from Kashima 34-m antenna. An example ofbase stations is shown in Figure 2. As a frequency
band assigned to the IMT-2000 is partly overlappedwith that of Kashima 34-m antenna (Figure 3), it
was essentially impossible to avoid severe interferences. To investigate a way to mitigate RFI problems, ﬁrstly we checked up whether an LNA was
saturated or not. The linearity of the LNA wasmeasured by switching a noise diode power on/oﬀ
with receiving maximum RFI signals (Figure 4).
Results were compared with those measured fora cold load input, then it was conﬁrmed that the
1 IMT-2000 (International Mobile Telecommunications2000) is the ITU (International Telecommunication Union)
globally coordinated definition of the next generation ofmobile service covering key issues such as frequency spectrum use and technical standards (see http://www.imt2000.org/portal/index.asp for details).

Figure 2. A top portion of a typical base station
for the mobile phone system.

LNA was not yet saturated. Followed by, necessary
attenuation to prevent an IF ampliﬁer from a saturation was determined as follows. An IF output
was monitored with changing the attenuation valueof the LNA output. When we inserted 42.7 dB attenuation in total to the LNA output, saturationof IF output disappeared (Figure 5). Necessary attenuation is, hence, estimated to be 60 dB taking
into account an 11 dB margin that is expected under more crowded traﬃc condition.

IVS CRL-TDC News No.21

10

CH2 S21

New S-band

log MAG

10 dB/

REF 0 dB

Old S-band
IMT-2000

2100

2200
2300
Frequency (MHz)2400

Figure 3. Frequency allocation of IMT-2000.

START 2 100 MHz

STOP 2 600 MHz

Figure 6. The characteristics of ﬁlter inserted to
LNA output.

Figure 4. A schematic block diagram of S-band receiving system of Kashima 34-m antenna on a linearity measurement.

ATT=42.7dB
Figure 7. An Filter inserted to LNA output.
Figure 5. An S-band IF spectrum when the LNA
output attenuation is 42.7 dB.

3.

A passive band pass filter

We ordered a band pass ﬁlter (BPF) that has
characteristics shown in Figure 6. The BPF has a
suﬃcient attenuation value at RFI frequencies. We
put the BPF between the LNA output and the IF
input (see Figure 7). Figure 8 shows an IF spectrum after the BPF was installed. As a result the
bandwidth of S-band has become narrow by 100
MHz as compared with before, we can make an
S-band observation again. Now frequency range

available to use for an S-band observation is 2250–
2350MHz.
4.

Concluding remarks

We experienced a severe RFI at the S-band of
Kashima 34-m antenna. Fortunately we could mitigate RFI by installing a passive band-pass ﬁlter to an LNA output. However, it is expected
to increase the number of IMT-2000 user year by
year. Moreover it is also supposed that anothermobile phone company will start an IMT-2000 service at Kashima in the near future. If RFI becomesstronger than the present situation, it will result inNovember 2002

11

Table 1. The characteristics of ﬁlters
Existing Filter
Passband
Attenuation
Insertion Loss
Tsys when settingat LNA input
Dimensions (mm)2250–2450 MHz>60 dB at 2170 MHz<1 dB

HTS Filter(70K operation)
2200–2400 MHz>80 dB at 2170 MHz<0.5 dB

72K+62K(at 296K)=134K

72K+8K(at 70K)=80K

260×42×27

φ60×14ing the feasibility of the use of a high-temperaturesuperconductor (HTS) ﬁlter that has a low loss andlow noise features. Table 1 summarizes the characteristics of conventional ﬁlter and those of HTS
ﬁlter. We are planning to test an HTS ﬁlter using
Kashima 34-m antenna. If it shows a good performance, we will replace the current ﬁlter to the HTS
one.
Acknowledgement: We wish to thank NTT DoCoMo Inc. for their helpful cooperation to carryout RFI measurements before regular IMT-2000
service started. We also would like to thank
DENSO CORPORATION Research Laboratories
for their aggressive contribution to develop an HTS
Figure 8. An S-band IF spectrum after ﬁlter inserﬁlter worked at an S-band.
tion.
Referencethe saturation of LNA. If it occurs, we have to in- Amagai, J., H. Kiuchi, and K. Sebata, The sigsert any ﬁlter in front of the LNA, which causes a
nal of a third-generation mobile system, IMT-2000,
system temperature increase. To reduce the systemjams KSP VLBI observations, IVS CRL-TDC News,
temperature as small as possible, we are investigatNo.19, pp.10, 2001.

IVS CRL-TDC News No.21

12

Measurements of Harmful In- The electromagnetic interference (EMI) probdescribed above had been investigated from
terferences in the HF-UHF lemsApril to July in 2002 by the PLC study group
Bands Caused by Extension organized by the Ministry of Public ManageHome Aﬀaires, Post and Telecommunicaof Power Line Communication ment,
tions (MPHPT) in Japan. The study group held
Bandwidtha working group on the ﬁeld experiments and exFuminori Tsuchiya1(tsuchiya@pparc.geophys.tohoku.ac.jp),
Hiroaki Misawa1 , Tomoyuki Nakajo1 ,Ichiro Tomizawa2 , Junichi Nakajima3 ,Masatoshi Ohishi4 , Takayuki Ono1 , andAkira Morioka1
1Graduate School of Science, Tohoku Univ.
Aramaki Aza Aoba, Aoba-ku, Sendai, 980-8578,
Japan
2
Univ. of Electro-Communications
1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585,
Japan
3
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki, 314-8501, Japan
4
National Astronomical Observatory
2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japanecuted collaborated ﬁeld experiments of the PLC
facility. In July 8-9 and 23-24, ﬁeld experiments
were carried out at Mt. Akagi in Gunma Prefecture, Japan. In the experiments, we measured interferences leaked from the PLC facility in HF andUHF bands in order to evaluate inﬂuences of the
expansion of PLC bandwidth on the radio astronomical observations and examine the presence ofspurious emissions over higher frequency. In thispaper, we report the experimental results in theﬁeld experiments, and compare the PLC noise withthe galaxy background level and the limit of harmful interference for radio astronomical observation
which is given in Recommendation ITU-R RA7691.
2.

Field Experiment of the PLC Facility

Figure 1 shows the conﬁguration of the ﬁeld experiment of the PLC facility at July 24. Powerlines used for the experiment were extended between electric poles (poles #1, #2, and #3 in Fig1. Extension of the PLC Bandwidth
ure 1) and a model house which was electromagPower line communication (PLC) has become netically shielded by wire meshes. Table 1 shows
available for a low bit rate network which is permit- a list of PLC modems tested in the experiment.
ted to use the frequency range from 10 kHz to 450 The “in-house” PLC system was set up inside thekHz. Due to the limited bandwidth for the cur- model house. Three pairs of laptop-type personal
rent PLC system, maximum data rate is limited. computers were connected into wall sockets by way
Recently, the fast power line telecommunication of the PLC modems (No. 5/6, 7/8, and 9/10 in Taequipments to archive data rates of several Mbit/s ble 1). The “access” system was set up between theare developed, and the broadband PLC system by model house and the electric poles. Two pairs ofextending the available frequency bandwidth up to modems were tested as the access system (No. 1/2
30 MHz is proposed. However, because power lines and 3/4). The modems and the computers conare designed not for telecommunication line but 50 nected at the outdoor side of power lines were set
Hz power distribution, high power transmission is on the pole #2. All the experimental data shown
required and the power lines emit substantial level in this paper are measured at July 24.
of electromagnetic noise in HF. In HF band, there
are a lot of radio stations for broadcasting, ama- 3. Interferences in HF Bandteurs, air-traﬃc control, and so on. If the PLC
Purpose of the experiment in HF band is to meausing HF band becomes operational, large portionsure
the interference level emitted from the PLC
of HF spectrum may become unusable for them.
facilityand examine the propagation characterisHF band is also worth for scientiﬁc observations
tics
in
order
to evaluate safety distance betweenof earth’s ionosphere, planets in the solar system,thePLC
facility
and a radio astronomical observaand astronomical objects. These observations have
tory.
Two
sets
of
equivalent T2FD antennas weresigniﬁcantly contributed to understand the enviset
up
atdistancesof 57 m and 180 m apart fromronment of the earth and scientiﬁc truth. Because
the
pole
#2
(T2FD
#1 and #2 in Figure 1, respecthe received signal level is usually very weak in thecase of the scientiﬁc observations, it is feared that tively). Height of each antenna from the groundinterferences from the power lines disable scientiﬁc was about 5 m. Outputs from the T2FD antennas
were directly connected with spectrum analyzers
observations.
and the radio spectra were measured in HF band.

November 2002

Figure 1. Map of the experiment site. Details aredescribed in the text.
For the quantitative measurements, we obtained 10
spectral traces for one spectrum measurement thenevaluated the deviations of the measurements.
Figure 2 shows one of the results of the spectral measurements. When the PLC system was
not in operation, a lot of broadcasting bands wereappeared over ﬂat noise ﬂoor which represented
noise level of the spectrum analyzer. After the modem 3/4 which was tested as an access system wasturned on, signiﬁcant increase of the noise ﬂoor wasobserved in the frequency range from 4 to 20 MHz
which was just used by the operational modem (seeTable 1). There were some narrow drops in theincreased noise ﬂoor at frequencies of 7, 10, 14,
and 18MHz, which were identical with frequencies
of notch ﬁlters in the modem unit. These characteristics indicated that increased noise level wascaused by the PLC facility. As shown in the ﬁgure, many broadcasting signals were interfered andsome of them were completely masked by the PLC
noise. The increase of the noise ﬂoor was also identiﬁed in the case of the modem 1/2, but about 5
dB smaller than that of the modem 3/4. In thecase of the other modems tested as the in-housesystem, distinct increases of the noise ﬂoor were
not observed because the in-house system was set
inside the shielding room.
Distance dependence of the PLC noise level was
examined assuming that the leakage electric ﬁeld
E is proportional to the power low of distance r,

13

Figure 2. Typical HF spectrum measured by T2FD
#1 when the PLC system was not in operation(top) and was running with the modem 3/4 (bottom). Error bars represent the standard deviationof signal intensity with the resolution bandwidth(RBW) of 10 kHz.

Table 1. PLC modems used for the ﬁeld experiment.
No.
1/2
3/4
5/6
7/8
9/10

Modulation
Principal
OFDM
SS
Multi-Carrier
OFDM
OFDM

Freq. Range[MHz]
4.3–20.9
4.0–20.0
2.622–11.202
3.8–11.8
7.9–22.8/3.8–17

SystemType
accessaccessin-house
in-house
in-housethat is, E = E0 r−α . From the measurements using
two T2FD antennas, the power index α distributed
from 0.5 to 1.0 depending on frequency. The reason
why the calculated index was smaller than that of
the far ﬁeld electric wave of 1.0 may be because thesource of the PLC noise was distributed along thelong power line cable.
In order to evaluate the interference level quantitatively, the T2FD antennas were calibrated. A
standard loop antenna (Antitsu MP414B) was set
just below the T2FD antenna, and we measured
electric ﬁeld intensity of some broadcasting frequencies simultaneously and calculated antenna

IVS CRL-TDC News No.21

14

Figure 3. Comparison plot for a HF spectrum measured by T2FD #1 during all the PLC modems
were running (upper line) and estimated galactic
level (lower line).

Figure 4. Dynamic spectrum around the frequencyof 327 MHz. Corresponding to the turning oﬀ of
the modem 3/4 at 15:04, the broadband noise andsome narrow band emissions were disappeared.

factors of T2FD in HF range. Figure 3 shows aresult of comparison between the PLC noise andgalactic level calculated by referring known galactic spectra (Alexander et al, 1969; Hartz, 1969) andthe calibrated antenna factors. The PLC noise exceeded the level of galactic noise with more than
30dB.

Figure 4 shows a dynamic spectrum in the frequency range from 297 to 357 MHz during an operation of the modem 3/4. When the modem wasturned oﬀ at 15:04, disappearance of broadband
noise and some narrow band emissions were clearlyobserved, which indicate the presence of spurious
emissions in UHF band. Figure 5 shows dependence of the spurious level on the distance and direction of the antenna with respect to the PLC facility. When the all modems were turned oﬀ or theantenna did not direct to the PLC facility, no spurious emission was detected. On the other hand,stronger spurious emission was received when theantenna directed and was closer to the facility. Assuming that electric ﬁeld intensity of the spurious
was proportional to power low of the distance fromthe pole #2, the power index was calculated to be
1.3, which was close to but larger than the far ﬁeld
value of 1.0. We compared the intensity of spurious
emission at the frequency of 327 MHz with a limitof harmful interference level for radio astronomical
observation which was regulated in Recommendation ITU-R RA 769-1. Assuming a system noise
temperature of 150 K at 327 MHz and a receiverband width of 120 kHz, the recommendation level
was calculated to be -247 dBW/m2 /Hz. The detected intensity of the spurious emission at the position of 35 m was -206 dBW/m2 /Hz, which was
greater than the recommendation level. The safety
distance for the radio astronomical observation was
calculated to be 4 km apart from the PLC facility assuming that the intensity of spurious electricﬁeld was anti-proportional to the distance from thesource.

4.

Spurious Emission in UHF Band

UHF band is an earth-based window for theradio astronomical observation and high sensitive
measurements of weak radio sources are possible.
Although the broadband PLC system dose not use
such a higher frequency band, it is necessary to conﬁrm the level of spurious emissions from the PLC
facility because the system noise temperature in
UHF band is very low in the radio astronomical observations. A log-periodic antenna (Create Design,
CLP-5130-1) and a receiver were set up at a distance of 55 m apart from the pole #2 (UHF #2 inFigure 1), and sometimes moved at a distance of 35
m (UHF #1). The receiver consisted of a high passﬁlter, low noise pre-ampliﬁer, and wide band ampliﬁer. The pre-ampliﬁer had a power gain of 40 dB
at the center frequency of 327 MHz, the bandwidthof about 20 MHz, and the minimum noise ﬁgure of
0.8 dB. The high pass ﬁlter whose cut oﬀ frequency
was 260 MHz prevented the saturation of the preampliﬁer by strong broadcasting signals in VHF
range. Spectra around 327 MHz were measured byspectrum analyzers, and automatically recorded bya personal computer via GPIB interface. In orderto check that the spurious emissions were actuallyoriginated from the PLC facility, we measured the
HF spectra simultaneously and examined dependences of spurious emission on distance and direction from the PLC facility.

November 200215

for the radio astronomical observation in both HF
and UHF bands. If PLC is widely operated, interference level will increase more and more and thesafety distance will become larger. Furthermore,because the radio waves in HF band are reﬂectedfrom the ionosphere and can propagate over long
distance, it becomes diﬃcult to prevent the harmful interferences of PLC.
Finally, it is noted that the measurements reported in this paper were carried out under a speciﬁc environment; only a few PLC modems wererunning in the rural area, the model house was electromagnetically shielded, and there was no homeelectronics plugged in the model house, which wasquite diﬀerent from that the general persons would
use the PLC modems for actually. Both the quality and quantity of the experiments were also notenough for the quantitative discussion. For example, because there were only two data points toevaluate the propagation characteristics, the power
Figure 5. Dependence of spurious emissions on theindex showed a large ambiguity from 0.5 to 1.3.
distance and direction of the log-periodic antenna
A more realistic environment and elaborated meawith respect to the PLC facility. Left: spectra measurements are necessary in the future experiment.
sured at 35m point. Right: Same as left but at
Especially, far ﬁeld measurements are important
55m point. Top: PLC was not operational. Middle:
for the quantitative evaluation of the harmful efPLC modem 3/4 was running and the antenna wasfect on the radio astronomical observations.
directed to the pole #2. Bottom: Same as middle
The experiments reported in this paper conpanels but the antenna pointed the opposite directributed to the results of the working group on
tion. In each panel, solid lines are averaged spectraﬁeld experiments. At the end of July, the PLC
around the frequency of 327 MHz and gray dotted
study group concluded that the extension of theline shows a spectrum when input of the receiver
PLC bandwidth at current technical level was not
was terminated. Some environmental noises which
permitted for commercial use based on results fromwere not related to the PLC were also identiﬁed asworking groups on hearing surveys and ﬁeld expernarrow band emissions which were received wheniments.
PLC was turned oﬀ and the antenna directed northward. A typical error bar in the measurements is
Referencesindicated in right-bottom panel.
5.

Discussion and Conclusion

Alexander, J.K., L. W. Brown,T. A. Clark, R. G. Stone,
and R. R. Weber, The Spectrum of the Cosmic Radio
Background between 0.4 and 6.5 MHz, Astrophys.
J., 157, L163, 1969.

From the spectral measurements in HF band, it
was conﬁrmed that the noise ﬂoor level signiﬁcantly Hartz, T. R., Radio Noise Levels Within and Above
increased in the frequency range which was used by
the Ionosphere, Proc. IEEE, 57, 1042, 1969.
the operational PLC modem. The intensity of theinterference was much stronger than that of radio
astronomical signals as shown in Figure 3. Fromthe experiments in UHF band, it was found thatthe spurious emissions were leaked from the PLC
facility and the intensity was grater than the limitof interference level regulated in Recommendation
ITU-R RA 769-1 at the experiment site. The safety
distance for the radio astronomical observatory of
4 km is not short because a distance between aradio observatory and the closest residential area
to the observatory will be generally less than 4 km
in Japan.
PLC seems to be a harmful interference source

IVS CRL-TDC News No.21

16

Advancement of Versatile
Scientific Sampling Processor(VSSP)
Hiro Osaki (osaki@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

Introduction

A personal computer (PC) based VLBI dataacquisition system was developed by Communications Research Laboratory (CRL) and Nihon
Tsushinki Co. Ltd. [Osaki et al., 2002]. The sys- Figure 1. A prototype K5 data recording/processing
tem was called versatile scientiﬁc sampling procesterminal.
sor (VSSP). This system adopted a PCI-bus VLBI
data sampler board and was capable of recording 4channel 64 Mbps data (16 Mbps for each channel).
Using four VSSP PCs, a 16-channel 256 Mbps data
recording/processing system was produced, which
was called “K5”. This system is expected to replacepresent tape-based VLBI observation system, because this system is less expensive and more convenient than present tape-based system. In thispaper we will report the advancement of VSSP so
far and introduce brieﬂy about some experimental
observations recorded using this system.
2.

Advancement of the VSSP

2.1

Software Environment of VSSP

At ﬁrst VSSP and PC-VLBI sampler board wasdeveloped on FreeBSD and Microsoft Windows, because device driver software of the sampler board
was developed only for these two operating systems (OS) [Osaki et al., 2002]. Recently device
driver for Linux was developed in order to fulﬁll
the users’ request. This driver was developed on
Red Hat Linux 7.3/kernel 2.4.18. It is also tested
on kernel 2.4.19 and works well. The developmentof the Linux driver must be good news for the VLBI
sampler board users.
Several VLBI application softwares have beendeveloped by CRL. They have been developed so
as to be compliant with both FreeBSD and Linuxsystems. The applications may easily be compiled
on some C compilers on Microsoft Windows system, but this compatibility is not tested yet. The
development of the Linux-based VSSP as well as
FreeBSD-based system will accelerate the development of the PC-based VLBI software. Moreover,the chance of the OS selection will prevent the users
from being annoyed with some OS install troubles,such as compatibility problem between the OS’sboot loader and the PC’s BIOS, or some device
recognition trouble used in one’s PC.
2.2

Examples of the VSSP PCs

As the VSSP is a ﬂexible system developed on
PC, it can be arranged according to the user’s

Figure 2. Inside of the VSSP PC used as one partof the K5 terminal.

requirement. For an example, CRL and Nihon
Tsushinki Co. Ltd. develop a system that will
replace today’s tape-based geodetic VLBI recordersystem. This system, called “K5”, is composed offour VSSP PCs. Figure 1 shows a prototype K5
system assembled by CRL. Each PC has 480 GB
data storage area with 4-channel PC-VLBI sampler board. Practically one-day geodetic observation data can be stored on this system. Figure 2
shows inside of a VSSP PC used as one unit of
the K5 terminal. The observed data is stored four
HDDs seen on the upper-right part of the picture.
The other HDD seen on the upper-left part is thesystem disk. For another example, a briefcase size
4-channel data recording/processing system is assembled by CRL. This system can be used as a mobile VSSP recording/processing terminal. Two 120
GB HDDs are installed on this system. 4 GB of oneof the HDD is used as system area. The remaining
236 GB is used as data storage area. If a user has

November 2002

17

Table 1. Speciﬁcation sheet of the VSSP PCs

CPU
RAM
HDD

Ether port
PCI busK5: 16-channel VSSP for
geodetic observation(composed of 4 PCs, followings are
specs for each PC)
Pentium III (1.2 GHz)
256 MB
120 GB × 4 for data strage
60 GB ×1 for system(7200rpm, Ultra ATA/100)
10/100 Base-T
6

to carry recorder/processor system and if 4 channel
sampling and 236 GB data storage area is enoughfor the purpose, this system may be an attractive selection. Another example shows that several
universities and institutes that have purchased the
IP-VLBI sampler board have assembled their own
VSSP-like system in accordance with their needs.
In order to exchange know-how to use the IP-VLBI
sampler board and to support the users each other,a users’ mailing list has been started by CRL. The
speciﬁcations of the VSSPs assembled by CRL are
shown on Table 1.

Mobile VSSP: Briefcase size
4-channel VSSP PC

Pentium IV (2.53 GHz)
512 MB
120 GB × 2; 4GB for system andremaining 236GB for data storage(7200rpm, Ultra ATA/100)
on-board 10/100 Base-T
2using Kashima-34m, Kashima-11m, Koganei-11m,
Usuda-64m, Gifu-11m, and Yamaguchi-32m antennas. These data were also processed with thesoftware correlator. The data was also recorded
by K4 systtem at the same time at Kashima34m, Kashima-11m, Koganei-11m, Gifu-11m, andTomakomai-11m antenna, to compare the resultwith VSSP. The fringes were successfully detectedby both systems. Those results are being examinednow.
4.

Summary

Recently VSSP PC can be set up on Linux aswell as FreeBSD. A PC-based geodetic VLBI reSeveral experimental observation have been ording system is produced by CRL by assembling
made using VSSP. In this section some of the ex- four VSSP PCs. This system is called K5. Application softwares like data recording scheduler, manperiments are introduced brieﬂy.
CRL Kashima and Haystack observatory pro- ual data sampler, a software correlator, and some
moted electric transmission of VLBI data (e-vlbi) more are developed for VSSP. Several observation
observation experiments. At CRL site the data experiments like e-vlbi between Haystack Mark-V
was recorded using K5 system. On the contrary, system and Kashima K5 system, and test observathe data was recorded using Mark-V system at tion preparing for delta-VLBI spacecraft positionHaystack site. Both systems recorded the data as ing are made. These experiments showed the ﬂexﬁles on HDDs. After the experiment the data was ibility and eﬀect of the PC-based VLBI system,transmitted via FTP over GEMnet and GALAXY especially in such process as data recording, data
network. At Haystack K5 data was converted to transportation, data convertion, and data processbe correlated with Mark-V data. At Kashima, on ing compared to those of the present tape-based
the other hand, Mark-V data was converted to VLBI systems.
be correlated with K5 data. The latter case thedata was processed using a software correlator de- References
veloped by CRL. Eventually both institutes found
the fringes of the observation. This shows that Osaki, H., T. Kondo, and M. Kimura, CRL IVS TDC
PC-based VLBI data recording systems are ﬂexinews No. 20, pp. 7-9, 2002.
ble enough to convert one data format to another,using software. The data conversion process must Ichikawa, R., T. Kondo, Y. Koyama, H. Osaki, and H.
Ohkubo, CRL IVS TDC news No. 20, pp. 10-11,
be easier compared with those of the present tapebased data recorder system.
2002.
VSSP is also used for spacecraft observation ex- Sekido M. and M. Yoshikawa, CRL IVS TDC news
periment [Ichikawa et al., 2002]. This system is exNo. 20, pp. 12-17, 2002.for Nozomi spacecraft, IVS
pected to play an important role in delta-VLBI obCRL Technology Development Center News, No. 19,
servation of the Nozomi spacecraft, especially popp.37-40, 2001.
sitioning before/after Earth swing-by [Sekido andYoshikawa, 2002]. In order to prepare for theswing-by, test observation experiment was made3.

Experimental Observations by VSSPIVS CRL-TDC News No.21

18

VLBI observations using IPVLBI system for orbit determination of deep space spacecraft – Group delay measurements of GEOTAIL and NOZOMI telemetry signals –Testuro Kondo (kondo@crl.go.jp), Ryuichi
Ichikawa, Yasuhiro Koyama, Mamoru
Sekido, and Hiro Osaki
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan1.

NOZOMI

1st Earth Swing-by
Dec. 2002
Mars orbit insertion
Leaving Earth
Jan. 2004
Dec. 1998
Mars

Sun
Earth
Orbit of Earth
Orbit of Mars

2nd Earth Swing-by
June 2003

Orbit of NOZOMI

Figure 1.
Trajectory of NOZOMI (after
http://www.isas.ac.jp/e/enterp/missions/nozomi/
traject.html).

Introduction

Communications Research Laboratory has promoted a research on the spacecraft positioning
technology by using a delta VLBI technique. A
general-purpose VLBI system using the Internet
and a personal computer has been developed asa part of this project and it is called an IP-VLBI
system [Kondo et al., 2000; Kondo et al., 2002]
or a VSSP system [Osaki et al., 2002]. The IPVLBI system aims at a real-time VLBI system,and oﬀ-line observations and correlation processing are possible at present. Delta VLBI test observations of “GEOTAIL”1 were carried out using the IP-VLBI system in collaboration with theInstitute of Space and Astronautical Science ofJapan (ISAS) and the National Astronomical Observatory of Japan (NAO) to check automatic observation software and to evaluate the accuracyof observed delay obtained by the IP-VLBI system. We intend to utilize the delta VLBI observation data for the orbit-determination of “NOZOMI” (PLANET-B), which is a Japanese spacecraft launched in 1998 to explore Mars [Yamamoto
and Tsuruda, 1998], during the period just before
the last earth swing-by planned in June 2003 toward Mars. Recently we made test observations
for “NOZOMI” to evaluate the feasibility of actual
orbit determination.
1 The GEOTAIL satellite was launched on July 24, 1992,
from Cape Canaveral, Florida, U.S.A. by the Delta II launchvehicle, and it is a joint program of the Institute of Spaceand Astronautical Science (ISAS) of Japan and the National
Aeronautics and Space Administration (NASA) of U.S.A toinvestigate near-earth space. ISAS developed the spacecraft
and provided about two thirds of the science instruments,
while NASA provided the launch and about one third of thescience instruments. The spacecraft is operated from ISAS
but the telemetry is received by both agencies [Nishida,1994].

Tomakomai

Mizusawa

Usuda
Kashima

Gifu
Yamaguchi

Koganei

500km

Figure 2. The location of staions participated in
GEOTAIL and NOZOMI VLBI observations.

2.

Why Delta-VLBI?

The NOZOMI is the ﬁrst Japanese Mars orbiter,
and was launched on July 4, 1998. It was planned
to arrive Mars in 1999 by using two-times lunar
swing-bys and a powered earth swing-by. However
due to malfunction of a thruster valve during thepowered earth swing-by and maneuvers to recover
the right trajectory to Mars, enough fuel is not left
to inject NOZOMI into a Mars orbit. The NOZOMI team found a new trajectory to Mars available to inject NOZOMI into a Mars orbit. Hencethe orbit insertion scheduled in 1999 was abandoned, and it is now scheduled early in 2004 after
two more earth swing-bys (Figure 1). The determination of spacecraft position is usually made on
the basis of range and range rate measurements using a telemetry link. However range measurement
is supposed to be diﬃcult during several months

November 2002

19

Table 1. GEOTAIL test observation schedule
Date(YYYY/MM/DD)
2002/06/04

Time(UT)
06:49-14:00

2002/06/25
2002/06/28
2002/07/20

08:30-14:38
01:58-03:00
01:05-04:16

Stations (name with antenna diameter in meter)
Usuda64, Kashima34, Kashima11
Mizusawa10∗1, Yamaguchi32∗2
Kashima34, Kashima11, Koganei11
Kashima34, Kashima11, Koganei11
Kashima11, Koganei11, Gifu11*1: unable to observe due to a thunderbolt damage*2: undetect correlation due to a clock problem

Figure 4. The diﬀerence of delay rates between that
calculated for the position of GEOATIL ﬁxed at the
middle of each scan (i.e., only diurnal motion isconsidered) and that calculated taking the motion
Figure 3. The position of GEOTAIL on the equa- in the equatorial corrdinates into account.
torial coordinates on June 4, 2002.
down-link signals and to investigate the feasibility of group delay measurements. We made observations using the IP-VLBI system. Test observations were conducted several times (see Table 1)
and data reduction software was developed for apreliminary analysis. Two of four-channel inputsof the IP-VLBI system are used for S and X bandsignals of which base band signal frequencies are
2258.90 MHz and 8473.60 MHz, respectively. Observations were made with a sampling frequency of
4 MHz and an A/D resolution of 4 bits. The location of stations participated in the observations isshown in Figure 2.
The GEOTAIL moves so fast in the sky (seeFigure 3) that a priori values calculated by using
software developed for geodetic processing have insuﬃcient accuracy, in particular in delay rate thatis necessary for fringe stopping, so that we developed new a-priori calculation software for correlation processing, in which the motion of GEO3. “GEOTAIL” Observations
TAIL is interpolated by using a spline interpolation
method. Figure 4 shows the diﬀerence between deVLBI observations were carried out for GEOlay rate calculated using the conventional a priori
TAIL to learn the characteristics of telemetry

before the last earth swing-by planned on June 19,
2003 to cruise to Mars, due to a bad geometrical
relation between spacecraft attitude and earth position, i.e., the high-gain antenna of NOZOMI does
not point the Earth during this period. However
it is very important to navigate the NOZOMI precisely during this period to succeed in the last earth
swing-by. CRL and ISAS started collaboration todetermine NOZOMI orbit using a delta VLBI technique and to lead a NOZOMI mission to a success[Yoshikawa et al., 2001].
A test VLBI observation was planned in June
2002 at ﬁrst. Unfortunately NOZOMI had someproblems at that time caused by the large solar
ﬂare occurred on April 21, 2002. Thus we had carried out a series of test VLBI observations using
GEOTAIL instead of NOZOMI until it was recovered in August 2002.

20

IVS CRL-TDC News No.21

Figure 5. A spectrum of X-band telemetry signals from GEOTAIL observed at Kashima34 (left panel)and coarse delay search function calculated from correlated data on Kashima34-Usuda64 baseline (rightpanel). Observation date is June 4, 2002.

Figure 6. A spectrum of S-band telemetry signals from GEOTAIL in a range measurement mode observed
at Kashima34 (left panel) and coarse delay search function calculated from correlated data on Kashima34Usuda64 baseline (right panel) observed on June 4, 2002. Two micro sec ambiguities arising from 500
kHz spacing between carrier and subcarrier frequencies can be seen in the coarse delay search plot.

calculation software and that using the newly developed software. In a former calculation the position of GEOATIL in the equatorial coordinates is
ﬁxed at the middle point of each scan, while actual
motion in the celestial position is considered in alatter one. Maximum discrepancy reaches about
3.5 × 109 s/s in this case. It corresponds to 28 Hz

fringe frequency at 8 GHz, and this will result inloss of correlation amplitude for 1 sec integration
period, which is typical period for a conventionalcorrelator. Correlation processing is carried out bysoftware able to run at any PC without any dedicated hardware for correlation processing.
A spectrum at X-band telemetry signals andNovember 2002

21

Table 2. NOZOMI test observation schedule
Date(YYYY/MM/DD)
2002/09/17
2002/10/17
2002/10/18
2002/10/21

Time(UT)
12:39-18:23
17:54-19:33
17:54-19:34
16:54-20:04

2002/10/21

16:54-20:03

Stations (name with antenna diameter in meter)
Kashima34, Koganei11
Kashima34, Kashima11, Koganei11
Kashima34, Kashima11, Koganei11
Kashima34, Kashima11, Koganei11, Usuda64
Gifu11, Tomokomai11, Ymaguchi32, Mizusawa20
Kashima34, Kashima11, Koganei11, Usuda64
Gifu11, Tomokomai11, Ymaguchi32, Mizusawa20

Figure 8. An example of closure delay test for
GEOTAIL observations. Observations were carried out on June 25, 2002 at three stations,Kashima34, Kashima11, and Koganei11. Datawith large error bars represent quasor observations.
Although data are lagely scattered aroound 176.45
Figure 7. An example of X-band coarse search days, standard deviation of total data is wel lessfunctions for a quasor (3C273B) on Kashima34- than 10 nsec (∼5 nsec).
Usuda64 baseline. Observation date is June 4,
2002.
Since then we have carried out VLBI observations using a NOZOMI telemetry signal siveral
coarse delay search function calculated from cor- times (Table 2). Only X-band signals were obrelated data are shown in Figure 5. As shown in served because NOZOMI’s S-band telemetry was
the ﬁgure, group delay can be obtained without already malfunctioned on July 5, 1999 The set-up
any ambiguities. Figure 6 shows an S-band power of IP-VLBI system is as same as that for GEOspectrum and coarse delay search function when TAIL except for a base band signal frequency
telemetry mode is in a range measurement mode. (8410.00MHz). Examples of fringes observed for
In this case 2 µsec ambiguities appeared in the de- NOZOMI telemetry signals are shown in Figure 9.
lay direction. Figure 7 is an example of coarse delay Figure 10 also shows fringes for NOZOMI but in asearch function for a quasor (3C273B).
very weak telemetry signal case. It is thought to
A closure delay test was carried out to check the simulate the case when actual delta VLBI is necaccuracy of observed group delays. It is conﬁrmed essary. In any case, we succeeded in determiningthat an rms error of a few nsec was attained with group delay without ambiguities.
coarse delay measurements (Figure 8).
5. Conclusions
4. “NOZOMI” Observations
We have carried out a series of delta-VLBI obserAs NOZOMI recovered from a trouble, a VLBI vations of GEOTAIL and NOZOMI using IP-VLBI
observation became possible late August 2002. system for several months to learn characteristics

IVS CRL-TDC News No.21

22

Figure 10. NOZOMI fringes for very weak signal
case detected on Kashima34-Usuda 64 baseline.

are transferred through GALAXY network maintained by the NTT in collaboration with CRL andNAO. We also would like to express our appreciation to all GALAXY collaboration team members
for their helpful technical assistance.
References
Osaki, H., T. Kondo, and M. Kimura, Development of
versatile scientiﬁc sampling processor (VSSP) – A
practical approach, IVS CRL Technology Development Center News, No.20, pp.7-9, 2000.

Figure 9. NOZOMI fringes for two diﬀerent Kondo, T., Y. Koyama, M. Sekido, J. Nakajima, H.
epochs. Telemetry mode changed slightly between
Okubo, H. Osaki, S. Nakagawa, and Y. Ichikawa,two epochs, however group delay without ambiguity
Development of the new real-time VLBI techniqueusing the Internet protocol, IVS CRL Technology
is easily determined for both cases.
Development Center News, No.17, pp.22-24, 2000.
Kondo, T., Y. Koyama, J. Nakajima, M. Sekido, R.
Ichikawa, E. Kawai, H. Okubo, H. Osaki, M. Kimura,Y. Ichikawa, and GALAXY team, Real-time Gigabit
VLBI System and Internet VLBI System, IVS 2002
General Meeting Proceedings, pp.142-146, 2002.

of satellite downlink signals and to investigate thefeasibility of delay measurements. Preliminary results show that most of the cases we can determine
group delays for telemetry signals without any seNishida, A., The GEOTAIL mission, Geopys. Res.
vere ambiguities. Now an attempt to reﬂect VLBI
Lett., 21, 2871-2873, 1994.
data to an orbit determination is carried out by an
ISAS team. Next VLBI observations will be per- Yamamoto T. and K. Tsuruda, The PLANET-B mission, Earth Planets Space, 50, 175-181, 1998.
formed several months before the last earth swingYoshikawa
M., M. Sekido, N. Kawaguchi, K. Fujisawa,by scheduled on June 19, 2003 to determine orbit
H.
Hanada,Y. Kono, H. Hirabayashi, Y. Murata, S.
and to lead a Mars exploring project to a success.
Acknowledgement: We would like to thank “NOZOMI” VLBI collaboration team members of
ISAS, NAO, Yamaguchi University, Gifu University, and Hokkaido University for their kind observational supports. A part of NOZOMI VLBI data

Sawada-Satoh, K. Wajima, Y. Asaki, J. Kawaguchi,
H. Yamakawa, T. Kato, T. Ichikawa, and T. Ohnishi,
Present status and future problems of the orbit determination for Nozomi spacecraft, IVS CRL Technology Development Center News, No. 19, pp.37-40,
2001.

November 2002

23

International e-VLBI experi- 2. Kashima-Westford Experiments
ments
Three sessions were scheduled with the KashimaWestford baseline. The dates and time of thesesessions are shown in Table 1. In evlbi1 and evlbi3
Yasuhiro Koyama1 (koyama@crl.go.jp),sessions, K5 VLBI observation system was used at
Tetsuro Kondo1 , Junichi Nakajima1 ,Kashima and Mark-5 VLBI data recording system
Moritaka Kimura1 , Hisao Uose2 , andwas used at Westford. Eight frequency channels
Sotetsu Iwamura2
were assigned to X-band and six frequency channels were assigned to S-band. Sampling rate of1
Kashima Space Research Center
each channel was 4MHz and the total data rate
Communications Research Laboratory
was 56Mbps. Frequency assignment was same with
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan the conventional geodetic VLBI experiments per2
NTT Laboratories
formed under the Crustal Dynamics Project in the
3-9-11 Midori-cho, Musashino, Tokyo 180-8585, past. In the evlbi2 session, K5 VLBI observationJapansystem was used at Kashima and the 4 channels
conﬁguration of the K5 VLBI observation system
1. Introduction
was used at Westford. The latter system is consist
Communications Research Laboratory and NTT of a PC system running on the FreeBSD operatLaboratories are collaborating together to develop ing system and an IP-VLBI board which can samhardware and software systems for e-VLBI observa- ple 4 channels of video signals at various samplingtions using high speed IP based shared networks. speed from 40kHz to 16MHz. Only the X-band
A series of test experiments using the newly de- signals were recorded with the observation systemveloped systems were carried out in September both at Kashima and at Westford. The full set
and October 2002. Two baselines were selected and the subset of the K5 VLBI observation system
for these test experiments. One is the Kashima- used for the Kashima-Westford e-VLBI test experWestford baseline. The 34m antenna station at iments are shown in Figure 1. The 4-channel set
Kashima and 20m antenna station at Westford, of the system was small enough to be stored in a
Massachusetts, USA were used. The other is the suitcase and was transported in a check-in baggage
Kashima-Metsähovi baseline. The 34m antenna at of airline between Japan and the USA.
Figure 2 illustrates the high speed network route
Kashima and 14m antenna at Metsähovi, Finland
usedin the test e-VLBI experiments. To prewere used. The details of the test experiments areparetheinternational e-VLBI experiments, theintroduced in the following sections.

(a)Figure 1. K5 VLBI observation system. The full set of the system (a) can record 16 channelsof data while the subset of the system (b) can record 4 channels of data.

(b)

IVS CRL-TDC News No.21

24

BOSSNET+GLOWNET(GigE)

Haystack Observatory(Westford Station)

To Kashima Station
via GALAXY network
GEMnet(20Mbps)
2.4Gbps(OC-48)
Abilene Network

Figure 2. High speed network which was used in the experiment between Kashima and Westford stations.

(a)

(b)

Figure 3. Detected fringes at X-band (a) and S-band (b) observations towards 4C39.25. The PC software
correlator was used to correlate Mark-5 data recorded at Westford station and K5 data recorded at
Kashima station.

Table 1. Three sessions done with the KashimaWestford in October, 2002.
Exp. Codeevlbi1
evlbi2
evlbi3Date
October 8, 2002
October 9, 2002
October 15, 2002

Time
17:30UT-19:30UT
12:00UT-15:00UT
17:30UT-18:40UTGALAXY network was connected to the GEMnet
network which is the high speed research networkof the NTT Service Integration Laboratories. The
GEMnet has an international link between Japanand the USA at the data rate of 30Mbps. 20Mbps
of the bandwidth is assigned to the connection to

the Abilene network which are used by universities
and institutions along the USA. Haystack Observatory has been connected to the Abilene networkby using BOSSnet and GLOWnet. At the timeof the e-VLBI experiments, the BOSSnet was notavailable, and the alternative route was used. The
backbone of the Abilene network has a capacity of
2.4Gbps (OC-48). In total, the expected limit ofthe data rate was 20Mbps which was restricted at
the transpaciﬁc connection provided by GEMnet.
After evlbi1 and evlbi3 sessions, the data
recorded by the Mark-5 system at Westford station were converted to transferable ﬁles and transfered to Kashima by using the high speed network

November 2002

25

(a)

(b)

Figure 4. The observation system used at Kashima station for the Kashima-Metshähovi experiments.
(a) The ADS1000 sampler unit (right) is connected to the PC-VSI2000-DIM board (front) installed in
the Linux PC system (behind). (b) The actual conﬁguration during the experiments.

and FTP protocol. The data ﬁles were then converted to K5 compatible format and processed withthe data recorded with the K5 system at Kashima
for correlation processing. Software correlator programs of the K5 system were used for the correlation processing. On the other hand, the data
recorded with the K5 system at Kashima weretransfered to Haystack Observatory by using thehigh speed network. The data ﬁles were then converted to Mark-5 disk system and processed withthe data recorded with the Mark-5 system at Westford station. The Mark-4 hardware correlator system was used for the correlation processing. Although evlbi1 session was not successful, fringes
were successfully found from the evlbi3 session byboth of the correlators. Figure 3 shows the detected fringes at X-band and S-band for the radiosource 4C39.25.
The evlbi2 session was performed to evaluate thecurrent performance of the realtime data transmission between K5 VLBI observation systems overthe intercontinental distance. The K5 system iscapable of transmiting observed data in realtime
to the network by using IP protocol. The realtime transmission was tried at various data ratefrom 40kbps to 2Mbps from Westford station to
Kashima station. As the results, the transmissions were successful up to the data rate of 1Mbps,
while the 2Mbps data transmission could not be
succeeded.

RF frequency from 21.98GHz to 22.48GHz were received by both antennas and converted to the baseband. The baseband signals were then sampledwith ADS1000 sampler units. The ADS1000 sampler is capable of sampling analog signal at the rateof 1024Msps with one or two bits per each sample.
In the test e-VLBI experiments, one bit sampling
mode was used. The sampled digital data is generated based on the VLBI Standard Interface Hardware (VSI-H) speciﬁcations. At Kashima station,
the PC-VSI disk based recorder system equippedwith PC-VSI2000-DIM board was used to record
the data. At Metsähovi station, two Linux PC systems each equipped with VSIB VSI-H PCI dataacquisition board were used to record the data.
Both systems are capable of recording digital data
through VSI-H interface connectors. These systems are shown in Figure 4.
The data recorded at Metsähovi station weretransfered to Kashima by using FTP protocol after observations and processed for correlation processing on a Linux PC system using software correlator programs. The ﬁrst successful fringe was
detected from the observation towards the W3OH
maser source made on October 16, 2002. Figure 5
shows the cross power spectrum after 15 seconds ofintegration time.
4.

Significance of the Test Experiments
and Future Prospects

The successes of the international e-VLBI experiments have many important meanings. The sucA series of test e-VLBI experiments were per- cess of the Kashima-Westford experiments demonformed with Kashima-Metsähovi baseline from the strated that the PC disk based recording systems
end of September. The 34m antenna at Kashima are ﬂexible enough and it is possible to achieve
and 14m antenna at Metsähovi Radio Observatory compatibility between one system and the other by
in Finland were used for these experiments. The software programs. It also demonstrated that the3.

Kashima-Metsähovi Experiments

26

IVS CRL-TDC News No.21

Figure 5. The ﬁrst fringe detected with the Kashima-Metsähovi baseline from the observation towards
W3OH.

international network connection has been drastically improved recently and the e-VLBI observations with intercontinental baselines are becoming
realistic. The success of the Kashima-Metsähovi
baseline experiments have an additional meaning.
Two diﬀerent VSI recording systems have beendeveloped by two independent teams and these
two systems were used with the same sampler
unit interfaced with the VSI-H speciﬁcations. The
successes to exchange data recorded by diﬀerent
recording systems demonstrated the intended results of the standardization of the interface by VSIH.
One of our purposes of the e-VLBI system developments are to achieve minimal turn aroundtime to process international geodetic VLBI sessions. The current speed of the network demonstrated with the test e-VLBI experiments are notyet satisfactory for this purpose. The speed of
the transpaciﬁc network could be improved if we
can use a faster transpaciﬁc network route. Thereseems to be a few possibilities and we are currently
investigating these possibilities to expand the net-

work capacity for the Kashima-Westford baseline
e-VLBI experiments in the future.
Meanwhile, we are planning to improve hardware systems and develop software systems to makethe entire system robust and routine processing become possible. We are also planning to test a highspeed VLBI data transmission system which has
the maximum speed of 256Mbps using multiple IP
streams. We would like to perform these test eVLBI experiments in the future and continue efforts to realize routine e-VLBI experiments withinternational and intercontinental baselines.
Acknowledgement: The authors would like to appreciate many members of the Haystack Observatory and Metsähovi Radio Observatory who jointly
participated in the test experiments.

November 2002

27

Yamaguchi 32m Radio Telescope and an On-line Observation System
Kenta Fujisawa (kenta@sci.yamaguchi-u.ac.jp)
Yamaguchi University
Yoshida 1677-1, Yamaguchi city,
Yamaguchi 753-8512, Japan
1.

Introduction

National Astronomical Observatory of Japanwas given a 32m radio antenna from KDDI corporation in 2001, and has made use it as a radio
telescope (Yamaguchi 32m telescope) under collaboration with Yamaguchi university and other institutes. The telescope is planned to use as a powerfulelement of VLBI network as well as a large single
dish telescope. In this article, we describe the current status and scientiﬁc targets of this telescope.
A special feature of network-oriented observationis also mentioned.
2.

The Telescope

The antenna (Figure 1) was constructed in 1979
for tracking, telemetry and command to a telecommunication satellite (INTELSAT) for the ﬁrst time.
The mount is Azimuth-Elevation type covering thefull sky. The diameter of the main reﬂector is
32m and the cassegrain optics system with focusedbeam reﬂector assembly is equipped. The antennaﬁnished its role of telecommunication in 2001, thenwe have started to modify it to a radio telescope.
The feed horn was changed from corrugate (46 GHz) to straight horn with 8 GHz dual-channel
circular polarization feed for astronomical observation. A cooled dual-channel 8 GHz HEMT receiver is mounted. The system noise temperature
is about 50 K at 8 GHz. A 6.7 GHz feed and room
temperature receiver is also available although it is
exclusive use with the 8 GHz system.
A simple tracking system (PC base) has beendeveloped by NAO and Yamaguchi university. Encoded angle values (Az and El) from the existing
antenna control unit (ACU) was detected by thePC, then the PC output the error voltage to the
ACU in real-time. The error voltage is proportional
to the angle between the current angle and the target one. The maximum speed is 0.25 deg/sec, andthe angular resolution is 0.01 degree that is enoughfor observation at 8 GHz. For 22 GHz observationin future, the upgrade of the angular resolution to
0.001 degree is planned.

Figure 1. Yamaguchi 32m telescope at the KDDI
Yamaguchi Satellite Earth Station. The telescopeis on a building where the receiver and tracking systems are installed.
A preliminary result of the aperture eﬃciency
measurement is 65 % at 8 GHz, which is suﬃcient for astronomical observation, also suggesting a potential up to 22 GHz observation (surface
accuracy of lesser than 1.0 mm rms is inferred).
Back-end systems, e.g. VLBI terminal, line observation system, and observation system software arealso under development. Along with completion ofthese astronomical observation systems, test observations including VLBI will be started by the endof this year.
3.

Purposes

The Yamaguchi 32m telescope will be usedmainly for VLBI observation. We are planning
to organize some 8 GHz telescopes in Japan andmake VLBI observation of variable active galactic
nuclei and radio active stars. Frequent VLBI observations by taking advantage of the much observing time would give a chance to investigate those
short time-scale variables. We expect to expand
this 8 GHz VLBI network to other countries in future. Yamaguchi 32m is also expected to be a coobserving telescope with VERA and future space
VLBI project (VSOP2).

IVS CRL-TDC News No.21

28

A technical study of spacecraft navigation by
VLBI has been carried out in Japan under collaboration of ISAS, CRL, NAO, NASDA and Yamaguchi university. The Yamaguchi 32m telescope
would be used as an element of this navigation network. We have succeeded in a VLBI observation of
downlink signal of a spacecraft NOZOMI in October 2002.
4.

On-line Observation

Yamaguchi 32m telescope is going to have a special feature of ‘network based observation’ system.
According to the rapid expansion of information
network and increasing potential of personal computer (PC), studies of new VLBI system based on
the network have been started in the world. Oneof them is the GALAXY project that is collaboration among NAO, CRL, ISAS, and NTT since 1998.
Large telescopes (Usuda 64m, Kashima 34m, andsome other telescopes) around the Kanto area areconnected by high-speed dedicated network in the
GALAXY project to achieve real-time VLBI observation. The GALAXY project has been achieved
1 Gbit/sec observation between Usuda 64m andKashima 34m telescopes resulting 2 mJy detection
sensitivity.
Yamaguchi 32m telescope is being planned tojoin such real-time VLBI network via Super-SINET
operated by the National Institute of Informatics(NII). The high sensitivity and the distant location(800 km west to Kanto) of the telescope would provide not only the high sensitivity but also the highresolution for the real-time VLBI observation.

Figure 2. A small radio telescope mounted on an
equatorial for amateur astronomer. Broadcastingsatellite system is used for the dish and receiver.

Not only the dedicated high-speed network, weare planning to connect the telescope to the Internet for a new way of VLBI observation fully basedon the PC and the internet. Process of VLBI observation, e.g., observation, data archiving, datatranssion, and correlation are all done on PCs. A
small radio telescope (Figure 2) for this internet
VLBI system is being constructed in Yamaguchi
university.
Acknowledgement: We thank colleagues of KDDIfor supporting the Yamaguchi 32m project.

November 2002

29

Development of compact VLBI the network backbone are not reachable and universities where they are not to aﬀord to operate
systemlarge dish, the CARAVAN will provide an enviIkuto Yonezawa1,2 , Junichi Nakajima1 ,Hiroshi Ohkubo1 , Masato Tsuboi2 , andTakashi Kasuga3
1Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
Ibaraki University
2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
3
Hosei University
3-7-2 Kajino, Koganei Tokyo 184-8584, Japanronment of VLBI experiment at their closely located network nodes. Since the CARAVAN uses
commercial products, the price of the observation
package is reduced drastically. Network observations with high-speed optical ﬁbers realize VLBI
observation without storage media. Furthermore,
observation data are processed immediately. Details of the CARAVAN and initial operation results
are reported in this paper.
2.

CARAVANThe prototype CARAVAN consists of an equator
mounted prime focus 65-cm parabolic antenna, an
1. Introduction
optical guide telescope, and a receiver. A handy
We have developed the compact VLBI system for controller with optical object database can track
network based VLBI observation. This system is sources automatically by entering Right Ascention
named as the “Compact Antenna of Radio Astron- and Declination of radio star. In other case, theomy for VLBI Adapted Network (CARAVAN)”. telescope can be programmed from a scheduling
A low noise LNA in normal temperature, a wide PC. The entire view of the CARAVAN is shown inbandwidth Giga-bit AD sampler, and inexpensive the Figure 1. The price the CARAVAN telescope
PC data recording system enabled VLBI observa- is less than ten thousand US dollars. The receivertion with the small antenna. The CARAVAN is in- and down converter are assembled in the aluminum
tegrated as portable telescope site. Followings are container and they are operated in normal temperthe advantages. At the large telescope site which ature. Observation frequency is 22GHz. Receiver
can use high-speed network, the CARAVAN is ded- noise temperature is 140K. System noise temperaicated to network experiment before telescope time ture is 210K.
allocated to large dish. In observation sites where

Receiver unit

Optical telescopefor guide

Telescope
controller

Figure 1. Left: The dish front view of CARAVAN. Prime focused horn is connected to thereceiver by waveguide. Right: The side view of CARAVAN. Low noise Ampliﬁer is locatedbehind the small dish. Optical telescope is mounted beside the dish. Right Ascention and
Declination axis are balanced by counter weight.

IVS CRL-TDC News No.21

30

Figure 3. View of the CARAVAN and Kashima
34m antenna toward a same object.
Figure 2. Cross-power spectrum of between CARAVAN and Kashima 34m. The feature of watermaser is visible at telescope IF baseband 430MHz.

5.

Future plan

The CARAVAN will be moved to Ibaraki University and VLBI observation is planned with 50km
3. Observation
baseline. This observation is scheduled in DecemSingle dish observations were made for conﬁr- ber 2002. We will carry the CARAVAN to highmation of basic parameter. From the astronomi- speed network nodes and VLBI observation will
cal measurement, HPBW of 1.5◦ and aperture eﬃ- be performed for further study of small telescope
ciency of 0.5 were obtained. Then an interferom- VLBI.
eteric observation was carried out. We observed
NSTAR-B (geo-stationary satellite) with CARAVAN as a reference antenna of holography observation to measure Kashima 34m surface accuracy.
On October 2nd, 2002, we observed water maser
source W49N with CARAVAN and Kashima 34m
antenna. We have detected W49N fringes (Figure2). This observation was performed with 1Gbps
AD sampler and Gbps real time Correlator (GICO). VLBI preparation is in progress (Figure 3). It
is expected that radio source stronger than 20Jy is
detectable by CARAVAN and the 34m antenna for
integration time of 1 second.
4.

Operation scheme

The ubiquitous (anywhere, anytime) VLBI package consists of 4 components, sampler, i.e., small
telescope, Giga-bit AD portable reference, and PC
based observation system (PC-VSI). The system
is simple so that these units are carried by a car.
Installation of the equator mount is straightforward. Electric axis of 65cm parabolic antenna iscollimated by an optical guide scope. Then theantenna is set up using the polar star and major
bright stars. Even without optical stars in clear
sky, the wide beam dish allows the set up using
the sun.

November 2002

31

The implementation of the PC shown in Figure 2. This interface board is full compatible with VSI standardization and maximum
based Giga bit VLBI system
performance is 2048Mbps. The major speciﬁcations of the PC is described in Table 1. This PC has
two 64bit/66MHz PCI interfaces for the PC-VLBI
Moritaka Kimura (mkimura@crl.go.jp)
capture board and IDE-RAID board. The normal
and Junichi Nakajima
recording rate is 1024Mbps using 4-IDE hard diskswith RAID-0 mode. The total recording time is
Kashima Space Research Center
96 minutes with four 180GB disks under 1Gbps. It
Communications Research Laboratory
can extend recording time with more capacity disks893-1 Hirai, Kashima, Ibaraki 314-8501, Japan or using software data re-sampling. The recording
time is shown in Table 2. This system has four re1. Introduction
moval IDE hard disk cases, the media is changed
We are developing new Giga bit VLBI system when the data reached maximum. Hot swap is posintegrated around personal computer (PC). The sible by the RAID card selection.
performance of personal computers is increasing
quickly every year, it can replace almost part of the
VLBI back-end system. The PC based system has
several advantages. These advantages are ﬂexible
data analysis, the low cost and the good compatibility to other PC-VLBI. The PC-VLBI utilizes
high performance CPUs for software correlaton. It
can be used for real-time fringe test via Internet
data transfer during observation[1]. The PC correlator can switch the algorithm XF and FX. It
provides high frequency resolution for maser observation by FX and high correlation speed for geodetic or continuum observations by XF. The cost of
PC-VLBI is inexpensive, it is two order lower thanformer back-end systems. The low price will spread
VLBI research to many applications. Universities Figure 1. The PC-VLBI system: PC with PCin Japan started VLBI study and PC-VLBI soft- VSI board, display and a giga-bit A/D sampler
ware development. Since, the sampling data of (ADS1000). In PC-VLBI observation whole telePC-VLBI is written on hard disk as standard ﬁle scope IF sampling is accomplished by this combinasystem, any PC-VLBI systems employ the ﬁle sys- tion.
tem can read another PC-VLBI data and correlate
between heterogenous systems[2]. The data compatibility between PC-VLBI systems is no longer
severe problem between systems. We report our
PC-VLBI system and performance of the software
correlation toward future.
2.

PC-VLBI System: Hardwares

Figure 1 shows the PC-VLBI system. This system is consist of the A/D sampler based on VSI
standardization[3] and a PC. We have two typesamplers named ADS1000 and ADS2000. The
speciﬁcation of the ADS1000 was introduced by
Nakajima et al.[4]. It has 1-channel of 1024Msps
with 2-bit quantization.
Another A/D sampler ADS2000 has 16-channels of 64Msps with 2bit quantization. The targets of ADS1000 and
ADS2000 are high sensitive astronomical VLBI
and geodetic VLBI respectively. The VSI data
generated from the sampler are introduced to
PC through a PCI-bus by PC-VSI2000DIM board

Figure 2. The PC-VSI data capture board. The
1024/2048Mbps VLBI data is transferred to PCIbus continuously.

3.

PC-VLBI Software and Further Ability

The software correlation is utilized in PC-VLBI.
It provides new ability at fringe test. The software correlator enables near real-time correlation

IVS CRL-TDC News No.21

32

Table 1. Speciﬁcations of PC for the PC-VLBI
CPU
AMD Athlon 1.6GHz dual
Memory4GByteHDD
IBM Deskstar 180GXP(7200rpm/ATA100) × 4
Ether card Intel Pro 1000/XT Server Adapter
RAID card Promise Fasttrek SX4000

Table 2. The recording time with four-180GB harddiskssampling
mode
1024Msps/1bit/1ch
512Msps/2bit/1ch
512Msps/1bit/1ch
256Msps/2bit/1ch
256Msps/1bit/1ch
128Msps/2bit/1ch
128Msps/1bit/1ch
64Msps/1bit/16ch
32Msps/2bit/16ch
32Msps/1bit/16ch
16Msps/2bit/16ch
16Msps/1bit/16ch

total data
rate [Mbps]
1024
1024
512
512
256
256
128
1024
1024
512
512
256

recordingtime [minute]
96
96
192
192
384
384
768
96
96
192
192
384

via Internet data transfer transportaion. In thiscorrelation, the required dataset for the fringe test
is relatively small. It can detect calibration sources(> 1Jy) within 1-second sampling data (128Mbyte)
between medium sized telescopes. Since, this correlator has large lag and rate windows, the fringeﬁnding is straightforward even with large clock
oﬀset. Since, a performance of nominal Internet
transfer rate is not reached 1-Gbps, disk transportation will need a while for the correlations.
Once data is available, the software correlator
speed does not requires the observation speed ofexactly 1Gbps. It is able to complete correlationin reasonal period by shareing data in the network.
CRL had been used the software correlation up to
3-base line in practice. Here we present that software can correlate multiple telescopes observation
more than three. In this method PCs correspondto number of telescopes are working with giga-bitether (GbE) connection. The correlation PCs havesame speciﬁcation as observation PCs. The ﬂow of
VLBI sampling data is shown in Figure 3 as thecase of 4-telescopes A, B, C, D observation. EachPC read sampling data from own disks and send apart of the data to other PC. The four station data

Figure 3. The concept of the network distributed
computing. PCs A,B,C and D have a dataset of
stations A,B,C and D. In ﬁrst step, PC-A and PCB exchange observation data 4n and 4n+1 second,
the PC-C and the PC-D exchange 4n+2 and 4n+3.
In second and third step, the similar exchanges aredone at each pairs. After three steps, correlated
result of 4n, 4n+1, 4n+2, 4n+3 seconds are in respectively in PC-A, PC-B, PC-C and PC-D.

is correlated at each PC in three steps in time sequence. This data transfer are executed in parallel.
After correlation at each PC, the correlation data
are gathered. Typical ability of the GbE network
is around 800Mbps. Even at the GbE network below the Gbps, above three steps ﬁnish correlation
within 4-seconds. The data switching distribution
is eﬀective at multi baselines and high speed correlation. In this case, the software correlation is fourNovember 2002

33

Performance of software correlation

Throughput [Msps]

10000

1000
2-station (1-baseline)
3-station (3-baseline)
4-station (6-baseline)

100

10
XF type correlation
FX type correlation

1
1

10

100

1000

10000

100000 1000000

Lag Number
Figure 4. The XF and FX cross correlation performance evaluation using one PC. CPU cash memory
size aﬀect the performance loss at large lag.

times faster than one PC, thus this will enable realtime correlation between high speed linked telescope even with software correlator of limited CPU
performance. This processing scheme is able to apply to N-telescopes observation with N-port switching hub.
As for each PC programming, correlation speed
was considered as the ﬁrst priority. Numericalcodes are written in Single Instruction Multiple
Data (SIMD) instructions and multi threading for
multi-way proseccers are employed. The results ofperformance test of software correlation in XF and
FX using one PC are shown in Figure 4. The PC
speciﬁcation used for this evaluation is also an ordinary one in Table 1. Three lines indicated in
Figure 4 are requirement for 1Gbps real-time correlation with station number 2,3 and 4. Already theGbps performance is achieved at small lag number by XF correlation. It is enough for geodetic
VLBI which uses small lag window. The FX correlation dose not reach real-time processing speed
at present, The correlation speed is expected to beachieved by simply using multi-way processors PC
in near future, for example AMD hammer 8-way
processors[5].

References[1] Nakajima, J. et al., IVS CRL-TDC News No.16,
pp.15, June 2000.
[2] Jouko, R., IVS CRL-TDC News No.20, pp.2,
June 2002.
[3] Whitney, A.R., http://ivscc.nasa.gov/.
[4] Nakajima, J. et al., IVS CRL-TDC News No.17,
pp.18, November 2000.
[5] AMD home page, http://www.amd.com/.

IVS CRL-TDC News No.21

34

VLBI development merge into 3. PC-VSI, PC VSI interface board
to PC commodity
Aim the data acquisition over 1-Gbps, PCJunichi Nakajima (nakaji@crl.go.jp),
Moritaka Kimura, Yasuhiro Koyama,
Hiro Osaki, and Tetsuro Kondo
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

Introduction

PCs on the market integrated around high performance CPU with high-speed bus have reachedability to carry out normal VLBI observation andcorrelation data rate up to 1Gbps. The VLBI
data rate had been categorized as extreme highspeed application which require specially integrated recorders. So far the sophisticated systems
developed in laboratories are operated in telescope
networks. But it caused incompatibility between
the diﬀerent systems, especially in their media.
Currently, a typical telescope data rate of 1-Gbps,
corresponding to a bandwidth of 500MHz sampled
at 2-bit level, is handled by ordinary PCs and thepart of the VLBI system formally called “backend” are replaced to widely used PCs.The PC backend is expected to dissolve the incompatibility by
its ﬁle system. CRL have developed variety of the
VLBI interface boards enable conjunction of thetape-VLBI and PC-VLBI. These are the PC-VSSP
which substitute current moderate speed VLBI including AD and the PC-VSI which enables highspeed data acquisition beyond the Gbps.
2.

PC-VSSP, PC Versatile Sampling Processor

PCs with 4-channel analog input boards, thename commonly known as the “IP-VLBI”, the system aim replacement of the VLBI system up to
256Mbps. In the PC-VSSP, AD samplers are integrated into the board. Analog inputs, reference
signal and 1-pps signals are connected to the board
through BNC receptacles and all VLBI components
except BBC (baseband converter) are disappearedin observation site. The data rate of the PC-VSSP
is variable to 1-Mbps to adapt available network
to put real-time VLBI into practice. Spectroscopy
up to 16MHz bandwidth using 4-bit quantization
extend its application. VLBI softwares in observation, correlation and bandwidth synthesis are put
together in the PC. Software for this board are intensively developed by VLBI users and evaluatedthrough the mail reﬂector.

VSI2000-DIM board had developed. Diﬀerent fromthe PC-VSSP, the interface to outside PC is a digital. Here, internationally agreed VSI-H interface is
employed and the connector is MDR-80. Using this
PC-VSI board, currently two samplers ADS1000
and ADS2000 are connected. The ADS1000 is
1Gsps (1024Msps) extremely low jitter high speed
1-ch AD sampler. The sampler enables direct telescope IF sampling. This is used for high sensitivity observation. The other ADS2000 supports
16-channels 64Msps for future geodetic VLBI. As
well as the samplers, VSI connector enables theconnection of other VSI instruments. For example,
a MMM converter released from Metsahovi observatory, Helsinki University of Technology, will enable the VLBA/Mk-V type data converted VSI.
Another PC-VSI2000-DOM board can outputs the
VSI data from PC side when the VSI raw data isneeded.
4.

Conversion of VLBI Development

These two developments are related in their software development. Hardware controls usually done
by RS232 and GPIB are conﬁned to device drivers.
A simple scheduling software or a commonly used
FS/9 ﬁeld system can control these boards using
VSI-S (software) protocols. The correlation software is not hardware dependent too. Hence, all
VLBI researchers can participate the correlation
programming for the desired purpose as well as
the successive analysis on the PC. Opportunities
to touch radio telescopes raw data will enable interference removal technique and other interests tothe data.
In Figure 1, we can perceive that the there aredevelopment part and commodity part in the PCVLBI. The PC related technologies are rapidly improving at huge commercial demand. We will makefull use of these available products. Bottleneck of
the recent PC technology is the PCI-bus limitation of 64bit/66MHz. This will be increased several
times in its alternated generation.
As for the removable media, we can expect optical RAID storage and holographic disc in near future. The kind of media does not have much importance in the PC-VLBI system, and only separated
telescopes in remote islands will need them. Froma engineering point of view, the VLBI researcher
had been captivated the hardware compatibility.
The VSI-H standard established this compatibility. The VLBI data rate is adapted to common PC
and the ﬁle system handles them as data set. Further point, less diﬃcult data ﬁle compatibility is re-November 2002

35

Figure 1. PC-VLBI conﬁguration keep up with emerging PC hardwares. Rationalized back-end by PC
commodity will decrease the load of back-end development work in VLBI. Conjunction to existing recordersystems are used as the data backup.

maining between researchers. In the development
part, AD converters are still important as study.
In higher band we have to increase the sensitivityof telescope by the AD speed. With the higher sensitivity, small telescope can participate VLBI andthis will increase the range of VLBI users toward
temporal communication dishes to high skilled amateurs.

Communications Research Laboratory continues
these development to expand the VLBI ﬁeld. We
encourage universities and observatories participate with their unique idea to activate the community.

IVS CRL-TDC News No.21

36

Current Status of the VERA
Osamu Kameya (kameya@miz.nao.ac.jp),
Hideyuki Kobayashi, and the VERA teamNational Astronomical Observatory Japan
Abstract: VERA (VLBI Experiment of Radio Astrometry) has ﬁnished construction in 2002 March,and test observations of it are under going.
1.

Introduction

The VERA system consists of four VLBI stations at Mizusawa, Iriki, Ogasawara (Chichijima), and Ishigakijima. The maximum baseline(Mizusawa,Ishigaki-jima ) is 2300 km. Construction of the former three stations of VERA started
in 2000, and ﬁnished in 2001. The construction of
the fourth station at Ishigaki-jima started in 2001
and ﬁnished in 2002 March.
The VERA is a newly developed VLBI system,
which is dedicated to the diﬀerential VLBI. We
have succeeded to obtain not only the ﬁrst lights ofall stations but also ﬁrst fringes between them (Figure 1). We have also succeeded simultaneous VLBI
observations using the 2 beam systems(Figure 2).

Figure 2. Resutls of 2beam simultaneous observation between Mizusawa and Iriki stations.

Figure 1. VERA ﬁrst fringe between Mizusawa and
Iriki stations.

Figure 3. Expected circle of 10% errors in distancedetermination with VERA on the face on view of
the Galaxy.

2.

forming regions; mass including dark matter distribution in the Galaxy; and phase referencing to
improve sensitivity with long integration; precise
measurements of moon satellites.

Scientific goal

The scientiﬁc goal of theVERA is mainly measurements of the proper motion and parallax ofmasers in the Galaxy (Figure 3). 3D map andvelocity ﬁeld of the Galaxy will be clear by using the results. Additionally, there are some otherinteresting scientiﬁc goals: detailed velocity structure of molecular gas around evolved stars and star

3.

The VERA System

VERA antenna has dual-beam system withwhich we can observe two adjacent sources, simultaneously. Minimum and Maximum angular separation is 0.3 deg and 2.2 deg, respectively (see Figure 4). Ampliﬁed radio signals are digitalized andtransmitted to the observation building by using

November 2002

37

Figure 4. Concept of the dual beam receiving system.

optical ﬁber. The backend system, the frequency
standard, and operation computer system are in
the observation building of each VERA station. We
can observe, S/X, 22GHz, 43GHz bands (Figure 5).

Figure 5. The real view of the receivers. S/X spiralhorn is seen.

IVS CRL-TDC News No.21

38

VSOP-2, a next generation
space-VLBI mission
Yasuhiro Murata1 (murata@vsop.isas.ac.jp),
Hisashi Hirabayashi1 , and members ofSpace VLBI WG1,2,3
1

Institute of Space and Astronautical Science
Yoshinodai 3-1-1, Sgamihara, Kanagawa
229-8510, Japan
2
National Astronomical Observatory of Japan
Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
3
Other institutes
Abstract: Following the success of the VLBI Space
Observatory Programme (VSOP), a next generation space VLBI mission, dubbed VSOP-2, is being plannned in Japan. Higher observing frequencies, cooled receivers, increased bandwidths, dualpolarization capability, and a largere telescope diameter will result in gains in resolution and sensitivity by factors of about 10 over the VSOP mission. VSOP-2 science goals include studies of emission mechanisms in conjunction with X-ray ancl
gamma-ray satellites, studies of magnetic ﬁeld orientation and evolution in jets, and the highest resolution studies of spcctral line masers and megamasers. Here we describe the development of thespace antenna, high speed sampler, and the satellite system.
1.

Introduction

The successes of the VLBI Space Observatory Programme (VSOP) are described elsewhere[Hirabayashi et al., 2000]. Planning for the next
generation space VLBI mission VSOP-2 is well underway. The VSOP-2 spacecraft will have a 10 mclass antenna with cryogenically cooled low- noise
receivers and a downlink data rate of at least 1
Gbps, resulting in an improvement of an order ofmagnitude in sensitivity over the VSOP mission[Hirabayashi et al., 2001]. Observing frequencies
up to 43 GHz will allow high angular resolution
observations of the optically thin emission in many
AGN cores. An apogee height of at least 30,000
km will allow an angular resolution of 25 microarcseconds to be achieved at 43 GHz, correspnding
to around 10 Schwarzchild radii at the distance of
M87.
2.

VSOP-2 mission

2.1

The satellite

The VSOP-2 spacecraft will, like HALCA, be
three-axis stabilized. However, the VSOP-2 satel-

Figure 1. Possible appearance of the VSOP-2 satellite.
lite will probably employ an oﬀ-axis paraboloid antenna, in contrast to the on-axis design of HALCA.
One of the technical challenges is be the requirement placed on the surface accuracy of the meshantenna by the highest observing frequency of 43
GHz (a wave length of 7 mm). A schematic viewof VSOP-2 satellite is shown in Figure 1.
Due mainly to mass constraints, HALCA detected only Left-hand Crcular Polarization (LCP)
radiation, and its front-end radio-astronomy receivers were not cooled. The VSOP-2 satellite
will detect both LCP and RCP, and will use
cryogenic cooler to reduce the system temperature of the receivers by a factor of around three.
Sensitivity is ultimately limited by the coherencetime, which becomes increasingly aﬀected by atmospheric ﬂuctuations above the ground telescopes athigher frequencies. Several posibilities for ”phasereferencing” to improve sensitivity by extending
the coherence time are under study.
Observing requires a two-way link between thesatellite and a tracking station: a reference tone,
derived from a hydrogen maser frequency standard
is uplinked, and the science data down-linked fromthe satellite in real-time. HALCA used the 15
GHz band for uplink and a 128 Mbps downlink,but VSOP-2 will probably require a shift to the
37 GHz band for the 1-giga-bit-per-second tracking link. Testing of potential high-speed samplers
for the on-board has been started.
The comparison of the speciﬁcations of the
VSOP and VSOP-2 satellites is shown in Table 1.
2.2

Ground radio telescopes

Over 25 ground telescopes and arrays from 14
countries have participated in VSOP observations.
By the time of the launch of the VSOP-2 spacecraft
a number of new arrays and telescopes will also be
operation. It is expected that upgrades of the sen-

November 2002

39

Table 1. Comparison of the speciﬁcations of the
VSOP and VSOP-2 satellites. The options column
gives possible extensions of the baseline speciﬁcation for the VSOP-2 satellite which are currently
under discussion. In comparison, the VLBA has aresolution of 0.078 mas at 7 mm and a sensitivityof 4.9 mJy at 6 cm.
Ant. Diameter
Apogee Height
PeriodPolarization
Downlink rate
Bands (GHz)
Resolution
Sensitivity
LaunchVSOP
8m
21,500 km
6.3 hours
LCP
128 Mbps
1.6, 5, (22)0.3 mas140 mJy
1997 Feb

VSOP-2(options)
10 m
10∼15 m30,000 km< 40,000 km
8.9 hours
LCP/RCP
1 Gbps
1∼2 Gbps
5/8, 22, 43
5 to 8, 86
0.025 mas
12mJy ( 5 GHz, 25 m GRT)
2008

sitivity of ground radio telescopes will further improve the VSOP-2 space-ground baseline sensitivity. The VERA array of the National Astronomical
Observatory of Japan gives the possibility of phasereferencing observations with the VSOP-2 spacecraft.
2.3

Scientific targets

The VSOP mission has produced astronomical
results on AGN jet structure and evolution, highbrightness temperature sources, and the plasma
torus around the AGN, and so on.
The science goals of the VSOP-2 mission include: the stucly of emission mechanism in conjunction with the next generation of X-ray andgamma-ray satellites; full polarization studies ofmagnetic ﬁeld orientation and evolution in jets, andmeasurements of Faraday rotation towards AGN
cores; high linear resolution observations of nearby
AGN to probe the formation and collimation of jets
and the environment, around super-massive black
holes; and the highest resolution studies of spectralline masers and mega-masers, and circum-nuclear
diskd. Other non-thermal objects such as X-ray binaries, SNR, the Galactic Center, and gravitational
lenses will also be able to be observed.

Figure 2. A model of the central part of a single
antenna module to evaluate the adjustment of thesurface accuracy. The size of the radial bars is 1/2of the actual antenna module.

is lower than that required for the VSOP-2 mission.
We made the model of the central part of 1 segment(Figure 2) to evaluate how accurately the antennasurface can be adjusted. We succeeded to get an
accuracy of less than 0.2 mm rms.
3.2

High speed sampler radiation test

3.

The activities of the development

One of the problems for VSOP-2 is how to sample the data on-board, if we follow the same approach as HALCA. We asume a giga-bit rate ofdata sampling to obtain the desired sensitivity.
However, we can not ﬁnd any A/D sampler LSI
chips qualiﬁed for use in space. We tested a 10
Gbps, 1 bit sampler and a 1:16 demultiplexer, todemonstrate a possible solution for the on-board
high speed sampler. We carried out a 1000 krad
total dose test and a single event test. Figure 3
shows the LSI’s on the test bench for the single
event test. We conﬁrmed we can use those LSI’s
on the VSOP-2 orbit.

3.1

Antenna development

3.3

A 7-segment, oﬀset, 10-m class antenna (Figure 1) is under development. This antenna has alighter weight, and easier adjustment mechanism,
than that of HALCA. The basic concept of thistype of antenna was developed by NASDA for the
ETS-VIII mission, which will be launched in 2004.
However, the planned surface accuracy of ETS-VIII

On-board cooler and the LNA system
study

We are now designing the front-end of the VSOP2 observing system including the cooling system.
We made a simulation of a single band obrserving
system with an existing cooler rated for space use,
and found we could cool to 30 K. We know thatthe temperature depends strongly on the design

IVS CRL-TDC News No.2140

system and accelerometer.
3.6

System development

The total system design, including studies of thepower, mass and thermal budgets, and compatibility with the rocket fairing is important. Thesedevelopments have not yet progressed far, as weare now mainly working with the development of
individual componentd. We will move on to thetotal system development in the near future.
4.

Submission

There has been considerable activity within the
USA recently, culminating in the submission of awhite paper to NASA’s Structure and Evolutionof the Universe (SEU) roadmap committee. The
white paper describes iARISE, an international future space VLBI mission involving two orbiting
satellites, with nominally one of these being the
VSOP-2 satellite and the other a US-funded satelFigure 3. Three sets of the 10 Gbps sampler andlite. The advantage of a two spacecraft mission isthe demultiplexer on the test bench for the single
that by placing the two satellites in perpendicuevent test.
lar orbits, a better all-sky coverage and more twodimensional (u, v)-coverages can be obtained. The
likelihood of a two spacecraft mission eventuatingof the three-band observing system. Now we are will be better known later this year.
designing the front-end feed. We are studying the
The international cooperation and coordination
use of a MMIC HEMT ampliﬁer using chips sold required for VSOP observations make it one of the
by a Japanese LSI company.
most complex space science missions undertaken,
and similar level of collaboration between all mis3.4 Giga-bit data linksion elements — ground radio telescopes, tracking
A giga-bit data transmission requires more than station, orbit determination teams, correlators etc.
1 GHz bandwidth frequency allocation. The only — will be required for VSOP-2. Submission of thepossible band based on frequency allocation regu- VSOP-2 proposal will take place within the next
lations is 37–38 GHz. The uplink frequency will be year. Launch on an ISAS M-V rocket could be as
moved to 40 GHz, so that we can use the same cir- early as 2008.
cuits for up- and down-link frequencies. We stud- Acknowledgement: We gratefully acknowledge allied the link budget including signal transmission collaborators who have joined discussions about
in bad weather. The detailed study of this issue is VSOP-2 mission. This mission is planned based on
described by Springett [2002]. We also need to de- discussions with researchers from JPL, NRAO, CfA
velop the modulator and demodulator for the giga- (US), DRAO, SGL (Canada.), ATNF (Australia),
bit data transmission.
JIVE (Europe), Univ. of Ibaraki, Hosei Univ., Yamaguchi Univ., NAOJ, and ISAS (Japan).
3.5 Possibility of the phase-referencing
Phase referencing observations are a powerful References
method to determine accurate relative positions Hirabayashi, H. et al., The VLBI space observatory programme and the radio-astronomical satelliteof radio sources, and longer integration times for
HALCA, PASJ, 52, 955, 2002.
weaker sources. High speed switching between
sources (or a multi-beam antenna like the VERA Hrabayashi, H. et al.,Current status of the VSOP-2
mission, Galaxies and their Constituents at the Highantenna) and a ∼ 1 cm orbit accuracy are required.
est Angular Resolutions, ed. R.T. Schilizzi, S.N. VoBoth are very diﬃcult. We are now studying thegel, F. Paresce, and M.S. Elvis (lAU Symposium 205)
possibility of fast switching using the control mopp.428–429, 2001.
ment gyro (CMG), which is a higher torque actuaSpringett,
J.C., Achieving Future SVLBI Gbit Data
tor. We are also studying the possibility of obtainRate,menro
for VSOP-2 mission, 2002.
ing a higher orbit accuracy using an on-board GPS

November 2002

41

- News - News - News - News - News - News - News - News - News - News - News -Farewell ceremony of the Kashima 26m antenna
Taizoh Yoshino (yosh@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, JapanOn the day we had an IVS TDC symposium at Kashima, we had a small ceremony to say ourfarewell to the 26m antenna since it will be dismantled in the ﬁscal year of 2002. The 26m antenna
was constructed in 1968 and has been used for the tests of satellite communications and pioneering
VLBI work in Japan. In 1992, it was donated to Geographical Survey Institute (GSI) to continue global
and domestic geodetic VLBI observations. It worked actively till the new 32m antenna construction
in Tsukuba by GSI. This informal ceremony was held by CRL and GSI jointly. At the ceremony, Dr.
Yukiyasu Suguri, who was a former director of Kashima Branch at the time of antenna construction,and six guests who worked with the 26m antenna attended the ceremony from the CRL side. And
Dr. Kazuo Komaki, Director of Geodetic Department and GSI staﬀ attended. The participants of thesymposium also took part in the ceremony. On that day, we had a beautiful weather. After the ﬁnal
antenna tour, we thanked again to the 34 year’s great activity of the 26m antenna.

Photo 1. The Kashima 26-m antenna and the participants of the farewell ceremony.

“IVS CRL Technology Development Center News” (IVS CRL-TDC News) published by theCommunications Research Laboratory (CRL) is the continuation of “International Earth Rotation Service - VLBI Technical Development Center News” (IERS TDC News) published by CRL.
In accordance with the establishment of the International VLBI Service (IVS) for Geodesy andAstrometry on March 1, 1999, the function of the IERS VLBI technical development center was
taken over by that of the IVS technology development center, and the name of center was changed
from “Technical Development Center” to “Technology Development Center”.
VLBI Technology Development Center (TDC) at CRL is supposed
1) to develop new observation techniques and new systems for advanced Earth’s rotation observations by VLBI and other space techniques,2) to promote research in Earth rotation using VLBI,
3) to distribute new VLBI technology,4) to contribute the standardization of VLBI interface, and5) to deploy the real-time VLBI technique.
The CRL TDC newsletter (IVS CRL-TDC News) is published biannually by CRL.

This news was edited by Tetsuro Kondo and Yasuhiro Koyama, Kashima Space Research Center,
who are editorial staﬀ members of TDC at the Communications Research Laboratory, Japan.
Inquires on this issue should be addressed to T. Kondo, Kashima Space Research Center, Communications Research Laboratory, 893-1 Hirai, Kashima, Ibaraki 314-8501, Japan, TEL : +81299-84-7137, FAX : +81-299-84-7159, e-mail : kondo@crl.go.jp.
Summaries of VLBI and related activities at the Communications Research Laboratory are on theWorld Wide Web (WWW). The URL to view the home page of the Radio Astronomy Applications
Section of the Kashima Space Research Center is : “http://www.crl.go.jp/ka/radioastro/”.

IVS CRL TECHNOLOGY DEVELOPMENT CENTER NEWS No.21, November 2002
International VLBI Service for Geodesy and Astrometry
CRL Technology Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan