Giga-bit Geodesy e-VLBI at 22GHz

Ｈｉｒｏｓｈｉ　 Takaba Gifu University, Japan

Pacific Plate

Philippine Sea Plate

Gifu Univ.11m

Eurasia Plate

North American Plate

NAOJKagoshima

20m

NTT Connection(2.4Gbps)JGN3 (10Gbps)Super Sinet(4.8Gbps)Future Plan

GSITsukuba

32m

NICTKashima

34m

Hokkaido Univ 11m

NAOJMizusawa

20m

ISAS Usuda 64m

NAOJYakaguchi

32m 　

NAOJNobeyama

45m

e-VLBI network

鵜飼　 Cormorant Fisher, a famous fishing method in Gifu

鮎（ＡＹＵ）

From May 11 to Oct 1

Accuracy of the Geodesy VLBI

Accuracy of delay time for one observation Δτ 　∝　 1/ ＳＮＲ Δτ 　∝ 1/Bandwidth ～ 1/(Radio Frequency)

Accuracy of the Geodesy VLBI Formal Error ∝ 　 Δτ/√(Number of observations)

=> e-VLBI with Higher Frequency!

Importance of Geodesy for Radio

Astrometry

For micro-arcseconds Astrometry=> less than 1mm accuracy is required! 　

VERA Project, NAOJS/X, 22GHz, 43GHz

Status for ２２ＧＨｚ System of Gifu 11m antenna

Install 22GHz receiver （ Dec. 2006 ） Cooled LNA to 11K, Trec ～ 20K Tsys ～ 100K at zenith 2Gbps e-VLBI Tests （ April-Dec. 2007 ）　　 with NICT Kashima 34m antenna 1Gbps geodesy VLBI (Tape Recording) with NAOJ VERA (Oct. 2007)

Gifu 11m － Kashima 34m 22GHz Band e-VLBI

２ Gbps 、 16seconds integration SNR ～５８　（ Apr.2007 ）

Purpose of this Work

Development of the 　　　 Giga-bit e-VLBI system at

22GHz　 for Geodesy 　 and

Astrometry, 2Gbps x 2ch (Now) 2Gbps x 4ch (Next Step)

Giga-bit e-VLBI System

Hardware　　 A/D converter(ADS1000): NICT 　 1024Msps, 2bit sampling =>2.048Gbps　　 Optical transceiver: NAOJ 　 XF type 256 lags Correlator: NAOJ Software　　 Observation Software: Gifu Univ. & NAOJ Analysis Software: Gifu Univ.,NICT & GSI

Giga-bit Realtime e-VLBI instruments at Gifu University

Optical Transceiver

2.4Gbps×2 links

A/D Converter2 channels

XF Correlator3 Baselines

Control Computer

Real timeCorrelator

Optical TransceiverOC48(2.4Gbps)× ２

A/D converter2Gbps×2ch

Super-Sinet OC48(2.4Gbps)

Super-Sinet OC48(2.4Gbps)

Super-Sinet OC48(2.4Gbps)

Fusion Research Lab. NAOJ （ Mitaka City ） High Energy Lab.

Tsukuba Gifu Univ.

11m Telescope 32m Telescope

Gifu Prefecture’sInformation Super Highway

TsukubaCATV

Super- Sinet

Super- Sinet

Geodesy 　 e-VLBI using the Super-Sinet

Optical TransceiverOC48(2.4Gbps)× ２

A/D converter2Gbps×2ch

Real timeCorrelator

S

X

S XS X

100km 7km

300km 100km

Real Time e-VLBI, Gifu11m-Tsukuba 32m 　　　　　　　 Sband was processed at Mitaka Correlator　　　　　　　 Xband was processed at Gifu Correlator　　　　　　　 Display the fringe pictures every 1 seconds

Sband

Xband

Geodesy VLBI with K4/K5 and e-VLBI

Results of the K4/K5 and e-VLBI coincidents within 3mm !

Problems for Wide-Band VLBI(found from S/X bands e-VLBI)

K4 or K5 uses Narrow Bands System with P-cal , video converters, and many samplers

=> Determine delay time by Band Width Synthesis Method

Giga-bit system uses Wide Band IF with only one sampler!

How can we determine Delay Time?

Tsukuba32m-Gifu11m e-VLBI data 1 second integration data 　

1024MHz sampling 　＝＞ 1 lag ～ 1 ns

Giga-bit e-VLBI data have very high SNRs ,can determine delay time every 1 second!

Delay time by Gaussian fitting

1ns

1 sigma 40ps, 100seconds =>4ps

-200

-150

-100

-50

0

50

100

150

200

0 100 200 300 400 500 600

[MHz]周波数

[]

位相

度

- 9000

- 8000

- 7000

- 6000

- 5000

- 4000

- 3000

- 2000

- 1000

00 100 200 300 400 500 600

Original data

Rotate phases when gap exists

Liner Fitting => delay time

psf 360

106

Delay time determination from phase gradient

Frequency (MHz)

Phase(degre

e)

Problem for the Phase Gradient Method

Phase shift caused by the band pass filter

Accuracy of the delay time,Gaussian fitting vs Phase gradient => Gaussian fitting method is better

0

30

60

90

120

150

0 30 60 90 120 150

σ [ps]従来の方法での

σ[p

s]位

相傾

斜法

での

Sigma of the delay time by Gaussian fitting [ps]

Sigm

a of the delay time by phase gradient [ps]

Strong Source

Weak Source

High Speed A/D converter

NAOJ is now developing 35GHz A/D => Direct Sampling should be possible at

22GHz with higher mode sampling mode => No Band Pass Filters, Down Converters!

=> Good phase stability for wider band width!

InP HBT AD Converterdeveloped by NAOJ

ADC

DMX

DMX

ＲＦ　Ｓｉｇｎａｌ

A 32-GHz signal was successfully digitized with 3 bits.

(Kawaguchi, 2006)

Another Problem for Giga-bit e-VLBI

Comparison of the delay time for K4, K5, and Giga-bit e-VLBI

=> large drift of the delay time exists

only for Giga-bit e-VLBI!

Differences of the delay time for K4 and Giga-bit e-VLBI

K4-sinet J D0404)（

-1000

-500

0

500

1000

0 20 40 60 80 100 120 140

遅延

時間

の差

（ｐ

ｓ）

１ｎｓ

Obs. #

Xband

pico-seconds

K4 - Giga-bit e-VLBI

1day

K5-sinet J D0404)（

-1000

-500

0

500

1000

0 20 40 60 80 100 120 140

遅延

時間

の差

（ｐ

ｓ）

Almost same as K4

Differences of the delay time for K5 and Giga-bit e-VLBI

Xband

pico-seconds

K5 - Giga-bit e-VLBI

K4-K5 (J D0404)

-1000

-500

0

500

1000

0 20 40 60 80 100 120 140

遅延

時間

の差

（ｐ

ｓ）

No large drift ！

Differences of the delay time for K4 and K5

Xband

pico-seconds

K4-K5 (JD0404)

K5-SINET (J D0509)

-1000

-500

0

500

1000

0 50 100 150 200

OBS. NUMBER

delt

a d

ela

y (

ps) X 　

band

-1000

-500

0

500

1000

0 50 100 150 200

OBS. NUMBER

delt

a d

ela

y(p

s) S 　band

K5 - Giga-bit e-VLBI

LNA

P-cal

HydrogenMaser

DownConverter

VLBIBack end

5MHz signal by co-axial copper cable

IF signal by optical fiber cable

Observation Room

Receiver Room

More than 100m for large Antenna

P-cal system cancels the delay time drift by using the same path for reference signal transfer with down converter!

Giga-bit e-VLBI system for 22GHz

High Speed Sampler, working at 22GHz Eliminate band-pass filter and down

converters Use digital filter for multi-channel analysis

P-cal injection for Phase calibration and delay time

correction

LNA

P-cal

HydrogenMaser

A/DConverter

VLBIBackend

5MHz signal by co-axial copper cable

VSI data by optical fiber cable

Observation Room

Receiver Room

More than 100m for large Antenna

DigitalFilter

Conclusion

Radio Astrometry needs Geodesy VLBI 22GHz e-VLBI system is under-developing

Some Problems were fond for Giga-bit e-VLBI, but will be cleared by using the new RF A/D converter and P-cal system!