Giga-bit Geodesy e-VLBI at 22GHz Ｈｉｒｏｓｈｉ Takaba Gifu University, Japan
e-VLBI network NTT Connection(2.4Gbps) JGN3 (10Gbps) Super Sinet(4.8Gbps) Future Plan North American Plate Hokkaido Univ 11m ISAS Usuda 64m NAOJ Mizusawa 20m Eurasia Plate NAOJ Nobeyama 45m Gifu Univ. 11m GSI Tsukuba 32m NAOJ Yakaguchi 32m NICT Kashima 34m NAOJ Kagoshima 20m Pacific Plate Philippine Sea Plate
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, NAOJ S/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 ２Gbps、16seconds integration SNR～５８ （Apr.2007）
Purpose of this Work • Development of the Giga-bit e-VLBI system at 22GHz for Geodesyand 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 Control Computer A/D Converter 2 channels XF Correlator 3 Baselines Optical Transceiver 2.4Gbps×2 links
Geodesye-VLBI using the Super-Sinet X Gifu Univ. Tsukuba 11m Telescope 32m Telescope S X S X Real time Correlator A/D converter 2Gbps×2ch A/D converter 2Gbps×2ch S Optical Transceiver OC48(2.4Gbps)×２ Optical Transceiver OC48(2.4Gbps)×２ Tsukuba CATV Gifu Prefecture’s Information Super Highway 100km 7km Real time Correlator Super- Sinet Super- Sinet Super-Sinet OC48(2.4Gbps) Super-Sinet OC48(2.4Gbps) Super-Sinet OC48(2.4Gbps) Fusion Research Lab. High Energy Lab. 300km 100km NAOJ（Mitaka City）
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 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 1024MHz sampling ＝＞1 lag ～ 1 ns
Delay time determination from phase gradient Phase(degree) Original data Frequency (MHz) Rotate phases when gap exists Liner Fitting => delay time
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 Sigma of the delay time by phase gradient [ps] Weak Source Strong Source Sigma of the delay time by Gaussian fitting [ps]
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 A 32-GHz signal was successfully digitized with 3 bits. (Kawaguchi, 2006) DMX ＲＦ Ｓｉｇｎａｌ DMX ADC
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 - Giga-bit e-VLBI Xband pico-seconds １ｎｓ 1day Obs. #
Differences of the delay time for K5 and Giga-bit e-VLBI Almost same as K4 K5 - Giga-bit e-VLBI Xband pico-seconds
Differences of the delay time for K4 and K5 No large drift！ K4-K5 (JD0404) Xband pico-seconds
K5 - Giga-bit e-VLBI Xband Sband
P-cal system cancels the delay time drift by using the same path for reference signal transfer with down converter! Receiver Room LNA P-cal Down Converter Observation Room VLBI Back end IF signal by optical fiber cable 5MHz signal by co-axial copper cable Hydrogen Maser More than 100m for large Antenna
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
Receiver Room LNA P-cal A/D Converter Digital Filter Observation Room VLBI Backend VSI data by optical fiber cable Hydrogen Maser 5MHz signal by co-axial copper cable More than 100m for large Antenna
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!