broadband delay system demonstration for vlbi2010 · 2008. 10. 2. · vlbi2010 progress report....
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VLBI2010 Progress Report 1NASA/GSFC January 28, 2008
Broadband Delay System Demonstration for VLBI2010
Arthur NiellMIT Haystack Observatory
for the Broadband Delay Development Team
VLBI2010 Progress Report 2September 26,2008
Geodetic VLBI
Terrestrial reference frame ~ 1 cmCelestial reference frameEarth orientation parameters
UT1 (time)NutationPolar motion
Two 24-hr “Rapid” sessions per weekAnother ~1.5 sessions/week for TRF and R&D
VLBI2010 Progress Report 3September 26,2008
Geodetic VLBI
Number of sites for geodetic VLBI ~ 40Use only 8 – 15 antennas per sessionLimited by:
Amount of observation time at individual sitesAmount of recording media
VLBI2010 Progress Report 4NASA/GSFC January 28, 2008
Motivation for new network
Current geodetic VLBI antennas and equipment are agingRadio frequency interference (RFI) is increasingAccuracy is limited by slow antennasGGOS requires geodetic position accuracy of 1 mm in 24 hours using VLBI, GPS, and SLR
VLBI2010 Progress Report 5NASA/GSFC January 28, 2008
IVS VLBI2010 Committee
Derive new system concept through simulations and sensitivity calculations
Turbulent atmosphere based on met dataClock and frequency standard performance System noise
Recommend small fast antennas with high delay precisionImplement in hardware to evaluate the concept
VLBI2010 Progress Report 6NASA/GSFC January 28, 2008
VLBI2010 Model
Fast slewing ≥12 meter diameter antennaNetwork of 16 – 40 antennas globally Broad-band feed and amplifiersMultiple bands covering 2 GHz to ~15 GHzData record rates of 8 gigabits per second and higherIdeally 24/7 operation and rapid results
VLBI2010 Progress Report 7NASA/GSFC January 28, 2008
~ 2.2 – 15 GHz Spanned RF Bandwidth
OLDOLD
Phase
Frequency (GHz) 142
Observing Frequency Bands
VLBI2010 Progress Report 8NASA/GSFC January 28, 2008
Main uncertainties
Atmosphere effectsTurbulence in space and timeMapping functions
Source structure phaseMust correct for structure phase over frequency range ~2.2 GHz to 14 GHz.
VLBI2010 Progress Report 9NASA/GSFC January 28, 2008
Structure–phase vs
frequency (simulation)
Generate spectrum from 1 GHz to 15 GHz from S and X band maps (Fey and Charlot2000) and approximated component spectraCalculate complex visibilities as function of frequency for 6400 km baseline at various orientations
VLBI2010 Progress Report 10NASA/GSFC January 28, 2008
0 5 10 15x 10
9
−1
−0.5
0
0.5
1
frequency(Hz)
visi
bilit
y ph
ase
(cyc
les)
0149+218
bsln: 6400 km
0° 30° 60° 90°120°150°
Structure Index 2/2(6 components)
VLBI2010 Progress Report 11NASA/GSFC January 28, 2008
0 5 10 15x 10
9
−1
−0.5
0
0.5
1
frequency(Hz)
visi
bilit
y ph
ase
(cyc
les)
0248+430
bsln: 6400 km
0° 30° 60° 90°120°150°
Structure Index 2/4(5 components)
Recovered source structure (Colliaud
and Charlot
2008 IVS GM)
δ=-40 δ=0 δ=+40 u-v plane
VLBI2010 Progress Report 13NASA/GSFC January 28, 2008
VLBI2010 Broadband Demonstration
Antennas - Westford 18 m and GGAO 5 mFeed
Phase cal injectionLow noise amplifiers
Optical fiberSplitter to 4 bands
Flexible local oscillatorsDigital back ends
Mark5B+ recorders
┐│Cooled ┘
(20K)
feed
LNA LNA
dewar
splitter splitter
UDC
UDC
UDC
iBOB Mk5B+
X1 Y1
iBOB
iBOB
iBOB
Mk5B+
Mk5B+
Mk5B+
UDC X2
X3
X4
Y2
Y3
Y4
X1 + Y1
X2 + Y2
X3 + Y3
X4 + Y4
DBE1
DBE2
X pol Y pol
2 gigabits/sec recorded on each Mk5B+
Total data rate: 8 gbps
Both senses of linear polarization used
Feed and LNAs cooled to ~20K
VLBI2010 Progress Report 15NASA/GSFC January 28, 2008
MV-3 5M Antenna @ GGAO
MV3Cryo
LNAs
& Feed in Dewar
8 gigabit/sec LOs
and
back end
VLBI2010 Progress Report 17NASA/GSFC January 28, 2008
Broadband Delay TeamBruce Whittier1, Mike Titus1, Jason SooHoo1, Dan Smythe1,
Alan Rogers1, Jay Redmond2, Mike Poirier1,Arthur
Niell1, Chuck Kodak3, Alan Hinton1, Ed Himwich3, Skip Gordon2, Mark
Evangelista2, Irv
Diegel2,
Brian Corey1, Tom Clark3 , Chris Beaudoin1
(in reverse alphabetical order)1
MIT Haystack Observatory
2
HTSI, Inc3
GSFC/NVI
with thanks to Sandy Weinreb
and Hamdi
Mani, Caltech
VLBI2010 Progress Report 18NASA/GSFC January 28, 2008
Status and plans -
2008 September
Fringes have been demonstrated for X-bandBoth sites set up for four-band observationPhase cal testing in progress
Phase cal is critical for phase delayFirst multi-band observations planned for next two weeks
VLBI2010 Progress Report 19NASA/GSFC January 28, 2008
Next stepsSet all four bands at same frequencySpread bands to demonstrate phase connection on simple sourceLook at effect of complex source structureImprove sensitivity of 5 m antennaOrder 12 m antenna to replace 5 m antenna near Washington, D.C., probably similar to NZ and AuScope antennas.
12 m Antenna
VLBI2010 Progress Report 22NASA/GSFC January 28, 2008
Lindgren feed(linear pol’n)
LNA Cryo Refrigerator
20K Station
77K Station