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