Demonstration of 16Gbps/station broadband-RF VLBI system
Alan Whitneyfor the VLBI2010 development team
MIT Haystack Observatory
22 October 20121st Intl VLBI Technology Workshop
MIT Haystack Observatory
1
VLBI data-rate drivers
• Geodetic VLBI (VLBI2010 project)• Near term: 16Gbps burst capture; 4Gbps sustained
– Can use of weaker sources/shorter integration times• Long term: ~32Gbps burst capture; ~8Gbps sustained
• mm-VLBI• Near term: Can use 16Gbps as soon as available
– Coherence time typically <30 sec• Long term: Phased-ALMA will support 64Gbps
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Goal of Demonstration experiment
• Assemble and demonstrate a complete dual-polarization VLBI broadband system capable of receiving and recording 4GHz of RF bandwidth
• Process recorded VLBI data through DiFX software correlator to produce fringes
– Analyze details to determine proper system functioning
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16 Gbps VLBI demonstration with Mark 6May/June 2012
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16 Gbps Mark 6Data System
32-diskarray(on four
10GigE lines)
DiFXSoftwareCorrelator
16 Gbps Mark 6Data System
32-diskarray(on four
10GigE lines)
Fringes!
Quasar
Westford(18m)
GGAO(12m)
8 x 500MHz
Up/down cnvtrs&
RDBE-S DigitalBackends
Up/down cnvtrs&
RDBE-S DigitalBackends
2-14 GHzdual-pol
System Block Diagram
5
Mark 6Recorder
32datadisks
16Gbps
Hpol
Vpol
BroadbandReceiver
Antenna
A
B
2x512MHz4Gbps
1
2
3
4
512-1024MHz
2-11 GHz
2-11 GHz
Up/DownConverters
RDBE-SDigital Backends
Nyquistfilter
Nyquistfilter
Effective LO8080 MHz
A
Nyquistfilter
Nyquistfilter
Effective LO9104 MHz
C
Nyquistfilter
Nyquistfilter
Effective LO8592 MHz
B
Nyquistfilter
Nyquistfilter
Effective LO9616 MHz
D
512-1024MHz
Sample at1024 Msps
VDIFFormat
Sample at1024 Msps
2x512MHz4Gbps
2x512MHz4Gbps
Sample at1024 Msps
Sample at1024 Msps
2x512MHz4Gbps
(2-11 GHz)
VDIFFormat
VDIFFormat
VDIFFormat
Front-end performance (Westford)
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RDBE-S Block Diagram
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4 Gbps
4 Gbps
Mark 6 prototype system
• Fully COTS hardware except for chassis and disk modules• Disk modules are variant of Mark 5-SATA modules• Fully open-source software• Prototype system used RAID0 disk management
– Slow-disk tolerant file system under development
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Prototype Mark 6 Recorder
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recording to 4 Mark 6 modules (32 disks)
DiFX correlation, postprocessing
• DiFX modified to support 1024 Msps sample rate/channel– HH and VV correlations done for all four frequency bands
• DiFX output converted to ‘Mark 4’ format and imported into HOPS• Fringe-processing through updated fourfit fringe-finding software• No phase-cal: For weak source, channel-to-channel phase adjustments
done by observing nearby stronger source
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0550+356 GGAO-Westford 16Gbps17 May 2012
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Delay rate (nsec/sec)
Time (sec)0 60
3C84 GGAO-Westford 16Gbps19 June 2012
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Delay rate (nsec/sec)
Time (sec)0 10
Summary
• Full 2x2GHz (dual-pol) RF bandwidth processed and recorded• Successful processing on DiFX software correlator• First demonstration of 16Gbps of type to be used for geodetic-
VLBI and mm-VLBI systems• Fundamentals of 16Gbps VLBI demonstrated; more work to do
before fully calibrated and operational system
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Questions?
16
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