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

2

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)

6

RDBE-S Block Diagram

7

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