1. Demonstration of 16Gbps/station broadband-RF VLBI system Alan Whitney for the VLBI2010 development team MIT Haystack Observatory 22 October 2012 1 st Intl VLBI Technology Workshop MIT Haystack Observatory 1

2. 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

3. 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 3

4. 16 Gbps VLBI demonstration with Mark 6 May/June 2012 4 2-14 GHz dual-pol

5. System Block Diagram 5

6. Front-end performance (Westford) 6

7. RDBE-S Block Diagram 7 4 Gbps

8. 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 8

9. Prototype Mark 6 Recorder 9 recording to 4 Mark 6 modules (32 disks)

10. Mark 6 Ethernet read rates 10

11. Mark 6 file-write rates 11

12. 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 12

13. 0550+356 GGAO-Westford 16Gbps 17 May 2012 13 Delay rate (nsec/sec) Time (sec) 0 60

14. 3C84 GGAO-Westford 16Gbps 19 June 2012 14 Delay rate (nsec/sec) Time (sec) 0 10

15. 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 15

16. Questions? 16