1. Mark 5 / VLBA Correlator Topics
2006/2/23
VLBA 4-Gbps Upgrade
Jon Romney
NRAO, Socorro
EVN DBBC CDR
Bologna
2007 / 4 / 24
2007 / 4 / 24
J. D. Romney

2. VLBA 4-Gbps Upgrade Overview
Replace All Equipment Downstream from IFs
Wideband Sampler/Filter module.
2x 500-MHz inputs; 4-Gbps output.
Replacing BBCs / Samplers / Formatter.
Further details to follow.
Wideband Recording system.
Disk-based; 4-Gbps capacity; “Mark 5C”.
Compatible with existing Mark 5 module pool.
Wideband Correlator.
Stand-alone mini-WIDAR – OR – software/cluster system.
Wider bandwidth / higher spectral resolution / more flexible.
2007 / 4 / 24 – jdr
EVN DBBC CDR

3. VLBA 4-Gbps Upgrade Funding & Schedule
Funding Status
Wideband Sampler/Filter module.
Design development funded.
Implementation funding requested*.
Wideband Recording system.
Design funding requested*.
Wideband Correlator.
Software correlator completion funded.
Implementation funding requested* for intermediate cluster.
* funds requested from GBT track warranty arbitration payment.
Target Completion Date
… for all 3 prototypes: / 12 / 31.
2007 / 4 / 24 – jdr
EVN DBBC CDR

4. Wideband Sampler/Filter Basic VLBA Requirements
IF Input
Minimal: 2 x 500 MHz.
Optional: 4 x 500 MHz for dual-band dual-polar (etc.) modes.
Sampling
Sample clock: MHz.
Sample precision: 8 bits.
Filtering: Two Selectable Modes
Polyphase filter bank, spanning contiguous 500-MHz band.
Tunable “digital BBC” filters: 8 (possibly 16).
Bandwidths 62.5 kHz – 256 MHz / tunable to 1% of bandwidth.
Output truncation: 1 – 8 bits/sample.
2007 / 4 / 24 – jdr
EVN DBBC CDR

5. Wideband Sampler/Filter Concept History
Original
Exploit experience developed at NRAO from EVLA project.
Adapt relevant portions of EVLA data transmission system & correlator designs.
Haystack Collaboration
Similarities to Haystack DBE recognized.
Joint development of “DBE-2” selected as excellent opportunity for collaboration.
… at first NRAO/Haystack Technical Meeting, 2006 / 10 / 25 – 26.
2007 / 4 / 24 – jdr
EVN DBBC CDR

6. Wideband Sampler/Filter VLBA Concept History [2]
Modification for VLBI-2010 Requirements
Doubled input bandwidths to total 4 x 1 GHz.
Doubled sampler clock to 2048 MHz.
Added 10G Ethernet output, channel-packetized.
Required largest Xilinx Virtex 5 chip & corner-turner memories.
Required 2-board configuration for full capability.
2007 / 4 / 24 – jdr
EVN DBBC CDR

7. Most Recent NRAO-Haystack “DBE-2” Block Diagram
2007 / 4 / 24 – jdr
EVN DBBC CDR

8. Wideband Sampler/Filter VLBA Concept History [3]
Impact of iBob-2
Discovered Casper group’s iBob-2 development recently.
Recognized similarities to most recent NRAO-Haystack board.
Development timescale a concern at NRAO.
Had hoped to complete prototype board by 2007 / 9 / 30.
Resolution currently not clear.
2007 / 4 / 24 – jdr
EVN DBBC CDR

9. Compatibility & Collaboration Considerations
Compatibility among DBBC/DBE Devices
NOT nearly as critical as recording systems.
No media to be interchanged.
But identical filter profiles important for optimal baseline closure.
Possible global agreement on filter characteristics.
Would require all devices to support same minimum number of taps.
Collaboration on Common Elements
Possible sharing of FPGA code for filters.
Would require all devices to use compatible FPGAs.
2007 / 4 / 24 – jdr
EVN DBBC CDR

10. Thank you
2007 / 4 / 24 – jdr
EVN DBBC CDR