1. Atacama Large Millimeter/submillimeter Array Expanded Very Large Array Robert C. Byrd Green Bank Telescope Very Long Baseline Array Spectrometer PDR John Ford (NRAO) – The preliminary Design

2. Why a New Spectrometer? New SpectrometerOld GBT Spectrometer Polyphase Filter Bank for RFI rejectionAutocorrelation Spectrometer 256 level samplers3 level samplers 16 high-speed samplers8 high-speed samplers 1350 MHz bandwidth/sampler800 MHz bandwidth/sampler 800 MB/s max disk I/O rate< 25 MB/s max disk I/O rate New technology (FPGA based, Virtex-{5,6} Designed and built in early 1990’s 2

3. Summary of Required Observing Modes 3

4. Overall Block Diagram 4

5. Analog System Adapts output of Converter Modules to the ADC – Low-pass filter – Amplification – Test tone injection Clock distribution – Split and amplify clock signal – Distribute to all ROACH boards 5

6. Roach Assembly

7. ROACH Block Diagram 7

8. ROACH 2 8

9. 3 GS/s ADC Board 9

10. Clock Synthesizer Board 10

11. Fujitsu Switch in its Natural Environment 11

12. Computing Nodes 12

13. Nehalem Node 13

14. Storage Subsystem Project will supply ~100 TB of disk subsystems – Connected to 10 GbEthernet – Fast enough to support writing directly into subsystem for most observing (But not pulsar searching) – Data accessible for astronomers simultaneously with spectrometer use Project will not supply – VAO integration – Archiving software or methodology – Long-term storage media 14

15. Preliminary Design Work Developing support hardware – IF system interface Anti-alias low-pass filters Noise/test signal injection Amplification – Analog to Digital Converter sampling clock generation/distribution – 1 Pulse Per Second distribution – Packaging 15

16. Preliminary Design Work Concentrating on the hard parts – 3 GS/s sampling and PFB/FFT calculations – Heterogeneous Computing Approach Divide processing into front/back ends Use FPGAs to fully process bandwidths greater than 200 MHz Use FPGA front-ends to pre-process, split and packetize data, then GPUs to provide fine channelization on narrower chunks – Software Design Adapting concepts and code from the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) Adding support for the K-band FPA processing pipeline Integrating with the GBT Monitor and Control System for user ease. 16