VEGAS Pulsar Project Meeting: 2015 November 2nd 2:00 - 3:00pm ET

Room / Connection Details

  • GB-137 / Soc 280
  • 434-817-6443

Housekeeping Details

  • Main wiki page
  • gbsapp Mailing List
  • Location and regular date and time of meeting - agreed weekly on Mondays; GB-137 / Soc-280; 2-3pm ET
  • ETK codes:
    • Electronics: 432510.GB3015
    • Software: 893252.GB3015
    • Science: 432540.GB3015

Resource Allocations

LYNCH, Ryan 0.25


  • Vereese, John, Marty, Justin, Jason, Richard, Ryan, Ray, Dave

BOF file status updates

  • c1500x4096 mode
    • Randy and Jason were able to build and test a first version of this mode
    • Previous version had bug affecting bandpass that had been attributed to timing errors, but turned out to be a bug in the model. This is now fixed.
    • Jason will send Ryan file name and Ryan will test
    • Will use this as a model build for other modes insofar as possible
  • Fix for nchan calculation in coherent modes
    • There were two levels of this bug that are now fixed in the above build, with a solution for future builds
  • Bandpass issues in i0800x0064, 0128, 8192
    • No updates right now (working on c1500x4096)
  • Duplicated signal in i0800x8192
    • No updates right now (working on c1500x4096)
  • Switch from 32 to to 16-bit port numbers
    • No updates (ask Randy), but consensus is that it shouldn't be a problem


  • Configtool MR
    • Questions about a few parameters
      • if3 is the center frequency given to VEGAS in baseband
    • How to tune to avoid Fs/4 spike in low bandwidth modes?
      • Clock valon at some higher sampling rate and shift center frequency to avoid spike
      • Can use lbw modes as a basis for 100 MHz and 200 MHz modes
      • In VEGAS 187 MHz bandwidth is set by digital filter, but this can probably be modified to handle 100 and 200 MHz
      • Run 100 MHz and 200 MHz bandwidth modes at Fs = 3 Gsamps/s
    • As previously discussed, we will only support different parfiles for different banks, but will keep in mind that we would like to provide greater flexibility going forward.
  • GBT Status shared memory parameters in PSRFITS headers
    • Ray will go for look at the script this week and make sure things are running properly
  • Switching signal generation
    • Manager invoking switching signal generator from backend class
      • Justin will implement in Manager
      • Ryan will test on srbs and/or GBT hardware this week during maintenance
    • Test of BOF files on srbs
      • Not done but don't do it until we see if the Manager modifications work
  • Matrix HPC
    • FITS writer
      • Writing something for HBW spectral line, still need to make sure it is writing something sensible
      • Once spectral line mode works will start looking at pulsar fits writer
    • ROACH tests of switching state and throughput
      • Continuing throughput tests. Can handle spectral modes, not sure yet about pulsar modes
      • If it can handle VEGAS mode 1, should be able to handle most pulsar modes
      • The tricky case will be the fast search modes with 10x throughput of H1K

GBT testing

  • Frequency shifting issue
    • Ryan to test Astrid fix on Tuesday
  • Dave would like to do some tests with Ray and Jason during maintenance to test BL hardware


  • PCB work underway

Discussion about VEGAS/DIBAS-style backend for FAST

  • FAST is definitely interested in a system like this
  • They are building their own digital backend but are behind schedule and would like a first-light backend on a short timescale
  • They are developing a receiver with a 270 -- 1000 and 1000 - 1700 MHz with both shifted to baseband and would also like to process entire 1430 MHz bandwidth on same system
    • Could do this on exisitng hardware and software
    • Would like to run all three cases simmultaneously and with a combination of spectral line and pulsar modes
    • Could handle this with dealer/player
    • We think we could just build another DIBAS
    • Would have to implement MMCM calibration in dealer/player and make modifications to spectral line modes for variable names
  • Would provide them with switching signal generator, valons, chasis but not IF modules
    • Could propose to build them an AP
  • They would like this by Spring so they can learn how to use is it by September 2016
  • They have offered to send 2--3 engineers to GB to do the work
    • Would have to bring them up to speed but they could probably make the mods themselves
  • Next step is to have FAST management make a formal request to NRAO
    • Simmultaneously make a high level estimate of what work would be necessary
  • FAST is also interested in ultra-high resolution spectroscopy (~1 million channels per bank)
    • Could use a similar approach as SETI, feeding 8 streams into 8 GPUs to do high-resolution spectroscopy
    • If we helped implement this it would be down the road
    • SETI is planning to do this off-line, FAST would want it on-line

Date / Time of Next Meeting

  • November 9

-- RyanLynch - 2015-11-02
Topic revision: r2 - 2015-11-02, RyanLynch
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