VEGAS Pulsar Project Meeting: 2015 October 12th 2:00 - 3:00pm ET

Room / Connection Details

  • GB-137 / Soc 280
  • 192.33.117.12##7144
  • 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

BLOSS, MARTIN ALAN 0.05
BRANDT, JOSEPH JOHN 0.10
CREAGER, RAY 0.65
DEMOREST, PAUL 0.05
RICHMOND-DECKER, JUSTIN 0.20
FORD, JOHN M 0.05
MELLO, MELINDA JANE 0.05
MCCULLOUGH, RANDY L 0.25
RAY, JASON 0.55
PRESTAGE, RICHARD 0.05
LYNCH, Ryan 0.25
VAN TONDER, VEREESE 0.10

Present

  • Ray, Justin, Vereese, Scott, Ryan, Paul, Marty

Agenda

BOF file status updates

  • c1500x4096 mode
    • From Randy: "Still working to resole timing errors with c1500x4096ch build. Plan to have another build running overnight tonight."
  • Fix for nchan calculation in coherent modes (no update)
  • Bandpass issues in i0800x0064, 0128, 8192 (no update)
  • Duplicated signal in i0800x8192 (no update)
  • Switch from 32 to to 16-bit port numbers (no update)

Software

  • Comments from Melinda on configtool MR
    • Melinda suggested some minor changes, but thinks it mostly looks good
    • Ryan and Justin will talk about use cases for, e.g., rest frequency updates
  • GBT Status shared memory parameters in PSRFITS headers
    • Expected behavior is that "something" reads from status shared memory and puts it in PSRFITS header
    • Manager does not typically put position, telescope, etc. because it is in other spectral line fits file, so nothing has to be changed in the manager
    • Need to identify the process that updates the fits headers; it is a python script that runs as a daemon and updates shared memory from the status database every second
    • Will need to check the frequency labels carefully for coherent dedispersion modes
  • Switching signal generation
    • Investigation of backend class
      • Can be applied to any backend class
      • Manager would be the one to apply this; Justin and Ray will investigate whether this is being called
    • Test of BOF files on srbs
  • Matrix HPC
    • Ray has a high bandwidth accumulator working
    • Justin is working on the FITS writer; will begin testing soon
    • Next step is to test it on a real roach to test switching state and throughput
    • Total power mode does work using package generator
  • TBIN rounding issue
    • Now using double precision float
    • Increased precision seems to have fixed this. Ryan's tests show no phase drift in any 1500 MHz modes.

GBT testing

  • Frequency shifting issue
    • Ryan injected test tone at the receiver and looked at recovered frequency
    • True shift was found to be 140 MHz (had originally reported ~138 MHz)
    • With help from Adam we were able to track this down to incorrect tuning of LO2 when switching from spectral line to pulsar modes
      • Ryan was configuring for spectral line mode with 1080 MHz bandwidth, which set Fs = 2160 MHz
      • configtool set LO2 such that sky frequency was centered at Fs/4 = 540 MHz for baseband input to VEGAS
      • When ROACH was reconfigured for pulsar mode with 800 MHz bandwidth, Fs was reset to 1600 MHz
      • LO2 should have been retuned so that sky frequency was centered at Fs/4 = 400 MHz, but was still set for 540 MHz, hence the 140 MHz difference
      • We confirmed this by predicting that configuring for 1500 MHz bandwidth in spectral line mode should lead to a 350 MHz shift in pulsar mode (Fs = 3000 MHz, shift = Fs/4 - 400 MHz). This is indeed what we observed
      • This will naturally be fixed once we have full configtool integration. In the meantime we can use calls SetValues to retune LO2. Ryan will test this fix this week.

Wideband

  • From Randy: "PCBs for WBAP ordered and expected to be delivered late this week or early next week. John Shelton and I are working on ordering a few remaining parts. Expect to begin populating PCBs next week."

Date / Time of Next Meeting

  • November 2

-- RyanLynch - 2015-10-26

This topic: CICADA > VegasPulsarModes > VegasPulsarProjectMeetings > VegasPulsarProjectMeeting2015Oct26
Topic revision: 2015-10-26, RyanLynch
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