[evlatests] Recent history of VLA-VLA phase jumps

[Michael Rupen]

VLA-VLA Phase Jumps
-------------------
mrupen  10oct06

The data:
   * all AR603 runs between 19sep06 and 7oct06 inclusive
   * mostly fast-switching scans
   * standard continuum, mostly C & X bands
   * 3.3s averaging

The procedure:
   According to Rick the easiest check is to look for differences between
   AC and BD phases (IF pairs).  These should ideally be consistent with a
   constant phase offset plus noise.

   To check this I did the following:
   * CALIB, phase only, with 3.3s SOLINT, using refant 10 (VLA ant. at E8)
   * SNPLT with OPCODE 'IFDF' to plot A-B, C-D phase differences, looking
     for jumps

Caveats:
   * many observations were quite short (see listed IATs), and "all ok"
     may not mean much in those cases
   * some weak calibrators --> may miss low phase jumps (up to 20-ish degs.)
   * didn't keep track of which EVLA antennas were present (easy to add if
     desired)
   * didn't look at actual phases, just phase differences (I did check
     a couple cases to be sure that I was indeed seeing real jumps)

--------------------------------------------------------------------------------

CONCLUSIONS
   * many scans/antennas show 10-20d drift and/or phase jumps within a
     scan (<2 mins.), when SNR is sufficient to see such
   * VLA in-scan phase jumps definitely present by 2oct06
   * VLA between-scan phase jumps definitely present by 26sep06
   * EVLA in-scan phase jumps come and go, as expected for an evolving
     system. As of  7oct06 ant. 16 showed two-state phases with a phase
     diff. of 70degs between them (as seen in AC-BD).

--------------------------------------------------------------------------------

SUMMARY OF ALL DATA

   19sep06  486
      X  2329-2415
        all ok

   19sep06  487
      C  2325-2445
        all ok

   21sep06  488
      C  2215-2310
        all ok

   23sep06  489
      C  0120-0152, 0218-0228
        ant. 14 RCP, LCP 100d phase jump at scan/band switch (02:20-ish)
        ant. 18      LCP three-state phase diffs (40, 70, 110), some
                         within a single scan

   23sep06  490
      X  0114-0119, 0219-0228
        ant. 18      LCP  40d phase jump within a scan (02:19:30-ish)
                          20d phase jump at scan/band switch (02:24-ish)

   23sep06  491
      Q  0155-0225
        all ok

   23sep06  492
      K  0205-0235
        all ok

   23sep06b 493
      X  2100-2310
        all ok

   23sep06b 494
      C  2100-2210, 2340-2400
        all ok

   26sep06  495
      X  1425-1450, 1518-1521
        ant.  4 RCP, LCP 120d jump from 1450 to 1518 (source/band change)

   26sep06  496
      C  1450-1520
        all ok

   29sep06  497  SN/5
      C  0130-0345
        ant. 14 RCP, LCP 100d jump at source/band change (02:40)
        ant. 22 LCP       20d jump in midst of fs scan (~02:35)
        Several 4-5d jumps on flux cal

   29sep06  498
      X  0220-0227, 0339-0341
        Several 4-5d jumps on 0339-0341 (flux cal)

    1oct06  499
      C  1810-2010
        ant.  3 RCP, LCP  30d drift from 18:30 to 18:45
        ant. 11 RCP       40d drift from 18:10 to 18:40
        ant. 14 RCP, LCP  50d jump from 1331 to 1407 (19:01)
        ant. 24 RCP, LCP  20d jump from fs to 1331/1407, then back down
                              (18:50, 19:15)

    1oct06  500
      X  1730-2030
        ant. 11 RCP       40d jump from 1331/1407 to 0958fs  (19:06)
        ant. 14 RCP, LCP 100d jump from 1331 to 1407 (19:02)
        ant. 24 RCP, LCP  40d jump from 1331/1407 to 0958fs  (19:06)

    2oct06  501
      C  1520-2030
        ant. 10 RCP       50d jump in midst of fs scan (~16:00)
        ant.  3 RCP, LCP  15d jump in midst of fs scan (~16:50)
        ant.  3      LCP  15d jump in midst of fs scan (~18:10)
        ant. 13 RCP, LCP  20d slow drift from 16:40 to 17:30, then steady
        ant. 14 RCP, LCP 100d jump from 1331 to 1407 (19:07)
        ant. 16 RCP, LCP  20d slow drift from 16:40 to 17:30, then steady
        ant. 22      LCP  30d jump in midst of fs scan (~16:50)
        ant. 25      LCP  10d jump in midst of fs scan (~15:40)

    2oct06  502
      X  1630-1640, 1907-1912
        nothing obvious, but very little data

    5oct06  503
      C  2320-2415
        nothing obvious

    7oct06  504
      C  1410-1440
        ant. 16 RCP, LCP  two states in last scan (0542+498), separated by
          ~70degs.

================================================================================