[evlatests] Baseline fitting and phase jumps (re-formatted)

[Vivek Dhawan]

Please discard the earlier mis-formatted message.
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Recent baseline runs, all at 50MHz continuum, standard Fluke
settings. Two kinds of phase variations are seen:

1. phase changes with elevation which are only on the EVLA.

2. Phase jumps of about +_90deg, which could be ascribed to
   either EVLA or VLA, hard to tell without additional clues.

   One clue, which points to the EVLA, is that there are occasions
   when only 13 or 18 jump by about +-90deg. There could also be 2
   bugs, one array-wide (either array), the other antenna specific
   (EVLA only).

date       band            result / comment

Sep 12       X   EA13, 16 can be fit - rms ~40deg each, but a fit
                 nevertheless. EA14 cannot be fit. ea24 not used.
                 ea18 is good, as usual. No phase jumps seen.
                 Last baseline run before antenna move.

Sep 25       X   After move (13 14 and 16 moved, I believe.
                 18 did not). 3 phase jumps on ea18, otherwise well
                 behaved.  EA13, 14, 16, 24 all have wild phase
                 changes with elevation, cannot be tamed by position
                 adjustment.

Sep 26       C   EVLA 13,14,16,18, have 5 phase jumps (and 4 reverse
                 jumps) by ~90deg relative to the VLA, all antennas
                 jump together, all IFs. EA13 has 1 extra jump, all
                 IFs. Otherwise, the phases are great - 13,14,16,18
                 all produce a good baseline fit, with residuals of
                 10-15deg, (EA18 as reference). Since this is the
                 only full baseline at C band, I don't quite believe
                 it yet.

Sep30        X   Business as usual - EA18 well behaved, except for 1
                 jump of +90 followed an hour later by a return.
                 EA13,14,16,24,26 all too variable to tell if they
                 have phase jumps or not.