[evlatests] Global, and Local Phase Jumps

[Rick Perley]

    With a spare bit of Friday software time left, I ran a test designed 
to encourage bad phase behavior ...

    1-minute observations of two adjacent calibrators (2007+404, 
2015+371), cycling through L, C, X, and K bands.  The observations began 
at Lband, and two complete cycles were completed (i.e., each source was 
observed twice at each band).   All observations were made with 50 MHz 
BW, in continuum, so there were no changes in Fluke synthesizer values. 

    Results:

    Only one 'global' jump was seen, as described below. 

    There was both a 'global' (EVLA to VLA) phase jump, and a 'local' 
(different for each different EVLA antenna) phase jump between the 
initial L-band scan (which was also the first observation in the file), 
and the next L-band scan. 

    A)  Global Jump.  Referenced to EVLA antenna 19, all VLA antennas 
changed phase by +130 degrees in IFs A and C, and by -40 degrees in IFs 
B and D. 

    B) Local Jump.  Most EVLA antennas changed phase, relative to ea19, 
between these same two observations.  The observed differences were 
different between IF pairs, as shown in the table below:

    Antenna      AC jump       BD jump
-----------------------------------------------------
       11                   0                -120
       13                   0                     0
       14              -100                  -90
       16                   0                     0
       17                 60                 -110
       18                   0                 -130
       19                  ref                  ref
       21                  60                     0
       23                    0                     0
       24                  60                     0
       25                  60                -120
       26                    0                     0
---------------------------------------------------

    The measurement accuracy is no better than 10 degrees.  Thus, ** 
except for antenna 14 **, there seems to be only two states:  0 and 60 
degrees for the AC side, 0 and -120 degrees for the BD side. 

    Other than the jumps described above, there were no other global 
jumps.   There were three other phase jumps events -- all of them seen 
on VLA antennas in the phase differences between the two IFs:  Antenna 
15 at C band, and antenna 20 at both C and X bands.