[evlatests] AC 'Global' phase jumps

[Rick Perley]

    I reported last night on the appearance of global phase jumps.  
These occurred in test data taken:

       a) At L-band, with 50 MHz BW, and default frequencies, in continuum
       b) Upon scan change, but with no change in mode, frequency, 
bandwidth, or source.  (Indeed, nothing changed at all, except for the 
observe script requesting a new observation). 

    It was noted that the 'global' EVLA to VLA phase jumps occurred in 
IFs A and C only, were of equal magnitude for both, and were of 
different amounts for each of the three scan changes, with no 
discernible relations amongst them. 

    My 'stress test' had one other repeated set of observations -- this 
at X-band, where there are three observations of the same source, same 
frequency, and same bandwidth.  However, in this case, the middle 
observation was in referenced pointing mode. 
    Curiously -- in this case, there are no phase jumps.  It seems 
unlikely that the pointing mode observation would suppress the phase 
change.  Perhaps more likely is that these observations were at X-band.