[evlatests] Phase Conjugated Holography Data!

[Rick Perley]

    The data taken last night are showing 'global' EVLA to VLA phase 
changes between the holography scans and the calibration (which, due to 
the problems described earlier, was only possible for EVLA antennas at 
the end).  The offsets are visible because the 'zero--point' phase can 
be seen when the center of the beam is on the source.    The 
'center-beam' phases for the EVLA antennas are 30 to 50 degrees off 
zero, compared to their phases on the single calibration scan. 

    These offsets reveal a remarkable fact:  The visibilities are 
conjugated (i.e., the phase is negated) when the reference antenna is 
numbered lower than the moving antenna!  This is true for all EVLA 
antennas, whether the reference antenna is another EVLA antenna, or 
whether it is a VLA antenna.  It is probably true also for VLA antennas 
-- but because holography phases are generally near 0 or 180 (when there 
is enough signal to give stability), and all the EVLA antennas are 
numbered higher than the two VLA antennas I chose to move (6 and 9) it's 
hard to be certain.