[evlatests] X-Band phantom, or not ...

[Rick Perley]

    Some numbers to quantify my earlier observation. 

    The observation this morning was for only 25 minutes integration on 
a noise source, located at declination 75 degrees ( -- meaning the phase 
rate is pretty low). 
    I removed antenna 21 (essentially dead), and antenna 4, which had 
horribly bad sensitivity.  Antennas 24 and 26 were partially bad in IF 
2, so the following tests used only IF #1.  There remained 8 EVLA 
antennas, and 17 VLA antennas. 
    Default X-band frequencies were used, 50 MHz BW, 0.418 seconds 
integration. 
    I 'QUACKed' only the first second (one second!) of data from the 
noise observations.  The calibrator data were carefully edited, based on 
the gain solutions. 

    I made an image of the blank field, with various combinations.  
Below are given the peak and rms in each map. 

    Test                         peak              rms
-----------------------------------------------
All                              .34 mJy          .048 mJy               
A real source was seen, not at the phase center.  No artifacts.
VLA only                  .37 mJy           .068 mJy               The 
same source was visible (barely)  No artifacts. 
EVLA only                .67 mJy          .17 mJy                  No 
sources visible.  No artifacts visible. 
VLA x EVLA           .33 mJy           .077 mJy               No sources 
or artifacts visible.  Nothing but noise. 
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