[evlatests] 3 and 8 bit polarization stability

[Rick Perley]

    At long last, I have completed the polarization calibration of the 
3/8 bit runs. 

    The results are quite amazing, and quite encouraging. 

    For both the 3-bit and 8-bit paths, the antenna cross-polarizations 
are extremely stable over time -- both between one day and another, and 
within the time of a single run.    'Extremely Stable' means the median 
difference between days -- and also between the A1C1 and A2C2 paths -- 
is perhaps a couple tenths of 1%.  There are a few places in the 
spectrum where a difference of up to 1% is found -- but these appear to 
be stable within a single day. 

    To illustrate, I attach two postcript files, showing the antenna 
cross-polarization of ea26 in both polarizations. 
   
    On the 8-bit plot, the two colors (yellow and green) represent the 
measured cross-polarization on two days, (separated by one day).   The 
span is 512 MHz (we changed the tuning between the two days).
    On the 3-bit plot, the four colors are: 

Yellow:  A1C1 on the 2nd day,
Green:  A2C2 on the 2nd day,
 Blue:  AC1 on the 1st day
 Red:  A2C2 on the 1st day. 

    The 3-bit plots are for the full 2.048 GHz (but I removed subband 16 
from the 1st day). 

   
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