[evlatests] Tables of 'PDif Compression'

[Rick Perley]

    To assist in discussion and perhaps understanding, I have assembled 
the attached tables, showing the compression in the demodulated switched 
power ('PDif') -- the ratio of the value when on Cygnus A to that when 
on cold sky.  It is quite clear that these values have not changed 
appreciably over time, since the last time we were looking at these 
things (many months ago). 

    Note that at S and especially Lband, we understand that we are 
overdriving the station board requantizers when we are on Cygnus A.  
Tests done last week show that decreasing the power to more appropriate 
levels decreases -- but in no way eliminates -- this compression 
affect.  Further tests are pending (and are one of the subjects for the 
Thursday morning meeting). 

    Note also that we have PDif *expansion* on a couple of antennas at 
C-band! 

    Finally, there is no table attached for the X-band measurements.  At 
this band, there are only a few antennas which show any 
compression/expansion when on Cygnus A.  Cyg A approximately doubles the 
system temperature.  Those antenna-IFs which show more than a 1% effect are:
    6A   0.98
    16A   0.87
    16C   0.98
    16B   0.98
    16D   0.98
    18C   0.98
    25B   0.95
   
    The AC frequency was 8300 MHz, the BD frequency was 11300 MHz. 


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