[evlatests] Another 128 MHz comb!

[Rick Perley]

    Ken ran the full 'spectra sweep' program, covering 1 through 50 GHz 
with 250 kHz channel resolution.    
    Some issues were discovered which prevent full utilization of the 
data -- these are understood and a new test will be done later.

    The data we got are certainly sufficient to uncover some interesting 
new effects:

    Another 128 MHz comb is found -- this one at Q-Band!  Seen are all 
harmonics from 378 through 390 (48384 through 49920 MHz).  These are 
seen on 9 baselines (there were 13 antennas in the array, so 78 
baselines were present).  Seven of these 9 baselines include antenna 
14!  The other antennas involved show no spatial correlation, so it's 
clear that the coupling is not through free space.  This is an internal 
tone, by far the strongest of which is in antenna 14, which is 
coherently seeing weaker tones from the other antennas.  The other 
antennas involved are 7, 10, 8, 12, 24, 26, and 27 (but note that the 
tones are only seen on a few of the baselines). 

   A 'grid' of close-spaced tones is seen centered near 26300 MHz.

    A very strong tone is seen at/near 29400 MHz.   Another near 35176 
MHz.  (exact frequencies will require a re-observation -- these current 
set are mislabeled). 

    An expected tone at 8192 MHz is seen. 

    The usual (and well known) RFI at the low bands (L, S, C) are seen. 

    A fuller report will be made when the corrected data are available.