[evlatests] VLA System health

[Rick Perley]

    From the short test, preparing for the 'flux densities', I find:

    1) L-band:  All antennas o.k., all PDifs are plausible. 

    2) S-band:  No fringes or PDif from ea03 -- presumably, the receiver 
is not yet in?  ea06, on IF 'A' gives a sinusoidally varying PDif of 20% 
amplitude, and 1 minute period.  (It has always done this). 

    3) C-band:  All antennas fringe.  ea14 gives a negative, or 
extremely weak, PDif on all IFs. 

    4) X-band:  No fringes from ea20.  PDif = 0 from ea02 and ea20.  
Both antennas show healthy PSum.  ea14 has very low PDif, but o.k. PSum.

    5) Ku-band:  No fringes from ea23, but PSum and PDif both normal.  
ea10 is showing large gain changes from scan to scan (0.7 dB).  All 
others o.k.

    6) K-band:  No fringes from ea23, and PDif is very small (Tsys 
claimed to be 500K).  Ea07 has system temeprature of about 300K.  All 
others o.k.

    7) Ka-band:  No fringes from ea23, and PDif equal zero on all IFs.  
(Or, Tsys >1000 K).  All others o.k. 

    8)  Q-band:  No fringes from ea 23 on IFs B and D (and PDif = 0).  
Fringes seen on IFs A and C. 
                         ea08 gives zero PDif on all IFs. 
                         Very high Tsys (> 200K) on ea 7 and ea18. 

    The lack of fringes from ea23 for Ku, K, Ka and Q band seems to 
indicate a problem with the UX downconverter