[evlatests] VLA System health

[Ken Sowinski]

On Wed, 6 Mar 2013, Rick Perley wrote:

>    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

I think the easiest way to explain ea23 is that the cables between the 
L301s and the high frequency recceivers and T303 are swapped somewhere.
That is the L301-1 output is going where the L302-2 should and vice versa.
Additional supporting evidence is that this is the most recent antenna to
have had its RF switches replaced.