[evlatests] more about antenna 13

[Ken Sowinski]

> An attempt was made to get 13 back but there are many problems.
> After much effort a reasonable fiber delay was found while observing
> at L band to minimize the effect of any pointing errors.  Other
> problems:
> 1.  The response was very poor in BD and even worse in AC.  An
> improvement of about 50 percent was realized by changing the azimuth
> offset by about 30 arc-min.  This seems unreasonable for a move to
> the same arm, so:
> 2.  I wonder if the subreflector is working properly.  Looking at
> the FRM with the device browser while changing bands leads me to
> doubt it is doing the right thing, but no systematic investigation
> was made.  Additional evidence is that even when the pointing was 
> "optimized" at L band there was almost no response at X, or even C band. 

It is clear that there is an FRM problem and it is being
repaired as I write this.  Given George's report from data
taken last night I suspect it worked for a while for him 
before failing.  That he saw reasonable amplitudes for a while
suggest that delays are close to right and pointing is good
enough for L band.  Based on this I will reset the Az encoder
offset to what it was before the antenna moved on the plausible
grounds that I was trying to correct pointing yesterday while
the subreflector was in the wrong place.  After that antenna 13
may be good enough to refine delays at all bands for which 
pointing is good too see a signal.