[evlatests] antenna 17 pointing results

[Ken Sowinski]

X band pointing was done last nighit using the end of SW
time and following unused dyanamic time to improve the
model for antenna 17.  It was modestly windy and overcast
but useful results were obtained.  I would not use these
data to refine any of the already well-known antnnas.

Since we have had an EVLA antenna on CW5 in the past I have
attributed the tilts and Az offset to the antenna rather
than the pad.  The changes were small and introduced in
the parameters database this morning.


This antenna was a poor pointer before being refurbished
and it still points poorly because it has a very large
2*Az term.  (What Jon Thunborg calls the 'potato chip' term.)
The peak-to-peak magnitude of the fitted term is 0.5 arc-min.
Perhaps this antenna represents the first strong argument for
implementing the 2 and 3 Az terms in the EVLA pointing model.
There are other antennnas that have bumps and holes that show
up when rotating in Azimuth which cannot be modeled by
cos(n*az) and sin(n*az) terms.  An alternative is to invent
something like the VLBA track model which will take care of
the more pathological cases if we can figure out how to
measure them.


I think work on 17 should now concentrate on finding the
missing G/T and continuing outfitting for the remaining bands.