[evlatests] collimation results and antenna 13 mystery

[Ken Sowinski]

There was a collimation run January 21 which gave puzzling
results for antenna 13.

There was a collimation run in early December which insisted
on small changes for antenna 13.  These changes were not made
then.  This time it wants larger changes and in the other
direction.  The simplest explanation is that the subreflector
rotation index point is migrating.  The signs of the changes
at the various bands is consistent with this hypothesis and
the location of the feeds on the feed circle.  I encourage
an index check of the subreflector at antenna 13 when it can
next easily be done.

I will not make any changes to the pointing parameters until
we have a good inderstanding of what is happening.

The other antennas were all well behaved and no changes are
required.  Antenna 23, however, which should have worked at
K band produced no valid pointing trials.  This will be
investigated tomorrow.