[evlatests] antenna 1 still needs work

[Ken Sowinski]

The antenna is still not behaving in an understandable mannere.

1.  Pointing runs are not good.  The pointing errors are small,
but do not fit the model at all so there are large residuals and
chi square.  I have not yet been able to discern any patterns in
the post-fit residuals.  Many pointing trials are rejected because
of an inferred beam size which is much too small.  There were
several trials, all at low elevations, where the antennas claimed
to be on source, but the correlated signal was a factor of ten
too low.

2.  Yesterday morning pointing was corrected for X, C and K bands
using 3C345.  After lunch it was all out of wack.  X band could
be improved by rotating the subreflector; but not C or K bands,
so it was not a simple rotation missetting.  Pointing showed an
azimuth change of about 1.5 arc-min explained the changes at
both X and K bands.  Later in the day as 2C345 got lower its
response got worse.

3.  Other evidence that it is pointing is that all IFs are affected
and problems are progressively worse at C, X and K bands.


There is little opportunity for more tests until next year so
I write this in hope a little thought can be applied.  From the
evidence it looks like something is loose or the ACU is misbehaving.
There is no evidence that the subreflector servo system is broken.
If there is a subreflector problem it must be a mechanical stability
issue.