[evlatests] Antenna 13 on April 5

[Barry Clark]

I fired up antenna 13 at C band during maintenance.  It looked pretty 
weak, so I thought I would tweak delays.  This resulted in pretty large
tweaks - 16ns in IFA, +15 in IFC.  IFs BD were much weaker yet, and 
did not change amplitude much during the delay stepping - the symptom
of very large delay errors.  So I tried 25 MHz bandwidth.  The amplitudes
on IFs A,C went down!  The amplitudes on IFs B,D went up considerably,
but it was still not very clear to me where the delay center was - 
there was a minimum near the nominal center, and the two ends were not
that different.  A quick check at 12.5 MHz bandwidth suggested the delays
for both IFs B and D wanted to be corrected negative about 40 ns.  Before 
I could check if this was producing reasonable amplitudes at 50 MHz bandwidth, 
the antenna stowed itself for wind, as did most VLA antennas.

Even at it's best, antenna 13, IFs A,C were a factor of about 4 below nominal
sensitivity.  If this is due to pointing, it is a very large offset.

The strange behavior of amplitudes with bandwidth suggests something might
be odd about the spectral shape, but I didn't have time to investigate
before the wind came up.