[evlatests] 4 meter results

[Ken Sowinski]

A quick test was done to see if 4 meters works.
It half works, BD seems to work, AC is incoherent.

Some uninterrupted continuum data was taken on 3C123 from
about 1740 to about 1752, if anyone cares to look at it
more carefully than I did.

The longer story.
To keep from overdriving the VLA T5s lots of attenuation is
needed in the downconverter.  A sampler RMS around 2 or 3
is what is required to no overdrive the T5 using the usual
defomratter ouput gain setting of 30.  If the downconverters
are set to provdie a sampler RMS between 5 and 10, the
output gain parameter has to be reduced to 2 or 3 to keep
the T5 happy.  I suppose this is somehow related to the narrow
bit of noise that is presented to the downconverter and the
eight bit sampler.  Remember that the T5 ALC is responding only
to the narrow band selected by the VLA backend filter.

The downconverter attenuator which keepe the T5s happy are now
in the parameters DB.

The fringes on BD seem to be real and went away when one of the
antennas was pointed far off source.  The AC data was incoherent
and did not look any different when an antenna was driven off
source.  All the synthesizers in both antennas claim to be in
lock at the right frequencies.  We must be missing something
fundamental.