[evlatests] status, Aug 3 2006; what happened to antnna 13?

[Ken Sowinski]

Not much was achieved today.  L band focus tests were reported
elsewhere.  The 13C DTS module was replace and works.  Both L301s
are now working in antenna 16.

The poor performance Michael reported for many antennas was
verified.  Observations were made to measure the correlation
coefficeint as well as observations with the T_sys correction
applied to distinguish T_sys problems from other problems.
The most striking problem is that antenna 13 is very bad at
all bands.

X band
13 and 18 are really bad; about 1/3 expected power.  18 looked
more reasonable with the T_sys correction applied suggestion
that T_sys is too high.  Moisture?

C band
13 is really bad.  16CD is weak; about 1/2 expected.

L band
13 is really, really bad; about 1/4 or less of what is expected.
14 is not good; about 2/3 of expected power.
18 is OK, but the L302-1 consistently fails to lock at the
standard L band setup.

K band
13 and 18 are really bad; about 1/3 of the expected power.

Q band
13 was bad, but pointing was not checked so that may be part
of the problem.


The problem with antenna 13 does not seem to have any of the
usual explanations.  The bandpasses look OK at X band.  There
are no delay errors.  The degradation does not scale with
frequency so it is unlikely to be pointing or a poor LO.
About the only thing left is extra noise getting in at or after
the downconverter.