[evlatests] EVLA tests, May 4 2006

[Ken Sowinski]

The L302-1 in antenna 13 was modified to change the sign
of the ramp while L302-2 was left untouched.  Careful
examination of K band data showed no sign of a sawtooth
in AC while it remained in BD.  I conclude that we should
implement this change in all L302s as they are updated.
There is no need to fit this in to the old L302s and the
timescale of the fix is not critical.

There were some oddities.  Antennas 14 and 16 did not go to
X band when commanded.  The bandswitch was left in the L band
position; I did not look at the synthesizers or FRM to see
where they were.  I have seen this before, but it does not
happen very often.  A little later the subreflector at
antenna 13 did not go to the K band rotation setting when
commanded.  The command echo was correct, but the FRM commanded
and readback positions were both wrong and identical to each
other.  It looks like the command made it to the MIB, but did
not make it to the FRM.  I have seen this happen to the VLA
and have always blamed the Modcomps.  We now have good evidence
that the problem is likely in the FRM controller; perhaps it
has a small window during which it ignores commands.

Since there were no objections I modified the antenna positions
in the EVLA database as I described in an earlier message.

Several holography tests were made.  Rick and Walter will report
on these.

An experiment was carried out to see if attenuator settings can
be optimized to improve sensitivity.  Again Rick and Walter will
report on this.

Rob and friends struggled most of the day and antenna 18 now
works at all four IFs.  Many of the problems were in the D rack.
Rob complains that the stock of T5s is becoming less reliable.

Antenna 13 BD woked today at both K and Q band.  It continues
to fail at Q band on antenna 16.