[evlatests] EVLA Tests, November 16 2005

[Ken Sowinski]

                 EVLA Struggles, Novmeber 16 2005

There was a collection of problems that had to be gotten through
to get back to the usual good behavior of the system.

1.  Last week the system was broken because I set the transition 
modules to use the wrong 64 MHz bandpass.  Today I was able to 
understand how that happened and proceed to other problems.  The
problem arose because the behvior of the deformatters a few weeks
ago led me to beleive that the sense of the Highpass command had
changed.  In fact it had not, but the command to set that switch
had not been used until last Friday and that is when the error
was discovered.

2.  Many delays had changed by a few tens of nanoseconds, but
even when delays were corrected 14A and 16B were still not good 
enough.  

3.  14A was much weaker than expected and 16B about half as good
as expected in power.  When I was able to put the system in line
mode and look at the bandpass it was clear that 14A had a problem
which was traced to the DTS module.  A flurry of formatter and
sampler resets and power cycles eventually got it to work normally.
The DTS problem confused me for a long time because narrowing the
bandwidth made it look better, but the reduced amplitude was caused
by something other than a delay error.  I ran out of energy and time
before tracking down the problem with 16B.


Both antennas are now working well with the exception of 16B.  Delays
and levels are reasonably well set.  Rick is planning to use time
tonight to check sensitivity at all bands, phase connectivity at source
changes at X band, and a long track at one band to look at longer term
stability.