[evlatests] evla confusion

[Barry Clark]

> From evlatests-bounces at donar.cv.nrao.edu  Wed Feb 15 17:51:49 2006
> Date: Wed, 15 Feb 2006 17:51:38 -0700 (MST)
> From: Barry Clark <bclark at aoc.nrao.edu>
> > Certainly the L302s are implicated.  Whether they are misbehaving
> > on their own or just being mislead is hard to distinguish.  My vote 
> > is that sometimes they choose the wrong heartbeat when commanding 
> > the DDSs.  It is not at all obvious to me how you can get them to 
> > do this.  
> 
> Just getting the wrong heartbeat for the DDS will not affect the amplitudes.  
> Getting the wrong heartbeat for the Walsh functions will not affect the
> phases (except maybe by 180d).  There are complicated ways for the L302 
> to go wrong, but nothing so simple.

I was wrong.  There is a simple failure that can explain many of the 
phenomena (trying to explain all problems from a single cause doesn't
work with this machine).  If the MIB software is attaching the wrong
time label to heartbeat interupts, displacing the walsh function will
drop the amplitude, and getting one wrong on the timing of the strobe to
the DDS will jump the phase.  We need to discuss with Pete whether this
can happen, and how to detect it if it does.