[evlatests] evla confusion

[Barry Clark]

> 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.