[evlatests] Slow focus motion on ea14

[Rick Perley]

     A test last weekend had all the antennas changing band every 30 
seconds.

     In general, results were very good.  But ea14 has a special 
problem.  It was clear that the visibility amplitudes and phases took 
much longer to stabilize upon change of band than any other antenna.  
Careful review of these showed that the amplitudes stabilized well 
before the phases.  This rules out subreflector rotation as the cause, 
and points the finger at *subreflector focus*.

     Only a few band combinations were affected.  My test runs the bands 
in order as the appear on the secondary focus:  L to X to C to S to Ku 
to K to Q to Ka.

     The effect was seen only in the C to S and S to Ku transitions.  
The former took 25 seconds for the subreflector to stabilize,  the 
latter took 40 seconds!  The S-band focus position is significantly 
different than the higher frequency ones, probably accounting for the 
extra time.  So either the focus motion on ea14 is especially slow, or 
the S-band focus on ea14 especially far from the normal (or the value in 
the tables is especially wrong ...)

     If a focus motion is to blame, we would expect the L to X 
transition to also suffer the problem -- but this is hidden as I do 
referenced pointing first (taking nearly 3 minutes).