[evlatests] A curious focus problem from Ku to K bands

[Rick Perley]

    In my recent tests, I've noted that when we change frequency from Ku 
to K bands, there are five antennas which  *always* take longer for the 
unflagged data stream to start up.  Specifically:
    ea02 takes 10 seconds longer to give good data than most others,
    ea08 takes 5 seconds longer,
    ea03, 04 and (less regularly) 13 all take 3 seconds longer than all 
the others. 
    The effect is seen in all four IFs.  It's not a correlator issue -- 
the data are present, but are correctly flagged -- the amplitudes during 
these intervals are low, but increasing.  So it has to be focus, 
pointing, or a slow subreflector.  This last one is unlikely, as this 
tardiness only occurs with the transition from Ku to K -- a very short 
travel for the subreflector. 

    Reviewing the flagging table gives the answer -- it's the focus.  Is 
there that large a difference in focus position between these two bands 
for those particular antennas?