[evlatests] Speeding up Correlator Configurations

[Rick Perley]

    The correlator gurus have found a way to considerably speed up 
correlator reconfigurations.  (Ken can provide the details). 

    Ken has executed a pair of short observations designed to measure 
the improvement.  This consisted of a ~1 hour observation utilizing my 
'flux density' script.  The method here is to change bands rapidly 
(typically 30 seconds on each band) for a number of sources.    This 
short section of the big script was run twice, once with the new system, 
and again with the old.  This permits direct comparison of the durations 
over which data were available from the correlator. 

    The results indicate that the configuration change has been sped up 
by about 10 seconds.  So, for the old method, the configuration change 
from S to Ku band took 14 seconds.  Now it takes 3.  (Nice!)

    Below I give the detailed times for each of the band changes in my 
script. 

    Transition        Difference
---------------------------------------
    Ka to L                 11 sec
    X to C                    8 sec
    C to S                     0 sec (no configuration change)
    S to Ku                  11 sec
    Ku to K                  9 sec
    K to  Q                   0 sec  (no configuration change)
    Q to Ka                  0 sec  (no configuration change)
----------------------------------------------------

    Note that most of these savings won't be seen if one is changing 
bands -- the subreflector motion is typically ~5 to 10 seconds between 
bands.  The big advantage is for changing modes without changing band.