[evlatests] ACU tests -- sky survey mode

[Rick Perley]

     I've been asked to continue testing of the new ACU-equipped 
antennas, using the new 'sky survey' modes.  These allow one to speed 
through a specified part of the sky at different rates.

     An initial test was run yesterday.  For this initial test, I picked 
two positions:  the first one (true) degree east of 3C48, the other one 
degree west of 3C48.    Six 'cuts' were specified, each traversing the 
two degree separation.   The idea was to get a nice cut through the 
primary beam, roughly from the 2nd null on one side to the second null 
on the other.  They specified cuts were:

     1) West side to East side in 4 minutes.  This is twice the 
'sidereal' rate.
     2) East side to West side in 4 minutes.         ditto
     3) West side to East side in 2 minutes.   This is 4X sidereal
     4) East side to West side in 2 minutes.           ditto
     5) West side to East side in 1 minute.    This is 8X sidereal
     6) East side to west side in 1 minute.             ditto

     Averaging time was set to 0.1 seconds.  For each of these six cuts, 
I specified 100 phase steps.  So, for the first two cuts, the number of 
integrations per phase step was 24.  For the next two, 12, and for the 
last two, 6 integrations/step.

     The results were *completely* different than expected.

     Each antenna moved at a different rate!  The only antennas which 
traveled at close to the specified rates were ea04, 06, 15, 17, 20, 22, 
and 28.  Some antennas zipped through the pattern at many, many times 
the specified rate.  The most extreme example was ea18, which went 
through the pattern at about six times the specified rate. This 
'amplification' factor was the same for all five completed cuts.  (For 
reasons unknown, the last cut was not executed).

     Furthermore, the profiles show that only the 'slow' antennas with 
smooth motion. The faster the cut, the more jagged the profile.  The 
fastest ones are actually in big steps -- looking rather like holography 
mode!

     It's easy to find the basic relation -- the antenna motion 
amplification is a factor of the fringe rate!  The target source was 
rising over the west arm -- elevation = 50 degrees, at which point the 
motion is almost entirely in elevation.  Fringe rates are high for the 
west arm, and low for the others.  All the 'fast' antennas were on the 
west arm -- the further out the arm, the faster the antenna moved (and 
the more steplike).  All the 'slow' antennas were near the center of the 
array, on the E and N arms.
     Examination of the cuts show that the antennas did not start and 
stop at the specified points, but overshot -- on both ends by a factor 
of up to  nearly six.

     So something is clearly not right here.  I don't think I did any 
illegal in the setup (the OPT is really simple for this mode).  But 
clearly it's not working in any sensible manner.