[evlatests] Referenced Pointing Problem understood

[Rick Perley]

     As part of the antenna optics alignment project, my summer student 
(Lucas Wilkins) and I discovered an important failure mode in referenced 
pointing.  The details of this are contained in various emails posts 
distributed last May, and will not be repeated here.    Due to the site 
power issues, it was not possible to diagnose/correct this problem over 
the summer.

     with power now restored, and the array now functional, Barry 
suggested, and Ken implemented, a 'quick fix' to this problem, which was 
tested yesterday.  Ken re-ran a Ku-band script used last May, both in 
the original mode, and with the 'fix' put in.

     The results are very clear:

     a) The original script showed the failure mode on every antenna, 
for every solution.  Resulting solutions (in azimuth) are erratic, and 
in error.

     b) The 'fixed' script showed no failures, and the solutions are 
consistent throughout the six referenced pointing solutions made.

     Barry tells me that the next step is to devise and test a more 
elegant solution to the problem, as the current fix is something of a 
kludge.  I note that the 'quick fix' solution adds ten seconds to every 
referenced pointing operation.  (The added 10 seconds is a separate 
scan, with the antennas on source).

     Until this is done, and the final solution tested and implemented, 
I strongly urge no observing be done utilizing referenced pointing.

     Rick