[evlatests] Referenced Pointing Tests

[Rick Perley]

    I ran a test of referenced pointing this morning.    There were two 
goals:

    1) Does 'wide-band' referenced pointing work as well and reliably as 
'narrow-band'?

    2) Does a 15-second cadence work as well as 20-second?  
(Explanation:  In the past, the system used 10 seconds to move from one 
position to the other, and 10 seconds to integrate.  But from holography 
we know that the move-and-settle time is less than 5 seconds, so a 
15-second (5+10) regimen should work). 

    To test these, I used 3C147 (~5 Jy) to measure pointing offsets at 
X-band, with four combinations:

    1) Narrow-band with 20 seconds.
    2) Narrow-band with 15 seconds.
    3) Wide-band with 20 seconds
    4) Wide-band with 15 seconds.  

    The intention was to observe each mode sufficiently long for 3 
consecutive pointing solutions.  Due to a blunder on my part, the 'fast' 
tests were observed long enough for only 2 solutions.  But that is still 
sufficient for the following conclusions:

    A) Wide-band mode works as well as narrow-band. 

    B) Fast mode appears to be as good as 'slow'. 

    There were a few failed solutions for all four trials -- the 
statistics are not good enough to claim that any one of these four is 
better or worse than the others.  Comparison of the actual solutions has 
been done for only one antenna (so far) -- there is no significant 
differences, other than an expected change in elevation offset as the 
sun rose. 

    By looking at the detailed log, the sequence of operations is easily 
discerned.  (Ken claims this may be unreliable, and he intends to peer 
deeper after lunch).  But, be this as it may, I deduce that the 
*absolute minimum* time needed for a single referenced pointing 
measurement is (presuming the antennas are on source) is:

    124 seconds for 'slow' mode,
    94 seconds for 'fast'.