[evlatests] Antenna 13 pointing, and Secondary Referenced pointing

[Rick Perley]

    I stole a few minutes of time from Maintenance time this morning to take
a look at the current antenna 13 pointing status, following a change to the
tilt parameters entered by Barry yesterday. 

    I ran primary and secondary pointing determinations on 3C84, at both
L-band and C-band. 

    A)  Secondary Referenced Pointing does not work for the EVLA antennas!

    This conclusion is perfectly clear from the data.  The 'secondary' 
pointing
solutions, for both bands, for all EVLA antennas, are identical to the 
primary
solutions.  For the VLA antennas, the secondary solutions are all nicely 
zeroed,
(to within the polarization offsets due to the squint), as they should 
be.  

    B) We still have problems with Antenna 13 pointing, and probably more. 
Here is a short table (Az and El in degrees, Deltas in arcminutes)

Band    Az      El      Delta El      Delta Az      Comment
-------------------------------------------------------------------------
L            53      22         -1.1            4.9         power low by 
factor of 2
C            55      25         +0.3           2.8         power low by 
factor of 3
-------------------------------------------------------------------------------

    The good news is that the large elevation offset is gone, so we can 
get reliable
positions at C-band.  (Most attempts yesterday failed at this band).
    The bad news is that the apparent collimation difference between L 
and C bands
is far too great.  For antennas 14 and 16, the collimation difference is 
about 0.2
arcminutes in both elevation and azimuth.  But for antenna 13, it is 1.4 
and 2.1
arcminutes. 
    The reported beamwidth for antenna 13 at L-band is normal.  At 
C-band, it
is reported as being 10% too small in azimuth.  I suspect this could be 
a manifestation
of the large azimuth pointing offset with the very simple beam model 
that 'Peek'
employs.