[evlatests] EVLA pointing, and antenna 13

[Rick Perley]

    Before the winds blew us off the air, we managed a quick
'reference pointing' look on VLA and EVLA antennas. 

    I tried this at L and C bands, followed by a spectral line
observation to determine delays.  The primary goal was to
see if we can figure out what's wrong with antenna 13.

    Some observations:

    1) We got *no* pointing solutions from any EVLA antenna
at L-band.  But all VLA antennas gave solutions.  How odd. 
Is referenced pointing somehow disabled for the EVLA at
L-band? 

    2) At C-band, EVLA antennas 13 14 and 16 gave solutions. 
18 did not.  All solutions (from all antennas both VLA and EVLA) gave 
positive offsets
in elevation.  I attribute this unlikely event to the high winds.  The
azimuth offsets were nearly all of negative sign.  Again, I'll blame
the winds. 

    3) Although there is a significant scatter in the solutions (again I
blame the wind), antenna 13's solution is definitely in the 6-sigma
department:  An elevation offset exceeding +4.3 arcminutes, and an
azimuth offset of +2.3 arcminutes.  I hope this is sufficient to explain
the weak amplitudes.  I suggest that Walter put these rough corrections
into the appropriate file, and we can try pointing again this evening
when the winds subside. 

    4) There is good evidence that secondary referenced pointing does
not work.  I (inadvertantly) did 'secondary' pointing at C-band, following
the referenced pointing mentioned above.  The intention was to do it
at X-band, but I put in the wrong band.  The results, however, are
instructive:  The VLA antennas gave small offsets, more or less centered
on zero (note the statement above that the original solutions were all
positive in elevation, and nearly all negative in azimuth).  However,
for the 3 EVLA antennas (18 gave no solutions), the corrections determined
were the same as the primary solutions. 

    We will likely attempt a proper pointing run this evening, when the
winds subside a bit.  All is stowed now.