[evlatests] pointing, April 26 2006

[Ken Sowinski]

Three of the EVLA antennas, antenna 18 was out of service,
were included in a standard X band pointing run the night
of double maintenance days this week.  Weather was good,
winds calm, and the data of good quality.  I think we now
have the X band pointing well set and can investigate
interband collimations.

Antenna 13
Required many changes.  The largest was a 1.6 arc-min change
to the X band elevation collimation.  The fit was noticably
improved by changes to the El centering terms and these were
changed.  Many pointing trials were rejected from consideration
because the fitted beam width was out of range.  I have not yet
looked to see how bad they were, but Rick has previously reported
anomalously small beamwidths from pointing trials for this
antenna.

Antenna 14
No changes were required.

Antenna 16
It wanted an 0.4 arc-min change in E-W tilt which was provided.
This antenna had the worst fit, but would be much improved if
independently fitted tilts were allowed.  There is funny behavior
in azimuth which can be acommodated by independent tilts;
probably something about the Az bearing.

All the antennas would benefit from fitting for and using
2*az and 3*az terms.  For antennas 13 and 14, the post fit
RMS is within the six arc-sec specification if these terms 
are accounted for.