[mmaimcal] Comparison of ALMA Antenna specs on offset pointing

[Al Wootten]

At the review, Jeff noted:
 It looks to me like the production antenna offset
       pointing spec was changed to half the region over which the spec
       applies.  The US prototype spec said: "...differential error
       over a solid angle of 2 degrees radius about the desired
       position, and then only the change in that differential error
       over a 15 minute period when tracking at sidereal rate".

And the production spec said:
   Fast switching phase calibration requires the antenna to move from the
   target source to a calibration source up to 1.5 degrees away on the sky.
   For design purposes, in the fast switching cycle to be considered here,
   the antenna shall perform steps of 1.5 degrees on the sky and settle to
   within 3 arcsec peak pointing error, all in 1.5 seconds of time. The
   antenna shall then track and integrate on a calibration source during one
   second, then it shall switch back to the target source with the same
   requirements on switching time and settling accuracy. It shall then track 
   on the target source. The time for a full cycle of target-calibrator-target 
   observation shall be 10 seconds.

As we discussed today, we should understand the ramifications of this change,
which has gone unremarked for several years now.

Comments?

Clear skies,
Al