VLA Test/Observation Coordination Meeting
                           B.G. Clark
                        October 18, 2001


1.  Dynamic range

R. Perley resurrected some old data taken on 3C 273 in mode PA that did 
not achieve the dynamic range he expected of it.  He has some similar
observations in various correlator modes, which he presents in hopes that
some systematic can be discerned.  Table below gives the factor by which
map off-source RMS exceeds theoretical noise (various amounts of data 
going into each observation):
Mode      * theoretical
Cont      8              but, midday, fairly low elevation
1A        4
2AC       5              but much worse than mode 1A
PA        5

2.  Short term phase variations

R. Perley displayed data showing raw R-L phases jumping around by up to
about 12d peak-to-peak.  But, this was D configuration, and the data 
were not incompatible with the well known delay cogging.

3.  Reference pointing

R. Perley had an observation involving peaking up on 3C 345 through 
a day of observing, which he did with secondary reference pointing,
leveraging a 7mm pointing observation from a 3.6cm one.  The blind pointing 
had a very large change during the day, typically 1'.  But this was well 
tracked by the 3.6cm pointing; the additional changes made by the 7mm
pointing observation were small, except for a short time around the 
transit of 3C 345.  The rapid changes at transit are probably due to 
the pointing model we use.  We assume that all deviations from blind 
pointing are collimations; in practice the suggestion is that they mostly
result from changes in tilt.  But it is not clear how to modify the 
pointing model to incorporate them.

4.  Holography

C. Carilli has been working away at accumulating good measurements over
the summer.  See his home page for details.  Antennas 1 and 18 are difficult
to understand.  Especially puzzling is Antenna 1, which looks very good
at 1.3 cm, but clearly has serious problems with the optics at 7mm.