[evlatests] Baselines - sorta.

[Vivek Dhawan]

An attempt was made to determine baselines (i.e. antenna position
offsets) on 2007Sep05, after the CALC use of atmospheric model was
corrected. In summary, things are improved but imperfect.  I will
get more data as the antennas move into B array next week. I cannot
say where the problem lies at this time.

Three antennas clearly have hardware problems:
11 and 18 have phase 'square waves' imposed on the AC IFs which must
be L302 misbehaviour. 14's phase is wildly unstable - perhaps a 
reference signal is not getting received correctly - a guess.

That's it for the summary. Details:

The table (attached) can be cut and paste into AIPS CLCOR, with the 
caveats below (sigh). It can be used as is - or comment out lines
with $.  Use of this table will not greatly improve data taken after
the Modcomps went offline (i.e. between June 28 and Sep 4th). It may
help earlier A-array Modcomp data, but I need to do more tests before
inflicting this on general users.

4, 11, 13, 16, 17, 19, 21 have offsets of ~1cm, and application of
these demonstrably improves the phase behaviour. Keep these.

18, 23, 26 also have cm-level corrections found by the fit, but the
application of the corrections is not a big improvement. Best to
comment these out, except for tests.

The rest of the antennas have small offsets, hard to tell if these are
useful or not - see last point.

VLA round-trip phase corrections are going in correctly, I believe, as
the VLA antennas show much smaller slopes than the EVLA (without RTP).

Finally, there are still phase deviations of upto 100 degrees,
quasi-sinusoidal with period of a few hours, not related to elevation,
but to distance of the antenna from center. This is seen on both EVLA
and VLA antennas. Hardware? Weather?  Earth tides? ??  (Note) The rms
in the table includes this and makes the residuals look worse. The phase
errors from position offsets have a ~30min period from the elevation
variation imposed by the observation sequence. The slope is in deg/day.

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