VLA Test/Observation Coordination Meeting
                           B.G. Clark
                       September 15, 2005

1.  EVLA

R. Perley had a look at short term phase stability at L band, and says 
that the phase excursions are comparable to VLA, but with a different
spectrum.  The issue is confused by the known phase cogging induced,
for all antennas, by the delay switching.  He also reports a dropout 
phenomenon in which the amplitude from antenna 14 drops out, to near 
zero, when viewed with a 400ms average.  This occurs every ten seconds 
(but not on a 10s IAT tick, and not in every scan).  In comparison
with VLA antennas, baselines with 14 and 16 are about 20% worse,
and the 14-16 baseline is about 40% worse.  (IF 14 B appears broken;
amplitudes take jumps of order one dB on a half second timescale.)

The autocorrelation spectra show a broad peak, about 500 kHz wide,
at about 1465 MHz.  This also appears in VLA antennas.

K. Sowinski reports that the pointing has a 'clunk' in azimuth.
There are two states, and the antenna sometimes switches state when
it is driven over-the-top.  He also notes that the Executor uses
a model atmosphere, rather than real measurements, for calculating
the refraction correction to pointing.  The effect is noticeable.

B. Clark reports that he looked at some measurements made by the
L351 phase meters of the round trip phase.  Measurements are well
behaved and changes are slow.  The main effect is the diurnal
thermal term, which need not be corrected for many types of 
observing, at it is removed in the calibration process.  At a time
when the antenna was observing a baseline file, the worst case jump
seen due to antenna motion was about 800 fs, or about 15d at Q
band.  From this he concludes:  1.) the L351 averaging time can be
changed from 1s to 10s, to decrease the output data rate; and 2.)
the phase is behaving well enough that the priority of implementing
the round-trip correction decreases below many other software tasks.

P. Napier raised the question of whether the current IF conversion 
scheme, which denies access to X band below 8.4 GHz is acceptable.
P. Palmer said the equivalent science could be gotten from recomb
lines higher in the band, but F. Owen said that that part of X band
is sometimes useful for Faraday rotation studies.