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<p>A curious flagging effect has been found from these recent P-band
data. <br>
</p>
<p>The observation required considerable antenna travel between the
Moon and DA 240 -- the Moon being south of the zenith, and the
other north of it, at the same RA, near meridian transit. <br>
</p>
<p>In investigating the data quality, I noticed that nine antennas <b>always</b>
got on source well before the other 18, as judged by the on-line
flags. The difference in time between the 'fast' and 'slow'
antennas ranged from a few, to up to 40 seconds. </p>
<p>The nine speedy antennas are: 04, 05, 06, 10, 12, 15, 18, 20,
and 26. Seven of these nine have old ACUs, according to the
Monday mornng summary. The two 'new' antennas in the speedy list
are 06 and 10. <br>
</p>
<p>Antennas 4 and 20 were always the first to reach the target
source, according to the flags. Antennas 06 and 10 were no
different than the others in terms of reaching the target. What
is quite remarkable is that the other 16 'new ACU' antennas always
reached the target source at <b>exactly</b> the same time --
every time. How remarkable this is! Is this really possible? <br>
</p>
<p>But were they really early on source? The evidence is mixed:</p>
<p> - When going to the strong calibrator 3C147, the 'early'
data were certainly fine. <br>
</p>
<p> - But when going to the Moon, these early data were not
good. The error level was very low, and not visible in the
individual 2-second integrations on this weak source. But the
problem was clearly evident in the vector sum data (generated via
DFTIM). What is remarkable here is that the period of the bad
data <b>always</b> ended at <b>exactly</b> the same time that
the 16 'new' ACU antennas were claimed to be on source (according
to the on-line flags). <br>
</p>
<p> Now -- how is this possible? It would seem that something
other than antenna position is influencing the flags. It's
definitely not the focus -- only one band (P) was utilized here.
<br>
</p>
<p> Rick<br>
</p>
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