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<pre>EW
</pre>
<pre>ea09 N16 0.21 -0.58 -0.37 123 -.030</pre>
<pre>NS</pre>
<pre>ea09 N16 -0.65 -1.20 -1.85 1182 -1.08
</pre>
<div class="moz-cite-prefix">On 4/4/2022 2:57 PM, Rick Perley via
evlatests wrote:<br>
</div>
<blockquote type="cite"
cite="mid:8a3c68bd-afeb-5412-9544-53a8b06d510d@nrao.edu">What are
the values for ea09 (at N16), which was the reference antenna I
used?
<br>
<br>
On 4/4/22 14:20, Barry Clark via evlatests wrote:
<br>
<blockquote type="cite">Just for specificity, I'll quote the tilts
actually in use. For VLA, we have separate tilts for the
antenna and the pad, so that in theory the antenna can be moved
from pad to pad without changing the pointing parameters. What
is used is the sum. What we are interested in is the tilt
relative to the vertical at the array center.
<br>
<br>
Ant. Pad AntEW tilt PadEW tilt SumEW tilt X CenterEW
tilt
<br>
<br>
ea01 W06 0.51 0.68 1.19 -261 1.33
<br>
ea03 W18 0.24 -1.95 -1.71 -1722 -2.85
<br>
ea05 E14 0.52 -5.37 -4.85 1001 -4.31
<br>
ea06 N06 0.52 -1.20 -0.68 22 -0.67
<br>
ea22 W12 1.10 0.10 1.20 -859 0.74
<br>
<br>
Ant AntNS tilt PadNS tilt SumNS tilt Z CenterNS
tilt
<br>
ea01 -0.44 1.74 2.18 -136 2.09
<br>
ea03 0.02 3.39 3.41 -900 2.82
<br>
ea05 -0.19 0.67 0.48 -442 0.20
<br>
ea06 0.43 -2.19 -1.76 220 -1.62
<br>
ea22 -0.44 0.60 0.16 -448 -0.13
<br>
<br>
<br>
On 4/1/22 10:41, rperley via evlatests wrote:
<br>
<blockquote type="cite">There is a simple explanation for the
R-L phase differentials -- a differential tilt between the two
antennas. If the two antennas' poles point in slightly
different directions, the parallactic angles seen by each are
different, which results in a different measured phase for the
two polarizations.
<br>
<br>
For the 'RR' correlation, the phase difference is -(delta par
angle), for the 'LL' correlation, it is +(delta par angle), so
the R-L difference is twice the difference is parallactic
angle between the two antennas.
<br>
<br>
This effect is independent of band -- it is purely
geometrical.
<br>
<br>
To show how these differentials vary with source declination,
I generated plots for the four sources observed: 3C286 (dec =
30.5), OQ208 (dec = 28.5), 3C287 (dec = 25.2), and 3C273 (dec
= 2.1). I generated curves for a E-W tilt, and a N-S tilt.
<br>
<br>
Attached is the resulting plot, showing the predicted R-L
phase in degrees as a function of Hour Angle, for the four
sources. Solid lines are for an E-W tilt, Dashed lines for N-S
tilt.
<br>
<br>
The match to the observed data is extremely good. (To be
fair, the match to the largest of the 'even' tilts is
extremely good). But I bet that a suitable combination of E-W
and N-S tilts would give a good fit to almost all of the data.
<br>
<br>
There is only one problem -- the amplitude of the tilt
required to give the size of the observed phase is about 5
times larger than the largest measured tilt. The plots were
generated with a tilt differential (between the two antennas)
of 6 arcminutes.
<br>
<br>
So, if this model has any relevance, it begs the question:
How do we measure the antenna tilts? Are these tilts
different than those used in the model?
<br>
<br>
Rick
<br>
<br>
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</blockquote>
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