[evlatests] Large Bz error?

[Vivek Dhawan]

WIDAR data from Sept 01 also show this - but I think its more
of a time error.

The phases after transfer from 3C286 to the 2 other targets show
residuals upto of 100deg, of opposite sign on the farthest E and W
antennas. The two target sources are Both about 1.5 deg away from
3C286 in declination, in the same sense, but their RA offsets are
<0.5 and ~4deg, and the farther one shows a much bigger EW phase diff.

I think this is more like a time error of ~0.5 second(!)
(I get this as follows: ~90deg @ 6cm =  1.5cm error over 1/10 radian
throw or 15cm at ends of C array, (Sep 1 was still C array)

This is only on WIDAR data, the VLA baselines data from sep 23 and 26
show only ~1cm offsets from the antenna moves, and with no systematic
dependence on arm position as would result from time offset.


Rick Perley wrote:
>     Further observations based on the Thursday night data ...
> 

> 
>     2) There is a very clear, and very large, time independent offset in 
> phase between the four sources.  The offset is clearly a function of the 
> source declination.  Such an offset is most likely due to a error in the 
> antenna position z-coordinate.    Not all antennas show this effect, but 
> those that show it strongly are all at the ends of the arms. 

snip

>     These position errors should explain why phase calibration of an 
> object which is a few degrees away from a calibrator returns a very poor 
> image. 
>    
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