[evlatests] Referenced Pointing Stats

[Barry Clark]

You might have a look and see if the loss of gain is related to the
size of the offset applied.  We went through a spate of that a while
ago, I think with Miriam handling it.  Any chance the fix became
unstuck?

Rick Perley wrote:
>     I have commented recently that 'referenced pointing' seems to be 
> less effective these days than in the past.  Here are some statistics to 
> back this claim up:
> 
>     In reviewing the long history of 'flux density' measurements, the 
> data taken in January 2006 stand out as exceptionally good.  I reviewed 
> the distribution of the gain solutions from the source 3C147 at 43 GHz 
> taken then, and compared these to the data taken in late December 2010, 
> of the same source is very similar weather (light winds, mostly clear 
> skies). 
> 
>     In January 2006, we had 15 observations of 3C147, using 22 
> antennas.  Of these ~330 solutions:
> 
>        Four had a amplitude low by 5%, and 19 others were low by 3 to 5%. 
> 
>     In December 2010, we had 9 observations of 3C147, using 25 
> antennas.  Of these ~240 solutions:
> 
>        Three had an amplitude low by 20%, 12 others low by 10 to 20%, 26 
> others low by 5 to 10%.  (It is meaningless to count the rest, as the 
> antenna pointing is too uncertain). 
>    
>     For reference:  at 43 GHz:
> 
>     A 9 arcsecond error results in an amplitude loss of 3%
>     A 12 arcsecond error ...........................................   5%
>     A 16 arcsecond error .............................................10%
>     A 22 arcsecond error .............................................20%
> 
>     Thus, in January 2006, ~1% of the antenna pointings were in error by 
> more than 12 arcseconds.
>     But in December 2010, 17% of the pointings were worse than this. 
> 
>     I need to emphasize that referenced pointing *is* making the large 
> corrections needed to get the beam 'more or less' on source.  But the 
> claimed accuracy -- which we have met in the past -- is not currently 
> being met. 
> 
>    
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