[evlatests] Referenced Pointing Problem understood

[Heidi Medlin]

The setup scans use the same source as the first ref ptg scan, so this 
scan would be affected.  No?

Heidi

On 09/12/2018 11:07 AM, Bryan Butler wrote:
>
> Please note that not every observation utilizing referenced pointing 
> is affected by this bug.  As I understand it, it only affects 
> observations where a reference pointing scan immediately follows a 
> scan on the same source.  Most observers do not set up their SBs in 
> that way, aside from the possibility of the very first source, so 
> should be immune from this.
>
>     -Bryan
>
>
> Rick Perley wrote on 9/12/18 10:01:
>>      As part of the antenna optics alignment project, my summer 
>> student (Lucas Wilkins) and I discovered an important failure mode in 
>> referenced pointing. The details of this are contained in various 
>> emails posts distributed last May, and will not be repeated here.    
>> Due to the site power issues, it was not possible to diagnose/correct 
>> this problem over the summer.
>>
>>      with power now restored, and the array now functional, Barry 
>> suggested, and Ken implemented, a 'quick fix' to this problem, which 
>> was tested yesterday.  Ken re-ran a Ku-band script used last May, 
>> both in the original mode, and with the 'fix' put in.
>>
>>      The results are very clear:
>>
>>      a) The original script showed the failure mode on every antenna, 
>> for every solution.  Resulting solutions (in azimuth) are erratic, 
>> and in error.
>>
>>      b) The 'fixed' script showed no failures, and the solutions are 
>> consistent throughout the six referenced pointing solutions made.
>>
>>      Barry tells me that the next step is to devise and test a more 
>> elegant solution to the problem, as the current fix is something of a 
>> kludge.  I note that the 'quick fix' solution adds ten seconds to 
>> every referenced pointing operation.  (The added 10 seconds is a 
>> separate scan, with the antennas on source).
>>
>>      Until this is done, and the final solution tested and 
>> implemented, I strongly urge no observing be done utilizing 
>> referenced pointing.
>>
>>      Rick
>>
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>
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