[evlatests] Phase jumps on EA14

[Rick Perley]

    That's one way.  Another is to dispense with the concept of a 'best' 
antenna, and fashion the algorithm to simply avoid  the 'bad' antennas.  
Simple comparisons (over time) of the difference phase between the two 
IF channels, for RCP and LCP should quickly identify the 'jumping' 
phenomenon.  For completeness, could also include the (R-L) phase.  The 
current preferences (fewer flags, and central location) are useful, and 
should be retained.  Since there are a limited number of reasonably 
central antennas, we don't need to check many antennas. 

Barry Clark wrote:
> Perhaps the better long term solution is to get rid of the concept of
> reference antenna for pipeline purposes.  Phase solutions are
> intrinsically floating (that is, the matrix is singular).  Assuming
> one antenna has phase zero is one way of supplying the extra bit of
> information to make the solution possible; more particularly, assuming
> one antenna doesn't have phase jumps is one way to tie two phase
> solutions together.  For lots of antennas, a better way is to say
> that the mean change for all antennas is zero.  (Probably one would
> want to use one of the robust means.)
>
> On 04/24/2013 07:31 AM, Claire Chandler wrote:
>   
>> We are working on this from the pipeline side, but at the same time, such
>> things need to be fixed from the technical sided as well.  The pipeline is
>> part of end-to-end operations now.  It really does try to do something
>> sensible in picking a refant -- it is based on location in the array and
>> the amount of unflagged data (to avoid picking an antenna that is shadowed
>> or missing a receiver).  But it cannot test for phase jumps.  I don't
>> think using the same on as Telcal is always going to work either.  We are
>> working on providing a list of antennas that it should NOT use.
>>
>> Claire
>>
>> On Wed, 24 Apr 2013, Michael Rupen wrote:
>>
>>     
>>> In general it would be nice if the pipeline were smarter about choosing
>>> reference antennas.  ea14 should of course be fixed, but one bad antenna
>>> should not produce such a "ripple effect" downstream.
>>>
>>> The intelligent choice of a ref.ant. is not entirely trivial.
>>> An interim solution might be to use the same antenna we use as a reference
>>> for TelCal, which we tend to keep a careful eye on operationally.
>>> This has the benefit of matching the reference used for phased array
>>> work.  That reference antenna at the moment is ea12, but might more
>>> usefully be described as the antenna on pad E8 -- one of the three
>>> antennas which is never moved when we change configurations, and central
>>> enough when it matters (i.e., for the more extended configurations).
>>>
>>> There is no obvious place in the SDM proper at the moment to store the
>>> suggested reference antenna.  We might consider adding an element to the
>>> ExecBlock Table to handle this:
>>>
>>>    Optional:
>>>    numRefAntenna  int
>>>    refAntenna[Nrefant], Tag[Nrefant]
>>>    description: "default reference antennas for calibration, in order
>>>      of preference"
>>>
>>> We actually do send such suggestions to TelCal at the moment, so recording
>>> that information (esp. useful for phased-array data) would seem reasonable.
>>>
>>>             Michael
>>>
>>>       
>>>> Hi All,
>>>>
>>>> We are seeing phase jumps on EA14 and right now the pipeline is choosing
>>>> EA14 as a reference antenna so, when there is a phase jump, the pipeline
>>>> output is not usable.
>>>>
>>>> Is there anyway someone can go out to EA14 on Maintenance day tomorrow to
>>>> see if this can be fixed?
>>>>
>>>> Thanks,
>>>> Deb
>>>>
>>>>
>>>>
>>>>         
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