[evlatests] Phase jumps on EA14

[Rick Perley]

    ... and why is it so hard for a script to identify phase-jumping 
antennas?  Such effects are trivially seen 'by eye' in any 
baseline-ordered phase plot.    Admittedly  harder for long baselines at 
high frequencies in poor weather.  Comparing phases between 'IFs' should 
help here. 

    BTW -- the phase problem in ea14 has been going on for some weeks.  
Most of the 'pipeline' data I reviewed clearly showed the effect, and 
was written up by me in my reports. 

Michael Rupen 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.
>>     
>
> Which might be one reason to apply the same considerations to on-line as to
> off-line calibration ;)
>
>   
>>  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).
>>     
>
> Of course this is true, and I didn't mean to say that the current
> choice was not rational. Basically I'm advocating adding another sensible 
> criterion to the list, based on global stability, which the pipeline
> fundamentally cannot know from internal information in the data set at 
> present.  I would like to add that long-term information eventually to the SDM 
> so that we can use it in post-processing, as we do in the real-time system. 
> Of course TelCal can and should learn from the post-processing approach as 
> well, though there I'd say the major issue is the robustness of the algorithm 
> to bad data, rather than the choice of reference antenna.
>
>   
>>  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.
>>     
>
> This seems a much harder problem to me than an ordered list of
> ones which we track carefully and believe *do* work.  Such a list can be
> as short as we want it to be -- we only need a few truly trustworthy
> dishes, after all -- and even better, that list already exists. We 
> cannot be in the mode of requiring that all antennas work perfectly at all 
> bands, or even requiring that we know immediately when any antenna/band/IF 
> combo goes bad -- the system is too large and complex for that, and we do not 
> have the manpower to make it as gloriously tracked as we'd like it to be. 
> Even if _we_ could, presumably we are aiming at this pipeline being extensible 
> to other and larger observatories -- at least ALMA, and I would hope others
> if we do a good job -- and those are going to be even more complex and
> harder to track.
>
>
>               Michael
>
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