[Difx-users] integration time

[Cormac Reynolds]

hi Sam,

just following up on Adam's point. The most common cause of a very high 
residual fringe rate (as yours appears to be) in an otherwise 
functioning array is an error in the station position(s). If you send 
the vex file you used, and the stations you are interested in, it should 
be straightforward to say if that is a likely cause or not.

cheers,
Cormac.

On 13/05/17 19:57, Hagatiana Andrianomena wrote:
> Hi Adam,
>
> Many thanks for your explanations.
>
> Cheers,
> Sam
>
> On Sat, May 13, 2017 at 1:37 PM, Adam Deller <adeller at astro.swin.edu.au
> <mailto:adeller at astro.swin.edu.au>> wrote:
>
>     Hi Sam,
>
>     Integration time will affect the maximum fringe rate you are
>     sensitive to.  Shorter integrations = higher fringe rate before you
>     lose signal due to decorrelation.  But normally this is not a
>     limitation.  I would be fairly surprised if a 1 second integration
>     time was a problem (unless there is an issue with the observing setup).
>
>     Spectral resolution will affect the maximum residual delay you are
>     sensitive too.  Finer spectral resolution = larger delay before you
>     lose signal due to decorrelation.
>
>     These are not DiFX-specific things, but general to radio
>     interferometers / correlators.  To know what values are reasonable,
>     you need to know your instrument and what the expected residual
>     fringe rate and delay are.
>
>     Cheers,
>     Adam
>
>     On 12 May 2017 at 23:59, Hagatiana Andrianomena
>     <handrianomena at ska.ac.za <mailto:handrianomena at ska.ac.za>> wrote:
>
>         Hi DiFX users,
>
>         I got a question regarding the integration time in the setup:
>         SETUP default
>         {
>           tInt = 1.000000
>           fftSpecRes = 0.12500000
>           specRes = 0.12500000
>           doPolar = True
>           maxNSBetweenACAvg = 2000000
>         }
>
>         I got this default setup by running oms2v2d using the .oms file
>         from the experiment. When running the difx I got no fringe but
>         from changing the tInt to
>         0.08 and both fftSpecRes and specRes the result seems to suggest
>         I got fringe (see plot attached).
>
>         I am not quite sure whether it is a naive question but I wonder
>         if there is a simple rule of thumb to get the right values of
>         those parameters in order to get fringe. I do not have much
>         experience with DiFX I must say though.
>
>         Regards,
>         Sam
>
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>
>
>     --
>     !=============================================================!
>     Dr. Adam Deller
>     ARC Future Fellow, Senior Lecturer
>     Centre for Astrophysics & Supercomputing
>     Swinburne University of Technology
>     John St, Hawthorn VIC 3122 Australia
>     phone: +61 3 9214 5307 <tel:+61%203%209214%205307>
>     fax: +61 3 9214 8797 <tel:+61%203%209214%208797>
>
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>
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