[Difx-users] integration time

[Mark Kettenis]

> From: Hagatiana Andrianomena <handrianomena at ska.ac.za>
> Date: Mon, 15 May 2017 08:51:59 +0200

Sam,

Note that if you are using $CLOCK parameters from a correlation with
SFXC, the rates may not be specified in a form that DiFX expects.  If
the "unit" isn't specified, SFXC will interpret the rate as usec/sec,
whereas DiFX will interpret the rate as sec/sec.

Cheers,

Mark

> Hi Cormac,
> 
> Please see attached the vex. I am interested in EF-YS-NK-HH-O8.
> 
> cheers,
> Sam
> 
> On Mon, May 15, 2017 at 7:45 AM, Cormac Reynolds <cormac.reynolds at csiro.au>
> wrote:
> 
> > 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>
> >>
> >>     office days (usually): Mon-Thu
> >>     !=============================================================!
> >>
> >>
> >>
> >>
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> >>
> >>
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> [2:application/octet-stream Show Save:n17c1.vex (66kB)]
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