[Difx-users] integration time

Wed May 17 12:33:16 EDT 2017

Hi Mark,

Many thanks for that very useful information.
I will double-check the $CLOCK values I was
using.

Cheers,
Sam

On Wed, May 17, 2017 at 5:02 PM, Mark Kettenis <kettenis at jive.eu> wrote:

> > 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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> nrao.edu>
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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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