[Difx-users] Question on changing data rates during observation {External} {External} {External}

[Adam Deller]

Agree with what Geoff and Walter wrote - if you can provide details of the
before and after recording setup (number of bands, bits, etc), then it
should be possible to advise on a way forward.  In general, if the
observation had been set up that way (i.e., the vex file describes a given
mode being used for a certain amount of time, then another one being used
after that time), then there should be no problem.  If this was an
'on-the-fly' change during the observation that wasn't planned, then a vex
file that matches reality would normally need to be created before the
correlation can be set up and performed (the exception being the cases that
Walter described, where for instance some VDIF threads just stop being
recorded).

Cheers,
Adam

On Fri, 10 Mar 2023 at 05:17, Walter Brisken via Difx-users <
difx-users at listmgr.nrao.edu> wrote:

>
> It depends...
>
> The vex file which yields the .input files still need to properly describe
> the data that were taken.  If, for example, the data rate dropped because
> each channel reduced its bandwidth by 50%, that would not fly well.
>
> However, if the data rate drop were due to some VDIF threads not being
> generated / recorded, that is a case where DiFX can cope.  Newer versions
> (trunk and the soon-to-be-released 2.8 series) handle this case better
> than previous versions.
>
>         -Walter
>
> -------------------------
> Walter Brisken
> NRAO
> Deputy Assistant Director for VLBA Development
> (505)-234-5912 (cell)
> (575)-835-7133 (office)
>
> On Thu, 9 Mar 2023, Geoff Crew via Difx-users wrote:
>
> > If what was done is consistent with the experiment vex.obs file, then
> ""the
> > is answer is no", but:
> >
> > It depends a bit on what you mean about recording rates.  If you are
> > switching the recording setup, then you will need a mode (for all
> stations)
> > that explains what mode on the relevant scans was used.
> >
> > If you are dropping half of the data on the floor, results will depend
> on
> > what you actually dropped.
> >
> > DiFX can't read anyone's mind or reverse engineer crazy things that
> happen in
> > the field.  That is always what the operators have to deal with....
> >
> > On 3/9/23 11:13, Michael Dutka via Difx-users wrote:
> >>  Hi All,
> >>  A coworker of mine had a question on changing data rates during an
> >>  observation.  She wants to know if you would have to do 2 different
> >>  calls to difx for each recording rate.  I think the answer is no
> >>  because the VDIF data should have all the info difx needs to know what
> >>  to do, but I want to confirm that.
> >>
> >>
> >>  "Is DIFX smart enough to adjust the recording rate of a VDIF station
> >>  during correlation? Katherine recorded at 256 Mbps for the first 3.5
> >>  hours of R41091, then swapped down to 128 Mbps for the rest."
> >>
> >>  -Mike
> >>
> > --
> > Geoff Crew
> > gbc at haystack.mit.edu
> >
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-- 
!=============================================================!
Prof. Adam Deller
Centre for Astrophysics & Supercomputing
Swinburne University of Technology
John St, Hawthorn VIC 3122 Australia
phone: +61 3 9214 5307
fax: +61 3 9214 8797
!=============================================================!
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