[Pafgbt] save PAF cross-correlations rather than formed beam outputs

[Felix J Lockman]

>From my experience looking at galactic HI profiles from the GBT, a
resolution of 2 kHz would seem the coarsest acceptable.  There are some
narrow lines out there.

Jay

> Brian,
>
> Oh, sure.  As opposed to citing number of channels then, let me just
> state frequency resolutions:
>
> Extragalactic HI:  24.414 kHz is fine.  (5.2 km/s)
>
> Galactic HI:  < 6.104 kHz is fine.  (1.3 km/s, although half that
> would be better).
>
> I think those numbers are consistent with what we said in the ATI
> proposal.  A factor of 2 worse frequency resolution is tolerable, but
> not ideal.  Speaking of the ATI, have you all heard anything?
>
> I need to read the Elmers paper as well to get back up to speed on all
> of the different considerations for the PAF.
>
> --D.J.
>
> On Tue, May 21, 2013 at 4:59 PM, Brian Jeffs <bjeffs at byu.edu> wrote:
>> Thanks D.J., that gives us some perspective.
>>
>> My note could have been a bit misleading since in the CASPER F engine,
>> for a 2048 point FFT we get 1024 frequency channels (real input data, so
>> we throw away the symmetric mirror image frequency bins).  I was quoting
>> N as FFT size, so to get the number of channels you mention requires an
>> FFT that is double the size, e.g. N=8192 for the 20 MHz BW Galactic HI
>> case would give 4096 channels.  This is more than we can do with our
>> existing system.  Perhaps with more ROACHs we could get this big an FFT
>> working on fewer inputs, but I have not seen it done.
>>
>> Brian
>
> ------------------------------------------------------------------------------------
> D.J. Pisano, Assistant Professor
> WVU Department of Physics      phone:  304-293-4886
> P.O. Box 6315                               fax:    304-293-5732
> Morgantown, WV 26506 USA    djpisano at mail.wvu.edu
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Felix J. Lockman           EMAIL:jlockman at nrao.edu
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