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

[D.J. Pisano]

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

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D.J. Pisano, Assistant Professor
WVU Department of Physics      phone:  304-293-4886
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