Forum: GNU Radio Mother of god, I'm doing FFTs with 16e6 points in them at 16Msps!

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558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2009-01-31 20:59
(Received via mailing list)
By not using the built-in-to-grc LOG POWER FFT block, and careful
selection of blocks, and eliminating blocks I didn't
  need (like the single-pole IIR filter), I was able to cut the virtual
size of the process from over 7GB to 3.5GB.  Still too
  large by (I think) a factor of two or more.

By hand-patching the grc_gnuradio/usrp library to load the 4rx_0tx FPGA
file, I can do decim=4 with 8-bit
  samples, which allows me to squirt 16Msps over the USB.

So, anyone want to buy me another 4GB of 667Mhz memory :-) :-) :-)

There are some spectral "funnies" using this scheme, since there's no
half-band filter, one has to rely on
  external filtering.  The DBS_RX has a programmable low-pass on the I
and Q baseband outputs, which
  I program with my usrp_ra_receiver  code, but I have no way to do that
within GRC, as far as I can tell.
  (Is there a way to put in arbitrary code blocks in GRC to do things
like setup the low-pass filters on
   the DBS_RX????).


--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
4252201ac30d6dd44d8090ce1070e35f?d=identicon&s=25 Josh Blum (Guest)
on 2009-01-31 21:52
(Received via mailing list)
Marcus D. Leech wrote:
> So, anyone want to buy me another 4GB of 667Mhz memory :-) :-) :-)
>
> There are some spectral "funnies" using this scheme, since there's no
> half-band filter, one has to rely on
>   external filtering.  The DBS_RX has a programmable low-pass on the I
> and Q baseband outputs, which

is this the set_bw() function?

>   I program with my usrp_ra_receiver  code, but I have no way to do that
> within GRC, as far as I can tell.
>   (Is there a way to put in arbitrary code blocks in GRC to do things
> like setup the low-pass filters on
>    the DBS_RX????).
>
>

yes, you could take the usrp_simpl_source_x.xml from grc, and put a
modified version into the ~/.grc_gnuradio/ folder

See http://gnuradio.org/trac/wiki/GNURadioCompanion#Ad...

you can add the lines to the <make>:

self.$(id)._subdev.set_bw(xxx)
self.$(id)._get_u().set_frimware(yyy)
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