Re: [Discuss-gnuradio] Mother of god, I'm doing FFTs with 16e6 points in them at 16Msps!

[Josh Blum]

Marcus D. Leech wrote:
> 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

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#AddingCustomBlocks

you can add the lines to the <make>:

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