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

[Marcus D. Leech]

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