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
Principal Investigator, Shirleys Bay Radio Astronomy Consortium