I’ll confess, I’ve kept some secrets from you. The fancy software radio baseband digitizer I mentioned back in November? I got it working not long after, and I’ve had some fun with it (see demo video, below). Here it is, connected to my ADRF6850 front-end board:
I wrote a quick-and-dirty capture program, starting with a libftdi (“master” branch) example program, stream_test.c. With it, I can sustain approximately 32MBytes/second. It appears my hard drive write speed is the bottleneck, as I get drop-outs periodically, but only if capturing to disk, not RAM.
I haven’t incorporated any low-pass filtering, or finished implementing proper digital downsampling of the raw baseband sample stream, so to test the system, I chose the most powerful signals available: FM broadcast. I captured about 8MHz of the local FM spectrum, centered around 101.9MHz, and was able to play it back and demodulate several channels using GNU Radio.
Up next, proper filtering, and some more interesting wideband signals! And maybe I should clean up my office before I make my next video…