Adafruit blog posted a video I shot of Software Define Radio on BeagleBone Black. This prompted the amazing Trammel Hudson (of Brooklyn hackerspace NYC Resistor) to comment about his efforts:
Using the RTL-SDR is great for very high or ultra high frequency work, but doesn't go low enough for HF amateur radio use. I wrote code for the PRU that uses an external DAC and synthesizes SSB modulated PSK31 encoded data on the 80m and lower bands. Details and source code: http://trmm.net/Soft_SSB
From his blog post: Soft SSB - Trammell Hudson's Projects
I'm working on an embedded software-defined radio for sending PSK31 telemetry data that can run in the BeagleBone Black PRU (or perhaps repurposing the LCD interface) as well as smaller devices like the Teensy 3.1 with an embedded Digital-to-analog converter. Preliminary source is available fromgithub.com/osresearch/soft-ssb
Using a BeagleBone Black instead of the teensy opens up more useful spectrum. The DAC on the Teensy is limited to mostly audio frequency ranges, but the PRU can easily generate a smooth 2.5 MHz carrier. A simple R2R DAC isn't the cleanest , but generates acceptable signal that was capable of being received a few meters from the IC-7000 without any amplifier.
cheers,
drew