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 from github.com/osresearch/soft-ssb. More details on Soft SSB.
Digital modes like PSK31 use an incredibly small amount of bandwidth for communication. I wrote an audio modulator for the AVR that generates the waveform. At the time I was also working on a DSS SSB modulator and succeeded in transmitting a very short distance with signally just from the digital output pin.
USB Morse Code Keyboard
I'm an Amateur Extra class radio operator and occasionally enjoy working the HF bands. For working digital modes like PSK31, this iambic paddle Morse code keyer acts as a USB keyboard when you key in correct codes and restores some of the old-fashioned feel. Read on for more details...
Summits on the air
W2VV, N2YTF and I hiked up South Beacon Peak as part of Summits on the Air and operated on 2m and 20m.