UK Licenced Amateur Radio Operator Jenny List G7CKF, has made available an RF Breakout kit and a Pi-HF direct conversion radio kit for the Raspberry Pi
The breakout kit provides a breakout board to use the Raspberry Pi clock generator as an RF source or simple amateur radio transmitter. The Raspberry Pi has a built-in clock generator, a powerful frequency synthesiser which can generate frequencies up to 250MHz. This is enough to provide a useful RF signal source for experimentation, or given suitable filtering and antennas to allow the Pi to be used as a low-power amateur radio transmitter.
The Pi-HF is primarily for frequencies between 130 kHz and 30 MHz, however it has a bandwidth over 100 MHz and so will also perform at higher frequencies including the 50 MHz (6m) and 70 MHz (4m) amateur bands with reduced performance. It is not a software-defined radio, instead it is a traditional direct conversion radio receiver with software control.
Raspberry Pi RF Breakout Kit (video) -
Language Spy - Amateur Radio and Raspberry Pi kits -