Many amateurs have done a lot with Raspberry Pi ranging from cat control to converting it to a full fledged SDR transceiver. The latest kid in the block of SDR Transceivers is Radioberry. It’s a combination of Raspberry Pi with a radio board developed using AD9866 12-bit microcontroller.
Radioberry Board actuall directly connects with the Raspberry Main Board. This braodband model mixed signal front end has been actually remodeled as a direct down and up conversion SDR Transceiver covering the entire HF spectrum (0-30 Mhz)
The radio card uses an Intell Cyclone 10LP FPGA, supporting the 10CL16 and 10CL25. The firmware will be loaded via the raspberry pi. Power supply for the radio card is provided by the raspberry pi. The radio is fully built by using open source software and open hardware.
Hereby an overview of links for more information:
Discussion Forum about the Radioberry
WIKI giving additonal information
Radioberry Releases making an easy install