GNU Radio + USRP
GNU Radio + USRP = SDR
GNU Radio is a project started in 1998 to have a common open source toolkit to interface with software defined radio hardware.
The USRP (the Universal Software Radio Peripheral) is a $550 ready-to-use hardware module that interfaces with a linux box through a USB 2.0 port, capable of emulating several different standards, from a simple FM receiver to a GPS receiver, or as a GSM terminal, or even as a DBT television receiver.
Imagine something like this on a single chip… a $10 chip! 
