"Don't have $1500 to drop on a USRP? A Linux kernel developer has discovered that a Realtek digital TV tuner chip has an undocumented mode that turns it into a software-defined radio, with a frequency range of 64-1700MHz. The going rate for one of these USB devices can be as low as US$11. If you're unfamiliar with software-defined radio and have 20 minutes to spare, Balint Seeber has a great video introduction."
Some of the links may take a second to load as they are getting "Slashdotted" right now (servers overloaded with requests).