This information about the rtl-sdr project is from Osmocom (4/21/2012):
(Please support Osmocom as they have been a/the great resource for rtl-sdr development)
DVB-T dongles based on the Realtek RTL2832U can be used as a cheap SDR, since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation. The possibility of this has been discovered by the V4L/DVB kernel developer Antti Palosaari.
The RTL2832U outputs 8-bit I/Q-samples, and the highest theoretically possible sample-rate is 3.2 MS/s, however, the highest sample-rate without lost samples that has been tested so far is 2.8 MS/s. The frequency range is highly dependent of the used tuner, dongles that use the Elonics E4000 offer the widest possible range (64 – 1700 MHz).
The following devices are known to work fine with RTLSDR software:
VID PID tuner device name 0x0bda 0x2832 all of them Generic RTL2832U (e.g. hama nano) 0x0bda 0x2838 E4000 ezcap USB 2.0 DVB-T/DAB/FM dongle 0x0ccd 0x00a9 FC0012 Terratec Cinergy T Stick Black (rev 1) 0x0ccd 0x00b3 FC0012 Terratec NOXON DAB/DAB+ USB dongle (rev 1) 0x0ccd 0x00d3 E4000 Terratec Cinergy T Stick RC (Rev.3) 0x0ccd 0x00e0 E4000 Terratec NOXON DAB/DAB+ USB dongle (rev 2) 0x185b 0x0620 E4000 Compro Videomate U620F 0x185b 0x0650 E4000 Compro Videomate U650F 0x1f4d 0xb803 FC0012 GTek T803 0x1f4d 0xc803 FC0012 Lifeview LV5TDeluxe 0x1b80 0xd3a4 FC0013 Twintech UT-40 0x1d19 0x1101 FC2580 Dexatek DK DVB-T Dongle (Logilink VG0002A) 0x1d19 0x1102 ? Dexatek DK DVB-T Dongle (MSI DigiVox? mini II V3.0) 0x1d19 0x1103 FC2580 Dexatek Technology Ltd. DK 5217 DVB-T Dongle 0x0458 0x707f ? Genius TVGo DVB-T03 USB dongle (Ver. B) 0x1b80 0xd393 FC0012 GIGABYTE GT-U7300 0x1b80 0xd394 ? DIKOM USB-DVBT HD 0x1b80 0xd395 FC0012 Peak 102569AGPK 0x1b80 0xd39d FC0012 SVEON STV20 DVB-T USB & FM
What is a SDR?
A software-defined radio system, or SDR, is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded computing devices. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible.
A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time.
In the long term, software-defined radios are expected by proponents like the SDRForum (now The Wireless Innovation Forum) to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio.