RTL-SDR

"RTL-SDR is a very cheap software defined radio that uses a DVB-T TV tuner dongle based on the RTL2832U chipset. With the combined efforts of Antti Palosaari, Eric Fry and Osmocom it was found that the signal I/Q data could be accessed directly, which allowed the DVB-T TV tuner to be converted into a wideband software defined radio via a new software driver.

Essentially, this means that a cheap $20 TV tuner USB dongle with the RTL2832U chip can be used as a computer based radio scanner. This sort of scanner capability would have cost hundreds or even thousands of dollars just a few years ago. The RTL-SDR is also often referred to as RTL2832U, DVB-T SDR, RTL dongle or the “$20 Software Defined Radio”.

There are many other software defined radios better than the RTL-SDR, but they all come at a higher price. Currently we think that the Airspy ($199) and SDRPlay ($149) SDR’s are the best low cost RX only SDR’s. Then there are the HackRF ($300USD) and BladeRF SDRs ($420 and $650), which can both transmit and receive.

The RTL-SDR can be used as a wide band radio scanner. Applications include:

• Listening to unencrypted Police/Ambulance/Fire/EMS conversations.
• Listening to aircraft traffic control conversations.
• Tracking aircraft positions like a radar with ADSB decoding.
• Decoding aircraft ACARS short messages.
• Scanning trunking radio conversations.
• Decoding unencrypted digital voice transmissions.
• Tracking maritime boat positions like a radar with AIS decoding.
• Decoding POCSAG/FLEX pager traffic.
• Scanning for cordless phones and baby monitors.
• Tracking and receiving meteorological agency launched weather balloon data.
• Tracking your own self launched high altitude balloon for payload recovery.
• Receiving wireless temperature sensors and wireless power meter sensors.
• Listening to VHF amateur radio.
• Decoding ham radio APRS packets.
• Watching analogue broadcast TV.
• Sniffing GSM signals.
• Using rtl-sdr on your Android device as a portable radio scanner.
• Receiving GPS signals and decoding them.
• Using rtl-sdr as a spectrum analyzer.
• Receiving NOAA weather satellite images.
• Listening to satellites and the ISS.
• Radio astronomy.
• Monitoring meteor scatter.
• Listening to FM radio, and decoding RDS information.
• Listening to DAB broadcast radio.
• Use rtl-sdr as a panadapter for your traditional hardware radio.
• Decoding taxi mobile data terminal signals.
• Use rtl-sdr as a high quality entropy source for random number generation.
• Use rtl-sdr as a noise figure indicator.
• Reverse engineering unknown protocols.
• Triangulating the source of a signal.
• Searching for RF noise sources.
• Characterizing RF filters and measuring antenna SWR.

Furthermore, with an upconverter or direct sampling mod to receive HF signals the applications are expanded to:

• Listening to amateur radio hams on SSB with LSB/USB modulation.
• Decoding digital amateur radio ham communications such as CW/PSK/RTTY/SSTV.
• Receiving HF weatherfax.
• Receiving digital radio monodial shortwave radio (DRM).
• Listening to international shortwave radio.
• Looking for RADAR signals like over the horizon (OTH) radar, and HAARP signals.

Note that not all the applications listed may be legal in your country. Please be responsible."

http://www.rtl-sdr.com/

https://en.wikipedia.org/wiki/Software-defined_radio

http://osmocom.org/projects/sdr/wiki/rtl-sdr

https://rtlsdr.org/

https://www.facebook.com/rtlsdrblog/