What is 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 just a few years ago. The RTL-SDR is also often referred to as RTL2832U, DVB-T SDR, or the “$20 Software Defined Radio”.
There are many other software defined radios similar to the RTL-SDR, but they all come at a much higher price. The FunCube PRO+ is a good receiver similar to the RTL-SDR, priced at around $190 USD. There is also the soon to be released HackRF (~$300USD) and BladeRF SDRs ($420 and $650), which can both transmit and receive.
What is Software Defined Radio?
Radio components such as modulators, demodulators and amplifiers are traditionally implemented in hardware components. The advent of modern computing allows these traditionally hardware based components to be implemented into software instead. Hence, the software defined radio. This enables easy signal processing and thus cheap wide band scanner radios to be produced.
What are some RTL-SDR Radio Scanner Applications?
The RTL-SDR can be used as a wide band radio scanner. Applications include
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.
What is the RTL-SDR frequency range?
This is dependant on the particular tuner variant used in the dongle.
||52 – 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)
|Rafael Micro R820T
||24 – 1766 MHz
||22 – 1100 MHz
||22 – 948.6 MHz
||146 – 308 MHz and 438 – 924 MHz (gap in between)
Table Source: Osmocom
As you can see from the table, the Elonics E4000 and Rafael Micro R820T dongles have the greatest frequency range.
What is the RTL-SDRs sample rate?
The maximum sample rate is 3.2 MS/s (mega samples per second). However, the rtl-sdr is unstable at this rate and may drop samples. The maximum sample rate that does not drop samples is 2.4 MS/s, however some people have had luck with 3.2 MS/s working well on USB 3.0.
What is the RTL-SDR’s ADC resolution?
The resolution is 8 bits.
What is the RTL-SDR input impedance?
Since these dongles are intended for TV, all dongles will have an input impedance of 75 Ohms. However, the mismatch loss when using 50 Ohm cabling will be very minimal at the frequencies the dongle can cover.
The 75 Ohm impedance for the R820T can be checked on the datasheet which can be downloaded here.
What dongle should I buy?
The cheapest, most common an generally best performing dongle at the moment is the Rafael Micro R820T. It can be bought for about $20 USD.
The Elonics E4000 used to be the most common, but Elonics has closed and ceased chip production, making the E4000 rarer and much more expensive these days.
The R820T also is generally regarded as having better performance and sensitivity for most interesting frequencies. For ADS-B, the R820T is much more sensitive at 1090 MHz. For these reasons, the R820T is currently the recommended dongle, unless you need the greater frequencies the E4000 provides.
Be careful when buying a dongle as certain sellers tend to misrepresent their devices (knowingly or unknowingly) as having compatible tuners, when in fact they may send out a device with an incompatible tuner. Also be wary when buying E4000 dongles from auction sites as there are many dodgy sellers incorrectly advertising R820T dongles as the rare E4000.
See the BUY RTL-SDR page for more information about where to obtain dongles from reputable sources.
I already have a USB TV Tuner, is it Compatible?
An up to date list on compatible and incompatible tuners can be found on this reddit wiki page.
Comparisons with other Wideband Commercial Software Defined Radios
||Tune Low (MHz)
||Tune Max (MHz)
||RX Sample Rate (MHz)
||ADC Resolution (Bits)
||400 & 650
http://sdr.osmocom.org/trac/wiki/rtl-sdr - Official rtl-sdr osmocom website
http://www.reddit.com/r/RTLSDR – Reddit rtl-sdr forum
https://groups.google.com/forum/#!forum/ultra-cheap-sdr - Google groups forum
www.sdrsharp.com - SDRSharp official website
www.rtlsdr.org - RTL-SDR community Wiki
http://www.dxzone.com/ - A good ham related database useful for research
http://www.dangerousprototypes.com - A blog about open source hardware projects that often has SDR related posts.
http://www.hackaday.com – A blog about DIY hardware that also often has SDR related posts.
http://sdrformariners.blogspot.com/ - SDR for mariners. A new blog about marine related RTL-SDR applications.
http://www.EEWeb.com - A large electrical engineering news and community website that sometimes feature SDR related stories.
http://labyrinth13.com/ - Strange Beacons. Radio user who records and makes videos about several interesting signals he finds. Often uses an RTL-SDR.
If you want to learn more about the RTL-SDR you may like our ebook available on Amazon.
The Hobbyist’s Guide to the RTL-SDR: Really Cheap Software Defined radio.