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 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.
What is Software Defined Radio?
Radio components such as modulators, demodulators and tuners are traditionally implemented in hardware components. The advent of modern computing allows most of these traditionally hardware based components to be implemented into software instead. Hence, the term 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 dependent on the particular tuner variant used in the dongle, and the particular implementation. Some dongles, like our RTL-SDR Blog V3 also utilize the direct sampling mode which can enable reception below 28 MHz.
||52 – 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)
|Rafael Micro R820T/2
||24 – 1766 MHz (Can be improved to ~13 – 1864 MHz with experimental drivers)
||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 2.8MS/s and 3.2 MS/s working well on some USB 3.0 ports.
What is the RTL-SDR’s ADC resolution?
The native resolution is 8 bits, but the Effective Number of Bits (ENOB) is estimated at ~7. Decimation in software may raise this value.
What is the RTL-SDR input impedance?
Since these dongles are intended for TV, most dongles will have an input impedance of about 75 Ohms. However, remember that the mismatch loss when using 50 Ohm cabling on a 75 Ohm input will be very minimal at less than 0.177 dB.
The 75 Ohm impedance for the R820T can be checked on the datasheet which can be downloaded here.
What are the minimum PC requirements?
Generally, at least a dual core processor of some sort will be required for most general GUI based software defined radio software. Command line tools and ADS-B decoders may work with less powerful hardware. Single board PCs like the Raspberry Pi 3, and Android mobile devices can also run several applications.
What dongle should I buy?
The cheapest, most common and generally best performing dongle at the moment is the Rafael Micro R820T/2. 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. Note that there seems to be a misconception that the E4000 is better than the R820T/2 because it costs more – this is not the case, the increased cost is only due to its rarity.
The R820T/2 is generally regarded as having better performance and sensitivity for most interesting frequencies compared to the E4000. For ADS-B, the R820T is much more sensitive at 1090 MHz. There are now also the R820T2 dongles, which offer increased sensitivity over the R820T. For these reasons, the R820T2 is currently the recommended dongle, unless you need the higher frequencies that the E4000 provides and are willing to pay a premium price.
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/2 dongles as the rare E4000.
See our RTL-SDR store page for more information about where to obtain dongles from reputable sources. We now sell our own “RTL-SDR Blog V3” dongles which come with several key improvements for the SDR crowd and we recommend these for users who want to mainly use their dongle for SDR.
I already have a USB TV Tuner, is it Compatible?
If your TV tuner contains an RTL2832U chip it is probably compatible. If it does not contain this chip, it is not compatible. A list (somewhat out of date) on compatible and incompatible tuners can be found on this reddit wiki page.
Comparisons with other common Wideband Commercial Software Defined Radios
||Tune Low (MHz)
||Tune Max (MHz)
||RX Bandwidth (MHz)
||ADC Resolution (Bits)
||400 & 650
For those who just want to receive a wide range of signals, we recommend the Airspy or SDRPlay as an upgrade to the RTL-SDR. If you are mainly interested in narrowband signals the Funcube Dongle Pro+ may be worth considering.
For a big list of more software defined radios see our roundup here http://www.rtl-sdr.com/roundup-software-defined-radios/.
No official schematic is available, but GGToshi has created his own reverse engineered schematic which is available at http://ggtoshi.at.webry.info/201406/article_6.html. Some application example schematics are also available in the R820T data sheet (see below).
There is no datasheet available for the RTL2832U as it is only available to manufacturers under NDA. The R820T tuner datasheet is available and can be downloaded here.
The Register Description datasheet can be downloaded here.
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.rtlsdr.org – RTL-SDR community Wiki (not updated in a while)
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://radioforeveryone.com/ – Formerly known as “SDR4Mariners”. Another blog about RTL-SDR and radio projects.
http://labyrinth13.com/ – Strange Beacons. Radio user who records and makes videos about several interesting signals he finds. Often uses an RTL-SDR.