About RTL SDR

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 with 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,  or DVB-T SDR
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.
The cheapest, most common an generally best performing dongle at the moment is the Rafael Micro R820T.

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.

 

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?

 

What is the RTL-SDR frequency range?
This is dependant on the particular tuner variant used in the dongle.


Tuner

Frequency range

Rafael Micro R820T

24 – 1766 MHz

 

 

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.

 

 

Comparisons with other Wideband Commercial Software Defined Radios


SDR

Tune Low (MHz)

Tune Max (MHz)

RX Sample Rate (MHz)

ADC Resolution (Bits)

Transmit?(Yes/No)

RTL-SDR (R820T)

24

 1766

3.2

8

No

Funcube Pro

64

1700

0.096

16

No

Funcube Pro+

0.15
410

260
2050

0.192

16

No

HackRF

30

6000

20

8

Yes

BladeRF

300

3800

40

12

Yes

USRP 1

DC

6000

64

12

Yes

MatchStiq

300

3800

28

12

Yes