RTL-SDR Monitoring Radio Wave

RTL-SDR Dongle

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 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.
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

• 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 true random number generator.

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.

Tuner	Frequency range
Elonics E4000	52 – 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)
Rafael Micro R820T	24 – 1766 MHz
Fitipower FC0013	22 – 1100 MHz
Fitipower FC0012	22 – 948.6 MHz
FCI FC2580	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 2.8 MS/s.

What is the RTL-SDR’s ADC resolution?

The resolution is 8 bits.

What is the RTL-SDR input impedance?

Input impedance is dependent on the tuner used in the dongle. Input impedance will always be either 50 or 75 ohms.
The R820T has an input impedance of 75 ohms according to the datasheet which can be downloaded here.

What dongle should I buy?

The cheapest and most common 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 ADSB, the R820T is much more sensitive at 1090MHz. 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.
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

SDR	Tune Low (MHz)	Tune Max (MHz)	RX Sample Rate (MHz)	ADC Resolution (Bits)	Transmit?(Yes/No)	Price ($USD)
RTL-SDR (R820T)	24	1766	3.2	8	No	~20
Funcube Pro	64	1700	0.096	16	No	150
Funcube Pro+	0.15 410	260 2050	0.192	16	No	200
HackRF	30	6000	20	8	Yes	~300
BladeRF	300	3800	40	12	Yes	400 & 650
USRP 1	DC	6000	64	12	Yes	700
MatchStiq	300	3800	28	12	Yes	4500

Useful Links

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.