A Brief RTL-SDR Introduction

Many of the links, topics, and structure were taken from the following blog post as inspiration.  https://www.rtl-sdr.com/about-rtl-sdr/

RTL-SDR is a cheap USB device that can be configured with software to allow for a computer based radio scanner that will allow you to receive live radio signals within a certain vicinity.  Depending on your budget and the RTL-SDR model you could receive frequencies from as low as 1 MHz all the way up to 6 GHz.  Additionally, nearly all of the software developed in conjunction with RTL-SDR hardware is open source, and provided free of charge.

According to the RTL-SDR Wiki page the origins of RTL-SDR stem from a mass produced DVB-T TV tuner that were developed with the RTL2832U chipset.  With the assistance of Antti Palosaari, Eric Fry, and the umbrella project regarding Open source mobile communications known as Osmocom it was discovered the RTL2832U chipset could be used to access raw I/Q data.  This allowed the DVB-T TV tuner to be converted into a wideband software defined radio.  Ever since it's discovery the RTL-SDR community has become extremely popular, and now anyone including hobbyists on a budget can indulge in the access of the radio spectrum.

What is Software Defined Radio?

Before SDR was around radio components such as modulators, demodulators, and tuners were implemented in hardware components.  With the rise of SDR and modern computing all of these components can now be implemented in software, or digitally.  Which allows for easy signal processing, and experimentation with more complex radio frequency builds.  

What can RTL-SDR Radio Scanner be used for?

The RTL-SDR can be used as a wide band radio scanner.  There are numerous applications that an RTL-SDR can be utilized for.  This is in no way an exhaustive list, but some applications include:

- Listening to EMS/Ambulance/Fire communications.
- Tracking aircraft positions like a radar with ADSB decoding.
- Decoding POCSAG/FLEX pager traffic.
- Scanning for cordless phones and baby monitors.
- Sniffing GSM signals.
- Receiving NOAA weather satellite images.
- Listening to satellites and the ISS.
- Radio astronomy.
- Listening to FM radio, and decoding RDS information.
- Reverse engineering unknown protocols.

All of the listed applications above are projects that I would eventually like to experiment with.  However, it should be noted that each individual country has it's own set of rules and regulations revolving around wireless broadcasting or receiving.  You should consult your local laws in order to understand what you can and cannot do with RTL-SDR.

What is the RTL-SDR frequency range?

This is very much dependent on the variant of USB device you purchased.  For example if you purchase a cheaper RTL-SDR on Amazon the ranges might be from 500 kHz to 1.7 GHz.  Whereas, if you were to purchase the more costly HackRF designed and sold by Great Scott Gadgets the range is from 1 MHz to 6 GHz

What is the RTL-SDRs sample rate?

What is sample rate?  Sample rate is defined as the number of samples of audio carried per second, measured in Hz or kHz.  Typically 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 input impedance?

What is input impedance?  The input impedance is defined as the measure of the opposition to current flow, both static and dynamic, into the load network being that is external to the electrical source.  Since these RTL-SDR USB devices are originally intended for TV, most devices will have an input impedance of approximately 75 Ohms, although it is unlikely to be exactly 75 Ohms over the entire frequency range.

PC requirements?

Since the majority of the components and signal processing is performed on the host machine there are some minimum PC requirements.  However, there are many RTL-SDR projects that being run on low end hardware such as Raspberry Pi single board devices.  The recommendations listed are generalized requirements, 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.  There are many different platforms for developing software defined radio applications. This can be done with a GUI environment such as GNURadio Companion or simply by running a simple Python script at the command line.

What USB device should I buy?

The cheapest, most common and generally best performing dongle at the moment is the Rafael Micro R820T2. It can be bought from the RTL-SDR website about $20 USD.  It should be noted I am in no way affiliated with this website, and I am not being sponsored to use their product page.

http://sdr.osmocom.org/trac/wiki/rtl-sdr - Official RTL-SDR Osmocom website

http://www.reddit.com/r/RTLSDR - Reddit RTL-SDR forum

http://www.reddit.com/r/SignalIdentifcation - Reddit Signal Identification forum

www.rtlsdr.org - RTL-SDR community Wiki (not updated in a while)

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.