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RTL-SDR: Seven Years Later | Hackaday

Before I swore allegiance to Jolly Wrencher, I wrote about several other sites, creating more or less the same kind of content that I do now. In fact, the current overlap was enough that from time to time these articles would be taken here in Hakkadai. One of these articles, who graced the pages of this site a little over seven years ago, was Getting started with RTL-SDR. The original related article is long gone, and the site it hosted is now apparently dedicated to Nintendo games, but you can probably tell what the title is all about.

RTL-SDR receiver “Old School”

When I wrote this article in 2012, the RTL-SDR project and her community was still in its infancy. It took real digging to find out which Realtek RTL2832U-based TV tuners are supported, what adapters you need to connect more capable antennas, and how to compile all the software needed to get them to listen outside the announced frequency range. range. This was not exactly the most user-friendly experience, and when all was said and done, you were largely left to your own devices. If you didn’t know how to create your own receivers on GNU Radio, there was nothing you could do but eavesdrop on hams or tune in to local FM broadcasts.

Almost a decade later, things have changed dramatically. The hardware and software of RTL-SDR have improved tremendously, but perhaps more importantly, the success of the project has given rise to something like a revolution in the world of software radio (SDR). Prior to 2012, SDRs were certainly not out of reach, but they were significantly more expensive. Then the most comparable device on the market would be the FUNcube dongle, a receiver with almost $ 200, which is actually designed to receive data from CubeSats. Anything cheaper than this is likely to be a kit and often operates in a narrower frequency range.

Today we would say that the RTL-SDR receiver is a must-have tool. With the price of a cheap set of screwdrivers, you can get access to a world that not so long ago would have been hidden from the amateur hacker. Let’s take a closer look at some of the obvious ways in which everyone’s favorite cheap SDRs have helped free the RF hacker gin from its bottle over the past few years.

Hardware evolution

Although the project is called RTL-SDR, the Realtek RTL2832U chip is actually only half of the equation; this is a USB demodulator chip that must be paired with a tuner to work. In the early days a number of different tuners were used and finding out who you were getting was quite a big deal. The Elonics E4000 was the most desired tuner as it had the widest frequency range, but it can be difficult to know in advance what you are getting.

The packaging and documentation were almost useless; either the manufacturer has not bothered to include the information, or if it has, it is often out of date as new revisions of the product are produced. The only way to be sure of what you are getting is to see if anyone has already purchased this particular model and reported their findings. Fortunately, the tuners were cheap enough for you to buy a pair and experiment. At the time, it was not uncommon to find RTL-SDR-compatible devices for less than $ 10.

Opening a modern RTL2832U + E4000 receiver, we can see that these were relatively simple cases. The hard plastic case doesn’t do much to prevent interference, and the Belling-Lee connector is designed for use with a traditional TV antenna. Note that this particular model has an IR receiver so that the user can switch TV channels with the remote control on; a reminder of what this device was actually created for.

Nowadays, you don’t have to flip through pages with almost identical USB TV tuners to find compatible hardware. There are now several RTL2832U-based receivers that are specifically designed to use the RTL-SDR, usually selling for about $ 30. These devices not only address the shortcomings of the original hardware offerings, but in many cases add new features. which just wouldn’t make sense to turn on when you were just watching TV on your computer.

Here we have the receiver “RTL-SDR Blog v3”, which is one of the most popular RTL-SDR receivers of the next generation. The plastic housing has been replaced with aluminum, which not only reduces interference but helps the board dissipate heat while working. The crystal is upgraded to a temperature compensated oscillator (TCXO), which helps reduce temperature drift. The R820T2 tuner is paired with a standard SMA antenna connector on both it and the RTL2832U has some unused pins if you want to get into the development of modifications or extensions to the underlying hardware.

Software library

Improvements to the basic RTL-SDR hardware are welcome, and it’s a good idea not to worry about whether the receiver you purchased will actually work with the drivers, but in reality these changes benefit mostly the harder users who push the edge of the envelope. If you just want to smell some 433 MHz thermometers, you don’t really need a TCXO. For most users, the biggest improvements come in the software side of things.

On the one hand, the RTL-SDR package will almost certainly be in the repository of your favorite GNU / Linux distribution. Unless you need a bleed feature, you will no longer need to compile driver tools and custom fields from the source. In principle, the same applies to the graphical interface of the SDR, namely gqrx by Alexandru Chete. These two packages are enough to show you on the air and look for interesting signals, but this is just the beginning. The rise of cheap SDRs has inspired a number of fantastic new software packages that are light years ahead of what was available before.

Of course one of the best examples is Universal Radio Hacker, a multifunctional tool that allows you to search, capture and ultimately decode wireless signals. Whether it’s a known protocol that already has a built-in decoder, or something completely new that you need to do a redesign, Universal Radio Hacker is a powerful tool for literally getting binary data out of nowhere. Those who want to reverse unknown wireless protocols should also take a look inspection, another tool developed in the last few years can be used to analyze captured waveforms.

Decode the captured ASK OOK signal in Universal Radio Hacker

If you are more interested in the practical application of these radios, there are also a number of very impressive turnkey applications that use the high availability of cheap SDRs. One such project is 1090, an ADS-B decoder specifically designed for use with RTL-SDR. With a distributed network of receivers, the software has allowed the community to democratize flight tracking through creation of open aircraft databases.

The gift of inspiration

In the years since its inception, the RTL-SDR project has become the de facto “first step” for anyone looking to experiment with radio. It’s cheap, it’s easy, and since the hardware can’t be transmitted, you don’t have to worry about accidentally bumping into the FCC or the local equivalent. Honestly, it’s hard to think of a good reason no add one of these little USB receivers to your trick bag; even if you use it only once, it will pay you more than itself.

After all, this is the biggest achievement of the RTL-SDR project. He pushed through the barrier to entry for radio experimentation and hacking are so low that they have ushered in a whole new era. From the unique point of view offered by Hackaday, we can see the sharp increase in RF projects, which correspond to the introduction of easy-to-use and extremely affordable software radio. People who may never have had a “real” radio, moreover, in their car, can now weaken the layers of obscurity that have kept most of us off the air in the past. This is a very exciting time for wireless hacking and from now on things only get more interesting. Long live RTL-SDR!

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