RTL-SDR: Seven Years Later

Before swearing my fealty to the Jolly Wrencher, I wrote for several other sites, creating more or less the same sort of content I do now. In fact, the topical overlap was enough that occasionally those articles would get picked up here on Hackaday. One of those articles, which graced the pages of this site a little more than seven years ago, was Getting Started with RTL-SDR. The original linked article has long since disappeared, and the site it was hosted on is now apparently dedicated to Nintendo games, but you can probably get the gist of what it was about from the title alone.

An “Old School” RTL-SDR Receiver

When I wrote that article in 2012, the RTL-SDR project and its community were still in their infancy. It took some real digging to find out which TV tuners based on the Realtek RTL2832U were supported, what adapters you needed to connect more capable antennas, and how to compile all the software necessary to get them listening outside of their advertised frequency range. It wasn’t exactly the most user-friendly experience, and when it was all said and done, you were left largely to your own devices. If you didn’t know how to create your own receivers in GNU Radio, there wasn’t a whole lot you could do other than eavesdrop on hams or tune into local FM broadcasts.

Nearly a decade later, things have changed dramatically. The RTL-SDR hardware and software has itself improved enormously, but perhaps more importantly, the success of the project has kicked off something of a revolution in the software defined radio (SDR) world. Prior to 2012, SDRs were certainly not unobtainable, but they were considerably more expensive. Back then, the most comparable device on the market would have been the FUNcube dongle, a nearly $200 USD receiver that was actually designed for receiving data from CubeSats. Anything cheaper than that was likely to be a kit, and often operated within a narrower range of frequencies.

Today, we would argue that an RTL-SDR receiver is a must-have tool. For the cost of a cheap set of screwdrivers, you can gain access to a world that not so long ago would have been all but hidden to the amateur hacker. Let’s take a closer look at a few obvious ways that everyone’s favorite low-cost SDR has helped free the RF hacking genie from its bottle in the last few years.

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Pluto (SDR) Goes Ethernet

Pluto may no longer be a planet, but it is still a fun software defined radio (SDR) set up from Analog Devices. The inexpensive radio uses a USB connector and looks somewhat like a network connection to your PC. But what if you want to really use it with a network? [SignalsEverywhere] shows you how to do it using a USB network adapter and a USB connection adapter.

Just plugging a USB dongle into the box isn’t sufficient, an extra power supply is required as well as a minor bit of configuration. The IP address will be static so you might want to use an IP that your DHCP server won’t hand out, or reserve the IP on your local network.

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This SDR Uses A Tube

When you think of a software defined radio (SDR) setup, maybe you imagine an IC or two, maybe feeding a computer. You probably don’t think of a vacuum tube. [Mirko Pavleski] built a one-tube shortwave SDR using some instructions from [Burkhard Kainka] which are in German, but Google Translate is good enough if you want to duplicate his feat. You can see a video of [Mirko’s] creation, below.

The build was an experiment to see if a tube receiver could be stable enough to receive digital shortwave radio broadcasts. To avoid AC line hum, the radio is battery operated and while the original uses an EL95 tube, [Mirko] used an EF80.

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MIT IAP Tackles Radio

MIT is well known for rigorous courses, but they also have a special four-week term at the start of each year called the IAP — Independent Activities Period. This year, the MIT Radio Society had several interesting presentations on both the history and application of radio. You weren’t there? No problem, as the nine lecture were all recorded for you to watch at your leisure. You can see one of the nine, below.

These aren’t some five minute quicky videos, either. They are basically live captures that run anywhere from an hour to almost two hours in length. The topics are a great mix including radio history, software-defined radio, propagation, radio astronomy, RADAR, and even 5G.

You might have to pick and choose. Some of the lectures are suitable for just about anyone. Some assume a bit more radio expertise in electronics or math. Still, they are all worth at least a cursory skim to see if you want to really sit and watch in detail. The only nitpick is that some presenters used a laser pointer that doesn’t show up on the inset slide graphics in the video. That makes sense because the inset slides are not really in the room, but it can make it a little difficult to understand what the speaker is pointing to on a crowded slide.

Of course, if you want to dive deep and you need more background, MIT — along with many other institutions — will let you use their learning material for free. We were especially fans of the circuits class but there are many others including just raw materials from OCW.

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Radio Telescopes Horn In With GNU Radio

Who doesn’t like to look up at the night sky? But if you are into radio, there’s a whole different way to look using radio telescopes. [John Makous] spoke at the GNU Radio Conference about how he’s worked to make a radio telescope (PDF) that is practical for even younger students to build and operate.

The only real high tech part of this build is the low noise amplifier (LNA) and the project is in reach of a typical teacher who might not be an expert on electronics. It uses things like paint thinner cans and lumber. [John] also built some blocks in GNU Radio that made it easy for other teachers to process the data from a telescope. As he put it, “This is the kind of nerdy stuff I like to do.” We can relate.

The telescope is made to pick up the 21 cm band to detect neutral hydrogen from the Milky Way. It can map the hydrogen in the galaxy and also measure the rotational speed of the galaxy using Doppler shift. Not bad for an upcycled paint thinner can. These are cheap enough, you can even build a fleet of them.

This would be a great project for anyone interested in radio telescopes or space. However, it is particularly set up for classroom use. Students can flex their skills in math, engineering, programming, and — of course — astronomy and physics.

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Radio Gets Ridiculous

There were plenty of great talks at this year’s Supercon, but we really liked the title of Dominic Spill’s talk: Ridiculous Radios. Let’s face it, it is one thing to make a radio or a computer or a drone the way you are supposed to. It is another thing altogether to make one out of things you shouldn’t be using. That’s [Dominic’s] approach. In a quick 30 minutes, he shows you two receivers and two transmitters. What makes them ridiculous? Consider one of the receivers. It is a software defined radio (SDR). How many bits should an SDR have? How about one bit? Ridiculous? Then you are getting the idea.

Dominic is pretty adept at taking a normal microcontroller and bending it to do strange RF things and the results are really entertaining. The breadboard SDR, for example, is a microcontroller with three components: an antenna, a diode, and a resistor. That’s it. If you missed the talk at Supercon, you can see the newly published video below, along with more highlights from Dominic’s talk.

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Hackaday Links: July 8, 2018

Software-defined radio has been around for years, but it’s only recently that it’s been accessible to those of us who don’t have tens of thousands of dollars worth of equipment in their lab. Here’s a new book from Analog Devices that gives you the lowdown on software-defined radio. It’s heavy on MATLAB and components from Analog, but it’s still a solid foundation for SDR.

Do you like cyberpunk? Do you like stories about rebellious people overthrowing the system? How about androids? Do you like androids? Here’s a Kickstarter that’s tying all of that togetherNeptune Frost is (will be?) a movie about an e-waste village in Burundi that’s home to the ‘world’s most subversive hacking collective’, a coltan miner and an inter-sex runaway. It’s literally got everything.

Hey, this is cool, Hackaday has been cited in a journal article. The title of the article is An open-source approach to automation in organic synthesis: The flow chemical formation of benzamides using an inline liquid-liquid extraction system and a homemade 3-axis autosampling/product-collection device,  and can be found in Tetrahedron Volume 74, Issue 25, 21 June 2018, Pages 3152-3157.

Asteroid day was a few days ago, and there’s a Kickstarter to go with it. The Planetary Society, headed up by Bill Nye (a science guy) is raising awareness about the threat of asteroid impacts. There’s hilarious swag that says ‘Kick Asteroid’, even though actually kicking an asteroid might be a bad idea; a gravity tractor would be the best method of nudging the orbit of an asteroid given enough time.

Last year, a company in the US trademarked the word ‘RetroPie’ and used that trademark to sell Raspberry Pis loaded up with (you guessed it) RetroPie software. This company also used the trademark to force anyone else doing the same to stop. Obviously, this didn’t sit well with the developers of RetroPie. After some generous legal help, the RetroPie trademark issue has been resolved. That’s a tip of the hat to Eckland & Blando who offered some pro bono legal work.