Jeremy Hong: Weaponizing the Radio Spectrum

Jeremy Hong knows a secret or two about things you shouldn’t do with radio frequency (RF), but he’s not sharing.

That seems an odd foundation upon which to build one’s 2018 Hackaday Superconference talk, but it’s for good reason. Jeremy knows how to do things like build GPS and radar jammers, which are federal crimes. Even he hasn’t put his knowledge to practical use, having built only devices that never actually emitted any RF.

So what does one talk about when circumspection is the order of the day? As it turns out, quite a lot. Jeremy focused on how the military leverages the power of radio frequency jamming to turn the tables on enemies, and how civilian police forces are fielding electronic countermeasures as well. It’s interesting stuff, and Jeremy proved to be an engaging guide on a whirlwind tour into the world of electronic warfare.

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Your USB Serial Adapter Just Became a SDR

To say that the RTL-SDR project was revolutionary might be something of an understatement. Taking a cheap little USB gadget and using it as a Software Defined Radio (SDR) to explore the radio spectrum from the tens of megahertz all the way into gigahertz frequencies with the addition of nothing more than some open source tools may go down as one of the greatest hacks of the decade. But even in the era of RTL-SDR, what [Ted Yapo] has manged to pull off is still pretty incredible.

With a Python script, a length of wire attached to the TX pin, and a mastery of the electron that we mere mortals can only hope to achieve, [Ted] has demonstrated using a common USB to serial adapter as an SDR transmitter. That’s right, using the cheap little UART adapter you’ve almost certainly got sitting in your parts bin right now and his software, you can transmit in the low megahertz frequencies and even up into VHF with some trickery. The project is still very much experimental, and though this may be the first time, we’re willing to bet this isn’t the last time you’ll be hearing about it.

The basic idea is that when sending certain characters over the UART serial line, they can combine with the start and stop bits to produce a square wave burst at half the baud rate. [Ted] found that sending a string of 0x55 at 19200 baud would generate a continuous square wave at 9600 Hz, and if he turned the baud rate all the way up to 2,000,000 where these USB adapters top out, that signal was transmitted at 1 MHz, right in the middle of the AM dial.

A neat trick to be sure, but alone not terribly useful. The next step was to modulate that signal by sending different characters over UART. [Ted] explains at great length his experiments with multi-level quantization and delta-sigma schemes, and each step of the way shows the improvement of the transmitted audio signal. Ultimately he comes up with a modulation scheme that produces a impressively clean signal, all things considered.

This alone is impressive, but [Ted] isn’t done yet. He realized that this method of transmission was generating some strong frequency harmonics which extended far beyond the theoretical maximum 1 MHz frequency of his UART SDR. In his experimentation he found he was able to pick up a signal from all the way out to 151 MHz, though it was too poor to be of any practical use. Dialing back the expectations a bit, he was able to successfully control a cheap 27 MHz RC toy using the 43rd harmonic of a 631 kHz signal at a range of about 10 feet with a FT232RL adapter, which he notes produces the cleanest signals in his testing.

[Ted] is still working on making transmissions cleaner and stronger by adding filters and amplifiers, but these early accomplishments are already very promising. His work reminds us of a low frequency version of the USB to VGA adapter turned GHz SDR transmitter, and we’re very eager to see where it goes from here.

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Putting That Airplane On The Map – Live And With Python

Mankind’s fascination with airplanes is unbroken. Whether you’re outside with your camera, getting an actual glimpse of the aircraft, or sitting at home with your RTL-SDR dongle and have a look at them from a distance, tracking them is a fun pastime activity. Provided, of course, that you are living close by an airport or in an area with high enough air traffic. If not, well there’s always real-time tracking online to fall back to, and as [geomatics] will show you, you can build your own live flight tracking system with a few lines of Python.

As it’s usually the case with Python, a lot of functionality is implemented and readily available from external modules, which lets you focus on the actual application without having to worry too much about the details. Similarly, plenty of data can be requested from all sorts of publicly accessible APIs nowadays. If you are looking for a simple-enough example to get into both subjects with a real-world application, [geomatics]’ flight tracker uses cartopy to create a map using Open Street Map data, and retrieves the flight information from ADS-B Exchange‘s public API.

We have seen ADS-B Exchange mentioned a few times before, for example with this ESP8266 based plane spotter and its successor. And if you’re more curious about the air traffic in your direct surroundings, it’s probably time for a DVB USB dongle.

SDR Is At the Heart of This Soup-Can Doppler Radar Set

Want to explore the world of radar but feel daunted by the mysteries of radio frequency electronics? Be daunted no more and abstract the RF complexities away with this tutorial on software-defined radar.

Taking inspiration from our own [Gregory L. Charvat], whose many radar projects have graced our pages before, [Luigi Freitas]’ plunge into radar is spare on the budgetary side but rich in learning opportunities. The front end of the radar set is almost entirely contained in a LimeSDR Mini, a software-defined radio that can both transmit and receive. The only additional components are a pair of soup can antennas and a cheap LNA for the receive side. The rest of the system runs on GNU Radio Companion running on a Raspberry Pi; the whole thing is powered by a USB battery pack and lives in a plastic tote. [Luigi] has the radar set up for the 2.4-GHz ISM band, and the video below shows it being calibrated with vehicles passing by at known speeds.

True, the LimeSDR isn’t exactly cheap, but it does a lot for the price and lowers a major barrier to getting into the radar field. And [Luigi] did a great job of documenting his work and making his code available, which will help too. Continue reading “SDR Is At the Heart of This Soup-Can Doppler Radar Set”

Sniffing RFID Readers With A Piece of Paper

We feature plenty of printed projects here on Hackaday, though they tend to be of the three dimensional type thanks to the proliferation of affordable 3D printers. But in this case, [Milosch Meriac] has managed to put together a printable design that’s not only a very cool hack, but is made up of a scant two dimensions. His creation, which could perhaps be considered something of an interactive circuit diagram, allows anyone with a paper printer and a few passive components to make a functional low-frequency RFID sniffer.

[Milosch] tells us the goal of the project is to lower the barrier for experimenting with the RFID technology that’s increasingly part of our everyday lives. Rather than having to use something expensive and complicated such as an oscilloscope, experimenters can simply plug their DIY RFID sniffer into their computer’s line-in jack and explore the produced waveform with open source tools.

To create a paper RFID sniffer, you start by printing the image out on a thick piece of paper, like card stock. You then apply foil tape where indicated to serve as traces in this makeshift PCB, and start soldering on the components as described in the text. [Milosch] says the assembly procedure is so simple even a kid can do it, and the total cost of each assembled sniffer is literally pennies; making this an excellent project for schools or really any large group.

If you want to play it safe the sniffer can be connected to a USB sound card rather than your machine’s primary sound hardware, and still come in dirt cheap. [Milosch] stops short of explaining the software side of things in this particular project, but any tool which can use input from the sound card as a makeshift oscilloscope should be a good start.

In the past we’ve seen [Milosch] perform low frequency RFID sniffing through the sound card with the powerful baudline tool, but if you want a little more capable hardware, we can point you in the right direction.

A Sneak Peek at Anechoic Chamber Testing

[Mathieu Stephan] has something new in the works, and while he isn’t ready to take the wraps off of it yet, he was kind enough to document his experience putting the mysterious new gadget through its paces inside an anechoic chamber. Considering the majority of us will never get inside of one of these rooms, much less have the opportunity to test our own hardware in one, he figured it was the least he could do.

If you’re not familiar with an anechoic chamber, don’t feel bad. It’s not exactly the sort of thing you’ll have at the local makerspace. Put simply it’s a room designed to not only to remove echos on the inside, but also be completely isolated from the outside. But we aren’t just talking about sound deadening, the principle can also be adapted to work for electromagnetic waves. So not only is in the inside of the anechoic chamber audibly silent, it can also be radio silent.

This is important if you want to test the performance of things like antennas, as it allows you to remove outside interference. As [Mathieu] explains, both the receiver and transmitter can be placed in the chamber and connected to a vector network analyzer (VNA). The device is able to quantify how much energy is being transferred between the two devices, but the results will only be accurate if that’s the only thing the VNA sees on its input port.

[Mathieu] can’t reveal images of the hardware or the results of the analysis because that would give too much away at this point, but he does provide the cleverly edited video after the break as well as some generic information on antenna analysis and the type of results one receives from this sort of testing. Our very own [Jenny List] has a bit more information on the subject if you’d like to continue to live vicariously through the accounts of others. For the rest of us, we’ll just have to settle for some chicken wire and a wooden crate.

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All The Goodies You Need For Your RTL-SDR

When the RTL2832-based USB digital TV sticks were revealed to have hidden capabilities that made the  an exceptionally cheap software-defined radio receiver, it was nothing short of a game-changing moment for the home radio experimenter. The RTL might not be the best radio available, but remains a pretty good deal for only $10 from your favourite online supplier.

Having bought your RTL SDR, you will soon find yourself needing a few accessories. A decent antenna perhaps, an HF upconverter, and maybe an attenuator. To help you, [IgrikXD] has come up with a repository containing open-source implementations of all those projects and more. There’s an HF upconverter handily in both SMD and through-hole versions, as well as a wideband active antenna. A resonant antenna for a single band will always out-perfom a wideband device if your interest lies on only one frequency, but when your receiver has such a wide range as that of the RTL it’s irresistible to look further afield so the wideband antenna is a useful choice.

The RTL SDR is a device that just keeps on giving, and has featured innumerable times here since since its first appearance a few years ago. Whether you are into passive radar or using it to decode data from RF-equipped devices it’s the unit of choice, though we rather like it as a piece of inexpensive test equipment.

Via Hacker News.

Header image: Joeceads [CC BY-SA 4.0].