LuaRadio Brings More Options to SDR

GNURadio is the swiss-army-knife of software-defined radio suites: it does everything and anything. It has a great GUI overlayer that makes creating radio flows fairly simple. There are only two areas where we could quibble with the whole system — it’s a gigantic suite of software, and it’s a lot harder to code up in Python than it is to use the GUI.

[Vanya Sergeev] started up his LuaRadio project to deal with these shortcomings. If you’re looking for the full-GUI experience, you’re barking up the wrong tree here. LuaRadio is aimed at keeping things easy to code and keeping the codebase small and tidy.

That doesn’t mean that it departs entirely from GNURadio’s very successful flow-graph programming paradigm, however, and if you’re comfortable with the procedure of hooking up a signal source to a filter block to an output, you’ll be doing fine here as well. Check out the obligatory FM radio demo — the “hello world” of SDR — and you’ll see how it works: instantiate the various blocks in code, and then issue “connect” commands to link them together.

LuaRadio’s main selling points are its size and the ease of programming it by hand. It’s got great documentation to boot. It’s written as a library that’s embeddable in your C code, so that you can write standalone programs that make use of its functionality.

LuaRadio is a new project and it doesn’t have a GUI either. It may not be the ideal introduction to SDR if you’re afraid of typing. (If you are new to SDR, start here.) But if you want to code up your SDR by coding, or run your radio on smaller devices, it’s probably worth a look. It’s at v0.1.1, so we’re looking forward to hearing more from LuaRadio in the future. Any of you out there use it? We’d love to hear in the comments.

GPS And SDR Combine Forces

Software-defined radio (or SDR) is a relatively new (to average tinkerers, at least) way of sending and receiving radio signals. The interest in SDR exploded recently with the realization that cheap USB TV tuner cards could be used to start exploring the frequency spectrum at an extremely reduced cost. One of the reasons that this is so advantageous is because of all of the options that a general-purpose computer opens up that go beyond transmitting and receiving, as [Chris] shows with his project that ties SDR together with GPS.

The goal of the project was to automatically tune a radio to the local police department’s frequency, regardless of location. To do this, a GPS receiver on a computer reports information about the current location. A JavaScript program feeds the location data to the SDR, which automatically tunes to the local emergency services frequencies. Of course, this relies on good data for what those frequencies are, but this is public information in most cases (at least in the US).

There are a lot of opportunities here for anyone with SDR. Maybe an emergency alert system that can tune to weather broadcasts if there’s a weather alert, or any of a number of other captivating projects. As for this project, [Chris] plans to use Google’s voice recognition software to transcribe the broadcasts as well. The world of SDR is at your fingertips to do anything you can imagine! And, if you’re looking to get started in it, be sure to check out the original post covering those USB TV tuner dongles.

Hackaday Dictionary: Software Defined Radio (SDR)

We are entering a new era of radio technology. A new approach to building radios has made devices like multi-band cell phones and the ubiquitous USB TV receivers that seamlessly flit from frequency to frequency possible. That technology is Software Defined Radio, or SDR.

A idealized radio involves a series of stages. Firstly, an antenna receives the radio signal, converting it into an electrical signal. This signal is fed into a tuned resonator which is tuned to a particular frequency. This amplifies the desired signal, which is then sent to a demodulator, a device which extracts the required information from the carrier signal. In a simple radio, this would be the audio signal that was encoded by the transmitter. Finally, this signal is output, usually to a speaker or headphones.

A replica foxhole crystal set. Photo: Bill Jackson
A replica foxhole crystal set. Photo: Bill Jackson

That’s how your basic crystal radio works: more sophisticated radios will add features like filters that remove unwanted frequencies or additional stages that will process the signal to create the output that you want. In an FM radio, for example, you would have a stage after the demodulator that detects if the signal is a stereo one, and separates the two stereo signals if so.

To change the frequency that this radio receives, you have to change the frequency that the resonator is tuned to. That could mean moving a wire on a crystal, or turning a knob that controls a variable capacitor, but there has to be a physical change in the circuit. The same is true of the additional mixing stages that refine the signal. These circuits may be embedded deeply in the guts of the radio, but they are still there. This is the limitation with normal receivers: the radio can’t receive a signal that is outside the range that the resonator circuit can tune to, or change the way it is demodulated and processed. If you want to receive multiple frequency bands or different types of signals, you need to have separate pathways for each band or type of signal, physically switching the signal between them. That’s why you have physical AM/FM switches on radios: they switch the signal from an AM radio processing path to an FM one.

Software Defined Radios remove that requirement. In these, the resonator and demodulator parts of the radio are replaced by computerized circuits, such as analog to digital converters (ADCs) and algorithms that extract the signal from the stream of data that the ADCs capture. They can change frequencies by simply changing the algorithm to look for another frequency: there is no need for a physical change in the circuit itself. So, an SDR radio can be tuned to any frequency that the ADC is capable of sampling: it is not restricted by the range that a resonator can tune to. Similarly, the demodulator that extracts the final signal you want can be updated by changing the algorithm, changing the way the signal is processed before it is output.

This idea was first developed in the 1970s, but it didn’t really become practical until the 1990s, when the development of flexible field-programmable gate array (FPGA) chips meant that there was enough processing power available to create single chip SDR devices. Once programmed, an FPGA has no problem handing the complex tasks of sampling, demodulating and processing in a single device.

Most modern SDRs don’t just use a single chip, though. Rather than directly converting the signal to digital, they use an analog front end that receives the raw signal, filters it and converts it down to a fixed frequency (called the intermediate frequency, or IF) that the ADCs in the FPGA can more easily digitize. This makes it cheaper to build: by converting the frequency of the signal to this intermediate frequency, you can use a simpler FPGA and a cheaper ADC, because they don’t have to directly convert the maximum frequency you want to receive, only the IF. As long as the front end can convert a band of signals down to an intermediate frequency that the FPGA can digitize, the SDR can work with it.

The BladeRF, a modern SDR device that can receive and transmit signals between 300 MHz and 3 GHz

This flexibility means that SDR devices can handle a huge range of signals at relatively low cost. The $420 BladeRF, for instance, can receive and transmit signals from 300 MHz to 3.8 GHz at the same time, while the $300 HackRF One can work with signals from 1 MHz up to an incredible 6 GHz. The ability of the BladeRF to both receive and transmit means that you can use it to build your own GSM phone network, while the low cost of the HackRF One makes it a favorite of radio hackers who want to do things like make portable radio analyzers. Mass produced models are even cheaper: by hacking a $20 USB TV receiver that contains an SDR, you can get a radio that can, with a suitable antenna, do things like track airplanes or receive satellite weather images. And all of this is possible because of the idea of Software Defined Radio.

[Main image source: DVB dongle by Dsimic on Wikipeda CC-BY-SA]

The Booths Of Hamvention

Hamvention was last weekend in Dayton, Ohio. Last weekend was also the Bay Area Maker Faire, and if you want tens of thousands of people who actually make stuff there’s really only one place to be. Bonus: you can also check out the US Air Force Museum at Wright-Patterson AFB. The ‘Space’ hangar was closed, so that’ll be another trip next year.

The biggest draw for Hamvention is the swap meet. Every year, thousands of cars pull up, set up a few tables and tents, and hock their wares. Everything from radios from the 1920s to computers from the 1980s can be found at the swap meet. This post is not about the swap meet; I still have several hundred pictures to go through, organize, label, and upload. Instead, this post is about the booths of Hamvention. Everything imaginable could be found at Hamvention, from the usual ARRL folks, to the preppers selling expired MREs, and even a few heros of Open Hardware.

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$25 Satellite Tracker Boasts “Usefulness Optional”

[Paul] is very up-front about the realities of his $25 Satellite Tracker, which aims a tape measure yagi antenna at a satellite of choice and keeps it tracking the satellite as it moves overhead. Does it work? Yes! Is it cheap? Of course! Is it useful? Well… did we mention it works and it’s cheap?

When [Paul] found himself wanting to see how cheaply he could make a satellite tracker he already had an RTL-SDR (which we have seen used for satellite communication before) and a yagi antenna made out of a tape measure, but wanted some way to automatically point the antenna at a satellite as it moved across the sky. He also wanted to see just how economically it could be done. Turns out that with some parts from China and code from SatNOGS (open-source satellite tracking network project and winner of the 2014 Hackaday Prize) you have most of what you need! A few modifications were still needed, and [Paul] describes them all in detail.

Satellite Tracker In Parking Lot ThumbnailSo is a $25 Satellite Tracker useful? As [Paul] says, “Probably not.” He explains, “Most people want satellite trackers so that they can put them outside and then control the antenna from inside, which someone probably can’t do with mine unless they live in a really nice place or build a radome. […] Driving somewhere, setting it up correctly (which involves reprogramming the Arduino for every satellite), and then sitting around is pretty much the opposite of useful.”

It might not be the most practical but it works, it’s cool, he learned a lot, and he wrote up the entire process for others to learn from or duplicate. If that’s not useful, we don’t know what is.

Satellite tracking is the focus of some interesting projects. We’ve even seen a project that points out satellite positions by shining a laser into the sky.

Software Defined Radio App Store

Software defined radios (SDRs) can–in theory–do almost anything you need a radio to do. Voice? Data? Frequency hopping? Trunking? No problem, you just write the correct software, and you are in.

That’s the problem, though. You need to know how to write the software. LimeSDR is an open source SDR with a crowdfunding campaign. By itself, that’s not anything special. There are plenty of SDR devices available. What makes LimeSDR interesting is that it is using Snappy Ubuntu Core as a sort of app store. Developers can make code available, and end-users can easily download and install that code.

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Build Your Own GSM Base Station For Fun And Profit

Over the last few years, news that police, military, and intelligence organizations use portable cellular phone surveillance devices – colloquially known as the ‘Stingray’ – has gotten out, despite their best efforts to keep a lid on the practice. There are legitimate privacy and legal concerns, but there’s also some fun tech in mobile cell-phone stations.

Off-the-shelf Stingray devices cost somewhere between $16,000 and $125,000, far too rich for a poor hacker’s pocketbook. Of course, what the government can do for $100,000, anyone else can do for five hundred. Here’s how you build your own Stingray using off the shelf hardware.

[Simone] has been playing around with a brand new BladeRF x40, a USB 3.0 software defined radio that operates in full duplex. It costs $420. This, combined with two rubber duck antennas, a Raspberry Pi 3, and a USB power bank is all the hardware you need. Software is a little trickier, but [Simone] has all the instructions.

Of course, if you want to look at the less legitimate applications of this hardware, [Simone]’s build is only good at receiving/tapping/intercepting unencrypted GSM signals. It’s great if you want to set up a few base stations at Burning Man and hand out SIM cards like ecstasy, but GSM has encryption. You won’t be able to decrypt every GSM signal this system can see without a little bit of work.

Luckily, GSM is horribly, horribly broken. At CCCamp in 2007, [Steve Schear] and [David Hulton] started building a rainbow table of the A5 cyphers that is used on a GSM network between the handset and tower. GSM cracking is open source, and there are flaws in GPRS, the method GSM networks use to relay data transmissions to handsets. In case you haven’t noticed, GSM is completely broken.

Thanks [Justin] for the tip.