Transmitting data with a Pi and RTL-SDR

Sometimes the best builds aren’t anything new, but rather combining two well-developed hacks. [Marc] was familiar with RTL-SDR, the $30 USB TV tuner come software defined radio, but was surprised no one had yet combined this cheap radio dongle with the ability to transmit radio from a Raspberry Pi. [Marc] combined these two builds and came up with the cheapest portable radio modem for the Raspberry Pi.

Turning the Raspi into a transmitter isn’t really that hard; it only requires a 20cm wire inserted into a GPIO pin, then toggling this pin at about 100 MHz. This resulting signal can be picked up fifty meters away, and through walls, even.

[Marc] combined this radio transmitter with minimodem, a program that generates audio modem tones at the required baud rate. Data is encoded in this audio stream, sent over the air, and decoded again with an RTL-SDR dongle.

It’s nothing new, per se, but if you’re looking for a short-range, low-bandwidth wireless connection between a computer and a Raspberry Pi, this is most certainly the easiest and cheapest method.

An RTL-SDR Spectrum Analyzer

With the combination of small, powerful, and pocketable computers and cheap, off-the-shelf software defined radio receivers, it was only a matter of time before someone built a homebrew spectrum analyzer with these ingredients. This great build is the project of [Stephen Ong] and he’s even released all the softwares for you to build this on your own.

The two main components of this build are a BeagleBone Black and its 7″ Touchscreen cape. The BeagleBone is running Angstrom Linux, a blazingly fast Linux distro for small embedded devices. The radio hardware consists of only a USB TV tuner supported by RTL-SDR. In his demo video, [Stephen] shows off his project and by all accounts it is remarkable, with a UI better than most desktop-oriented SDR software suites.

You can grab the BeagleBone image [Stephen] is using over on his blog, but for more enterprising reader, he’s also put up the source of his ViewRF software up on GitHub.

Listening to aircraft transponders with a Raspberry Pi

Last year’s big hack was software-defined radio; a small USB TV tuner that could listen in on radio broadcasts anywhere between 64 and 1200 MHz. This year, it’s all about the Raspberry Pi, so it’s surprising we’re only just now seeing a mashup of these two pieces of hardware. [Corq] is using a Raspi and RTLSDR TV tuner to listen in on aircraft transponders, and getting a whole bunch of data from aircraft flying overhead.

Even though the ADS-B decoder [Corq] is using is written for OS X, he’s reading the data coming from the USB TV tuner over the network with a program called Dump1090. This program allows [Corq] to attach his SDR to a Raspbery Pi and put it somewhere the antenna will get good reception – an attic, or an outdoor weatherproof case – and stream data to his desktop over a WiFi or network connection.

With a USB TV tuner and a Raspberry Pi, [Corq] is able read the tail numbers, altitude, latitude, longitude, speed, heading, and even the type of aircraft currently flying over his house. That’s cool enough, but the fact that he can effectively do this over the Internet makes it a brilliant hardware mashup.

Stealing cars and ringing doorbells with radio

The cheap software defined radio platforms that can be built out of a USB TV tuner aren’t getting much love on the Hackaday tip line of late. Thankfully, [Adam] sent in a great guide to cracking sub-GHz wireless protocols wide open, and ringing doorbells, opening cars, and potentially setting houses on fire in the process.

The first wireless hack [Adam] managed to whip up is figuring out how a wireless doorbell transmitter communicates with its receiver. [Adam] connected a FUNcube software defined radio dongle (although any one of the many USB TV tuner dongles we’ve seen would also work) and used GNU Radio to send the radio signals received to a WAV file. When looking at this audio file in Audacity, [Adam] saw the tell-tale signs of digital data, leaving with a string of 1s and 0s that would trigger his wireless doorbell.

The FUNcube dongle doesn’t have the ability to transmit, though, so [Adam] needed a more capable software defined radio to emulate the inner workings of a doorbell transmitter. He found one in the Ettus Research USRP, a software designed radio that’s doing a good job of keeping [Balint], Hackaday SDR extraordinaire, very busy. By sending the data [Adam] decoded with the FUNcube dongle over the USRP, he was able to trigger his wireless doorbell using nothing but a few hundred dollars of radio equipment and software ingenuity.

Doorbells are a low-stakes game, so [Adam] decided to step things up a little and unlock his son’s car by capturing and replaying the signals from a key fob remote. Modern cars use a rolling code for their keyless entry, so that entire endeavour is just a party trick. Other RF-enabled appliances, such as a remote-controlled mains outlet, are a much larger threat to home and office security, but still one [Adam] managed to crack wide open.

Listening in on weather balloons with RTL SDR


Every day, twice a day, over 800 weather balloons are launched around the world at exactly the same time. The data transmitted from these radiosondes is received by government agencies and shared with climatologists and meteorologist to develop climate models and predect the weather. Near [Carl]’s native Auckland, a weather balloon is launched twice a day, and since they transmit at 403 MHz, he decided to use a USB TV tuner to receive data directly from an atmospheric probe.

The hardware portion of this project consisted of building a high gain antenna designed for 162 MHz. Even though the radiosonde transmits at 403 MHz, [Carl] was easily able to receive on his out-of-band antenna.

For the software, [Carl] used SDRSharp and SondeMonitor, allowing him to convert the coded transmissions from a weather balloon into pressure, temperature, humidity, and GPS data.

Pictures from weather satellites with a USB TV tuner


Several times a day, a NOAA weather satellite passes over your head, beaming down pictures of weather systems and cloud formations. These transmissions aren’t encrypted, and given the requisite hardware it’s possible for you to download these images from space as [Lovro] shows us in a tutorial video.

To get these near real-time satellite pictures, [Lovro] used one of those USB TV tuners we’ve grown so fond of. A somewhat specialized antenna is required to receive the right hand polarized transmissions from NOAA weather satellites, but with a few bits of wood and wire, [Lovro] made a helical antenna to listen in on the weather satellites transmitting around 137 MHz. After gathering a whole bunch of data from the satellites with SDRsharp, [Lovro] used an image decoder to turn an audio file into a picture taken from space just hours ago.

This isn’t the first time we’ve seen images from a NOAA weather satellite downloaded with a software defined radio; last year [hpux735] did just that with a somewhat inexpensive Softrock SDR. [Lovro]’s use of a USB TV tuner to receive the transmission from NOAA satellites is a lot easier on the pocketbook, though, with the largest expense being an investment in time to build a helical antenna.

Still more software defined radio fun on the Mac

Even though the world of software defined radio started out as a Linux-only endeavor, several recent software releases have put the ball fully into the court of OS X users. [hpux735]’s new Cocoa Radio release provides a (nearly) fully functional software defined radio for anyone with a USB TV tuner and a mac.

Earlier this week, we saw (and tested)  [Elias]‘ port of gqrx and were reasonably impressed. [hpux735]’s app does the same job and also provides the source so you can compile it yourself.

Previously, [hpux735] ported the osmocom driver for these RTL2832U-based USB TV tuner dongles to the Mac and wrote a small Cocoa driver. The new Cocoa Radio software uses this driver and adds all the features you’d expect from a software radio package; in the title pic for this post, you can see a top 40 radio station near my house and their insipid hatred of dynamic range.

[hpux735] posted a few videos of his development process. You can check those out after the break.

Continue reading “Still more software defined radio fun on the Mac”