Real time GPS decoding with software defined radio

In case the Realtek RTL2832u-based USB TV tuner dongle isn’t useful enough, the folks behind a project to get a software defined GPS receiver off the ground successfully plotted GPS data in real-time with this very inexpensive radio.

Previously, we’ve seen these dongles grab data from GPS satellites – useful if you’re building a GPS-based clock – but this build required hours of data collection to plot your location on a map.

The folks working on the GNSS-SDR project used an RTL2832 USB TV tuner and a Garmin active GPS antenna to track up to four GPS satellites in real-time and plot a location accurate to about 200 meters.

The Google Earth plot for this post shows the data collected by the GNSS-SDR team; the antenna was fixed at the red arrow for the entirety of the test, and the  yellow lines represent a change in the calculated location every 10 seconds. Amazing work, and only goes to show what this remarkable piece of hardware is capable of.

Hackaday Links: July 20, 2012

Hey, it’s the 43rd anniversary of men first walking on the moon. Here’s some stuff we found to celebrate that. Fun trivia: for Apollo 11, [Neil] and [Buzz] didn’t go more than 200 feet from the LEM.

This is so incredibly sad

Remember Heathkit? A lot of cool kit-based electronics came from them. They’re out of business, but you can get all the Heathkit swag you can imagine from the repo man. A ton of stuff from the old Heathkit headquarters is being auctioned off in Byron Center, Michigan this Tuesday, July 24. Notable lots include a HE-Robot and a nice pair of o’scopes. If someone wants to pick up one of the catalog lots for us, we’d be thankful.

Troll Physics: ‘What is with this guy’ edition

We’ve seen [Fredzislaw]‘s LED trickery before. The first time was a crazy 3 LED circuit, the reveal of which showed two AC power supplies in a battery connector. This time, [Fred] has two switches and an LED. Turn one switch on, the LED lights up. Turn that switch off and flip the other one, the LED still lights up. Turn both switches on, the LED goes off. Your guess is as good as ours.

Prototyping with a key fob remote

[Gary] wrote in to tell us about the dev board he’s been working on. It has either a PIC or AVR on the back side, broken out into 0.1 inch headers on the front. There’s a small solderless breadboard and an on-board RF link that uses a five-button key fob remote. Seems very useful, no matter what side of the PIC/AVR holy war you’re on.

Consumer Alerts: Software defined radio

Over on the RTLSDR subreddit, [photoscotty] bought this TV tuner dongle from Deal Extreme and received the inferior EZTV645 tuner. Unsurprisingly, Chinese manufacturers will just grab whatever is available, put it in an envelope, and ship it off on a slow boat from China. [photoscotty] is trying to return his dongle to DX, but until Sparkfun or Adafruit start selling these things (yes, there’s a market now get on it) you’ll have to be careful out there.

Wouldn’t this feel terrible against your skin all day?

[Colin] printed a watch band on his Makerbot. Apparently Shenzhen humidity didn’t play nicely with his nylon strap, so [Colin] made his own out of plastic. It’s flexible and has a neat looking clasp, as well as an awesome demo for what a 3D printer can actually do. Thingiverse files here.

Software-Defined Radio remotely using a Linux wall wart

Here’s a interesting idea; if the hardware seen above is dropped at a location, you can monitor radio signals remotely via the Internet. [MS3FGX] has been toying with the idea for a little while now. He wanted to use a DVB dongle with a portable Linux solution to offer Software-Defined Radio (SDR) capability without the need to actually be there.

The white box is a PWN Plug, a branded version of the SheevaPlug. The black dongle that plugs into it is a DVB tuner dongle. It’s meant to receive television signals over the radio, but recently the hardware has been used as a simple way to implement SDR. Combine the two (along with the antenna), stir in a network connection, and you’ve got a remote listening post. What can you listen to? Just about anything that’s within the dongle’s bandwidth range. [MS3FGX] mentions walkie-talkie traffic and pager signals, to name just two.

He even wrote an installation script that gets you up and running in no time.

Adding more frequencies to your software defined radio

[regveg] was looking for a way to receive signals outside the normal 64-1700MHz range his TV tuner software defined radio dongle can get. After finding a few $100+ upconverters on the Internet, he stumbled across a DIY project that greatly expands the frequencies his RTLSDR can receive.

[George]‘s upconverter uses heterodyning to increase the frequencies received by a SDR dongle. The basic idea is mixing a signal from an antenna with a 100MHz frequency oscillator. The resulting output will be λ + 100MHz and λ – 100MHz, allowing for a wider range of frequencies that can be received by the SDR TV tuner dongle.

Now [regveg] has a board and schematic that makes it possible to receive just about anything with his TV tuner dongle. Interestingly, this upconverter contains less than $10 in parts and is easily etched at home thanks to a single-sided construction and through-hole parts.

As a small aside, [Andrew] sent in a tip a few days ago telling us his RTL dongle didn’t have any ESD protection. This is a very bad thing, but the good news is the fix is very cheap: just solder in a 10 cent diode and you’re good to go.

Getting started with software defined radio

In the last few months, software defined radio has seen an explosion in popularity thanks to a small USB TV tuner dongle able to receive anything broadcast between 64 and 1700 MHz. It’s a very neat project that opens the door to a whole bunch of radio experimentations, but getting started in the SDR world can be a bit daunting. To help everyone out, [MS3FGX] is writing a getting started guide so everyone can get into the world of software defined radio.

After getting one of the TV tuners supported by the RTL-SDR project (by far the most commonly used is this one from Dealextreme), the next thing you’ll need is a decent antenna. [MS3FGX] has had some success with this Radio Shack antenna, but it’s very easy to make your own.

The most popular software package to use with the RTL TV dongle is GNU Radio, and [MS3FGX] goes over the ins and outs of setting this up along with a brief aside for the Gqrx receiver.

After your hardware and software is set up, the only thing left to do is tuning into a few of your favorite stations. The range of frequencies the RTL covers includes AM and FM radio, along with GSM and GPS signals. Of course there’s a whole lot more you can do with this project like listening in on your car’s keyless entry fob, pagers, and wireless weather stations.

Two software defined radio hacks from our resident SDR guru

It seem [Balint] is becoming somewhat of a SDR guru around these parts; in the past few months, he’s gotten a USB TV tuner receiver working with GNU Radio, started a software defined radio tutorial YouTube channel, and even used this project to listen in on conversations between airplanes and air traffic control. This time, [Balint] is back using this cheap USB TV tuner for radio direction finding and running HDSDR in Linux and OS X.

[Balint]‘s radio direction finding presentation goes over traditional means of direction finding using the doppler effect and mechanically rotated antennas. Because [Balint] is dealing with frequencies around 150MHz (about 2 meter wavelength), building a physical direction finding setup requires spinning antennas at around 40,000 RPM; much to fast for any hardware build. [Balint]‘s solution was to attach 4 antennas around the circumference of a circle and electronically switch between them many thousands of times a second. [Balint] put up a wiki page going over all the theory and implementation details of his build.

[Balint] also put wrote up a neat app to control software defined radios – including the Realtek TV dongle –  over a network. Spread over a wide enough geographic area, it could become extremely easy for anyone to play air traffic controller. The BorIP Server can also be used to run HDSDR in Linux and OS X under Wine; just connect HDSDR to the network loopback on the same machine, and you get around Wine’s distaste for accessing hardware natively.

Awesome work, and we can’t wait to see what comes out of [Balint]‘s laboratory next.

Edit: instead of the dongle, [Balnt] is using a ‘real’ software radio board. A lot of people are messaging him asking if the same method of direction finding is possible with the dongle. Here’s what [Balint] has to say:

The trick, as I see it, would be to create some (more or less simple) additional hardware to take the clock signal straight off the dongle’s on-board oscillator and divide it down for use with the antenna switch, i.e. 28 MHz à tens of kHz (this is the bit that’s done in ‘software’ on the FPGA). One problem still remains however: the counter needs to remain calibrated against the known direction the antenna was pointing at the time – otherwise a stop/start of the data stream from the dongle will mean the direction will go out of sync by 90/180/270 degrees each stop/start. Perhaps someone will figure out an elegant solution for this slight hurdle!

So there you go. Up for a challenge?

[Balint] is starting a software-defined radio tutorial series

A few months ago, we saw a hack where a $20 USB TV tuner was transformed into a software-defined radio capable of reading GPS signals, listening to radio transmissions between aircraft and a control tower, and even a simple FM radio. This project is a perfect introduction to the RTL-SDR and Ham radio scene, but getting these projects up and running can be a bit overwhelming for anyone who hasn’t played around with this before. [Balint] is tackling this problem head on with a series of YouTube tutorials to get SDR noobs up and running with GNU Radio and the Realtec USB TV tuner.

To demonstrate the power of software-defined radio, [Balint] is using GNU Radio and the USB TV tuner that started it all, the Ezcap EZTV668 (conveniently back in stock at DealExtreme, but other options exist). Because software-defined radio is a touch confusing for a beginner to wrap their head around, [Balint] is beginning his tutorial series by explaining radio sources, sinks, and the GNU Radio interface.

Already, [Balint] has put up 5 tutorials and made the flowgraph files available in his gr-baz project. He’s doing a wonderful job opening up the software-defined radio scene to beginners, but he’s still looking for some feedback. If you have a suggestion on what [Balint] should cover next, leave a note in the YouTube comments and we’re sure [Balint] will get around to that eventually.