A $20 SDR that Fits in Your Pocket?

A while back, some ingenious radio amateurs figured out that they could pair a $20 USB dongle meant for watching television in other parts of the world with some SDR software and listen to the ham bands (and more).

The “and more” part is what first caught my attention.  Much of the area uses digital trunked systems for their emergency communications and something like a TrunkTracker IV, despite being one of the more affordable pieces of equipment in this category, is still a bit out of my reach.  As someone who lives close to the site of a HAZMAT train derailment as well as a massive tire fire, and having had police chases that end in stand-offs go racing past my house, the ability to be “in the know” sounds like a good idea.  I haven’t got up and running with digital trunking systems yet (watch for a future post?), but I have definitely already got more than my $20 worth of use out of this gadget.

The first thing I did was order a Nooelec RTL2832U & R820TSB dongle.  Once it arrived, the package contained the USB dongle (which looks like a fat jump drive), a stubby little antenna with a few feet of coax and a small, mostly useless remote control.  I was ready to get started!  

Installation

Hardware & Drivers

Unfortunately, getting going isn’t as easy as just plugging the USB stick into your computer and letting things sort themselves out.  My unit didn’t come with a driver CD, but I’ve heard rumors that it’s basically a Chinese virus installation disk.  Windows isn’t much help either; it will automagically find a driver and install it but I couldn’t get anything to work with those drivers.  You will want to use the Zadig drivers instead.  If you plan on using SDR# (SDR Sharp), as I did, the correct drivers come bundled with that download.  If you plan on using some other software, you probably want to download the drivers directly from the Zadig site (note the different versions for Windows XP vs Windows Vista/7).

Using the Zadig installer isn’t rocket science, but there are a couple steps that might not be entirely intuitive.  Check out this guide for a step-by-step walk-through.

Software

Which software you use will depend largely on what you want to do with your RTL-SDR and your operating system.  I haven’t had a chance (or desire, really) to use this on any of my Linux installations, but the tools are out there to do so (here is an Instructable on how one person got it working on Ubuntu).  So far, I have only been using my device on Windows 7-based PCs.

For general listening, I have been using SDR#.  You can download SDR# here for free.  Installation is easy but if you need help, check out the quick start guide.

In addition to just listening to radio traffic, it’s also fun to track local aircraft.  For that, I use RTL1090 to decode the 1090MHz ADS-B signals, but other tools are available such as ADSB# or dump1090  Once you have the ADS-B signals, you turn the data into something human readable – like a map that shows where the aircraft are.  There are a number of tools that do this such as Virtual Radar Server and PlanePlotter.  I usually take the easy route and feed my ADS-B data into FR24 using their FlightRadar24 ADS-B software in conjunction with RTL1090.

Using It

Antenna

It should first be noted that the antenna that comes with the dongle isn’t very good.  How could it be?  It’s about six inches long and has almost enough coax with it to allow it to sit on top of your desk from your PC’s USB port.  Something like a scantenna or discone are popular, or you can build your own especially suited for your needs.

The dongle utilizes an MCX connector, with male on the antenna and female on the unit.  As such, when you buy or build an antenna, you will need to make sure that you either have your coax terminated with an MCX connector or use an MCX-to-SO239/PL259 adapter or MCX-to-F adapter to hook up to a more traditional antenna connection.

HF Bands

Out of the box, the RTL-SDR covers approximately the 25MHz-1750MHz range.  To cover HF bands, Nooelec also makes an add on unit called the Ham-It-Up SDR Upconverter that allows the user to listen to HF/MF bands.  It comes as a bare circuit board, however, so if you want to keep the components protected, you may want to get an enclosure to go with it.

There is, however, an alternative way to listen outside of the off-the-shelf frequency range of the dongle.  Although Nooelec will gladly tell you how to do it, they strongly recommend against it due to the risk to the dongle.  Here is the email we received from them:

You can find instructions here:  http://www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/

 

Note that performance will not be very high with this method, and soldering to the PCB will void your warranty with us…but it is the cheapest way to enable HF 🙂

Listening

Using SDR# for listening to radio traffic is pretty simple.  If your drivers are set up correctly and and your RTL-SDR is plugged in, you should find RTL-SDR / USB listed in the drop down menu at the top of the window.  Select that option, hit the Play button and it should start playing what it hears.  Depending on your location and antenna, you may have to fiddle with the RF gain settings in the configuration menu to get to hear anything – you will almost certainly need to do this with the included antenna.

There is a VFO at the top of the window that you can use for direct frequency entry or you can scroll through the waterfall display. Available modes include both wide and narrow FM, AM, upper and lower sideband, CW and more with bandwidths user adjustable.  A quick overview guide on how to use the software is available here although the interface should be mostly intuitive for a ham.

As previously mentioned, one of the things that got me interested in the RTL-SDR was the possibility of listening to trunked systems.  Although it is possible to listen to trunked systems with this device, there a a lot of steps and I haven’t had the chance to fool with it yet.  I leave that for future work.

Aircraft Tracking

Using the RTL1090 software described above is nearly foolproof.  Once it is installed, as long as your RTL-SDR is  set up correctly, you just run the RTL1090 software and it starts looking for aircraft ADS-B signals to track.  The GUI displays a list of signals that it can see along with a number of parameters such as the 24 bit aircraft address, callsign, altitude, vertical speed, ground speed, true track, and Mode A SSR.

That data is great but, practically, it doesn’t do us much good in that format, so we need to feed it into something that displays it in a more useful fashion.  There are tools that allow you to plot the aircraft data on a map and display it locally, but I prefer to pipe my data into FlightRadar24.  An overview of some of the various tools is available here.

Sending data to FlightRadar24 is easy and, provided that you have your RTL-SDR set up and RTL1090 running, the bulk of your work consists of double clicking on the software to run it.  You will need to tell it how to get the shared information from RTL1090 and you need to tell it how to share that data with their servers, but that’s about it.

An added bonus of feeding your data into the FR24 network is that it gets you access to FlightRadar24 Premium, which normally costs $3/month.  Any time your software uploads new aircraft data to the FR24 network, it extends your rolling free subscription out to a week.  This is great because I can leave the software running at home and have premium FR24 flight map access via any computer or my smartphone and tablet apps.  Those maps show all aircraft data from the network, not just the data that I have fed into the system.

Summary

As far as ham radio equipment (and the associated costs) go, dropping $20 on a little device that does all of this is a great deal.  The ability to have something this small that takes up next to no space is great.  I plan on trying out different aircraft tracking tools and I’m still holding on to the hope that I’ll get the trunk tracking stuff going.  I’d also like to try it out on one of my Raspberry Pi units and see what kind of ideas I can come up with to do with a pocket sized Linux SDR.

If you have experience with RTL-SDR units, we’d love to hear about it in the comments section below.