Friday, May 1, 2015

Adventures in SDR: Software Defined Radio For Cheap

Background (Not For TV!)

My quest originally involved looking for a cheap TV tuner while I stay out in a cabin in the woods, rehabbing my sister's property in a very rural area. I can get satellite but I don't watch much TV. I could stream Netflix or something but I'm lucky to have this semi-reliable, low-bandwidth Wi-Fi connection across a small valley to the neighbor's house.

So I bought this $13 dongle from Amazon which says "TV" in its name. I didn't catch that other identical versions of this product from other sellers had obvious reviews complaining that this USB dongle did not decode ATSC, meaning you can not use it to watch TV in the USA. The only reviews I noticed just mentioned how awesome this device is.

For anyone who doesn't understand, the irony of these USB devices based on the RTL2832U chipset is that they can basically receive anything but TV.

I was about to return this dongle when I did a little research, stumbling on one of the coolest hobbyist toys I've ever owned, and the second most fun I've ever had for 13 bucks.

Software Defined Radio: SDR

It's exactly what it sounds like: a programmable tuner. Mine has the Rafael Micro R820T tuner in it, meaning it can receive radio frequencies from 24 MHz to 1766 MHz, which is a very wide range for something under 20 dollars.

Lucky for us, an electronics enthusiast discovered a fluke (?) in the chipset of these dongles a few years ago, and now there's a whole community and a boat load of software making use of this dongle. There are applications for Linux, Android and Windows which can do everything from receive FM radio transmissions to police scanners and even some exotic things like pick up airplane transponder data and satellite signals.

Magnetic base stuck to a wood screw!

What Can It Pick Up? 

This dongle can basically pick up any signal in its frequency range, which is wide. Not only is the frequency range large, but so are the implications for its use because most of us take for granted all the little wireless gadgets we have.

  • CB: Citizen's Band
  • FM Stereo Radio 
  • Standard Police and Fire Frequencies
  • Weather and Emergency Broadcasts
  • CDMA and GSM celluar signals from phones and towers
  • Family Radio and other store-bought walkie talkie frequencies
  • Store bought baby monitors and similar devices
  • Automotive key fobs and garage door openers
  • Weather balloons
  • Radio Astronomy
  • Airplane transponder data

Jeez, What Can't It Pick Up?

  • American ATSC TV, which it doesn't have the bandwidth for.
  • Ham radio is below its range, and so is AM radio
  • Wi-Fi is above its range
  • Most land-line wireless phones are above its range
  • It obviously can't decrypt encrypted radio transmissions

The Sky Is The Limit

Actually since this thing can pick up signals from airplane transponders and satellites, so the sky isn't the limit. For the most part, the capabilities of this device is limited more by the software than the hardware. It can't fully decode ATSC television signals, though there is an app which can partially decode TV and give you an almost clear black-and-white TV picture ... no thanks.

The great thing about these RTL2832U dongles is that they run on so many platforms. I just ordered a Raspberry Pi 2 kit yesterday and I intend to hook it up to my dongle and put my SDR device on the network.

SDR# Software For Windows

If you are using this device for Windows, which most of us are, then your best best is probably SDR# which is pronounced "SDR Sharp" because it is written in the C# language and is open source. Here is a link to their web site. Once you download the ZIP file, all you need to do is:
  1. Unzip the ZIP file into its own folder
  2. Run the installer batch file and let it download the software
  3. Run the zadiag.exe diagnostic program, list the devices, and install the driver for your dongle
  4. Run SDR sharp and choose "RTL-SDR / USB" for your device
  5. Press the Play button
To listen to FM radio, just tune somewhere between 88,000,000 and 108,000,00 making sure to select "WFM" as your modulation setting. What's nice about SDR#'s built in FM radio is that it picks up the song and station information as you can see in the screen shot below. I've seen it called "the most complicated way possible to listen to FM radio"

There are lots of plugins on their web site, and I use one as a scanner, where I can set the frequency range and cut it loose to listen to local fire, police and medical. Below the scanner stopped to listen to the local police dispatch. 

More Resources for Software Defined Radio

The SDR Wiki Page is a good starting point
RTL-SDR.COM is a good resource
OSMOCOM who are the experts
SDR# is a must if you are using Windows
Hack RF is a powerful but expensive alternative platform
Web SDR radios can be connected to and controlled over the web!
Reddit has a whole community devoted to SDR

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