Sustainable electronics enthusiast Philip Le Riche has published a guide to "software defined radio on a shoestring," using a low-cost RTL-based TV tuner dongle to receive signals traditionally outside its capabilities.
"So now you need a satnav to receive GPS signals, a DAB radio for digital broadcasts, a smartphone for mobile voice and data, a Wi-Fi-enabled computer for WiFi, a garage door to respond to your fob and ... well, the list goes on," Le Riche writes. "There must be a better way? Fanfare of trumpets please! Enter Stage Left the Software-Defined Radio (or SDR to its friends).
"A computer can do anything, provided you can break it down into logical steps. You're looking at one now! So why not program it to interpret a radio signal? With a different program you can receive whatever you like, including old fashioned AM and FM broadcasts."
While software-defined radio devices span the spectrum from pocket-friendly to price-on-application, Le Riche has focused on the popular RTL family of off-the-shelf SDR devices — built, originally, to receive DAB and FM radio and DVB-T televisual signals.
Le Riche combines the device with a homebrew aerial — one created from a co-axial lead taken from an old television, and another made using a co-ax connector and a single piece of stiff wire — with a laptop running the SDR# software, and runs through detecting and decoding a range of signals normally beyond the capabilities of the TV tuner. For the home automation fan, there's a section on discovering and decoding devices which use the 433MHz part of the industrial, scientific, and medical (ISM) spectrum.
Le Riche's full guide is available on Instructables.