RTL-SDR: Decoding Radio Signals on your PC

"They have the radio on computers now?" That was my first thought when I learned about Software Defined Radio (SDR) after I started studying for my HAM radio license exam. It was one of the more interesting tidbits I passed over while hitting the main question pool info such as antenna set-up, band plans, basic circuitry etc. But, it intrigued me. It was one area where HAM radio has taken a leap forward, providing inexpensive access to digital signal decoding to learners and hobbyists.

My PC showing SDR# software

Home SDR for hobbyists got a big boost in 2012 when Realtek launched the RTL-SDR dongle; it's a USB plug-in about as big as a "fun"-sized Halloween candy. One end plugs into your PC's USB port, and the other side has a coaxial connection that can be fixed to an antenna, or antenna system. Once the RTL-SDR is installed with all the drivers, and attached to an antenna, it will immediately begin feeding radio signals from the air to your PC. 

The big difference between SDR and most PC radio applications is that sound is not simply being streamed through your internet service provider, it's actually being picked up from the airwaves flying around you every second of everyday. You can un-plug your Wifi or data connection, and the RTL-SDR will still pick up those radio frequencies. It can even listen for, and decode, signals no normal PC or radio would ever get such as the amateur radio bands, nautical communications between boats and ships, and ADS-B and UAT transponder data from all aircraft both large and small. None of these signals are encrypted, and it's perfectly legal for hobbyists to listen in, provided they do not transmit on these frequencies in a way that could disrupt normal communications. 

The RTL-SDR dongle & antenna 

When I first unpacked my RTL-SDR and antenna set, which I ordered at RTL-SDR.com for roughly $60 USD including all components and shipping, I didn't quite know where to start. So, I also ordered The Hobbyist's Guide to The RTL-SDR by Carl Laufer as my starter guide. The book is a well-indexed set of step-by-step tutorials and trouble shooting techniques combined with general information about SDR and the various signals hobbyists can decode. Page nine discusses the initial installation of the RTL-SDR dongle, its drivers, plug-ins, and port numbers; page 13 provides a step-by-step tutorial on SDR# (or SDR sharp), a basic application for decoding, viewing and listening to signals received by the dongle. 

After a few read-through's, I was ready to test my new set-up. For my first test, I decided to get the daily weather. I tuned my SDR# app to 162.400 MHz, the frequency for NOAA Weather Radio for Akron and inland northeast Ohio, and it worked! I used my RTL-SDR to get weather (in possibly the most complex way possible). 

But, the test was a success. I could not only hear the weather report clearly, I could see all of the RF and modulation info-graphics necessary to locate and tune lots of different voice broadcasts and data transmissions. In the video above you can see the graph peaking at exactly 162.400 MHz, the NOAA station for Akron. The smaller peak just to the right is 162.550 MHz, the weather station for Cleveland and the Lake Erie shore. Both are in listening rage of my little antenna, but the higher peak is the closer signal. The digitally decoded graphics, and filtering options offered by RTL-SDR and SDR# are the perfect addition to any HAM radio base station. 

"The Hobbyist's Guide to the RTL-SDR: Really Cheap Software Defined Radio." Fourth Edition. (2024), Carl Laufer.