I recently watched Melissa Elliot’s talk from DEFCON 21 titled Noise Floor Exploring Unintentional Radio Emissions 2013 which inspired me to buy a Realtek SDR (software defined radio) dongle from eBay.

I am running Ubuntu (13.04 to be specific).

I am assuming that you already have your SDR dongle working and gqrx installed on your system.

Sources

I have compiled these instructions from a couple of sources:

• GQRX SDR Google Group thread: Using gqrx with Virtual pulseaudio source?
• Kersle.net blog: Redirect Audio Out to Mic In (Linux)

DSD

DSD is the digital speech decoder that you need to pass the audio output from your software radio (gqrx in our case) through in order to get useful audio output on the other side.

When listening to decoded digital speech radio, it is bothersome to have the raw radio traffic playing in my ears over top of the decoded sound. To get around this, I am bridging the output of gqrx to a Pulseaudio null sink which dsd is listening on.

I found this answer on askubuntu.com that shows how to create a Pulseaudio null sink in a single line. I’m sure I could have looked through the Pulseaudio docs, but this was one of the first hits on Google.