Using Websdr with Ubuntu, Jack, PulseAudio and Fldigi to Demodulate Digital Signals

Websdr Screenshot

This "How To" is written for Ubuntu 10.10 (Maverick Meerkat), and it explains how to use PulseAudio, Jack Audio Connection Kit, Firefox with Sun Java 6, and Fldigi to decode digital modes received from a Websdr server.

Get Sun Java6 and PulseAudio Playing Together

The first thing to do is to get Sun Java 6 to work with PusleAudio.

1) Enable third party repositories, and install the following packages:

sudo apt-get install sun-java6-plugin sun-java6-jre sun-java6-bin openjdk-6-jre pavucontrol fldigi libportaudi

2) Copy some libraries from openjdk-6-jre to sun-java-6:

sudo cp /usr/lib/jvm/java-6-openjdk/jre/lib/i386/ /usr/lib/jvm/java-6-sun-

sudo cp /usr/lib/jvm/java-6-openjdk/jre/lib/ext/pulse-java.jar /usr/lib/jvm/java-6-sun-

3) Move the to a backup position:

sudo mv /usr/lib/jvm/java-6-sun- /usr/lib/jvm/java-6-sun-

4) Edit /etc/java-6-sun/ to add the following four lines:




5) Shut down Firefox or any other Java applications. Re-start them along with the Pulse Audio Volume Control (pavucontrol), and make sure sound works by going to a Websdr server and listening.  You may have to open pavucontrol (Applications->Sound & Video->PulseAudio Volume Control), and go to the playback tab and select the right output for the Java Audio Stream (Websdr) that is running, and sometimes the mute buttons need to be unmuted.  

Using Jack Audio Connection Kit (Optional)

1)  First if you are still listening to Websdr, close that tab in Firefox, go to a terminal and install the Jack packages.
sudo apt-get install jackd2 pulseaudio-module-jack qjackctl
2)  Start Jack from Applications->Sound & Video->Audio Production->Jack Control, and press the play button (green triangle).  (You may need to make changes in the Setup window as well, depending on your hardware.)
3) From the terminal, load the pulse modules for Jack.
pactl load-module module-jack-sink
pactl load-module module-jack-source
4)  Open a Websdr page in Firefox.
5)  Open the Connection Panel of Jack Control.
6)  Open the PulseAudio Volume Control and see the Jack sinks and sources in the Record and Playback tabs.

Fldigi (Optional if all you want to do is listen to a Websdr server)

Start Fldigi from the Applications->Hamradio menu.  Go to the Configure-Sound Card menu item.  Select the Capture device as either Pulse or Portaudio as you desire.  Check to see if the waterfall is showing audio coming in.  Tune with Firefox to the frequency you wish to listen and select in Fldigi the mode you want to listen to and watch the text scroll across the screen.  More help for Fldigi is available in the Help and PDF files on the Fldigi download page.

The results look like my screen below:


You can use this method with Fldigi to report spots and run your own robotic radio, even without any radio hardware of your own.  You can find out more about the server setup at K7UEB here.  If you wish to build your own receiver to use on your computer locally, Tony Parks, KB9YIG sells wonderful little inexpensive Softrock kits.  With one of these, a good sound card, an antenna, and your computer, you have your own robotic radio receiver to spot stations from your location.