Quisk and Fldigi

This is a follow-on to the Quisk and PulseAudio exercise. The goal is to decode digital transmissions using a Quisk controlled Softrock Ensemble II RX and Fldigi as the digital modem.

This exercise covers only the signal path and not the VFO control. See the Conclusion and Future Work sections below for a more complete discussion of the limitations.


  • Quisk is installed, working, and configured to work with PulseAudio. If not, start with the  Quisk and PulseAudio exercise.
  • Fldigi is installed. I am using the PPA version by Kamal Mostafa because it is updated more frequently than the standard version in the Ubuntu 10.04 archives.
  • Ubuntu 10.04


If you have completed the Quisk and PulseAudio exercise then no other preparation is needed.


To avoid any conflict with an existing Fldigi setup you might have, use a separate configuration directory. The extra arguments (>/dev/null 2>&1 &) on the fldigi command line discard the warning messages and put fldigi in the background so that I don't have to use a separate window to start quisk and pavucontrol in the following steps.

$ cd
$ fldigi --config-dir fldigiQuisk >/dev/null 2>&1 &

Fill out the fldigi configuration. We are not going to be able to transmit using this Fldigi/Quisk combination, so you can skip the Operator Information dialog. The configuration dialog of interest to this exercise is for the Audio Devices. The configuration is very easy, simply select PulseAudio. Leave Server String box empty:

Skip the following configuration dialog (Transceiver control) and click on Finish button. The main fldigi window will appear.

Now start quisk.:

$ cd ~/quisk-3.5.8/
$ python ./quisk -c ~/quisk_pulse_conf.py >/dev/null 2>&1 &

Once quisk gets started and you hear received audio on your speakers (or headphones), fldigi may show the received signal in its waterfall display. If so, you could quit at this point- fldigi and quisk would be configured to work together. However, if fldigi does not show the received signal, or you're curious about the PulseAudio settings needed, then follow on!

Start pavucontrol so that we can adjust the PulseAudio connections:

$ pavucontrol

The important setting is on the Recording tab. Set the Fldigi:capture channel to record from the Monitor of Internal Audio Analog Stereo:

The Monitor of Internal Audio Analog Stereo input is connection to what you hear on your speakers (or headphones).

As soon as you set the Recording source, fldigi should start to show the received signal in the waterfall display and you can select signals from the fldigi waterfall display to decode.

Here is what the quisk/fldigi combination looks when it is decoding a PSK31 signal:

Note that the frequency displayed by fldigi is wrong and that you can not control the frequency from fldigi.


That seemed pretty simple, though I did have the quisk audio stop a couple of times on me. Everything looked OK, the quisk waterfall continued but there was no audio heard on my speakers and the fldigi waterfall went dark. Restarting quisk would solve the problem.

Without a valid frequency report to fldigi, or better yet controlling the frequency from fldigi, this setup is more a novelty than really useful. Still, it does allow for some experiments (watch what happens to the fldigi waterfall when you change the quisk bandwidth setting) and you finally start decoding some of those mysterious signals you are seeing with quisk.

Future Work

  • Connect the fldigi rig control to quisk.
  • Debug the quisk audio drop-out.