Using the KiwiSDR to provide receive audio to WSJT-X

Listening to modes such as CW, SSB and AM using the KiwiSDR is straightforward as the default output of the HTML5 sound from the browser goes to the default soundcard, which typically powers speakers or headphones.

A challenge in using digital modes is that the output from the browser needs to be sent to a third party application, such as WSJT-X, using a virtual audio cable. A limitation of the common browsers is that they do not provide any options to re-route the sound to other devices. This post pertains to Windows – Linux provides various other options.

After some research, a solution was found in the form of a Firefox Add-on:

The following steps were followed:
1) Downgrade Firefox to release 56 (the Add-on is not yet compatible with Firefox Quantum).
2) Once installed, disable automatic Firefox updates. As you now are not running the most recent release, there are security considerations. In my configuration these concerns are minimized as the Firefox instance is running on a separate machine and used only for accessing the KiwiSDR (no general browsing).
3) Install the Add-on.

4) Configure the Add-on. Select your virtual audio cable in ‘Options’.
5) In WSJT-X audio settings, select the correct virtual audio cable for audio input.


As a test, a QSO was attempted in JT65 mode on 20m using WSJT-X.
The KiwiSDR was started in Firefox and set to the correct frequency.
After verifying that the receive audio from the KiwiSDR was being decoded in WSJT-X correctly, I chose to reply to the CQ of S53PM to test the configuration.
1) There was a significant disparity in sent and received signal reports. This was anticipated due to the large difference in effectiveness between the respective transmit and receive antennas.
2) The internet adds delay, which is manageable within the generous DT (Difference in Time) tolerances of JT65/JT9, but it made FT8 a challenge. The receive audio delay was typically between 1 and 2 seconds. In FT8 you have to be really fast to double click the callsign of interest to start the QSO (as otherwise your first transmission will start too late and not be decoded) – however if you can do this the auto sequence works normally from that point onwards.
KiwiSDR (over internet) on the left, local (IC7100) on the right

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