SDR and software

WSJT-X Full Duplex FT4 test with IC-9700 via RS-44

The latest version of WSJT-X Improved, from v2.7.1, it is possible to use full duplex, that is listening and decoding at the same time you are transmitting. For satellite operators, mainly QO-100, you can now have full duplex control over your transmission avoiding drifting of your FTx signal.

I did a test with FT4 over RS-44 as I will try to describe here in this post. I’m using Icom IC-9700 and PstRotator for doppler control but the concept is the same if you are using other rigs and doppler control software.

First download WSJT-X Improved, use version from v2.7.1.

To be able to use doppler control from PstRotator and at the same time control PTT from WSJT-X use Omnirig (setup not described in this post).

For IC-9700 you must set up the USB soundcard in Windows to use both channels (“Kanal 2” in swedish means “2 channels”):

In WSJT-X use the USB left channel from the IC-9700 – left channel is the main band audio.

Set up for Full Duplex Mode in WSJT-X:

Below is an animated GIF when using FT4 via RS-44. Transmitting power is at 0% (zero) so very little uplink power is needed. You see that after every TX sequence WSJT-X is decoding my signal:

And below you see the WSJT-X spectrum as an animated GIF. What you see is my transmitted FT4 signal received in full duplex.


The Full Duplex version of WSJT-X improved is working perfect for FT4 via satellite!


Webmaster and member of the AMSAT-SM steering group.

2 replies on “WSJT-X Full Duplex FT4 test with IC-9700 via RS-44”

Hello i am SV1CEV Vagelis from Greece
i have the same equipment, and this time try connect to rs-44 via FT4 mode
maybe by see you on this satellite
Thank you very match for this best report

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