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FLEX 6400 - WSJT-X loses transmit audio after update to 3.5.8

Since updating to 3.5.8 WSJT-X randomly stops transmitting. I am using Windows 10 on a Dell desktop. I can be in the middle of an FT8 QSO and I will see that my power has dropped to zero. I can see that the FLEX is in transmit and will have keyed my Elecraft KPA500 if I'm running it. Receive continues to decode but transmit audio is gone. To resume running FT8 I need to restart both SmartSDR and WSJT-X. This is a new condition although previously I would occasionally see a similar condition if I left FT8 running for a long time with the radio idle. Restarting FT8 would restore operation.

This appears to be a new problem that I have not seen before. I tried connecting to the 6400 with an HP laptop running 3.5.8 on Windows 11 over Wi-Fi and FT8 seems stable.

I am not sure what settings to check on the Dell desktop.

Phil N3ZP


  • Al K0VM
    Al K0VM Member ✭✭✭

    Observe the level of TX stream in the DAX GUI, the level indicator in SSDR and the RF output indicator both when working and when not working. Should give you a hint of where the problem might be.

    AL, K0VM

  • Phil N3ZP
    Phil N3ZP Member ✭✭

    I could see that DAX TX wasn't working and there was no RF output. TUNE in WSJT-X also showed no output. TUNE in SmartSDR did produce output though. At first this seemed to only be happening on my Dell desktop but now I am using my laptop since the hard disk failed in the desktop. FT8 will transmit for a short time when I start WSJT-X but stops after some period of time. Other than restarting everything I don't know what to check next,

    Phil N3ZP

  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭

    I find that I have to restart WSJT-X frequently to restore transmit output. The time between restarts varies considerably. I do not need to restart SmartSDR, the radio, or the PC.

  • Phil N3ZP
    Phil N3ZP Member ✭✭

    It does seem that just starting WSJT-X does work most of the time. Prior to the latest update, I only needed to re-start WSJT-X if I left it running without transmitting for a period of time.

    Phil N3ZP

  • LZ2BE
    LZ2BE Member ✭✭

    It happen also on RTTY and restarting SSDR DAX cures the problem.

    Boyan LZ2BE

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Phil, I would try resetting the radio as an idea.

    I have been running non-step VHF and UHF FT8 for the past 6 days without an issue. This is the first time I have seen the bands do that in years. Initially, it doesn't seem to be related to 3.5.8.


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