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Minimal power output only on 20m FT-8

Using flex 6500, and KPA 500 for FT-8 contacts and have been happy; about 5 watts from Flex yields 100-110 watts from the KPA 500. Today was going between 18m and 20m looking for dx and on 20m could not drive the KPA 500 with the usual watts so went up to 40 watts on Flex. On transmit only saw 25 watts from KPA and frs stack3 showed about 18 watts output from flex. Hooked up dummy load and got consistent 100 watts rf power on load and also

on Flex. Tried all bands on FT8 and all others showed the usual 5 watts yielding about 100 watts from the KPA 500. Ran all bands on different modes all were acting as expected. So this seems to be only with FT8 and 20m. Did factory reset of Flex with no change. A typical 20m SDR shot is attached. I welcome any ideas

Thanks Greg Zych K4GAZ


  • Patrick
    Patrick Member ✭✭✭
    edited January 2022

    If you are using wsjt-x check the power output slider in wsjt app as in your picture the audio level is low which will be reflected as low power output, even with the SDR power slider up at 100%. I usually run it so that the peak indicator is up near zero. The Average indicator will be at around -5. In wsjt-x, the power slider will set the power level (as seen on SmartSDR MIC level) for each band separately, so if the 20 meter one is low then power will be low. The ultimate power level is set from the DAX TX level and is affected by the wsjt-x power slider. They work in series and of course affect drive which is adjusted by the power level adjustment for the xcvr power amp. Hope this helps, I have been burned by this low or no power when wsjt-x versions are updated. Some times they fiddle with the level.

  • Salty Z
    Salty Z Member ✭✭

    Patrick you are exactly right. The power slider on FT8 was only about 60% so boosting it to top made everything ok. Thanks for your excellent advice

    73 Greg K4GAZ

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