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FT8 Transmission Level

Juan TG9AJRJuan TG9AJR Member
edited June 2 in SmartSDR for Windows
Hello, I have a Flex 6600. What is the ideal or optimal transmission LEVEL when transmitting on FT8 ?

I notice there is a LEVEL meter on the right hand side of SmartSDR and just above COMPRESSION, that goes from -40dB (Left) to 0 (Right in red), and when I transmit I get a full color line and at the end of this line to the right I small square marker in the same color of the color line.

Some one told me in -10 in yellow/green color and the solid square in between -10 and 0.


  • edited April 2019
    Yes, "Someone told me in -10 in yellow/green color and the solid square in between -10 and 0." Just don't go into the red and you'll be good to go.

    Scott N1SER
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2019

    Simple Answers--- It Depends

    1.  NEVER let it go into the RED

    2.  If you are running barefoot (100W or less) then a bit of yellow will not degrade your XMT signal

    3.  If you are using an AMP (100W++) then avoid letting it go into the yellow as you do not want to be amplifying distortion products.
  • dlwarnbergdlwarnberg Member
    edited May 2019
    Jaun.... FYI... am listening for you now. 
  • dlwarnbergdlwarnberg Member
    edited April 2019
    Howard, been out of the digital game some time but 100 watts?  Last I played I rarely exceed 10 watts, then again that was JT65... if FT8 all that much different?

  • dlwarnbergdlwarnberg Member
    edited April 2019
    Clarification, listening for you now on 20 meters, FT8
  • Neal Pollack, N6YFMNeal Pollack, N6YFM Member ✭✭
    edited April 2019
    When running without an amp;
       +   Thje Flex Audio Level bar should just touch 0 dB on peaks, never over.
             This puts the average solid bar a little below the 0 dB line and that is fine.

       +  When using an amplifier;
            Try to keep the peaks around -8 dB approx, and the
            solid green average bar around -10 dB approx.
            This will yield an exceptionally clean on-air signal.

    There is really no absolute right/wrong way here, with the exception that once peaks
    go over the 0 dB mark, you can start distorting and splattering.


  • Juan TG9AJRJuan TG9AJR Member
    edited February 23
    OK thank you Howard.

    And if I may ask what is the proper way to adjust that LEVEL ?
    Using the DAX TX Gain and/or the Adjust TX Audio Level (PWR) the vertical slide on JTDX/WSJT-X ?
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2019


    That said use only the power your need to use to make the contact.

    if the other station is weak.. say -22 or less then it is likely you will need to use power for him to hear you

    ALSO... with Flex DAX your decoding is entirely in the Digital Chain vs external boxes such as Rigblaster that do A/D and D/A conversions.. so it is likely you will have a 3-6 dB gain advantage over the other guy..  This means that if you are hearing him at say-18 then it is likely given equivalent antennas and power that you are being heard at -18-6=-24  - hence you need power for him to overcome his equipment deficiencies so that he can hear you.
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2019

    I use DAX TX gain to control levels
  • DH2IDDH2ID Member ✭✭
    edited April 2019
    Very good advice! I have a very clear signal using the same settings, measured
    with my spectrum analyzer and harmonic distortion measurement.
  • PatrickPatrick WH6HI Member ✭✭
    edited June 2
    Another way of getting proper audio level is to set the Xmt. Level in the wsjt-x app at no more then 80 % then set DAX to run as high as possible without going into the red on the peaks on the audio drive level . As you move from band to band check the level and adjust audio drive as needed. The radio will remember that level on a band by band basis.
  • Neal Pollack, N6YFMNeal Pollack, N6YFM Member ✭✭
    edited April 2019
    Juan:    YES :-)

    Adjusting any of;

    + DAX TX level slider
    + WSJT-X Power Slider
    + Windows Playback Device Levels Tab

    will all affect this SSDR Flex TX level.
    For personal preferrence and no real scientific reason, I tend to
    make sure that the windows level tab slider is not set above 80%,
    and also that the WSJT-X power slider is set around/approx 80%,
    then I use the DAX TX level slider to do the final level adjustment.
    This is one of more than a dozen ways to properly adjust the level.
    Whatever you choose, just don't let the peaks go over the 0 dB level
    on the Flex SSDR or Maestro interface.


  • Ned K1NJNed K1NJ Member ✭✭
    edited April 2019
       Weak signal modes are used to -hear and decode- weak signals, not
    necessarily to transmit them.  For example:  EME, moonbounce, might
    best use a "weak signal mode", but it still would take considerable power
    from your antenna to make the trip.
                                     Ned,  K1NJ
  • Juan TG9AJRJuan TG9AJR Member
    edited April 2019
    Thank You all I really appreciate all the feedback, 73.
  • Dwayne_AB6ADwayne_AB6A Member ✭✭
    edited June 2019
    Just a follow up to this question, given the radio is rated 25W max in AM and FM modes and digital modes have similar duty cycles, does that confirm max power in digital modes should be 25W regardless?
  • Neal Pollack, N6YFMNeal Pollack, N6YFM Member ✭✭
    edited June 2019
    I run FT-8 at 80 to 90 watts routinely, both with my Flex and with my Icom 7300.
    In fact, my ICOM 7300 was dragged to an island for IOTA this year, and ran 3 days and nights
    at 100 watts with FT-8.  The fans are there to protect the finals, and the finals are designed assuming
    that "AMATEURS", not broadcast professionals, are going to use them.

    The finals will not complain, and the Flex 6xxx has over-temperature cutback that will protect it
    if you make it too hot.    The same can NOT be said for magnetics.   If you are using 100 watt external band-pass filters (with torroids), or end-fed antenna's with match-boxes, digital mode duty cycles like FT-8 will overheat the torroid core.   We melted a few 200 watt band-pass filters with our DXpedition while running FT-8 at 80 watts.   Antenna match boxes and band-pass filters are rated these days using a B.S. market-speak fake-news term called ICAS.   ICAS is weasel-word garbage, and frankly not referenced to much of anything that can be reproduced in a lab or measured.   It reminds me of the 1970's all over again, when a stereo amplifier that could produce 25 watts RMS with a clean signal, was advertised in the store windows as 700 watts peak-impulse-power.   Um, er, ah, uh, WHAT!?   Oh, sure, fake news. :-)
    In actual testing we did for antenna match boxes, using temperature meters, talking to the torroid manufacturer, and using basic lab and mesurement practices, we determined that a 2 kilowatt end-fed matchbox is typically good for about 250 to 300 watts MAX on FT-8.     

    Once you hit a certain temperature with magnetics (ferite/torroid-cores), the material and binder is damaged and the effect is permanent.   You don't want to go there.  We have ruined plenty of them.

    The 200 watt band-pass filters melt at 80 watts FT-8 when used for an all day run.
    Don't worry about the amp finals, worry about the external magnetics that are in your transmission line and antenna path way.   If you have external match boxes and band-pass filters, you MUST choose to over-size them 5 to 1 when using FT-8.   That means, for example, that many of us who are planning for 100 watt FT-8 at Field Day this year are buying 500 watt band-pass filters after melting the 200 watt versions :-)

    Ratings?   Lies?    No De-France...   Buyer beware!



  • Dwayne_AB6ADwayne_AB6A Member ✭✭
    edited June 2019
    Thanks Neal... Since you mention ICAS, this is what prompted my question. From Flex's home page... 

    1500 Watt FT8 on 160m – 6m!
    Punch through on FT8 with power
    • 100W = +50 dBm
    • 1000W = +60 dBm
    • 1500W = +62.7 dBm
    and then for the amp: ''Full ICAS duty cycle - FT8''

    As a friend pointed out, the I in ICAS stands for intermittent, there is no full intermittent duty cycle, so what does this mean? Can this or any amp run 1500W in FT8 or any other mode continuously? Can the bare Radio run 100W??


  • Neal Pollack, N6YFMNeal Pollack, N6YFM Member ✭✭
    edited June 2019
    Full ICAS duty cycle has no meaning. Someone left the cage door open in Marketing again. But in general, two piece amps with a larger power supply can go key down for longer periods of time.
  • Dwayne_AB6ADwayne_AB6A Member ✭✭
    edited June 2019
    Thank you! I just want to be sure what I am sending is clean. Totally understand what you are saying around magnetics. I have a Watt limited EF antenna I am working to replace with a home-brew solution using improved 5kW UnUn's and Baluns.

  • Tim N9PUZTim N9PUZ Member ✭✭
    edited September 2019
    I do not have the reference handy but I recall that many manufacturers who quote an ICAS rating refer to it as 50% duty cycle. I believe the ICAS rating actually means that the device should work at the stated power output for up to 3 minutes but each active period must be followed by an "off" period of the equal duration.

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