Testing and checking output quality for FT8

Discussion in 'Working Different Modes' started by WA4KBM, Jun 28, 2021.

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  1. WA4KBM

    WA4KBM Premium Subscriber QRZ Page

    I want to fine tune my WSJT-X set up in order to be able to enable further distance transmissions without causing splatter or overdriving the signal so that it steps on other people.
    There are a number of different controls and setting along the signal path that can add or reduce the tones being produced as well as the power output of the transmitter.

    How to you adjust for quality and not raw power?

    My rig consists of:

    Yaesu FTDX-1200,
    Signalink external modem
    RPI 4 with WSJT-X installed
    (I also have JS8 Call and other software available)
     
  2. NG1H

    NG1H XML Subscriber QRZ Page

    1) On the radio turn off all audio manipulation including equalization. This means reading the manual for ALL settings.
    2) There are multiple gain/level adjustment stages: Software -> OS -> Signalink -> Radio. Make sure each stage has a good SNR with minimal distortion. This can be a fine balance. Get one too low and your noise ratio increases and when you compensate by increasing the gain on another stage you can add distortion/clipping on top of that noise. Since each computer (even with the same OS) is different as is each radio there is no one setting that is best for everyone. Start with the recommended settings and experiment to find the best settings.
     
  3. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    I never touch any of the controls on the radio when going from SSB to digital modes. I control all audio levels on the computer end.
     
  4. K3RW

    K3RW Premium Subscriber QRZ Page

    Watch the ALC on output. It depends on the rig if you want some vs little to none, so research that. For my Icom I run little to none.

    A full scale ALC means you're output signal is unusually wide and wasting power.
     
  5. AB6RF

    AB6RF Premium Subscriber QRZ Page

    It actually can be quite simple, if you choose to keep it simple.

    Splatter and TX signal distortion are caused by nonlinearities ANYWHERE in the TX chain.
    And in reverse, if your entire TX chain is kept linear, you’re transmitting a clean signal.

    Simple way to make sure the entire TX chain is pretty linear (=nothing is saturating or clipping) is to look at the TX RF power meter while you just slightly reduce the TX level in WSJT-X. If the RF power drops as soon as you drop the TX level in WSJT-X then you know for a fact that nothing is clipping and no stage is far into saturation.

    it is as simple as that, if you choose to keep it simple.
     
  6. N3RYB

    N3RYB Premium Subscriber QRZ Page

    You can also monitor your own signals with one of the many websdrs around.

    That said, here is how I adjust my FT-897D for digital modes. First set the rig to max power output at 100W. Then adjust the audio drive on the computer until I see the ALC activate(or the radio hits max power). When I do that, I know that I cannot ever set the audio drive into the radio any higher than that. At that point, I reduce the audio into the rig on the computer side until I have the TX power level I want. At least with this radio anyways, if the ALC is activating, its going to cause distortion. WSJT-X can save the audio levels per band for you as well.
     
    AB6RF likes this.
  7. K2WH

    K2WH Premium Subscriber QRZ Page

    No NB either.
     

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