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Spurious Emissions?

PaulB
PaulB Member ✭✭
in SmartSDR for Windows

Anyone have an idea what this could be? Running JS8Call at about 30w with SWR at 1.5...curious why the transmission lower than the tx frequency.

signal-2024-02-03-155027_002.jpeg


Comments

  • PaulB
    PaulB Member ✭✭
    signal-2024-02-03-161044_002.jpeg


  • PaulB
    PaulB Member ✭✭
    signal-2024-02-03-161855_002.jpeg


  • PaulB
    PaulB Member ✭✭
    signal-2024-02-03-162525_002.jpeg

    All of those spikes on either side are when I TX. This was FT8

  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭✭
    edited February 2024

    Ensure that you are not over-driving

    image.png


    Note though that those 'spikes' are at a very low level and probably not being transmitted. Check this by putting your radio into Full Duplex (FDX button, lower left) and open a second panadapter. Select the RX A receiver (no antenna connected). Transmit the FT8 sig into a dummy load. The second panadapter can be zoomed in or out to give you a good look at the signal. This will be a much better representation of what you are actually transmitting.

    Because FT8 messages are transmitted using frequency shift keying, the visual representation does not keep up with the carrier signal variation and everyone will see some of these spikes. If you are not over-driving and not actually transmitting them then it is all ok. The paper "The FT8 and FT4 Communication Protocols" by K9AN and K1JT on the WSJX web site provides a complete explanation.

    Long answer short: just ensure you are not over-driving and if not do not worry.

  • PaulB
    PaulB Member ✭✭

    Thank you very much for the detailed response. What would be a normal TX level setting? I brought the DAX TX level way down to around 25 or so and it seems to take care of the issue, but want to be sure what the signal looks like on the other end

  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭✭

    For me, the TX Stream setting is 48. There are some more knowledgeable elmers on here who can confirm or correct. 48 gives me the level seen in the picture.

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

    Paul

    Can you show the entire SmartSDR screen please including the antenna selections and the scale on the right side of the Panadapter. Without the scale, it doesn't really tell us much.

    Your audio level is too high is the first thought. Dial it down a bit.

    Mike

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