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Pulsing during transmit FT8

I get theses pulse when I transmit for FT8. Any ideas what could be causing them?


  • Al K0VM
    Al K0VM Retired Member ✭✭✭

    That looks like short breaks in the TX audio stream usually attributed to DAX buffer corruption. The usually fix is to close and restart the DAX GUI. If they return soon, rebooting the PC may help as will reducing the load CPU load on the PC.

    AL, K0VM

  • Paul Carff
    Paul Carff Member ✭✭

    I have a beefy gaming PC that I have converted for ham radio and nothing else is running - so I don't think it is loading.

    I have restarted the computer and I am seeing this same behavior using different computers.

  • Mike W9OJ
    Mike W9OJ Member ✭✭

    I've had transmit audio cut out intermittently on FT8 on some bands while running higher power. I'm running 450 Ohm line and may have some RF in the shack.

    Does it happen to you on all bands at all power levels?

    73 de Mike W9OJ

  • You are not alone Paul!!!

    I have been trying to solve this issue for several weeks now and it is most likely network related. Let me describe our setup and issue:

    We (HB9RYZ, Wolfgang and myself) are operating the Mount Rigi Remote Station at 1660m ASL in Central Switzerland. We are using the FLEX-6700 and an spe Expert 1.3K - FA PA. The antennas are a LZA-10-5 and a 54m Longwire using a JC-4s remote antenna tuner. Before anybody jumps at me an shouts: "RF FEEDBACK!" I can assure you that this is not causing our pulsing. Pulsing ONLY happens when we are using SmartLink. Pulsing is NOT influenced by the power output level or band! We have a local PC up there and if we do FT8 locally there is no pulsing. We have observed pulsing in SSB as well, but it is more difficult to detect. It reduces the audio quality, which is bad news, because we used to get excellent audio reports. Since we have the pulsing issue we get mediocre reports.

    Now before you say "Bad Internet connection" let me tell you that we have a fiber connection up there with 100 MBit/s up and down. Latency is 5ms!!!! This is a very good fiber connection. Both operators have this issue and we both have very fast internet connections at 600 Mbit/s with low latency that we have thoroughly checked. I usually check for pulsing using a 1 kHz tune tone on FT8. Here you can see two screenshots that I took at home using the Colibri SDR that I operate as a panadapter with my IC-7800. First operating locally (using Anydesk to the local PC) and second operating remote with SmartLink:

    The large horizontal bar is probably a lightning - ignore that, but the rest is ugly enough! Considering all checks that we have done so far we think that the issue is related to the network. It was OK before, so we do not think it is a SmartLink issue. We have pulsing with the PC and the Mac version of SmartSDR. Our Router is a FritzBox 7590. It is possible that the issue is with the router, but whatever we have tried so far did not change the pulsing issue. It cannot be a local network issue because when operating locally all is fine, nevertheless we checked all cables and are using CAT6 shielded cables with ferrite cores. We tried different MTU values - no change. The next thing we may try is changing the router, but since the site IS remote in all respects it will take some time.

    If you want to learn more about the Remote Station you can lookup my website at https://hb9cqk.ch/news.html or the website of Wolfgang at http://www.hb9ryz.ch/remote-dx-station/index.html

    I hope we can solve that together!

    73, Frederic, HB9CQK

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