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Interference Across the Spectrum

Hi Flex Community,

Have any of you an idea what the signal occurring as three stripes in the waterfall repeating across the 40 meter band in the screen shot below might be? It occurs intermittently across much of the HF spectrum at times. Thanks and 73, w7phg.


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Craig, well that could be any of a number of things. Usually, you want to verify that it is not originating from your shack. Unplug everything possible to see if it goes away. TV sets, wall warts, washing machines are all good candidates.

    If your whole house comes up clean, then it is likely something at a close neighbor's house. A portable SDR receiver can help track down the location.

  • Ha Gei
    Ha Gei Member ✭✭✭

    I see similar signs , but more on higher bands, If they , demodulated in AM sound like hum, the are harmonics of power supplies or inverters. If the are corelated to shini9ng sun, look for solar power supplies


  • John KB4DU
    John KB4DU Member ✭✭✭✭

    The way the frequency wobbles around, this is most likely a switching type power supply of some sort. For me the first step was to operate with only battery power, ups for the flex and laptop computer. Cut the main breaker and see what happens. If the noise goes away,it’s something in the house, so turn on the main and turn off breakers one at a time. Mine was a wireless external speaker charging by usb. If the noise persists, it could be external, but sometimes in the house by a device that has a “keep alive” battery, which can be a challenge to locate.

  • Mike Steventon
    Mike Steventon Member ✭✭✭

    Here in the UK we get a lot of grief from Very High Speed Digital Subscriber Line (VDSL) internet connections via wire to property, which reveals itself as sharp and major spikes on the 40m band, at 4kHz intervals. It MIGHT be to do with internet, or as the other replies suggest, switched-mode power supplies nearby?

    Mike. G4GWH

  • jim
    jim Member ✭✭

    My washing machine will do that and also a wireless phone charger makes a lot of noise broadband.

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