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What could be causing these weird QRM patterns in the noise?

Discussion in 'Working Different Modes' started by AB7RU, Mar 22, 2021.

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  1. AB7RU

    AB7RU XML Subscriber QRZ Page

    I live in an apartment setting, so there is a lot of noise, manmade interference from who knows what. My noise level here is usually at least S7-S9 and so I don't hear a lot using my in-door HF antennas. But I do notice curious patterns that come and go as vertical traces that vary in freq, like this screenshot I just took.


    Do you folks ever see linear noise patterns like that on your waterfalls? They come and go, so it must be some appliance or gadget that is used for a while and then turns off? I have no idea. The patterns are symmetrical in places which adds to the weirdness. I can't hear any change in the noise though so they are very faint signals whatever they are.
  2. K1APJ

    K1APJ Premium Subscriber QRZ Page

    Yup- See them all the time, they are much more impressive when you see them in CW skimmer. I'll post some screen captures later, I am not in the shack right now.

    I note that you are on the west coast, I am on the east coast, so it is apparently not a local thing..
    AB7RU likes this.
  3. KD9VV

    KD9VV Ham Member QRZ Page

    Google "Ionosonde"
    Also, in coastal areas you may be seeing "Wave Height Radar"
    ..and military "ALE" automatic Link Establishment.

    All of these show regular patterns, cover a large swath of RF spectrum and are intermittent.
    AB7RU likes this.
  4. W2SGM

    W2SGM XML Subscriber QRZ Page

    That looks like those screamer switching power supplies to me. Have your radio prepared to run on battery ahead of your next power outage-- or don't, because then you'll get a glimpse of what you're missing when that hash isn't there. :eek:
    AB7RU likes this.
  5. N7EKU

    N7EKU Ham Member QRZ Page


    Switching power supplies, wall warts, etc. typically run with square waves around 40-100kHz (although the Wikipedia article says up to 1MHz). So on badly filtered ones, you can see harmonic noise with this spacing quite aways up the band. Eventually they fade out as you get high enough (40m or so).

    They can be intermittant if they are running battery chargers (charging you laptop or phone battery) as these don't run constantly.

    I see most of this noise coming locally (one's one residence and nearby neighbors).

    Grow lights can make tremendous noise that travels for hundreds of yards.


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  6. K1APJ

    K1APJ Premium Subscriber QRZ Page

    Here is a nice shot from CW Skimmer.

    Last edited: Mar 23, 2021
    W1BR likes this.
  7. AB7RU

    AB7RU XML Subscriber QRZ Page

    Thanks K1APJ, someone mentioned Ionosonde so I have been looking into that as one possibility. 73s
  8. AB7RU

    AB7RU XML Subscriber QRZ Page

    Hey thanks KD9VV, I did google that, very interesting. Thanks for the input! 73's
  9. AB7RU

    AB7RU XML Subscriber QRZ Page

    Yes! I remember one evening we had a power outage here in Spokane in the middle of the night, and I immediately turned on the rig to give a listen and see how much different the background noise was. I couldn't believe how quiet it was. I thought maybe I was having antenna troubles. No, it really was that quiet! Apartment buildings have to be rife with so many wal-warts and like you said "screamer" switching supplies which I guess all or most of it is just that. thanks for the comment 73's!
    N7EKU likes this.

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