Propgtn Why Does HF Noise Floor Change?

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air-scan

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I am talking about the subtle hash without signals in the upper HF at 27MHZ 11m area. Sometimes on some days there may be a band opening but between signals the noise floor has noticeable change in amplitude by a small percentage. Constantly rising and falling in amplitude until the band closes.
 

air-scan

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The weird thing is my antenna is only 10 feet wire. SFU was 69 at the time couldn't be solar influence but more atmospheric. I don't know. There where storms early morning before the band opened. More forecasted.
 

RFI-EMI-GUY

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Sometimes you can see the noise floor rise channel by channel in 11M CB. It is all those many CB radio transmitters in the world mixing and propogating around the country or globe.
 

majoco

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OTOH if you are receiving cosmic and atmospheric noise, you should really be happy! Most of us are plagued with TV's, AM BC intermod, random electrical noise etc etc that far exceed the background noise!
 

n5rv

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If it were only atmospheric noise, this is from what I suspect a cheap battery charger close by..... pictured is the full 40m ham band...

 

majoco

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No signal level reference on that screen dump but I would hazard a guess to say you have more to worry about than cosmic noise! My background noise is around -120dBm on a WinRadio G33DDC!
 

n5rv

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The S meter is running S9, and the IARU standard for that is about -73dbm. So it's pretty strong, but the source is not within my property. I suspect my neighbor to the east of me. The signal varies so I think it is something moveable such as a battery charger for his side-by-side 4-wheeler, or for his 2 motorcycles. I rarely see it during the 2 nets I check into early mornings on 40 or 75 meters. Usually kicks up around mid morning or sometimes mid afternoon.
 
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