Noise burst on Spectrum Display

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  • Question
  • Updated 1 year ago
I see these bursts of noise from time to time on 40 meters.  I have expanded the spectrum display and it is fairly broad band but it varies in amplitude across the spectrum.  It doesn't look like typical noise and sometimes I wonder if it is a sampling Phenomenon in the SDR as a reaction to a noise input.  Has anyone else seen this.  Today when I saw it I logged into my buddies system, a Flex 6700 in North Carolina to see if it was wide spread.  Didn't see it at all on his Flex.  I have uploaded a short video from my phone camera. 

Does anyone have an idea what this might be?
http://www.n4rfc.com/wp-content/uploads/2017/02/VID_20170207_100642447.mp4

Alternate Link
http://www.n4rfc.com/?p=1383
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Bob Cheek

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Posted 1 year ago

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Mike va3mw

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Would this be different than what Lightning would look like?

Mike
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Bob Cheek

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Yes, static crashes from lightning move the whole noise floor up.  This noise is spikes over a wide spectrum.
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Ken - NM9P, Elmer

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Possible explanations:

1) Electric fence in the neighborhood (even a mile away can travel if it is arcing enough.)

2) Lightning 

3) How high is your WNB?  it might be triggering on something.

4) bad ballast on a streetlight or desk lamp trying to trigger and failing.

5) tree limb rubbing on power line

6) tree limb rubbing on antenna wire?

Lots of possibilities here....

Ken - NM9P
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Bob Cheek

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Wideband noise blanker is off.
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Bill W2PKY

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On the Display Tab see if you have Weighted Average on
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Bob Cheek

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Weighted Average is off.
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Mike va3mw

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I just looked at the video.  That is external to the Flex radio.  It is could be just about anything that Ken suggested.  I bet it goes away when you remove the antenna.

Mike va3mw
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Jim Caldwell

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I have seen the same noise on 40M - F6500.  Heavy storms locally today but no evidence of the noise seen. K4JPM
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Bob Cheek

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I have seen this when the band is otherwise quiet, no static at all.  I see it only occasionally, but today it was very persistent for some reason.
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Bob Cheek

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The thing I find interesting is that if you look closely you will see there are a series of fairly narrow spikes of noise and then sometime the spikes are wider and it looks like the noise floor moved up and the narrow spikes are pointed down.  Very strange.  More like a spread spectrum digital burst than noise.  All that you hear in the speaker is a small pop like a static crash.   If I was using my FT-1000MP I would not know any better and think it is a small static crash.
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Watts - K4QJZ

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I have seen the same type of noise many times across the country with work. If you set the spectral display correctly you will see a digital components in the wide signal. I suspect there is more to the wide noise than published. I have seen this on six different Flex receives 6700R in different locations on an given day 2-3 receives thousands of miles apart showed it. At my home location 60 mi west of D.C. I see it quite a bit, even with all on batteries?
K4QJZ
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John - K3MA

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I have exactly the same issue with the station in a rural setting.  I believe it to be an electric fence used by one of the farms in the area.  It also shows up on some other frequencies as more of a light line across the waterfall every 1.5 seconds plus or minus.
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Bob Cheek

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I just had an Ah-Ha moment.  While listening on a fairly static ridden 40 meters I went to Display and switched Weighted Average ON.  The display started showing these noise bursts on the louder static crashes.  Switching Weighted Average OFF eliminated the noise bursts.  Dropping down to 80 meters I see the same thing.  So, It appears to be something in the sampling that is doing it. 
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Tim - W4TME, Customer Experience Manager

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Yes, that it is what weighted averaging does.  With weighted averaging, each FFT bin sample value does not contribute equally to the average.  Data with higher magnitudes contribute more to the average calculation.  This feature is intended to be used when you are looking for weak signals; you want the signal to be more pronounced visually than noise.  On a noisy band, this will make the display "jumpy" which is why it is off by default.
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