28 KHz periodic wave on 40M

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  • Updated 2 years ago
My background noise on and around 40M has a persistent wave of about 28 KHz and about 5 dB peak-to-peak - see attached image.  This is solid down to about 6 MHz and up to about 9 MHz.  It tapers off in amplitude at both end points.  I only see this between 6-9 MHz, elsewhere the noise base is flat.  It does not seem to cause any communication problems - just curious.  Any ideas?  
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Dick B

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  • curious.

Posted 2 years ago

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ON5AM

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I have the same... in Belgium
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K0UNX

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While I'm not seeing THAT in Colorado, I can draw a parallel to a similar noise that we tracked down here.  Ours started right at 3.8 and went up to 5.1.  That turned out to be the phone company's VDSL service.  Specifically, it was traced to a CUSTOMER MODEM, and it was the RETURN stream of their VDSL service.  Several local hams, the FCC and a phone company engineer finally found it, and corrected the problem.  That one device caused havoc over a 10 kM distance!  

I might add that inclusion of the WATERFALL in your graphic would have helped.  It was easier to spot the VDSL noise using the waterfall.

Jim
K0UNX
Littleton, Co.
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Richard Fusinhski

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I have had similar repetitious noise. I found mine to be noisy walwarts. Use a portable radio preferably one that  can tune the frequency of interest. Go around and sniff near all your walwarts. I found one that was the culprit, unplugging it got rid of all my noise.

Rich
K8NDS
Prescott, AZ
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Dick B

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Let's try this again ... Excellent point Jim ... here is the watefall ... 
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K0UNX

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Aye.  Very similar, but a different band.  You can tell if it is local by comparing day to night.  If it stays the same, it is local.  I'll bet it is.  Next, grab a laptop, stick your Flex in the car, and go mobile, and see if you can find where it peaks.  Mine was 900 metres from my house, and only 30 metres from that of W0DGD's place.  But it could be seen by other hams 10 kM from here.  We all got relief as soon as the malfunctioning modem was taken off line.
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EA4GLI - 8P9EH - Salvador

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Not much going on on 40m for me. 
I do have that signal right on 7140 all the time though.

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Michael Coslo

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Can you post a waterfall image? 

Note that there are some nasty RFI sources in those pointless laser light devices that put little stas or splotches of color on your house. Hopefully they will go away soon, except for the folks who keep their Christmas lights on all year round.
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K0UNX

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Aye.
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Michael Coslo

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Okay - completely different than mine. I'll post it later in a differetn thread, so as not to add an element of confusion in this one
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AA5JD John

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I've seen similar periodic noise on 40M and it always coincided with my wife walking on our new Proform treadmill! No treadmill then no noise. Guess who has to wait to use his new Flex 6700. :-)
73
AA5JD John D
San Antonio, TX
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Norm - W7CK

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I've got some noise that I've never been able to locate.  I run all of my equipment off of solar / 12v battery bank.  I've turned off the power to my house, turned off the solar charge controller, run SmartSDR from my laptop, and still have the noise.  It shows up on every band, It isn't coming from my house and all of the utilities in my neighborhood are underground.  Here's a snippit from 15m....

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Norm - W7CK

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Here's another Snippit where I've zoomed in a little bit more.  Some of the signals wave back and forth creating a crosshatch design.  Others are fairly steady like a carrier.  All of them disappear when I disconnect my antenna.  15m and 17m seem to be the worse.  40m & 80m (my favorites) aren't too bad at all. 

Some of them are wide like on 21.007, 21.033 and21.060
Others are sharper like on 20.990, 21.045, 21.058, etc....
Most of this just started within the past 6 weeks.  Never stops day or night.



Makes me wonder what the heck the FCC does.  They don't clean up the illegal activity on the bands, and they certainly don't seem to be monitoring RF radiation coming from electronic devices, electrical motors etc.   Shoot, we could save a bunch of money by just getting rid of the FCC.
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Dick B

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A lot of the spikes are caused by Ethernet routers/switches.  I have them on 20M-10M.  They usually don't bother me and I can use a TNF if one of them does.  I have not tried putting ferrites on all of the cables, about six of them, but do plan to put a ferrite on the power cord, which is reported to be a typical culprit.  
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Ken W9IE

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Here are 2 Screen shots of what I have been putting up with for over a year
24/7.
The peaks switch back and forth every second or less.

Ken  W9IE