[RFI] Broadband RFI...

Dave Cole dave at nk7z.net
Tue May 31 17:49:53 EDT 2016

On Tue, 2016-05-31 at 16:34 +0000, David Robbins wrote:
> The output of any switching supply like that goes down in power as it
> goes up in frequency... that may be offset by the wires attached to it
> becoming more efficient antennas so it can be hard to predict.  If it
> is one of those try going down to 160m and see if it becomes more
> narrow band.  One of the things I saw was that at the fundamental
> around 100khz it was 3khz wide, of course every time you double the
> frequency you also double the bandwidth, so by 160m it was 50khz wide
> and by 40m it was so wide that it just blanketed the band.  So going
> lower in frequency may make it easier to detect both because it may be
> less spread out, but also because the signal may be stronger.

That little tidbit might make it a lot simpler to locate if this is one
of those, thank you!  I have been seeing a very wide band of noise
rotate around now and then, and I suspect it might have been someone

I spent an hour or so with K7OLN driving around to twenty five
locations, all around my QTH, taking S meter readings while the RFI was
not there.  We will be doing the same thing at around 9:15 PM tonight,
after the RFI has had about 45 minutes to stable down.  

My hope is that I can get a rough area of where the RFI is originating
based on a higher than normal S meter readings in an area.  I was hoping
I could hear it on 2 meters, but that may be the case based on what you
said...  I will check 80 and 160... 

I have and will be putting results up at:


I updated the FFT movie to show the end of the RFI, as well as the
start.  The FFT is showing a fairly narrow range, (look at the scale on
the left), so it looks worse than it is...  

I figure I am loosing between 12 and 15 db of noise floor.  I will
verify this this today by doing some JT65 tests prior to and after the
RFI left...  Find a local get his S/N, on JT without RFI, then do it
again tonight after it is at full potential, then look at the
difference!  I think that will tell me what the noise floor is doing.

Again, thanks for the tip on the 160 Meter bandwidth/power changes... I
will more than likely need that into at some point in this process...

73's, and thanks,
Dave (NK7Z)
For software/hardware reviews see:
73's, and thanks,
Dave (NK7Z)
For software/hardware reviews see:

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