[RFI] What would cause noise like this?

David Robbins k1ttt.dave at gmail.com
Sat Nov 2 08:39:57 EDT 2019

I would generally agree that you are more likely to find the source with
boots on the ground than on a computer screen... but there are a couple
hints you might get from watching the waterfall.

1. wideband unstable noise is likely power line related, but could be dc
motors, fishtank heaters, or other unregulated devices.
2. not so wideband stuff that wanders in frequency is likely a power supply
for something, a battery charger, light, heater, etc.
3. narrow and frequency stable stuff is mostly computer or video related,
though this can include some motor controllers and some power supplies with
stable loads and clocks.
4. when does it occur, only at night makes it more likely to be a light,
only when the sun is up means maybe solar array, only when dry or raining
means likely outside power line related, only at meal times could be
microwave or other appliance,  12hr on/off cycle is likely a grow light,
etc... making a 24 or 48 hour recording with an sdr is a handy way to
analyze this.
5. strong signals across wide bandwidths are either closer or higher power
devices, narrow bandwidths(not counting your antenna bandwidth) are often
farther away(they will get wider as you get closer), or low power devices.

To me those changing line spacings look like a step start for a motor or
some other device that is being turned on and off.  The fact that it doesn't
drift during startup shows it is something with a stable controller like a
computer or micro processor.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: telnet://k1ttt.net:7373

-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Don Kirk
Sent: Saturday, November 02, 2019 12:08
To: Frank O'Donnell
Subject: Re: [RFI] What would cause noise like this?

Hi Frank and gang,

I see lots of folks on the RFI reflector "wondering what an interference
waveform might be from", and honestly after many years of tracking down RFI
I have found that guessing what the source might be is almost counter
productive, except for understanding if the noise source might be power line
noise as that helps me determine what DF gear to pack.  What works best for
me is "boots on the ground', meaning that I get out DF gear (radio direction
finding gear), and then track down the property that's generating the noise,
and then we locate (track down) the offending device within that property.
I find it much better to keep an open mind regarding what the source might

Just my opinion based on many years of tracking down sources of RFI.
Tracking down RFI has unfortunately become a main part of my ham radio

Don (wd8dsb)

On Fri, Nov 1, 2019 at 7:30 PM Frank O'Donnell <vfo at inkbox.net> wrote:

> Hi all, new to this list, hoping to learn enough to chase down some of 
> my yet-unsolved RFI issues.
> As a start, I'm wondering if the way that RFI I saw the other morning 
> appeared in the receiver's waterfall might suggest anything about what 
> the source of noise could be.
> Here are two brief video clips from SDR Console, displaying a 
> waterfall covering the LF/MF spectrum with input from an Elad FDM-S2 
> SDR and broadband vertical antenna.
> The first clip is at 6:08 a.m. PDT, exactly one hour before local sunrise:
> https://vimeo.com/370416556/e3cf9bcb09
> At 00:23 of that clip, a pattern of heavy RFI starts, with lines in 
> the waterfall spaced ~16 kHz apart (approx 6 lines per 100 kHz).
> A couple of minutes later, I noticed that the RFI started toggling, 
> with the pattern changing for a second or two, and then the RFI 
> disappearing briefly before restarting. In the following clip this 
> pattern starts at
> 00:09:
> https://vimeo.com/370418392/afb0a0c4ef
> Any thoughts? We live in a suburban neighborhood where lots are all 
> approx 50 x 200 feet. There are at least two houses with solar panels 
> within ~200 feet of us, and more down the block. I gather that RFI 
> from solar panels can vary, based on the type of system and the 
> deficiency responsible for the RFI. Do these clips show any kind of 
> visual signature that might suggest the source?
> Thanks and 73,
> Frank K6FOD
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