[RFI] What would cause noise like this?

Dave Cole dave at nk7z.net
Sat Nov 2 08:24:49 EDT 2019

Hi Don,

I must agree with you here...

I have only once or twice guessed what something was in over 10 years of 
hunting RFI, based solely on the RFI signature...  I have guessed based 
on timings of the on/off etc., and been correct...  But, based on just 
the RF signature, not so often...

It all boils down to understanding what you are looking at, then getting 
out an antenna and looking for that particular signal...

There are some items that can be "inferred" by an RFI signature, but it 
is very general in nature...

Things like interference that comes on each morning, then shifts a few 
minutes each day...  Probably something controlled by sun light, yard 
lights, solar, etc.

Something that comes on at precisely the same instant every night, and 
ends at the same instant each morning, probably something like a 
lighting array, but probably not solar.

Very general inferences are very helpful in locating RFI...  But pinning 
to a source, not likely on a regular basis...

For the fellow looking at his RFI, see:




73, and thanks,
Dave (NK7Z)
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 11/2/19 5:08 AM, Don Kirk wrote:
> 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 be.
> 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
> hobby.
> 73,
> 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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