[RFI] What would cause noise like this?

Charles Gallo charlie at thegallos.com
Sat Nov 2 09:20:09 EDT 2019

Another pattern Starts circa 8:00am (or 9:00am), ends 4-6pm, Monday to Friday, with maybe stuff Saturday- think business/industrial

73 de KG2V

> On Nov 2, 2019, at 8:40 AM, David Robbins <k1ttt.dave at gmail.com> wrote:
> 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
> Cc: RFI
> 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
> 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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