[RFI] 160 Meter RFI

Hare, Ed W1RFI w1rfi at arrl.org
Thu Dec 6 10:30:06 EST 2018

Switchers generally show the following characteristics:

They create noise every N kHz over a broad frequency range, with N typically being 10 to 100 kHz.
The may be on continuously, but may also come on or off depending on whether the equipment they are powering is being used
Some are on continuously to enable instant on functions, but will often change the nature of the noise they create when powered equipment it turned on and off
Noise levels can vary as different lights and other equipment in a building is turned on and off
They typically drift slowly with temperature changes
They usually respond to voltage fluctuations with slight changes in frequency

You really don't want to ask, "what is it?" If someone told you that your noise appears to be coming from a Noisyo model XYZ-1 power supply, unless you knew you had one in your own house, you would then move on to the real question:  Where is it?  And if a Raucuso model ABC supply had the same characteristics so your Noisyo identification was misleading, you might be looking for the wrong device.  Finding where it is, isolating it by flipping breakers then looking at what may be plugged in to that circuit is more reliable.

If the noise is being radiated by a house, a good DFing loop and triangulation may pin point the house.  You can also get a good idea of where the noisy device is by using a handheld AM or SSB mode receiver with an S meter.  If you position yourself a foot away from different house electrical wiring (external light, power meter), the house with the noisy device will generally be much louder than the others.  If the noise is being heard over a wide geographical area, if you go from pole transformer to pole transformer and put the receiver with a short antenna about a foot from the ground wires of the poles, or a foot from pad-mounted distribution transformers, the one with the house with the noisy equipment will generally be louder.

Now, you can still be misled, because other houses may have noisy devices, too, so the best way to find the source is to hear if from your own station, then be able to follow it down the lines until it gets stronger at one house or one pole.


-----Original Message-----
From: RFI <rfi-bounces at contesting.com> On Behalf Of Dave Cole (NK7Z)
Sent: Wednesday, December 5, 2018 5:29 PM
To: rfi at contesting.com
Subject: Re: [RFI] 160 Meter RFI

Hi Ray,

Trying to guess the source from looking at captures can be tough... 
That said, here are a few questions:

1.  Does it ever change sound?
2.  Does it run on a schedule?
3.  It is always the same?
4.  Is it just on 160?

If it runs on s schedule, kill your house power at one of the run times for it to test if it is in your home...

It looks like a SMPS.  Once you get proof it is not in your home, buy or better yet, build a loop.

Look over Jim's paper, it does make a difference for the better, if you follow his steps for quieting down your RF environment.

Take a look at my page at:

That is part I of a two part series on getting to know your RFI environment using an SDR.  There are several other links on the right dealing with RFI as well...

73s and thanks,
Dave (NK7Z/NNR0DC)
ARRL Technical Specialist
ARRL Volunteer Examiner
ARRL OOC for Oregon

On 12/5/18 9:10 AM, Ray wrote:
> I have this 160 Meter RFI :  https://youtu.be/QI08sE2FS40 It shows up 
> once or twice an hour for 5 to 10 minutes. Any ideas what it is?
> Thanks,
> Ray K9RS
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> RFI mailing list
> RFI at contesting.com
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