[RFI] Power Line Radiated Interference Limits

[Hare, Ed, W1RFI]

Power lines are "incidental radiators" as defined by Part 15 rules. As such, there are no specific radiated or conducted emissions limits for the noise they make. The operator of an incidental emitter is required to use it in a way that does not cause harmful interference.

Power line noise exhibits a few characteristics:

Power-line noise level is relatively constant across a particular band, +- antenna resonance.  So, when you tune the band, its noise does not get louder, quieter, louder quieter, but is pretty constant across the band. Many other noise sources have noise that peaks every "N" kHz across the band.

Power-line noise has a strong 120-Hz component, although in rare cases, it can have a 60-Hz signature.  Put your receiver in AM mode, 6 or more kHz bandwidth, and give a listen. You can also make a .wav or .mp3 file and run it through a free program called 'Audacity" and analyze that spectrum, with the understanding that your receiver bandwidth is usually limited below 200 Hz or so, so that 120-Hz component may be reduced in amplitude.

In the time domain, you may see spikes or a repeating 120-Hz pattern. (Audacity does that, too).  The peaks sometimes vary fron the nominal 120-Hz, 8.3 MHz, as wind and vibration moves the gap that is causing the noise around.

Power-line noise usually varies with weather, usually going away on rainy days, but sometimes getting worse, and as wind blows lines around, the noise can show variations.

Other devices like switching supplies have peaks and dips up and down the band.  Switchers can be drifty, with the frequency of those peaks changing as the device warms up and sometimes doing little jumps as voltages exhibit small surges and dips. If the noise comes on suddenly in response to what people are doing, it is usually a device. Switchers are used in almost every electronic device made today, and they are sometimes confused with power-line noise.

Here are the basic steps to follow:

o Determine that there is probable cause to think it is power-line noise
o Contact your power company through its customer-service representatives. The key words are radio interference, television interference or even tell them their help screens could be looking for "noise" or "RTVI."
o Give it time.  In about 25% of the cases we initiate from reports, we hear back a week later saying that the power company was out to fix it.
o In most cases, the power company does not contact you, although it should. So, no response doesn't mean that it is not being worked on.  The new IEEE standard on power-line noise explains why it is important that the power-company staff coordinate with complainants, but that is not in effect yet.
o If that doesn't work, contact ARRL by filling out the intake form at:

 https://form.jotform.com/212425939918163

The Lab staff will then run through a process it has worked out with the FCC to first have ARRL try to persuade your power company to work on and fix the problem, then ultimately turn over a well-documented case to the FCC.

Ed Hare, W1RFI
ARRL Lab


REPORT OF POSSIBLE INTERFERENCE FROM ELECTRIC UTILITY TO AN AMATEUR RADIO STATION<https://form.jotform.com/212425939918163>
Please click the link to complete this form.
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________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of Charles Plunk <af4o at twc.com>
Sent: Sunday, June 5, 2022 11:41 PM
To: rfi at contesting.com <rfi at contesting.com>
Subject: Re: [RFI] Power Line Radiated Interference Limits

Oh, I would try to exhaust all other tactful ways of getting it fixed
before pointing out reg's to them. If they worked with you 7-8 years ago
then likely they will now. But I understand if you are trying to get
prepared "just in case". Knowledge is power they say.

I would be prepared to explain to them why you believe its power line
rfi and not another source. Such as a way of identifying the 120hz.
There are ways to do this. I usually record the noise and expand it out
on a audio manipulation program such as Audacity and count the 120hz
spikes. Others do it differently.

And of course, you have shut down your main breaker to your house while
powering a receiver on battery to try that first?

After doing those things, hope your power co is large enough to have RFI
location gear. Mine is small thus I find the poles myself with my
accumulation of various gear, some homemade :-).

73

Chuck
W4NBO

On 6/5/22 21:12, Riki, K7NJ wrote:
> I've recently become plagued by power line interference that is most
> noticeable on 80M and 160M.  In the past,, the local power company had been
> cooperative in fixing the source(s) of such interference.  However it's been
> about 7 or 8 years since I've been in touch with them about such issues.
> Just to be prepared, I would like to know what specific limits there are on
> power line emissions (if any).  I know that in the past, the requirements
> were very lenient - only requiring power companies to follow good
> engineering practice without any quantitative emission limits.  In any case,
> having the actual reference paragraph numbers in the FCC rules would be most
> helpful. As I recall, this had been somewhere in Part 15. Any help would be
> appreciated.
>
> 73, Riki K7NJ
>
>
>
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