[RFI] Tip on approach to, or where to start looking for new noise source

[Hare, Ed, W1RFI]

I just found a device in my own home operating at 45 dB above the FCC emissions limits.  In one of the boxes of junque donated to the ARRL Lab was a charger that fit the Lab's GPS. I took it home and plugged it in.

Not being on the air from home right now (being corrected!), I didn't notice the noise.  But I didn't correlate the use of the charger with one of my AFCI breakers tripping seemingly at random.   There was no symptoms of an arc, so swapped out the breaker.  No dice.  Finally, I decided to start unplugging various things on the circuit.  The first thing I unplugged was two wall-wart chargers.  Three days later, with no more tripping, it seems that I had found my problem.

I took the charger into the Lab and measured its conducted emissions per FCC standards.  The little bugger was making switch-mode-supply noise at 45.5 dB above the FCC limits, mostly below 2 MHz.  This one device was making as much noise as 35,000 legal devices.  It is a No-Name supply, so it's not actionable in any way, but this is now the 2nd such device I have found.

I have a box of about 100 such switching supplies and chargers. I am going to bring them all in and test them one at a time and put together a report that describes the level of noise from these devices found "in the wild."  This will make a great article for the IEEE EMC Society magazine, showing that devices out there are making some serious noise.

Now, we all know that noise levels go up at night on the lower bands. The increase vs time is generally gradual, so it sure appears that this is coming in by skywave.  Now, if this is from the aggregate of millions of legal devices, there is not much that can be done, but if it is from a much smaller number of strong noise sources, including an illegal device like this one, in the long run, it may be possible to document this and investigate what can be done with enforcement.

We had investigated one grow light that was 58 dB over the limits.  This one device was making as much noise as 650,000 legal devices.  It would only take a few of these in any given area to add up to the equivalent of millions of devices.

The discussions about obtaining a contour map of noise sources is really intriguing.  Maybe when I finally retire, I will take on the project and try to map an entire community. This may give us what to expect from legal devices and it may identify a few outliers.

Ed, W1RFI





________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of mstangelo at comcast.net <mstangelo at comcast.net>
Sent: Sunday, January 1, 2023 11:24 AM
To: RFI List <rfi at contesting.com>
Subject: Re: [RFI] Tip on approach to, or where to start looking for new noise source

Good advice. When you turn off breakers don't forget to turn off any battery backup devices during your investigation.

I had a nagging noise on 60 meters. I turned off all circuit breakers but still had the noise. I turned off the battery backup system I have in the shack and the noise disappeared. I turned on the power and disconnected each power supply connected to the battery backup and isolated the noise to a power supply to our wireless phone. I had to place a Fair Rite 31 toroid on the power cord near the power supply and one at the phone to eliminate the noise.

Mike N2MS


> On 01/01/2023 4:48 AM Hare, Ed, W1RFI <w1rfi at arrl.org> wrote:
>
>
> <But, first, exercise your breakers at home and if you can, run your receiver / transceiver on battery power so you can shut off the entire house to start your search.>
>
> I can't emphasize enough how important this is. Get a battery-operated receiver and connect it to your antenna. Then, flip off all of the breakers in your house.  If the noise goes away, it is you!  If so, turn the breakers back on, one at a time, and note any noise increase. Turn that breaker off (important!) and move on to the next breaker.
>
> Be on the lookout for devices that may have a backup battery, keeping them "on" when the breaker is off.
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