Ed, when I bought my Microsoft Surface I, of course, had to run it by the
spectrum analyzers, probes, and antennas. The surface, itself, looked
excellent from "DC" to 1 GHz (I quit at 1 GHz as there wasn't above 500
MHz). Apple typically addresses RFI/EMC better than most (no, I'm not an
Apple man). However, plugging in the provided charger...... well......it
was terrible. It did not have the Apple name on it and I assume they
spec'ed and procured it from China, like most of the other wall warts these
days. So, the MS Surface got a clean bill of EMC/RFI. The charger did not!
On another job, we had to come up with a clean USB dedicated charger.
They're all switchers from China. We searched the lab and managed to
borrow/scrounge 7 of the little white boxes. Only one, yes, a single USB
charger, was relatively clean. It was from Apple.
Dave - WØLEV
On Mon, Jan 2, 2023 at 12:15 AM Hare, Ed, W1RFI <w1rfi@arrl.org> wrote:
> 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@contesting.com> on behalf of
> mstangelo@comcast.net <mstangelo@comcast.net>
> Sent: Sunday, January 1, 2023 11:24 AM
> To: RFI List <rfi@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@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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>
--
*Dave - WØLEV*
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