The one i have experience was a Class D amp intended to be wall mounted and
connected to with bluetooth. A ham with a very sensitive setup was hearing it
1700 feet away. Yikes!
Now, here's the interesting story that I need to find time to document so I can
present it at a future IEEE EMC Symposium, or at least publish it as a
peer-reviewed article. It really points out a problem that could impact future
standardization.
So, I bought one of the Class D amps in question. I terminated its speaker
outputs in 15 ohms and I tested its conducted emissions in "standby" and
powered on. It measured about 10 dB below the Part 15 Class B limits. What the
actual heck is going on? There is no way the conducted emissions could be
heard that far away, so I explored farther. I connected a signal generator to
it and cranked it up. Conducted emissions increased slightly, but not to the
point where I believed this to be the radiated problem.
So, I assumed that the speaker leads were the radiators, so I took off the
8-ohm resistors and put them at the end of 16-foot speaker wires, zip type,
untwisted, to be a reasonable worst case. I brought out the EMCO loop antenna
and put it about 10 meters away. (Yes, this was in the Lab, so scatterers
galore, but I was looking for gross problems. Yup, it was loud. So I then put
an L/C filter in the speaker lead and a ferrrite choke. It was STILL pretty
loud. I then happened to look at the conducted emissions. The CONDUCTED
emissions were about 20 dB or more higher.
It turns out that the coupling from the common-mode currents put on the speaker
leads to nearby conductors unbalanced the conducted emissions, creating a
substantial common-mode current that changed conducted emissions. So, when
tested in a Lab with 8-ohm resistive terminations on the speaker lead, the unit
"passed," but when used in its normal fashion, with real speakers, it did not.
I had remembered years back we were testing an LED bulb that just passed Part
15B, when I went to unscrew it, the conducted emissions rose quite a bit.
Well, I knew that there is no way FCC would consider that to be actionable, so
I forgot about it and did the rest of my tests. But the incident with the
Class D amp piqued my curiousity, so i got out some spotlight LED bulbs that
were near the limit and tested them again. Sure enough, putting my hand near
them caused conducted emissions to rise. Interesting, but still not actionable.
My test fixture was a simple ceramic socket, placed in a C63.4 compliant room.
I then purchased on of the "cans" that most spotlight bulbs are installed in,
and grounded it to the room ground plane. The conducted emissions increased by
8 dB simply by using the bulb in a way that it is very likely to be used. To
me, this speaks loudly to the need to make revisions to the test standards,
which simply measure the bulb pretty much the way I did.
There is plenty of work to keep me busy for the rest of my life! 🙂
Ed Hare, W1RFI
ARRL Lab
________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org@contesting.com> on behalf of David
Eckhardt <davearea51a@gmail.com>
Sent: Sunday, December 25, 2022 3:22 PM
To: Henry Pfizenmayer <pfizenmayer@q.com>
Cc: rfi@contesting.com <rfi@contesting.com>
Subject: Re: [RFI] : Solar Panerl RFI / noise in sync with music
It likely was a Class-E amp (or worse). They can be dirty as $%^& when
stressed (by the strong bass notes).
I once tested a Class-E home automation system with all kinds of Class-E
amps (for intercoms and distribution of music from a number of sources).
It was the ONLY product in 35+ years we had to install an 20 dB attenuator
in series with the input to the R&S conducted emissions receiver!
Dave - WØLEV
On Sun, Dec 25, 2022 at 8:09 PM Henry Pfizenmayer via RFI <
rfi@contesting.com> wrote:
> Mike et al ---If that was not tongue in cheek as they say -- this last
> summer I started getting thumps of
>
> noise on 6 meters -and was far worse at 25 mhz -- Then I noticed it was
> in sync with neighbors outside
>
> speakers thumping out a strong bass line. I went out with my IcomR10 rx
> and loop -
> and yep that was the source. The amp was obviously going into oscillation
> in sync with the loud bass notes .
> No use talking to that guy - so I just prayed the damn amp would fry
> itself . Prayers were answered
>
> in just a hour or so and noise never re-appeared.
>
>
>
> 73 Hank K7HP
>
>
>
>
>
>
>
>
>
> Message: 1
> Date: Sun, 25 Dec 2022 11:51:20 -0500
> From: Michael Martin <mike@rfiservices.com>
> To: "Dave (NK7Z)" <dave@nk7z.net>
> Cc: Rfi List <rfi@contesting.com>
> Subject: Re: [RFI] Another Solar Panel RFI System
> Message-ID:
> <CAPZkRSEvyTNyLcJT-3e1gNnkTP+WNX15DFXUXHpqf5YZa67YEw@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> I'm trying to capture a noise with the intermittency rhythm in sync with
> Christmas music
>
> Michael Martin
> RFI Services
> 51 W Bay Front Rd
> Lothian, MD 20711
>
> 240-508-3760
> mike@rfiservices.com
> [http://www.rfiservices.com<]www.rfiservices.com<
> https://webmail.centurylink.net/app/www.rfiservices.com>
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
--
*Dave - WØLEV*
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