[RFI] : Solar Panerl RFI / noise in sync with music

Sun Dec 25 18:32:36 EST 2022

The only way to test a solar system is on an OATS, although the chambers at GM in Detroit would probably be big enough.  The interference reports we are seeing are all on HF, unless we have a smattering of reports on VHF, and, from all indications of the system we were able to probe closely, the AC mains are not the primary radiating element on HF, so it is our belief that the system meets the FCC emissions limits.

In the long run, in response to changes in technology, I think that FCC will need to specify conducted limits for secondary wiring, too, but even if an NPRM were to come out tomorrow, 10 years would probably be a realistic time frame in which to expect a decision.

IMHO, we are better off gathering the industry to create a Recommended Practice that sets "voluntary" limits, defines good installation practices, provides an Annex to provide information for consumers and outlines appropriate complaint responses.  By my guess, building on (subtracting, actually) what was accomplished for the electric-utility industry, this could be in IEEE ballot within 3 years.
________________________________
From: David Eckhardt <davearea51a at gmail.com>
Sent: Sunday, December 25, 2022 6:11 PM
To: Hare, Ed, W1RFI <w1rfi at arrl.org>
Cc: Henry Pfizenmayer <pfizenmayer at q.com>; rfi at contesting.com <rfi at contesting.com>
Subject: Re: [RFI] : Solar Panerl RFI / noise in sync with music

Thanks for relating, Ed.  And you (et.al<http://et.al>) should wonder why I see a crying need to revisit limits, measurement philosophies, and even C63.4.  But it won't happen in my lifetime as I just turned 76 (pray for a flip of the magnetic poles of the earth????).

I've always tested to "as typically installed or used by the consumer".  We all know resistors are (ideally) non-reactive and convert electric energy to heat (and some infrared electromagnetic radiation, but that's for the safety guys).  Not so with speaker "antenna" wires.

And the real problem with solar power is how do you satisfy that requirement in a typical 10-meter Semi Anechoic Chamber?  With all the connecting wiring, it doesn't fit on the turntable.  Man, I still favor OATS in a nice quiet valley in the Rockies.  We used to have just such an installation, but the guy lost his accreditation due to not keeping up with the paperwork.

Dave - WØLEV

On Sun, Dec 25, 2022 at 9:14 PM Hare, Ed, W1RFI <w1rfi at arrl.org<mailto:w1rfi at arrl.org>> wrote:
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 at contesting.com<mailto:arrl.org at contesting.com>> on behalf of David Eckhardt <davearea51a at gmail.com<mailto:davearea51a at gmail.com>>
Sent: Sunday, December 25, 2022 3:22 PM
To: Henry Pfizenmayer <pfizenmayer at q.com<mailto:pfizenmayer at q.com>>
Cc: rfi at contesting.com<mailto:rfi at contesting.com> <rfi at contesting.com<mailto:rfi at 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 at contesting.com<mailto:rfi at 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 at rfiservices.com<mailto:mike at rfiservices.com>>
> To: "Dave (NK7Z)" <dave at nk7z.net<mailto:dave at nk7z.net>>
> Cc: Rfi List <rfi at contesting.com<mailto:rfi at contesting.com>>
> Subject: Re: [RFI] Another Solar Panel RFI System
> Message-ID:
> <CAPZkRSEvyTNyLcJT-3e1gNnkTP+WNX15DFXUXHpqf5YZa67YEw at mail.gmail.com<mailto:CAPZkRSEvyTNyLcJT-3e1gNnkTP%2BWNX15DFXUXHpqf5YZa67YEw at 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 at rfiservices.com<mailto:mike at rfiservices.com>
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*Dave - WØLEV*
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