[RFI] RFI on 160 meters at WD8DSB from Hi-Fi Amp or its power supply 0.27 miles away.

[David Eckhardt]

Several years ago as an EMC engineer, I had an assembly of home automation
equipment I had to test for regulatory purposes - FCC.  It contained many
audio amplifiers which were Class-D and Class-E for distribution throughout
any installation.  It was the ONLY product in my some 30+ years as an
EMC/RFI engineer we had to install a 35 dB, yes, you read correctly, 35 dB
attenuator (!!!) between the product connection to the AC power (LISN) and
the conducted emission receiver.  Fortunately, R&S had built in a crowbar
for exceptionally high signals which saved the expensive receiver from
damage.  The owner of the lab had never seen anything that 'dirty', either.

Dave - WØLEV

On Mon, Apr 11, 2022 at 12:40 PM Don Kirk <wd8dsb at gmail.com> wrote:

> Hi Jim (K9YC),
>
> I suspect you're absolutely right about it being a class D type amp based
> on its size, weight, and power output rating.
>
> Yesterday I dropped off brownies at both homes I worked with on this case
> which is my normal modus operandi.  Not sure if and when the homeowner with
> the RFI generating system will get back with me for in depth
> troubleshooting as she appeared to have a lot going on in her life and
> definitely not concerned about using this system ever again as she
> mentioned they have lots of other ways to listen to music.
>
> Thanks, and 73.
> Don (wd8dsb)
>
>
> On Fri, Apr 8, 2022 at 11:04 PM Jim Brown <jim at audiosystemsgroup.com>
> wrote:
>
> > On 4/8/2022 5:51 PM, Don Kirk wrote:
> > > Turns out the RFI was from a Hi-Fi Digital Amplifier MN180BT or its
> > > power supply located 0.27 miles from my house.
> >
> > The clue may be "Digital Power Amp," meaning not an analog output stage,
> > but a digital one, known in that world as "Class D." In which case the
> > output stage is not properly low-pass filtered differentially, and the
> > antenna would include speaker wiring. If you can chase down a mfr, that
> > might help.
> >
> > Some fixes if it's differential -- replace speaker wiring with twisted
> > pair. If they're audiophiles, use #12 twisted (homebrew by twisting with
> > a drill motor with the other end in a bench vise). Twist it more than
> > you need, let it sit at least overnight before releasing. It will
> > untwist a bit, but that won't matter.
> >
> > For common mode, of course, the usual turns of #31.
> >
> > Let us know what you learn at what works.
> >
> > 73, Jim K9YC
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> >
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-- 
*Dave - WØLEV*
*Just Let Darwin Work*