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

[Don Kirk]

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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