Jim, 160m through 10m. 20 m generates biggest induced signal whivh I
surmised is from the t-stat wire being ~1/4 wavelength.
73, Dan
On Wed, Jan 7, 2026, 1:16 AM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 1/6/2026 6:39 PM, Dave (NK7Z) wrote:
> > If it were me, and I had that problem, I'd get some FT-240-31 ferrite
> > cores from Arrow, or one of the parts houses. I have some of core part
> > numbers, and where to find them at web site:
> >
> > https://www.nk7z.net/rfi-now-house-cleaning/
> >
> > The ferrite part numbers are listed there, about half way down the page,
> > with links to the manufactures site.
>
> Hi Dan,
>
> You didn't say what bands were a problem, but yes, some of the wiring
> connected to the electronics controlling the furnace is functioning as a
> long wire receiving antenna, and the solution is multiple turns through
> a #31 Fair-Rite core. I try to solve problems like this with clamp-on
> cores just large enough to wind 4-5 turns through them, ideally without
> breaking existing wiring. I don't see the need go inside any of the
> hardware, but you do want the choke (the windings on the ferrite) as
> close as possible to the victim.
>
> I keep three sizes of clamp-ons in my stash for this use. 1/2-in,
> 3/4-in, and 1-in i.d. The same cores are useful for killing noise
> generated by the dozens of switch-mode power supplies that are in all of
> our homes, so I suggest that you buy a bunch of the two smaller sizes,
> at least enough to get the first price break and to get you free shipping.
>
> There's tutorial material on my website about how to look for noise in
> our homes and in the homes of our neighbors (if they will let us). And I
> also like Arrow as a source.
>
> 73, Jim K9YC
>
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