Hi Jim,
Yes, always fun when I work you during a contest even though it was not on
160 meters this time around:)
I actually always carry with me a power cord with a FT240-31 wound with 14
turns as well as a commercial dual stage differential mode filter. I
always test one and then the other as well as both in series to figure out
what works best. I also carry naked cores. We did not have time to run
these tests when we found the source but that’s exactly what our plan is
and I’m currently winding a common mode choke using just a two conductor
power cord versus the 3 conductor one I carry because the mini fridge uses
a 2 conductor cord. I’m also packaging a commercial single stage
differential mode filter so it’s plug and play for our tests (and if it
works it’s lower cost than the dual stage one). Plan to run these filter
tests with the mini fridge homeowner within the next week using the various
filters I have. I’m often most successful with both types of filters in
series but I’m typically working with a 3 conductor power cord which
helps. I definitely prefer just the common mode choke if I can get away
with it for numerous reasons.
73,
Don wd8dsb
On Tue, Jan 14, 2025 at 12:09 AM Jim Brown <jim@audiosystemsgroup.com>
wrote:
> http://k9yc.com/RFI-Ham.pdf
> Bad fingers!
>
> 73, Jim K9YC
>
>
> On 1/13/2025 11:16 AM, Jim Brown wrote:
> > On 1/13/2025 9:16 AM, Don Kirk wrote:
> >
> >> Next step will be to try various filters that I have on the power cord
> to
> >> see if we can eliminate the RFI. Note: The fridge plugs directly into a
> >> 120 Vac outlet (no external power supply) and it uses a 2 prong plug.
> It
> >> also has a power jack if you want to power it with a 12 Vdc 3 amp power
> >> supply.
> > Hi Don. Thanks for the NAQP QSO.
> >
> > The unit is feeding common mode RF current to the power system in that
> > home, which is acting as an end-fed long wire. The first thing I would
> > try is to wind the power cord through a #31 Fair-Rite 2.4-in toroid
> > following the recommendations in my 2018 Cookbook for the transmitting
> > chokes. Alternatively, wind as many turns as you can through a 1-in i.d
> > #31 clamp-on, WITH THE TURNS BEING IN ORDER AROUND IT! See Fig 28b and
> > 28c in RFI-Ham.pdf@kyyc.com If the power cord isn't long enough, or is
> > too big, add a choke into a short section of power cable. Wind that
> > choke with as many turns as you can in a single layer of #18 zip cord.
> > This choke is for maximum effectiveness on the lower bands.
> >
> > Traditional power line filters are unlikely to do much, because they
> > need access to the chassis of the source for their differential mode
> > networks to work.
> >
> > 73, Jim K9YC
> >
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> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
>
>
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