Hi Mike,
Study k9yc.com/RFI-Ham.pdf
Ferite chokes work primarily by self-resonance, and a single turn
through these cores has a broad resonance near 2M. Winding turns lowers
the resonance to lower bands. Most small cores you're likely to find are
similar to #43, because they're designed to get equipment past FCC Rules.
If all of the radiation is from the wire you clamped, adding more cores
will help. But if that last 10 dB is coming from something else (like
from within the box itself or another wire), you'll need to work on that.
73, Jim K9YC
On 11/17/2021 1:10 PM, nlsa@nlsa.com wrote:
Dear Jim,
I just installed some clip-ons (unknown ferrite mix) and they reduced the
radiated emission by 30dB. I think that the last 10dB will take some more
work.
I'm curious what you mean by, "... without a second turn on wiring connected
to the source."
73,
Mike, W9IP
-----Original Message-----
From: RFI <rfi-bounces+nlsa=nlsa.com@contesting.com> On Behalf Of Jim Brown
Sent: Wednesday, November 17, 2021 2:59 PM
To: rfi@contesting.com
Subject: Re: [RFI] RFI from geothermal furnace cathodic protection circuit
RFI at 2M is a good candidate for #43 or #31 clamp-ons without a second turn
on wiring connected to the source. You may need more than one.
Multiple turns through #31 will be required for suppression at HF.
73, Jim K9YC
On 11/17/2021 6:05 AM, nlsa@nlsa.com wrote:
Dear friends,
I am seeing RFI on 2m from the cathodic protection circuit in our
geothermal heating system. The protective circuit's on-board SMPS
generates a large broad emission around 150 MHz, verified with a
spectrum analyzer and sniffer. Before I dive in with the usual
filters and toroids, does anyone on the list have experience and
suggestions?
Thank you,
Michael Owen
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