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Re: [RFI] SO2R 2nd Harmonic Interference

To: rfi@contesting.com
Subject: Re: [RFI] SO2R 2nd Harmonic Interference
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sat, 29 Sep 2018 16:13:52 -0700
List-post: <mailto:rfi@contesting.com>
On 9/29/2018 1:52 PM, Randall K Martin wrote:
I tried wrapping the 12V leads of the current charger roughly 10 x through a large toroid and there was little if any reduction in interference.

Several thoughts. Since you feel a replacement supply is a problem, here are some more ideas. Remember that the power line is also a great transmitting antenna, so try plugging the unit in to a small extension cord and apply the choke (turns on the toroid) to that cord.

Also, how many turns you need will depend on what the toroid is -- what mix, how big. A ferrite choke is a parallel resonant circuit, which is tuned by varying the number of turns. The resonance will also depend strongly on which mix is used. #43 needs a lot more turns than #31, #61 is next to useless for this. Thicker, longer cores need fewer turns than toroids. If you use too many turns, the resonance can be too low.

73, Jim


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