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Re: [RFI] Info needed

To: rfi@contesting.com
Subject: Re: [RFI] Info needed
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Wed, 17 Jul 2024 12:50:41 -0700
List-post: <mailto:rfi@contesting.com>
On 7/17/2024 12:16 PM, Dave (NK7Z) wrote:
If you are trying to suppress 14 MHz and lower I would use mix31, if above 14, mix43.
Fair-Rite #43 is NEVER a good choice below 30 MHz. Mix #31 is the only 
good choice for 160M through 10M, and slightly better than #43 for 6M.
Place about 7 to 10 wraps of cable on a ferrite.  Each pass through 
center counts as a turn...
Number of turns needed depends strongly on the core. For most #31 
clamp-ons, 2 turns is about right for 6M, 3 for 10M, 5 for 40-10M.
It is CRITICAL that turns are sequential around the center of the core. 
Out of sequence turns cancel. I ran into this with the year-plus of lab 
research that produced the latest (2018) Cookbook. It can be difficult 
to get 5 turns in sequence through a clamp-on and have them stay that 
way, although cable-ties can help. Depending on the o.d. of the cable 
and the i.d. of the core, even 4 turns can be difficult. There are a 
couple of photos showing this on page 22 of my latest update of my 
original RFI tutorial.
http://k9yc.com/RFI-Ham.pdf

73, Jim K9YC






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