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Re: [TowerTalk] Ferrites 31 vs. 77 material

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 29 Oct 2019 22:39:34 -0700
List-post: <mailto:towertalk@contesting.com>
On 10/27/2019 1:31 PM, David Gilbert wrote:
I'm sure K9YC, who knows at least 20 dB more on the subject that I do, will have a more thorough explanation but basically the reason is that Type 31 material has desirable loss at HF frequencies instead of only contributing inductance.  When relying only on inductance for common mode chokes you can get undesirable resonances that actually subvert the purpose of using them, whereas the loss in the Type 31 material gives you the low Q performance you want and it does so across a wide frequency range.
Yes. Common mode chokes work by forming low Q parallel resonances in the 
common mode circuit by winding multiple turns around a suitable 
material. #31 is the only suitable material for transmitting chokes at 
HF. 77 is not, and #43 is not. See http://k9yc.com/2018Cookbook.pdf and 
study k9yc.com/RFI-Ham.pdf for more discussion of the the theoretical 
concepts.
73, Jim K9YC
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