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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