[Elecraft] Bad Ham Radio Day

[John Oppenheimer]

I've found preferred method for evaluating Ferrite Choke Balun common
mode rejection performance is to measure common mode rejection (CMR).

Some various 43 material examples, which demonstrate CMR is a function
of device inductance.
https://www.kn5l.net/Balun-CM/Balun-43material/

FT140-43 7T CMR measured using four different methods to ensure
correlation and correct CMR measurement process. Also demonstrate
correlation with SimSmith model using Fair-Rite Complex permeability file.
https://www.kn5l.net/Balun-CM/FT140/

Comparing 31 and 43 material which demonstrate, for a given inductance,
43 material results with improved CMR. With equal turns, 31 material has
small CMR improvement.
https://www.kn5l.net/Balun-CM/Balun31-43/

John KN5L

On 9/4/21 9:14 PM, Jim Brown wrote:
> On 9/4/2021 2:48 PM, jerry wrote:
>> 31-mix is supposed to be the hot ticket for HF common mode
>> chokes.  One turn through one core is supposed to be 98 ohms at 5MHz. So 
>> four cores should give me about 400 ohms, which should give a worthwhile 
>> attenuation in a 50 ohm system.  Thanks for the references.
> 
> I'm the guy that did the original work on this, beginning in 2003, when 
> #31 was a brand new mix. I got five of the first #31 toroids from the 
> pre-production run, a few months after I suggested that they would be 
> quite useful. My first publication was a paper to a 2005 international 
> meeting of the Audio Engineering Society, of which I'm a Fellow. First 
> publication to the ham world was RFI-Ham.pdf in 2007. And you are 
> mistaken about the value of four cores at HF. Study that paper. It's a 
> tutorial on how RFI happens and how chokes work.
> 
> 73, Jim K9YC