[TowerTalk] Ferrites 31 vs. 77 material

[Richard (Rick) Karlquist]

To expand on what Jim said:

I was once trying to design a conducted power line EMI
filter that had to have a lot of attenuation at one
frequency around 100 kHz, and the power level was several
kW.  I needed a rather huge expensive choke which was
problematical.  I got the bright? idea that I could
resonate the choke at 100 kHz with a capacitor.  I went
into the lab and breadboarded the filter and it worked
beautifully with a fairly small common mode choke.

Fast forward:  all known vendors of chokes had extremely
loose tolerances on inductance, like +/25% or even +/-50%.
The vendors blamed this on the core manufacturers, and
I confirmed that none of them made closely specified cores,
and on top of that, the tempco was high, so I couldn't
even hand tune them by picking the cap values.

I ended up using two large expensive chokes that I could
barely shoehorn into the allotted area.

Rick N6RK

On 10/30/2019 10:51 AM, Jim Brown wrote:
> On 10/30/2019 6:43 AM, Roger Parsons via TowerTalk wrote:
>> K9YC wrote:
>>
>> "Yes, but virtually all of the recommendations for #43 and #52 
>> material are WRONG!"
>>
>> Steve is sadly no longer with us and unable to defend himself. 
>> However, he had previously rigorously defended his methodology. He was 
>> very technically able in both theoretical and practical matters, and I 
>> personally trust his results.
> 
> There is nothing wrong with his methodology nor his measurements. The 
> thing he missed, and that I also missed until recently, is the effect of 
> component tolerances. About a year ago, I bought 40 of the #52 Fair-Rite 
> cores, split into four orders over about a month from four Fair-Rite 
> distributors measured the characteristics of each, and put the data in a 
> spreadsheet. I then selected cores at the limits of Rs and Xs and wound 
> chokes following Steve's guidelines. None of those chokes were even 
> close to his published data.
> 
> My methodology is discussed in detail in
> http://k9yc.com/2018Cookbook.pdf
> 
> 73, Jim K9YC
> 
> 
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