Many (many) years ago I was a component engineer at Collins Radio with
responsibility for passive components, including ferrite cores. I was
told by the core vendor that fabricating them was best likened to baking
bread ... with all the potential variability that entailed.
73,
Dave AB7E
On 10/30/2019 8:46 PM, Richard (Rick) Karlquist wrote:
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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