yeah - the book by Snelling discusses all the variables.
The Fair-rite catalog also goes into the mfr process.
There's a reminder at the bottom of most of the pages that says "if you need
better, call us, and we can talk"
You can get better surface finish (less "flash" from the mold, for instance),
better size tolerances, etc.
But for the vast majority of applications - the designer just accounts for the
variability and moves on. That ferrite lump around the keyboard cable? If it's
off by 20% or even 50%, they'll still pass Part 15 and CISPR tests.
On Mon, 3 Nov 2025 18:50:06 -0700, David Gilbert <ab7echo@gmail.com> wrote:
Most of a lifetime ago I was a component engineer at Collins Radio, and
one of the products I was responsible for was a small ferrite core. The
manufacturer's rep explained the manufacturing process to me, which is
basically like making a ceramic mug, and likened it to baking a cake.
The process variables are many and significant, and even with automation
the end result varies a lot.
ChatGPT provided a summary of the potential process considerations:
https://chatgpt.com/share/69095b41-ed34-8001-83ba-6c412e5e473e
Dave AB7E
On 11/3/2025 4:40 PM, Jim Lux wrote:
> 20-25% is actually what Fair-rite gives as a tolerance for their cores (at
> least for the EMI suppression family) - Chip beads are 25%
> So if you've measured 20% variation, that's probably within spec.
>
>
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