[TenTec] Ferrite Data

[Dr. Gerald N. Johnson]

On Mon, 2008-06-09 at 23:58 -0700, Jim Brown K9YC wrote:
> On Mon, 09 Jun 2008 17:18:42 -0600, Dr. Gerald N. Johnson wrote:
> 
> >Typical materials good up to 30 MHz in
> >ferrite have a permeability of 50 though those with permeability of  125
> >are good cores at 20 MHz and down, if you want reactance. If you want
> >loss you want a much higher permeability.
> 
> It defies logic to speak of materials as having a single-valued 
> permeability. Permeability of ferrite materials is neither a real number 
> nor constant with frequency.

True, but there are permeability classes or groups (typical of a
material at some convenient flux for simple measuring) and those with
initial permeability ratings of 50 and 125 tend to be good for HF
transformers with low loss.

> Fair-Rite publishes graphs of the complex 
> permeability, which is another way of stating the loss component. If you 
> don't understand the variation of u' and u'' with frequency, you don't 
> understand the material. nor do you understand how to use it. 

I understand all those things, yet when applying ferrite cores for power
we found at Collins that we needed more data which we had to develop
experimentally, by applying RF power to a winding to see if the core
heating was acceptable or could be adequately cooled whether it took
simple oil immersion, or power circulated oil, or spaced cores with heat
sinking between the cores to get the heat to the oil better. All that
was very critical at the 50 KW power level and many a core was cooked
making that Collins balun work.

Yes the Amidon data is simplistic, yet it can be compared to Fair-rite
data and there are 200 ham applications of Amidon ferrites to each
published Fair-rite application. Maybe more. I don't recall seeing any
publications calling for Fair-Rite parts.
> 
> 73,
> 
> Jim Brown K9YC
> 
73, Jerry, K0CQ