[Amps] RF Chokes

[Angel Vilaseca]

Hello Richard

Thanks for your answer. I do not have a professional background in
electronics so from time to time I need to ask some questions that will
probably seem quite basic to many of this list readers. Please correct
me if you find errors in what follows.

>From what I understood reading the literature I could find, core
saturation is related to the current in the windings. Any
core can saturate, even at audio frequencies, even at DC, if you apply
enough
current and if you use few windings. Indeed, for a given signal power,
with increasing frequency, reactance would also increase hence current
in the windings would decrease and the core would go away from
saturation. 

So how could a core saturate *above* a given frequency?

On the other hand, if you use a core at too high a frequency, the core
will heat due to RF losses, not saturation. This is a different effect.
Unlike saturation, RF heating will increase with frequency and happen at
any power level, even very small. 


Now for the harmonics generation:
>From what I could understand from the handbooks, to produce harmonics, a
given device must have non-linear properties. You can use a class-c
biased transistor or tube or a diode for instance. 

How severe is harmonics generation in a ferrite? A ferrite core going
from saturated to non-saturated will obviously behave non-linearly and
generate harmonics. But the transition from linear to non-linear needs
to be sharp for an afficient harmonics generation. It is indeed very
sharp in a snap-varactor, for instance, but how sharp is it in a
ferrite?

I did not have much luck trying to find information about harmonics
generated by ferrite cores, searching  with Google or in the handbooks. 

As a bottom line, I would tend to think that the best protection against
ferrite-generated harmonics is to use as large a core as practical, with
low permeability, and with a lot of windings over it.

What do you think?


Regards

Angel Vilaseca HB9SLV

"R. Measures" wrote:

> >
> > If a ferrite core is used, could the ferrite saturate and generate
> > harmonics?
> 
> Yes.  Mu = 125 ferrite rod material begins to saturate at c. 13MHz, so
> it's a risky business.  Powdered-iron has the advantage of not
> saturating.
> >
> > How large sould the ferrite core be and which mu should it have?
> 
> For less than 13MHz, Mu = 125 is okay.
> >