Hi Rich,
> With an air core, a 90uH choke resonates in the neighborhood of 20MHz.
>Ferrite cores have a well-deserved reputation for saturating in actual
use. .
The winding used, in the cited example, calculates to be approx.12uH
without the ferrite core. This gives an effective permeability of about
7½ for the core, and while the article did not state a material
permeability, it was likely greater than 100. Thus, the core is
intercepting relatively little of the magnetic field compared to a tight
winding. Additionally, rod cores with their open magnetic structure are
very difficult to saturate compared to a toroid or other closed loop
form.
Since relatively little RF current flows through this coil, if things
are working correctly, the DC component probably creates more flux.
>The Collins antenna tuner used in the B-52 had a roller coil with a
>ferrite core at one end of the coil. . The core only came into play
at
>low frequencies. I have never heard of a ferrite core being
successfully
>used in a hv rfc.
A tuned circuit is a much more demanding application... probably
requiring something in the neighborhood of 100x the power handling
capability.
Phil gave two examples of ferrite core chokes of this type in his
reply.
73,
Marv WC6W
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