[TowerTalk] ferrites for antenna tuners?

Tom Rauch w8ji at contesting.com
Thu Nov 10 06:50:43 EST 2005

> Turns uH
> 1       .11
> 2       .22
> 3       .39
> 4       .59
> 7       1.25
> 11      2.5
> 17      5.0
> 25      10
> Note well that the uH doesn't track the number of turns
squared... (which
> it should...).

The "number of turns squared" only applies when there is
negligible capacitance distributed throughout and across the
winding and the flux leakage is zero.

You'll find for example with a -2 core there is so much flux
leakage that you can vary inductance over a 2:1 range just
by spreading or squeezing turns.

> Is there any one mix that will work for this (we ARE
talking about more
> than a 10:1 frequency range)

Easily a -2 mix will work over HF with good Q. Many other
cores will also. Much of the reason core materials are
changed with frequency is to optimize winding turns
requirements. No one wants to use a core that requires only
two turns or a core needing 50 turns.

The biggest problem in a stepped component autotuner is the
component switching, not the L/C components themselves.

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