Topband: Core for K9AY loop transformer

Tom Rauch w8ji at
Wed Mar 28 13:06:36 EST 2007

> For a common mode suppressor, you simply want enough 
> inductive reactance to
> impede current flow. The type of core does not matter --  
> air, low mu or hi
> mu materials -- as long as the result is at least a few 
> hundred ohms
> reactance. 10 turns through 43 material is roughly 1000 
> ohms at 160M, which
> should work well.

....unless the common mode impedance is capacitive, which it 
can be. In that case the choke will increase common mode 
problems. Also the impedance depends on the core hole length 
where the wire passes through more than any other dimension. 
It's a nearly linear progression with core depth, so a 1" 
deep hole has twice the impedance of a 1/2" deep hole for a 
given core material.

Suppression devices should normally be mostly resistive 
unless the impedance is controlled. Adding a resistance will 
always improve things. Adding an inductance might make 
things worse.

73 Tom

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