[TowerTalk] Baluns! Ack!

[Jim Brown]

On Tue, 08 Nov 2005 11:07:13 -0900, Justin Burket wrote:

>My question is; with such a high permeability can I make any use of 
>these for a balun?  I'm constantly coming across a need for one and I 
>would love to make use of these toroids instead of having them sitting 
>around in my desk drawer.

Permeability for a ferrite is not a single number, it varies with 
frequency. AND, it is a complex number -- that is, there is a real part 
that describes the inductive component of its series equivalent circuit, 
and there is an imaginary part that defines the resistive (loss) component 
of the series equivalent circuit. To know whether (or how well) these 
things will work as a balun, you need to know what those values are at the 
transmitting frequency. 

The fact that these parts came from a DC-DC converter suggests that they 
are a material that has low loss at LOW frequencies, but not at the higher 
frequencies where you will be transmitting. Loss will cause them to 
overheat when you transmit. One toroidal cores that makes a good 
transmitting balun is made from a ferrite material like Fair-Rite #61, that 
has very low loss in most of the HF spectrum. 

>I have to admit I'm a bit confused about the theory of baluns and 
>searching around the net left me even more confused..

The ARRL website has many good references. If you are a member, you can 
access them at no charge. There are also two applications notes in the 
publications section of my website. They don't address baluns, but they do 
explain ferrites. 

http://audiosystemsgroup.com/publish.htm

73,

Jim Brown  K9YC