[TowerTalk] Subject: Re: Managing Balanced line transitions

Jim Brown jim at audiosystemsgroup.com
Mon Feb 5 10:08:32 EST 2007

On Mon, 05 Feb 2007 08:16:44 -0600, Cecil Moore wrote:

> A husky 1:1
>choke with a few thousand ohms of choking impedance works well to
>reduce the common-mode current. If the choke is placed at a balanced
>to unbalanced junction, it is also functioning as an elementary balun.

There are some serious misconceptions here. 

Transformer baluns and choke baluns are fundamentally different. A 
transformer balun MUST have low loss (all the transmitter power goes 
through the core, so loss converts it to heat), while a choke balun works 
far better if it has a lot of loss -- only the common mode current excites 
the core, and a high value of (resistance) loss is better if it reduces the 
common mode current to a very small value.  

A transformer balun makes a poor choke balun, and a choke balun makes a 
lousy transformer balun.  

You may find the material on baluns in my RFI tutorial helpful. 



Jim Brown K9YC

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