[TowerTalk] Subject: Re: Managing Balanced line transitions
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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