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[Towertalk] Common-Mode choke at 430 MHz.

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Subject: [Towertalk] Common-Mode choke at 430 MHz.
From: (Tom Rauch)
Date: Thu, 18 Jul 2002 18:58:19 -0400
> Finally, if you want to see if a balun is working, one simple crude
> test is to monitor the VSWR while running your hand around and along
> the feedline (outside the antennas immediate feed). Large changes in
> VSWR indicate poor balun decoupling. The simplest way to feed small
> Yagis is to bring the feed line from the driven element back behind
> the reflector and use rear mounting.

I've seen this done before. 

If you test for common mode isolation by moving you hand along a 
cable, most baluns would look very good. Even very poor baluns.

The only way to tell if a balun is working or not is to either 
measure feedline radiation, or to measure common mode feedline 

73, Tom W8JI 

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