[TowerTalk] Coax, conduit and toroids

Jim Brown jim at audiosystemsgroup.com
Wed Jun 27 11:20:59 PDT 2012

On 6/27/2012 9:59 AM, Steve Hunt wrote:
> Jim's comment should not be misunderstood. A 1:1 choke balun feeding a
> _perfectly_  balanced load does not have zero common-mode voltage across
> it; the choke CM voltage will be exactly half the voltage across the load.

This is incorrect.  First, it is a CHOKE, not a "balun."  Second, if the 
CIRCUIT is balanced, the common mode voltage and the common mode 
current, by definition, will be zero.  Third, both the differential 
circuit and the common mode circuit are complex -- they include the 
antenna, the feedline, and the termination of the feedline at the 
transmitter.  The contribution of the feedline is also exquisitely 
dependent on its length AS A COMMON MODE ELEMENT, especially if it is coax.

73, Jim K9YC

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