[TowerTalk] Coax, conduit and toroids
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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