[TowerTalk] Choking on chokes

[Earl Morse]

Yeah, matched was a bad choice of words.  I wasn't speaking totally of impedance.  Hooking up a balanced dipole to an unbalanced coaxial transmission line isn't really matched and begs the dividing of the shield coaxial current into the current on the inside and outside of the coax.  Adding the CM choke inserts the impedance on the coaxial shield that reduces that Icm component on the outside of the coaxial shield.  Pretty much means that you'll have to do something if you are going to feed a balanced antenna with an unbalanced feedline in order to reduce the CM current on the outer coaxial shield.

Choking on chokes was a good title for this topic.

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The level of CM current on a transmission line is *not* directly related 
to how well it is matched. You can have a badly mismatched line with no 
CM current, and you can have a perfectly-matched line with lots of CM 
current.

If what you say is true, you would not need a CM choke when feeding a 50 
Ohm balanced antenna with 50 Ohm coax.

Steve G3TXQ