[TowerTalk] Ladderline - what are the facts??/

[Jim Brown]

On Tue, 21 Apr 2009 00:14:50 -0500, chas wrote:

>WHERE are the facts about ladderline??

Ladderline does not radiate differential mode current (the power it 
carries from the transmitter to the antenna). Ladderline DOES 
radiate COMMON MODE current. So does coax. 

Common mode current is the result of imperfect balance at either end 
of the feedline. Nearly all practical ham antennas are unbalanced by 
their surroundings. Common mode current causes radiation, and 
antenna imbalance causes common mode receive current.

An important difference between coax and ladder line is that coax 
can be CHOKED to kill common mode current, but ladder line cannot. 
To understand why, study 

http://audiosystemsgroup.com/RFI-Ham.pdf

and also the Power Point on Coaxial Chokes at 

http://audiosystemsgroup.com/publish

73,

Jim Brown K9YC