[TowerTalk] common mode chokes, baluns and multiband, doublets

[Jim Brown]

The inductance of a coil of coax is in series with the rest of the 
transmission line, and if that line looks capacitive (by virtue of its 
length), the coil of coax DOES NOT WORK to provide isolation. Indeed, it 
increases common mode current on the line rather than reducing it.

Effective common mode chokes work as a result of a high value of 
RESISTANCE that is inductively coupled from a lossy ferrite core. 
Resistance cannot be cancelled, so it always reduces the common mode 
current. You can find a thorough discussion of these principles in 
k9yc.com/RFI-Ham.pdf  and in the ARRL Handbook.

73, Jim K9YC

On 12/12/2017 10:02 AM, Chuck Gooden wrote:
> A coil of wire is an inductor with an air core and the principle of of 
> a inductor will still apply.  However an air core inductor will not be 
> as efficient as an inductor with a core depending on the mu of the 
> material used.