[TowerTalk] Fields and coax

[Jim Brown]

On Sun, 24 Jul 2005 16:36:15 +0100 (BST), Roger Parsons wrote:

>there is always an external field even with perfectly shielded
>coaxial cable. 

What do you mean by "perfect?" Perfect means that there would be no 
external field, perfect uniformity of shield current around the 
circumference of the shield, no "holes" in the shield, and implies a 
solid shield like hardline. 

It is also well known that, thanks to skin effect, at radio 
frequencies, SIGNAL current tends to flow on the inside of a coaxial 
shield, and NOISE current (that is, current due to external 
excitation) tends to flow on the outside of the shield. 


Jim Brown  K9YC