[RFI] Earth isolation

[Jim Brown]

On Wed, 8 Sep 2004 22:39:22 +0100, Ian White, G3SEK wrote:

>The cure was to place an RF block in the shack mains 
>feed, using a three-wire filter which includes a ground-line choke. 

What you really did was reduce the current flowing in those unintential antennas by adding 
impedance to the return path. That was a band-aid made necessary by the pin 1 problems 
in the gear. The more fundamental fix would have been to prevent those currents from 
flowing into the gear by fixing the pin 1 problems.  

Also, it is NOT a good or safe technique to place high impedances in ground leads. 
Lightning wants to see a low impedance path to earth. The peak energy of lightning is 
around 1 MHz, and it is a very broad peak (that is, lots of energy both above and below 1 
MHz). When you place a choke in the ground lead, you essentially throw away any lightning 
protection by defeating the required bond between safety grounds. Not a good thing. 
Mother nature has a way of reminding us that such techniques are not a good idea. 


Jim Brown  K9YC