[RFI] Earth isolation

[Ian White, G3SEK]

Tom Rauch wrote:
>
>I think I know what you meant, but I'm not sure I agree with that 
>picture. RF that is accidentally picked up doesn't need to flow 
>anywhere. It isn't a bucket of something we have to pour out somewhere.
>
Sorry, Tom, but it is precisely that!  Kirchhoff's Law applies 
rigorously inside the shack: whatever RF current comes in, must have 
some path out again. If it didn't have, it wouldn't come in.

(There are some exceptions, particularly on the higher bands where 
wiring lengths inside the shack are a significant fraction of a 
wavelength; but they don't overturn the basic principle. Particularly on 
the low bands, I've measured a good balance between incoming and 
outgoing currents.)

I do agree that feedline chokes are needed on almost all antennas, and 
they should always be the first thing you try. But they may only be part 
of the solution.

In some situations (which may not apply to you personally, Tom, but they 
do apply to some others) it may be necessary to choke both the entry 
path *and* the exit path to get a complete solution.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek