[Elecraft] Re: RF Coupleing

[Vic K2VCO]

Don Wilhelm wrote:
> Vic,
> 
> The K3 uses only a single wire to connect to the SO-239 jacks.  The 
> return path is through the chassis metal.  If one adds a direct return 
> path from the SO-239, that eliminates the potential for a haphazard path 
> for the return current.  While a chassis return may be good enough in 
> one situation, let's suppose that the builder did not tighten the SO-239 
> mounting screws adequately, or the mounting hardware has begun to 
> oxidize, then the return path becomes more 'iffy'.  Attaching a return 
> wire from a lug on the SO-239 to the board ground provides a fixed 
> return path that is not dependent on the chassis.  Note that the return 
> currents for the two antenna connections can possibly interfere with 
> each other if there is any small voltage differential on the chassis 
> (there always is a differential, the question is just how small a 
> differential is tolerable).

That's certainly part of the problem. But just adding a ground wire 
might create a ground loop. I guess the best way to do it would be to 
insulate the SO239's from the chassis, and use hoods on them with coax!
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco