If the coax in the shack sees a low impedance path to ground, and it is
an odd multiple of a quarter-wave up to the feedpoint, very little CM
current flows; and for any that does flow the shack end is at a voltage
*minimum* of the CM standing wave. It's very clear if you look at the
current distributions in a model.
Of course, if the shack is on a second floor all bets are off - the coax
may well not see a low impedance path to ground.
On 21/04/2012 14:09, Joe Subich, W4TV wrote:
> I would disagree with you there. Coax lengths that are an odd multiple
> of a quarter wave are the worst lengths for common mode problems in the
> shack as they place the shack at a voltage maximum. Proper grounding
> will help but with so many shacks on the second floor or the opposite
> end of the structure from the power (utility) entrance, obtaining
> proper grounds is uncertain at best.
> ... Joe, W4TV
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