Hi, Everybody,

In the process of modeling a vertical antenna (specifically, I am using
EZNEC 5.0) I am noticing an effect I did not expect which could be the
result of a modeling error on my part.

The antenna is a 34-foot vertical above (12) 34-foot radials, making it a
1/4 wave on 40 and a 1/2 wave on 20.

On 40, the antenna works as I expected; as the ground conductivity goes up,
the gain and efficiency of the antenna both increase, too.

But on 20, if I increase the ground conductivity from, say, 0.005 to 0.008
S/m, the max gain and efficiency *decrease*! This is counter-intuitive to
me.

Can anyone point to something I'm doing wrong?

Thanks,

Al W6LX