Rick and Tom (W8JI),
thanks for the great information!
In NEC I have not been able to create a symmetrical radial field in which the
impedance rises with additional radials. The radial lengths explored varied
from 45 to 180 degrees. However, I have seen the input impedance increase with
some unsymmetrical radial installations - like the ones we hams must use
around our houses. In fact, the N30X radial field does this. And this is the
very
radial field for which I recommended the "decreasing input impedance method" of
evaluation! N30X and I wondered about these results. I though originally that
it was due to the system current maxima occurring along the ground system,
rather than at the feedpoint, but this is not the case
So, I stand corrected on being too loose with the method. I should have
pointed out the limitation of the "decreasing input impedance method." And that
limitation is that the radials must be symmetrical and all of the same length.
Now it sounds like even this is not the case with actual measurements. Have
you measured increasing input impedance for additional radials in a symmetrical
arrangement? If so, I would like to understand this. Understanding and
getting sims to match measurements (and vise versa) is what I do.
I have NEC-4 on the way and I hope that this will help with this. I so take
the NEC-2 radials simulations with a grain of salt. I have a work-around for
some limited cases. Using NEC-4 I hope to greatly refine these work-arounds so
that those with NEC-2 can obtain useful simulations of ground mounted verticals.
This debate is just the thing to educate the members (most of all myself) of
the reflector and dispell some myths and rules-of-thumb.
Dave WX7G
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