Topband: 1/4 versus 1/2 wave vert.

[Tom Rauch]

> Again, the EZNEC results are probably not very accurate on
an absolute
> basis but as a comparison they may be more valid.  If so,
they don't
> suggest that it is worth the extra hassle of hanging twice
the wire from
> the sky unless adequate radials for a quarter-wave
vertical are simply
> out of the question.


We have to always remember that Eznec and other amateur
radio modeling programs assume flat earth and "infinite"
distance from the antenna as the point where FS is taken.
They also model the earth as a homogenous media and not as
what it really is.

If you look at the ground level field strength of a vertical
over realistic soil in a program, you see it is zero. If you
go out 10 miles and look at a real antenna, you find it is
not anywhere even remotely near zero.  This oddity is
because earth loss adds attenuation with distance and free
space has no dissipative loss at all. By the time the model
looks at field strength hundreds of wavelengths from the
antenna (the point of viewing) the attenuation caused by a
small loss makes low angle FS look terrible. This is true
even with excellent conductivity soil.

The pattern you see is never the real pattern at low angles,
so the data we compare at that angle is also meaningless. We
can only see low angle radiation and pattern when the ground
type is set to lossless, and none of us live there.
Fortunately we almost never use that angle.

73 Tom