Topband: 160 vertical advice needed

[Tom Rauch]

> I have one multi-part question - ground mounted radials
vs. elevated
> radials?  My soil, according to the FCC's map, is
"excellent", conductivity
> of 30 millisiemens/meter.

Unless you are over saltwater or a salt marsh, it makes
little difference what your soil is.  30 ms/m isn't that
much different than 3.

The difference primarily shows up in extended groundwave
paths, when small changes in local attenuation add up over a
long distance. Now if you were talking 1s/m, it would be
different.

If you want a good ground system, use at least 30 radials
1/8th to 1/4 wl long. Bury them, float them in the air, or
whatever you like. You will NOT need a ground screen, it
does no good if the radial system is adequate.

The flattening of the efficiency curve occurs around 4-8
elevated radials if the radials are 1/4 wl above earth, and
with about 16 radials if they are .05WL above earth. For
radials on the ground, someplace between 25-50 will get it
out on the flat part of the efficiency curve. At 60 radials,
you pretty much will have a perfect system. BC stations use
120 because the FCC wants to be sure they always have
overkill.

If you use 4 radials a few feet in the air, expect to lose
at least 5-10dB. Never depend on models for this, because
models have been notoriously inaccurate for wires near
earth.

73 Tom