At 06:43 PM 4/2/2007, Gary Schafer wrote:
>I mentioned long ago in this thread that a 1/2 wave vertical needs almost no
>ground to work pretty well and most seemed to want to ignore it and continue
>to bitch about how many radials you need or the antenna won't work.
A more accurate statement would be that the performance starts to be
determined more by the far field ground properties, which, with a
vertically polarized antenna, are pretty important to overall performance.
I think once you've gotten beyond the "nearfield ground loss" issues
(which can be neatly short cutted by, say, a loaded vertical dipole,
a'la Force12, etc.) then you're in the regime where it's the soil
properties hundreds of feet away are the most important, regardless
of ground radials or not, especially for low angle radiation.
It would be an interesting analysis to see where the tradeoff lies..
at what radiator length/height do the radials start to be less
important than the far field soil properties. And, what pushes the
trade one way or another (e.g. if the soil conductivity doubles (or
halves) what happens to the tradeoff)
I suspect that this is why verticals with a few radials/counterpoise,
the whole thing well elevated (say up 30 ft on top of a two story
house), work reasonably well (assuming your neighbor's soil
properties are decent). Sure, the radials may not be perfectly
resonant, but, neither are the legs on a G5RV matched or individually
resonant, and anyway, you're going to take the reactive component out
some other way, either with funky feedlines, matching networks at the
antenna, or matching networks at the transmitter.
Jim, W6RMK
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