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In rec.radio.amateur.antenna Spike wrote:
Imagine a short rod vertical aerial not connected to ground, for the (say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed with RF energy and operating over ground of average conductivity. Three different waves will be launched from this: the sky wave, the space wave (including the reflected ray), and the surface wave. Each of these have their own characteristics, inasmuch as the sky wave is launched willy-nilly even if the band isn't open for that mode, the space wave depends on the path to the receiver, and the surface wave depends on the electromagnetic characteristics of the air and the surface material, although to some extent the latter affects all the waves generated. These "waves" are actually called skywave and surface wave and are a propagation phenomena. See: http://en.wikipedia.org/wiki/Skywave http://en.wikipedia.org/wiki/Surface_wave http://en.wikipedia.org/wiki/Line-of-sight_propagation for how signals propagate. -- Jim Pennino |
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