Diffraction is reciprocal, regardless of asymmetries in the terrain.
Most "one way" propagation is due to different noise levels at the
two ends of the path, not non-reciprocal propagation.
Rick N6RK
David Gilbert wrote:
> HFTA clearly shows that signals can be refracted over sharp terrain
> features to bend closer to the horizon (sometimes significantly so) than
> would otherwise occur based upon the actual antenna height above
> ground. Some portion of the transmitted signal might end up with an
> effective takeoff angle of, for example, six degrees that wouldn't be
> there without a fortuitously located hill. Since terrain features are
> almost never symmetrical, though, there doesn't seem to be any guarantee
> that a return signal from the DX end would necessarily bend back down to
> the local antenna, at least not in exactly the same way. I would think
> that the sharper side of a hill would defract a signal differently than
> a gently rounded side.
>
> I wonder if this could possibly explain some of the non-symmetrical
> "propagation" that most of us think we may have occasionally
> experienced. I would think even a large building of the right shape and
> composition could act like a terrain feature ... especially on the
> higher frequency bands.
>
> Dave AB7E
>
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