[TowerTalk] Takeoff Angles and Non-Reciprocal Propagation

[Richard (Rick) Karlquist]

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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