[UFO Chicago] Wirelessness in Chicago

[Nick Moffitt]

begin  Nate Riffe  quotation:
> The fresnel zone is the egg-shaped area around the line-of-sight.
> It too, should be free of obstructions in order to have a _clear_
> line-of-sight.  An obstruction in this zone introduces what is
> called a "knife-edge diffraction" which is different from either
> attenuation or reflection, but I am not yet familiar with the
> details of this phenomenon.

If you shine a laser on the gap between two razor blades spaced a
hair's breadth apart, the wave nature of light kicks in and causes the
light to emerge in a pattern on the opposite surface.  It's part
attenuation and part reflection, as I understand it.  It's an easy
trick to perform with a modern laser pointer and a couple of sheets of
paper if you have the time.

Diffraction is largely still a mystery to me, despite all of the
laserplay I had to do in university physics.

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