[TowerTalk] fresnel zone/free space path loss

[Jim Lux]

At 09:11 AM 6/16/2004 -0700, Peter Garcia wrote:
>I have a question hopefully you can answer. I 'm in school for 
>Communications and was wondering if Fresnel Zones affect Free Space Path 
>Loss, or are they two seperate things.
>
>e-mail.
>engine_nueve at yahoo.com

They're different.

Fresnel zones have to do with a specific propagation path, specifically 
with the effect of obstacles that are in the line of sight between 
transmitter and receiver.

Free Space Path Loss is just that... path loss through free space, and is 
entirely due to the uniform spreading of all electromagnetic radiation 
(including light), resulting in the well-known inverse square law.

In general, the path loss between a transmitter and receiver for a real 
path over real earth will be different than one would calculate from the 
free space path loss (also referred to as the "spreading loss").  There may 
be multiple propagation paths that reinforce or cancel each other 
(multipath is but one case), there will be a paths including reflections 
from the earth in between transmitter and receiver that can add or subtract 
from the "direct path".

There can also be paths that propagate in a non-line of sight manner over 
ridges or around corners (by diffraction).

Jim, W6RMK