|To:||Peter Garcia <email@example.com>, firstname.lastname@example.org|
|Subject:||Re: [TowerTalk] fresnel zone/free space path loss|
|From:||Jim Lux <email@example.com>|
|Date:||Wed, 16 Jun 2004 15:16:18 -0700|
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.
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).
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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