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Difference between revisions of "Mesh/Terms"
→Fresnel Zone
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== Fresnel Zone == | == Fresnel Zone == | ||
The Fresnel Zone is a football shaped | The Fresnel Zone is a football shaped radio wave path whose implications are important in finding optimal signalling. There are an infinite number of "zones" which are concentrically spread out. As radio waves travel from transmitter to receiver, they can be reflected off of physical objects and off of eachother. As waves are reflected, their timing can be affected. Therefore, some of the waves will arrive out of phase and interfere with the reception of the signal. | ||
The first Fresnel Zone contributes to the most in-phase signalling, while the second zone can contribute to more out of phase signalling. It seems like a good rule is to keep the first fresnel zone as clear as possible, with leeway up to about 20%. | |||
The concept of the Fresnel Zone is why in long distance point to point communications, elevated antennas serve better than antennas on the ground even when there is direct line of sight. For example, if two people are standing on opposite sides of lake merritt and can see each other, the signal between their two antennas might still be greatly interfered with. To visualize, imagine standing on one side of the lake and seeing an enormous football shaped 3d pattern connecting on two ends your antenna and your friends. Likely, the bottom half of the football shape would be mostly in the water and therefore obstructed. If you were able to elevate the antennas on both ends, your results would likely be much better. | |||
The wikipedia article has a formula for calculating the fresnel zone radius at any point in between two endpoints. I believe there's also software which incorporates the Fresnel Zone into mapping and planning nodes. | |||
https://en.wikipedia.org/wiki/Fresnal_zone | https://en.wikipedia.org/wiki/Fresnal_zone | ||