Parabolic & dish
Building an antenna
Fresnel zone is an elliptical area around the visual line of sight between two antennas.
Because signal spreads out after leaving the antenna, objects in this zone attenuate the signal, especially if they are reflective (metallic and glass objects) or has large moisture content (rivers, trees etc). At least 60% of the Fresnel zone must be unobstructed.
The Fresnel zone can be calculated.
For long distance network links, you must include the curve of the earth in your calculation witch is about 20 cm per 1 km.