The Fresnel zone describes an elliptical area around the direct line-of-sight (LOS) path between two antennas. Obstructions within this zone can cause diffraction and signal degradation, even if they are not in the direct LOS.

The first Fresnel zone radius at a given point between the antennas is calculated with: \[ F_1 = \sqrt{ \frac{\lambda \cdot d_1 \cdot d_2}{d_1 + d_2} } \] where:

• \( \lambda \) = wavelength in meters
• d₁ and d₂ = distances from each antenna to the obstruction point

To maintain signal integrity, at least 60% of the first Fresnel zone should be clear of obstructions. This calculator helps estimate how much vertical clearance is needed.