When to use: Use for point-to-point microwave and Wi-Fi bridge links to determine how much physical clearance is needed above obstacles for a true line-of-sight path. The first Fresnel zone must be at least 60% clear of obstructions for the link to perform close to free-space. Obstructions inside the first zone cause signal diffraction loss. Includes earth-bulge correction for links over 5 km. Applies to rooftop-to-rooftop, tower-to-tower, and building-to-building links.