tools / RF & SDR
Fresnel Zone Calculator
Line of sight is not enough on its own. This gives the first Fresnel zone radius at the midpoint and the 60% clearance you want kept free of obstacles, so a tree line or ridge does not quietly eat half your signal.
Keep at least 60% of this radius clear of obstacles, above and below the sightline.
How it works
Zone radius
The first Fresnel zone radius at a point is 17.32·sqrt((d1·d2)/(f·d)) metres, with distances in km and frequency in GHz. It is widest at the midpoint of the path.
The 60% rule
Keep at least 60% of the first zone clear and diffraction loss stays small. Anything poking into that radius, even below the straight sightline, starts costing you signal.
FAQ
Why does the Fresnel zone matter if I have line of sight?
Radio does not travel in a pencil-thin ray. An obstacle near the path, but below the direct line, still blocks part of the wavefront and adds loss. Clear the zone, not just the sightline.
