Determines the required line-of-sight clearance utilizing the standard 60% rule of the first Fresnel zone radius (R = 17.32 * sqrt(d/(4f))) to avoid diffraction loss.
First Fresnel Zone Radius (R1):
0.00 m
60% Clearance Requirement:
0.00 m
Disclaimer: for preliminary estimation only, not a substitute for review by a qualified/licensed engineer.
For wireless link planners and RF site surveyors who must prove a microwave or PtP path clears terrain and rooftops before committing to antenna heights, this tool provides a critical preliminary estimate. By entering the total link distance, operating frequency, and the position of a potential obstruction, you can quickly determine the required clearance in metres. This allows you to assess the viability of a path or adjust antenna heights without relying on approximations.
It utilizes the standard 60% rule of the first Fresnel zone radius (R = 17.32 * sqrt(d/(4f))) to avoid diffraction loss, ensuring reliable signal propagation.
Q: What is the 60% Fresnel zone rule?
A: Keep at least 60% of the first Fresnel zone radius free of obstructions — doing so avoids the diffraction loss that a partially blocked path would introduce.
Q: Which units does this calculator expect?
A: Distances in kilometres and frequency in GHz; the results are returned in metres, because the 17.32 constant is defined for exactly those units.
Q: Where along the path is the Fresnel zone widest?
A: At the midpoint, where d1 = d2 = D/2 — the radius is smallest at the antennas and grows to its maximum at mid-path, so that is the hardest point to clear.
Q: What happens if the obstacle sits right next to an antenna?
A: The product d1·d2 collapses toward zero, so the first Fresnel zone radius and the 60% clearance both approach 0 m there — clearance requirements only become meaningful away from the endpoints.