Fresnel Zone Calculator
Calculate clearance requirements for wireless links.
Maximum F1 Radius Reference
| Distance | 900 MHz | 2.4 GHz | 5.8 GHz |
|---|---|---|---|
| 1 km | 9.1 m | 5.6 m | 3.6 m |
| 5 km | 20.4 m | 12.5 m | 8.0 m |
| 10 km | 28.9 m | 17.7 m | 11.4 m |
| 20 km | 40.8 m | 25.0 m | 16.1 m |
Understanding Fresnel Zones
What is a Fresnel Zone?
A Fresnel zone is an ellipsoid-shaped region around the line-of-sight path between a transmitter and receiver. RF energy travels not just in a straight line, but in an expanding wavefront. Obstructions within this zone can cause signal degradation even if they don't block the direct path.
Fresnel Zone Formula
Fn = sqrt(n * λ * d1 * d2 / D)
where n = zone number, λ = wavelength, d1/d2 = distances to point, D = total path
where n = zone number, λ = wavelength, d1/d2 = distances to point, D = total path
Clearance Guidelines
- 100% F1: Theoretical ideal, no additional loss
- 80% F1: Excellent, negligible loss (~0.5 dB)
- 60% F1: Good, acceptable loss (~1-2 dB)
- 40% F1: Marginal, noticeable degradation
- 0% F1: Line-of-sight only, ~6 dB additional loss
Practical Tips
Consider tree growth, building construction, and earth curvature for long links. The Fresnel zone is widest at the midpoint of the path.