A line-of-sight planning aid for estimating first-Fresnel-zone clearance.
Open the Fresnel clearance calculator in a full window
Version and review status
Formula set: v1.2
Staging review date: 17 August 2026
Status: Staging beta pending user acceptance and cross-browser checks.
Using this calculator
A line-of-sight planning aid for estimating first-Fresnel-zone clearance.
Inputs and units
| Input | Unit or format |
|---|---|
| Frequency | GHz |
| Link distance | km |
| Obstacle distance from site A | km |
| Available clearance | m |
| Clearance target | % (60–100) |
| Clearance reference | corrected profile / flat reference |
| Effective-Earth k-factor (flat reference only) | dimensionless |
Model and formula
The embedded RF app uses r₁ = √[λd₁d₂ / (d₁ + d₂)], with distances and wavelength in metres. Required clearance = r₁ × selected clearance fraction. For a flat reference only, Earth bulge = d₁d₂ / (2kR), where R = 6,371,000 m. Margin = available clearance − Earth bulge − required clearance. A corrected profile receives no second Earth correction.
Worked example
At 5.8 GHz over 8 km, assess a point 3.6 km from site A with 9 m available clearance, a corrected-profile reference and a 60% target. Radius is 10.116 m, required clearance 6.070 m and margin 2.930 m. If the same 9 m is instead a flat-reference clearance at k = 4/3, Earth bulge is 0.932 m and clearance margin is 1.998 m.
Interpreting the result
Choose the reference used by the surveyed path profile to avoid applying curvature twice. The 60% option is a screening target, not a guarantee of service availability. Check the full path, vegetation growth, buildings and the relevant design assumptions; this tool does not predict diffraction loss, terrain uncertainty, rain or multipath availability.
Limits and verification
- Clearance is not a complete propagation analysis or proof of availability.
- The optional flat-reference Earth correction uses a constant k-factor. Terrain, vegetation, buildings, antenna patterns and diffraction loss are not modelled.
- Use surveyed path profiles and representative propagation tools for design assurance.
Worked examples checked against the calculator source on . These are reproducible calculation checks, not aircraft trials, site measurements or operational approval. Existing formula versions and technical review status remain as stated above.