Radio Horizon Calculator

First-order path geometry tool

Radio horizon calculator controls and results

Explore the curvature-only horizon created by antenna height, Earth curvature, and a selected refraction assumption.

Station A
Station B

Enter height above local ground at each station. This model does not know site elevation above sea level or the terrain between stations.

Horizon model
Display units
Advanced horizon assumptions
Effective Earth-radius factor (k)

The 4/3-Earth model approximates standard atmospheric refraction by treating Earth as if its effective radius were larger. Actual refractivity varies with weather and vertical atmospheric structure.

Understanding the curvature-only radio horizon

This calculator uses antenna height above local ground, a smooth spherical Earth, and an effective-Earth-radius factor. It deliberately does not use coordinates, endpoint elevation, or a terrain profile.

How the model works

For each station, the calculator finds the tangent distance to a smooth effective Earth using d = √(2Reffh + h²). The combined modeled horizon is the sum of the two endpoint distances. The standard radio option uses the conventional 4/3-Earth engineering approximation; geometric Earth uses k = 1.

Terrain is the missing context

A ridge can obstruct a path well inside this modeled horizon, while elevated sites can see much farther than their AGL heights suggest. Terrain-aware path analysis requires endpoint elevations and the complete profile between them.

Common questions

Does this predict communications coverage? No. It is a curvature/refraction geometry baseline, not a propagation or coverage prediction.

Why is there no frequency? Frequency becomes relevant to Fresnel clearance, diffraction, path loss, and propagation—none of which this calculator models.