Radio Horizon Calculator

Work out how far two antennas can see each other, and how high one end must be to reach a target distance.

Enter the two antenna heights to find the horizon.

Horizon per antenna = √(2 × k × R × h), with k = 4/3 for standard atmospheric refraction and R = 6,371 km: about 4.12 × √h kilometres for h in metres. The two horizons add for a link, and a target beyond A's horizon gives the height B needs to close the gap. The model assumes a smooth spherical earth with no terrain, buildings or Fresnel-zone clearance, so real paths are usually shorter — check obstructions before deploying. Everything runs locally in your browser.