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Radio horizon
Estimate the geometric horizon of two antennas with a k-factor.
HB3YAQ · Ajdin HadzicLearning to take awayhttps://hb3yaq.ch/en/tools/radio-horizon
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Formula & context
d = [√(2kRh₁ + h₁²) + √(2kRh₂ + h₂²)] / 1000
The model replaces Earth with a sphere of radius kR. k = 1 is purely geometric; 4/3 is a common standard assumption for atmospheric refraction.
A worked example
10 m and 2 m with k = 4/3 give approximately 18.9 km horizon distance.
Assumptions & limits
Heights refer to the imagined smooth surface, not automatically to sea level. Terrain, diffraction and changing refraction are excluded.
Antenna height and radio horizonUnderstand the reasoning →From reading to experimenting
Radio horizon
10 m and 2 m with k = 4/3 give approximately 18.9 km horizon distance.
Open example with starting values →Antenna height A: 10 m · Antenna height B: 2 m · Effective Earth radius factor k: 1.3333333333333333 Back to the learning article →Then change exactly one value. Compare the result and use the formula to explain why it changes. The model limits below the calculator also apply here.