Radio horizon calculator for VHF and above
How far does a radio reach on 2 m or 70 cm? Above about 30 MHz range is limited mainly by the curvature of the earth. The calculator determines the radio horizon from both antenna heights and works out the link with loss and power budget.
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No installation, no sign-up needed.
What the page does
- Radio horizon from transmitter and receiver height
- Free-space path loss for a given frequency and distance
- Link budget with antenna gain, cable loss and sensitivity
- Terrain profile with Fresnel zone on its own page
- Results with worked steps
Background
With the usual effective earth radius factor k = 4/3, which accounts for refraction in the standard atmosphere, approximately d ≈ 4.12 · (√h₁ + √h₂) km with heights in metres. Two antennas at 10 m give about 26 km. Free-space path loss is 32.45 + 20 log₁₀(f/MHz) + 20 log₁₀(d/km) dB. Mountains, buildings and vegetation shorten the range, tropospheric ducting extends it.
In practice
How it works: enter the frequency, both antenna heights above ground and the distance. The calculator shows whether the other station lies within the radio horizon, how large the free-space loss is and how much margin the link budget leaves. For precise planning with hills and valleys, continue with the terrain profile and Fresnel zone. Heights above sea level belong there, not in the horizon calculator.
Frequently asked questions
Does the radio horizon apply to HF?
No. HF reaches long distances via the ionosphere; there is a separate propagation page.
Why k = 4/3?
Air density decreases with height, so waves bend slightly toward the earth. Mathematically the earth appears one third larger.