Also known as: radio horizon

The radio horizon is the farthest point a line-of-sight signal reaches before the Earth’s curvature gets in the way.¹ It lies slightly beyond the visual horizon because the atmosphere refracts radio waves a little.

The radio horizon is the farthest line-of-sight point before the Earth's curve blocks it; raising the antenna extends it.

How it works

Raising either antenna pushes the radio horizon outward, which is why repeaters sit on towers and hilltops and why getting a receive antenna up high extends range at VHF/UHF.

Relevance to SDR

For line-of-sight bands, antenna height is often the most effective way to reach more distant systems.

Sources

1. Line-of-sight propagation — Wikipedia, on the radio horizon, Earth curvature, and atmospheric refraction. ↩

See also

• Radio propagation
• Frequency bands (HF/VHF/UHF)
• Antenna

Learn it step by step

• How signals travel