Worked example: A TV tower is 100 m tall and your rooftop antenna is 10 m high. How far can the space wave reach? Step 1: Horizon distance for the tower: d₁ = 4.12 × √100 = 4.12 × 10 = 41.2 km. Step 2: Horizon distance for your antenna: d₂ = 4.12 × √10 ≈ 4.12 × 3.16 ≈ 13.0 km. Step 3: Total line-of-sight range = d₁ + d₂ ≈ 54 km. Conclusion: beyond ~54 km the Earth's curvature blocks the space wave — that is why TV and FM are local services, and why a 30 m tower would extend coverage to about 4.12×√30 ≈ 22.6 km on its own. Sky-wave shortwave, by contrast, can hop continents.