VHF signals used by VOR generally propagate as space waves with approximately line-of-sight coverage.

VHF signals travel mainly as **space waves**, approximately directly between transmitter and receiver. Terrain and the Earth's curvature limit coverage, so a higher aircraft altitude generally increases reception range. **Key takeaway:** VHF range is strongly affected by altitude and line of sight. **Glossary:** **Space wave**: radio propagation directly through the atmosphere.