>[!abstract] >The Earth bulge refers to the curvature of the Earth that begins to obstruct the radio [[Line of sight|line-of-sight]] (RLOS) path between the transmitter and the receiver as they move farther apart during long-range (BVLOS) UAV operations. The rule of thumb is that a transmitter at sea level has an RLOS of 7 mi / 11 km before the Earth bulge starts obstructing the signal. >[!related] >- **North** (upstream): — >- **West** (similar): — >- **East** (different): — >- **South** (downstream): [[Line of sight]]