Link Engineering and RF Path Planning
Earth bulge

Earth curvature becomes a concern for links longer than 11 km (7 miles). Line of sight disappears at 25 km (16 miles). Therefore, the curvature of the Earth must be considered when determining the antenna mounting height, as indicated in Figure . To allow for Earth bulge obstruction, the antennas must be raised higher off the ground, than if the Earth were flat. Figure illustrates this.