For folks that believe the Earth is flat. Good for you. It is nonsense, but I am a firm believer in folks doing, thinking and believing whatever they want. If you aren't hurting anyone else, then speculate away. The Earth isn't flat. It isn't quite round either. It is actually an oblong spheroid. It's mostly round, but a little narrower in the middle than the two poles of its axis. The curvature of the earth has an effect on line of sight. On a wide open field, you won't see the curvature, unless you have another known height object or person in the distance. At approximately 6 miles distance, two men at six feet tall will barely be able to see the tops of each others heads. In radio communications this becomes an issue. Utilizing UHF radios, the curvature of the Earth becomes a barrier to communications because the radio waves continue in a tangent line to the curvature of the Earth arc. At a certain distance the line continues out into the atmosphere where it penetrates the troposphere and out into space. The only way to extend UHF is to elevate your antenna for a higher angle relative to the Earth. Another way to simply say this is, if there is no line of sight, you aren't going to be able to communicate. Other bands have different properties and can actually curve around the surface of the Earth in what is called a ground wave. This occurs below the lower range of VHF frequencies, down into the HF range. The ground wave only travels so far and then it is lost due to surface absorption and dissipation (typically 40-65 miles). HF then has a unique ability to bounce between the ionosphere and the surface of the Earth to achieve long range communications, this is called a Sky wave.