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Why must television transmitters often be placed on tall towers or hilltops?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — electromagnetic radiation Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Television transmitters are placed on tall towers or hilltops primarily because television signals operate at frequencies higher than 40 MHz. Unlike lower-frequency radio waves, which can be reflected by the ionosphere to travel long distances around the globe, these higher-frequency television signals travel in straight lines and are not reflected back to Earth by the atmosphere.1

Because electromagnetic radiation travels in straight lines, the range of these signals is limited by the curvature of the Earth. Placing transmitters at higher elevations increases the line-of-sight distance, allowing the signal to reach a larger geographic area and overcome the obstruction posed by the Earth's horizon. This elevation is essential for ensuring that the broadcast signal can effectively reach receiving antennas within the intended service area.12