What is the effect of increasing antenna height on horizon visibility in line-of-sight communications?

• A. Increasing height reduces earth curvature and obstructions, expanding horizon distance and improving line-of-sight reliability.
• B. Increasing height increases atmospheric noise.
• C. Increasing height has no effect on horizon visibility.
• D. Increasing height reduces the antenna gain.

Answer: (A)

Raising the antenna height expands horizon visibility because line-of-sight radio signals travel in straight paths and the Earth's curvature plus terrain block what you can see at lower elevations. When the antenna is higher, you clear more of the Earth's curvature and any ground obstacles, so the clear-path distance to the horizon increases. The basic math shows horizon distance grows with the square root of height, so even modest height gains yield a noticeable LOS improvement. In practice, the radio path is also a bit farther than the geometric horizon due to atmospheric refraction, which bends signals slightly downward and extends reach a bit further.

Height doesn’t change atmospheric noise levels, and it doesn’t inherently increase the antenna’s gain—the gain comes from the antenna design itself, not how high it’s mounted. So the correct idea is that increasing height reduces obstructions and the curvature effect, expanding horizon distance and improving line-of-sight reliability.