What is the primary effect of increasing antenna height in line-of-sight communications?

• A. Increases horizon distance and reduces obstructions.
• B. Increases interference from atmospheric noise.
• C. Decreases signal strength at target.
• D. Has no effect.

Answer: (A)

Raising the antenna height expands line-of-sight range because the radio path is a straight line and Earth’s curvature hides more of the path at lower heights. Increasing height pushes the horizon farther away, so the signal can reach farther before the ground blocks it. In practical terms, the horizon distance grows roughly with the square root of height, so even moderate height increases can noticeably extend LOS range. Higher antennas also help clear terrain and man-made obstructions within the path and keep the Fresnel zone open, which improves the chances of a reliable link.

Atmospheric noise doesn’t rise simply because you put the antenna higher, and the signal strength at a given target isn’t inherently reduced by height. The main benefit here is access to longer, unobstructed paths.