Why is the radio horizon for VHF and UHF signals more distant than the visual horizon?

• A. Radio signals are more powerful
• B. The atmosphere refracts radio waves slightly
• C. The terrain is higher
• D. Radio signals travel faster than light

Answer: (B)

The radio horizon for VHF and UHF signals extends further than the visual horizon primarily because the atmosphere refracts radio waves slightly. Refraction occurs when a wave passes through different media, which changes its speed and direction. In the case of radio waves, they travel through the atmosphere, and the varying density of the atmosphere causes these waves to bend, allowing them to propagate beyond the geometric line of sight.

While visual horizon is limited to what can be seen at eye level—essentially constrained by the curvature of the Earth—the refraction effect enables radio signals to reach further distances. As a result, stations operating at VHF and UHF frequencies can communicate over longer distances, making effective use of the available signal range that would otherwise be limited if only the line of sight were considered. This phenomenon is critical for amateur radio operators and is foundational to understanding how VHF and UHF communications can function effectively in various operational scenarios.