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

The radio horizon for VHF (Very High Frequency) and UHF (Ultra High Frequency) signals extends further than the visual horizon primarily due to the phenomenon of atmospheric refraction. When radio waves travel through the atmosphere, they can be bent or refracted around obstacles and through layers of differing air densities. This bending allows the signals to reach beyond the line of sight that limits human visibility.

The visual horizon, on the other hand, is determined by the curvature of the Earth and the observer's height above sea level. Since radio waves can follow curved paths due to refraction, their effective range can be much greater than that of visible light, which is limited by direct line of sight.

While radio waves are indeed less likely to be affected by dust particles compared to visible light, the primary factor in extending the radio horizon is the refractive properties of the atmosphere itself. This behavior of radio waves is key to understanding radio communication, especially at VHF and UHF frequencies.