Why are simplex UHF signals rarely heard beyond their radio horizon?

• A. UHF signals use skywave propagation
• B. UHF signals have high bandwidth
• C. UHF signals are usually not propagated by the ionosphere
• D. UHF signals are affected by ground wave losses

Answer: (C)

The correct answer highlights a fundamental aspect of UHF signal propagation. UHF signals, which operate in the frequency range of 300 MHz to 3 GHz, primarily rely on line-of-sight propagation. This means that they travel in a straight line from the transmitter to the receiver, making them particularly susceptible to obstructions such as buildings, trees, and the curvature of the Earth.

The ionosphere, a layer of the atmosphere that can refract radio waves, is effective at reflecting certain lower-frequency signals, particularly those in the HF band (3 to 30 MHz). However, UHF signals do not typically reach the ionosphere at these frequencies to be reflected back to the ground. Instead, they tend to dissipate beyond the radio horizon, where the direct line of sight is interrupted. This phenomenon leads to very limited range for UHF simplex communications, especially over longer distances.

The other options describe characteristics or behaviors of radio waves that do not apply to UHF signals in the same context. For instance, while UHF signals may utilize ground wave to some extent, it is primarily strong at lower frequencies. Similarly, high bandwidth does not influence the range limitations of UHF signals as much as their propagation characteristics do. The assertion regarding skywave