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

UHF signals are rarely heard beyond their radio horizon primarily because they are not effectively propagated by the ionosphere. This frequency range, typically between 300 MHz and 3 GHz, generally operates in line-of-sight conditions. Unlike lower frequency signals, which can reflect off the ionosphere and travel much longer distances, UHF transmissions do not have the same capability for skywave propagation. As a result, their range is limited to the curvature of the Earth and any obstructions in the environment, which is why once you move beyond the horizon, the signals cannot be effectively received.

Understanding this characteristic is crucial for amateur radio operators as it informs them about the limitations of UHF communications and encourages them to consider higher-frequency bands or different propagation methods when trying to reach distant stations.