What is a characteristic of HF communication compared with communications on VHF and higher frequencies?

HF communication is distinguished by its ability to utilize ionospheric propagation for long-distance communication, a characteristic that is not as prevalent in VHF and higher frequencies. The ionosphere, which is a layer of the Earth's atmosphere filled with ionized particles, reflects HF signals back to the ground, enabling these signals to reach regions that are far beyond the horizon. This allows amateur radio operators to communicate over thousands of miles with relatively low power.

In contrast, VHF and higher frequencies typically rely on line-of-sight propagation, which limits their effective communication range to a much shorter distance, thereby making HF a preferred choice for long-range communications. The ability to reflect off the ionosphere is a unique attribute of HF, contributing to its effectiveness for global communications, particularly during certain times of the day when ionospheric conditions are optimal.