Which technology enables the reflection of radio waves for long-distance communication?

The correct answer is ionospheric reflection, which is a phenomenon where radio waves are reflected off the ionosphere, allowing them to travel over the horizon and enabling long-distance communication.

The ionosphere is a region of the Earth's upper atmosphere, filled with ionized particles. When radio waves emitted from a transmitter reach this layer, they can be reflected back toward the Earth, effectively extending the range of radio communications beyond the line-of-sight limitations of terrestrial systems. This reflection depends on various factors, including the frequency of the radio waves and the state of the ionosphere, which can be influenced by solar activity.

In contrast, amplitude modulation and frequency modulation are types of signal modulation used to encode information onto radio waves, but they do not relate to the long-distance transmission capabilities provided by the ionosphere. Wave dispersion is a phenomenon that describes the spreading of waves as they propagate through a medium, impacting the signal quality rather than enabling long-distance radio communication. Hence, ionospheric reflection stands out as the key technology for enabling extended communication distances through the use of reflected radio waves.