What do long-range communications use?

What do long-range communications use?

• A. Sky waves when bounced off ionosphere
• B. Ground waves along the surface
• C. Microwave beams
• D. Optical signals

Answer: (A)

Long-range radio communication relies on sky waves, which are radio waves sent upward and reflected back to Earth by the ionosphere. The ionosphere acts like a mirror at the right frequencies, letting signals travel beyond the horizon by bouncing between the ionosphere and the surface. This is why long-distance shortwave communications can reach across continents and oceans. Ground waves stay close to the surface and attenuate with distance, so they’re more limited in range. Microwave beams and optical signals depend on a clear line of sight and infrastructure, making them less suited for broad, globe-spanning coverage without towers, satellites, or unobstructed paths.

Long-range radio communication relies on sky waves, which are radio waves sent upward and reflected back to Earth by the ionosphere. The ionosphere acts like a mirror at the right frequencies, letting signals travel beyond the horizon by bouncing between the ionosphere and the surface. This is why long-distance shortwave communications can reach across continents and oceans. Ground waves stay close to the surface and attenuate with distance, so they’re more limited in range. Microwave beams and optical signals depend on a clear line of sight and infrastructure, making them less suited for broad, globe-spanning coverage without towers, satellites, or unobstructed paths.