Which propagation mode is capable of long-distance communication by reflecting off the ionosphere?

Which propagation mode is capable of long-distance communication by reflecting off the ionosphere?

• A. Sky (skip) wave.
• B. Ground wave.
• C. Space wave.
• D. Absorption.

Answer: (A)

Long-distance radio communication through reflection off the ionosphere is achieved by sky waves. When a signal in the HF range hits the ionized layers of the ionosphere at an angle, those layers act like a mirror and reflect the wave back toward the Earth. This bounce can happen one or more times (multi-hop), letting the signal reach faraway locations well beyond line-of-sight. The ability to do this depends on frequency and ionospheric conditions, with certain HF frequencies reflecting best depending on time of day and solar activity. Ground waves travel along the Earth’s surface and weaken with distance, so they’re only good for relatively shorter ranges. Space waves travel in a straight line and are limited to line-of-sight distances unless you have repeaters or satellites. Absorption is a loss mechanism that degrades any mode, not a way to achieve long-distance reach.

Long-distance radio communication through reflection off the ionosphere is achieved by sky waves. When a signal in the HF range hits the ionized layers of the ionosphere at an angle, those layers act like a mirror and reflect the wave back toward the Earth. This bounce can happen one or more times (multi-hop), letting the signal reach faraway locations well beyond line-of-sight. The ability to do this depends on frequency and ionospheric conditions, with certain HF frequencies reflecting best depending on time of day and solar activity.

Ground waves travel along the Earth’s surface and weaken with distance, so they’re only good for relatively shorter ranges. Space waves travel in a straight line and are limited to line-of-sight distances unless you have repeaters or satellites. Absorption is a loss mechanism that degrades any mode, not a way to achieve long-distance reach.