Which propagation mode is used for long-range communications by relying on ionospheric reflection?

Which propagation mode is used for long-range communications by relying on ionospheric reflection?

• A. Surface waves
• B. Sky waves
• C. Ground waves
• D. Space waves

Answer: (B)

Sky waves use the ionosphere to bounce radio signals back to Earth, letting them travel far beyond the horizon. When a signal is sent at frequencies that the ionized layers can reflect, it is refracted by the ionosphere and returns to the surface, enabling long-range, intercontinental communication. This is different from surface or ground waves, which stay close to the ground and attenuate with distance, and space waves, which go directly through space and are limited to line-of-sight distances. The ionospheric reflection is what makes long-range HF communication possible through sky waves.

Sky waves use the ionosphere to bounce radio signals back to Earth, letting them travel far beyond the horizon. When a signal is sent at frequencies that the ionized layers can reflect, it is refracted by the ionosphere and returns to the surface, enabling long-range, intercontinental communication. This is different from surface or ground waves, which stay close to the ground and attenuate with distance, and space waves, which go directly through space and are limited to line-of-sight distances. The ionospheric reflection is what makes long-range HF communication possible through sky waves.