The ionosphere acts as the reflecting surface for the waves in which of the following modes of propagation?

Question

The ionosphere acts as the reflecting surface for the waves in which of the following modes of propagation?

1. A. Ground wave
2. B. Space wave
3. C. Sky wave (Correct answer)
4. D. LOS

Correct Answer

Option C — Sky wave

Detailed Solution & Explanation

The correct answer is Sky wave.

Key Points

• In sky wave propagation the transmitted wave travels upward, is refracted back to earth by the ionosphere, and so reaches receivers far beyond the horizon.
• Ground wave propagation follows the curvature of the earth along its surface and does not involve the ionosphere.
• Space wave and LOS (line of sight) propagation travel directly between transmitting and receiving antennas, which is why they are limited by the horizon.

Additional Information

• Sky wave propagation is effective in the HF band, 3-30 MHz, and is what makes long-distance shortwave broadcasting possible.
• Refraction takes place mainly in the F layer, and the phenomenon is strictly speaking successive refraction rather than true reflection.
• Signals above roughly 30 MHz pass straight through the ionosphere instead of returning, which is why VHF and above are used for satellite links.