Question
How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
Answer Options
- A) They are refracted back to Earth
- B) They pass through the ionosphere
- C) They are amplified by interaction with the ionosphere
- D) They are refracted and trapped in the ionosphere to circle Earth
Correct Answer: A
Explanation
The operational ‘window’ for skywave communications is defined by the Maximum Usable Frequency (MUF) and the Lowest Usable Frequency (LUF). The MUF is the upper limit for refraction, and the LUF is the lowest frequency that avoids excessive signal absorption in the D-region.
Any radio wave with a frequency between the LUF and the MUF has sufficient energy to pass through the lower, highly absorbent D-region and then be refracted back to Earth by the higher F2 region. This is the desired mechanism for long-distance HF communication.
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