Question
What usually happens to radio waves with frequencies below the LUF?
Answer Options
- A) They are refracted back to Earth
- B) They pass through the ionosphere
- C) They are attenuated before reaching the destination
- D) They are refracted and trapped in the ionosphere to circle Earth
Correct Answer: C
Explanation
The Lowest Usable Frequency (LUF) is the frequency at which ionospheric absorption becomes so high that the signal received is too weak to be intelligible, even if it is technically refracted back to Earth. Signals with frequencies below the LUF are absorbed primarily by the D-region of the ionosphere.
Therefore, radio waves with frequencies below the LUF are heavily attenuated (absorbed) before reaching the destination. While the signal might be refracted, the loss of power due to absorption makes the path unusable for communication, hence the term ‘Lowest Usable Frequency’.
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