Question
Which ionospheric region is the most absorbent of signals below 10 MHz during daylight hours?
Answer Options
- A) The F2 region
- B) The F1 region
- C) The E region
- D) The D region
Correct Answer: D
Explanation
Ionospheric absorption is primarily a daytime phenomenon caused by the presence of solar radiation. The lowest layer of the ionosphere, the D region, is the most absorbent of radio signals, particularly those below 10 MHz.
During daylight hours, the D region effectively absorbs the energy of these lower HF signals before they can reach the higher, refracting layers. This absorption is responsible for the dramatic reduction in range or complete failure of long-distance communication on the 40-meter, 80-meter, and 160-meter bands during the day.
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