Question
What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
Answer Options
- A) Switch to a higher frequency HF band
- B) Switch to a lower frequency HF band
- C) Change to an antenna with a higher takeoff angle
- D) Change to an antenna with greater beam width
Correct Answer: B
Explanation
The Maximum Usable Frequency (MUF) for ionospheric propagation changes significantly throughout the day and night. During daylight, solar radiation intensely ionizes the F2 layer, supporting communication on higher HF bands (like 15, 12, or 10 meters). As night falls and the F2 layer recombination begins, the density of ionization decreases.
When the MUF for a path decreases due to darkness, the higher frequencies can no longer be refracted by the ionosphere and simply pass through to space. To maintain the long-distance contact, the operator must compensate for this drop in MUF by successfully finding a lower frequency that is still refracted back to Earth. Therefore, the operator should switch to a lower frequency HF band (such as 40, 80, or 160 meters).
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