Question
Which of the following are the least reliable bands for long-distance communications during periods of low solar activity?
Answer Options
- A) 80 meters and 160 meters
- B) 60 meters and 40 meters
- C) 30 meters and 20 meters
- D) 15 meters, 12 meters, and 10 meters
Correct Answer: D
Explanation
Periods of low solar activity mean that the sunspot number and solar flux index are low. This reduces the amount of ionizing radiation reaching Earth, leading to a thinner, weaker F2 ionospheric layer. The F2 layer is responsible for refracting the higher HF frequencies back to Earth.
Since the Maximum Usable Frequency (MUF) is directly related to the ionization level, low solar activity results in a low MUF. This causes the 15-meter, 12-meter, and 10-meter bands to frequently ‘go dead’ for long-distance communication (skip) because their signals pass straight through the ionosphere into space instead of being refracted back to Earth. Conversely, the lower HF bands (80m, 40m) remain reliable during these times.
This topic was automatically created to facilitate community discussion about this exam question. Feel free to share study tips, memory tricks, or additional explanations!