Which of the following are the least reliable bands for long-distance communications during periods of low solar activity?
The correct answer is D: 15 meters, 12 meters, and 10 meters. The least reliable bands for long-distance communications during periods of low solar activity are 15 meters, 12 meters, and 10 meters. These higher frequency bands require more ionization to propagate, which is lacking during low solar activity. For amateur radio operators, these bands may be dead during solar minimum. Understanding this helps explain why higher bands need more solar activity.
Exam Tip
Least reliable during low solar activity = 15m, 12m, 10m. Think 'L'ow 'S'olar = 'L'ess reliable on 'S'uper high frequencies (15m, 12m, 10m). Higher frequency bands need more ionization, so they're least reliable during low solar activity. Lower bands are more reliable.
Memory Aid
"Least reliable during low solar activity = 15m, 12m, 10m. Think 'L'ow 'S'olar = 'L'ess reliable on 'S'uper high frequencies. Higher frequency bands (15m, 12m, 10m) need more ionization, so they're least reliable during low solar activity."
Real-World Application
During solar minimum (low sunspot numbers), 15 meters, 12 meters, and 10 meters may be completely dead - no propagation. These higher bands need strong ionization that's lacking during low solar activity. Meanwhile, lower bands (40m, 80m) may still work because they need less ionization.
Key Concepts
Why Other Options Are Wrong
Option A (80m, 160m): Incorrect. Lower bands are more reliable during low solar activity - they need less ionization. 80m and 160m often work better during solar minimum.
Option B (60m, 40m): Incorrect. These bands are more reliable during low solar activity - they need less ionization than higher bands.
Option C (30m, 20m): Incorrect. 30m and 20m are more reliable than 15m, 12m, 10m during low solar activity - they're lower frequency and need less ionization.
题目解析
The correct answer is D: 15 meters, 12 meters, and 10 meters. The least reliable bands for long-distance communications during periods of low solar activity are 15 meters, 12 meters, and 10 meters. These higher frequency bands require more ionization to propagate, which is lacking during low solar activity. For amateur radio operators, these bands may be dead during solar minimum. Understanding this helps explain why higher bands need more solar activity.
考试技巧
Least reliable during low solar activity = 15m, 12m, 10m. Think 'L'ow 'S'olar = 'L'ess reliable on 'S'uper high frequencies (15m, 12m, 10m). Higher frequency bands need more ionization, so they're least reliable during low solar activity. Lower bands are more reliable.
记忆口诀
Least reliable during low solar activity = 15m, 12m, 10m. Think 'L'ow 'S'olar = 'L'ess reliable on 'S'uper high frequencies. Higher frequency bands (15m, 12m, 10m) need more ionization, so they're least reliable during low solar activity.
实际应用示例
During solar minimum (low sunspot numbers), 15 meters, 12 meters, and 10 meters may be completely dead - no propagation. These higher bands need strong ionization that's lacking during low solar activity. Meanwhile, lower bands (40m, 80m) may still work because they need less ionization.
错误选项分析
Option A (80m, 160m): Incorrect. Lower bands are more reliable during low solar activity - they need less ionization. 80m and 160m often work better during solar minimum. Option B (60m, 40m): Incorrect. These bands are more reliable during low solar activity - they need less ionization than higher bands. Option C (30m, 20m): Incorrect. 30m and 20m are more reliable than 15m, 12m, 10m during low solar activity - they're lower frequency and need less ionization.
知识点
Low solar activity, Higher frequency bands, 15m, 12m, 10m, Propagation reliability
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.