Why is long-distance communication on the 40-, 60-, 80-, and 160-meter bands more difficult during the day?
The correct answer is C: The D region absorbs signals at these frequencies during daylight hours. Why long-distance communication on the 40-, 60-, 80-, and 160-meter bands is more difficult during the day is that the D region absorbs signals at these frequencies during daylight hours. D region is ionized by sunlight, creating absorption that affects lower frequencies. For amateur radio operators, this explains why lower bands work better at night. Understanding this helps explain day/night propagation differences.
Exam Tip
Lower bands difficult during day = D region absorbs signals. Think 'D'aytime = 'D' region 'D'isrupts. D region is ionized by sunlight, creating absorption that affects lower frequencies (40m, 60m, 80m, 160m). Not F region, not E region - just D region absorption.
Memory Aid
"Lower bands difficult during day = D region absorbs signals. Think 'D'aytime = 'D' region 'D'isrupts. D region is ionized by sunlight, creating absorption that affects lower frequencies. Nighttime D region de-ionizes, reducing absorption."
Real-World Application
You try to operate on 80 meters during the day. The D region is ionized by sunlight, creating strong absorption that weakens or blocks your signal. At night, the D region de-ionizes, reducing absorption, and 80 meters works much better. This is why lower bands are more difficult during daylight hours.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. F region doesn't absorb signals - it reflects them. D region is the absorber, not F region.
Option B: Incorrect. F region isn't unstable during daylight - it's actually more stable during day. D region absorption is the issue.
Option D: Incorrect. E region isn't unstable during daylight - E region is present and stable. D region absorption is the issue.
题目解析
The correct answer is C: The D region absorbs signals at these frequencies during daylight hours. Why long-distance communication on the 40-, 60-, 80-, and 160-meter bands is more difficult during the day is that the D region absorbs signals at these frequencies during daylight hours. D region is ionized by sunlight, creating absorption that affects lower frequencies. For amateur radio operators, this explains why lower bands work better at night. Understanding this helps explain day/night propagation differences.
考试技巧
Lower bands difficult during day = D region absorbs signals. Think 'D'aytime = 'D' region 'D'isrupts. D region is ionized by sunlight, creating absorption that affects lower frequencies (40m, 60m, 80m, 160m). Not F region, not E region - just D region absorption.
记忆口诀
Lower bands difficult during day = D region absorbs signals. Think 'D'aytime = 'D' region 'D'isrupts. D region is ionized by sunlight, creating absorption that affects lower frequencies. Nighttime D region de-ionizes, reducing absorption.
实际应用示例
You try to operate on 80 meters during the day. The D region is ionized by sunlight, creating strong absorption that weakens or blocks your signal. At night, the D region de-ionizes, reducing absorption, and 80 meters works much better. This is why lower bands are more difficult during daylight hours.
错误选项分析
Option A: Incorrect. F region doesn't absorb signals - it reflects them. D region is the absorber, not F region. Option B: Incorrect. F region isn't unstable during daylight - it's actually more stable during day. D region absorption is the issue. Option D: Incorrect. E region isn't unstable during daylight - E region is present and stable. D region absorption is the issue.
知识点
D region absorption, Daytime propagation, Lower frequencies, Day/night differences
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.