Which ionospheric region is the most absorbent of signals below 10 MHz during daylight hours?
The correct answer is D: The D region. The ionospheric region that is the most absorbent of signals below 10 MHz during daylight hours is the D region. D region is ionized by sunlight, creating strong absorption that affects lower frequencies. For amateur radio operators, this explains why lower bands (160m, 80m, 40m) work better at night. Understanding this helps explain day/night propagation differences.
Exam Tip
Most absorbent below 10 MHz during day = D region. Think 'D' region = 'D'aytime 'D'isrupts (absorbs). D region is ionized by sunlight, creating strong absorption for lower frequencies. F2, F1, and E reflect - only D absorbs significantly.
Memory Aid
"Most absorbent below 10 MHz during day = D region. Think 'D' region = 'D'aytime 'D'isrupts. D region is ionized by sunlight, creating strong absorption for lower frequencies. Only D region significantly absorbs - others reflect."
Real-World Application
You try to operate on 80 meters during the day. The D region is strongly ionized by sunlight, creating heavy absorption that weakens or blocks your signal. At night, the D region de-ionizes, absorption decreases, and 80 meters works much better. D region is the primary absorber of lower frequencies during daylight.
Key Concepts
Why Other Options Are Wrong
Option A (F2 region): Incorrect. F2 region reflects signals, it doesn't absorb them. F2 is for reflection, not absorption.
Option B (F1 region): Incorrect. F1 region reflects signals, it doesn't absorb them. F1 is for reflection, not absorption.
Option C (E region): Incorrect. E region reflects signals, it doesn't absorb them. E region is for reflection, not absorption.
题目解析
The correct answer is D: The D region. The ionospheric region that is the most absorbent of signals below 10 MHz during daylight hours is the D region. D region is ionized by sunlight, creating strong absorption that affects lower frequencies. For amateur radio operators, this explains why lower bands (160m, 80m, 40m) work better at night. Understanding this helps explain day/night propagation differences.
考试技巧
Most absorbent below 10 MHz during day = D region. Think 'D' region = 'D'aytime 'D'isrupts (absorbs). D region is ionized by sunlight, creating strong absorption for lower frequencies. F2, F1, and E reflect - only D absorbs significantly.
记忆口诀
Most absorbent below 10 MHz during day = D region. Think 'D' region = 'D'aytime 'D'isrupts. D region is ionized by sunlight, creating strong absorption for lower frequencies. Only D region significantly absorbs - others reflect.
实际应用示例
You try to operate on 80 meters during the day. The D region is strongly ionized by sunlight, creating heavy absorption that weakens or blocks your signal. At night, the D region de-ionizes, absorption decreases, and 80 meters works much better. D region is the primary absorber of lower frequencies during daylight.
错误选项分析
Option A (F2 region): Incorrect. F2 region reflects signals, it doesn't absorb them. F2 is for reflection, not absorption. Option B (F1 region): Incorrect. F1 region reflects signals, it doesn't absorb them. F1 is for reflection, not absorption. Option C (E region): Incorrect. E region reflects signals, it doesn't absorb them. E region is for reflection, not absorption.
知识点
D region, Absorption, Below 10 MHz, Daylight hours
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.