How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
The correct answer is A: They are refracted back to Earth. How the ionosphere affects radio waves with frequencies below the MUF and above the LUF is that they are refracted back to Earth. These frequencies are within the usable range - they're refracted (bent) by the ionosphere and return to Earth, enabling skywave propagation. For amateur radio operators, this explains how skywave propagation works. Understanding this helps explain ionospheric propagation.
Exam Tip
Frequencies below MUF and above LUF = refracted back to Earth. Think 'R'efracted = 'R'eturn to Earth. Frequencies in the usable range (below MUF, above LUF) are refracted by ionosphere and return to Earth. Not pass through, not amplified, not trapped - just refracted back.
Memory Aid
"Frequencies below MUF and above LUF = refracted back to Earth. Think 'R'efracted = 'R'eturn to Earth. Frequencies in usable range are refracted by ionosphere and return to Earth. Enables skywave propagation."
Real-World Application
You transmit on 20 meters (14 MHz), which is below MUF (21 MHz) and above LUF (7 MHz). The ionosphere refracts (bends) your signal, returning it to Earth hundreds or thousands of miles away. This is skywave propagation - the signal is refracted, not passing through, amplified, or trapped.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Frequencies below MUF and above LUF don't pass through - they're refracted back. Only frequencies above MUF pass through.
Option C: Incorrect. The ionosphere doesn't amplify signals - it refracts them. Amplification isn't the mechanism.
Option D: Incorrect. Frequencies aren't trapped in the ionosphere to circle Earth - they're refracted back to Earth. Trapping isn't the mechanism.
题目解析
The correct answer is A: They are refracted back to Earth. How the ionosphere affects radio waves with frequencies below the MUF and above the LUF is that they are refracted back to Earth. These frequencies are within the usable range - they're refracted (bent) by the ionosphere and return to Earth, enabling skywave propagation. For amateur radio operators, this explains how skywave propagation works. Understanding this helps explain ionospheric propagation.
考试技巧
Frequencies below MUF and above LUF = refracted back to Earth. Think 'R'efracted = 'R'eturn to Earth. Frequencies in the usable range (below MUF, above LUF) are refracted by ionosphere and return to Earth. Not pass through, not amplified, not trapped - just refracted back.
记忆口诀
Frequencies below MUF and above LUF = refracted back to Earth. Think 'R'efracted = 'R'eturn to Earth. Frequencies in usable range are refracted by ionosphere and return to Earth. Enables skywave propagation.
实际应用示例
You transmit on 20 meters (14 MHz), which is below MUF (21 MHz) and above LUF (7 MHz). The ionosphere refracts (bends) your signal, returning it to Earth hundreds or thousands of miles away. This is skywave propagation - the signal is refracted, not passing through, amplified, or trapped.
错误选项分析
Option B: Incorrect. Frequencies below MUF and above LUF don't pass through - they're refracted back. Only frequencies above MUF pass through. Option C: Incorrect. The ionosphere doesn't amplify signals - it refracts them. Amplification isn't the mechanism. Option D: Incorrect. Frequencies aren't trapped in the ionosphere to circle Earth - they're refracted back to Earth. Trapping isn't the mechanism.
知识点
Ionospheric refraction, MUF and LUF, Skywave propagation, Radio wave refraction
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.