Which region of the atmosphere can refract or bend HF and VHF radio waves?
The correct answer is C: The ionosphere. The ionosphere is the region of the atmosphere that can refract or bend HF and VHF radio waves, allowing them to travel beyond the horizon. The ionosphere is located approximately 50-400 km above Earth's surface and contains ionized particles.
The ionosphere is created by solar radiation ionizing atoms and molecules in the upper atmosphere. These ionized particles can refract (bend) radio waves, causing them to return to Earth far from the transmitter. This is what makes long-distance HF communications possible - signals that would normally travel off into space are bent back to Earth by the ionosphere. Different layers of the ionosphere (D, E, F1, F2) affect different frequency ranges and provide different propagation characteristics.
Exam Tip
Refracts HF/VHF = Ionosphere. Remember: The ionosphere is the region that refracts (bends) HF and VHF radio waves, making long-distance communications possible.
Memory Aid
"**I**onosphere = **I**onized **R**efraction (think 'I = IR' = Ionized Refraction)"
Real-World Application
You're operating on 20 meters (HF) and make a contact 3000 miles away. Your signal travels upward, enters the ionosphere, and is refracted (bent) by the ionized particles. Instead of continuing into space, the signal is bent back toward Earth and reaches the distant station. Without the ionosphere, your HF signal would travel in a straight line and be lost to space, making long-distance contacts impossible.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The stratosphere is below the ionosphere and doesn't significantly refract radio waves. It's not ionized.
Option B: Incorrect. The troposphere is the lowest layer and doesn't significantly refract HF/VHF waves. It can affect higher frequencies through ducting, but not through ionization.
Option D: Incorrect. The mesosphere is between the stratosphere and ionosphere but doesn't significantly refract radio waves. The ionosphere is the key region.
题目解析
The correct answer is C: The ionosphere. The ionosphere is the region of the atmosphere that can refract or bend HF and VHF radio waves, allowing them to travel beyond the horizon. The ionosphere is located approximately 50-400 km above Earth's surface and contains ionized particles. The ionosphere is created by solar radiation ionizing atoms and molecules in the upper atmosphere. These ionized particles can refract (bend) radio waves, causing them to return to Earth far from the transmitter. This is what makes long-distance HF communications possible - signals that would normally travel off into space are bent back to Earth by the ionosphere. Different layers of the ionosphere (D, E, F1, F2) affect different frequency ranges and provide different propagation characteristics.
考试技巧
Refracts HF/VHF = Ionosphere. Remember: The ionosphere is the region that refracts (bends) HF and VHF radio waves, making long-distance communications possible.
记忆口诀
**I**onosphere = **I**onized **R**efraction (think 'I = IR' = Ionized Refraction)
实际应用示例
You're operating on 20 meters (HF) and make a contact 3000 miles away. Your signal travels upward, enters the ionosphere, and is refracted (bent) by the ionized particles. Instead of continuing into space, the signal is bent back toward Earth and reaches the distant station. Without the ionosphere, your HF signal would travel in a straight line and be lost to space, making long-distance contacts impossible.
错误选项分析
Option A: Incorrect. The stratosphere is below the ionosphere and doesn't significantly refract radio waves. It's not ionized. Option B: Incorrect. The troposphere is the lowest layer and doesn't significantly refract HF/VHF waves. It can affect higher frequencies through ducting, but not through ionization. Option D: Incorrect. The mesosphere is between the stratosphere and ionosphere but doesn't significantly refract radio waves. The ionosphere is the key region.
知识点
Ionosphere, Radio wave refraction, HF propagation, VHF propagation
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.