What happens when antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?
The correct answer is B: Received signal strength is reduced. When antennas at opposite ends of a VHF or UHF line-of-sight radio link are not using the same polarization, the received signal strength is reduced. This is called polarization mismatch loss.
For maximum signal transfer, transmitting and receiving antennas should have the same polarization. If one is vertical and the other is horizontal, there's a significant signal loss (typically 20-30 dB or more). The signal isn't completely lost, but it's much weaker. This is why it's important to match polarization - if you're using a vertical antenna, the other station should also use vertical for best results. Mixed polarization results in reduced signal strength.
Exam Tip
Polarization mismatch = Reduced signal. Remember: When antennas have different polarizations, received signal strength is reduced. Match polarization for best performance.
Memory Aid
"**P**olarization **M**ismatch = **P**oor **M**atch (think 'PM = PM' = Poor Match, reduced signal)"
Real-World Application
You're using a vertical antenna on 2 meters, and you're trying to contact a station using a horizontal antenna. Even though you're both within line of sight and have good signal paths, your received signal strength is much weaker than it would be if you both used the same polarization. If you switch to a horizontal antenna to match theirs, your signal strength improves significantly.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Polarization mismatch doesn't invert modulation sidebands. It reduces signal strength, but doesn't affect the modulation structure.
Option C: Incorrect. Polarization mismatch doesn't cause echo effects. Echo is typically caused by multipath or timing issues, not polarization.
Option D: Incorrect. Polarization mismatch does have a significant effect - it reduces received signal strength substantially.
题目解析
The correct answer is B: Received signal strength is reduced. When antennas at opposite ends of a VHF or UHF line-of-sight radio link are not using the same polarization, the received signal strength is reduced. This is called polarization mismatch loss. For maximum signal transfer, transmitting and receiving antennas should have the same polarization. If one is vertical and the other is horizontal, there's a significant signal loss (typically 20-30 dB or more). The signal isn't completely lost, but it's much weaker. This is why it's important to match polarization - if you're using a vertical antenna, the other station should also use vertical for best results. Mixed polarization results in reduced signal strength.
考试技巧
Polarization mismatch = Reduced signal. Remember: When antennas have different polarizations, received signal strength is reduced. Match polarization for best performance.
记忆口诀
**P**olarization **M**ismatch = **P**oor **M**atch (think 'PM = PM' = Poor Match, reduced signal)
实际应用示例
You're using a vertical antenna on 2 meters, and you're trying to contact a station using a horizontal antenna. Even though you're both within line of sight and have good signal paths, your received signal strength is much weaker than it would be if you both used the same polarization. If you switch to a horizontal antenna to match theirs, your signal strength improves significantly.
错误选项分析
Option A: Incorrect. Polarization mismatch doesn't invert modulation sidebands. It reduces signal strength, but doesn't affect the modulation structure. Option C: Incorrect. Polarization mismatch doesn't cause echo effects. Echo is typically caused by multipath or timing issues, not polarization. Option D: Incorrect. Polarization mismatch does have a significant effect - it reduces received signal strength substantially.
知识点
Polarization mismatch, Signal strength, VHF/UHF, Line-of-sight
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.