What is the effect of vegetation on UHF and microwave signals?
The correct answer is B: Absorption. Vegetation (trees, leaves, etc.) absorbs UHF and microwave signals, reducing signal strength. This is because water in the vegetation absorbs radio energy at these frequencies.
UHF and microwave frequencies are particularly affected by water content. Since vegetation contains significant water, it acts as an absorber, converting the radio energy into heat. This is why UHF/microwave signals are weaker when antennas are near trees or when signals must pass through vegetation. The higher the frequency, the more pronounced this effect becomes. This is one reason why UHF/microwave antennas are often mounted high and clear of trees.
Exam Tip
Vegetation on UHF/microwave = Absorption. Remember: Vegetation absorbs UHF and microwave signals because of water content. This reduces signal strength, so keep antennas clear of trees.
Memory Aid
"**V**egetation **U**HF = **V**ery **U**nhelpful (think 'VU = VU' = Very Unhelpful, absorbs signals)"
Real-World Application
You install a 70-centimeter antenna near a large tree. During summer when the tree has full leaves, your signal strength drops significantly compared to winter when the tree is bare. The water in the leaves is absorbing your UHF signal energy. Moving the antenna away from the tree or mounting it higher improves your signal because there's less vegetation in the signal path.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Knife-edge diffraction occurs at sharp edges (like mountain ridges), not from vegetation. Vegetation causes absorption, not diffraction.
Option C: Incorrect. Vegetation doesn't amplify signals - it absorbs them, reducing signal strength.
Option D: Incorrect. Vegetation doesn't rotate polarization. It absorbs the signal regardless of polarization.
题目解析
The correct answer is B: Absorption. Vegetation (trees, leaves, etc.) absorbs UHF and microwave signals, reducing signal strength. This is because water in the vegetation absorbs radio energy at these frequencies. UHF and microwave frequencies are particularly affected by water content. Since vegetation contains significant water, it acts as an absorber, converting the radio energy into heat. This is why UHF/microwave signals are weaker when antennas are near trees or when signals must pass through vegetation. The higher the frequency, the more pronounced this effect becomes. This is one reason why UHF/microwave antennas are often mounted high and clear of trees.
考试技巧
Vegetation on UHF/microwave = Absorption. Remember: Vegetation absorbs UHF and microwave signals because of water content. This reduces signal strength, so keep antennas clear of trees.
记忆口诀
**V**egetation **U**HF = **V**ery **U**nhelpful (think 'VU = VU' = Very Unhelpful, absorbs signals)
实际应用示例
You install a 70-centimeter antenna near a large tree. During summer when the tree has full leaves, your signal strength drops significantly compared to winter when the tree is bare. The water in the leaves is absorbing your UHF signal energy. Moving the antenna away from the tree or mounting it higher improves your signal because there's less vegetation in the signal path.
错误选项分析
Option A: Incorrect. Knife-edge diffraction occurs at sharp edges (like mountain ridges), not from vegetation. Vegetation causes absorption, not diffraction. Option C: Incorrect. Vegetation doesn't amplify signals - it absorbs them, reducing signal strength. Option D: Incorrect. Vegetation doesn't rotate polarization. It absorbs the signal regardless of polarization.
知识点
Vegetation, UHF, Microwave, Signal absorption
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.