Why should the outer jacket of coaxial cable be resistant to ultraviolet light?
The correct answer is D: Ultraviolet light can damage the jacket and allow water to enter the cable. The outer jacket of coaxial cable should be resistant to ultraviolet light because UV light can damage the jacket and allow water to enter the cable. UV radiation from sunlight breaks down many plastic materials over time, causing the jacket to crack, become brittle, and eventually fail. Once the jacket fails, water can enter, leading to cable failure. For amateur radio operators, UV-resistant cable is essential for outdoor installations exposed to sunlight. This is especially important for feed lines running outside or on towers.
Exam Tip
UV resistance = prevents jacket damage and water entry. Think 'U'V resistance = 'U'nder 'V'isible protection. UV damages jacket, allowing water entry. Not about harmonics, losses, or interference mixing.
Memory Aid
"UV resistance = prevents jacket damage and water entry. Think 'U'V resistance = 'U'nder 'V'isible protection. UV damages jacket, water enters, cable fails. Use UV-resistant cable outdoors."
Real-World Application
Your feed line runs outside along a fence, exposed to direct sunlight. After a few years, the cable jacket becomes brittle and cracks. Water enters through the cracks, causing high losses and cable failure. Using UV-resistant cable would have prevented this - the special jacket material resists UV degradation, maintaining its integrity and keeping water out for many years.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. UV-resistant jackets don't prevent harmonic radiation - harmonics are generated by transmitters, not by cable jackets. UV resistance is for physical protection.
Option B: Incorrect. UV light doesn't increase losses in the jacket material itself - it damages the jacket physically, allowing water entry which then causes losses.
Option C: Incorrect. UV and RF signals don't mix to cause interference - they're completely different phenomena. UV is light, RF is radio waves.
题目解析
The correct answer is D: Ultraviolet light can damage the jacket and allow water to enter the cable. The outer jacket of coaxial cable should be resistant to ultraviolet light because UV light can damage the jacket and allow water to enter the cable. UV radiation from sunlight breaks down many plastic materials over time, causing the jacket to crack, become brittle, and eventually fail. Once the jacket fails, water can enter, leading to cable failure. For amateur radio operators, UV-resistant cable is essential for outdoor installations exposed to sunlight. This is especially important for feed lines running outside or on towers.
考试技巧
UV resistance = prevents jacket damage and water entry. Think 'U'V resistance = 'U'nder 'V'isible protection. UV damages jacket, allowing water entry. Not about harmonics, losses, or interference mixing.
记忆口诀
UV resistance = prevents jacket damage and water entry. Think 'U'V resistance = 'U'nder 'V'isible protection. UV damages jacket, water enters, cable fails. Use UV-resistant cable outdoors.
实际应用示例
Your feed line runs outside along a fence, exposed to direct sunlight. After a few years, the cable jacket becomes brittle and cracks. Water enters through the cracks, causing high losses and cable failure. Using UV-resistant cable would have prevented this - the special jacket material resists UV degradation, maintaining its integrity and keeping water out for many years.
错误选项分析
Option A: Incorrect. UV-resistant jackets don't prevent harmonic radiation - harmonics are generated by transmitters, not by cable jackets. UV resistance is for physical protection. Option B: Incorrect. UV light doesn't increase losses in the jacket material itself - it damages the jacket physically, allowing water entry which then causes losses. Option C: Incorrect. UV and RF signals don't mix to cause interference - they're completely different phenomena. UV is light, RF is radio waves.
知识点
UV resistance, Cable jacket protection, Moisture prevention, Outdoor installations
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.