What is the nominal characteristic impedance of “window line” transmission line?
The correct answer is D: 450 ohms. The nominal characteristic impedance of 'window line' transmission line is 450 ohms. Window line (ladder line) is a type of parallel conductor feed line with 450-ohm characteristic impedance. For amateur radio operators, this is important when selecting feed lines. Understanding this helps when designing antenna systems.
Exam Tip
Window line impedance = 450 ohms. Think 'W'indow 'L'ine = 'W'ide spacing = '4'50 ohms. Window line (ladder line) has 450-ohm characteristic impedance. Not 50 ohms (coax), not 75 ohms (TV coax), not 100 ohms - just 450 ohms.
Memory Aid
"Window line impedance = 450 ohms. Think 'W'indow 'L'ine = '4'50 ohms. Window line (ladder line) has 450-ohm characteristic impedance. Standard window line impedance."
Real-World Application
Window line (ladder line): This parallel conductor feed line has a nominal characteristic impedance of 450 ohms. It's called 'window line' because of the window-like openings in the insulation. Window line is commonly used for multiband antennas because of its low loss and 450-ohm impedance.
Key Concepts
Why Other Options Are Wrong
Option A (50 ohms): Incorrect. 50 ohms is for coaxial cable, not window line - window line is 450 ohms. 50 ohms is wrong.
Option B (75 ohms): Incorrect. 75 ohms is for TV coax, not window line - window line is 450 ohms. 75 ohms is wrong.
Option C (100 ohms): Incorrect. 100 ohms isn't a standard window line impedance - window line is 450 ohms. 100 ohms is wrong.
题目解析
The correct answer is D: 450 ohms. The nominal characteristic impedance of 'window line' transmission line is 450 ohms. Window line (ladder line) is a type of parallel conductor feed line with 450-ohm characteristic impedance. For amateur radio operators, this is important when selecting feed lines. Understanding this helps when designing antenna systems.
考试技巧
Window line impedance = 450 ohms. Think 'W'indow 'L'ine = 'W'ide spacing = '4'50 ohms. Window line (ladder line) has 450-ohm characteristic impedance. Not 50 ohms (coax), not 75 ohms (TV coax), not 100 ohms - just 450 ohms.
记忆口诀
Window line impedance = 450 ohms. Think 'W'indow 'L'ine = '4'50 ohms. Window line (ladder line) has 450-ohm characteristic impedance. Standard window line impedance.
实际应用示例
Window line (ladder line): This parallel conductor feed line has a nominal characteristic impedance of 450 ohms. It's called 'window line' because of the window-like openings in the insulation. Window line is commonly used for multiband antennas because of its low loss and 450-ohm impedance.
错误选项分析
Option A (50 ohms): Incorrect. 50 ohms is for coaxial cable, not window line - window line is 450 ohms. 50 ohms is wrong. Option B (75 ohms): Incorrect. 75 ohms is for TV coax, not window line - window line is 450 ohms. 75 ohms is wrong. Option C (100 ohms): Incorrect. 100 ohms isn't a standard window line impedance - window line is 450 ohms. 100 ohms is wrong.
知识点
Window line, Characteristic impedance, 450 ohms, Ladder line
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.