How does the feed point impedance of a 1/2 wave dipole change as the feed point is moved from the center toward the ends?
The correct answer is A: It steadily increases. How the feed point impedance of a 1/2 wave dipole changes as the feed point is moved from the center toward the ends is that it steadily increases. Moving the feed point away from the center (where current is maximum) increases impedance. For amateur radio operators, this explains off-center fed dipoles. Understanding this helps when designing dipoles.
Exam Tip
Dipole impedance vs feed point = steadily increases as moved from center. Think 'M'oving from 'C'enter = 'M'ore 'C'urrent path = 'I'ncreased impedance. Moving feed point away from center (where current is maximum) increases impedance. Not decreases, not peaks, not unaffected - just steadily increases.
Memory Aid
"Dipole impedance vs feed point = steadily increases as moved from center. Think 'M'oving from 'C'enter = 'I'ncreased impedance. Moving feed point away from center increases impedance. Important for off-center fed dipoles."
Real-World Application
A 1/2 wave dipole: Feed point at center gives about 73 ohms. As feed point is moved toward the ends, impedance steadily increases (e.g., 100 ohms, 200 ohms, etc.). Moving away from the center (where current is maximum) increases impedance. This is why off-center fed dipoles have higher impedance.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Impedance doesn't steadily decrease - it increases as feed point moves from center. Decrease is wrong.
Option C: Incorrect. Impedance doesn't peak at 1/8 wavelength from end - it steadily increases as feed point moves from center. Peak isn't the behavior.
Option D: Incorrect. Impedance is affected by feed point location - moving from center changes impedance. No effect is wrong.
题目解析
The correct answer is A: It steadily increases. How the feed point impedance of a 1/2 wave dipole changes as the feed point is moved from the center toward the ends is that it steadily increases. Moving the feed point away from the center (where current is maximum) increases impedance. For amateur radio operators, this explains off-center fed dipoles. Understanding this helps when designing dipoles.
考试技巧
Dipole impedance vs feed point = steadily increases as moved from center. Think 'M'oving from 'C'enter = 'M'ore 'C'urrent path = 'I'ncreased impedance. Moving feed point away from center (where current is maximum) increases impedance. Not decreases, not peaks, not unaffected - just steadily increases.
记忆口诀
Dipole impedance vs feed point = steadily increases as moved from center. Think 'M'oving from 'C'enter = 'I'ncreased impedance. Moving feed point away from center increases impedance. Important for off-center fed dipoles.
实际应用示例
A 1/2 wave dipole: Feed point at center gives about 73 ohms. As feed point is moved toward the ends, impedance steadily increases (e.g., 100 ohms, 200 ohms, etc.). Moving away from the center (where current is maximum) increases impedance. This is why off-center fed dipoles have higher impedance.
错误选项分析
Option B: Incorrect. Impedance doesn't steadily decrease - it increases as feed point moves from center. Decrease is wrong. Option C: Incorrect. Impedance doesn't peak at 1/8 wavelength from end - it steadily increases as feed point moves from center. Peak isn't the behavior. Option D: Incorrect. Impedance is affected by feed point location - moving from center changes impedance. No effect is wrong.
知识点
Dipole feed point, Feed point impedance, Moving from center, Impedance increase
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.