Deep Dive: G9B08
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9B
Reference: 2023-2027 Question Pool · G9 - Antennas and Feed Lines
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G9B topic.