Deep Dive: G9A04
The correct answer is C: A difference between feed line impedance and antenna feed point impedance. What causes reflected power at an antenna's feed point is a difference between feed line impedance and antenna feed point impedance. When impedances don't match, power is reflected, creating standing waves. For amateur radio operators, this is why impedance matching is important. Understanding this helps when troubleshooting SWR problems.
Why Other Answers Are Wrong
Option A: Incorrect. Operating at resonant frequency doesn't cause reflected power - resonance affects reactance, but impedance mismatch causes reflection. Resonance isn't the cause. Option B: Incorrect. Using more power than antenna can handle doesn't cause reflected power - it might damage the antenna, but impedance mismatch causes reflection. Power level isn't the cause. Option D: Incorrect. Feeding with unbalanced feed line doesn't necessarily cause reflected power - impedance mismatch causes reflection, not balance. Balance isn't the cause.
Exam Tip
Reflected power cause = impedance mismatch between feed line and antenna. Think 'R'eflected 'P'ower = 'R'esults from 'P'oor impedance match. When impedances don't match, power is reflected. Not resonance, not power level, not balance - just impedance mismatch.
Memory Aid
Reflected power cause = impedance mismatch between feed line and antenna. Think 'R'eflected 'P'ower = 'R'esults from 'P'oor match. When impedances don't match, power is reflected. Why impedance matching is important.
Real-World Example
An antenna feed point has 100-ohm impedance, but the feed line is 50 ohms. The impedance mismatch causes power to be reflected back toward the transmitter, creating standing waves. This is why impedance matching is important - to minimize reflected power. Impedance mismatch is the cause of reflected power.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9A
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 G9A topic.