Why should antenna loading coils have a high ratio of reactance to resistance?
The correct answer is C: To maximize efficiency. Antenna loading coils should have a high ratio of reactance to resistance (high Q) to maximize efficiency. High Q means low losses - most of the energy is stored in the magnetic field (reactance) rather than lost as heat (resistance).
Loading coils have both inductive reactance (XL) and resistance (R). The Q (quality factor) is XL/R. High Q means the reactance is much larger than the resistance, so losses are low. A high-Q coil stores energy efficiently with minimal loss. Low-Q coils (high resistance relative to reactance) waste power as heat, reducing antenna efficiency. This is why loading coils are made with low-resistance wire and sometimes use ferrite cores to increase inductance (reactance) without adding much resistance.
Exam Tip
Loading coil Q = High for efficiency. Remember: Loading coils should have high reactance-to-resistance ratio (high Q) to maximize efficiency. High Q means low losses.
Memory Aid
"**L**oading **C**oil **Q** = **H**igh for **E**fficiency (think 'LCQ = HE')"
Real-World Application
You're choosing a loading coil for your shortened vertical. You select a high-Q coil (maybe Q=200) with high reactance relative to resistance. This means most energy is stored in the magnetic field with minimal loss as heat. A low-Q coil (high resistance) would waste power and reduce your antenna's efficiency.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. High Q doesn't swamp out harmonics. Harmonic suppression requires filters, not just high-Q loading coils.
Option B: Incorrect. Loading coil Q doesn't affect radiation angle. Radiation angle is determined by antenna height and ground characteristics, not coil Q.
Option D: Incorrect. High Q means high reactance/resistance ratio, which maximizes Q, not minimizes it. The goal is high Q for efficiency.
题目解析
The correct answer is C: To maximize efficiency. Antenna loading coils should have a high ratio of reactance to resistance (high Q) to maximize efficiency. High Q means low losses - most of the energy is stored in the magnetic field (reactance) rather than lost as heat (resistance). Loading coils have both inductive reactance (XL) and resistance (R). The Q (quality factor) is XL/R. High Q means the reactance is much larger than the resistance, so losses are low. A high-Q coil stores energy efficiently with minimal loss. Low-Q coils (high resistance relative to reactance) waste power as heat, reducing antenna efficiency. This is why loading coils are made with low-resistance wire and sometimes use ferrite cores to increase inductance (reactance) without adding much resistance.
考试技巧
Loading coil Q = High for efficiency. Remember: Loading coils should have high reactance-to-resistance ratio (high Q) to maximize efficiency. High Q means low losses.
记忆口诀
**L**oading **C**oil **Q** = **H**igh for **E**fficiency (think 'LCQ = HE')
实际应用示例
You're choosing a loading coil for your shortened vertical. You select a high-Q coil (maybe Q=200) with high reactance relative to resistance. This means most energy is stored in the magnetic field with minimal loss as heat. A low-Q coil (high resistance) would waste power and reduce your antenna's efficiency.
错误选项分析
Option A: Incorrect. High Q doesn't swamp out harmonics. Harmonic suppression requires filters, not just high-Q loading coils. Option B: Incorrect. Loading coil Q doesn't affect radiation angle. Radiation angle is determined by antenna height and ground characteristics, not coil Q. Option D: Incorrect. High Q means high reactance/resistance ratio, which maximizes Q, not minimizes it. The goal is high Q for efficiency.
知识点
Loading coil, Q factor, Reactance to resistance ratio, Efficiency
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.