What does an SWR reading of 4:1 indicate?
The correct answer is D: Impedance mismatch. An SWR reading of 4:1 indicates an impedance mismatch between the antenna and feed line. SWR (Standing Wave Ratio) measures how well the antenna impedance matches the feed line impedance. A 4:1 SWR means significant mismatch - only about 69% of power is transferred to the antenna, with 31% reflected back. For amateur radio operators, 4:1 SWR is considered poor and should be improved. While some transmitters can operate at 4:1 (with reduced power due to protection circuits), it's not ideal. Understanding SWR readings helps diagnose antenna and feed line problems.
Exam Tip
4:1 SWR = impedance mismatch. Think '4:1 = 'F'our to one = 'F'aulty match. High SWR indicates mismatch. Lower is better (1:1 is perfect). 4:1 is poor and needs improvement.
Memory Aid
"4:1 SWR = impedance mismatch. Think '4:1 = 'F'our to one = 'F'aulty impedance match. High SWR = poor match. Need to improve antenna tuning or fix problems."
Real-World Application
You check your antenna system and find 4:1 SWR. This indicates your antenna impedance doesn't match your 50-ohm feed line - perhaps the antenna is broken, the feed point is wrong, or there's a problem with the feed line. You need to investigate and fix the problem. At 4:1, your transmitter's protection circuit may reduce power, and you're losing significant power to reflections.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. SWR doesn't directly indicate loss in dB. While high SWR causes losses, the relationship isn't a simple -4 dB. Loss depends on feed line characteristics and length.
Option B: Incorrect. 4:1 SWR is not a good match - it's a significant mismatch. A good match would be 1.5:1 or better.
Option C: Incorrect. SWR doesn't indicate gain - there's no such thing as gain from SWR. High SWR causes losses, not gains.
题目解析
The correct answer is D: Impedance mismatch. An SWR reading of 4:1 indicates an impedance mismatch between the antenna and feed line. SWR (Standing Wave Ratio) measures how well the antenna impedance matches the feed line impedance. A 4:1 SWR means significant mismatch - only about 69% of power is transferred to the antenna, with 31% reflected back. For amateur radio operators, 4:1 SWR is considered poor and should be improved. While some transmitters can operate at 4:1 (with reduced power due to protection circuits), it's not ideal. Understanding SWR readings helps diagnose antenna and feed line problems.
考试技巧
4:1 SWR = impedance mismatch. Think '4:1 = 'F'our to one = 'F'aulty match. High SWR indicates mismatch. Lower is better (1:1 is perfect). 4:1 is poor and needs improvement.
记忆口诀
4:1 SWR = impedance mismatch. Think '4:1 = 'F'our to one = 'F'aulty impedance match. High SWR = poor match. Need to improve antenna tuning or fix problems.
实际应用示例
You check your antenna system and find 4:1 SWR. This indicates your antenna impedance doesn't match your 50-ohm feed line - perhaps the antenna is broken, the feed point is wrong, or there's a problem with the feed line. You need to investigate and fix the problem. At 4:1, your transmitter's protection circuit may reduce power, and you're losing significant power to reflections.
错误选项分析
Option A: Incorrect. SWR doesn't directly indicate loss in dB. While high SWR causes losses, the relationship isn't a simple -4 dB. Loss depends on feed line characteristics and length. Option B: Incorrect. 4:1 SWR is not a good match - it's a significant mismatch. A good match would be 1.5:1 or better. Option C: Incorrect. SWR doesn't indicate gain - there's no such thing as gain from SWR. High SWR causes losses, not gains.
知识点
SWR, Impedance mismatch, High SWR, Antenna problems
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.