Deep Dive: T7C06
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T7C
Reference: 2022-2026 Question Pool · T7 - Practical circuits
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T7C topic.