Question T7C06
From subelement T7 - T7C
What does an SWR reading of 4:1 indicate?
Why is this correct?
An SWR reading of 4:1 indicates impedance mismatch between the antenna and feed line. SWR (Standing Wave Ratio) measures how well impedances match - a perfect 1:1 reading means perfect match, while higher ratios indicate greater mismatch. At 4:1, significant power is being reflected back to the transmitter instead of radiating from the antenna. This is well beyond acceptable levels (typically 2:1 or lower). The other options are incorrect: SWR doesn't directly measure dB loss, 4:1 is definitely not a good match, and SWR readings don't indicate gain.
Memory tip
Remember the pattern: SWR ratios work like fractions - the closer to 1:1, the better the match. Any reading significantly above 2:1 signals trouble. Higher numbers always mean worse impedance matching, never better performance or gain.
Learn more
In practical operation, 4:1 SWR triggers protective circuits in most solid-state transmitters, automatically reducing output power to prevent damage to output amplifier transistors. This high SWR causes substantial reflected power, converting transmitted energy into heat in the feed line rather than useful radiation. Understanding impedance matching is crucial for efficient station operation and equipment longevity under Part 97 emission standards.
Think about it
Why do you think modern transceivers automatically reduce power when they detect high SWR readings like 4:1, rather than simply allowing full power transmission?