BEGINNERANTENNA BASICS
SWR BASICS &
FIXING HIGH SWR
What the number really tells you, how to measure it in the field, and what to check when it’s high.
SWR (standing wave ratio) is the number every portable operator learns to watch. It’s a quick way to see how well your antenna and feedline match your radio, and it’s useful, but it doesn’t tell the whole story.
What SWR Means
Your radio expects a 50-ohm load. When the antenna system presents something else, part of your signal bounces back toward the radio instead of going out. SWR is the ratio that describes that mismatch. 1:1 is a perfect match, and higher numbers mean more mismatch.
| SWR | POWER REFLECTED | WHAT IT MEANS |
|---|---|---|
| 1.0:1 | 0% | Perfect match. |
| 1.5:1 | about 4% | Excellent. Nothing to fix. |
| 2:1 | about 11% | Fine for most portable use. |
| 3:1 | about 25% | Worth fixing. Many radios start reducing power around here. |
Check your radio’s manual for the point where it lowers power to protect itself.
What SWR Doesn’t Tell You
A low SWR doesn’t mean a good antenna. A dummy load has a perfect SWR and radiates nothing. A long run of lossy coax can also make SWR look good at the radio, because the loss hides the reflection. Use SWR to see whether the antenna is tuned, and use good coax, good radials and a good location to make it work.
Measuring It in the Field
- Connect an antenna analyzer or SWR meter to the antenna, using the coax you’ll actually operate with.
- Sweep or check the band you want, and find the frequency where SWR is lowest. That’s the antenna’s resonant frequency.
- Compare it with where you want to operate.
- If the dip is below your target frequency, the antenna is too long, so shorten it a little.
- If the dip is above your target, it’s too short, so lengthen it a little.
Make small changes, and re-check after each one. Tune at about the height you’ll operate at.
High SWR? Check These First
KPC FIELD REMINDER: Never transmit into a badly mismatched antenna for long. Measure at low power, fix the problem, then go to your operating power.
73 from KPC — Measure, Adjust, Verify!
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