SWR to Power Loss Calculator

SWR Power Loss Reference Table

What These Numbers Mean in Practice

A 2:1 SWR — the point where many hams start to worry — loses only 11% of power to reflection. At 50 watts, that is 5.5 watts lost. The practical impact on signal at the receiving end: less than 0.5 dB, undetectable by most operators. The real concern with high SWR is stress on the radio's finals from reflected power, not the relatively small amount of power lost.

A 3:1 SWR is where it becomes more meaningful — 25% power loss, about 1.25 dB. Still often acceptable for casual operation. At 5:1 SWR and above, the reflected power becomes significant enough to potentially damage transmitter finals if sustained, and most modern radios will automatically reduce power to protect the output stage.

• At what SWR should I stop transmitting?
  Most modern amateur radios include automatic SWR protection that reduces power when SWR rises above 2:1 to 3:1, protecting the finals from damage. As a general rule: investigate anything above 2.5:1, and avoid sustained transmission above 5:1. A single brief test transmission at high SWR rarely causes damage — it is sustained operation at high reflected power that stresses the output transistors.
• Does SWR affect my ability to receive signals?
  Yes, equally in both directions. A feed line mismatch that causes 3 dB of loss on transmit also causes 3 dB of loss on receive. Your ability to hear weak signals is degraded by the same factor as your transmitted signal is reduced. This is why fixing antenna mismatch improves both your transmitted signal and your receive sensitivity simultaneously.