SWR (Standing Wave Ratio) affects the power output of your radio. The following table shows the effect of SWR for a transmitter with 100 watts of transmitted power.
| SWR Reading | % Of Loss | Eff. Radiated Power | Power Output in Watts | Power Loss in Watts |
|---|---|---|---|---|
| 1.0:1 | 0.0% | 100.0% | 100.00 | 0.0 |
| 1.1:1 | 0.2% | 99.8% | 99.8 | 0.2 |
| 1.2:1 | 0.8% | 99.2% | 99.2 | 0.8 |
| 1.3:1 | 1.7% | 98.3% | 98.3 | 1.7 |
| 1.4:1 | 2.8% | 97.2% | 97.2 | 2.8 |
| 1.5:1 | 4.0% | 96.0% | 96 | 4 |
| 1.6:1 | 5.3% | 94.7% | 94.7 | 5.3 |
| 1.7:1 | 6.7% | 93.3% | 93.3 | 6.7 |
| 1.8:1 | 8.2% | 91.8% | 91.8 | 8.2 |
| 2.0:1 | 11.1% | 88.9% | 88.9 | 11.1 |
| 2.2:1 | 14.1% | 85.9% | 85.9 | 14.1 |
| 2.4:1 | 17.0% | 83.0% | 83 | 17.0 |
| 2.6:1 | 19.8% | 80.2% | 80.2 | 19.8 |
| 3.0:1 | 25.0% | 75.0% | 75 | 25 |
| 4.0:1 | 36.0% | 64.0% | 64 | 36 |
| 5.0:1 | 44.4% | 55.6% | 55.6 | 44.4 |
| 6.0:1 | 51.0% | 49.0% | 49 | 51 |
| 7.0:1 | 56.3% | 43.8% | 43.8 | 56.3 |
| 8.0:1 | 60.5% | 39.5.0% | 39.5 | 60.5 |
| 9.0:1 | 64.0% | 36.0% | 36 | 64 |
| 10.0:1 | 66.9% | 33.1% | 33.1 | 66.9 |
To compute your useful output power into the antenna, read your output power, and multiply it by the ERP percentage above, using your SWR reading.
Example: If your transceiver output is 75.0 Watts, and the VSWR is 1.5. From the table above 1.5:1 the radiating efficiency is 96.0% percent. Simply multiply 75.0 Watts by 0.96 (96/100 to decimal). The result is 72.0 Watts.