Categories: Amateur Radio

Power Loss at Various SWR readings and Residual Power

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 LossEff. Radiated PowerPower Output in WattsPower Loss in Watts
1.0:10.0%100.0%100.000.0
1.1:10.2%99.8%99.80.2
1.2:10.8%99.2%99.20.8
1.3:11.7%98.3%98.31.7
1.4:12.8%97.2%97.22.8
1.5:14.0%96.0%964
1.6:15.3%94.7%94.75.3
1.7:16.7%93.3%93.36.7
1.8:18.2%91.8%91.88.2
2.0:111.1%88.9%88.911.1
2.2:114.1%85.9%85.914.1
2.4:117.0%83.0%8317.0
2.6:119.8%80.2%80.219.8
3.0:125.0%75.0%7525
4.0:136.0%64.0%6436
5.0:144.4%55.6%55.644.4
6.0:151.0%49.0%4951
7.0:156.3%43.8%43.856.3
8.0:160.5%39.5.0%39.560.5
9.0:164.0%36.0%3664
10.0:166.9%33.1%33.166.9

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.

Ephraim Gariguez

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