POWER LOSS AT VARIOUS SWR READINGS

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.

* ERP = Percentage of Effective Radiated Power, Unity Gain.

SWR READING % OF LOSS ERP* WATTS AVAILABLE
1.0:1 0.0% 100.0% 100.00
1.1:1 0.2% 99.8% 99.8
1.2:1 0.8% 99.2% 99.2
1.3:1 1.7% 98.3% 98.3
1.4:1 2.8% 97.2% 97.2
1.5:1 4.0% 96.0% 96
1.6:1 5.3% 94.7% 94.7
1.7:1 6.7% 93.3% 93.3
1.8:1 8.2% 91.8% 91.8
2.0:1 11.1% 88.9% 88.9
2.2:1 14.1% 85.9% 85.9
2.4:1 17.0% 83.0% 83
2.6:1 19.8% 80.2% 80.2
3.0:1 25.0% 75.0% 75
4.0:1 36.0% 64.0% 64
5.0:1 44.4% 55.6% 55.6
6.0:1 51.0% 49.0% 49
7.0:1 56.3% 43.8% 43.8
8.0:1 60.5% 39.5% 39.5
9.0:1 64.0% 36.0% 36
10.0:1 66.9% 33.1% 33.1

You can easily calculate your own loss, based on your radio's power output.  Simply take your output power, and multiply it by the ERP percentage in the chart above, based on your SWR reading.  For Example:

If I have a radio I know puts out 35 watts, and my measured SWR is 1.3, looking at the chart above, a 1.3:1 reading means I am radiating at 98.3% efficiency.  So, 35 watts, multiplied by .983 (the percentage) results in 34.4 watts of effective radiated power.  Keep in mind, this is a simple calculation that does NOT take into account an antenna with gain, or coax loss. This if simplistic for a unity gain antenna and short coax run.  If you wish to calculate further, subtract the coax loss from the power out, then add any gain you have from the antenna for true Effective Radiated Power. (ERP)

AI4JI
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