If a feeder has a characteristic impedance differ compare to the load a part of RF power going from the transmitter in the feeder is reflected from the load back to the transmitter. In this case the load uses a part of RF power of the transmitter. Table 1 shows the losses of RF power when a feeder has SWR.

By Igor Grigorov, RK3ZK

Note: A mismatch of a transmitter's output impedance to the feeder's characteristic impedance does not cause a SWR mode if the antenna (load) is matched to the feeder's characteristic impedance.

SWR in the Feeder	Losses at Reflection from the Load, %	RF Power going to the load from the transmitter, %	Losses at Reflection from the Load, dB
1:1.0	0.00	100.0	0.00
1:1.1	0.23	99.8	-0.01
1:1.2	0.83	99.2	-0.04
1:1.3	1.7	98.3	-0.08
1:1.4	2.78	97.2	-0.12
1:1.5	4.0	96.0	-0.18
1:1.6	5.33	94.5	-0.25
1:1.7	6.72	93.7	-0.28
1:1.8	8.16	91.8	-0.37
1:1.9	9.63	90.4	-0.44
1.2.0	11.1	88.9	-0.51
1:2.2	14.1	85.9	-0.66
1:2.4	17.0	83.0	-0.81
1:2.6	19.8	80.2	-0.96
1:2.8	22.4	77.6	-1.10
1:3.0	25.0	75.0	-1.25
1:3.5	30.9	69.1	-1.61
1:4.0	36.0	64.0	-1.94
1:5.0	44.4	55.6	-2.55
1:7.0	56.3	43.7	-3.6
1:10	67.0	33.0	-4.81
1:20	81.9	18.1	-7.42
1:50	92.3	7.7	-11.10

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