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Actual vs. apparent s.w.r.

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Technical Editor, QST:
The following is an easy way of getting the true s.w.r. at the load. This information can be gotten from the Smith Chart, but the method below is easier.

Eq 1

For K' see the accompanying graph.

Fig 1
Fig. 1. Graph used in determining the relationship between s.w.r. measured at the transmitter and true s.w.r. at the load, when line losses are appreciable (W9GBD).

Example: Matched line loss = 2 dB and SWR = 3

Eq 2

From the graph, K' = 1.6 (K) = (1.6) (0.5) = 0.8.

Eq 3

The value at which K' = 1 corresponds to the s.w.r. (read at the transmitter) with line shorted. Values of K' greater than 1 have no meaning, since higher readings are not possible.

Bob Gold, W9GBD.