Richard Fry wrote:
SWR may be calculated as (A+B)/(A-B), where A & B are square roots of
expressions containing both the complex load impedance, and the
reference impedance against which the SWR is referred.

I have an EXCEL spreadsheet that calculates SWR seven different
ways, if I remember correctly.
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73, Cecil http://www.qsl.net/w5dxp