"Reg Edwards" :
SWR is the dimensionless ratio of two voltages, a maximum and a
minimum, which may be measured along a transmission line,
spaced apart by 1/4-wavelength of line.
It is fully described without reference to line impedance, source
impedance, terminating impedance, line length, or where the max and
min volts are located.
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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.

RF