Reg Edwards wrote:
You can't measure SWR on a line which is less than 1/4-wave long.

Because your measurements are taken 1/4WL apart, your SWR value
will be in error for all feedlines except lossless ones.

SWR can be had at any point on a transmission line.
Measure the forward power and reflected power at any point.
SWR = [SQRT(Pfor)+SQRT(Pref)]/[SQRT(Pfor)-SQRT(Pref)]

The transmission line length must only be long enough such that
the V/I ratio is forced to the Z0 value. According to some pretty
smart guys I asked, that's about 2% of a wavelength.
--
73, Cecil http://www.qsl.net/w5dxp