Reg Edwards wrote:
There is a bridge configuration which is not quite so obvious. But
instead of a current transformer the current is picked off by means of
a short length of wire in parallel with the coaxial inner conductor by
virtue of their mutual inductance. The line is too short for
propagation effects to play a significant part.

The pickup lines in my Heathkit HM-15 are terminated on one
end with a 50 ohm resistor. One pickup line thus attenuates
the reflected traveling wave and allows the forward traveling
wave to be rectified. The other pickup line attenuates the
forward traveling wave and allows the reflected traveling wave
to be rectified. Knowing the peak values of both of these two
traveling waves allows a calibrated meter to indicate SWR.
--
73, Cecil http://www.qsl.net/w5dxp