Cecil, W5DXP wrote:
"Reg, you have a black box in the middle of a transmission line with a
high SWR. You measure the current into the box and out of the box, You
measure 1 amp into the box and out of the box, You measure 1 amp and 0
degrees going in and 1 amp at 180 degrees going out. This means that
both currents are flowing into the box at the same time. There is no
third wire. What`s in the box?"

A phase inverter.

You could have a center-tapped coil in the box. One end and the center
could take the input. The other end and the center could provide an
output 180-degrees out of phase with the input.

This requires a minimum of three terminals but only 2 wires in and 2
wires out. If 2 directions of travel are allowed on a pair, an open or a
short reverses the direction (phase) of the reflected wave.

Best regards, Richard Harrison, KB5WZI