Richard Harrison wrote:
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.

Yep, that's one answer. Another answer is a piece of low-loss transmission
line that shifts the phase by 180 degrees, i.e. 1/2WL of transmission line.

Point is that unequal currents at the input and output of a black box are
easy to achieve and do not violate Kirchhoff's laws. Although physically
small, this black box does not meet the definition of a lumped circuit.

A bugcatcher coil on a 75m mobile antenna also does not meet the
definition of a lumped circuit.
--
73, Cecil http://www.qsl.net/w5dxp



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