Richard Clark wrote:
Two energies pass without interaction unless there is a load.

The exception to that statement is two coherent waves
traveling an identical path in the same direction. If
the two waves are of equal magnitudes and opposite phases,
they cancel completely in their original direction of
travel. In a transmission line, their combined energy
components reverse direction in order to satisfy the
conservation of energy principle. In the absence of
any additional sources or loads, destructive interference
energy must exactly equal constructive interference energy.

The above can occur at a lossless impedance discontinuity
in a transmission line - no load required.

Power is the summation of all energies into a load.

Often power is simply the joules/sec existing at a unit-
area plane or passing a point on a transmission line. The
power-flow (Poynting) vector doesn't require a load. All
it requires is an EM wave.
--
73, Cecil, http://www.qsl.net/w5dxp

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