Gene Fuller wrote:
All we need now is that you also understand that waves flowing in the
SAME direction do NOT interact unless there is an interface or other
discontinuity.

Please stop implying things that I have never said. When I
asserted that reflections only happen at a physical impedance
discontinuity, that implies that interaction can only happen
at a physical impedance discontinuity. It is impossible to
get two coherent waves flowing in the same direction except
at a physical impedance discontinuity.

Assume b1 = s11(a1) + a12(s2) = 0

What I have said is that s11(a1) and s12(a2) are wave components
that cancel without ever being incident upon an impedance discontinuity.
Those two wave components originate at the impedance discontinuity
flowing *AWAY FROM* the impedance discontinuity. They are canceled
in a delta-t, i.e. a very short time. Those two waves are the result
of interaction at the impedance discontinuity but neither of them
ever interacted with the impedance discontinuity because they
originated at the impedance discontinuity.
--
73, Cecil, w5dxp.com