Alan Peake wrote:

Owen Duffy wrote:
But is it possible to inject two coherent waves travelling
independently in the same direction?

In a transmission line? Wouldn't they both have the same propagation
velocity? If so, how would you distinguish between them?

They become indistinguishable, i.e. they interact. If they
interact destructively, they give up energy to constructive
interference in the opposite direction. If they interact
constructively, they require destructive interference
energy from the opposite direction. In a transmission line,
interference is one-dimensional.
--
73, Cecil http://www.w5dxp.com