Jim Kelley wrote in message ...
Ur right, thanks Dave. I meant to say voltage rather than power. Let
me ask the question properly.

Tom,
Since rho represents the fraction of forward voltage that is reflected,
what does a negative value for rho indicate?

Jim,

I suppose your question has been answered sufficiently (Thanks, Roy,
Cecil and Tam), but I'd like to offer a bit different viewpoint than
is implied by your "fraction that is reflected."

I prefer to think of it not as "a fraction that's reflected" but
rather as a resolution of a particular voltage and current into two
modes. There are two modes of propagation supported by TEM line, one
in each direction along the line. If you excite a line to
steady-state at one frequency, there will be some sinusoidal current
at each point along the line, and some sinusoidal voltage across the
line at each point along its length. (You can have a load at one end
and a source at the other, or two sources each with its own internal
impedance, one at each end, so long as they are on the same
frequency.) That set of voltages and currents can be resolved
mathematically into two components, one corresponding to the mode of
propagation in one direction and one corresponding to the mode in the
other direction. Rho is simply a number representing that resolution
at the point on the line where that rho is measured (or calculated).
It's a complex number because it represents both phase and amplitude.

(Note that our resolution of measured voltage and current into the two
modes generally assumes that we know the line's Zo, and the degree to
which we don't know that will introduce an error in our determination
of rho. But that's a whole 'nuther topic...)

Cheers,
Tom