On Thu, 17 Apr 2008 09:46:55 -0500
Cecil Moore wrote:

Roger Sparks wrote:
"A third way is to allow the energy to be stored in constructive
and destructive interference SOME PLACE IN THE SYSTEM." In this
quote, I capitalized "SOME PLACE IN THE SYSTEM" because we need
to understand where interference is located.

Actually, all we need to realize is that, in a
distributed network, the current through the source
is NOT equal to the current being provided by the
source. It is the source current superposed with
reflected current and re-reflected current. The fact
that the *NET* power is negative is NOT because the
source is sinking power. It is caused by the other
"sources" of energy in the system, i.e. the energy
in the reflected waves.

Yes, in nature the returning power will affect the frequency of the source. The ideal voltage source absorbs the reflected power rather than allowing a change in frequency.

Are you expecting additional reflections?

Once steady-state is reached, the magnitude of the
reflections are also steady-state. The total energy
flowing toward the load is the forward energy. The
total energy flowing in the other direction is the
reflected energy. Both of those magnitudes are fixed
during steady-state.

I have asked multiple times that this simple mental
experiment be performed and my request has been ignored.

Please install an ideal 50 ohm directional wattmeter
at point 'x' and tell us what are those readings
for forward power and reflected power.

GND--Vs--x--Rs--------45deg 50 ohm----short
100v 50ohm

Once the forward and reverse energy flows at point
'x' are understood, it will become clear that all
of the net current through the source is NOT being
provided by the source. That the source is sinking
energy is an illusion caused by reflections.

This circuit has an impedance of 73.5 + J44.1 ohms at the point x. Energy sinking into the source occurs during the cycle. It is not an illusion.

Think of things this way. Any signal must contain energy. A signal without energy is not a signal. Nature must have some method of signaling between source and load when the load does not match the impedance of power flow. This is simple logic based on the known fact that the apparent impedance of a transmission line depends upon the load at the end of the transmission line.

Power returning to the source is the signal nature requires to throttle the output of the source. Power returning to the source will change the frequency of the source in nature, but in our ideal voltage source, nature is suspended and the frequency is held constant. Our problem as engineers is to isolate each effect and to make valid predictions so that we can build more intelligently.
--
73, Roger, W7WKB