On Tue, 15 Apr 2008 01:22:11 GMT
Cecil Moore wrote:

Roger Sparks wrote:
I offered the examples of two real sources that will absorb
power when the returning voltage exceeds the output voltage
(a battery and a generator turned into a motor). I think that
we must allow our voltage source to have that same real property.

A battery converts electrical energy to chemical energy, i.e.
it transforms the electrical energy. A motor converts electrical
energy into physical work, i.e. it transforms the electrical
energy. An ideal source does not dissipate power and there is
no mechanism for storing energy. It seems what you are objecting
to is the artificial separation of Vs and Rs.

No, the separation of Vs and Rs was made to better understand why no interference would occur in Figure 1-1. found at http://www.w5dxp.com/nointfr.htm.

Here is a quote from Part 1.
"4. Since the transmission line is 1/8 wavelength (45 degrees) long and the load is purely resistive, the reflected wave incident upon the source resistor will be 2(45) = 90 degrees out of phase with the forward wave at the source resistor. This is the necessary and sufficient condition to produce zero interference at the source resistor."

The problem is that the source and reflected waves behave as two power sources out of time by 90 degrees. As a result, the current flows as the result of two sine waves, and can be described by only one sine wave. The one sine wave description necessarily shows that power *does* flow into the source during part of the cycle. Interference techniques are used to combine the two sine waves into one wave so it would appear that statement 4 is incorrect.

I do understand that when we allow the source to receive
power, then we need to address source impedance.

The series source impedance is zero. It acts like a short
circuit to reflections, i.e. there are no reflections.
However, there seem to be 100% reflection from the GND on
the other side of the source.

It is not the reflections from the source that is the root of the problem. The root is the way two sine waves combine into one wave that runs at a third phase compared to either of the source waves.

Does the idea of source receiving power run counter to what
you were planning to write in Parts 2 and 3?

The source will be shown to adjust its output until an
energy balance is achieved. It will throttle back when
destructive interference occurs at the source resistor
and will gear up when constructive interference requires
more energy.

I am trying to
understand why you have such great reluctance to accept that
the source could receive power for part of a cycle, especially
when it could easily bring the instantaneous power and energy
calculations into balance.

There is no known mechanism that would allow an ideal
source to dissipate or store energy. Consider that the
energy you see flowing back into the source is reflected
back through the source by the ground on the other side
and becomes part of the forward wave out of the source.
That would satisfy the distributed network model and
explain why interference exists in the source.

I can understand a voltage source that throttles up and down but I can't understand why the throttle all has to be on the plus side. What logic prevents the power from returning to the ideal source from whence it just left?

Our real limit is that only one current can flow for only one voltage for each instant at any place in the circuit. This is how we justify a "one sine wave" description. It is why whenever we have a reflection, we also have interference. It is also the reason that we must have power flowing back into the source for part of the cycle.
--
73, Roger, W7WKB