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

I wasn't talking about my article. I was talking about Vs & Rs
models in general. In the real world, Vs is not separated from
Rs. That only occurs in the ideal model. In the ideal model,
all dissipation is confined to Rs and there is none in Vs.

The problem is that the source and reflected waves behave as
two power sources out of time by 90 degrees.

Not quite correct. The problem is that the forward waves
and reflected waves flowing through the source behave as
two power sources out of time by 90 degrees. The source
wave is the net superposition of the forward wave and
reflected wave. An ideal 50 ohm directional wattmeter
in the circuit will not read the source power. It will
read a forward power which is a different magnitude
than the source power. In any case, only Rs and RL
dissipate power in the system.

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.

It is not all on the plus side. Whatever energy flows, flows.
Sometimes the flow is forward and sometimes it is backwards.
That's the way AC works. If destructive interference is
present, the source reduces its output power. If constructive
interference is present, the source increases its output
power. But the ideal source does not dissipate power, i.e.
doesn't heat up. All of the heat generated in the entire
system comes from Rs and RL.

Our real limit is that only one current can flow for only one
voltage for each instant at any place in the circuit.

You are, of course, talking about the *net* voltage and the
*net* current after superposition of all the components. But
this discussion is not about net voltage and net current.

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.

I don't know where you got the idea that energy doesn't
flow back into the source for part of the cycle. Since
it is AC, it does flow forward and backward but none is
dissipated, i.e. none is turned into heat in an ideal
source. An equal amount of destructive and constructive
interference occurs during each complete cycle.
--
73, Cecil http://www.w5dxp.com