Revisiting the Power Explanation
 

Cecil Moore wrote:
Keith Dysart wrote:
Consider the 75 Ohm resistor at the right hand end of a 75 Ohm
transmission line. The load is matched to the line and there
is no discontinuity and (dare I say it?) no reflection.

Yet that violates the convention that reflected energy
absorbed by the source was never sourced. Why do you
think that convention was adopted in the first place?

I may have misread Keith's posting. I thought we were
talking about sources. Is the above posting about a
75 ohm load devoid of any source?

Consider a 75 ohm load resistor terminating a 75 ohm
transmission line. There are no reflections and the
system is called "flat". Now add a source at that
load end. There will indeed be both forward and reverse
traveling waves.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

On Apr 5, 9:37 am, Cecil Moore wrote:
Cecil Moore wrote:
Keith Dysart wrote:
Consider the 75 Ohm resistor at the right hand end of a 75 Ohm
transmission line. The load is matched to the line and there
is no discontinuity and (dare I say it?) no reflection.

Yet that violates the convention that reflected energy
absorbed by the source was never sourced. Why do you
think that convention was adopted in the first place?

I may have misread Keith's posting. I thought we were
talking about sources. Is the above posting about a
75 ohm load devoid of any source?

Consider a 75 ohm load resistor terminating a 75 ohm
transmission line. There are no reflections and the
system is called "flat". Now add a source at that
load end. There will indeed be both forward and reverse
traveling waves.

Yes indeed. And the beautiful part is that you can use
superposition to analyze the two directions independantly.

The forward wave reaches the 75 Ohm termination and there
is no reflection. The reverse wave leaves the 75 Ohm generator
and heads down the line.

The total response at any point on the line is the sum of
the two waves at the desired instant at that point.

This works in all cases:
- The waves can have differing phases.
- The waves can have different frequencies.
- The signals do not have to be sinusoids. It works for all
waveshapes: step, square, pulse, you name it.
- The signals don't need to have the same waveshape, though
the arithmetic becomes quite tedious for complex wave
shapes.

The generality is astounding.

Of course sticking to steady state sinusoids at a single
frequency does offer useful simplifications such as 'effective
impedance', 'forward power' and 'reverse power', but care must
be taken with their application since they are not part of
the general solution.

....Keith

Revisiting the Power Explanation
 

On Thu, 05 Apr 2007 13:00:31 GMT, Cecil Moore
wrote:

When I find myself in an error, Richard, I correct it.

Yourself, or the error? Yes, once again your style shows.

Revisiting the Power Explanation
 

Keith Dysart wrote:
The total response at any point on the line is the sum of
the two waves at the desired instant at that point.

True for any *passive* point on the line. Apparently
not true at the heart of a dynamic active source which
is easy to prove on the bench. Seems to me that based
on real-world bench experiments, we must conclude that
the principle of superposition doesn't apply to sources
because the act of applying DC power to the source
changes the configuration of the system which is a
violation of the principle of superposition rules.
Ramo and Whinnery warn us about attaching any real-
world significance to the power dissipation in an
equivalent source.

Obviously, if any system conditions change when power is
applied the basic rules for the superposition principle
have been violated.

Hopefully, you are beginning to understand why the
convention of 100% rejection of reflected energy
by the source was adopted.
--
73, Cecil, w5dxp.com

Revisiting the Power Explanation
 

On Thu, 05 Apr 2007 11:30:59 -0500, Cecil Moore
wrote:

we must conclude that
the principle of superposition doesn't apply to sources
because the act of applying DC power to the source
changes the configuration of the system which is a
violation of the principle of superposition rules.

.... a variation on "yet it moves" as superposition rules explicitly
state how sources are to be treated.

So much for value in the mea culpas, appologies, admissions and
explanations for errors - paid (in debased coin) to the victims of
accuracy.

Revisiting the Power Explanation
 

Richard Clark wrote:
... a variation on "yet it moves" as superposition rules explicitly
state how sources are to be treated.

But since it leads to a contradiction as far as energy
goes, it must be in error. The raging inferno that is
the source is apparently not transparent to waves traveling
in the opposite direction.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

On Thu, 05 Apr 2007 23:13:15 GMT, Cecil Moore
wrote:

Richard Clark wrote:
... a variation on "yet it moves" as superposition rules explicitly
state how sources are to be treated.

But since it leads to a contradiction as far as energy
goes, it must be in error.

Superposition is in contradiction to superposition and is in error!
....classic fulfillment of your hackneyed quote of Galileo. Any fires
of purgation you may feel for not accepting Keith's explanation for
(what you call) sources is your own sin - you may as well condemn the
Church (in a muttering whisper, of course) and go back to your cell of
righteousness.

Revisiting the Power Explanation
 

Richard Clark wrote:
Superposition is in contradiction to superposition and is in error!

It should be easy to prove. Hook up two IC-706's in
series driving a 50 ohm dummy load. Install some
feedback to make them coherent. Turn one off and
one on. Then turn the other off and the other on.
Then turn them both on. Do they satisfy the
principle of superposition?
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

On Apr 5, 12:30 pm, Cecil Moore wrote:
Keith Dysart wrote:
The total response at any point on the line is the sum of
the two waves at the desired instant at that point.

True for any *passive* point on the line. Apparently
not true at the heart of a dynamic active source which
is easy to prove on the bench. Seems to me that based
on real-world bench experiments, we must conclude that
the principle of superposition doesn't apply to sources
because the act of applying DC power to the source
changes the configuration of the system which is a
violation of the principle of superposition rules.
Ramo and Whinnery warn us about attaching any real-
world significance to the power dissipation in an
equivalent source.

Obviously, if any system conditions change when power is
applied the basic rules for the superposition principle
have been violated.

Firstly, the principle of conservation of energy always holds.
I don't think anyone has ever disputed that.

Secondly, about superposition. A sufficient condition for
superposition to hold is that all the components are linear
and time-invariant. Examining the ideal transmission lines
used in our simple examples, this is true and superposition
holds on the transmission line. This is also true for the
components in our simple generators so superposition holds
there as well. And it holds for the system consisting of the
generator and the transmission line.

But as I understand, you have done some analysis which brings
superposition into conflict with conservation of energy and
you have concluded that one of them must be wrong. (And having
had strong success with conservation of energy, you have
chosen superposition to be wrong.)

But there is a third choice. Perhaps there is an error in the
way that you have connected the dots between superposition
and conservation of energy. Perhaps, as a result, superposition
and conservation of energy are not in conflict at all.

And this is indeed the case. Since both are true, the error must
be in how the dots are connected.

I suggest you carefully examine the chain of logic that causes
you to conclude that they disagree. That is the path to resolving
the contradiction.

If you would care to lay out the chain that connects the dots, I
would be happy to attempt to help with locating the misstep.

....Keith

Revisiting the Power Explanation
 

Keith Dysart wrote:
This is also true for the
components in our simple generators so superposition holds
there as well.

I've asked Richard how to hook up two IC-706's in
series to get them to meet the requirements of
the superposition principle. Maybe you can show
us how to do it.
--
73, Cecil http://www.w5dxp.com