Standing-Wave Current vs Traveling-Wave Current
 

On Mon, 31 Dec 2007 05:42:16 -0800, Roger wrote:

Several responders discussed the Norton or Thévenin equivalent circuits.
These circuits assume steady state conditions, and are intended to be
replacements for groups of components. A very useful concept, but not
appropriate for startup excitation of a transmission line unless the
intent was to investigate the source AND transmission line as a system.

Hi Roger,

Quite a bizarre stance. Do you regularly come to these points of view
without further thought, elaboration, or analysis? It seems you have
assigned some remarkable characteristics to the Norton and Thevenin
source and you don't offer us anything substantive beyond what would
be called "Arthur's proposition."

To cut to the chase, Norton and Thevenin sources are appropriate to
network analysis irrespective of your perception. You should look
closer at your issues of difficulty because it does not reside in
their classic application to classic situations.

More later. I as still thinking about the "perfect power source".

That's fine, but it is now turning into a mantra rather than a
productive examination. You would do well to spill your guts as to
why you commit so much of the calendar to this thought. Alone, it is
as meaningful as announcing that one is thinking about "cold fusion."

73's
Richard Clark, KB7QHC

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
Cecil Moore wrote:
Lots of energy is flowing in both directions.
Only the *NET* energy flow is zero.

I guess you still have not gone back to the books to try to understand
what electromagnetic energy is all about. A good review of the Poynting
theorem would help to minimize the sort of nonsense you spouted above.

You mean like Ramo & Whinnery in "Fields and Waves ..."
2nd edition, page 291? (begin quote)

In such problems we are often most interested in the ratio
of power in the reflected wave to that in the incident wave,
and this ratio is given by the square of the magnitude of
[rho], as can be shown by considering the Poynting vectors:

Pz-/Pz+ = |rho|^2

end quote.

Pz+ is the forward power Poynting vector. Pz- is the reflected
power Poynting vector. The *NET* Poynting vector is the
difference between those two Poynting vectors.

If Pz+ = Pz-, then the net Poynting vector is zero but
the component Poynting vectors still exist. If you disagree,
please take it up with Ramo & Whinnery.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
It is interesting that you ridicule zero impedance ideal sources, and
then you provide an example with a circulator. Do you really think a
circulator is more ideal than a good voltage source?

If models alleviate ignorance, they are good.
If models promote ignorance, they are bad.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Richard Clark wrote:
To cut to the chase, Norton and Thevenin sources are appropriate to
network analysis irrespective of your perception.

All my references indicate that those sources are only
appropriate for *steady-state* use. Roger is searching
for a transient state source.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Roger wrote:
The problem is that "We want to investigate a 1/2 wave length of
transmission line, excited at one end. How soon is stability reached?"

I guess the answer depends upon your definition of
"stability" above.

You might start with a loaded version:

http://www.w5dxp.com/1secsgat.gif

Yes, this is the idea, exactly.

The loaded version is much more complicated than the unloaded version.

Stability is always reached provided power input contains a maximum.

73, Roger, W7WKB

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Richard Clark wrote:
To cut to the chase, Norton and Thevenin sources are appropriate to
network analysis irrespective of your perception.

All my references indicate that those sources are only
appropriate for *steady-state* use. Roger is searching
for a transient state source.

Right!

73, Roger, W7WKB

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
Cecil Moore wrote:
Lots of energy is flowing in both directions.
Only the *NET* energy flow is zero.

I guess you still have not gone back to the books to try to understand
what electromagnetic energy is all about. A good review of the Poynting
theorem would help to minimize the sort of nonsense you spouted above.

Another example from HP's AN 95-1

b1 = s11*a1 + s12*a2 b2 = s21*a1 + s22*a2

Z01 Z02
-------------+-------------
Pfor1--|--Pfor2
Pref1--|--Pref2

|a1|^2 = Pfor1 |b2|^2 = Pfor2
|b1|^2 = Pref1 |a2|^2 = Pref2
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
The loaded version is much more complicated than the unloaded version.

The problem is that with the unloaded version, an ideal
autotuner might have trouble achieving a 50 ohm match
to an infinite impedance. :-)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Gene Fuller wrote:
Cecil Moore wrote:
Lots of energy is flowing in both directions.
Only the *NET* energy flow is zero.

I guess you still have not gone back to the books to try to understand
what electromagnetic energy is all about. A good review of the
Poynting theorem would help to minimize the sort of nonsense you
spouted above.

You mean like Ramo & Whinnery in "Fields and Waves ..."
2nd edition, page 291? (begin quote)

In such problems we are often most interested in the ratio
of power in the reflected wave to that in the incident wave,
and this ratio is given by the square of the magnitude of
[rho], as can be shown by considering the Poynting vectors:

Pz-/Pz+ = |rho|^2

end quote.

Pz+ is the forward power Poynting vector. Pz- is the reflected
power Poynting vector. The *NET* Poynting vector is the
difference between those two Poynting vectors.

If Pz+ = Pz-, then the net Poynting vector is zero but
the component Poynting vectors still exist. If you disagree,
please take it up with Ramo & Whinnery.

Cecil,

As usual, you have taken something generally accepted as true, and then
you have added your own special spin. You might have noticed that Ramo &
Whinnery did not go into all of the "net" baloney, and neither did HP in
AN-95. That stuff is only in your imagination.

The last I heard, energy is a scalar quantity. In the cases we are
considering, energy is only positive or zero, not negative. How do two
non-negative scalar quantities "flow" past each other, adding up to a
"net" of zero, unless the initial quantities themselves are zero?

I agree that the concepts included in R&W and in AN-95 are widely used.
However, they were never intended to be distorted into your dream world.

The bouncing traveling wave model is an extremely useful mathematical
device. It does not trump physical reality.

73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
As usual, you have taken something generally accepted as true, and then
you have added your own special spin. You might have noticed that Ramo &
Whinnery did not go into all of the "net" baloney, and neither did HP in
AN-95. That stuff is only in your imagination.

Translation: I don't have the balls to argue with
Ramo & Whinnery and HP over issues that are more than
obvious to any casual initiated observer.

The last I heard, energy is a scalar quantity. In the cases we are
considering, energy is only positive or zero, not negative.

As you well know, the convention is to apply a negative
sign to positive energy flowing in the opposite direction
from the "forward" energy which is arbitrarily assigned
a plus sign. When Ramo & Whinnery say, using Poynting
vectors, that Pz(net) = Pz+ - Pz-, they are not implying
negative power. They are just using the Poynting vector
convention of direction of energy flow in a transmission
line. We are saying the same thing when we say:

P(load) = P(forward) - P(reflected) = P(net)

Transmission lines have the advantage of having only two
directions so '+' can be assigned to one direction and
'-' assigned to the other. It is completely arbitrary -
the signs can be swapped and the results remain the same.

I agree that the concepts included in R&W and in AN-95 are widely used.
However, they were never intended to be distorted into your dream world.

See "Translation" above.
--
73, Cecil http://www.w5dxp.com