Gene Fuller wrote:
Cecil Moore wrote:
Gene Fuller wrote:
Waves are useful. However, they are not living objects. They have no
will to survive. There is nothing in the standard E&M science based
on Maxwell's laws that requires waves to be "canceled" if they no
longer exist. There is no conservation law of wave-ality.

All EM waves must obey the conservation of energy and
conservation of momentum principles. It is not a will
to survive - it is simply the laws of physics.

Here is an example for you to explain. The source is
a signal generator equipped with an ideal circulator
and a load resistor:

Steady-state #1: Rho at '+' equals 0.7143. Load equals
300 ohms.

100w SGCL--50 ohm feedline--+--1/2WL 300 ohm feedline--300 ohm load
Pfor1=100w-- Pfor2=49w--
--Pref1=51w --Pref2=0w

Pref1 is an 51w EM wave whose energy and momentum must be
conserved.

Steady-state #2: Rho at '+' equals 0.7143. Load is switched
to 50 ohms.

100w SGCL--50 ohm feedline--+--1/2WL 300 ohm feedline--50 ohm load
Pfor1=100w-- Pfor2=204W--
--Pref1=0w --Pref2=104w

*Note that Rho has NOT changed!*

The only question that you need to answer is during the
process that changes Pref1 from 51 joules/sec in the direction
of the source to 0 joules/sec (canceled), *exactly* what happens
to the energy and momentum? Please be specific.

You first.

Cop out. Why am I not surprised that you, yet once again, refuse
to answer the question? Could it be because you would immediately
be proven wrong? Do you really believe that diversions are a tool
of technical knowledge?

The original 51 joule/sec reflected wave toward the source interacts
with the newly reflected wave from the load and is partially
canceled which through constructive interference, delivers more
forward power toward the load, which results in an increase in the
energy in the reflected wave from the load, which results in more
wave cancellation at '+', etc. until steady-state #2 is reached.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:


Cop out. Why am I not surprised that you, yet once again, refuse
to answer the question? Could it be because you would immediately
be proven wrong? Do you really believe that diversions are a tool
of technical knowledge?

The original 51 joule/sec reflected wave toward the source interacts
with the newly reflected wave from the load and is partially
canceled which through constructive interference, delivers more
forward power toward the load, which results in an increase in the
energy in the reflected wave from the load, which results in more
wave cancellation at '+', etc. until steady-state #2 is reached.

Blah, Blah, Blah. Totally useless drivel. Let's see some real numbers.
Then we can discuss cop out.

You might also check your favorite reference to try to figure out what
conservation of energy really means. Then you would realize that even a
full solution to your idealized problem would demonstrate absolutely
nothing with respect to conservation of energy.

73,
Gene
W4SZ

Gene Fuller wrote:
Cecil Moore wrote:
Cop out. Why am I not surprised that you, yet once again, refuse
to answer the question? Could it be because you would immediately
be proven wrong? Do you really believe that diversions are a tool
of technical knowledge?

The original 51 joule/sec reflected wave toward the source interacts
with the newly reflected wave from the load and is partially
canceled which through constructive interference, delivers more
forward power toward the load, which results in an increase in the
energy in the reflected wave from the load, which results in more
wave cancellation at '+', etc. until steady-state #2 is reached.

Blah, Blah, Blah. Totally useless drivel. Let's see some real numbers.
Then we can discuss cop out.

In the words of the biggest cop out artist I know, "You first".
I've already posted the numbers for the graphic at:
http://www.w5dxp.com/thinfilm.gif

Instead of responding, you tucked tail and ran.

You might also check your favorite reference to try to figure out what
conservation of energy really means. Then you would realize that even a
full solution to your idealized problem would demonstrate absolutely
nothing with respect to conservation of energy.

That's exactly the problem. Lots of people pay lip service to
the conservation of energy principle without realizing they
advocate violation of it.
--
73, Cecil http://www.w5dxp.com

Gene Fuller wrote:
Let's see some real numbers.

The numbers are trivial. What is important is the concept.
In the experiment, the Pref1 wave disappears between
steady-state #1 and steady-state #2. Here's the question
that you and others have refused to answer.

When an EM wave disappears in its original direction of
travel, what happens to its energy?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
Let's see some real numbers.

The numbers are trivial. What is important is the concept.
In the experiment, the Pref1 wave disappears between
steady-state #1 and steady-state #2. Here's the question
that you and others have refused to answer.

When an EM wave disappears in its original direction of
travel, what happens to its energy?

OK, but first let's set the ground rules.

The ONLY thing under discussion here is our disagreement about the
canceling waves heading back toward the source from the match point. You
claim those waves must exist and then cancel over a short distance (I
believe you reduced the distance to 'dx' or something similar.) I claim
those waves never exist at all and therefore don't need to be canceled.

If you have anything else in mind, then enjoy your solo activity,
whatever that might be.

So just what "trivial" numbers are required?

First, it is not clear how one make an instant transition from a 50 ohm
environment to a 300 ohm environment. Do you just connect a 50 ohm coax
to a 300 ohm coax? Or do you prefer to connect a 50 ohm twin-lead to a
300 ohm twin-lead? (Good luck with either of these.) If you want to
connect a 50 ohm coax to a 300 ohm twin-lead then you are going to need
some sort of transition device.

Oops! Where is the match point now? Ordinarily we would not really care
very much about such things, but you have stated that important things
are happening within the "dx" zone. It is a safe bet that the Z0
transition is not abrupt either. The "trivial" numbers just got a bit
more complicated.

Let's look at the conservation of energy part. You like to use the
Poynting vector, so we can stick with that. The first thing to note is
that the Poynting vector is E x H, not V x I. Perhaps only a minor bump
in the road, but the transition from E to V and H to I is not quite so
trivial at discontinuities such as the "match point".

But let's muddle ahead in any case. The integral form of the Poynting
theorem goes like the following.

* Define a test volume with a closed surface. There is no particular
size required, although infinite and zero don't work well for practical
reasons.

* Calculate the Poynting vector at all points on the closed surface.

* Integrate the 'normal' component of the Poynting vector over the
entire surface. This integral then represents the net electromagnetic
energy flowing into (or out of) the test volume. I believe this is what
you would consider the energy carried by the waves of interest. Note
that all waves are combined together; they are not treated separately.

* The Poynting theorem says that the net energy flow must be balanced by
the change in electromagnetic energy content within the test volume and
the work done by the fields on any charges within the test volume.

* Note that a change in field strength within the test volume is tied to
the change in electromagnetic energy content. Any charges within the
test volume can be accelerated. Remember, this sort of match point
cannot exist in free space, so there are charges in the region of interest.


This sort of description and the associated derivations can be found in
any ordinary E&M textbook.


You might notice that the Poynting theorem, i.e. conservation of energy
law for EM, says nothing about the sanctity of waves or about the
conservation of energy in waves. It does not say that the integral of
the Poynting vector over the test volume surface must be zero.

Even more importantly for this discussion, the Poynting theorem does not
help at all with your assertion that important things are happening in
the 'dx' zone. If you make the test volume size smaller than your 'dx'
then you run into trouble with the finite size of the transition region
described above. If you make the test volume large enough to contain the
'dx', then all of the purported interesting stuff happens inside. Again,
the Poynting theorem tells nothing.


If you want to believe in the conservation of waves, go right ahead.
Just don't expect conservation of energy to support your case.
Mathematically it cannot.


73,
Gene
W4SZ

this thread is still going?!?!? geez, how far has it evolved? maybe i
should bypass all my plonks and see who is still argueing in here and about
what? but why bother, its probably mostly the same ole arguments about
waves, reflections, conservation of this and that, and obviously by most of
the same old contributers that i have mostly blocked. why don't you guys
just go back and take fields and waves 101, it would save you all a lot of
time and energy.

Gene Fuller wrote:

I'm going to ignore your hodge-podge of obfuscations and
concentrate on only one point.

The ONLY thing under discussion here is our disagreement about the
canceling waves heading back toward the source from the match point. You
claim those waves must exist and then cancel over a short distance (I
believe you reduced the distance to 'dx' or something similar.) I claim
those waves never exist at all and therefore don't need to be canceled.

You say a physical impedance discontinuity can exist without
reflecting waves (in violation of the laws of physics). Please
explain how a physical impedance discontinuity can avoid
reflecting the incident wave.

A 70.7 volt EM wave is incident upon an impedance discontinuity
with a reflection coefficient of 0.7143 at point '+'. Exactly
how does that forward wave avoid being partially reflected from
the Rho=0.7143 impedance discontinuity at point '+'?

Here's the circuit:

SGCL---50 ohm T-line---+---1/2WL 300 ohm T-line---50 ohm load
Pfor1=100w--

Why are there no reflections at point '+' where the physical
reflection coefficient is 0.7143? Gene's Magic at work?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:


You say a physical impedance discontinuity can exist without
reflecting waves (in violation of the laws of physics). Please
explain how a physical impedance discontinuity can avoid
reflecting the incident wave.

Did I say that?

Strange, I don't remember any discussion at all along that line.

Since we are annoying "Dave" (whoever he is), I will stop now.

73,
Gene
W4SZ

Gene Fuller wrote:
Cecil Moore wrote:
You say a physical impedance discontinuity can exist without
reflecting waves (in violation of the laws of physics). Please
explain how a physical impedance discontinuity can avoid
reflecting the incident wave.

Did I say that?

Yes, you did. Funny you would forget so quickly.

Strange, I don't remember any discussion at all along that line.

Here's what you said:

I claim those waves never exist at all and therefore don't need to be canceled.

The physical impedance discontinuity certainly exists yet
you say it doesn't reflect any waves because the "waves
never exist at all".

So the question still remains: Exactly how does a physical
impedance discontinuity not reflect any waves (in violation
of the laws of physics)? Why doesn't a Rho of 0.7143 reflect
71.43% of the incident voltage like it is supposed to?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

When an EM wave disappears in its original direction of
travel, what happens to its energy?

What happens to the energy flowing in the lamp cord when you turn out
your desk lamp? :-)

73, ac6xg