On Tue, 09 Aug 2005 16:37:38 -0400, Walter Maxwell
wrote:

How do you
suppose that had it not been for wave interferencethe energy would
have continued on in a particular radial direction,

Hi Walt,

What stopped it if not a physical barrier?

but due to the
interference the result was a null

A null is not the absence of energy, but is the combination of equal
and opposing forces. If you were the Ref at a title bout, and stepped
between two punches of equal magnitude; then you wouldn't move very
far, the motions would cancel, but most would doubt you'd be up again
before the "count."

Nulls are evidenced quite clearly in bridges of many designs. They
may balance between huge potentials (energy), but evidence absolutely
no current (or power from energy times current). If you unplugged the
equipment from a bridge, the absence of current would not be an
indication of a null. Nulls within the context of engineering
necessarily carries the implication of energy present.

in that direction and an increased
amount of energy in the opposite, or forward direction, achieving gain
in that direction?

Linear systems do not exhibit "gain." The combination of forces are
due to the total field in comparison to the region of interest.

It is by similar simplifications that we have contributors here who
offer that the radials of elevated ground planes do not radiate
energy. Their contribution to producing a power at a remote load may
cancel such that no power is evident, but this does not negate the
radiation nor the energy present.

73's
Richard Clark, KB7QHC

Jim Kelley wrote:


Cecil Moore wrote:

Please note above that I said wave interference indeed *can*
cause a redistribution of energy. I chose "can" instead of
"will" because wave interference is not sufficient to cause
the redistribution of energy. Wave cancellation is a special
case of wave interference in which the waves *cease to exist*
in their original direction of travel. The conservation of
energy principle dictates that the energy contained in those
waves before they are canceled, must necessarily be redistributed
along a different path. Note: Any different path in a transmission
line is necessarily the opposite direction, i.e. a reflection.

All correct - neither proving your point or disputing mine.

I keep telling you that our only technical disagreements are over
extremely minor points. You keep posting stuff as if we disagree
when we don't and it is mostly just a ruse. You keep trying to
forcefully shove your strawmen into my head so you can shoot them
down, but that is just another ruse.

It appears to me that you think wave cancellation is a one time event,
like shooting a deer. The deer dies and that's that. But wave cancellation
is not a one time event. Wave cancellation is a continuous steady-state
infinite series of infinitessimal events. Wave cancellation is not possible
without steady-state standing waves. If the forward power anywhere in the
system is greater than the source power, then wave cancellation and
constructive interference are continuously occuring during steady-state.

The thing you really need to consider is: how much energy is actually
"in" a wave (whatever that means) that delivers no energy.

"In" in this context means "associated with" (and two letters is
seven times as efficient as 14 letters). Energy is always associated
with any wave, else the wave would never exist. For you to talk
about canceled waves containing no energy is a contradiction. Dr.
Best talked about canceled waves that keep flowing toward the source,
canceling each other all the way, but containing zero energy. They
exist only in his mind.

All waves deliver energy somewhere even if it takes forever as in the
case of the detected background radiation. In a lossless transmission
line, all waves deliver energy to the load (and possibly to the source
after power to the source is removed). Rearward-traveling canceled waves
deliver their energy components in the direction of the load to later
become incident upon the load. Anything else would violate the
conservation of energy principle. The path the canceled waves take can
be deduced by observing ghosts on a TV screen.

There is no such thing in reality as a wave that delivers no energy.
Waves cannot even exist without energy. Canceled waves have associated
energy components before they were canceled. The Melles-Griot web page
calls that energy the "lost" energy and says it is not lost at all.
Those energy components must be redistributed in different directions
after the waves are canceled. Redistribution of energy in a transmission
line means changing direction, since there are only two directions.
--
73, Cecil http://www.qsl.net/w5dxp


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Jim Kelley wrote:
I can find no support in the literature
for a claim that interference changes the direction of the Poynting
vector - or for that matter, is a cause for any other phenomenon to
occur.

The Melles-Groit web page certainly supports wave cancellation
being the cause of the "lost" reflected energy joining the
forward wave. The Molecular Expressions web page certainly
supports that same energy redistribution resulting from wave
cancellation.

And given the following example from "Fields & Waves ..." by
Ramo & Whinnery, what do you think changes the direction of
the Pz2- Poynting Vector such that it vectorally adds to the
Pz1+ Poynting Vector resulting in the Pz2+ Poynting Vector?

100W XMTR---50 ohm line---+---291.4 ohm line---1698.5 ohm load
Pz1+ = 100W-- Pz2+ = 200W--
--Pz1- = 0W --Pz2- = 100W

If you can answer that simple question to the satisfaction of
everyone, the discussion will be over.
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Clark wrote:
Linear systems do not exhibit "gain."

From the IEEE Dictionary: "gain - The ratio of radiation
intensity, in a given direction, to the radiation intensity
that would be obtained if the power accepted by the antenna
were radiated isotropically."

That is the gain that Walt is talking about. That is the
gain that EZNEC reports.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:

And given the following example from "Fields & Waves ..." by
Ramo & Whinnery, what do you think changes the direction of
the Pz2- Poynting Vector such that it vectorally adds to the
Pz1+ Poynting Vector resulting in the Pz2+ Poynting Vector?

100W XMTR---50 ohm line---+---291.4 ohm line---1698.5 ohm load
Pz1+ = 100W-- Pz2+ = 200W--
--Pz1- = 0W --Pz2- = 100W

If you can answer that simple question to the satisfaction of
everyone, the discussion will be over.

Any reflections (and Poynting vector reversals) would be caused by the
presence of impedance discontinuities - not by anything else. In the
absence of impedance discontinuities, the transmission line would appear
to be infinitely long and would not produce reflections.

ac6xg

Cecil Moore wrote:


It appears to me that you think wave cancellation is a one time event,
like shooting a deer.

That would only be a naive perception on your part. Perhaps it is part
of your misunderstanding?


All waves deliver energy somewhere even if it takes forever as in the
case of the detected background radiation. In a lossless transmission
line, all waves deliver energy to the load (and possibly to the source
after power to the source is removed).

So your claim is that energy is delivered by two waves that are equal in
amplitude and opposite in phase?

There is no such thing in reality as a wave that delivers no energy.

See Born and Wolf for examples.

Waves cannot even exist without energy.

Correction. Waves cannot be created without energy. Electromagnetic
fields can indeed exist without necessarily conveying energy from one
place to another.

ac6xg

On Tue, 09 Aug 2005 17:11:41 -0700, Jim Kelley
wrote:
There is no such thing in reality as a wave that delivers no energy.
See Born and Wolf for examples.

Hi Jim,

This is intriguing for a wave (I presume you were adhering to the
singular). For those who lack these references, do you have any
concrete examples?

73's
Richard Clark, KB7QHC

Jim Kelley wrote:

Cecil Moore wrote:
And given the following example from "Fields & Waves ..." by
Ramo & Whinnery, what do you think changes the direction of
the Pz2- Poynting Vector such that it vectorally adds to the
Pz1+ Poynting Vector resulting in the Pz2+ Poynting Vector?

100W XMTR---50 ohm line---+---291.4 ohm line---1698.5 ohm load
Pz1+ = 100W-- Pz2+ = 200W--
--Pz1- = 0W --Pz2- = 100W

If you can answer that simple question to the satisfaction of
everyone, the discussion will be over.

Any reflections (and Poynting vector reversals) would be caused by the
presence of impedance discontinuities - not by anything else.

The impedance discontinuity is certainly in the cause and effect *chain*
as is the Poynting vector reversal. But simply asserting that the
impedance discontinuity causes the Poynting vector reversal is
a sophmoric begging of the question and leaves out some important
details. A causes B. B causes C. C causes D. You are certainly logically
correct in saying that A causes D, but your statement leaves out some
important intermediate details, namely B and C. (see below)

For instance, the impedance discontinuity causes nothing unless the
source energy exists and is taken into account as a cause. The
question is what are the necessary and sufficient conditions for an
impedance discontinuity to result in a complete reversal of the
(Pz2-) Poynting vector? Since a source is necessary, the source can
be considered as a cause. (The creator of our species can even be
considered as a necessary cause as can the Big Bang.)

Looking at it from a scientific standpoint, the impedance discontinuity
can only directly reverse half the magnitude of the Poynting Vector because
the physical power reflection coefficient is 0.5. So how does the other half
of the magnitude of the Poynting Vector get reversed? It's all been covered
by the Melles-Griot web page and the Molecular Expressions FSU web page.

In the presence of EM source energy, the impedance discontinuity causes
reflections. One of those reflections reverses half the magnitude of the
(Pz2-) Pointing Vector. That magnitude is (Pz2-)(rho^2).

Two of those reflections engage in wave cancellation. One is (Pz1+)(rho^2).
The other is (Pz2-)(1-rho^2), the other half of the (Pz2-) Poynting Vector.
These two reflections have equal magnitudes and opposite phases and therefore
cancel. Their energy components reverse direction and head back toward the load
as explained on the Melles-Groit and Molecular Expressions web pages.

And that's how the (Pz2-) Poynting Vector gets reversed. It's a two-step
process, each step involving half of Pz2- in the above example.

In the
absence of impedance discontinuities, the transmission line would appear
to be infinitely long and would not produce reflections.

That's true. The impedance discontinuity causes the reflections that engage
in wave cancellation. In steps, it goes like this.

A. Impedance discontinuity driven by a source of EM energy

B. Reflections (implied mismatch)

C. Wave Cancellation (permanent destructive interference)

D. Energy direction and momentum reversal (constructive interference)

A causes B. B causes C. C causes D. This is in any freshman logic book.
You are certainly logically correct in saying that A causes D, but
your statement leaves out some important intermediate details. Those
intermediate details are what this discussion is all about.
--
73, Cecil http://www.qsl.net/w5dxp


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Jim Kelley wrote:
So your claim is that energy is delivered by two waves that are equal in
amplitude and opposite in phase?

Naturally, zero energy is delivered in the direction of the complete
wave cancellation. The energy in the two canceled waves is delivered
in the opposite direction from their power-flow vectors. Anything else
would violate the conservation of energy principle.

It's not really my claim. That is what is claimed by the Melles-Groit
and Molecular Expressions web pages. That is what is claimed by Hecht,
in "Optics". That is what is claimed by Walter Maxwell in "Reflections".
Walt calls it a "virtual short". I had forgotten that he had described
it so well until I re-read it. Walt's QST articles in the 70's were where
I encountered these principles for the first time.

Maxwell, Walter, Reflections II, © 2001 Worldradio Books

Page 4-3, "The destructive wave interference between these two complementary
waves ... causes a complete cancellation of energy flow in the direction toward
the generator. Conversely, the constructive wave interference produces an energy
maximum in the direction toward the load, ..."

(I had forgotten about that being in "Reflections". "Optics" was only
a refresher of the "Reflections" material.)

Page 23-9, "Consequently, all corresponding voltage and current phasors are 180
deg out of phase at the matching point. ... With equal magnitudes and opposite
phase at the same point (point A, the matching point), the sum of the two
(reflected) waves is zero."

Waves cannot even exist without energy.

Correction. Waves cannot be created without energy. Electromagnetic
fields can indeed exist without necessarily conveying energy from one
place to another.

Correction. DC electromagnetic fields can exist without conveying energy
but the context is RF EM waves. EM wave-fields cannot exist without energy.
They can only exist at the speed of light, i.e. with ExM joules/sec
passing a point. The use of your tricky-dicky definition for "convey"
doesn't change those facts of physics.
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Clark wrote:

Jim Kelley wrote:

There is no such thing in reality as a wave that delivers no energy.

See Born and Wolf for examples.

This is intriguing for a wave (I presume you were adhering to the
singular). For those who lack these references, do you have any
concrete examples?

Beware when Jim uses the words, "power", "deliver", "convey",
"transfer", etc. They don't mean to him what you, I, Webster,
and the IEEE Dictionary say they mean. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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