Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:

Who said powers can never be added?


Must have been someone who was unfamiliar with the expression 'figures
can lie and liars can figure'. :-)


You reckon Eugene Hecht was lying when he shows us how to
add two irradiances to obtain the total irradiance (power
per unit-area) in _Optics_?

Eugene Hecht doesn't have a dog in this fight, Cecil. But the quote is
a truism that applies in any case. Wrong numbers added correctly
produce a wrong number; correct numbers added incorrectly produce an
incorrect number; and in the special case, certain wrong numbers added
in a particular incorrect way can produce a desired result.

You take too great a liberty with the name Eugene Hecht. Among the
things which won't be found in any of Dr. Hecht's texts is a minus sign
in front of number expressing an irradiance. Nor will we find a
negative scalar quantity accompanied by the claim that the negative sign
indicates a change in direction, as you have done. Eugene Hecht also
did not claim that interference could be a cause for energy to reflect
or otherwise change direction, as you have done. Such claims are
blatently false.

Power and irradiance are derived and dependent quantities, not
fundamental independent quantities in nature. And although an
automobile moves at some speed, the scaler quantity itself is not
something which moves. Similarly, power and irradiance do not
physically propagate and they do not physically interact. 'They' do not
reflect, refract, diffract, disperse, interfere, or act upon other
'powers' or 'irradiances'. JC Maxwell and others observed that it is
electric and magnetic fields which propagate, interact with matter, and
add algebraically and vectorially. When fields physically interact with
matter, we can measure their effect and can quantify such things as
voltage, current, and heat, and hence calculate such things as power or
irradiance. But it is actually the fields themselves which
algebraically sum. Of course the interference equation accurately
expresses power and irradiance. The fact that power and irradiance
generally go as the square of the fields allows us to correctly make
certain additional mathematical assumptions. One must still be careful
not to mistake an effect for a cause. But it is the 2nd Amendment, the
internet, and the absence of peer review which afford men the freedom
and means to work equations and describe physical phenomena in any way
they like.

73, ac6xg

Jim Kelley wrote:

Jim, you have a habit of erecting strawmen somewhat like:
"I don't care what you say, the sun will rise tomorrow." For that
reason, I'm going to trim the parts of your posting with which I
agree and have never disagreed.

You take too great a liberty with the name Eugene Hecht. Among the
things which won't be found in any of Dr. Hecht's texts is a minus sign
in front of number expressing an irradiance.

Sure wish you would read the book before making such statements.

On the contrary, here's equation (9.16) representing total destructive
interference.

Imin = I1 + I2 - 2*SQRT(I1*I2) = 0

The third term is indeed a minus sign in front of a number expressing
irradiance. However, total average irradiance cannot be less than zero.
And for the record, I have never said total average power could be less
than zero but, like Hecht, I treat destructive interference energy as a
negative term and constructive interference energy as a positive term.

Dr. Stephen Best, VE9SRB, did the same thing for his "Wave Mechanics
of Transmission Lines, Part 3:" QEX article, Nov/Dec 2001. He said:

"When the voltages V1 and V2 are exactly 180 deg out of phase, the
total power can be determined as follows:"

"PFtotal = P1 + P2 - 2*SQRT(P1)*SQRT(P2)"

so if you don't like negative power terms, you should confront both
Eugene Hecht and Dr. Best.

Nor will we find a
negative scalar quantity accompanied by the claim that the negative sign
indicates a change in direction, as you have done.

On the contrary, in equation 9.16 above, according to Hecht, the
interference term is negative indicating "total destructive
interference", his words, not mine. Here's Hecht's quote from _Optics_.

“The principle of
conservation of energy makes it clear that if there is constructive
interference at one point, the ‘extra’ energy at that location must have
come from somewhere else. There must therefore be destructive
interference somewhere else."

Sorry, but a negative interference term denotes destructive
interference. A positive interference term denotes constructive
interference. In a transmission line with only two directions,
if destructive interference occurs in one direction, then
constructive interference must occur in the only other direction
in order to satisfy the conservation of energy principle.

A wave cancellation event in a transmission line implies an equal
constructive interference event in the opposite direction. Anything
else violates the laws of physics.

Similarly, power and irradiance do not
physically propagate and they do not physically interact.

On the contrary, they do physically interact for coherent waves as can
be inferred by the interference equations. Please reference Chapter 9
in _Optics_, by Hecht. The mathematical interaction of power and
irradiance is a *result* of superposition of coherent EM waves. That's
where the interference equations involving irradiance come from.

JC Maxwell and others observed that it is
electric and magnetic fields which propagate, interact with matter, and
add algebraically and vectorially.

And contain power equal to ExH. EM waves cannot exist without energy.
If EM waves interact, their energy components interact. Destructive
and constructive interference cannot occur without energy components
which follow the laws of physics.

Of course the interference equation accurately expresses power and
irradiance.

That is some progress on your part so there's hope. What you need to
realize is that those interference equations define what happens to
the energy at a match point in a transmission line. Dr. Best kicked
this discussion off by his QEX article. He just didn't realize that
the equations he published were virtually identical to the classical
optical interference equations.
--
73, Cecil http://www.qsl.net/w5dxp


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On Tue, 12 Jul 2005 22:48:00 -0500, Cecil Moore
wrote:

Nor will we find a
negative scalar quantity accompanied by the claim that the negative sign
indicates a change in direction, as you have done.

On the contrary, in equation 9.16 above, according to Hecht, the
interference term is negative indicating "total destructive
interference", his words, not mine. Here's Hecht's quote from _Optics_.

[Hecht rolls his eyes] Jim's point is won, absolutely nothing quoted
here explicitly states a change in direction. That is, as Jim points
out, the math follows the physics, it does not create the physics.
There is a vast gulf between being descriptive and being proscriptive.

Richard Clark wrote:
[Hecht rolls his eyes]

I'm going to trim and ignore the condescending ad hominem stuff.

... the math follows the physics, it does not create the physics.

Your argument has that exact flaw. "What Cecil is describing doesn't
exist in the common math model. Therefore, the math model prohibits
it from existing in physics." Please follow your own advice. There
is a vast gulf between being descriptive and being prohibitive.

There is a vast gulf between being descriptive and being proscriptive.

I didn't choose to quote the entire book, Richard. Hecht also says:
"If two or more electromagnetic waves arrive at point P out-of-phase
and cancel, 'What does that mean as far as their energy is concerned?'
Energy can be distributed, but it doesn’t cancel out. ... The
superposition of coherent waves generally has the effect of altering
the spatial distribution of the energy but not the total amount
(of energy) present."

"Altering the spatial distribution of the energy" in a transmission
line is a binary function since there are only two directions. If
the spatial distribution is altered, it necessarily changes directions.

The following does explicitly state a change in direction, i.e. "A
NEW DIRECTION".

http://micro.magnet.fsu.edu/primer/j...ons/index.html

"When two waves of equal amplitude and wavelength that are 180-degrees
out of phase with each other meet, they are not actually annihilated.
All of the photon energy present in these waves must somehow be
recovered or REDISTRIBUTED IN A NEW DIRECTION, according to the law
of energy conservation ... Instead, upon meeting, the photons are
redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves
and photon energy rather than the spontaneous construction or
destruction of light." (Emphasis mine.)

A transmission line has only two directions. If wave cancellation, i.e.
permanent destructive interference, takes place in one direction, the
necessary corresponding constructive interference must be "redistributed
in a new direction". In a transmission line, there is only one "new
direction", the opposite direction from the old direction.
--
73, Cecil http://www.qsl.net/w5dxp

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On Wed, 13 Jul 2005 07:28:21 -0500, Cecil Moore
wrote:
There is a vast gulf between being descriptive and being proscriptive.
I didn't choose to quote the entire book
[Hecht rolls his eyes] That would have been futile because no portion
of it contains the proscription.

What has been offered makes as much sense as ascribing the value of
$100 to a button simply because you sewed it to a jacket and found
$100 in the pocket of that jacket. -Superstition-

Cecil. W5DXP wrote:
In a transmission line, there is only one "new direction", the opposite
direction."

Tes, and there is no cumulative long-term buildup on the line. We could
sense an accumulation. The energy in the steady state is lost on the
line or dissipated in lhe load or source.

Best regards, Richard Harrison, KB5WZI

Cecil Moore, W5DXP is alleged to have written:
"Nor will we find a negative scalar quantity accompanied by the claim
that the negative sign indicates a change in direction as you have
done."

Have not read Hscht, but I`ve read Terman and realize that a
transmission line can guide a wave only forward and backward. Sometimes
backward is considered the negative direction.

Terman gives an example on page 90 of his 1955 edition:
"When the load end of the line is shorted, that is Eload =0 , reference
to Eq. (4-14) shows the reflection coefficient has the value -1.0 on an
angle of 0-deg.= 1.0 on an angle of 180-deg. As in the open-circuited
case, the reflected wave has an amplitude equal to the amplitude of the
incident wave. However, the refleection now takes place with a reversal
in phase of the voltage and without change in phase of the current."

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Cecil Moore, W5DXP is alleged to have written:

Jim Kelley actually claims to have written it.

"Nor will we find a negative scalar quantity accompanied by the claim
that the negative sign indicates a change in direction as you have
done."

Have not read Hscht, but I`ve read Terman and realize that a
transmission line can guide a wave only forward and backward. Sometimes
backward is considered the negative direction.

Yes, for vector quantities expressed as a function of position or time.

Terman gives an example on page 90 of his 1955 edition:
"When the load end of the line is shorted, that is Eload =0 , reference
to Eq. (4-14) shows the reflection coefficient has the value -1.0 on an
angle of 0-deg.= 1.0 on an angle of 180-deg. As in the open-circuited
case, the reflected wave has an amplitude equal to the amplitude of the
incident wave. However, the refleection now takes place with a reversal
in phase of the voltage and without change in phase of the current."

From Webster's Collegiate:
Scalar - a quantity such as mass or time that has a magnitude
describable by a real number and no direction

Power as a scalar quantity does not have direction, and so one could not
for example subtract power 'moving' in one direction from power 'moving'
in the other direction by arbitrarily multiplying one of the magnitudes
by negative one.

73, ac6xg

Jim Kelley wrote:
Power as a scalar quantity does not have direction, and so one could not
for example subtract power 'moving' in one direction from power 'moving'
in the other direction by arbitrarily multiplying one of the magnitudes
by negative one.

For engineers, the direction of the arrow for the Power
Flow Vector in joules/sec is generally accepted to be the
same as the direction of the joules.

From the IEEE Dictionary: "power-flow vector - Vector-
characterizing energy propagation caused by a wave and
giving magnitude and direction of power per unit-area
propagating in the wave."

Please note the "*DIRECTION OF POWER* ... *PROPAGATING*
in the wave", a direct contradiction to your above assertion.
The power measured at the source somehow finds its way to the
load in spite of not having any direction (according to you. :-)

Most of your rantings and ravings over what I have said
are simply semantics and definitions. RF energy and RF
power are so closely related that Walter C. Johnson talks
about the "principle of conservation of power".
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:

For engineers, the direction of the arrow for the Power
Flow Vector in joules/sec is generally accepted to be the
same as the direction of the joules.

I am an engineer, Cecil. I just happen to work in the field of physics.
I could be wrong, but I don't think a Bird wattmeter measures or
displays Power Flow Vector.

From the IEEE Dictionary: "power-flow vector - Vector-
characterizing energy propagation caused by a wave and
giving magnitude and direction of power per unit-area
propagating in the wave."


Please note the "*DIRECTION OF POWER* ... *PROPAGATING*
in the wave", a direct contradiction to your above assertion.

The power measured at the source somehow finds its way to the
load in spite of not having any direction (according to you. :-)

Well, it's true for me and probably for most other people who have a
grasp of the subject. It's actually energy which does the moving.
Power is just the rate at which energy finds its way there.

It's like this. Let's say you're riding your Harley through town at 50
MPH and somebody pulls out of a side street right in front of you. Does
the speed of your motorcycle collide with the car, or does your
motorcycle collide with it?

73, ac6xg