Constructive interference in radiowave propagation
 

Jim Kelley wrote:

Cecil Moore wrote:
What happens to reverse the direction and momentum of
the internal reflection in the thin film?

That's what I was asking you. You seem to be hinting at something, but
not actually saying it. What, other than reflection, are you suggesting
causes electromagnetic waves to reverse their direction of propagation
in the system you describe?

I have published my take on that reflection. It is a two
step process involving:

1. A normal reflection from a physical impedance discontinuity
that doesn't account for all the reflected energy since the
physical reflection coefficient is not 1.0.

2. Wave cancellation between two reflected wave components
in the direction of the source results in a redistribution
of that energy in the direction of the load. This accounts
for the rest of the reflected wave energy.

You have objected to step 2 as invalid so the onus is upon
you to provide an alternate explanation. Please post the
governing equations. So far you have refused to do anything
except harp, nit-pick, and kibitz while wildly engaging in
hand-waving. Time to put up or shut up. Please explain the
process of 100% re-reflection of the internal reflected wave.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

Jim Kelley wrote:


Cecil Moore wrote:

"Powers, treated as scalars, are incapable of
interference."


And when powers sic are not treated as scalers, ...


There you go again, Jim, trying to set up a straw man.
I do NOT treat powers as anything except scalars.

It was curious that someone would qualify his statement that way to
begin with - "treated as scalars". What's that supposed to imply if
not that there are other ways to treat "powers" sic.

Is there, or is there NOT a cosine term in the interference equation?
How can a scalar have a PHASE ANGLE, and how can the cosine term
possibly apply to anything OTHER than the terms used IN THE EQUATION?!!

I wonder if you'd care to comment on the other mathematical techniques
you introduced to the group this week:

Subtracting power that isn't somewhere else from a number that's
apparently higher than it should be in order to get the right answer,
and averaging power with zero as a means for reducing an excessively
large number by a factor of two in order for the answer to come out
right. I'm still trying to parse how neglecting units makes it ok to
use equations as you see fit. $100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere
else and should therefore be mine.) ;-)

73, Jim AC6XG

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

I have published my take on that reflection. It is a two
step process involving:

1. A normal reflection from a physical impedance discontinuity
that doesn't account for all the reflected energy since the
physical reflection coefficient is not 1.0.

2. Wave cancellation between two reflected wave components
in the direction of the source results in a redistribution
of that energy in the direction of the load. This accounts
for the rest of the reflected wave energy.

Right. But the question still remains, what is your claim regarding
the exact nature of the "redistribution" if NOT reflection from a
partially reflective surface?

73, Jim AC6XG

Constructive interference in radiowave propagation
 

On Fri, 13 Apr 2007 12:55:46 -0700, Jim Kelley
wrote:

$100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere
else and should therefore be mine.) ;-)

Hi Jim,

By substitution, EVERYONE knows TIME is money:
24Hrs + 24Hrs + 2*SQRT(24Hrs*24Hrs) = a work week

Hmmm, does time superpose? Can we find two coherent generators of
time? We can certainly find two generators of money like Ron Popiel's
vegamatic or George Forman's diet grill and as anyone can tell they
superpose with a veggie-burger.

73's
Richard Clark, KB7QHC

Constructive interference in radiowave propagation
 

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
It was curious that someone would qualify his statement that way to
begin with - "treated as scalars". What's that supposed to imply if not
that there are other ways to treat "powers" sic.

You falsely accused me of treating powers other than
as scalars. Now you are trying to twist my denial into
something untoward. Just how low are you willing to
stoop to discredit Hecht, Born & Wolf, and Dr. Best?

Is there, or is there NOT a cosine term in the interference equation?

Yes, there is. Look in Born and Wolf and Hecht's "Optics".
There it is. I didn't put it there. The cosine term is
the angle between the two interfering voltages. All three
authorities, Hecht, Born, and Wolf, present the same
watts/unit-area equation with a term that they call the
interference term. Your argument is with them, not with me.
Watts/unit-area is certainly a scalar, yet all the experts
insert a cosine term into the scalar equation. That you don't
comprehend is somewhat ironic, wouldn't you say?

I wonder if you'd care to comment on the other mathematical techniques
you introduced to the group this week:

Subtracting power that isn't somewhere else from a number that's
apparently higher than it should be in order to get the right answer,
and averaging power with zero as a means for reducing an excessively
large number by a factor of two in order for the answer to come out
right.

Please don't blame me. Hecht says in "Optics" that destructive
interference somewhere else allows the constructive interference
that we are experiencing. I didn't invent the concept. It was
invented by optical physicists before I was born. That you
are completely ignorant of the concept is downright appalling.
It just goes to show that people who believe they know everything
rarely know anything.

I'm still trying to parse how neglecting units makes it ok to
use equations as you see fit. $100 + $100 + 2*SQRT($100*$100) = $400
(The third term represents the amount of money that isn't somewhere else
and should therefore be mine.) ;-)

Here's equation (15) on page 259 of Born and Wolf's, "Principles
of Optics". Intensity is certainly a scalar value in watts/unit-area.
Why do you think Born and Wolf would put a cosine function into a
scalar equation? Up until you discovered them doing such a
dastardly thing, they were your heroes.

Imax = I1 + I2 + 2*SQRT(I1*I2)*cos(A) (15)

Does watts/unit-area have a phase angle? No. But there is a
phase angle associated with the corresponding two E-fields.

As far as I know, a money equation doesn't possess an interference
term but intensity equations, irradiance equations, and Poynting
vector equations do indeed possess an inteference term. Here's
what Hecht says in "Optics". " Briefly then, optical interference
corresponds to the interaction of two or more lightwaves yielding
a resultant irradiance that DEVIATES FROM THE SUM OF THE COMPONENT
IRRADIANCES." You are objecting to the deviation from the sum of
the component power densities. Please take that up with Hecht.

Maybe the head of your department could explain the interference
term in the irradiance-intensity-Poynting vector equation to you.
But if I were you, I wouldn't expose your gross ignorance to him.

All anyone reading this posting has to do to see just how confused
Jim really is, is to read a copy of "Optics" by Hecht, or a copy
of "Principles of Optics", by Born and Wolf.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Right. But the question still remains, what is your claim regarding the
exact nature of the "redistribution" if NOT reflection from a partially
reflective surface?

It is impossible for a "partially reflective surface"
to reflect 100% of the intensity. My two step process
explains 100% reflection. Walt's virtual short explains
100% reflection. How do *you* explain 100% reflection
from a partially reflective surface? Time to cease the
mealy-mouthing and hand-waving and give us some facts.

A B
i=1.0 | i=5.83 | i=1.0
100w laser---air---|--1/2WL thin-film--|---air---...
--Pref1=0w | --Pref2=100w | --Pref3=0w
Pfor1=100w | Pfor2=200w-- | Pfor3=100w--

The intensity reflection coefficient seen by the internal
reflected wave is 0.5 yet the net reflection is 100%. I
have explained how that is possible through wave cancellation.
You have not explained how that is possible without wave
cancellation. Time to put up or shut up.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:

It just goes to show that people who believe they know everything
rarely know anything.

That's probably a bit of an overstatement. But they certainly can be
annoying.

ac6xg

Constructive interference in radiowave propagation
 

Richard Clark wrote:

Hi Jim,

By substitution, EVERYONE knows TIME is money:
24Hrs + 24Hrs + 2*SQRT(24Hrs*24Hrs) = a work week

Heaven help us if the unions ever find out about it.

Hmmm, does time superpose?

Interesting point, Richard. Evidently that doesn't actually matter as
long the answer comes out as desired.

73, ac6xg

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Jim Kelley wrote:
You seem to be implying that there's something different about how
these electromagnetic waves change direction compared to other
electromagnetic waves. Why is that?

There is something different but not unusual. We don't
often observe wave cancellation of visible light waves
because of the problem of getting coherent beams of light
perfectly aligned. Yet, we experience RF wave cancellation
every time we adjust our antenna tuners for a Z0-match
because the perfect alignment of coherent RF waves inside
a piece of coax is an automatic given.

[Example snipped]

Cecil,

This is a rather curious notion. Where did you get the idea that waves
must be perfectly aligned to "cancel"?

Suppose I set up an experiment in which two coherent laser beams are
misaligned by, say, one picoradian. The phases are adjusted so that the
waves "cancel" in the region of overlap. This is much the same as the
Java picture you like to reference from the FSU Magnet Lab. Any
measurement that might be made in the overlap region would show the
destructive interference, or "cancellation" if you wish. However, the
beams are not perfectly aligned, so eventually the overlap ceases, and
the individual beams proceed on toward infinity. I believe most people
would agree that those exiting beams would not be altered by any
interaction or interference that might have occurred in the lengthy
overlap region. (That is a very easy experiment that can be conducted in
any elementary optics lab.)

OK, so now we fine tune the illuminating mechanism so that the two beams
are perfectly aligned. Are you saying that there is now some fundamental
physical difference, and that the beams indeed cancel?

What is the equation that provides such a dramatic change resulting from
an adjustment of one picoradian? What reference is there for this
dramatic change mechanism?

73,
Gene
W4SZ

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Cecil Moore wrote:

It just goes to show that people who believe they know everything
rarely know anything.

That's probably a bit of an overstatement. But they certainly can be
annoying.

Again, I post the Hecht and Born & Wolf equation for intensity-
irradiance, which is certainly an equation involving scalar values.
Please answer the question: Why do Hecht and Born & Wolf insert a
cosine term into their scalar intensity-irradiance equations? If
it is OK for them to do it, why is it not OK for me to do it?

Itot = I1 + I2 + 2*SQRT(I1*I2)*cos(A)

You seem to think the act of inserting a cosine term into a
scalar equation is an abomination. Please explain that criticism
of Hecht, Born & Wolf, and me. It's past time to put up or shut up.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Gene Fuller wrote:
Cecil Moore wrote:
Jim Kelley wrote:
You seem to be implying that there's something different about how
these electromagnetic waves change direction compared to other
electromagnetic waves. Why is that?

There is something different but not unusual. We don't
often observe wave cancellation of visible light waves
because of the problem of getting coherent beams of light
perfectly aligned. Yet, we experience RF wave cancellation
every time we adjust our antenna tuners for a Z0-match
because the perfect alignment of coherent RF waves inside
a piece of coax is an automatic given.

This is a rather curious notion. Where did you get the idea that waves
must be perfectly aligned to "cancel"?

Apologies - what I meant to say was that waves must be perfectly
aligned to totally cancel. When I say "wave cancellation", I
am usually talking about total wave cancellation, as occurs at
a perfect Z0-match. I will try not to make that same mistake
in the future.

Waves need not be perfectly aligned to partially cancel.
Waves must be perfectly aligned to totally cancel. Hope
that clears up the confusion about what I meant to say.

And of course, partial wave cancellation can extend from
almost none to almost total. However, total wave cancellation
obviously requires perfect alignment.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:


It is impossible for a "partially reflective surface"
to reflect 100% of the intensity.

But that's wrong. If it was right, then a partially reflective
surface couldn't be used to prevent reflections either.

Think about the transient period. You're right that after the first
bounce only half the intensity, for example, is apparent. But using
the physical reflection coefficient you can plot the intensity
increase steadily as a function of time all the way up to steady
state. That's because at every time t, the remainder of all previous
reflections are superposed. Yes, interference describes
macroscopically what happens - it's a short cut to steady state. But
nothing about the reflective surface changes - before or after steady
state. It is only your idea of 'energy in the wave' that needs to
change a little.

73, ac6xg

Constructive interference in radiowave propagation
 

Jim Kelley wrote:

Cecil Moore wrote:
It is impossible for a "partially reflective surface"
to reflect 100% of the intensity.

But that's wrong. If it was right, then a partially reflective surface
couldn't be used to prevent reflections either.

That's faulty logic born out of ignorance.
Assume s11 = 0.707 in the S-Parameter reflected
voltage equation. a1 is the normalized forward
voltage from the source. Let's assume a1 = 10.

b1 = s11(a1) + s12(a2)

the initial transient state reflection is

b1 = s11(a1) = 0.707(10) = 7.07 normalized volts

and *that term remains constant* throughout the transient
state and throughout steady-state. The impedance discontinuity
with s11=0.707 reflects 70.7% of the incident voltage, period,
no more and no less. The magnitude of a1 reflected by that
impedance discontinuity *DOES NOT CHANGE* from the very
first incidence of a1. So your statement above is obviously
false. Physical impedance discontinuities do not change their
reflection coefficients based on your whim.

So how does b1 wind up at zero? Not by changing s11(a1) as
you imply. b1 is eventually canceled by the buildup to steady-
state of s12(a2) from zero to a magnitude equal to s11(a1) and
a phase opposite of s11(a1). That's *wave cancellation* in action.
What happens to the energy in the canceled waves?

So your premise is completely flawed. s11(a1) doesn't change.
s12 doesn't change. s21 doesn't change. s22 doesn't change.
What changes is the s12(a2) term which is the reflections
from the load. b1 decreases increment by increment due to
the wave cancellation between the fixed value of s11(a1)
and the ever increasing value of s12(a2) until steady-state
is reached and b1 has become zero. At steady-state, s11(a1)
is still equal to 7.07 normalized volts. It has not changed.
Contrary to your assertion, it will not change as long as
a1 is applied.

s11(a1) = 7.07 unchanging throughout the initial transient
build-up and through steady-state. Anything else would
require magic.

b1 is initially equal to 7.07 because a2 is zero.

s12(a2) will eventually build up from 0 to 7.07 at which
point the *net reflections are eliminated by wave cancellation*.

As b1 is decreasing to zero at steady-state, b2 is increasing
to its steady-state value in the other direction. b1 is
undergoing increasing destructive interference and b2 is
undergoing increasing constructive interference until the
time when b1 = 0 and therefore |b1|^2 = 0, i.e. net reflections
are eliminated.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Owen Duffy wrote:
"I am not quite sure about the concept of energy at a point that you
discuss, isn`t it zero."

Not when radio waves are passing by. These waves were likely produced by
electrical energy in a wire somewhere that spread into space around the
wire. Radio waves alternate around a zero value. If symmetrical about an
axis, the waveforms may have zero average values. But that is not how we
value the intensity of a rafio wave. We give it an rms or effective
value which is 0.707 times its maximum voltage profuced during the
cycle.

When speaking of power in an alternating energy value, it is not correct
to say rms power. The effective a-c power value is its average.

I`m not a teacher, never have been, and never intend to be. I think I
got into this discussion by declaring that 50% of the power in a wave
resided in each of its two constituents.

I shall argue no more nor try to explain any more on the topic of radio
waves in this thread. Fred Terman is the master of all masters in my
books and I suggest beginning on page one of his 1955 version of
"Electronic and Radio Engineering" to learn all about "Radio Waves".

From page 1:
"One-half of the electrical energy contained in the wave exists in the
form of electrostatic energy, while the remaining half is in the form of
magnetic energy."

Best regards, Richard Harrison, KB5WZI

Constructive interference in radiowave propagation
 

On Apr 13, 6:13 pm, Cecil Moore wrote:
Jim Kelley wrote:

Cecil Moore wrote:
It is impossible for a "partially reflective surface"
to reflect 100% of the intensity.

But that's wrong. If it was right, then a partially reflective surface
couldn't be used to prevent reflections either.

That's faulty logic born out of ignorance.

Partially reflective surfaces can (and are) in fact used to prevent
reflections, just as they are used to 100% re-reflect partial
reflections from a load.

The magnitude of a1 reflected by that
impedance discontinuity *DOES NOT CHANGE* from the very
first incidence of a1.

That was the main point of my post, Cecil. The reflective coefficient
DOES NOT CHANGE. You're the one who claims that it does.

What happens to the energy in the canceled waves?

There is no energy "in" cancelled waves. Your ideas in that regard are
faulty. Energy only exists where fields aren't cancelled. That
should be obvious even to someone with propensities such as yours.

ac6xg

Constructive interference in radiowave propagation
 

On 14 Apr 2007 09:53:11 -0700, "Jim Kelley" wrote:

What happens to the energy in the canceled waves?

There is no energy "in" cancelled waves.

Hi Jim,

How has this inversion arrived? Cecileo offering emphatic testimony
to the Cardinals "It certainly doesn't move!" and no energy "in"
cancelled waves?

Both waves exist as the absence of either would easily reveal. There
may be no power to extract due to their offsetting contributions, but
that doesn't prove they have vanished (which, in the context of sight,
interference, and light diminishing in regions necessarily demands a
load to demonstrate).

The language of photon shuffling and energy re-distribution lends the
logic of divine intervention to scientific theory. These verbs are
active and require an actor. If we were to travel down that path, the
patterns of intelligent design interference would be explained in
epicycles and crystalline spheres of angels' guiding results.

73's
Richard Clark, KB7QHC

Constructive interference in radiowave propagation
 

On Apr 14, 11:27 am, Richard Clark wrote:
On 14 Apr 2007 09:53:11 -0700, "Jim Kelley" wrote:

What happens to the energy in the canceled waves?

There is no energy "in" cancelled waves.

Hi Jim,

How has this inversion arrived? Cecileo offering emphatic testimony
to the Cardinals "It certainly doesn't move!" and no energy "in"
cancelled waves?

Both waves exist as the absence of either would easily reveal. There
may be no power to extract due to their offsetting contributions, but
that doesn't prove they have vanished (which, in the context of sight,
interference, and light diminishing in regions necessarily demands a
load to demonstrate).

The language of photon shuffling and energy re-distribution lends the
logic of divine intervention to scientific theory. These verbs are
active and require an actor. If we were to travel down that path, the
patterns of intelligent design interference would be explained in
epicycles and crystalline spheres of angels' guiding results.

73's
Richard Clark, KB7QHC

Hi Richard,

I have to admit that I do have difficulty arguing with nonsense, and
you've caught me at it. I've tried explaining this to Cecil in the
context of energy transfer, but without success. So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

73, ac6xg

Constructive interference in radiowave propagation
 

On Sat, 14 Apr 2007 11:27:11 -0700, Richard Clark wrote:

On 14 Apr 2007 09:53:11 -0700, "Jim Kelley" wrote:

What happens to the energy in the canceled waves?

There is no energy "in" cancelled waves.

Hi Jim,

How has this inversion arrived? Cecileo offering emphatic testimony
to the Cardinals "It certainly doesn't move!" and no energy "in"
cancelled waves?

Both waves exist as the absence of either would easily reveal. There
may be no power to extract due to their offsetting contributions, but
that doesn't prove they have vanished (which, in the context of sight,
interference, and light diminishing in regions necessarily demands a
load to demonstrate).

The language of photon shuffling and energy re-distribution lends the
logic of divine intervention to scientific theory. These verbs are
active and require an actor. If we were to travel down that path, the
patterns of intelligent design interference would be explained in
epicycles and crystalline spheres of angels' guiding results.

73's
Richard Clark, KB7QHC

Richard, I love the way you talk about 'epicycles and crystalline spheres of angels'.

Walt

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Partially reflective surfaces can (and are) in fact used to prevent
reflections, just as they are used to 100% re-reflect partial
reflections from a load.

Partially reflective surfaces cannot, by themselves,
reflect 100% of the incident energy. If it's partial,
it's not 100%, by definition. Any partially reflective
surface needs help from interference in order to
achieve 100% reflection. You know, that interference
that you deny exists.

That was the main point of my post, Cecil. The reflective coefficient
DOES NOT CHANGE. You're the one who claims that it does.

You continue to lie about what I said. I have said any
number of times that the physical reflection coefficient,
s11, is fixed and does NOT change. Why does someone who
is technically correct need to stoop to lying?

There is no energy "in" cancelled waves.

The waves existed along with their energy components before
they were canceled. What happens to those energy components
after the waves are canceled. If one sets one phase equal
zero and the other phase equal 180 degrees, what happens to
the energy in the two waves at:

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

There are two waves on the left existing with their respective
voltage and joules/sec. The result of total destructive interference
is zero voltage and zero joules/sec. What happened to the original
joule/sec components?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

But that's just the point, Jim. You seem to believe the
pre-existing energy in those waves has been destroyed.
They obviously possessed energy before cancellation and
you say they possess zero energy after cancellation. If
that pre-existing energy is not destroyed, where did it go?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On 14 Apr 2007 14:46:22 -0700, "Jim Kelley" wrote:

So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

Hi Jim,

That would be flogging the asphalt through the stripped ribs of a dead
horse.

73's
Richard Clark, KB7QHC

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

No need for that, Jim. Florida State University has done
an excellent job of explaining how wave cancellation
"redistributes" the pre-existing wave energy in "new
directions" such as the opposite direction in a
transmission line (the only other direction possible).

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

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Jim Kelley wrote:
So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

No need for that, Jim. Florida State University has done
an excellent job of explaining how wave cancellation
"redistributes" the pre-existing wave energy in "new
directions" such as the opposite direction in a
transmission line (the only other direction possible).

"... 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."

The killer is that word "somehow"... "all of the photon energy must
somehow be redistributed".

Well of course it must! Nobody denies that conservation of energy will
hold, in a system with properly defined boundaries. But the weakness of
a photon model is that it cannot provide a detailed nuts-and-bolts
explanation of the mechanism by which that energy becomes redistributed
in time and space.

A wave model will provide all of that detail - and in transmission-line
problems we can use it. If we trace what happens to forward and
reflected waves of voltage (and/or current) we can predict the
magnitudes and phases of those quantities at any location, at any
instant. That gives us a complete time-dependent map of the voltage and
current across the entire system.

From that, we can also find out where the energy is - the inputs,
outputs, losses and stored energy. Sure enough, we will find that energy
is conserved within the system boundaries... but that is no big deal, we
always knew it would. In a wave model, conservation of energy is
something you should check for, but only as an overall confirmation that
you've done the sums correctly. All the useful detail came from the
analysis of the voltage and/or current waves.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Constructive interference in radiowave propagation
 

Ian White GM3SEK wrote:
Cecil Moore wrote:
"... 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."

The killer is that word "somehow"... "all of the photon energy must
somehow be redistributed".

That's not a killer, Ian, that's a challenge to people
like me to figure out how. If there is indeed a "somehow",
then there has to be a "how". Please don't try to dampen
my curiosity like the church priests tried to dampen Galileo's
curiosity.

Well of course it must! Nobody denies that conservation of energy will
hold, in a system with properly defined boundaries. But the weakness of
a photon model is that it cannot provide a detailed nuts-and-bolts
explanation of the mechanism by which that energy becomes redistributed
in time and space.

I'm sure a QED explanation exists but we might have trouble
understanding it. I would like for you and others to follow
me through an energy analysis to see if you can find anything
technically wrong with it besides your revulsion to the approach.

A wave model will provide all of that detail - and in transmission-line
problems we can use it. If we trace what happens to forward and
reflected waves of voltage (and/or current) we can predict the
magnitudes and phases of those quantities at any location, at any
instant. That gives us a complete time-dependent map of the voltage and
current across the entire system.

From that, we can also find out where the energy is - the inputs,
outputs, losses and stored energy. Sure enough, we will find that energy
is conserved within the system boundaries... but that is no big deal, we
always knew it would. In a wave model, conservation of energy is
something you should check for, but only as an overall confirmation that
you've done the sums correctly. All the useful detail came from the
analysis of the voltage and/or current waves.

I agree with everything except your last sentence.
There is lots of useful information to be had from
tracking the energy through the system including
how and why the energy in the reflected wave changes
direction and momentum. If you think that information
doesn't matter or is not useful, then that's your
opinion. But please don't condemn the individuals who
find that information useful and go for an explanation.
And please don't say that explanation is wrong if you
cannot prove it to be invalid.

In the process of tracing forward and reflected waves,
we must remember that they obey the laws of physics
including their energy contents. The average forward energy
per unit time in a forward voltage of Vf RMS volts is
Vf^2/Z0 joules/sec, an assumption upon which the S-Parameter
analysis system is based. The average reflected energy per
unit time in a reflected RMS voltage is Vr^2/Z0 joules/sec.

In an S-Parameter analysis, if you square any of the
normalized voltage terms, you get joules/sec. Someone
said that at microwave frequencies, the powers are
often easier to measure than the voltages and currents.
The powers can be measured and the voltages and currents
calculated from the power measurements.

In optics, physicists don't have the luxury of dealing
with voltages and currents. They must necessarily deal
with energy and power. That field of physics is older
(and wiser) than RF engineering and they deal with power
reflection coefficients, not voltage reflection coefficients.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Partially reflective surfaces can (and are) in fact used to prevent
reflections, just as they are used to 100% re-reflect partial
reflections from a load.

Let's look at one of those reflective surfaces from
the standpoint of the forward wave in an S-Parameter
analysis.

a1----|
|----s21(a1)
s11(a1)----|

a1 is the normalized forward voltage, e.g. 10
s11 is the voltage reflection coefficient, e.g. 0.707
s21 is the voltage transmission coefficient

|a1|^2 is the forward power called Pfor1 in my energy
analysis article.

|s11(a1)|^2 is the reflected power called P3 in my
energy analysis article.

|s21(a1)|^2 is the transmitted power called P1 in
my energy analysis article.

The point is that s11(a1) is a steady-state value for
normalized reflected voltage that never makes it through
the impedance discontinuity.

|s11(a1)|^2 is the steady-state reflected joules/sec
that never makes it through the impedance discontinuity.

Here is a fill in the blank question for you and anyone
else who wants to respond.

If a Z0-match exists, the above values of normalized voltage
and joules/sec do not reach the source during steady-state
because __________________________________________________ _.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
The point is that s11(a1) is a steady-state value for
normalized reflected voltage that never makes it through
the impedance discontinuity.

I ended the sentence too soon. It never makes it through
the impedance discontinuity without help from somewhere.

|s11(a1)|^2 is the steady-state reflected joules/sec
that never makes it through the impedance discontinuity.

Same he It never makes it through the impedance discontinuity
without help from somewhere.

If a Z0-match exists, the above values of normalized voltage
and joules/sec do not reach the source during steady-state
because __________________________________________________ _.

What is the nature of that "help from somewhere"?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Jim Kelley wrote:
Partially reflective surfaces can (and are) in fact used to prevent
reflections, just as they are used to 100% re-reflect partial
reflections from a load.

Partially reflective surfaces cannot, by themselves,
reflect 100% of the incident energy. If it's partial,
it's not 100%, by definition. Any partially reflective
surface needs help from interference in order to
achieve 100% reflection. You know, that interference
that you deny exists.

That was the main point of my post, Cecil. The reflective coefficient
DOES NOT CHANGE. You're the one who claims that it does.

You continue to lie about what I said. I have said any
number of times that the physical reflection coefficient,
s11, is fixed and does NOT change. Why does someone who
is technically correct need to stoop to lying?

There is no energy "in" cancelled waves.

The waves existed along with their energy components before
they were canceled. What happens to those energy components
after the waves are canceled. If one sets one phase equal
zero and the other phase equal 180 degrees, what happens to
the energy in the two waves at:

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


There are two waves on the left existing with their respective
voltage and joules/sec. The result of total destructive interference
is zero voltage and zero joules/sec. What happened to the original
joule/sec components?


Cecil,

I pointed out a few days ago that the FSU Java applet you lean on so
heavily these days is a simple tutorial device designed by a grad
student and a programmer. As shown, it is physically impossible, since
there is no mechanism in place to cause the waves to suddenly jump
together and interfere.

It is a useful picture showing how sine waves with differing phases add
together; no more and no less. It is a simple matter of mathematics. It
is not a new discovery in the world of RF or optics.

73,
Gene
W4SZ

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Jim Kelley wrote:
So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

But that's just the point, Jim. You seem to believe the
pre-existing energy in those waves has been destroyed.
They obviously possessed energy before cancellation and
you say they possess zero energy after cancellation. If
that pre-existing energy is not destroyed, where did it go?


Cecil,

Now that you have access to a copy of Born and Wolf, you might dig
inside to see if you can improve your understanding of conservation of
energy. It is not quite as simple as you seem to believe.

B&W discuss the Poynting vector and its use in an overview in the first
chapter. I don't have the 4th edition. I have a couple of later editions
that contain identical language, so perhaps the same thing is in the 4th
edition.

In any case, here is the relevant quote. My explanations are enclosed in
[...]. Otherwise the paragraph is completely intact.

"It should be noted that the interpretation of S [Poynting vector] as
energy flow (more precisely as the density of energy flow) is an
abstraction which introduces a certain degree of arbitrariness. For the
quantity which is physically significant is, according to (41), not S
itself, but the integral of S [dot] n taken over a closed surface.
Clearly, from the value of the integral, no unambiguous conclusion can
be drawn about the detailed distribution of S, and alternative
definitions of the energy flux density are therefore possible. One can
always add to S the curl of an arbitrary vector, since such a term will
not contribute to the surface integral as can be seen from Gauss'
theorem and the identity div curl = 0. However, when the definition has
been applied cautiously, in particular for averages of small but finite
regions of space or time, no contradictions with experiments have been
found. We shall therefore accept the above definition in terms of the
Poynting vector of the density of the energy flow."

[ S and n are vectors, shown in bold type in the original. ]

Now for my comments.

Two important concepts are contained in the B&W quote. First, the math
involved with Poynting vectors is not quite as simple as many amateur
radio operators seem to believe. It does not make any sense to simply
add and subtract Poynting vectors in elementary fashion and expect to
get correct results. This is true even for your favorite case of a
one-dimensional problem such as a transmission line.

Second, the Poynting vector by itself means little. It is only the
integral over a closed surface that has physical reality. In your
favorite case of reflections and re-reflections the only useful
non-trivial application of the Poynting vector would be the integration
of the Poynting vector over a small region that includes the line
discontinuity inside. And even then, only the total energy balance can
be determined. Put in direct terms, there is no available information,
and no need for any information about what happens to the energy
contained in the various component waves you like to consider. It simply
does not matter. The only energy balance that counts is the net energy
flowing through the surface of the integration volume. Anything else is
merely in your imagination. B&W allow you to add anything you like, as
long as it is the curl of a vector. But there is no physical reality in
doing so.

It has been pointed out numerous times that modern physical theory is
correct by design. Ian again pointed out that fact earlier today. If the
wave equations, the field equations, force equations, or whatever are
analyzed correctly the energy balance will automatically work out
correctly as well. A check of energy balance is sometimes useful to
highlight any errors that might have been made in the math, but no new
physical information should be expected.

Finally, it is well known by all physicists, and I believe most
engineers, that energy considerations by themselves can be very useful
for analyzing physical problems. Much of higher level classical
mechanics and essentially all of quantum mechanics techniques are energy
based. The so-called Hamiltonian formulation is well-known and widely
used. It is no more or less correct than techniques based on forces and
other fields, but the Hamiltonian technique is often much more
computationally convenient.

73,
Gene
W4SZ

Constructive interference in radiowave propagation
 

Gene Fuller wrote:
I pointed out a few days ago that the FSU Java applet you lean on so
heavily these days is a simple tutorial device designed by a grad
student and a programmer. As shown, it is physically impossible, since
there is no mechanism in place to cause the waves to suddenly jump
together and interfere.

Good Grief, Gene! You are arguing that because you cannot
view them in the present that they never existed in the
past. Such is nonsense.The left hand side is a historical
plot of the points of the waves before they interfere.
Of course, those points only exist back in history and
no longer exist in the present because everything in the
present is happening at a point. Do you also deny the
existence of the historical yearly temperature plot points
because they don't still exist today? Please get real.
Here's a temperature chart to which you can apply your
"impossible" logic concepts.

http://en.wikipedia.org/wiki/Global_warming

Paraphrasing your idea: "As shown, it is physically
impossible, since there is no mechanism in place to
cause more than one temperature to exist at the
present time."

That java example is an example of implementing the
S-Parameter equation b1 = s11(a1) + s12(a2) which
is CERTAINLY NOT IMPOSSIBLE. By adjusting the magnitudes
and phase angles of a1 and a2, any degree of interference
can be obtained. One wave is s11(a1) and the other wave
is s12(a2). Of course, the interference happens at a point
(or plane) so fast that it is impossible to view in real
time. But by using deductive reasoning and the known
laws of physics, we are able to come up with valid java
scripts like the above. Your confusion is in assuming
all those points have to exist simultaneously in the
present, a really, really ridiculous notion.

They do not and cannot exist simultaneously in the present
just as temperatures on a temperature plot of past years
do not and cannot exist in the present anymore. Those points
on the java script existed back in time and are plotted in
a similar manner to plotting temperatures that no longer
exist in the present.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:
Gene Fuller wrote:
I pointed out a few days ago that the FSU Java applet you lean on so
heavily these days is a simple tutorial device designed by a grad
student and a programmer. As shown, it is physically impossible, since
there is no mechanism in place to cause the waves to suddenly jump
together and interfere.

Good Grief, Gene! You are arguing that because you cannot
view them in the present that they never existed in the
past. Such is nonsense.The left hand side is a historical
plot of the points of the waves before they interfere.
Of course, those points only exist back in history and
no longer exist in the present because everything in the
present is happening at a point. Do you also deny the
existence of the historical yearly temperature plot points
because they don't still exist today? Please get real.
Here's a temperature chart to which you can apply your
"impossible" logic concepts.

http://en.wikipedia.org/wiki/Global_warming

Paraphrasing your idea: "As shown, it is physically
impossible, since there is no mechanism in place to
cause more than one temperature to exist at the
present time."

That java example is an example of implementing the
S-Parameter equation b1 = s11(a1) + s12(a2) which
is CERTAINLY NOT IMPOSSIBLE. By adjusting the magnitudes
and phase angles of a1 and a2, any degree of interference
can be obtained. One wave is s11(a1) and the other wave
is s12(a2). Of course, the interference happens at a point
(or plane) so fast that it is impossible to view in real
time. But by using deductive reasoning and the known
laws of physics, we are able to come up with valid java
scripts like the above. Your confusion is in assuming
all those points have to exist simultaneously in the
present, a really, really ridiculous notion.

They do not and cannot exist simultaneously in the present
just as temperatures on a temperature plot of past years
do not and cannot exist in the present anymore. Those points
on the java script existed back in time and are plotted in
a similar manner to plotting temperatures that no longer
exist in the present.



Cecil,

Why don't you simply stop being such a nitwit. I understand perfectly
what the Java applet is and is not. S-parameters are not a new branch of
science. No one is confused except you.

73,
Gene
W4SZ

Constructive interference in radiowave propagation
 

Gene Fuller wrote:
quoting Born & Wolf:
"However, when the definition has
been applied cautiously, in particular for averages of small but finite
regions of space or time, no contradictions with experiments have been
found. We shall therefore accept the above definition in terms of the
Poynting vector of the density of the energy flow."

There's the meat of the quote as far as transmission lines
are concerned. Given that transmission lines are "small but
finite regions of space or time", and since there are only
two possible directions in a transmission line, Born and
Wolf seem to give us permission to do exactly what you
are complaining about. Your concerns about light waves
in three dimensional free space just don't exist for the
primarily single dimensional "space" in a transmission line.
Ideally, the power density exists only between the inner and
outer conductors of the coax.

It does not make any sense to simply
add and subtract Poynting vectors in elementary fashion and expect to
get correct results.

Born & Wolf's own words in the quote above provided by you
contradict that assertion.

It simply does not matter.

You sure make a lot of postings about it for it not
to matter to you. :-) It certainly matters to me
and others and we will not stop the discussion
until it is resolved to everyone's satisfaction.
What are you afraid we will uncover if we keep
digging? Your ignorance?

It has been pointed out numerous times that modern physical theory is
correct by design. Ian again pointed out that fact earlier today. If the
wave equations, the field equations, force equations, or whatever are
analyzed correctly the energy balance will automatically work out
correctly as well.

The assertions that reflected waves don't exist or if they
do exist, they contain no energy, are false assertions. Trying
to sweep them under the rug by mealy-mouthing some automatic
energy balance religion is just another copout.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Gene Fuller wrote:
Why don't you simply stop being such a nitwit. I understand perfectly
what the Java applet is and is not. S-parameters are not a new branch of
science. No one is confused except you.

Before I explained it to you, you obviously had no
clue what that java script represented since you
said it was impossible. Not only is it possible,
it happens every time someone adjusts an antenna
tuner for a match.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 14, 8:57 pm, Cecil Moore wrote:
Jim Kelley wrote:
So I'm happy to
leave it to you to explain to Cecil how waves cancel but without
anhiliating the energy "in" them.

But that's just the point, Jim. You seem to believe the
pre-existing energy in those waves has been destroyed.
They obviously possessed energy before cancellation and
you say they possess zero energy after cancellation. If
that pre-existing energy is not destroyed, where did it go?
--
73, Cecil http://www.w5dxp.com

As I said, Cecil, your ideas about waves 'possessing energy' need a
little work.

ac6xg

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
As I said, Cecil, your ideas about waves 'possessing energy' need a
little work.

Complete lack of technical content or technical defense
of your assertions is noted - nothing but a bunch of
hand-waving.

One more challenge for you, Jim. If you can prove that
an EM wave can exist without the associated ExB energy, you
will no doubt win a Nobel Prize in Physics.

Here's what Hecht says: "Any electromagnetic wave exists
within some region of space, and it is therefore natural
to consider the *radiant energy per unit volume*, or
*energy density*. We suppose that the electric field itself
can somehow store energy. This is a major logical step
since it imparts to the field the attribute of physical
reality - if the field has energy, it is a thing-in-itself."

Maybe it's past time for you to take that logical step
that Hecht took so long ago?

"To represent the flow of electromagnetic energy associated
with a traveling wave, let 'S' symbolize the transport of
energy per unit time (the power) across a unit area. ...
it has come to be known as the *Poynting vector*."

Hecht labels the energy per unit time in an EM wave as
"power". Hecht's Poynting vector equations contain cosine
terms. Hecht shoots down virtually every one of your
assertions and objections.

I notice you carefully avoided my S-Parameter example.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

On Apr 15, 11:58 am, Cecil Moore wrote:
I notice you carefully avoided my S-Parameter example.

I try to comment only on technical things that you say with which I
disagree, Cecil. Though as it happens, most of the objectionable
comments you make are not techincal.

ac6xg

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
As I said, Cecil, your ideas about waves 'possessing energy' need a
little work.

All it takes to prove you wrong is a
look at a typical S-Parameter equation involving
the superposition of two terms. In the following the
'@' sign is used for the angle sign. a1 and a2 are
normalized voltages. s21 is a transmission coefficient.
s22 is a reflection coefficient.

b2 = s21(a1) + s22(a2)

Given a1 = 10 @ 0 deg, a2 = 10 @ 180 deg,
s21 = 0.707 @ 0 deg, s22 = 0.707 @ 180 deg

s21(a1) = 0.707@0(10@0) = 7.07 @ 0 deg

s22(a2) = 0.707@180(10@180) = 7.07 @ 0 deg

superposing those two values gives:

b2 = 14.14 @ 0 deg

All is well and good. Multiply b2 by SQRT(Z0) to get
total forward voltage.

Now let's look at the powers in accordance with HP's
Ap Note 95-1. For that, we don't need to know the Z0.
The beauty of an S-Parameter analysis is that if one
squares the normalized voltages, one gets power.

|s21(a1)|^2 = 50 watts

|s22(a2)|^2 = 50 watts

|b2|^2 = 200 watts

Even in the S-Parameter analysis, superposing two 50W
waves in phase yields 200 watts. Constructive interference
not only makes it possible but demands it.

Jim, I challenge you to find anything wrong with this S-
Parameter analysis. It follows exactly Born and Wolf's
intensity equations for constructive interference when
the phase angle between a1 and a2 is 180 degrees and
their magnitudes are equal.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
Cecil Moore wrote:
I notice you carefully avoided my S-Parameter example.

I try to comment only on technical things that you say with which I
disagree, Cecil. Though as it happens, most of the objectionable
comments you make are not techincal.

Translation: I agree with you technically but I dislike your
personal style so I am going to keep harassing you with
false quotations and kibitzing. Please see my latest S-Parameter
posting where the S-Parameter equations agree perfectly
with Hecht and Born & Wolf, and disagree with you.
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote in news:0svUh.417$Yo2.402
@newssvr19.news.prodigy.net:

Now let's look at the powers in accordance with HP's
Ap Note 95-1. For that, we don't need to know the Z0.
The beauty of an S-Parameter analysis is that if one
squares the normalized voltages, one gets power.

Cecil,

AN95-1 is a slide show, it is a presentation to accompany a talk, and as
such is incomplete.

Another HP note is AN154 which is derived from a training seminar, but is
more complete in its development. Chapter 1 is relevant to your use of S
parameters.


Let me quote:

Notice that the square of the magnitude of these
new variables has the dimension of power. |a1|2
can then be thought of as the incident power on
port one; |b1|2 as power reflected from port one.
These new waves can be called traveling power
waves rather than traveling voltage waves.
Throughout this seminar, we will simply refer to
these waves as traveling waves.

It is a leap to move from "can be thought of as power" or "has the
dimension of power" to your statement (which you attribute to HP AN95-1)
"The beauty of an S-Parameter analysis is that if one squares the
normalized voltages, one gets power." Did AN95-1 state clearly that which
you suggest?

Nowhere in Chapter 1 of AN154 do they perform alegebraic operations on
power, the chapter is full of expressions, but they do not use |Sxx|^2.


|s21(a1)|^2 = 50 watts

|s22(a2)|^2 = 50 watts

|b2|^2 = 200 watts

Even in the S-Parameter analysis, superposing two 50W
waves in phase yields 200 watts. Constructive interference
not only makes it possible but demands it.

So not you are superposing power to "yield" a resultant power. Did HP
show you how to do that, or is it all your own work?

Owen

Constructive interference in radiowave propagation
 

A couple of typos fixed:

Cecil Moore wrote in news:0svUh.417$Yo2.402
@newssvr19.news.prodigy.net:

Now let's look at the powers in accordance with HP's
Ap Note 95-1. For that, we don't need to know the Z0.
The beauty of an S-Parameter analysis is that if one
squares the normalized voltages, one gets power.

Cecil,

AN95-1 is a slide show, it is a presentation to accompany a talk, and as
such is incomplete.

Another HP note is AN154 which is derived from a training seminar, but is
more complete in its development. Chapter 1 is relevant to your use of S
parameters.


Let me quote:

Notice that the square of the magnitude of these
new variables has the dimension of power. |a1|^2
can then be thought of as the incident power on
port one; |b1|^2 as power reflected from port one.
These new waves can be called traveling power
waves rather than traveling voltage waves.
Throughout this seminar, we will simply refer to
these waves as traveling waves.

It is a leap to move from "can be thought of as power" or "has the
dimension of power" to your statement (which you attribute to HP AN95-1)
"The beauty of an S-Parameter analysis is that if one squares the
normalized voltages, one gets power." Did AN95-1 state clearly that which
you suggest?

Nowhere in Chapter 1 of AN154 do they perform alegebraic operations on
power, the chapter is full of expressions, but they do not use |Sxx*ax|^
2.


|s21(a1)|^2 = 50 watts

|s22(a2)|^2 = 50 watts

|b2|^2 = 200 watts

Even in the S-Parameter analysis, superposing two 50W
waves in phase yields 200 watts. Constructive interference
not only makes it possible but demands it.

So now you are superposing power to "yield" a resultant power. Did HP
show you how to do that, or is it all your own work?

Owen