Superposition
 

Cecil Moore wrote:

Then exactly what "redistributes the photons to regions that
permit constructive interference", as the FSU web page says?

I don't think it reasonable to be held responsible to explain what
other people write. It's not a particularly rigorous or precise
treatise, Cecil.

Is it really imagination that accomplishes that magic feat?

How clever. You'll forgive me if I thought it better to ask you to
visualize the concept than for me to try to draw a football field
sized pair of capacitor plates with you between them using ASCII
characters. I suspect most other readers were able to accomplish the
task.

Jim, you have *NEVER* said what you think causes total
re-reflection of reflected waves (aside from your magical
imagination).

In fact, I have repeatedly explained it to you. Ad naseum. And so
have many other people on this group.

Please enlighten us with some math and details
that don't violate the laws of physics.

Texts like Born and Wolf and Jackson say it much more elegantly than I
ever could. There's a pretty good picture of it (albeit pitifully
notated) on your web site.

73, ac6xg

Superposition
 

Cecil Moore wrote:
Gene Fuller wrote:
"the intensity varies between a maximum value Imax = 4I1, and a
minimum value Imin = 0"

Yes, that's essentially what I have been saying. The peak
intensity (irradiance) can be double the intensity of
the combined intensity of both superposed waves.

What B&W *don't* say is anything about two 1 watt waves interacting,
waves exhibiting constructive and destructive interference, cause and
effects relationships, or even energy conservation.

Eugene Hecht calls the last term in the irradiance equation
the "interference term". He talks about "total destructive
interference" and "total constructive interference". The sign
of the interference term indicates whether the interference
is destructive (-) or constructive (+).

All of those are things written by more casual writers, such as Hecht,
Melles-Griot, and the FSU Java dudes. There is nothing wrong with that
type of explanation for simple illustration, but it runs out of gas
when trying to support detailed analysis. One quickly ends up with
silliness such as waves that are launched and then cancel
destructively within a short (but undefined) distance. None of that
nonsense occurs if one simply applies the standard analysis techniques
such as used by B&W.

Exactly what nonsense are you referring to? Please be specific. It
is difficult to defend myself from assertions of "nonsense" with no
specific allegations.

I gather from the above that wave cancellation due to superposition
is against your religion. Since all impedance discontinuities cause
reflections, exactly how and why do those reflected waves cease to
exist? Please be specific.

Cecil,

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.

If the proper equations are set up and the proper boundary conditions
are applied (not always easy to do), then waves will exist where they
are needed to describe the physical reality and they will not exist
where they are not needed.

There is no need to worry about waves that don't exist.

As for the "nonsense", we had this discussion a few times, including a
couple of months ago. I don't feel like finding the exact messages, but
the gist was something like:

"Wave 4 and wave 5 return toward the source from a match point, but they
are opposite phase and therefore cancel after a short journey."

If you don't recognize that exchange, let's just drop it.

73,
Gene
W4SZ

Superposition
 

Gene Fuller wrote:
Cecil Moore wrote:

Cecil,

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.

If the proper equations are set up and the proper boundary conditions
are applied (not always easy to do), then waves will exist where they
are needed to describe the physical reality and they will not exist
where they are not needed.

There is no need to worry about waves that don't exist.

As for the "nonsense", we had this discussion a few times, including a
couple of months ago. I don't feel like finding the exact messages, but
the gist was something like:

"Wave 4 and wave 5 return toward the source from a match point, but they
are opposite phase and therefore cancel after a short journey."

If you don't recognize that exchange, let's just drop it.

73,
Gene
W4SZ

Hi Gene,

Yes. The short journey was described by the term "dt". According to
Cecil, that is the amount of time after energy is reflected and before
it 'turns around and goes the other way as it is required to do by the
law of conservation of energy'. You may recall that it is forced to
go the other way 'because there are only two directions in a
transmission line'.

73, ac6xg

Superposition
 

On Tue, 20 Nov 2007 14:37:41 -0800, Jim Kelley
wrote:

The short journey was described by the term "dt".

Ah, suffering the dt's.

As Ed McMahon would prompt Johnny:
"Just how short was that journey?"

My guess it will either be too short to do the job, or much too large
to be true.

This thread should be called:
"Supposition"
or
"Imposition"
or
"Superstition"

73's
Richard Clark, KB7QHC

Superposition
 

Cecil Moore wrote:

Given the power-density equation:

Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(A)

May I assume that from what you have said so far, that P1
and P2 never existed in the first place????

Being an under defined problem, it's difficult to know. But it is
certainly possible that P1, or P2, or both never existed.
Particularly the latter, if the fields happen to be co-located in
space and are at every point equal in magnitude and opposite in phase.

If they never
existed, wouldn't their magnitudes be zero in violation
of every rule of physics concerning reflections????

I assure that no 'physics violations' are implied or intended by
anything I post with my name, callsign, and email address attached to
it. It would not...um.....reflect well. ;-)

73, Jim AC6XG

Superposition
 

Jim Kelley wrote:
Jim, you have *NEVER* said what you think causes total
re-reflection of reflected waves (aside from your magical
imagination).

In fact, I have repeatedly explained it to you. Ad naseum. And so have
many other people on this group.

Nope, you never have - you just say you have hoping
nobody will notice that you have never done anything
except wave your hands.

What happens to the external reflected wave energy
at the moment the internal reflected wave arrives?

If you don't want to duplicate your effort please
re-post your previous posting on the subject. If
you don't respond, it will be obvious that there
was no previous posting.
--
73, Cecil http://www.w5dxp.com

Superposition
 

Jim Kelley wrote:
But it is
certainly possible that P1, or P2, or both never existed. Particularly
the latter, if the fields happen to be co-located in space and are at
every point equal in magnitude and opposite in phase.

You cannot have it both ways, Jim. Either the reflections
existed or they they never existed. Please tell us why
and how a physical impedance discontinuity with a reflection
coefficient of 0.707 avoids causing reflections (in violation
of the laws of physics).
--
73, Cecil http://www.w5dxp.com

Superposition
 

Cecil Moore wrote:

You cannot have it both ways, Jim. Either the reflections
existed or they they never existed.

You want people to believe that the behavior of an antireflective
coating is, first light reflects from it, and then it's cancelled -
before anybody see's it. That's trying to have it both ways.

You're of course entitled to believe whatever you like. But you
really owe it to people to include a disclaimer when you proselytize
about it here.

End of commentary.

73, ac6xg

Superposition
 

Jim Kelley wrote:
You want people to believe that the behavior of an antireflective
coating is, first light reflects from it, and then it's cancelled -
before anybody see's it. That's trying to have it both ways.

No, that is obviously what happens, Jim. Since it happens
at the speed of light, our eyes just cannot see it. But
for the instant of time it takes the light wave to travel
the 1/2WL round trip through the thin-film and back, there
exists a reflection from the thin-film. The laws of physics
will not allow anything else.

It's a lot easier to detect at RF frequencies where 1/4WL
takes some time for the RF wave to travel. For instance,
1/4WL at 4 MHz is 61.5 feet. It takes RF a measurable
length of time to travel that distance and for that length
of time during the transient state, a reflection exists
which is canceled if a Z0-match is achieved. That's just
simple physics. Here is an example:

XMTR---50 ohm T-line---+---1/4WL 291.4 ohm T-line---50 ohm load

Rho at the impedance discontinuity is 0.707. For the length
of time it takes the first reflection to arrive back from
the load at point '+', 1/2 of the forward power is reflected
back toward the source. That's a reflected wave that is
subsequently canceled. Exactly what causes the cancellation
of that reflected wave? You have *never* answered that
question.
--
73, Cecil http://www.w5dxp.com

Superposition
 

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