Michael Coslo wrote:
At the risk of being both a dullard and messing up all the fun, does
not every destructive interference have to be balanced by a constructive
interference, which in turn leads to a condition of "Okey dokey?"

A canceled wave needs a reinforced wave, and then nothing is lost,
nothing is gained.

- 73 de Mike N3LI -

Hi Mike -

One could suggest a number of different possible scenarios in which
nothing is lost or gained. But an impossible scenario is one which
violates thermodynamic principles. Another might describe phenomena
which is not in accord with Maxwell's equations. One should therefore
feel comfortable discarding any description which is inconsistent with
both thermodynamics and Maxwell's equations.

73, ac6xg

Michael Coslo wrote:
At the risk of being both a dullard and messing up all the fun, does
not every destructive interference have to be balanced by a constructive
interference, which in turn leads to a condition of "Okey dokey?"

Yep, any destructive interference toward the source is exactly
offset by constructive interference toward the antenna. If one
takes time to calculate the component phasor voltages on both
sides of a Z0-match located away from the source, the constructive
and destructive interference is obvious.

A canceled wave needs a reinforced wave, and then nothing is lost,
nothing is gained.

Exactly. The reflected energy that appears to be lost as
destructive interference in the direction of the source
when a Z0-match is achieved, is recovered in the forward
wave as constructive interference energy traveling toward
the antenna.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Jim Kelley wrote:

The momentum in reflected waves changes direction upon reflection.
What part of that do you need to have explained?


What causes 100% reflection when the power reflection
coefficient (reflectance) is only 0.5?

If you would just work the problem the hard way, you would see where
you're misconception lies. Any given wave front will never reflect
100% from a surface which is only 50% reflective, no matter how
vicious your insults become, how may URLs you cut and paste, or how
furiously you wave your hands. But when you work the problem as has
been suggested you will see how energy gets from source to load. It
does not rely on macroscopic layman's explanations or mathematical
shortcuts in order to get there.

The only energy "lost" by partial reflection in the process is that
which is reflected back toward the source or stored in the system
during the transient period. The sum of all the partial reflections
equals the energy stored in the system (less the portion of energy
admitted to the load or reflected back to the source). After the
transient period, no energy is reflected back to the source, and the
energy entering the system from the source equals the energy existed
the system through the load.

I know that you understand the difference between potential and
kinetic energy in mechanics. Please try to consider that the concepts
are no less valid in electromagnetism. (Note that we even use the
word 'potential' to describe voltage.)

73, ac6xg

Jim Kelley wrote:
Any given wave front will never reflect 100%
from a surface which is only 50% reflective,

That's all you have to say, Jim, to defeat your argument.
If you would stop refusing to perform a simple calculation
involving my example at:

http://www.w5dxp.com/thinfilm.GIF

you would understand. When the internal (0.009801w)
wave reflection arrives at t3 and interferes with the
(0.01w) external reflection wave, what is the resulting
reflected power back toward the source. When you calculate
the results and realize that it is not 0.01 - 0.009801 watts,
you will begin to understand the nature of interference.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Jim Kelley wrote:

Any given wave front will never reflect 100% from a surface which is
only 50% reflective,


That's all you have to say, Jim, to defeat your argument.

I am quite content to agree to disagree on that point if you wish.
Any exceptions to it that you would try to make could only derive from
fiction.

73, ac6xg

Jim Kelley wrote:

Cecil Moore wrote:

Jim Kelley wrote:
Any given wave front will never reflect 100% from a surface which is
only 50% reflective,

That's all you have to say, Jim, to defeat your argument.

I am quite content to agree to disagree on that point if you wish. Any
exceptions to it that you would try to make could only derive from fiction.

I seriously doubt that you are blind to the contradictions
in your argument and are simply hoping to slip them through
while no one is paying attention. Suffice it to say, it is
impossible for a 50% reflective surface to cause 100% reflections
without help from interference in the form of wave cancellation
due to permanent destructive interference. Anybody who understands
the process of anti-reflective thin-film coatings understands
the process of destructive interference redistributing the energy
in the direction that allows for constructive interference.

http://www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and
the thickness of the film are such that a phase difference
exists between reflections of p, then reflected wavefronts
interfere destructively, and overall reflected intensity is
a minimum. If the two reflections are of equal amplitude,
then this amplitude (and hence intensity) minimum will be
zero." (Referring to 1/4 wavelength thin films.)

"In the absence of absorption or scatter, the principle of
conservation of energy indicates all 'lost' reflected intensity
will appear as enhanced intensity in the transmitted beam.
The sum of the reflected and transmitted beam intensities is
always equal to the incident intensity. This important fact
has been confirmed experimentally."

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

Michael Coslo wrote:

At the risk of being both a dullard and messing up all the fun, does
not every destructive interference have to be balanced by a constructive
interference, which in turn leads to a condition of "Okey dokey?"

A canceled wave needs a reinforced wave, and then nothing is lost,
nothing is gained.

Not quite, but close. It's ok to have two waves that cancel at one place
but go their separate ways at others without reinforcing. Any
combination of canceled, reinforced, and independent waves is ok as long
as the energy all adds up to the amount put into the system.

The purveyors of these contrived questions have never been able to
explain how they create these exquisite co-traveling canceled waves
without also creating those nagging reinforced or non-canceled waves.
Since it requires magic to create them, it should be no surprise that it
requires magic to explain what happens to the energy once the magical
canceling waves have been conjured up.

Roy Lewallen, W7EL

Roy Lewallen wrote:
The purveyors of these contrived questions have never been able to
explain how they create these exquisite co-traveling canceled waves
without also creating those nagging reinforced or non-canceled waves.

Strawman alert!
To the best of my knowledge, nobody has ever been stupid enough
to say waves cancel and the energy in them is destroyed. In fact,
I have said exactly the opposite, i.e. waves cancel and the energy
that existed in them before they were canceled is preserved.

I believe it is you who is on record as not caring where the
energy goes.
--
73, Cecil http://www.w5dxp.com