Roy Lewallen wrote:
Anyone who's interested can find more interesting cases in "Food for
thought - Forward and Reverse Power.txt" at
http://eznec.com/misc/food_for_thought/. And those who aren't
interested, well, you're welcome to believe what you choose. Just don't
look too closely at the evidence.

(*) Anybody fond of the notion that reverse power "goes" somewhere or
gets dissipated in the source or re-reflected back needs to come to
grips with this problem before building further on the flawed model of
bouncing waves of flowing power.

Roy, I have had an article for review into QEX for more than two
months that explains what is missing from your analysis. Unfortunately,
I have not heard a word from QEX since I submitted the article.

So I will introduce a concept new to the field of RF but completely
understood in the field of optics. I actually introduced this concept
three years ago in discussions on r.r.a.a with Dr. Best but I was
apparently unable to convey the concept.

If I ask you what things can cause 100% reflection, I assume you would
list three things: 1. A short-circuit, 2. An open-circuit, and
3. A pure reactance. And that is indeed true for loads upon which a
single wave is incident.

But the field of optics recognizes an additional thing that can cause
100% reflection and that's wave cancellation. If two coherent EM waves
are traveling the same path in the same direction in a transmission
line and they are 180 degrees out of phase, the waves will cancel and
the energy components in the two waves, which must be conserved, will
be 100% reflected in the opposite direction. The following two optics
web pages verify that fact for EM waves: (near the bottom of the pages)

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

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

What is happening in your "food for thought" assertions is that you
are neglecting the ability of the phenomenon of wave cancellation to
cause 100% reflection of the energy components in the two canceled
waves, something that is well understood in the field of optics.
Dr. Best also neglected to take interference energy into account in
his QEX article on transmission lines.

"Optics", by Hecht asserts that for every incidence of constructive
interference there must be an equal magnitude of destructive
interference to satisfy the conservation of energy principle. (That
is unless the source itself is capable of delivering extra power.)
By the same token, if the source doesn't absorb constructive
interference energy, it must go somewhere else. In a transmission
line with only two directions, there is only one other way it can
possibly go and it becomes a reflection or a re-reflection.

What is happening in your "food for thought" examples is that
destructive interference/wave cancellation between the forward wave
and reflected wave is occurring at your source. That wave cancellation
event is feeding constructive interference energy back into the
feedline which joins the forward wave energy. Your discussions
ignore the effect of interference energy which must necessarily
be conserved.

Your argument goes something like this: I am ignoring the
constructive/destructive interference energy involved in wave
cancellation. Therefore, it never existed in the first place.
That's a petitio principii type of argument.
--
73, Cecil http://www.qsl.net/w5dxp


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