Jim Kelley wrote:

Cecil Moore wrote:
It never encounters the source resistor as it is re-reflected by
wave cancellation, not by an impedance discontinuity. I have a QEX
article coming soon that will explain the details.

The Journal of Irreproducible Results could also be persuaded to publish
that claim, Cecil. Any implication that almost half of Maxwell's
equations are superfluous should easily qualify as an irreproducible
result. :-)

Don't know exactly what you are inferring but the editors of QEX
have seen the light, :-) even if at RF frequencies. Quite a few
sources from the field of optics indicate that the phenomenon is well
known in that field even if not well understood in the field of RF.

It is very simple physics, Jim. When two coherent EM waves of equal
amplitudes and opposite phases attempt to travel in the same direction
in the same path, they cancel each other in their original direction
of travel. This is explained under "total destructive interference"
in "Optics" by Hecht. Since the energy in the two waves cannot be
canceled, that energy goes somewhere else. In a transmission line,
there are only two directions. If two waves cancel in one direction,
their combined energy components head back in the only other direction.
Everyone has seen that light interference pattern with his/her own eyes
and some just never realized what was happening.

Here's an example. If you wade through it, you will be forced to admit
that the destructive interference/wave cancellation at the non-glare
surface 'A' causes a reversal in the direction of the reflected
irradiance. That, my friend, is a 100% re-reflection, just as Walter
Maxwell has been saying for decades. 'n' is the index of refraction:

n=1.0 | n=1.2222 | n=1.4938
Laser-------air-------|---1/4WL thin film---|---infinite glass----...
| |
A B

The reflection from surface 'A' is canceled by an equal magnitude
and opposite phase reflection from surface 'B'. The energy components
in those two canceled waves join the forward wave because energy
cannot be destroyed (even though that concept seems to have serious
consequences to your mental health :-). Here's a quote from the
following web page.

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.”

In an RF transmission line, since there are only two possible
directions, the only “regions that permit constructive interference”
and "redistribution in a new direction" at an impedance discontinuity
is the opposite direction from the direction of destructive
interference/wave cancellation.

The above laser example is virtually identical to the following:

RF XMTR--50 ohm coax--+--1/4WL 61 ohm coax--+--infinite 75 ohm coax

If we use a coherent laser beam, no coax is required, so the
behavior of the actual EM waves is relatively easy to analyze.
--
73, Cecil http://www.qsl.net/w5dxp

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