Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
Well something causes you to latch up and bail with
"its not real world", ...

Don't feel unique - I do the same thing when someone
says God created the heavens and earth in 6 days.

You are either confused about what I said (or deliberately
bearing false witness). Please correct your confusion
(or lack of ethics) or I will stop responding.

Bottom line: At points '+' in the example before any
cutting, either reflections exist or they don't.

If reflections exist, there has to exist an impedance
discontinuity to cause the reflections. There is no
impedance discontinuity.

If reflections don't exist, there is nothing to change
the direction of the flowing energy. Therefore, energy
is flowing both ways through the '+' points. The *NET*
energy flow is zero. But it is easily proven that
energy is flowing from one SGCL to the other.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
So do the travelling waves "reflect" off each
other? Save the term "reflect" for those cases
where there is an impedance discontinuity and
use "bounce" for those cases where no energy
is crossing a point and even Cecil may be
happy. But bounce it does.

If your model requires EM waves to bounce off of
each other, it doesn't represent reality. What
you may be seeing is the case where destructive
interference in one direction has to equal constructive
interference in the other direction. This is simple
wave cancellation, not bouncing.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Roy Lewallen wrote:
Yes, that is correct. The impedance of the source (a perfect voltage
source) is zero, so the reflection coefficient seen by the reverse
traveling wave is -1.

The logic of this assumption eludes me. In fact, it seems completely
illogical and counter to the concept of how voltage and current waves
are observed to move on a transmission line.

The reason that the logic eludes you, Roger, is that it
can exist only in the human mind where anything is possible.
Roy's above statement requires a belief in the supernatural.

The impedance of a real world source is never zero and
Roy cannot leap tall buildings at a single bound except
in his mind. :-)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Roy and I are talking about this on other postings. I guess the purest
might point out that a 50 ohm generator only has a voltage to current
ratio of 50, but we don't know if it also has a resistor to absorb
energy. It is like a black box where the only thing we know about it is
that when we connect a 50 ohm resistor to it through a 50 ohm
transmission line, there are no standing waves.

Good for you, Roger, every reference I have on Thevenin
equivalent boxes say that what is happening inside the
box is irrelevant because it bears no resemblance to
reality.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Cecil Moore wrote:
In the absence of a real physical impedance discontinuity,
they cannot "reflect off one another". In a constant Z0 transmission
line, reflections can only occur at the ends of the line and only
then at an impedance discontinuity.

Cecil, this sounds more like a pronouncement from God than like an
conclusion from observations.

Sorry, it wasn't meant that way. It is just a fact of
physics that is obvious. EM waves possess energy and
momentum. Both of those values must be preserved. In
a passive constant-Z0 transmission line, if there are
no impedance discontinuities to cause reflections, then
reflections cannot exist. If reflections don't exist,
the momentum of the EM waves doesn't change.

Where we differ is that you allow traveling waves to "reflect
off one another". There are no laws of physics which allow
that in the absence of a physical impedance discontinuity.
EM waves simply do not bounce off each other.

I am not aware of any laws of physics that prevent it either.

Why doesn't a reflection coefficient equal to zero
imply no bouncing?

I don't
see any evidence that it happens in open space, like light bouncing off
light. It might happen on transmission lines however. I just cannot
find any convincing evidence either way. What I have deduced so far
indicates that it makes no difference which happens.

If it doesn't happen with light waves, it probably doesn't
happen with RF waves - they are identical except for
wavelength.

I am stating a negative premise, that EM waves do not bounce
off of each other. A negative premise cannot be proved. It
can only be disproved and it only takes one case to do so.

If anyone can offer just one proven case of one EM wave bouncing
off of another EM wave in the complete absence of a change in
the media, then I will be proven wrong.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
No need for translation, though this is not quite what
was said above. Note the words "automatically" in the
first quote and "may be quite different" in the second.
The original authors allow for the possibility that it
might be the same, while your "translation" removes
that possibility.

They engaged in typical author-speak. My university
professors had no such limitations. They were quite
harsh on anyone who tried to figure out where the
power goes inside a Thevenin or Norton equivalent
source.

It is not I who wants it both ways. For me it is clear
that there is no reflection when the output (source)
impedance is the same as Z0. And when it is not equal
to Z0, there is a reflection.

Apparently that is NOT clear to you. In the earlier
example, there is no impedance discontinuity at the
'+' points, yet you require reflections at those
points. That's what you cannot have both ways.

If there's no traveling wave energy flowing through
the '+' points, there must exist reflections. If
reflections exist, there must exist an impedance
discontinuity. There is no impedance discontinuity.

Not when the output (source) impedance is known. It is
then easy to compute the magnitude of the reflection
using the standard rules for reflection coeficient.

Although many have tried to prove that the output (source)
impedance is the impedance encountered by the reflected waves,
all of those numerous experiments have failed. Therefore,
there is a high probability that the impedance encountered
by the reflected waves is *NOT* the output (source) impedance.
The argument has raged loud and long since at least the 1980's.
You are not going to resolve it by hand-waving.

Keith, if you can prove that the reflected waves encounter
the output (source) impedance, you are a better man than all
of the many others who have tried and failed.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
Agreed. Either view produces the same results.

Either view, Creationism or the Big Bang, produces
the same results. :-)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
Also consider that field lines never cross. It would
therefore seem impossible for the two electric fields
associated with two EM waves to pass each other
without interaction.

They certainly superpose so the field lines don't
cross but superposition doesn't cause interaction
in free space or in a constant-Z0 transmission line
where neither medium changes. Free space superposition
results in zero reflections.

And whether the wave in space is viewed as passing
or bouncing, the results should be the same, just
as it is on a transmission line.

Any "view" is possible in your mind but not every
view of yours that is possible is associated with
reality. Your view could just as easily be the
same as my mother's (RIP), i.e. that God is
responsible for everything.

If your view is disassociated from reality, it is
no better than a religion.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

John Smith wrote:
Oh gawd, this gripes me most of all "t", as in rotations of the earth,
now what the hell has that got to do with rf? Distance is OK ...

What do minutes and seconds have to do with spherical
angular rotation? Shirley, you jest.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roy Lewallen wrote:
I'll put my money on each of the waves arriving at the opposite end
unchanged. What do you predict will happen?

I predict that Keith will say that square waves and
triangular waves are not steady-state. :-)
--
73, Cecil http://www.w5dxp.com