Roy Lewallen wrote:
2. I don't understand the mechanism which causes waves to bounce.

I don't understand the mechanism which causes waves to slosh.
Would you mind posting the sloshing equation?
--
73, Cecil http://www.w5dxp.com

Gene Fuller wrote:
I challenged you to find any case in AN 95-1 that supports your claim of
counter-traveling waves in a transmission line, with each wave carrying
its own energy that somehow nets out to zero.

I did exactly that earlier and you didn't comprehend
it then - but here it is again.

(b1)^2 = (s11*a1 + s12*a2)^2 = 0

(b1)^2 is reflected power. It is only zero when
(s11*a1 + s12*a2)^2 = 0

(b1)^2 = (s11*a1)^2 + (s12*a2)^2 + 2(s11*a1)(s12*a2)

Since a1 and a2 are phasors, their multiplication
involves cos(A) of the Angle between them.

Pref1 = P1 + P2 + 2*SQRT(P1*P2)cos(A)

Does that equation look familiar? Please reference the
s-parameter ap note, pages 16 & 17, for the meaning of
those squared terms. The power density equation can be
derived from the s-parameter equation.

http://www.ecs.umass.edu/ece/labs/an...parameters.pdf
--
73, Cecil http://www.w5dxp.com

Gene Fuller wrote:
No one has ever said anything different. No one has ever denied
interference.

Denying that you ever argued about something is a first
step in the direction of understanding. Before long, you
will be arguing that you knew all of this stuff long ago.
--
73, Cecil http://www.w5dxp.com

On Jan 2, 2:32*pm, Cecil Moore wrote:
Keith Dysart wrote:
But this same information has been repeatedly provided
and ignored. Will this time be different?

And Cecil provides the answer: No!

The requested information is provided but then
completely ignored in the response.

I'm not the one who is ignoring that information.
Where are your calculations involving destructive
and constructive interference? Until you provide
that information, you are just blowing smoke.

...Keith

On Jan 2, 2:33*pm, Cecil Moore wrote:
Keith Dysart wrote:
Cecil Moore wrote:
There can be a large difference in the output
impedance of an amplifier designed to drive a 50 ohm
load and a 50 ohm Thevenin equivalent circuit.

Then your Thevenin circuit is not an equivalent
for the amplifier, is it?

No it isn't! So why are you trying to stuff it down
my throat?

I must have missed something.

You brought up the 50 ohm Thevenin equivalent circuit
which turned out not to be an equivalent circuit.

And now you think I am trying to stuff it down
your throat.

Amusing.

...Keith

On Jan 2, 2:36*pm, Cecil Moore wrote:
Keith Dysart wrote:
You should really spend some time looking for a
reference to support your assertion that "It will
not be the impedance needed to calculate the
reflection coefficient seen by the reflected
waves."

You will not find one.

You have got to be kidding, Keith. Even some of the
people on your side will admit that the effective
reflection coefficient for a source supplying zero
power is |1.0| nowhere near the value you calculated.
I believe that is what Roy said.

Bluster!

I am just waiting for a reference.

Still can't find one, can you?

...Keith

Keith Dysart wrote:
I am just waiting for a reference.
Still can't find one, can you?

Since the reflected wave is reflected, the reflection
coefficient cannot be zero.

If the reflected wave is not reflected, there
would exist current in the source, but there
is none.

There are no references for pathological thinking.
--
73, Cecil http://www.w5dxp.com

On Jan 2, 4:57*pm, Jim Kelley wrote:
Keith Dysart wrote:
On Dec 29, 2:31 pm, Cecil Moore wrote:

Roger wrote:

Are there reflections at point "+"? *Traveling waves going in opposite
directions must pass here, therefore they must either pass through one
another, or reflect off one another.

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.

Roger: an astute observation. And Cecil thinks he has
the ONLY answer. Allow me to provide an alternative.

Many years ago, when I first encountered this news group
and started really learning about transmission lines, I
found it useful to consider not only sinusoidallly
excited transmission lines, but also pulse excitation.
It sometimes helps remove some of the confusion and
clarify the thinking. So for this example, I will use
pulses.

Consider a 50 ohm transmission line that is 4 seconds
long with a pulse generator at one end and a 50 ohm
resistor at the other.

The pulse generator generates a single 1 second pulse
of 50 volts into the line. Before and after the pulse
its output voltage is 0. While generating the pulse,
1 amp (1 coulomb/s) is being put into the line, so
the generator is providing 50 watts to the line.

After one second the pulse is completely in the line.
The pulse is one second long, contains 1 coulomb of
charge and 50 joules of energy. It is 50 volts with
1 amp: 50 watts.

Let's examine the midpoint (2 second) on the line.
At two seconds the leading edge of the pulse arrives
at the midpoint. The voltage rises to 50 volts and
the current becomes 1 amp. One second later, the
voltage drops back to 0, as does the current. The
charge and the energy have completely passed the
midpoint.

When the pulse reaches the end of the line, 50
joules are dissipated in the terminating resistor.

Notice a key point about this description. It is
completely in terms of charge. There is not a single
mention of EM waves, travelling or otherwise.

Now we expand the experiment by placing a pulse
generator at each end of the line and triggering
them to each generate a 50V one second pulse at
the same time. So after one second a pulse has
completely entered each end of the line and these
pulse are racing towards each other at the speed
of light (in the line). In another second these
pulses will collide at the middle of the line.

What will happen? Recall one of the basics about
charge: like charge repel. So it is no surprise
that these two pulses of charge bounce off each
and head back from where they came. At the center
of the line, for one second the voltage is 100 V
(50 V from each pulse), while the current is
always zero. No charge crossed the mid-point. No
energy crossed the mid-point (how could it if
the current is always zero (i.e. no charge
moves) at the mid-point.

It is a minor extension to have this model deal
with sinusoidal excitation.

What happens when these pulses arrive back at the
generator? This depends on generator output
impedance. If it is 50 ohms (i.e. equal to Z0),
then there is no reflection and 1 joule is
dissipated in each generator. Other values
of impedance result in more complicated
behaviour.

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.

...Keith

It's fairly safe to make this argument when both pulses are identical.
* I challenge you to obtain this result when they are not. *:-)

The example was carefully chosen to illustrate the
point, of course. But that is the value of particular
examples.

When the pulses are not identical, the energy that crosses
the point is exactly sufficient to turn one pulse
into the other. The remainder of the energy must bounce
because it does not cross the mid-point.

...Keith

On Jan 2, 11:58*pm, Cecil Moore wrote:
Keith Dysart wrote:
I am just waiting for a reference.
Still can't find one, can you?

Since the reflected wave is reflected, the reflection
coefficient cannot be zero.

If the reflected wave is not reflected, there
would exist current in the source, but there
is none.

There are no references for pathological thinking.

Still can't find one? ?

...Keith

On 2 Jan, 20:18, Cecil Moore wrote:
Roy Lewallen wrote:
* 2. I don't understand the mechanism which causes waves to bounce.

I don't understand the mechanism which causes waves to slosh.
Would you mind posting the sloshing equation?
--
73, Cecil *http://www.w5dxp.com

Cecil,
All of the bickering come to a halt if you consider a full wave
radiator
instead of a half wave antenna. Yes, both can be resonant but only
one is in a state of equilibrium. The underpinnings of all laws
whether
mechanical or electrical is that all is in a state of equilibrium
otherwise the laws do not apply.
When there is a state of equilibrium one cannot have a collision of
waves.
The sequence for equilibrium is a magnetic field followed by a
electric field
which equals one period. Sloshing is a poor word. When current is
moving forward
you are charging up the `capacitor when the current changes direction
the capacitor
discharges as if it was shorted and creates a near instantaneous
electrostatic field
which dissapates while charging up the inductance which is also the
transition of
generating a magnetic field around the inductance.
During this time there is also a side ways force that affects or
depletes the current
by deflection which allows for propagation.This force is what is
termed "curl"
amongst many other names
At no time are there any counter waves because, not only are we
resonant but
we are also in a state of equilibrium. Move away from a fractional
wavelength
to a full wave length so both sides starts from a common point ie
resonant
and in a state of equilibrium and your difference will then be
resolved quickly.
Hope the above helps to stop posters from talking past each other.
My best regards
Art Unwin KB9MZ....XG(UK)