Jim Kelley wrote:


Cecil Moore wrote:
There existed energy in the two waves before they were canceled.

I really don't want to go on ad infinitum about this, but the only
"before" would have been "before" the conditions for wave cancellation
existed.

Wave cancellation is a continuous steady-state process.
Every instant of present time, reflected waves are in
the process of being canceled. The power density equation,

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

is a continuous steady-state process.

The s-parameter equation, b1 = s11*a1 + s12*a2, is a
continuous steady-state process. If you square both
sides of the equation you get the power density equation
above. IT IS A CONTINUOUS STEADY-STATE PROCESS that
spans the past, present, and future until the power
down transient state begins.
--
73, Cecil http://www.w5dxp.com

"Jim Kelley" wrote in message
...


Cecil Moore wrote:

If an EM wave exists, it's
Poynting vector is ExM. The energy in that individual wave *must*
be conserved. If that energy is not conserved, the conservation
of energy principle is violated.

When a wave is canceled, there is no wave. Therefore there can be no
energy associated with that wave. If there is energy, then it must be
associated with a wave that is not canceled. Same thing is true when I
have candy. If it's not in my left hand, then it must be in my right
hand. It's all very profound.


but you can neither create nor destroy energy, so it can't just be
'canceled' it has to be either converted to some other form of energy or go
somewhere else... it can't just disappear.

Cecil Moore wrote:

Jim Kelley wrote:



Cecil Moore wrote:

There existed energy in the two waves before they were canceled.


I really don't want to go on ad infinitum about this, but the only
"before" would have been "before" the conditions for wave cancellation
existed.


Wave cancellation is a continuous steady-state process.
Every instant of present time, reflected waves are in
the process of being canceled.

During which time everything "before" is exactly the same as
everything "after".

ac6xg

Keith Dysart wrote:
On Jan 15, 2:24 am, Roy Lewallen wrote:
The little program I wrote shows that, on the line being analyzed, the
energy is changing -- moving -- on both sides of a point of zero power.
Energy is flowing into that point from both directions at equal rates,
then flowing out at equal rates. This causes the energy at that point to
increase and decrease. What zero power at a given point means is that
there is no *net* energy moving in either direction past that point.

"*net* energy moving" seems to be a bit of a dangerous notion.

If "*net* energy moving" is the time averaged power, then
it is zero at *every* point on the line under consideration.
And I do not mind this definition.

That was probably a bad choice of words on my part. By net I didn't mean
an average over some period of time. I meant energy moving past a single
point.

One possibility I envisioned was some energy moving past the point from
left to right, and at the same time an equal amount moving at the same
rate past the point from right to left, resulting in zero power at the
point. However, on reflection, this couldn't happen; energy flows
"downhill". But the phenomenon observed on the open circuited line does
occur, where energy flows into the point from both directions equally,
and out of the point to both directions equally, resulting in zero power
at the point. No energy is flowing past the point, period -- the
modifier "net" isn't necessary.

But at the points where the current or voltage is always
zero, it seems to me unnecessary to use the qualifier "*net*"
since the power IS always zero [from p(t)=v(t)*i(t)]. That
is, unless you are introducing another interpretation of
"*net*".

You're right. Please consider "net" retracted.

Roy Lewallen, W7EL

Roy Lewallen wrote:
But the phenomenon observed on the open circuited line does
occur, where energy flows into the point from both directions equally,
and out of the point to both directions equally, resulting in zero power
at the point. No energy is flowing past the point, period --

Either energy flows past the point or else it is reflected.
Please provide an example of reflections occurring in a
homogeneous medium.
--
73, Cecil http://www.w5dxp.com

Jim Kelley wrote:
During which time everything "before" is exactly the same as everything
"after".

Yes, we want the reflections to be continuously canceled
in real time and for the reflected energy to be redistributed
back toward the load in real time.
--
73, Cecil http://www.w5dxp.com

Dave wrote:
"Jim Kelley" wrote in message
...


Cecil Moore wrote:


If an EM wave exists, it's
Poynting vector is ExM. The energy in that individual wave *must*
be conserved. If that energy is not conserved, the conservation
of energy principle is violated.

When a wave is canceled, there is no wave. Therefore there can be no
energy associated with that wave. If there is energy, then it must be
associated with a wave that is not canceled. Same thing is true when I
have candy. If it's not in my left hand, then it must be in my right
hand. It's all very profound.



but you can neither create nor destroy energy, so it can't just be
'canceled' it has to be either converted to some other form of energy or go
somewhere else... it can't just disappear.

Hi Dave -

I think most people here are already quite aware of that. To what
energy do you specifically refer?

ac6xg

Jim Kelley wrote:
I think most people here are already quite aware of that. To what energy
do you specifically refer?

Probably the wave energy that you say never existed.
But you have never provided an example of waves
that can exist without energy.

Set the FSU flash example to 180 degrees out of
phase and please explain conceptually where the
energy in those two waves goes when they
superpose to zero in a transmission line.

http://micro.magnet.fsu.edu/primer/j...ons/index.html
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Jim Kelley wrote:

I think most people here are already quite aware of that. To what
energy do you specifically refer?


Probably the wave energy that you say never existed.

So unless somebody can point to the energy that is "in" waves which
don't exist, then I will have to stick with the idea that there is no
energy to be associated with waves that don't exist. To me it is the
only logical way to look at it, even though I may be subject to abuse
from crackpots. ;-)

ac6xg

Cecil Moore wrote:

Jim Kelley wrote:

So unless somebody can point to the energy that is "in" waves which
don't exist, then I will have to stick with the idea that there is no
energy to be associated with waves that don't exist.


Jim, here is the s-parameter equation for the waves that
you assert don't exist.

b1 = s11*a1 + s12*a2 = 0

s11*a1 is not zero. s12*a2 is not zero. How you can assert
that they don't exist is really strange.

Perhaps I just understand the meaning of zero better than you do?

ac6xg