W5DXP wrote:

wrote:
In reality there is not zero volts in the incident wave or in the
reflected wave. There`s full voltage coming and going. The volts just
happen to be out-of-phase at this point.

Yes, indeed. But there is no power.

Power is the same as irradiance in optics. When total V=0, it is simply
the result of destructive interference. Perhaps this quote from _Optics_,
by Hecht, will enlighten you. "The principle of conservation of energy
makes it clear that if there is constructive interference at one point,
the "extra" energy at that location must have come from elsewhere. There
must therefore be destructive interference somewhere else."

My knowledge of optics is insufficient to comment on any analogies you
choose to draw. Fortunately, a knowledge of optics is unnecessary to
understand circuits and transmission lines.

The voltage goes to zero because two voltage waves are engaged in destructive
interference. The current goes to maximum because two current waves are engaged
in constructive interference. The momentum in the voltage waves simply transfers
to the current waves and they just keep on rolling along. There is no mechanism
of physics existing at that point to change the momentum of the waves. Believing
that no energy crosses a superposed V=0 boundary is just a wet dream.

This puts you in
group a) P(t) is not always equal to V(t) * I(t); or
group c) "double think".

Care to think about which and comment?

The current
is at an absolute maximum point so plenty of charge carriers are crossing that
boundary.

Yes indeed, but current by itself is not energy. Remember
P(t) = V(t) * I(t) [unless you choose option a)]
Both volts and amps are simultaneously necessary for power.

....Keith

wrote:
My knowledge of optics is insufficient to comment on any analogies you
choose to draw. Fortunately, a knowledge of optics is unnecessary to
understand ... transmission lines.

Equally unfortunately, that's just a delusion of yours.

Care to think about which and comment?

I have no idea what you are talking about.

Yes indeed, but current by itself is not energy.

Hmmmmm, I^2*Z0 is not power? (Somebody get the net).
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

W5DXP wrote:
It happens all the time in optics and no optics engineer
would be silly enough to assert that the bright ring energy is trapped
and circulating between the dark rings.

Nor would he be silly enough to assert that energy first goes to the
dark ring and then turns around and goes to bright ring.

ac6xg

Keith wrote:
"Are you sure you want to discard all thoughts of the instantaneous?

Certainly not, but it has little application to power in transmission
line problems.

Power is the rate of transferring energy or the rate of doing work.
Electrical power is measured in joules per seconds or more succinctly in
watts.

What is the value in watts or joules per second when seconds equal
zero? I venture an answer: It is the V x I x cos. theta at that instant,
but since work is power x time, it won`t do anything for you in zero
seconds.

Best regards, Richard Harrison, KB5WZI

Keith wrote:
"Are you sure you want to discard all thoughts of the instantaneous?

Certainly not, but it has little application to power in transmission
line problems.

Power is the rate of transferring energy or the rate of doing work.
Electrical power is measured in joules per seconds or more succinctly in
watts.

What is the value in watts or joules per second when seconds equal
zero? I venture an answer: It is the V x I x cos. theta at that instant,
but since work is power x time, it won`t do anything for you in zero
seconds.

Best regards, Richard Harrison, KB5WZI


If Zeno were around today, he could prove that - based on Cecil's idea
that, as dt goes to zero, energy transfer also goes to zero - there
can be no transfer of energy in a transmission line, since any number
times zero is still zero. Of course, we can all see the fallacy in
that argument, can't we?

Tdonaly wrote:
If Zeno were around today, he could prove that - based on Cecil's idea
that, as dt goes to zero, energy transfer also goes to zero - there
can be no transfer of energy in a transmission line, since any number
times zero is still zero. Of course, we can all see the fallacy in
that argument, can't we?

What's the fallacy? If dt=0, then time stands still,
and of course, nothing happens and nothing moves.
--
73, Cecil, W5DXP

Tdonaly wrote:
If Zeno were around today, he could prove that - based on Cecil's idea
that, as dt goes to zero, energy transfer also goes to zero - there
can be no transfer of energy in a transmission line, since any number
times zero is still zero. Of course, we can all see the fallacy in
that argument, can't we?

What's the fallacy? If dt=0, then time stands still,
and of course, nothing happens and nothing moves.
--
73, Cecil, W5DXP


So you think it's impossible to send energy from one
place to another via a transmission line? Hmmm. I
guess Achilles never did catch that turtle.
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
So you think it's impossible to send energy from one
place to another via a transmission line?

In zero time, yes. Isn't that what the speed of light
limit is all about?
--
73, Cecil, W5DXP

Richard Harrison wrote:

Keith wrote:
"Are you sure you want to discard all thoughts of the instantaneous?

Certainly not, but it has little application to power in transmission
line problems.

Power is the rate of transferring energy or the rate of doing work.
Electrical power is measured in joules per seconds or more succinctly in
watts.

What is the value in watts or joules per second when seconds equal
zero? I venture an answer: It is the V x I x cos. theta at that instant,
but since work is power x time, it won`t do anything for you in zero
seconds.

But then instantaneous velocity and instantaneous acceleration won't do
anything for you in zero seconds, either. And yet, for example,
inertial navigation systems successfully operate by integrating these
instantaneous values.

Back to your assertion "but it has little application to power in
transmission line problems".

It is certainly true that for RF, average power is of most interest. It
is what gets you communicating.

But if you want to understand how things work, exploring the land of
the instantaneous is quite valuable. It is instantaneous voltages which
make standing waves. It is instantaneous signals which cause distortion
in diode demodulators. It is instantaneous voltages and currents which
are added and subtracted in Bird wattmeters. It is instantaneous
voltages and currents which interact at impedance discontinuities to
do all the neat stuff. And it is instantaneous voltages and currents
which produce instantaneous power.

But I notice an instantaneous willingness to reject the value of
instantaneous power. I suspect this is because the conclusions reached
when thinking in terms of instantaneous power are inconsistent with
some of your long held beliefs and rather than re-examine these
beliefs it is simpler to just reject instantaneous power.

But to reject instantaneous power in a consistent manner, you need to
explain why you do not also reject instantaneous velocity, acceleration,
current, flow or any of the many other interesting things which are a
derivative with respect to time.

For if we accept the argument "in zero time, no energy can flow" then
we should also accept:
- "in zero time, no charge can flow" -- say bye to instantaneous current
- "in zero time, we can move no distance" -- say bye to instantaneous
velocity
- etc., etc.

When you can't find any fundamental reason that the instantaneousness
of power is different from the instantaneousness of other common
measures like velocity, current, etc., you may wish to return to the
original assertion which caused all this fuss:

Assertion A:
"In a shorted ideal transmission line which has reached steady state,
no energy can cross a voltage or current minimum because
p(t) = v(t) * i(t) and at a voltage or current minimum, the voltage
or current is always zero, so the power is always zero, so there is
no energy flow across a voltage or current minimum."

This conclusion contradicts a commonly held belief:

Belief B:
"that in steady-state, energy is flowing along the transmission line
to the end where it is reflected and travels back to the beginning."

Unless you can find an error in the logic of Assertion A, it would
seem reasonable that you re-assess your acceptance of Belief B.

Assertion A caused me to reject Belief B and the world did not
collapse:
- Bird wattmeters still give useful indications
- ghosts still occur on TVs
- echoes still occur on phone lines
- bidirectional communications still occur on two wire lines
but the simplistic explanations for these phenomena offered by
Belief B need to be re-examined. A better understanding is all
that you stand to gain by discarding Belief B.

....Keith



....Keith

Keith wrote:
"---you need to explain why you do not reject instantaneous velocity,
acceleration, ---."

I don`t reject instantaneous anything including power. Instantaneous
power is not particularly useful in working with radio transmission
lines.

Like infinity, the infinitesimal is unmeasurable. Like infinity, the
infinitesimal is useless in calculations. The idea of the infinitesimal
is useful in perceiving targeted values approached as a variable
approaches a limit.

A differential "d" is an infinitesimal smaller than a difference. "dy"
is the differential of y. "dx" is the differential of x. "dt" is the
differential of t. The ratio "dy/dx" is a slope defined at a point and
is equal to the limit as x goes to zero of the ratio delta y over delta
x.

The basis of differentation is superfluous to this discussion, but Keith
asks, why not reject things which are a derivative with respect to time
including acceleration.

Acceleration may be a good example. Calculus can give the rate at which
a variable varies. On the other hand, it can give a function if the rate
of change is given.

Velocity is the variable in acceleration. Assume velocity is increasing
and you have a definition of the function. For a given velocity the
acceleration can be determined, and for a given acceleration, the
velocity can be determined.

My point, repeated again, is that when delta time is zero, no distance
is traversed, not that acceleration and velocity are zero.

Power x time = energy. Thast`s how the electric power company calculates
your bill. If no time elapses during which power is available, no energy
is consumed.

Best regards, Richard Harrison, KB5WZI