Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:


As you well know, the convention is to apply a negative
sign to positive energy flowing in the opposite direction
from the "forward" energy which is arbitrarily assigned
a plus sign.

Still using that vivid imagination, I see.

Let's see even one reference that mentions explicitly the concept of
applying a negative sign to positive energy. Not power, not voltage, not
current, not waves, but energy.



73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
Cecil Moore wrote:
As you well know, the convention is to apply a negative
sign to positive energy flowing in the opposite direction
from the "forward" energy which is arbitrarily assigned
a plus sign.

Let's see even one reference that mentions explicitly the concept of
applying a negative sign to positive energy. Not power, not voltage, not
current, not waves, but energy.

If you keep feigning ignorance like that Gene, you are
going to lose all respect. If the Poynting vector has
a negative sign, as used by Ramo & Whinnery, that sign
is an indication of the *direction of energy flow*,
see quote below.

From Ramo & Whinnery:

The Poynting vector is "the vector giving *direction* and
magnitude of *energy flow*". When Ramo & Whinnery hang a
sign on a Poynting vector in a transmission line, it is
an indication of the direction of energy flow.

For pure standing waves,
"The average [NET] value of Poynting vector is zero
at every cross-sectional plane; this emphasizes the
fact that on the average as much energy is carried
away by the reflected wave as is brought by the
incident wave."

What? Reflected waves "carrying" energy? Shame on
Ramo & Whinnery for contradicting the rraa gurus.

It is impossible to satisfy you, Gene. When I quote
reference after reference about reflected power, you
say power doesn't reflect. When I change it to reflected
energy, you ask for a reference.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

On Mon, 31 Dec 2007 08:11:49 -0800, Roger wrote:

Cecil Moore wrote:
Richard Clark wrote:
To cut to the chase, Norton and Thevenin sources are appropriate to
network analysis irrespective of your perception.

All my references indicate that those sources are only
appropriate for *steady-state* use. Roger is searching
for a transient state source.

Right!

Really, the wail and torment of your two's grief is no more
sophisticated than: the dog ate my homework. This is a noble quest in
search of a "free lunch."

In the end, it serves absolutely no purpose in trying to resolve the
"confusion" of why a traveling wave antenna has standing wave energy
where the purpose of this thread was strangled in the crib by Cecil
when I dropped that one. ;-)

73's
Richard Clark, KB7QHC

Standing-Wave Current vs Traveling-Wave Current
 

Richard Clark wrote:
Really, the wail and torment of your two's grief is no more
sophisticated than: the dog ate my homework.

Nope, it's more like the gurus ate reality.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Cecil Moore wrote:
Roger wrote:
The problem is that "We want to investigate a 1/2 wave length of
transmission line, excited at one end. How soon is stability reached?"

I guess the answer depends upon your definition of
"stability" above.

You might start with a loaded version:

http://www.w5dxp.com/1secsgat.gif

Yes, this is the idea, exactly.

The loaded version is much more complicated than the unloaded version.

Stability is always reached provided power input contains a maximum.

73, Roger, W7WKB

If "stability" means steady state, a transmission line with any
resistance at either end or both ends is less complicated to analyze
than the particularly difficult lossless case I used for my analysis
which never reaches a true steady state. The presence of resistance
allows the system to settle to steady state, and that process can easily
and quantifiably be shown. And in two special cases, the process from
turn-on to steady state is trivially simple -- If the line is terminated
with Z0 (technically, its conjugate, but the two are the same for a
lossless line since Z0 is purely resistive), steady state is reached
just as soon as the initial forward wave arrives at the far end of the
line. No reflections at all are present or needed for the analysis. The
second simple case is when the source impedance equals Z0, resulting in
a source reflection coefficient of zero. In that case, there is a single
reflection from the far end (assuming it's not also terminated with Z0),
but no re-reflection from the source, and steady state is reached as
soon as the first reflected wave arrives at the source.

Roy Lewallen, W7EL

Standing-Wave Current vs Traveling-Wave Current
 

Roy Lewallen wrote:
In that case, there is a single
reflection from the far end (assuming it's not also terminated with Z0),
but no re-reflection from the source, and steady state is reached as
soon as the first reflected wave arrives at the source.

Assuming that reflection cannot exist without energy,
where does the ExH*t energy in the reflected wave go?

(OK now, everyone hold their breath for an answer.)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

On Mon, 31 Dec 2007 14:13:43 -0600, Cecil Moore
wrote:

You've got a battery in one pocket, and a mouse in the other. Where
did the energy go?

(OK now, everyone hold their breath for an answer.)

Standing-Wave Current vs Traveling-Wave Current
 

Richard Clark wrote:
You've got a battery in one pocket, and a mouse in the other. Where
did the energy go?

Unfortunately for your argument, neither a mouse nor
a battery exists inside a transmission line. Outside
of usually minor heat losses, nothing exists besides
EM waves traveling at the speed of light.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Cecil, W5DXP wrote:
"In such problems we are often most interested in the ratio of power in
the reflected wave to that in the incident wave, and the ratio is given
by the square of the magnitude of [rho] as can be shown by considering
the Poynting vectors:"

Terman agrees. On page 98 of his 1955 opus, Terman shows the value of
[rho] vs. SWR.

On page 97 Terman writes:
"This definition of standing-wave ratio is sometimes called the voltage
standing-wave ratio (VSWR) to distinguish it from the standing-wave
ratio expressed as a power ratio which is (Emax/Emin)squared."

Best regards, Richard Harrison, KB5WZI

Standing-Wave Current vs Traveling-Wave Current
 

On Mon, 31 Dec 2007 14:30:55 -0600, Cecil Moore
wrote:

Richard Clark wrote:
You've got a battery in one pocket, and a mouse in the other. Where
did the energy go?

Unfortunately for your argument, neither a mouse nor
a battery exists inside a transmission line. Outside
of usually minor heat losses, nothing exists besides
EM waves traveling at the speed of light.

So, you refuse, or cannot account for the energy? Energy is conserved
in every system, even pockets and when the units of volts in one case
are conveniently offered, your theory fails to balance the pockets.

(OK now, everyone hold their breath for an answer.)