Richard,

Your point is correct of course, but I must highlight an ASCII-based
spot of confusion in my post.

Both area and time are in the denominator. I was sloppy in writing the
equation.

energy / (area * time)

Of course the area is still there, and it is an energy flow 'density'.

But hey, what's a few missing units among friends?

73,
Gene
W4Sz

Richard Clark wrote:
On Thu, 02 Dec 2004 14:46:34 -0600, Cecil Moore
wrote:

Gene Fuller wrote:

...energy/area/time.

sounds like joules/sec (power) to me. The IEEE Dictionary agrees.

If so, then a strange dictionary indeed (or strange reader),
Gene's term reduces to energy·time·area^-1 not energy·time^-1

What kind of sound was that anyway?

Richard Clark wrote:
Cecil Moore wrote:

Gene Fuller wrote:
...energy/area/time.

sounds like joules/sec (power) to me. The IEEE Dictionary agrees.

If so, then a strange dictionary indeed (or strange reader),
Gene's term reduces to energy·time·area^-1 not energy·time^-1

I'm surprised that you don't know that energy/(area*time) is the
same as energy/(time*area) which is watts per square meter. The
IEEE Dictionary certainly knows that.
--
73, Cecil http://www.qsl.net/w5dxp

Jim Kelley wrote:
They also point out that the integral of the Poynting vector over an
arbitrary volume which contains no radiator or absorber of energy, or
where no mechanical work is done, is equal to zero. They cite
conservation of energy as the directive.

All that says is: if the flowing energy doesn't change, it hasn't
been dissipated or radiated. The energy is in the process of being
losslessly transferred from one place to another with joules/sec
passing an infinite number of points in space. From _Optics_,
by Hecht: "The energy streaming through space in the form of an
electromagnetic wave, is shared equally between the constituent
electric and magnetic fields. ... We now make the reasonable
assumption (for isotropic media) that the energy flows in the
direction of the propagation of the wave."
--
73, Cecil http://www.qsl.net/w5dxp

On Thu, 02 Dec 2004 18:10:14 -0600, Cecil Moore
wrote:
sounds like joules/sec (power) to me.
energy/(area*time) is the same as energy/(time*area) which is watts per square meter.
Which still leaves you high and shy of area^-1

What was that sound?

On Thu, 02 Dec 2004 14:28:26 -0800, Jim Kelley
wrote:
Born and Wolf does observe that the Poynting vector is adequately
defined as the "density of the energy flow", "the amount of energy which
crosses a boundary surface per second a unit area normal to the
directions of E and H."

Hi Jim,

You were desirous of "value added" writing, I believe. The
explanation and Gene's observation that this vector is not about power
has more correlatives in radiation, of the observable kind. We may as
well tread into the optics side of the family as long as we are here.

The same area bounded expression for light is Lux whose definition is
Lumens (power or energy/second) per square Meter (area).

Lumens are printed (mandate of law) on every box of light bulbs.

[Daggers fly here]
Unfortunately our resident Optical (sic) wizard here, has never been
able to express ANY answer for his Optical pronouncements in ANY
Optical term, not even Lumens. Bringing such topics as Optics to the
discussion and leaving them adrift demands sneers in response to such
babbling sophistries.

73's
Richard Clark, KB7QHC

On Thu, 02 Dec 2004 23:08:00 GMT, Gene Fuller
wrote:
But hey, what's a few missing units among friends?

Hi Gene,

Well, I knew that, and it didn't matter to me. The point of response
was not to correct the mistake of transcription (a lesser
transgression), but to correct the mistake of confirmation (a sin)
which is one of those things that can cascade into attributions
supporting faulty Initial Conditions.

73's
Richard Clark, KB7QHC

Jim Kelley wrote:

I think the source of part of the confusion here is that some people
apparently interpret the 'forward power' reading on their meter to mean
the power into their transmission line.

It's not.

The power input to the transmission line is the instantaneous power,
V(t) * I(t), averaged over one cycle. This is the value indicated by a
classic AC wattmeter used in the power industry. The Bird wattmeter
indicates a so called 'forward' and 'reverse' power, neither of which
are truly power, and have been discussed ad infinitum in this newsgroup.
The difference between the 'forward' and 'reverse' reading on the Bird
wattmeter is equal to the power entering the transmission line.

bart
wb6hqk

Bart Rowlett wrote:
The difference between the 'forward' and 'reverse' reading on the Bird
wattmeter is equal to the power entering the transmission line.

It can easily be proven that the energy in the forward wave that
has not yet been reflected plus the reflected energy is still in
the transmission line. It can be proven, using TV ghosting, that
the reflected energy has made a round trip to the load and back.

It sure would alleviate the confusion if everyone would say,
"... is equal to the net power entering the transmission line."

re dB:

If one is measuring the losses in a 1/4WL stub with the following
configuration using a signal generator equipped with an ideal
circulator and circulator load resistor (SGCL):

SGCL----1/4WL stub-----

What are the losses in the stub in dB? :-)
--
73, Cecil http://www.qsl.net/w5dxp

On Thu, 02 Dec 2004 09:47:54 -0600, Cecil Moore
wrote:


Consider an earlier example made up of lossless lines:

100W XMTR---50 ohm---+---one second long 291.5 ohm---50 ohm load

The voltage reflection coefficient at the load is 0.707. The power
reflection at the load is 0.5, i.e. half the power is reflected.

After steady-state has been reached, the XMTR has output 300 more
joules than the load has accepted. A smaller real-world experiment
will easily verify that it is a fact that all energy sourced that
has not reached the load must necessarily be confined to circulating
energy or losses in the transmission line.

Question: In the above example, where are those 300 joules of energy
located and what is happening to them?

We know that 300 joules is wave energy and RF waves always move
at the speed of light, i.e. they cannot stand still. So please
determine how much energy is moving and in which of only two
possible directions.

Dear Cecil,

Here's my guesses -
The 300 joules of energy decays at a particular rate - i.e., in a
certain interval of time, 63.2% of it will have been converted to and
become dissipated as heat. During that same time interval,Ti, there
will be an equal amount of energy introduced to replenish the amount
lost. In other words, there will be a continuum of energy transferring
into the transmission line to exactly make up for that lost in any
given period of time.

Eventually, someone will disconnect the source generator at time T2.
However, the load will continue to receive energy for a length of
time, Ti, at which point roughly 63.2% of 300 joules of energy will
have been dissipated in the load. If we wait long enough, 99.9% of the
300 joules will have been dissipated, but it will take forever for the
last little bit to disappear.

It kind of makes you think in terms of "life everlasting", doesn't it?

73,

Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

Richard Clark wrote:

On Thu, 02 Dec 2004 14:28:26 -0800, Jim Kelley
wrote:

Born and Wolf does observe that the Poynting vector is adequately
defined as the "density of the energy flow", "the amount of energy which
crosses a boundary surface per second a unit area normal to the
directions of E and H."


Hi Jim,

You were desirous of "value added" writing, I believe. The
explanation and Gene's observation that this vector is not about power
has more correlatives in radiation, of the observable kind.

It's accurate to say that power is something which itself doesn't
propagate in any fashion, at any wavelength.

[Daggers fly here]
Unfortunately our resident Optical (sic) wizard here, has never been
able to express ANY answer for his Optical pronouncements in ANY
Optical term, not even Lumens. Bringing such topics as Optics to the
discussion and leaving them adrift demands sneers in response to such
babbling sophistries.

When Maxwell wanted to draw such distinctions, he included a frequency
dependent term - but allowed the same units throughout.

73, Jim AC6XG

73's
Richard Clark, KB7QHC