Reg Edwards wrote:
So I leave it to Cecil and Co. to add further to the complications and
confusion.

Reg, how about these statements from a recent QEX article?

"Contrary to popular views, the forward and reverse
waves on a transmission line are not separate fields."
"I wish to emphasize the fact that the forward and
reverse waves really do not exist separately, ..."
"Dual Directional Wattmeters", Eric von Valtier, K8LV,
_QEX_, May/June 2006.

The article obviously rejects the wave reflection model
for transmission lines as presented by Ramo/Whinnery,
Johnson, etc.

If forward and reverse waves do not exist separately,
how is it possible for a circulator to separate them?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil,

I think you are conflating models with nature, and trying to champion
one correct model over another correct model! It's confusing to
onlookers and boring.

There is NO inconsistency between saying "there's only one
electromagnetic field in a transmission line" and "a circulator
seperates the forward wave from the reflected wave" if you've suitably
defined what all those terms mean and you do the correct math.

The electromagnetic field as a function of space and time in the
coaxial transmission line is a three-dimensional time dependent field.
There's a description wherein one single vector valued function
E(r,phi,z, t) describes the electric field and another describes the
magnetic field, and of course, you can get one from the other, so in
some sense, all you need to describe what's going on is E(r,phi,z,t).

Now, in the coaxial TEM mode the radial and azimuthal dependence of the
fields becomes trivial, and you're just left with some function E'(z,t)
to describe the electric field, and one B'(z,t) for the magnetic field
(once again, you can of course, get one from the other) It turns out
that mathematically you can represent this function as a superposition
of other functions, forward and reverse traveling waves. It's just a
DIFFERENT WAY OF WRITING IT DOWN.

A circulator *doesn't know math*. Its operation may have a simple
description in the language of forward and reverse waves, but it does
what it does no matter what model you use to describe it. If you get
different answers using a forward and reflected wave description than
some other description, then one or both of your descriptions are
wrong. The conversion of one mathematical description of the
electromagnetic field into a series of statements in English and the
argument based on those words never gets you anywhere on this topic.
Why not pick up a copy of Jackson's Electrodynamics and write down what
you're trying to say mathematically. If you're right, everyone will
have to be convinced.

73,
Dan

wrote:
I think you are conflating models with nature, and trying to champion
one correct model over another correct model!

Nope, the mainstream wave reflection model is being attacked
as incorrect.

I'm trying to correct some misconceptions concerning
violations of the conservation of energy principle
by simplified model shortcuts. Modern RF EM textbooks don't
deal with conservation of energy. There's no equations to
quote because the textbooks ignore the problem.

For instance, it can be shown that a one-second long lossless
transmission line with a measured forward power of 200 watts
and a measured reflected power of 100 watts does indeed in
reality contain 300 joules of RF energy traveling at the speed
of light. Is there really any more logical location for those
300 joules than in the forward and reflected waves which are
necessary for standing waves to exist?

Einstein said a math model of reality should be as simple as
possible but not too simple.
--
73, Cecil, http://www.qsl.net/w5dxp

Hey Cecil,

Can you sum up the problem with conservation of energy that modern RF
textbooks get wrong?

Dan

wrote:
Can you sum up the problem with conservation of energy that modern RF
textbooks get wrong?

They don't get it wrong - they just don't discuss it at all.
But here is an example of the problem:

http://eznec.com/misc/food_for_thought/

First article - last paragraph. W7EL considers
steady-state conditions while ignoring the previous
transient state conditions. He implies that the
energy in the reflected wave cannot be recovered but
it is indeed dissipated as power in the system after
power is removed from the source. The source supplies
exactly the amount of energy during the transient power
up conditions needed to support the forward and reflected
waves during steady-state. This is easy to prove. But
W7EL's Ivory Tower protects Him from peons like me.
--
73, Cecil http://www.qsl.net/w5dxp

The net power flux in the line gets smaller as the reflected wave gets
stronger while maintaining a constant electric field (constant voltage
as in Roy's example). If you can match to the new impedance at the
line input; that is, make the electric fields both stronger, you can
get a larger net power flux even in the presence of some elevated SWR.

See LaTeX formatted math at
http://en.wikipedia.org/wiki/Useran_Zimmerman/Sandbox

The flux of stored power in the line, interestingly enough, is a
sinusoidal function of position.

I'm still thinking what to make of it, but I thought I'd post the math
for people to look at (and check, please!!!!)

... I'll be back later.

73,
Dan

wrote:
I'm still thinking what to make of it, but I thought I'd post the math
for people to look at (and check, please!!!!)

Thanks, Dan.

If I understand correctly, Roy's argument is that since
the source is not supplying any steady-state energy to
the lossless stub, there is no energy in the reflected
wave within the stub.

If we make Roy's lossless stub one second long, the
picture becomes clearer. For the first two seconds,
the 100 watt source pours 200 joules of RF energy
into the stub. After that, during steady-state, the
source supplies zero energy. But those 200 joules
are still in the stub, 100 joules in the forward
wave and 100 joules in the reflected wave, and they must
obey the conservation of energy principle.

There is *always* the exact amount of energy in the
forward and reflected waves as required to achieve
the forward and reflected power readings in a Z0
calibrated environment.
--
73, Cecil, W5DXP

"Cecil Moore" wrote
If forward and reverse waves do not exist separately,
how is it possible for a circulator to separate them?

=========================================
Cec,

You forgot to allow TIME into the argument.

The two waves do NOT, and cannot, exist seperately in time.

The circulator merely divides the STEADY STATE, instantaneous, at the
same time, power in the wave into two parts according to what the
operator, or by design, has set it to do.

When the generator is switched off both parts disappear
simultaneously.

I know this won't satisfy you.
----
Reg.

Reg Edwards wrote:
"Cecil Moore" wrote
If forward and reverse waves do not exist separately,
how is it possible for a circulator to separate them?

You forgot to allow TIME into the argument.
The two waves do NOT, and cannot, exist seperately in time.

I'm not sure what your point is. If a laser beam is
aimed at a mirror, do the forward wave and reflected
wave exist separately in time? If we send a forward
wave down a one-second lossless feedline for one second
and turn it off, nothing happens for one second. Then
we receive a reflected wave for one second. Do those
waves not exist separately in time?

The circulator merely divides the STEADY STATE, instantaneous, at the
same time, power in the wave into two parts according to what the
operator, or by design, has set it to do.

The point is that one of those parts has made a round
trip to the load and back as can be proved by observing
ghosting in TV signals.

When the generator is switched off both parts disappear
simultaneously.

Not entirely true. The reflected wave would continue to
exist until the energy in the transmission line is
dissipated.
--
73, Cecil, http://www.qsl.net/w5dxp