On Apr 2, 9:40 pm, Jim Kelley wrote:
Walter Maxwell wrote:
On Wed, 28 Mar 2007 16:26:10 -0700, Jim Kelley wrote:

Hi Cecil -

We've been over this a hundred times already. The only way to get
past it is for you to try to understand that my comment and Eugene
Hecht's are both true. You need to find a way to understand that
there is no contradiction. You could start by noting that Hecht does
not contradict anything that I said. Nowhere does he claim that
interference redirects energy. That's your claim! And I haven't said
that energy isn't redirected. If redirection of energy takes place,
it takes place by reflection - not interference. It's just basic optics.

73, ac6xg

Sorry Jim, but I take exception to your statement, "If redirection of energy takes place,
it takes place by reflection - not interference."

It is the interference between the forward and reflected voltages and beween the forward and reflected
currents that yields the resultant voltage and current values of rho at the matching point which produces
either a virtual short or a virtual open circuit that causes the re-reflection. I have shown this to be true
in my QEX article of Mar/Apr 1998, entitled, "Examining the Mechanics of Wave Interference in Impedance
Matching. It is also Chapter 23 in Reflections 2.

Using the complex values of rho I have shown the magnitude and phase relationships of the aforementioned
voltages and currents at the stub point that result in a virtual open circuit at the stub point to waves
reflected from a 3:1 mismatched load. The result is no reflections on the line between the stub and the
source, but a 3:1 SWR on the line between the mismatched load and the stub. If you don't have a copy of this
article please let me know and I'll send you one via email.

Walt, W2DU

Hello Walt,

Please know that all of my comments are offered with all due respect,
and there is a lot of respect due, and sincerely felt. However,
though the numbers work out as one would expect given the effects
that are observed, cause can only be attributed to
phenomenon which is observed in nature. Electromagnetic
waves can reflect only from real media. Though I admire the procedure
you have devised for describing the complex effects of these
reflections, the attempts to extend those ideas to describe real (not
virtual) physical phenomena are unsupported from a scientific
standpoint. Inference is insufficient proof.

Specifically: The nature of reflective surfaces does not depend on
whether or not steady state has been reached. Their reflectivity does
not change as a function voltage. Their nature does not depend on
things which lie at the other end of the transmission line - even
though the overall performance of the system certainly does. The
nature of reflective surfaces does not depend on how many times the
wave has bounced back and forth since the signal was initiated. These
things are implied by your claim, unfortunately.

In the case of optical media, reflectivity is determined by the
relative indices of refraction of the optical media comprising the
reflective surface. Neither the
indices, nor their ratio changes in response to illumination.
Likewise, the reflective nature of impedance discontinuities on a
transmission line depend entirely on physical constants analogous to
optical indices of refraction. These attributes do not tend to change
when illuminated by RF.

I thought we had covered this ground back a couple of years ago when
the topic of reflections from virtual shorts and opens came up on this
newsgroup. At that time it became clear that certain of the
predictions made under the model did not match well with reality.
For example, the virtual short circuit which can appear at the
entrance to a stub on a transmission line would, according to the
model, prevent the very currents necessary for creating the virtual
condition from entering the stub in the first place. Reflections can
occur only at physical discontinuities, not at a voltage to current ratio.

I was encouraged by the work we did on your transmission line
impedance matching transformer diagram. In that, it seemed we agreed
that the reflective coefficients were constant, were determined by the
characteristic impedance's of the transmission lines, and that steady
state was in fact comprised of the summation of a long series of
multiple partial reflections. And, it correlates exactly with the
descriptions and drawings of the analogous optical phenomena in the
physics texts.

I really admire your work, Walt, but I feel this one point is clearly
inconsistent with nature. Let me hasten to add that I see nothing at
all wrong with making calculations based on this model. Its utility
and beauty lies in its accuracy at the macroscopic level. I also
think that your treatise on interference as it applies to the
reflections found in RF systems is well done. The error I find is in
your notion of interference as a cause of reflection, which I assume
is extrapolated from your notion that virtual shorts and opens cause
reflections, and, that real reflective coefficients may be calculated
from virtual impedance's.

Best Regards,

Jim Kelley- Hide quoted text -

- Show quoted text -

Hi Jim,

Thanks for taking the time to write such an insightful response--I
was
expecting it.

At the moment I'm in a hotel in Jacksonville, going through pre-op for
spinal
surgery. I'll be home Wednesday, and that will be the earliest I'll
have the
opportunity to review your comments. So I'll get back with you after
having the
time to review it.

Thanks again, Jim,