I've enjoyed reading this and related threads. Some comments have been
made about using calculus. Though I spent a significant portion of my
pre-retirement life attempting to teach that subject to undergraduates, I
don't believe in using calculus whenever simple geometry and/or algebra
makes it unnecessary. A proof that avoids calculus can be meaningful for
those who don't know calculus, or who haven't used it for a while.

With that said, I have a few comments to make about some of the assertions
I have read here recently, some of which have appeared without explicit
proof.

(1) The surge impedance of a (lossy) transmission line cannot have an
angle more than 45 degrees away from the real axis.

This is true. Z_0 = sqrt((R + jwL)/(G + jwC)) (here I am using "w" instead
of omega). Both the numerator and denominator lie in the first quadrant,
so their quotient lies in the right half plane (angles subtract when one
divides), and the square root of that has an angle lying between - 45
degrees and + 45 degrees. (The branch of the square root with positive
real part has to be taken; if you can find coax whose surge impedance has
a negative real component, I'll pay you good money for it.)

[Since this angle lies between - 45 degrees and + 45 degrees, peculiar
consequences deduced from calculations involving surge impedances such as
50 - j200 can be ignored.]

(2) There is a nice geometrical interpretation for the reflection
coefficient, or rather for its magnitude. Since the coefficient is (Z_L -
Z_0)/(Z_L + Z_0), its magnitude expresses how much further Z_L is from the
surge impedance Z_0 than it is from the negative, - Z_0, of the surge
impedance. If Z_L is equidistant from Z_0 and - Z_0, then the magnitude of
the reflection coefficient is 1. If Z_L is closer in the complex plane to
Z_0 than it is to - Z_0, then the magnitude of the reflection coefficient
is less than 1. If Z_L is closer to - Z_0 than to Z_0, then the reflection
coefficient's magnitude exceeds 1. Now plot the points Z_0 and - Z_0 and
draw the perpendicular bisector of the segment joining them. If Z_L is on
that perpendicular bisector, the magnitude of the reflection coefficient
is 1; if it is on Z_0's side of the bisector, the magnitude is less than
1; if it is on - Z_0's side, the magnitude exceeds 1. Of course Z_L has to
stay in the right half plane; if it didn't have to do this, you could take
Z_L very close to - Z_0 and get enormous reflection coefficient
magnitudes.

(3) Consider an ellipse having Z_0 and - Z_0 as its foci. There are
infinitely many such ellipses, including a degenerate one (just the
segment between the "foci"). All these different ellipses fill up the
complex plane, and no point in the plane is on more than one of them. On
any one such ellipse, the sum of the distances from a point on the ellipse
to the two foci Z_0 and - Z_0 is constant (definition of an ellipse), the
value of that constant depending upon which ellipse it is but the constant
has to be at least as large as the interfocal distance. We should ignore
points on the ellipse that are in the left half plane. A portion of the
ellipse will be in the same quadrant as Z_0, and a portion will be in the
quadrant that contains the conjugate of Z_0. (Remember we are ignoring the
points in the left half plane.) All of the points on the ellipse that are
in Z_0's quadrant are closer to Z_0 than to - Z_0, so they'll give
reflection coefficients with magnitude less than 1. So will those of the
points on the ellipse in the other quadrant under consideration that are
between the real axis and the perpendicular bisector. But those that are
between the perpendicular bisector and the imaginary axis will be closer
to - Z_0 than to Z_0 and thus will yield reflection coefficients with
magnitudes greater than 1. It should be obvious that, along any given
ellipse, the one for which the magnitude of the reflection coefficient is
greatest is the one on the imaginary axis, since as we move along the
ellipse towards that point, the distance to - Z_0 decreases and the
distance from Z_0 increases (remember, their sum is constant along the
ellipse). So on any *one* ellipse, the largest reflection coefficient
magnitude occurs where the ellipse meets the imaginary axis, and thus Z_L
has real part 0 and imaginary part of opposite sign to that of Z_0.

(4) Start with Z_0 real, and slowly rotate Z_0 into either the first or
fourth quadrant, but not more than 45 degrees in either direction, keeping
the same magnitude while you rotate. The segments joining Z_0 and - Z_0,
their perpendicular bisectors, and the various ellipses will all
simultaneously rotate. It's now obvious that for ellipses of any fixed
size, the one producing the largest magnitude for the reflection
coefficient will occur when Z_0 is at + 45 degrees or - 45 degrees. So if
we want to maximize the reflection coefficient magnitude, we can restrict
attention to those two cases. The - 45 degree case (capacitive surge
impedance) is the more familiar one, but the math is the same either way.
The only question is, which one of the ellipses should we use, if we wish
to maximize the magnitude of the reflection coefficient?

(5) So now we're going to assume Z_0 = k(1 - j), and thus - Z_0 = k(-1 +
j), while Z_L = ktj. It's clear that the factor k is going to cancel out
when calculating the reflection coefficient, so I will henceforth ignore
it (i.e., normalize it to k = 1 by appropriate choice of units). If you
are of a geometrical turn of mind, you can produce a geometrical argument
showing that the best one can do is to make sure the ellipse meets the
imaginary axis at the same distance from the origin as the two foci, i.e.
at j*sqrt(2). If you are of an algebraic turn of mind, you can make an
algebraic argument involving completing the square to demonstrate the same
thing. If you insist on using calculus, it's now just one variable
calculus, not multivariable calculus, since the only independent variable
is t, which will turn out to be sqrt(2) at the maximum. (Hint: don't look
at the ratio of distances; look at the square of that ratio, so as to get
rid of all those square roots.)

(6) Once all that is done, it's just a bit of algebra to show that when t
= sqrt(2) then the magnitude of the reflection coefficient is 1 + sqrt(2).
That's the best (worst?) you can do. And if you can find some coax whose
surge impedance angle is - 45 degrees, you can indeed do it.

All the above was done from first principles. I am not fortunate enough to
own a copy of Chipman, though I wish I were, but if this is what he says,
then I am in full agreement with him.

David, ex-W8EZE, willing to part with some of my pension money for a copy
of Chipman if you know where one can be found (Powell's doesn't have any
copies)

--
David or Jo Anne Ryeburn

To send e-mail, remove the letter "z" from this address.

David or Jo Anne Ryeburn wrote:

David, ex-W8EZE, willing to part with some of my pension money for a
copy of Chipman if you know where one can be found (Powell's doesn't
have any copies)

When looking for a copy yesterday, it seemed incredible that none of the
major US dealers had even one for sale.

However, copies might also have been catalogued under "Schaum" as the
author, the book being one of the Schaum's Outline series.

I only discovered this possibility when it was too late to do anything
about it, so it may be worth a second look at the US dealers.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

On Fri, 29 Aug 2003 08:16:35 +0100, "Ian White, G3SEK"
wrote:

David or Jo Anne Ryeburn wrote:

David, ex-W8EZE, willing to part with some of my pension money for a
copy of Chipman if you know where one can be found (Powell's doesn't
have any copies)

When looking for a copy yesterday, it seemed incredible that none of the
major US dealers had even one for sale.


Hi All,

One very reliable source gave me two other sources with multiple
copies to choose from:
http://www.bookfinder.com/search/?ac...0558_2:268:527

73's
Richard Clark, KB7QHC

(David or Jo Anne Ryeburn) wrote in message .. .
I've enjoyed reading this and related threads. Some comments have been
made about using calculus. Though I spent a significant portion of my
pre-retirement life attempting to teach that subject to undergraduates, I
don't believe in using calculus whenever simple geometry and/or algebra
makes it unnecessary. A proof that avoids calculus can be meaningful for
those who don't know calculus, or who haven't used it for a while.


The the area within the rho=1 circle of the Smith is reserved for
passive networks. Outside rho=1, where the reflection is greater than
one, is reserved for active networks only.


Slick

On Fri, 29 Aug 2003 17:28:24 -0400, "Tom Coates"
wrote:

Search Amazon.com and www.addall.com for ISBN 0070107475.
They're my favorite book-finding tools.

Tom, N3IJ

Hi Tom,

Thanks for the new lead to a book site.

73's
Richard Clark, KB7QHC

Group:

Another very good and inexpensive reference on waves that might be of
interest to this group is:

William C. Elmore and Mark A Heald, "Physics of Waves", first published in
1969, but
most recently published in paperback by Dover Publications, New York, 1985
and
generally available in reprints even today for around US$17.00. A real
bargain.
ISBN: 0-486-64926-1 LCCN: 85-10419.

Be aware, since this is a Physics book it is loaded with gratuitous partial
differential
equations.

This book is interesting because it covers the *whole* field of waves, not
just
electromagnetic waves.

Electromagnetic waves are particularly simple when compared to general wave
phenomena,
since em waves are transverse only.

This book covers waves on strings and membranes, waves in and on fluids,
waves in compressible
media such as the earth [the seismic wavefield]etc... and so covers many of
the "analogies" that
posters to this news group like to draw upon, often drawing false
conclusions.

Are ocean waves at the beach *really* analogous to em waves?

This book will explain why not.

The earth supports both transverse and compressive-dillutive waves as well
as surface seismic waves. Are compressive-dillutive waves different either
qualitatively or quantitatively from electromagnetic transverse waves, this
book answers the question.

etc, etc...

Expand your wave horizons beyond mere em waves, if you are deeply interested
in waves, this book is more than worth the price at US$17.00. It's
available from Amazon.

--
Peter K1PO
Indialantic By-the-Sea, FL


"David or Jo Anne Ryeburn" wrote in message
...
I've enjoyed reading this and related threads. Some comments have been
made about using calculus. Though I spent a significant portion of my
pre-retirement life attempting to teach that subject to undergraduates, I
don't believe in using calculus whenever simple geometry and/or algebra
makes it unnecessary. A proof that avoids calculus can be meaningful for
those who don't know calculus, or who haven't used it for a while.

With that said, I have a few comments to make about some of the assertions
I have read here recently, some of which have appeared without explicit
proof.

(1) The surge impedance of a (lossy) transmission line cannot have an
angle more than 45 degrees away from the real axis.

This is true. Z_0 = sqrt((R + jwL)/(G + jwC)) (here I am using "w" instead
of omega). Both the numerator and denominator lie in the first quadrant,
so their quotient lies in the right half plane (angles subtract when one
divides), and the square root of that has an angle lying between - 45
degrees and + 45 degrees. (The branch of the square root with positive
real part has to be taken; if you can find coax whose surge impedance has
a negative real component, I'll pay you good money for it.)

[Since this angle lies between - 45 degrees and + 45 degrees, peculiar
consequences deduced from calculations involving surge impedances such as
50 - j200 can be ignored.]

(2) There is a nice geometrical interpretation for the reflection
coefficient, or rather for its magnitude. Since the coefficient is (Z_L -
Z_0)/(Z_L + Z_0), its magnitude expresses how much further Z_L is from the
surge impedance Z_0 than it is from the negative, - Z_0, of the surge
impedance. If Z_L is equidistant from Z_0 and - Z_0, then the magnitude of
the reflection coefficient is 1. If Z_L is closer in the complex plane to
Z_0 than it is to - Z_0, then the magnitude of the reflection coefficient
is less than 1. If Z_L is closer to - Z_0 than to Z_0, then the reflection
coefficient's magnitude exceeds 1. Now plot the points Z_0 and - Z_0 and
draw the perpendicular bisector of the segment joining them. If Z_L is on
that perpendicular bisector, the magnitude of the reflection coefficient
is 1; if it is on Z_0's side of the bisector, the magnitude is less than
1; if it is on - Z_0's side, the magnitude exceeds 1. Of course Z_L has to
stay in the right half plane; if it didn't have to do this, you could take
Z_L very close to - Z_0 and get enormous reflection coefficient
magnitudes.

(3) Consider an ellipse having Z_0 and - Z_0 as its foci. There are
infinitely many such ellipses, including a degenerate one (just the
segment between the "foci"). All these different ellipses fill up the
complex plane, and no point in the plane is on more than one of them. On
any one such ellipse, the sum of the distances from a point on the ellipse
to the two foci Z_0 and - Z_0 is constant (definition of an ellipse), the
value of that constant depending upon which ellipse it is but the constant
has to be at least as large as the interfocal distance. We should ignore
points on the ellipse that are in the left half plane. A portion of the
ellipse will be in the same quadrant as Z_0, and a portion will be in the
quadrant that contains the conjugate of Z_0. (Remember we are ignoring the
points in the left half plane.) All of the points on the ellipse that are
in Z_0's quadrant are closer to Z_0 than to - Z_0, so they'll give
reflection coefficients with magnitude less than 1. So will those of the
points on the ellipse in the other quadrant under consideration that are
between the real axis and the perpendicular bisector. But those that are
between the perpendicular bisector and the imaginary axis will be closer
to - Z_0 than to Z_0 and thus will yield reflection coefficients with
magnitudes greater than 1. It should be obvious that, along any given
ellipse, the one for which the magnitude of the reflection coefficient is
greatest is the one on the imaginary axis, since as we move along the
ellipse towards that point, the distance to - Z_0 decreases and the
distance from Z_0 increases (remember, their sum is constant along the
ellipse). So on any *one* ellipse, the largest reflection coefficient
magnitude occurs where the ellipse meets the imaginary axis, and thus Z_L
has real part 0 and imaginary part of opposite sign to that of Z_0.

(4) Start with Z_0 real, and slowly rotate Z_0 into either the first or
fourth quadrant, but not more than 45 degrees in either direction, keeping
the same magnitude while you rotate. The segments joining Z_0 and - Z_0,
their perpendicular bisectors, and the various ellipses will all
simultaneously rotate. It's now obvious that for ellipses of any fixed
size, the one producing the largest magnitude for the reflection
coefficient will occur when Z_0 is at + 45 degrees or - 45 degrees. So if
we want to maximize the reflection coefficient magnitude, we can restrict
attention to those two cases. The - 45 degree case (capacitive surge
impedance) is the more familiar one, but the math is the same either way.
The only question is, which one of the ellipses should we use, if we wish
to maximize the magnitude of the reflection coefficient?

(5) So now we're going to assume Z_0 = k(1 - j), and thus - Z_0 = k(-1 +
j), while Z_L = ktj. It's clear that the factor k is going to cancel out
when calculating the reflection coefficient, so I will henceforth ignore
it (i.e., normalize it to k = 1 by appropriate choice of units). If you
are of a geometrical turn of mind, you can produce a geometrical argument
showing that the best one can do is to make sure the ellipse meets the
imaginary axis at the same distance from the origin as the two foci, i.e.
at j*sqrt(2). If you are of an algebraic turn of mind, you can make an
algebraic argument involving completing the square to demonstrate the same
thing. If you insist on using calculus, it's now just one variable
calculus, not multivariable calculus, since the only independent variable
is t, which will turn out to be sqrt(2) at the maximum. (Hint: don't look
at the ratio of distances; look at the square of that ratio, so as to get
rid of all those square roots.)

(6) Once all that is done, it's just a bit of algebra to show that when t
= sqrt(2) then the magnitude of the reflection coefficient is 1 + sqrt(2).
That's the best (worst?) you can do. And if you can find some coax whose
surge impedance angle is - 45 degrees, you can indeed do it.

All the above was done from first principles. I am not fortunate enough to
own a copy of Chipman, though I wish I were, but if this is what he says,
then I am in full agreement with him.

David, ex-W8EZE, willing to part with some of my pension money for a copy
of Chipman if you know where one can be found (Powell's doesn't have any
copies)

--
David or Jo Anne Ryeburn

To send e-mail, remove the letter "z" from this address.

Roy:

[snip]
I thought this was only true for waves moving through a lossless medium
or in a lossless transmission line that supports TEM waves. Either the
electric or magnetic field isn't transverse in a hollow waveguide, and
either or both can be non-transverse in a lossy medium.

Or am I mistaken about this?

Roy Lewallen, W7EL
[snip]

Compressive-dillutive waves occur only in media that is compressible, like
the earth or the air, or springs, etc... With compressive-dillutive waves
the "vibrations" occur in the effective density of the medium.

Electromagnetic waves propagate with transversal vibrations of the E and H
fields, viz. Side to side vibrations, not shortening and lenghtening
vibrations. If an electromagnetic wave is supported in the Transverse
Electromagnetic or TEM mode then [theoretically] the E and H fields are at
right angles to each other and to the direction of propagation, in the
terminology of TEM, the term transverse referes to the orientation of the
wave with respect to it's guides, and not to it's vibration mode in the
longitudinal - transverse sense.

Visualize a long "slinky" coil attached to the wall. Shake one end up and
down to create a transverse wave in which the slinky moves up and down.
Push and pull on the end to produce compression and dilution to cause
longitudinal waves in which the slinky does not move up and down but in
which the distance between turns moves back and forth. This slinky analogy
sort of illustrates the differences. Meanwhile in electromagnetic wave
phenomena you have as well as the most common TEM mode which is only
transverse vibrations, also there exists a plethora of TM and/or TE modes,
or even in the near field, where the fields may not be at right angles to
each other or to the direction of propagation, but the vibrations are still
talways transverse, i.e. not compressive-dilutive.

Back in the mid-1800's after Maxwell produced his celebrated equations and
Heaviside improved them by expressing them in vector form most scientists
of the time noted that Maxwell's formulation provided no explicit form for a
medium for the electromagnetic waves to propagate in, and they also noted
that there were only transverse and not longitudinal [compressive-dilutive]
vibrations supported by his equations. Several eminent scientists of the
day felt that this left openings for several more discoveries and so...
Then ensued for several decades a search for the "ether". The "ether" was
supposed to be the media which supported the electromagnetic waves. During
that period several of the eminent scientists of the time proposed that the
"ether" once it was found might actually be compressible and they proposed
that Maxwell and Heaviside had left out of their formulations the
possibility of compressive-dilutive or longitudinal vibrations. Several
scientists of the time actually formulated equations which supported
compressive-dilutive em waves and actually conconcted and, to no avail,
actually conducted experiments to try to find out if such
compressive-dilutive vibrations actually occured with electromagnetic
phenomena.

As we all know, eventually the existence of the "ether" was discredited,
mainly by the Michelson-Morley experiments, and today we all know that
electromagnetic waves do not have a media or "ether" to support their
propagation and vibrations.

Electromagnetic waves propagate just fine in a complete vacuum, and a vacuum
is incompressible, and so the search for compressive-dilutive vibrations of
electromagnetic waves became moot and a search for experimental evidence of
them was abandoned by all who were interested. One can add terms to the
Maxwell-Heaviside equations to support compressive waves, and this has been
done by several theoretical physicists, but there is no sense doing so since
none have ever been discovered!

The book, I referred to above, "Physics of Waves" gives all the details of
the wave equation for media that supports compressive waves. An important
such field is the field of seismology. Indeed the field of siesmology
studies waves that vibrate in all modes, transversally and longitudinally,
as well as surface waves. Seismic waves are processed regularly with beam
forming arrays of seismometers and processed by tomographic techniques to
image the earth in all wave modes.

Seismology is a facinating field and seismologists are generally the most
sophisticated of all wave mechaics!

A good modern book on the seismic wavefield is:

B. L. N. Kennett, "The Siesmic Wavefield", Cambridge University Press, New
York, NY, 2001. ISBN: 0-521-00663-5.

But be aware it is full of gratuitous partial differential equations and
tensor analysis. The stress-strain variables of compressible-dillutive
media are expressed as tensors and the partial differential equations are
cast in tensor form.

All this to say that electromagnetic wave phenomena are a particularly
simple form of wave phenomena when compared to the most complicated types.

--
Peter K1PO
Indialantic By-the-Sea, FL.

Thanks for the most interesting discussion of slinkys, "ether", and
seismology. But I'm a little vague on what you mean by "vibrations".
You're describing a field whose orientation isn't necessarily at a right
angle (transverse) to the direction of propagation (as in a TE or TM
mode wave), yet whose "vibrations" are nevertheless at a right angle to
the direction of propagation. So the "vibrations" are in a different
direction than the field. I'd like to learn more about this phenomenon,
but I can't find "vibrations" in the indexes of any of my
electromagnetics texts. Do they have another name?

Roy Lewallen, W7EL

Peter O. Brackett wrote:
. . .
Visualize a long "slinky" coil attached to the wall. Shake one end up and
down to create a transverse wave in which the slinky moves up and down.
Push and pull on the end to produce compression and dilution to cause
longitudinal waves in which the slinky does not move up and down but in
which the distance between turns moves back and forth. This slinky analogy
sort of illustrates the differences. Meanwhile in electromagnetic wave
phenomena you have as well as the most common TEM mode which is only
transverse vibrations, also there exists a plethora of TM and/or TE modes,
or even in the near field, where the fields may not be at right angles to
each other or to the direction of propagation, but the vibrations are still
talways transverse, i.e. not compressive-dilutive.
. . .

Peter O. Brackett wrote:
Electromagnetic waves propagate with transversal vibrations of the E and H
fields, ...

Heh, heh, not wearing the particle physics hat today, Peter? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Thanks for the most interesting discussion of slinkys, "ether", and
seismology. But I'm a little vague on what you mean by "vibrations".
You're describing a field whose orientation isn't necessarily at a right
angle (transverse) to the direction of propagation (as in a TE or TM
mode wave), yet whose "vibrations" are nevertheless at a right angle to
the direction of propagation. So the "vibrations" are in a different
direction than the field. I'd like to learn more about this phenomenon,
but I can't find "vibrations" in the indexes of any of my
electromagnetics texts. Do they have another name?

Roy Lewallen, W7EL

Yes, "vibes." I think Peter is regressing back to the '60's.
73,
Tom Donaly, KA6RUH