Cecil, W5DXP wrote:
"I am assuming anything with the dimensions of "ohms" is "ohmic" but I
could be wrong."

That would apply to a transmission line where "The characteristic
impedance Zo is the ratio of voltage to current in an individual
wave;---it is also the impedance of a line that is infinitely long ---"
or terminated in ZL = Zo.

As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

Best regards, Richard Harrison, KB5WZI

On Wed, 10 Mar 2004 22:43:11 -0600, Cecil Moore
wrote:

So you disagree with "Wave Mechanics of Transmission Lines, Part 3:"
by S. R. Best, QEX Nov/Dec 2001?

Cecil, are you saying you believe the total nonsense in Steve's Part 3? The
fiction he wrote there is totally incorrect and misleading. He introduced nine
new misconceptions that need dispelling, misconceptions that totally dispute my
explanations of the role of wave mechanics in impedance matching, including my
references from MIT and Harvard EE professors.

I can't disclose what's about to happen in the immediate future on this issue,
but when it does happen you'll see mathematical proof of where herr Best went
wrong. And it also totally supports your argument with Gene, who apparently
doesn't get it either, because I heard him claim that Steve's article is one of
the most illuminating and definitive he's read. Unfortunately, Steve's QEX
article is total BS.

Walt, kW2DU

Richard Harrison wrote:
Cecil, W5DXP wrote:
"I am assuming anything with the dimensions of "ohms" is "ohmic" but I
could be wrong."

As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

But some people play semantic games. The IEEE dictionary generally
avoids definitions of adjectives and favors adjectives plus nouns,
e.g. "ohmic contact".

From my physics book, an ohmic conductor is one whose resistivity
is constant with changing voltage. Does "resistivity" imply dissipation?
--
73, Cecil http://www.qsl.net/w5dxp



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As Reg once noted, you could measure Zo with your ohmmeter in an
infinite line.

===========================

It would not be a steady reading on the ohmeter. It would be a quick
deflection followed by a slower subsidence.

Zo of real lines is a function of frequency. As frequency decreases Zo
increases and becomes more reactive ultimately approaching -45 degrees.
This affects in a complex manner the behaviour of the ohmeter pointer.

The ohmeter reading changes from an initial low value to a higher value
versus time. The actual values and time taken depend on Zo and on the
voltmeter resistance. The final value is never achieved just as the final
voltage across a capacitor being charged up via a resistor is never
achieved.

To calculate input resistance versus time as recorded on the ohmeter
requires a large amount of calculation using Heaviside's operational
calculus.

An infinite series of complicated terms is involved. This type of
calculation on transmission lines must have been amongst the very first
carried out by the young Heaviside himself round about 1872. It is closely
related to the distortion of keying waveshapes along telegraph cables.
Imagine the pleasure he experienced, using his own calculus, as he with his
sliderule produced the very first sets of figures and graphs describing the
waveshapes. It is still related to distortion of digital signals in this
modern electronic age but now we have oscilloscopes.
----
Reg, G4FGQ

Walter Maxwell wrote:

Cecil Moore wrote:
So you disagree with "Wave Mechanics of Transmission Lines, Part 3:"
by S. R. Best, QEX Nov/Dec 2001?

Cecil, are you saying you believe the total nonsense in Steve's Part 3?

No, Steve assumes the existence of forward and reflected energy waves.
I also assume the existence of forward and reflected energy waves and
think their existence can be proven. I assume that you agree with Steve
that forward and reflected energy waves exist. If I understand Gene
correctly, he believes that reflected energy waves do not exist in
a matched system even though there is a mismatch at the load.

I probably should have said: "So you disagree with the very existence
of reflected energy waves which is assumed by S. R. Best in his QEX
Nov/Dec 2001 article.

Since Steve's article asserts the existence of forward and reflected
energy waves, it cannot be "total nonsense". In fact, Steve's equation
for total forward power yields the correct answer. In a matched system,

Ptotal = P1 + P2 + 2*SQRT(P1*P2)

indeed yields the correct result given that:

P1 = Psource(1-rho)^2 = Psource times the power transmission coefficient

P2 = Pref(rho)^2 = Preflected times the power reflection coefficient

Steve's problem was that he did not recognize (actually denied) the role
of interference, destructive and constructive, and therefore left out half
of the explanation. In optics, 2*SQRT(P1*P2) is known as the "interference term"
and equal magnitudes of interference happen on both sides of the match point. In
a perfectly matched system, at the match point, there exists total destructive
interference toward the source, i.e. zero reflections, and total constructive
interference toward the load, i.e. all the energy winds up flowing toward the load.

The following two problems are virtually identical. 'n' is the index of
refraction.

air | glass
Laser-------------|---------
n=1.0 | n=1.5

XMTR---50 ohm coax---75 ohm load

The magnitudes of the reflection coefficients are identical at |0.2|

The solutions to those problems are virtually identical.

air | 1/4WL thin-film | glass
Laser-------------|------------------|-----------
n=1.0 | n=1.225 | n=1.5

XMTR---50 ohm coax--x--1/4WL 61.2 ohm coax--75 ohm load

Optical physicists fully understand what happens with the Laser. It is explained
on the Melles-Griot web page and in _Optics_, by Hecht. From the Melles-Griot web
page: http://www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and the thickness of the film
are such that a phase difference exists between reflections of p, then reflected
wavefronts interfere destructively, and overall reflected intensity is a minimum.
If the two reflections are of equal amplitude, then this amplitude (and hence intensity)
minimum will be zero. In the absence of absorption or scatter, the principle of conservation
of energy indicates all "lost" reflected intensity will appear as enhanced intensity in the
transmitted beam."

This fits perfectly with Reflections II, chapter 23: "Therefore, while reflection
angles for waves reflected at the input mismatch (point x above) are 180 deg for voltage,
and 0 deg for current, the corresponding angles at the input for the waves reflected
from the output mismatch (75 ohm load above) are reversed, 0 deg for voltage and 180
deg for current. Consequently, all corresponding voltage and current phasors are 180
deg out of phase at the matching point. ... With equal magnitudes and opposite phase
at the same point (point x, the matching point) the sum of the two waves is zero."

That is a perfect description of total destructive interference. I have your reference,
J. C. Slater's book, _Microwave_Transmission_, on order.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"Does "resistivity" imply dissipation?"

I haven`t looked it up but the word "resistivity" automatically
generates a definition in my mind:

Rho = length / area.

Best regards, Richard Harrison, KB5WZI

On Thu, 11 Mar 2004 09:52:28 -0600, Cecil Moore
wrote:

Walter Maxwell wrote:

Cecil Moore wrote:
So you disagree with "Wave Mechanics of Transmission Lines, Part 3:"
by S. R. Best, QEX Nov/Dec 2001?

Cecil, are you saying you believe the total nonsense in Steve's Part 3?

No, Steve assumes the existence of forward and reflected energy waves.
I also assume the existence of forward and reflected energy waves and
think their existence can be proven. I assume that you agree with Steve
that forward and reflected energy waves exist. If I understand Gene
correctly, he believes that reflected energy waves do not exist in
a matched system even though there is a mismatch at the load.

I probably should have said: "So you disagree with the very existence
of reflected energy waves which is assumed by S. R. Best in his QEX
Nov/Dec 2001 article.

Cecil, it's not whether reflected waves exist that's wrong with Steve's paper,
it's his misuse them that's wrong, and it's the misuse that is 'total nonsense'.

Since Steve's article asserts the existence of forward and reflected
energy waves, it cannot be "total nonsense". In fact, Steve's equation
for total forward power yields the correct answer. In a matched system,

Ptotal = P1 + P2 + 2*SQRT(P1*P2)

indeed yields the correct result given that:

P1 = Psource(1-rho)^2 = Psource times the power transmission coefficient

P2 = Pref(rho)^2 = Preflected times the power reflection coefficient

Cecil, your equations for P1 and P2 yield absurd answers if you plug the numbers
into them. The value for P1 should read "Psource (1 - rho^2) = ..., and the
value for P2 should read "P2 = Pref (rho^2). Beega difference! Then the value
for Ptotal will be correct.

Steve's problem was that he did not recognize (actually denied) the role
of interference, destructive and constructive, and therefore left out half
of the explanation.

Exactly!!! And it's the correct interference relationship I present in QEX and
Reflections that he insists is incorrect. In much earlier emails with Steve he
told me that using my statements appearing there he could prove me technically
incompetent. He simply would not accept any of my pleadings with him to see the
correct application of the interference between reflected waves that achieves
the impedance match.

In optics, 2*SQRT(P1*P2) is known as the "interference term"
and equal magnitudes of interference happen on both sides of the match point. In
a perfectly matched system, at the match point, there exists total destructive
interference toward the source, i.e. zero reflections, and total constructive
interference toward the load, i.e. all the energy winds up flowing toward the load.

The following two problems are virtually identical. 'n' is the index of
refraction.

air | glass
Laser-------------|---------
n=1.0 | n=1.5

XMTR---50 ohm coax---75 ohm load

The magnitudes of the reflection coefficients are identical at |0.2|

The solutions to those problems are virtually identical.

air | 1/4WL thin-film | glass
Laser-------------|------------------|-----------
n=1.0 | n=1.225 | n=1.5

XMTR---50 ohm coax--x--1/4WL 61.2 ohm coax--75 ohm load

Optical physicists fully understand what happens with the Laser. It is explained
on the Melles-Griot web page and in _Optics_, by Hecht. From the Melles-Griot web
page: http://www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and the thickness of the film
are such that a phase difference exists between reflections of p, then reflected
wavefronts interfere destructively, and overall reflected intensity is a minimum.
If the two reflections are of equal amplitude, then this amplitude (and hence intensity)
minimum will be zero. In the absence of absorption or scatter, the principle of conservation
of energy indicates all "lost" reflected intensity will appear as enhanced intensity in the
transmitted beam."

No one in his right mind can successfully argue against this. Anyone who would
argue against this is either of closed mind or an ignorant moron.

This fits perfectly with Reflections II, chapter 23: "Therefore, while reflection
angles for waves reflected at the input mismatch (point x above) are 180 deg for voltage,
and 0 deg for current, the corresponding angles at the input for the waves reflected
from the output mismatch (75 ohm load above) are reversed, 0 deg for voltage and 180
deg for current. Consequently, all corresponding voltage and current phasors are 180
deg out of phase at the matching point. ... With equal magnitudes and opposite phase
at the same point (point x, the matching point) the sum of the two waves is zero."

I'm glad you find that Chapter 23 fits, because I've known all along that it
fits perfectly with Melles-Griot. Steve (Best), on the other hand says Chapter
23 is totally wrong. You might also note that Chapter 23 is identical with my
paper in QEX in the Mar/Apr 1998 issue, which Steve also disputes in all three
parts of his QEX article.

That is a perfect description of total destructive interference. I have your reference,
J. C. Slater's book, _Microwave_Transmission_, on order.

You might find Slater (1943) difficult to obtain. I can email you a copy of the
pertinent part if you wish.

Walt, W2DU

In all these sort of discussions I have never heard any mention of
"Interaction Loss", ie., that which occurs directly between the reflection
coefficients of the source and load.

It seems something important has long been and is still being neglected. It
may be that some points of dispute could be resolved by taking Interaction
Loss into account.
----
Reg.

Walter Maxwell wrote:
Cecil, your equations for P1 and P2 yield absurd answers if you plug the numbers
into them. The value for P1 should read "Psource (1 - rho^2) = ..., and the
value for P2 should read "P2 = Pref (rho^2). Beega difference! Then the value
for Ptotal will be correct.

Yep, Walt, I made a typo. It should be (1-rho^2). When I think in words while
typing, "one minus rho squared", is ambiguous. Obviously (rho)^2 + (1-rho^2)
*must* equal unity, i.e. the total.

I'm glad you find that Chapter 23 fits, because I've known all along that it
fits perfectly with Melles-Griot. Steve (Best), on the other hand says Chapter
23 is totally wrong.

I don't know how he can say that. The Melles-Griot data for perfect non-glare
glass depends upon two 'I' irradiance equations.

Irradiance toward the source (reflected irradiance) equals:

Ir1 + Ir2 - 2*(Ir1*Ir2) = 0 = Ir1 + Ir2 - total_destructive_interference

Irradiance toward the load (total forward irradiance) equals:

If1 + If2 + 2*(If1*If2) = If1 + If2 + total_constructive_interference

It may not be apparent but (Ir1*Ir2) *must* equal (If1*If2).

Steve and I had an argument about this stuff years ago before he published his
QEX article. He denied that any interference exists even though his 2*SQRT(P1*P2)
term is know as the "interference term".

Irradiance, 'I', for a laser beam, is equivalent to power. Reflectance, 'R' in optics, is
the power reflection coefficient. Transmittance, 'T' in optics, is the power transmission
coefficient. Thus:

Ir1 = R*Isource Ir2 = T*Iref If1 = T*Isource If2 = R*Iref

You might find Slater (1943) difficult to obtain. I can email you a copy of the
pertinent part if you wish.

Thanks, but my used copy has already shipped through http://www.powellsbooks.com

Walt, as you know, QEX refused to publish my rebuttal of Steve's article. There's
some good stuff and some bad stuff in his article. This is not a black and white
argument. IMO, about a third of Steve's Part 3 article is valid. My objections
are with the other 2/3.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg Edwards wrote:
In all these sort of discussions I have never heard any mention of
"Interaction Loss", ie., that which occurs directly between the reflection
coefficients of the source and load.

It seems something important has long been and is still being neglected. It
may be that some points of dispute could be resolved by taking Interaction
Loss into account.

We usually discuss Z0-matched systems. In a Z0-matched system,
the reflection coefficients at the two reflection points are
equal in magnitude and opposite in sign. If no reflections are
allowed to reach the source, there is zero "Interaction Loss".
--
73, Cecil, W5DXP