On Dec 14, 7:59 pm, "AI4QJ" wrote:
"Roger" wrote in message

. ..





AI4QJ wrote:
"Richard Clark" wrote in message
. ..
In a 231 line posting that contains only original 57 lines:
On Thu, 13 Dec 2007 17:26:17 -0800, Roger wrote:

Hi Roger,

This last round has piqued my interest when we dipped into DC. Those
"formulas" would lead us to a DC wave velocity?
Hi Richard,

Here are two links to pages that cover the derivation of the formula
Zo
= 1/cC and much more.

http://www.speedingedge.com/PDF-File...stic_Impedance...
http://www.ece.uci.edu/docs/hspice/h...001_2-269.html

Here is the way I proposed to Kevin Schmidt nearly seven years ago
after
seeing him use the formula on a web page:
Hi Roger,

However, none of what you respond with actually gives a DC wave
velocity. At a stretch, it is a transient with the potential of an
infinite number of waves (which could suffer dispersion from the
line's frequency characteristics making for an infinite number of
velocities). The infinite is a trivial observation in the scheme of
things when we return to DC.

Attaching a battery casts it into a role of AC generation (for however
long the transmission line takes to settle to an irresolvable
ringing). Discarding the term DC returns us to conventional
transmission line mechanics.

DC, in and of itself, has no wave velocity.

For the model provided, R= 0, therefore we have a transmission line
consisting of superconductors. The speed at which steady state DC current
is injected into the model will equal the maximum speed of DC current in
the model. Although the electrons themselves will move very slowly, for
each coulomb injected in, one coulomb will be injected out at the same
velocity they were injected in (not to be confused with 'current' which
is the number of coulombs per second). If it were possible for the source
to provide DC current at c, then the DC current moves at c. The
capacitance C can be any value and Zo has no meaning. The only model that
works here is the one with a cardboard tube filled with ping pong balls,
in this case with 0 distance between them.

Ah, but of so little importance because the model is not reality.
While R (ohmic resistance) is specified as zero, impedance is what we are
looking for. Impedance is the ratio of voltage to current.

Roger the impedance is zero because the current is steady state DC. F = 0,

Zo = 0 -j*2*pi*0*C =0

I'd suggest that this is an inaccurate interpretation.
For an ideal line we have

Z0 = sqrt( L/C )
and
velocity = 1/sqrt( LC )

These are the fundamental equations based on the
charactistics (distributed L and C) of the line.

These equations can be manipulated to yield
Z0 = 1/(velocity * C)
and
Z0 = velocity * L

But Z0 continues to exist regardless of the signal
being applied.

Think of the "velocity" as the velocity at which a
perturbation to the signal propagates down the
line.

When you turn on the constant voltage, the step
propagates down the line at "velocity", when you
change the voltage, the new step propagates at
"velocity". Over any region of the line where
the signal has a constant amplitude, it will
be difficult to discern this "velocity" but on
other regions of the line where a change is
present, it will be possible.

So if there are no perturbations, the "velocity"
can not be observed, but it would a mistake
to think that it goes away (or that Z0 does).

....Keith

On Dec 14, 9:10 pm, "AI4QJ" wrote:
Where did the extra black box come from and who made the restriction on
frequency? I should be able to use any voltage or frequency I want, don't
you think?

The original problem statement discused -j567 as
an impedance. This is implicitly frequency dependant.

The Smith chart is normalized for impedance
and frequency.

When allowed to excite the black boxes with different
signals there are many ways to determine an internal
equivalent circuit. The question here was did the various
ways of making -j567 affect the results for sinusoidal
single frequency excitation.

....Keith

On Dec 14, 10:00 pm, "AI4QJ" wrote:
"Keith Dysart" wrote in message

...

On Dec 14, 9:10 pm, "AI4QJ" wrote:
Where did the extra black box come from and who made the restriction on
frequency? I should be able to use any voltage or frequency I want, don't
you think?

The original problem statement discused -j567 as
an impedance. This is implicitly frequency dependant.

Not if I change the capacitance.

Each of the different ways mentioned for obtaining -j567
will produce a different impedance if the frequency is
changed. They were all frequency dependant.

The Smith chart is normalized for impedance
and frequency.

The smith chart is normalized *only* by Zo.

Tell me, how is Zo related to frequency :-)

Or better, tell me how the smith
chart is normalized by frequency?

Everything is done in terms of degrees along a wave.
This implicitly normalizes for frequency.

When allowed to excite the black boxes with different
signals there are many ways to determine an internal
equivalent circuit. The question here was did the various
ways of making -j567 affect the results for sinusoidal
single frequency excitation.

In the example, -j567 was merely due to a phase change due to the abrupt
impedance discontinuity. You are the one who suggested putting things in
black boxes. I suppose you could devise ways to phase shifts due to -j567 in
black boxes but I will have to leave that to you since you are the one who
brought up the idea.

Several ways were mentioned for obtaining the -j567:
a capacitor, some length of 100 ohm line, a different
length of 600 ohm line. Regardless of how the -j567
impedance is obtained, the same input impedance
to the 600 ohm line results. And yet each appears
to have a different phase shift occurring at the terminals.

Putting things in black boxes is a thought experiment
which helps isolate which aspects are important.
Any box containing a circuit which produces -j567
at the terminals will result in exactly the same
impedance at the input to the 600 ohm line, so
clearly -j567 is important.

Is the "phase shift" at the discontinuity important
when the results can be determined without knowing
the value. In fact, the "phase shift", in all the
examples, was computed last, after all the results
were known. How important can it be?

Do you suggest that there is no phase shift?

I suggest that there is no value in thinking about
the "phase shift" at the discontinuity (which depending
on the black box chosen might not be present), and
merely think about the results of connecting the
-j567 impedance to the 600 ohm line.

Then how do you explain the smith chart results?

Starting with the 100 ohm line, the normalized
input impedance was computed using the Smith
chart. This impedance was denormalized and then
renormalized to the 600 ohm. The new value was
plotted on a new Smith chart (the chart normalized
to 600 ohms) and the length of the 600 ohm line
was determined. The two lines have lengths, call
them Z1len and Z2len. 90 - (Z1len + Z2len) will
give a number which Cecil/you have called the
"phase shift" at the discontinuity. Alternatively,
it is just what happens when -j567 is attached
to the appropriate length of 600 ohm line.

Cecil did not answer the question, so I will
pose it again. If knowing the phase shift at
the terminals of the black box is important,
and you can not know it without knowing the
internals of the box, given a black box of
unknown internals but told that its terminals
present -j567 at the frequency of interest,
would you refuse to calculate the length
of 600 ohm line needed to produce 0 ohms?

I suggest that there is no need to refuse
since the only information that is required
is -j567. Whether the box achieves this with
600 ohm line ("no phase shift"), 100 ohm
line ("some phase shift"), a capacitor or
some other technique is irrelevant.

....Keith

AI4QJ wrote:
"Roy Lewallen" wrote in message
...
AI4QJ wrote:
. . .
(I sure am learning a lot about antennas and transmission lines here)
I'm glad to hear that. Does the new knowledge include a way to tell the
four black boxes apart at one steady state frequency, or how many
"electrical degrees" each one contains?

Roy Lewallen, W7EL

Where did the extra black box come from and who made the restriction on
frequency? I should be able to use any voltage or frequency I want, don't
you think?

Sure, you can do anything you like. But can you tell the boxes apart by
measuring at just one frequency (the one at which their impedances are
the same)? Do they have the same or different numbers of "electrical
degrees" at that frequency?

The fourth box was my proposal, a box containing a capacitor with the
same reactance as the contents of the other boxes, and which I claimed
couldn't be distinguished from the others.

Roy Lewallen, W7EL

AI4QJ wrote:

I also eventually agreed that I went too far to suggest one *could* tell the
differences. I could go back and find the post where I made that retraction
but it might take some time. It was a 'by the way' sort of thing; it seemed
to be almost corroborative but it was definitely was incorrect although not
very important in the overall discussion. Thank you for having corrected me
before. I thought I previously had submitted to the lashes of the whoop
haung (or whatever they call that thing at ARRL that you use to punish
hams).

Thanks, I had missed that posting. Did you also conclude, then, that all
the boxes contain the same number of "electrical degrees"?

Roy Lewallen, W7EL

On Fri, 14 Dec 2007 11:35:25 -0800, Roger wrote:

The derivation did several things for me. It clearly explains why we do
not have a runaway current when we first connect a voltage to a
transmission line,

Hi Roger,

It doesn't describe why the current flows in the first place, does it?

what transmission line impedance is, that moving
particles can not be the entire explanation for the electromagnetic wave
(because the energy field moves much faster than the electrons), and
puts into place a richer understanding of inductance.

And here we begin on the wonderful world of spiraling explanations,
not found in the original source: "Moving particles cannot be the
entire explanation?" How about that in the first place, particles
don't inhabit the explanation at all?

What is your point here? Are implying that the formula is incorrect
because a sine wave was not mentioned in the derivation. I am sure that
all of the sophisticated readers of this news group understand that the
sharp corner of the square wave is composed of ever higher frequency
waves.

I'm even convinced most of them would not call this DC too.

We would complicate the concept and thereby begin to confuse people if
we insisted on using the "Stepped Wave" term.

They would've been confused anyway.

It is a simple step to
recognize that if we can make a wave front with one battery, we can use
a lot of batteries and carefully place and switch them to form a sine
wave. The more batteries and switches, the better the representation.

And this is still DC?

Is there some harm in considering Zo = 1/cC?

This is best left in the privacy of the home.

However, none of your comments respond to the question: What is with
this death grip on DC? What makes it so important that it be so
tightly wedded to Waves? What mystery of the cosmos is answered with
this union that has so long escaped the notice of centuries of trained
thought?

73's
Richard Clark, KB7QHC

"AI4QJ" wrote in message
...

"Roger" wrote in message
. ..
AI4QJ wrote:
"Richard Clark" wrote in message
...
In a 231 line posting that contains only original 57 lines:
On Thu, 13 Dec 2007 17:26:17 -0800, Roger wrote:

Hi Roger,

This last round has piqued my interest when we dipped into DC. Those
"formulas" would lead us to a DC wave velocity?
Hi Richard,

Here are two links to pages that cover the derivation of the formula
Zo
= 1/cC and much more.

http://www.speedingedge.com/PDF-File..._Impedance.pdf
http://www.ece.uci.edu/docs/hspice/h...001_2-269.html

Here is the way I proposed to Kevin Schmidt nearly seven years ago
after
seeing him use the formula on a web page:
Hi Roger,

However, none of what you respond with actually gives a DC wave
velocity. At a stretch, it is a transient with the potential of an
infinite number of waves (which could suffer dispersion from the
line's frequency characteristics making for an infinite number of
velocities). The infinite is a trivial observation in the scheme of
things when we return to DC.

Attaching a battery casts it into a role of AC generation (for however
long the transmission line takes to settle to an irresolvable
ringing). Discarding the term DC returns us to conventional
transmission line mechanics.

DC, in and of itself, has no wave velocity.

For the model provided, R= 0, therefore we have a transmission line
consisting of superconductors. The speed at which steady state DC
current is injected into the model will equal the maximum speed of DC
current in the model. Although the electrons themselves will move very
slowly, for each coulomb injected in, one coulomb will be injected out
at the same velocity they were injected in (not to be confused with
'current' which is the number of coulombs per second). If it were
possible for the source to provide DC current at c, then the DC current
moves at c. The capacitance C can be any value and Zo has no meaning.
The only model that works here is the one with a cardboard tube filled
with ping pong balls, in this case with 0 distance between them.

Ah, but of so little importance because the model is not reality.
While R (ohmic resistance) is specified as zero, impedance is what we are
looking for. Impedance is the ratio of voltage to current.

Roger the impedance is zero because the current is steady state DC. F = 0,

Zo = 0 -j*2*pi*0*C =0

It was already stated that we should ignore the wavefront of the step
function. What we are left with is steady state. So impedance is not what
'we' are looking for.

(I sure am learning a lot about antennas and transmission lines here)

actually it is what you are looking for, you have just, again,
misinterpreted the results. in the DC case you have to remember that not
only is f=0, but wavelenght is infinite. so a shorted stub of any length of
transmission line appears to be 0% of a wavelength. using the normal
equations, or smith chart, to transform the impedance at the far end of the
line to the connection point will result in exactly the same impedance at
the connection point as is at the far end. so feed a DC current into a
shorted line of any length and in steady state you get infinite
current(assuming no loss in the line of course), use an open line and you
get zero current. put a resistive load out there and you see the load
resistance. it all works, you just have to know what to look for and just
what the conditions you have specified really mean.

as far as probing the 'black box' with varying frequencies or pulses to see
what is in it, you again must more clearly state the conditions. when it
was suggested that you could stick all the different circuits you used to
obtain the same impedance in a box and it was added to that a single
capacitor would look the same, the implicit assumption is that you are ONLY
going to examine the circuits in sinusoidal steady state at a single
frequency. that is the ONLY case where that type of replacement is valid.
if you allow transients or multiple frequencies than you can not substitute
a 'black box' for the unknown circuit. refer to any book from a circuits
101 course for the full analysis.

On Dec 14, 1:52 pm, Cecil Moore wrote:
Keith Dysart wrote:
Do photons also explain how sound can move
at a 1000 ft/s, while the air molecules barely
move at all?

No, mechanical longitudinal waves are well understood.
It is impossible for them to achieve the speed of light.

Non-sequitor.

No? Not clear then why they are needed for
electrons.

Do you think electrons support mechanical waves?

Simplicity itself. Electrons are charged. Like charges
repel. Move an electron and the next electron will tend
to move away.

The fields of TEM waves consist of photons traveling
at the speed of light.

I've been told that near the antenna, there are just
varying electric and magnetic fields and that some
distance from the antenna the electro-magnetic
wave forms. How does the varying field turn into a
photon? At what point? Where does the simply
varying field end and the photons begin? Or does
the antenna emit photons?

....Keith

On Dec 14, 11:53 pm, "AI4QJ" wrote:
"Keith Dysart" wrote in message

...





On Dec 14, 10:00 pm, "AI4QJ" wrote:
"Keith Dysart" wrote in message

...

On Dec 14, 9:10 pm, "AI4QJ" wrote:
Where did the extra black box come from and who made the restriction
on
frequency? I should be able to use any voltage or frequency I want,
don't
you think?

The original problem statement discused -j567 as
an impedance. This is implicitly frequency dependant.

Not if I change the capacitance.

Each of the different ways mentioned for obtaining -j567
will produce a different impedance if the frequency is
changed. They were all frequency dependant.

The Smith chart is normalized for impedance
and frequency.

The smith chart is normalized *only* by Zo.

Tell me, how is Zo related to frequency :-)

Or better, tell me how the smith
chart is normalized by frequency?

Everything is done in terms of degrees along a wave.
This implicitly normalizes for frequency.

There is a specific recognized usage of the term "normalize" when referring
to a smith chart. It does not involve frequency.

Agreed. But I needed a word to capture the similar concept
for frequency so I chose "normalize". Feel free to propose
another, and possibly less confusing, word.

When allowed to excite the black boxes with different
signals there are many ways to determine an internal
equivalent circuit. The question here was did the various
ways of making -j567 affect the results for sinusoidal
single frequency excitation.

In the example, -j567 was merely due to a phase change due to the abrupt
impedance discontinuity. You are the one who suggested putting things in
black boxes. I suppose you could devise ways to phase shifts due to -j567
in
black boxes but I will have to leave that to you since you are the one
who
brought up the idea.

Several ways were mentioned for obtaining the -j567:
a capacitor, some length of 100 ohm line, a different
length of 600 ohm line. Regardless of how the -j567
impedance is obtained, the same input impedance
to the 600 ohm line results. And yet each appears
to have a different phase shift occurring at the terminals.

Putting things in black boxes is a thought experiment
which helps isolate which aspects are important.
Any box containing a circuit which produces -j567
at the terminals will result in exactly the same
impedance at the input to the 600 ohm line, so
clearly -j567 is important.

Is the "phase shift" at the discontinuity important
when the results can be determined without knowing
the value. In fact, the "phase shift", in all the
examples, was computed last, after all the results
were known. How important can it be?

Do you suggest that there is no phase shift?

I suggest that there is no value in thinking about
the "phase shift" at the discontinuity (which depending
on the black box chosen might not be present), and
merely think about the results of connecting the
-j567 impedance to the 600 ohm line.

The value is more obvious when applying the concept to a loaded whip
antenna.

I am not convinced. The value is still being determined
by accounting for all the other phase shifts and then
subtracting from 90. I would be more convinced of the
utility if the value could be computed from first principles
and then used, for example, to compute the length of
the whip.

Then how do you explain the smith chart results?

Starting with the 100 ohm line, the normalized
input impedance was computed using the Smith
chart. This impedance was denormalized and then
renormalized to the 600 ohm. The new value was
plotted on a new Smith chart (the chart normalized
to 600 ohms) and the length of the 600 ohm line
was determined. The two lines have lengths, call
them Z1len and Z2len. 90 - (Z1len + Z2len) will
give a number which Cecil/you have called the
"phase shift" at the discontinuity. Alternatively,
it is just what happens when -j567 is attached
to the appropriate length of 600 ohm line.

But you have 10 degrees of 100 ohm line and you have 43 degrees of 600 ohm
line.

You also have resonance at 1/4W.

For 1/4W resonance you must have 90 degrees.

What happened to the missing 37 degrees?

Perhaps, like the missing dollar, it is simply a number
with no meaning.

If some do not care, then I agree that it is not important. It comes out of
a black box for all they care.

Others find it fascinating what nature does in order to keep following its
rules. I would never go through all the trouble to calculate this using math
but with the smith chart calculating for you, information like this jumps
out at you. When it does, many people yawn, others relate it to how antennas
with loading coils work and reveals one reason why Dr. Corum had to make
corrections for the true behavior of coils

Well I am not sure about the "true" nature of coils. When I look
at one of those coils, I think it is one big complicated mess of
distributed capacitance and inductance. There is intra and inter
turn capacitance and capacitance to ground. A mess.

Some say such a coil can be adequately modelled using a lumped
inductor. Corum thinks he can do better, but I doubt that even he
would claim that he has the "true" nature of such coils.

As an aside, allowing the possibility of this "phase shift" at
the joint, how would you compute the phase shift when a
parallel stub is used, or when multiple parallel stubs are
used to obtain the desired result? And which stub will be
used to define the 90 degrees from which the others are
subtracted?

....Keith

"Keith Dysart" wrote in message
...
On Dec 14, 1:52 pm, Cecil Moore wrote:
Keith Dysart wrote:
Do photons also explain how sound can move
at a 1000 ft/s, while the air molecules barely
move at all?

No, mechanical longitudinal waves are well understood.
It is impossible for them to achieve the speed of light.

Non-sequitor.

No? Not clear then why they are needed for
electrons.

Do you think electrons support mechanical waves?

Simplicity itself. Electrons are charged. Like charges
repel. Move an electron and the next electron will tend
to move away.

The fields of TEM waves consist of photons traveling
at the speed of light.

I've been told that near the antenna, there are just
varying electric and magnetic fields and that some
distance from the antenna the electro-magnetic
wave forms. How does the varying field turn into a
photon? At what point? Where does the simply
varying field end and the photons begin? Or does
the antenna emit photons?

...Keith

photons are a non-sequitar... or waves are, take your pick. but never the
twain shall meet... except in some odd quantum mechanics cases where waves
and photons are equally valid. For working with antennas at HF it is best
to forget photons, they will just confuse you. if you get into the inner
workings of lasers or BEC's or other quantum level effects then you might
need to use photons. EM fields and waves in the macro world are all that is
necessary to completely describe the solution to any problem you may
encounter in amateur radio. likewise in transmission lines, forget photons,
use currents and voltages, you will never run into a case where photons are
necessary, or even useful, in transmission line problems.