On 5/19/2011 7:03 AM, Cecil Moore wrote:
On May 18, 6:13 pm, John wrote:
So, you're saying that the Smith chart is wrong?

The Smith Chart is a tool - a blank graph. How could it be wrong?
Like any tool, it has limitations and can be abused.


In that case I have no need of S11 or reflections or light. I only need
to know that the Smith chart tells me that a 200 ohm load looks like a
50 ohm load through a 1/4WL-100 ohm line. I made it as simple as
possible but no simpler.

John

On 5/19/2011 12:27 AM, K7ITM wrote:
On May 18, 3:42 pm, John wrote:
...
I'm not speaking for Wim, but I think we are both saying the following:

* You have a known load
* You have a transmission line with known characteristics
* Is is possible to use a Smith chart to get the impedance at the input
to the transmission line.
* We now know the load applied to the transmitter.

All we need to know we get from the chart. We admit that reflections are
responsible for the impedance transformation from load to line input.
But, we don't need to know anything about the reflection details, energy
content of the line, nor how light would like it.

So, we are saying that the load at the line input can be viewed as a
lumped circuit. So now we have a transmitter loaded with a lumped
circuit for further analysis.

That's all. It's simple.

John

Exactly so, John. Good summary. So long as the transmitter's
bandwidth is small enough that you are always operating practically at
steady-state conditions, the transmitter can't tell the difference
between whatever assembly of transmission lines and lumped loads
distributed along those lines you want, and a simple lumped circuit
that presents the same impedance as the steady-state value of the
jumble of transmission lines out there. (For very narrow-band loads,
you might want to use a lumped equivalent that presents sensibly the
same impedance as the load across the whole transmitted bandwidth, not
just at one point.)

It is NOT that anyone is assuming "faster than speed of light," it's
that we're recognizing that the (HF voice-bandwidth) transmitter is
slower than molasses relative to the propagation times involved in a
couple hundred feet of coax, or probably even a couple thousand feet.
The attenuation per foot of the lines we use is high enough that it's
just about impossible to deviate significantly from steady-state
conditions for the bandwidths we use.

That's certainly not true for pulsed radar signals, or for fast-scan
TV, or for other wideband signals. In those cases, you'll probably
find it pays to insure the line is matched to the load so there aren't
significant reflections, and you may want to arrange the source (PA/
transmitter) to have an output impedance close to the line impedance
so it absorbs any reflections that do happen at the load end of the
line. (If you want to get fancy, you might use a circulator to insure
dissipation of such returning signals.)

Cheers,
Tom


I understand, Tom, and thank your for your input. Of course, we are
discussing an ideal setup, so I did not emphasize those points. But, I
know you know that. Nevertheless, thank your for the disclaimers.

Cheers & 73,
John

On May 19, 9:03*am, Wimpie wrote:
From simulation, but now a pi filter C=6pF, L=72u, C=6pF, load = 2570
Ohms

You just proved one of my points. Inventing impedors that do not exist
in reality in order to rationalize the real-world delay through a real-
world loading coil is exactly what I have been complaining about. Are
the imaginary lumped-circuit capacitors, to which you are forced to
resort, part of the actual impedance in reality or a figment of your
imagination?

http://hamwaves.com/antennas/inductance/corum.pdf
"The concept of coil 'self-capacitance' is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior." About the capacitors you added
above it says: "Of course, this is merely a statistical determination
appropriate for computations ... and *not at all a physical
quantity*."

The reason that the source voltage and source current are in phase in
the example is because the load resistor equals the Z0 of the coil
which is functioning in transmission line mode with a VF = 0.019, i.e.
like a transmission line, it is indeed 0.1167 wavelengths long
electrically. I have verified such (within a certain degree of
accuracy) through bench experiments.
--
73, Cecil, w5dxp.com

On May 19, 11:59*am, Wimpie wrote:
I have a source 100Vp, 4 MHz, sinusoidal, in series with a capacitance
of 796 pF (that is a capacitive reactance of 50 Ohms).

:-) I saw a similar example over a half-century ago - a zero ohm
source that is 100% efficient no matter what the load. A conjugate
match provides enough power to destroy the universe. Question is: If a
source impedance is a pure reactance, can it deliver any power?
--
73, Cecil, w5dxp.com

On May 19, 12:53*pm, John KD5YI wrote:
In that case I have no need of S11 or reflections or light. I only need
to know that the Smith chart tells me that a 200 ohm load looks like a
50 ohm load through a 1/4WL-100 ohm line.

Well there you go - my point exactly - it "looks like" but appearances
can be deceiving. You and I know that they are not identical because
we are smarter than the average bear and the IEEE has different
definitions for those two radically different kinds of impedances. We
know that it is a virtual image of 50 ohms because no 50 ohm resistor
exists in reality and no zero reflection coefficient exists in
reality. In mathematical terms, there is no one to one correspondence
between a 50 ohm dummy load and a 50 ohm antenna.
--
73, Cecil, w5dxp.com

On 19 mayo, 20:38, Cecil Moore wrote:
On May 19, 11:59*am, Wimpie wrote:

I have a source 100Vp, 4 MHz, sinusoidal, in series with a capacitance
of 796 pF (that is a capacitive reactance of 50 Ohms).

:-) I saw a similar example over a half-century ago - a zero ohm
source that is 100% efficient no matter what the load. A conjugate
match provides enough power to destroy the universe. Question is: If a
source impedance is a pure reactance, can it deliver any power?
--
73, Cecil, w5dxp.com

Cecil,

Just solve this source brainteaser (that contains the capacitor) with
the principles outlined in a reference provided by you. Efficiency is
not of importance here, so please don't lure us into new non-relevant
issues.

Though its seems just theoretically, I source providing 100W at 4 MHz
with Zout is = 1 ohm (or less) can be made with today's components.

Wim
PA3DJS
www.tetech.nl

On May 19, 11:25*am, Cecil Moore wrote:
On May 19, 9:03*am, Wimpie wrote:

From simulation, but now a pi filter C=6pF, L=72u, C=6pF, load = 2570
Ohms

You just proved one of my points. Inventing impedors that do not exist
in reality in order to rationalize the real-world delay through a real-
world loading coil is exactly what I have been complaining about. Are
the imaginary lumped-circuit capacitors, to which you are forced to
resort, part of the actual impedance in reality or a figment of your
imagination?

http://hamwaves.com/antennas/inductance/corum.pdf
"The concept of coil 'self-capacitance' is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior." About the capacitors you added
above it says: "Of course, this is merely a statistical determination
appropriate for computations ... and *not at all a physical
quantity*."

The reason that the source voltage and source current are in phase in
the example is because the load resistor equals the Z0 of the coil
which is functioning in transmission line mode with a VF = 0.019, i.e.
like a transmission line, it is indeed 0.1167 wavelengths long
electrically. I have verified such (within a certain degree of
accuracy) through bench experiments.
--
73, Cecil, w5dxp.com

First I'll point out that the model Wim used doesn't match "the
concept of coil self-capacitance," so it's not clear that the rest of
what you wrote is relevant.

Now, what do you do about your coils when you discover that they do
NOT behave like a TEM transmission line? Indeed they do not; it's
pretty easy to verify from measurements on real coils and real
circuits. It seems like now you are stuck, because you (seem to) have
a lot of trouble looking at a circuit and understanding what's really
important and what isn't, with regard to performance in a particular
application. Sometimes it's appropriate to use a model that goes well
beyond a simple transmission line model of a coil; sometimes the
simple transmission line model is far more complex than you need. See
Wim's previous posting about the value of understanding that.

FWIW, I understand perfectly well where the capacitances Wim put into
his model come from. I know exactly how I would estimate them from a
particular physical configuration, and I suppose Wim does something
very similar to what I would. They come very much from the real
physical world, not from our imaginations.

Cheers,
Tom

On 19 mayo, 20:25, Cecil Moore wrote:
On May 19, 9:03*am, Wimpie wrote:

From simulation, but now a pi filter C=6pF, L=72u, C=6pF, load = 2570
Ohms

You just proved one of my points. Inventing impedors that do not exist
in reality in order to rationalize the real-world delay through a real-
world loading coil is exactly what I have been complaining about. Are
the imaginary lumped-circuit capacitors, to which you are forced to
resort, part of the actual impedance in reality or a figment of your
imagination?

http://hamwaves.com/antennas/inductance/corum.pdf
"The concept of coil 'self-capacitance' is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior." About the capacitors you added
above it says: "Of course, this is merely a statistical determination
appropriate for computations ... and *not at all a physical
quantity*."

The reason that the source voltage and source current are in phase in
the example is because the load resistor equals the Z0 of the coil
which is functioning in transmission line mode with a VF = 0.019, i.e.
like a transmission line, it is indeed 0.1167 wavelengths long
electrically. I have verified such (within a certain degree of
accuracy) through bench experiments.
--
73, Cecil, w5dxp.com

Cecil,

Lumped circuit approach gives a good solution for your brainteaser
(maybe against your expectations or hope). It is just distributed
capacitance to ground that can be concentrated into 1 or more
capacitors if you are well below the first resonance frequency.

In a real application when using a lumped 72uH inductor for
calculations, one will find out that the capacitors for a certain
application (for example pi-filter section) have to be somewhat
smaller then based on the lumped circuit calculation.

Regarding transmission line behavior
It is the reason to mention "without using transmission line
sections". Because my PSPICE package also allows use of transmission
lines, if convenient I use them. Do you know how I made my first guess
for the capacitors? Just by using transmission line theory. BTW,
what is the wire length of the inductor in your HF rig (for 4 MHz
band)? It is very likely well below the length for the bugcatcher
example.

Did you know that many delay lines were/are made by using multiple CLC
sections (for example used in oscilloscopes)?

Again, look to the circuits of your rig, do you really think that the
design is carried out by modelling each component as a transmission
line. The answer is no (for sure).

We have various religions around the globe; I think we don't need
another one based on transmission lines! Maybe for you it was
wonderful to explore transmission line theory, but for RF Engineers/
Designers (antenna designers included), it is just one of their means
to get the job done.

Wim
PA3DJS
www.tetech.nl

On 19 mayo, 20:25, Cecil Moore wrote:
On May 19, 9:03*am, Wimpie wrote:

From simulation, but now a pi filter C=6pF, L=72u, C=6pF, load = 2570
Ohms

You just proved one of my points. Inventing impedors that do not exist
in reality in order to rationalize the real-world delay through a real-
world loading coil is exactly what I have been complaining about. Are
the imaginary lumped-circuit capacitors, to which you are forced to
resort, part of the actual impedance in reality or a figment of your
imagination?

http://hamwaves.com/antennas/inductance/corum.pdf
"The concept of coil 'self-capacitance' is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior." About the capacitors you added
above it says: "Of course, this is merely a statistical determination
appropriate for computations ... and *not at all a physical
quantity*."

The reason that the source voltage and source current are in phase in
the example is because the load resistor equals the Z0 of the coil
which is functioning in transmission line mode with a VF = 0.019, i.e.
like a transmission line, it is indeed 0.1167 wavelengths long
electrically. I have verified such (within a certain degree of
accuracy) through bench experiments.
--
73, Cecil, w5dxp.com

Cecil,

Lumped circuit approach gives a good solution for your brainteaser
(maybe against your expectations or hope). It is just distributed
capacitance to ground that can be concentrated into 1 or more
capacitors if you are well below the first resonance frequency.

In a real application when using a lumped 72uH inductor for
calculations, one will find out that the capacitors for a certain
application (for example pi-filter section) have to be somewhat
smaller then based on the lumped circuit calculation.

Regarding transmission line behavior
It is the reason to mention "without using transmission line
sections". Because my PSPICE package also allows use of transmission
lines, if convenient I use them. Do you know how I made my first guess
for the capacitors? Just by using transmission line theory. BTW,
what is the wire length of the inductor in your HF rig (for 4 MHz
band)? It is very likely well below the length for the bugcatcher
example.

Did you know that many delay lines were/are made by using multiple CLC
sections (for example used in oscilloscopes)?

Again, look to the circuits of your rig, do you really think that the
design is carried out by modelling each component as a transmission
line. The answer is no (for sure).

We have various religions around the globe; I think we don't need
another one based on transmission lines! Maybe for you it was
wonderful to explore transmission line theory, but for RF Engineers/
Designers (antenna designers included), it is just one of their means
to get the job done.

Wim
PA3DJS
www.tetech.nl

On May 19, 2:17*pm, Wimpie wrote:
Just solve this source brainteaser (that contains the capacitor) with
the principles outlined in a reference provided by you.

Maximum power transfer occurs when the load is the conjugate of the
source impedance. Of course, in this case, when the source is purely
reactive, no power transfer is possible with a conjugate match. I
don't think our models were designed to handle magical situations so
I'm assuming this exercise is designed to waste my time (of which I
have precious little left). Come to think of it, didn't you call my
examples, "off topic", and refuse to have anything to do with them?
--
73, Cecil, w5dxp.com