On Fri, 13 Apr 2007 16:37:02 GMT, Walter Maxwell
wrote:

Hi Walt,

1: The input impedance of a lossless half-wave (180°) transmission line
There are two parts to the following statement:
terminated in a physical short circuit is zero ohms, a short circuit,
which is the causal relationship;
but a VIRTUAL short circuit because it was achieved only by the interference
between the source voltage wave incident on the input (0°) and the reflected voltage wave (180°) returning to
the input after 360° of two-way travel on the line and the 180° phase reversal at the physical short
terminating the line.
this is the correlationship.

Without the cause, there is no correlation.

There is nothing to be disputed beyond that.

The reflected current wave on return to the input encountered no phase change during its
travel, thus the current reflection coefficient is in phase with that of the source current, allowing the
short circuit to occur.

Allowing, as a verb, suggests causality. The cause is established in
the short. All intermediary apparatus merely maintain the
correlation. There is nothing to be disputed beyond that.

2: The input impedance of a lossless quarter-wave (90°) transmission line terminated in a physical open
circuit
which is the causal relationship;
is zero ohms, a short circuit, but a VIRTUAL short circuit because it was achieved only by the
interference between the voltage wave incident on the input (0°) and the reflected voltage wave (180°)
returning to the input after 180° of two-way travel on the line and the 0° phase reversal at the physical open
circuit terminating the line.
this is the correlationship.

The current reflection coefficient occurs in the same manner as with the
half-wave line above.

It is merely the correlation to an existing, physical open without
which the VIRTUAL short circuit would disappear. All intermediary
apparatus merely maintain the correlation. There is nothing to be
disputed beyond that.

These two examples can be confirmed by referring to any reputable text concerning transmission line theory.
There is nothing to be disputed beyond that.

The voltage reflection coefficient at the input of these two transmission lines is 1.0 at 180°, and the
current reflection coefficient at this point is 1.0 at 0°. These are the reflection coefficients that would be
found when measuring at any short circuit, no matter whether it is physical or virtual. Consequently, both
physical and virtual short or open circuits placed on a transmission line can cause reflections.

And here we get to the nut of the matter - causality. It is already
established that either the physical short, or physical open, whose
absence would render any correlation invalid, dominates the action.
The proof follows the quality of the physical open or the physical
short. A poor physical open or poor physical short will never be
improved by ANY transmission line mechanics. On the other hand, poor
transmission line mechanics will never deliver the action of the best
physical short or the best physical open.

We have thus proved that the virtual short circuit established at the stub point is actually performing as a
real short circuit.

There is nothing to be disputed beyond that. This is not, however, a
proof that the VIRTUAL short (or open) is the cause.

This may appear to be a criticism of semantics (English to some).
However, engineering relies on a far stricter degree of meaning than
most endeavors. Correlation is not Causality is one particular
admonition that comes to mind from the field of logic. It applies
here too.

Walt, it seems to me that you have a need to distinguish VIRTUAL from
physical for reasons other than the transmission line mechanics of
combining loads (or as I distinguished in other threads, routing
energies). A VIRTUAL short or open is metaphor, and it is an useful
metaphor for describing systems. What I see beyond these examples you
have provided are statements (in other discussions) that tend to
confer a reality to the VIRTUAL which is obviously a contradiction on
the face of it. Other than that, there is absolutely nothing in your
published work that is in dispute.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Fri, 13 Apr 2007 16:37:02 GMT, Walter Maxwell
wrote:

The voltage reflection coefficient at the input of these two transmission lines is 1.0 at 180°, and the
current reflection coefficient at this point is 1.0 at 0°. These are the reflection coefficients that would be
found when measuring at any short circuit, no matter whether it is physical or virtual. Consequently, both
physical and virtual short or open circuits placed on a transmission line can cause reflections.


And here we get to the nut of the matter - causality. It is already
established that either the physical short, or physical open, whose
absence would render any correlation invalid, dominates the action.
The proof follows the quality of the physical open or the physical
short. A poor physical open or poor physical short will never be
improved by ANY transmission line mechanics. On the other hand, poor
transmission line mechanics will never deliver the action of the best
physical short or the best physical open.

I agree that this is the problem in Walt's otherwise brilliant work.
Reflections are only caused by the direct interaction between
electromagnetic waves and matter. It is nevertheless valid to say
that systems behave as though virtual impedances cause reflections.
Virtual reflection coefficients are a clever tool and methodology for
systems analysis. But it must be remembered that the propagation of
electromagnetic waves is effected only by certain physical properties
of matter, as described eloquently by James C. Maxwell and others.
Those fundamentals of wave behavior are not different in the steady
state than at other times.

A VIRTUAL short or open is metaphor, and it is an useful
metaphor for describing systems. What I see beyond these examples you
have provided are statements (in other discussions) that tend to
confer a reality to the VIRTUAL which is obviously a contradiction on
the face of it. Other than that, there is absolutely nothing in your
published work that is in dispute.

I completely agree. I think if we got past this one issue, the
newsgroup might actually find itself devoted more to discussions of
antennas.

73, Jim AC6XG

On Apr 13, 11:40 am, Richard Clark wrote:


[lotsa good stuff snipped]

A poor physical open or poor physical short will never be
improved by ANY transmission line mechanics.

Well, I dunno about that. Try this experiment:

Take a "poor" short, say 1 ohm, and transform it through a lossless
1/4 wavelength line of Zo=200 ohm. The result will be 40,000 ohm.
Now transform this 40K ohm load through another lossless 1/4
wavelength line of Zo=10 ohm. The result of this transformation will
be a "virtual" 0.003 ohm.

Is that an improvement? [g]

Regards,

Wes

On 13 Apr 2007 15:56:26 -0700, "Wes" wrote:

On Apr 13, 11:40 am, Richard Clark wrote:


[lotsa good stuff snipped]

A poor physical open or poor physical short will never be
improved by ANY transmission line mechanics.

Well, I dunno about that. Try this experiment:

Take a "poor" short, say 1 ohm, and transform it through a lossless
1/4 wavelength line of Zo=200 ohm. The result will be 40,000 ohm.
Now transform this 40K ohm load through another lossless 1/4
wavelength line of Zo=10 ohm. The result of this transformation will
be a "virtual" 0.003 ohm.

Is that an improvement? [g]

Hi Wes,

There is always a rational example to deflate absolutisms. Thanx for
the interesting twist of transmission line.

However, I wouldn't want to be the wallet that pays for this.

73's
Richard Clark, KB7QHC

Richard Clark, KB7QHC wrote:
"A poor physical open or physical short will never be improved by ANY
transmission line mechanics."

An open-circuit 1/4-wave stub is an open circuit at both ends,
physically. As such, its input is a poor short-circuit until it receives
a reflection from its far end. After the reflection reaches the stub`s
input, it becomes a virtual short-circuit. This occurs at its "poor
physical short" input.

This is a dramatic improvement by transmission line mechanics when this
is the desired effect.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
An open-circuit 1/4-wave stub is an open circuit at both ends,
physically.

Let's look at a 1/4WL open stub.

source ----------------------------------+
|
| 1/4WL
|
|
open

The transmission line and stub are the same Z0 and
both are lossless.

The virtual impedance at point '+' is zero but there
is no physical impedance discontinuity at point '+'.
Are there any reflections originating at point '+'?

If we straighten out the line,

1/4WL
source-----------------------------------+------------open

Are there any reflections originating at point '+'?
--
73, Cecil http://www.w5dxp.com

On Fri, 13 Apr 2007 20:34:56 -0500, (Richard
Harrison) wrote:

This is a dramatic improvement by transmission line mechanics when this
is the desired effect.

Hi Richard,

This kind of drama is found only on the stage.

A poor open is a poor short in reflection. Ever try tuning one that
didn't wander the landscape? Burning money to achieve a working
solution does not render it a dramatic improvement when other methods
(like simply building a good shorted halfwave) are better.

Give me a reason why you suffered to build an open quarterwave, and it
will embrace the issues of quality I already covered.

73's
Richard Clark, KB7QHC