On Jun 11, 10:36*am, K1TTT wrote:
i wouldn't call it a 'virtual' impedance, it is a very real impedance.

Yes, it meets the (B) non-dissipative definition of impedance from
"The IEEE Dictionary". It doesn't meet the (A) dissipative definition
and it is not an impedor as it only exists as a V/I ratio. That's why
I call it a virtual impedance. There is no resistor, there is no
inductor, and there is no capacitor. There is only a V/I ratio caused
by something else.

it is the steady state impedance seen by the transmitter at its output
terminals. *

And it is a V/I ratio caused by the superposition of the forward wave
and reflected wave, i.e. it would NOT be the same impedance without
the reflected wave. That fact of physics is undeniable.

When we have an actual impedor, i.e. a resistor plus an inductor or a
capacitor, the voltage/current ratio is caused by the impedor. When we
have a virtual impedance, the cause/effect procedure is reversed and
the impedance is caused by the voltage/current ratio which may (or may
not) contain both forward and reflected values.

For the two definitions of impedance, (A) and (B), given in "The IEEE
Dictionary", cause and effect are reversed.

Let's take an example. Assume a 50 ohm load resistor fed with 1/2WL of
300 ohm lossless line. If we assume a 100 watt (50 ohm) source, the
forward power will be 204 watts and the reflected power will be 104
watts.

100w Source----1/2WL 300 ohm feedline----50 ohm load

In the feedline, a forward power of 204 watts is a forward voltage of
247.3 volts and a forward current of 0.825 amps.

In the feedline, a reflected power of 104 watts is a reflected voltage
of 176.6 volts and a reflected current of 0.589 amps.

The reflected voltage is 180 degrees out of phase with the forward
voltage at the transmitter, so the superposed voltage at the
transmitter is 70.7 volts. The reflected current is in phase with the
forward current at the transmitter so the superposed current is 1.414
amps. Since everything is either in phase or 180 degrees out of phase,
phasor addition is not needed. So I repeat, the impedance seen by the
transmitter is:

Z = (Vfor - Vref)/(Ifor + Iref)

Z = (247.3 - 176.6)/(0.825 + 0.589)

Z = 70.7/1.414 = 50 ohms, NON-DISSIPATIVE!

It is clear that the superposition of the forward wave with the
reflected wave is the CAUSE of the 50 ohm impedance. That particular
impedance cannot exist without the effects of the reflected wave.

Using a math model for answers to problems for so long that one comes
to believe that the model dictates reality is a major contributor to
the myths and old wives' tales that exist in amateur radio today. It's
time to get back to the basics even if it causes a few old rusty
brains to be put in gear for the first time in decades.
--
73, Cecil, w5dxp.com

On Jun 11, 4:18*pm, Cecil Moore wrote:
On Jun 11, 10:36*am, K1TTT wrote:

i wouldn't call it a 'virtual' impedance, it is a very real impedance.

Yes, it meets the (B) non-dissipative definition of impedance from
"The IEEE Dictionary". It doesn't meet the (A) dissipative definition
and it is not an impedor as it only exists as a V/I ratio. That's why
I call it a virtual impedance. There is no resistor, there is no

and that is part of the problem in here... 'you call it'. what is the
definition of 'virtual impedance' in the ieee dictionary?

On Jun 11, 12:28*pm, K1TTT wrote:
and that is part of the problem in here... 'you call it'. *what is the
definition of 'virtual impedance' in the ieee dictionary?

"The IEEE Dictionary" has no such definition. Those are my words
adopted from "Reflections", by Walter Maxwell, and designed to
differentiate between the (A) and (B) definitions of "impedance" in
"The IEEE Dictionary". Calling the V/I (B) definition of impedance,
"virtual", is much more descriptive than calling it "the (B)
definition".

Walt is arguing that the impedance of an RF source is "non-
dissipative". Ratios of V/I are non-dissipative if they exist devoid
of an impedor. Walt adopted the word "virtual" from the optics
"virtual image". It is an image that is not really there in reality. A
virtual impedance would therefore be the image of an impedor that is
not really there.

I'm not hung up on the word "virtual". What adjective would you use to
differentiate between a dissipative impedor and a V/I non-dissipative
impedance? I am not trying to be difficult - just trying to
communicate. I'm willing to adopt any convention that you suggest for
the duration of this discussion.
--
73, Cecil, w5dxp.com

On Jun 11, 7:19*pm, Cecil Moore wrote:
On Jun 11, 12:28*pm, K1TTT wrote:

and that is part of the problem in here... 'you call it'. *what is the
definition of 'virtual impedance' in the ieee dictionary?

"The IEEE Dictionary" has no such definition. Those are my words
adopted from "Reflections", by Walter Maxwell, and designed to
differentiate between the (A) and (B) definitions of "impedance" in
"The IEEE Dictionary". Calling the V/I (B) definition of impedance,
"virtual", is much more descriptive than calling it "the (B)
definition".

Walt is arguing that the impedance of an RF source is "non-
dissipative". Ratios of V/I are non-dissipative if they exist devoid
of an impedor. Walt adopted the word "virtual" from the optics
"virtual image". It is an image that is not really there in reality. A
virtual impedance would therefore be the image of an impedor that is
not really there.

what is an 'impedor' in this context? that is a relatively rarely
used term in circuit and wave analysis, but is generically defined as
anything that has an impedance. that doesn't seem to fit your
definition though if you can qualify an impedance as non-dissipative
if they don't have one.


I'm not hung up on the word "virtual". What adjective would you use to
differentiate between a dissipative impedor and a V/I non-dissipative
impedance? I am not trying to be difficult - just trying to
communicate. I'm willing to adopt any convention that you suggest for
the duration of this discussion.

the ieee dictionary qualifiers of dissipative and non-dissipative seem
adequate to me. no need to make up any other terms or qualifiers.

On Jun 11, 4:29*pm, K1TTT wrote:
what is an 'impedor' in this context?

Hopefully, the same IEEE Dictionary definition as any other context:
"impedor - a device, the purpose of which is to introduce impedance
into an electric circuit." Note that it has a material existence.

the ieee dictionary qualifiers of dissipative and non-dissipative seem
adequate to me. *no need to make up any other terms or qualifiers.

OK, I will change "virtual impedance" to "non-dissipative impedance"
although if the resistance is zero, that still doesn't solve the
semantic problem. The word "virtual" as used by Walter Maxwell over
the past half-century conveys the meaning as well as any other words,
IMO.

The fact remains that a dissipative impedor is something that exists
in the material world and can cause an outcome. A non-dissipative
impedance is a *result* of a superposed V/I ratio, not a cause of
anything.

Roy once challenged me to detect the difference between a 50 ohm
antenna and a 50 ohm dummy load. I said, "Simple, use a field strength
meter."
--
73, Cecil, w5dxp.com

On Fri, 11 Jun 2010 14:29:17 -0700 (PDT), K1TTT
wrote:

you can qualify an impedance as non-dissipative

It's called reactance.

There are certainly some contortions that have evolved from an
argument that the source lacks the ability to dissipate.

Impedance = (R ± jX) Ohm

This is well known by all and yet it seems unsatisfactory and
impossible to measure in a Tube even when R is exhibited both by
measurement and by heat - something that by all normal accounts is
evidence of dissipation. That same heat seems to be unaccountable
because it's non-linear? If you use this heat on an ice cube, do you
get harmonics? Even or odd?

If it doesn't dissipate it must be because it has NOhms. If we embark
further on this mysterious Load Conjugation with a loss-less resistor,
what would we see for the Load Objurgation formula?

rraaZ = (Rr ± iR ± jX) NOhm

We must now have a Nimpedance measured along a second (hither too
unreported) imaginary axis. I can imagine the dawn of the new Photon
Ninterferences that will emerge from this.

KEWEL !

73's
Richard Clark, KB7QHC

On Jun 11, 11:27*pm, Richard Clark wrote:
On Fri, 11 Jun 2010 14:29:17 -0700 (PDT), K1TTT
wrote:

you can qualify an impedance as non-dissipative

It's called reactance.

not always. there is a non-dissipative resistance. a lossless
transmission line has a pure real impedance, but no dissipation.

On Fri, 11 Jun 2010 17:35:34 -0700 (PDT), K1TTT
wrote:

you can qualify an impedance as non-dissipative

It's called reactance.

not always. there is a non-dissipative resistance. a lossless
transmission line has a pure real impedance, but no dissipation.

Hi David,

Ah! The appeal of the infinite, lossless transmission line. You
forgot radiation.

I think we can both agree that it can be measured, even by the
inference of a chain of measurements and those measurements would
consistently show the absence of heat.

I think you would enjoy the absurdity of its appeal to being the plate
"resistance" when the 1400 Ohms there would be embodied in 28
infinitely long lossless cables being tucked inside the tube.

For others,

If it were so (where those 28 infinitely long lines are tucked into
another convenient dimension that sprang into being to satisfy
argument), then what is the source of the heat of the plate that is in
excess of that of the DC operating point?

If some feel compelled to jump on the losslessness of radiation loss
(now, if that isn't a paradox) - all fine and well for Art's short
wound self-resonant radiators that would eventually devolve in size to
the plate tank. If plate resistance was due to radiation, what need
for antennas? Of course, we could add another rhetorical dimension
that absorbs radiation....

73's
Richard Clark, KB7QHC