On 11 jun, 23:26, Cecil Moore wrote:
On Jun 11, 5:03*pm, lu6etj wrote:

From my perspective your main differences are reducible

The basic argument revolves around what math shortcuts can be used to
solve a particular problem vs what is actually happening in reality
according to the accepted laws of physics. I agree one doesn't
necessarily need to understand the laws of physics to solve a problem
but one should probably know enough physics to recognize when those
laws of physics are being violated by one's argument.
--
73, Cecil, w5dxp.com
............
of course, but that is no fun!
I agree
......
As a courtesy to me, a foreigner tourist ham, would you mind stop for
a brief moment your more general differences and tell me if you agree
on the behavior of a Thevenin generator with a series resistance of 50
ohms in relation to changes in impedance of a lossless TL predicted by
the Telegrapher's equations solutions in terms of the power dissipated
on the load resistance and series resistence of Thevenin source?
I am pretty serious about this: until today I could not know if you
agree in that!! :)

On Jun 12, 4:24*am, lu6etj wrote:
On 11 jun, 23:26, Cecil Moore wrote: On Jun 11, 5:03*pm, lu6etj wrote:

From my perspective your main differences are reducible

The basic argument revolves around what math shortcuts can be used to
solve a particular problem vs what is actually happening in reality
according to the accepted laws of physics. I agree one doesn't
necessarily need to understand the laws of physics to solve a problem
but one should probably know enough physics to recognize when those
laws of physics are being violated by one's argument.
--
73, Cecil, w5dxp.com
...........
of course, but that is no fun!

I agree
.....
As a courtesy to me, a foreigner tourist ham, would you mind stop for
a brief moment your more general differences and tell me if you agree
on the behavior of a Thevenin generator with a series resistance of 50
ohms in relation to changes in impedance of a lossless TL predicted by
the Telegrapher's equations solutions in terms of the power dissipated
on the load resistance and series resistence of Thevenin source?
I am pretty serious about this: until today I could not know if you
agree in that!! :)

sure, if you properly apply the telegrapher's equations and the
thevenin equivalent methods. The real problem is that if you try to
do that for most amateur radio transmitters the source impedance is
not linear, and even worse may be time varying, which renders the
thevenin equivalent source substitution invalid.

Note though that in real world cases you need to use the full set of
equations, usually called by engineers the 'general transmission line
equations'. beware, some places may over simplify the telegrapher's
equations which may make them invalid in some cases. The
Telegrapher's equations (http://en.wikipedia.org/wiki/Telegrapher
%27s_equations), are often considered a subset of the 'General
transmission line equations (http://en.wikipedia.org/wiki/
Transmission_line) that are taught in distributed circuits and fields
and waves courses in engineering schools.

....
As a courtesy to me, a foreigner tourist ham, would you mind stop for
a brief moment your more general differences and tell me if you agree
on the behavior of a Thevenin generator with a series resistance of 50
ohms in relation to changes in impedance of a lossless TL predicted by
the Telegrapher's equations solutions in terms of the power dissipated
on the load resistance and series resistence of Thevenin source?
I am pretty serious about this: until today I could not know if you
agree in that!! :)

sure, if you properly apply the telegrapher's equations and the
thevenin equivalent methods. *The real problem is that if you try to
do that for most amateur radio transmitters the source impedance is
not linear, and even worse may be time varying, which renders the
thevenin equivalent source substitution invalid.

OK. Thank you very much. This clarify so much the issue to me. Please,
another question: On the same system-example, who does not agree with
the notion that the reflected power is never dissipated in Thevenin
Rs? (I am referring to habitual posters in these threads, of course)

lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

....
OK. Thank you very much. This clarify so much the issue to me. Please,
another question: On the same system-example, who does not agree with
the notion that the reflected power is never dissipated in Thevenin
Rs? (I am referring to habitual posters in these threads, of course)


Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.

It is the implementation of the source that provides the answer to your
question, and the word "never" is too strong for the general case.

In respect of typical HF ham transmitters, you may find my article
entitled "Does SWR damage HF ham transmitters?" at
http://vk1od.net/blog/?p=1081 of interest.

Owen

On 12 jun, 17:28, Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

...

OK. Thank you very much. This clarify so much the issue to me. Please,
another question: On the same system-example, who does not agree with
the notion that the reflected power is never dissipated in Thevenin
Rs? (I am referring to habitual posters in these threads, of course)

Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.

It is the implementation of the source that provides the answer to your
question, and the word "never" is too strong for the general case.

In respect of typical HF ham transmitters, you may find my article
entitled "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081of interest.

Owen

Hello Owen thank you for your answer: Sorry I do not quite understand
your answer. I choose a Thevenin model of circuit theory because it is
an idealization consisting of an idealized constant voltaje source in
series with an idealized resistance without any relation with
practical implementation of such imaginary electrical (and
mathematical) entity.

I first interested get from you such idealized model answer as a
reductionistic aproximation method to try arrive later at subsequent
interpretations of practical situations. I think we all used to
working with idealized models and we accept its limitations, but we
also know frequently they are very useful to clear the "field" (as in
football "field")
(I said "never" because Cecil seem say "sometimes").
For example: ideal conjugate mirror in Maxwell article in my
interpretation implicates "never". Reflected power do not return to
the source in that context.
If you prefer I would be equally satisfied knowing who agree with
"never", who with "sometimes" and who with "always". But I would not
be too annoying :)

73

Miguel Ghezzi LU6ETJ

lu6etj wrote in
:

On 12 jun, 17:28, Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

...

OK. Thank you very much. This clarify so much the issue to me.
Please, another question: On the same system-example, who does not
agree with the notion that the reflected power is never dissipated
in Thevenin Rs? (I am referring to habitual posters in these
threads, of course)

Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.

It is the implementation of the source that provides the answer to
your question, and the word "never" is too strong for the general
case.

In respect of typical HF ham transmitters, you may find my article
entitled "Does SWR damage HF ham transmitters?"
athttp://vk1od.net/blog/?p=1081of interest.

Owen

Hello Owen thank you for your answer: Sorry I do not quite understand
your answer. I choose a Thevenin model of circuit theory because it is
an idealization consisting of an idealized constant voltaje source in
series with an idealized resistance without any relation with
practical implementation of such imaginary electrical (and
mathematical) entity.

I first interested get from you such idealized model answer as a
reductionistic aproximation method to try arrive later at subsequent
interpretations of practical situations. I think we all used to
working with idealized models and we accept its limitations, but we
also know frequently they are very useful to clear the "field" (as in
football "field")

Miguel,

From Wikipedia: "Thévenin's theorem for linear electrical networks states
that any combination of voltage sources, current sources and resistors
with two terminals is electrically equivalent to a single voltage source
V and a single series resistor R. For single frequency AC systems the
theorem can also be applied to general impedances, not just resistors."

The theorem does not state or imply that the Thevenin equivalent circuit
dissipates the same internal power as the real source, just that any
*linear* two terminal circuit containing sources and impedances can be
reduced to this two component equivalent (at a single frequency), and V
and I at the network terminals will be the same as the original network,
irrespective of the external load attached to the network terminals.

It is a simple exercise to develop two source networks with the same
Thevenin equivalent circuit, but that have quite different internal
efficiencies. It is easy to demonstrate that both networks deliver the
same power to any given load, but that the internal dissipation of those
source networks is different in both cases, and not explainable simply as
absorbing 'reflected power'.

This is basic linear circuit theory.

If there was a valid Thevenin equivalent circuit for a transmitter (and
that is questionable), then you can not use that equivalent circuit to
make any inference about the internal dissipation of the source (the
transmitter in this case), or its efficiency. Nevertheless, I see people
trying to do this one way or another in the various threads here.

(I said "never" because Cecil seem say "sometimes").
For example: ideal conjugate mirror in Maxwell article in my
interpretation implicates "never". Reflected power do not return to
the source in that context.
If you prefer I would be equally satisfied knowing who agree with
"never", who with "sometimes" and who with "always". But I would not
be too annoying :)

I know that in this age of instant gratification, people reading posts in
these fora tend to accept simple dogmatic statements as sure sign of
author credibility, and qualifications such as 'often', 'usually' etc as
a sign of uncertainty, of a lack of understanding, of weakness in the
author. The opposite is often, if not usually true.

In English, we have a saying "never say never".

What 'never'? 'Hardly ever'... to borrow some dialogue.

A man who is hardly ever wrong doesn't use words like 'always' and
'never' much, or imply as much in general statements.

Owen

On 12 jun, 22:52, Owen Duffy wrote:
lu6etj wrote :





On 12 jun, 17:28, Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

...

OK. Thank you very much. This clarify so much the issue to me.
Please, another question: On the same system-example, who does not
agree with the notion that the reflected power is never dissipated
in Thevenin Rs? (I am referring to habitual posters in these
threads, of course)

Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.

It is the implementation of the source that provides the answer to
your question, and the word "never" is too strong for the general
case.

In respect of typical HF ham transmitters, you may find my article
entitled "Does SWR damage HF ham transmitters?"
athttp://vk1od.net/blog/?p=1081ofinterest.

Owen

Hello Owen thank you for your answer: Sorry I do not quite understand
your answer. I choose a Thevenin model of circuit theory because it is
an idealization consisting of an idealized constant voltaje source in
series with an idealized resistance without any relation with
practical implementation of such imaginary electrical (and
mathematical) entity.

I first interested get from you such idealized model answer as a
reductionistic aproximation method to try arrive later at subsequent
interpretations of practical situations. I think we all used to
working with idealized models and we accept its limitations, but we
also know frequently they are very useful to clear the "field" (as in
football "field")

Miguel,

From Wikipedia: "Thévenin's theorem for linear electrical networks states
that any combination of voltage sources, current sources and resistors *
with two terminals is electrically equivalent to a single voltage source
V and a single series resistor R. For single frequency AC systems the
theorem can also be applied to general impedances, not just resistors."

The theorem does not state or imply that the Thevenin equivalent circuit
dissipates the same internal power as the real source, just that any
*linear* two terminal circuit containing sources and impedances can be
reduced to this two component equivalent (at a single frequency), and V
and I at the network terminals will be the same as the original network,
irrespective of the external load attached to the network terminals.

It is a simple exercise to develop two source networks with the same
Thevenin equivalent circuit, but that have quite different internal
efficiencies. It is easy to demonstrate that both networks deliver the
same power to any given load, but that the internal dissipation of those
source networks is different in both cases, and not explainable simply as
absorbing 'reflected power'.

This is basic linear circuit theory.

If there was a valid Thevenin equivalent circuit for a transmitter (and
that is questionable), then you can not use that equivalent circuit to
make any inference about the internal dissipation of the source (the
transmitter in this case), or its efficiency. Nevertheless, I see people
trying to do this one way or another in the various threads here.

(I said "never" because Cecil seem say "sometimes").
For example: ideal conjugate mirror in Maxwell article in my
interpretation implicates "never". Reflected power do not return to
the source in that context.
If you prefer I would be equally satisfied knowing who agree with
"never", who with "sometimes" and who with "always". But I would not
be too annoying :)

I know that in this age of instant gratification, people reading posts in
these fora tend to accept simple dogmatic statements as sure sign of
author credibility, and qualifications such as 'often', 'usually' etc as
a sign of uncertainty, of a lack of understanding, of weakness in the
author. The opposite is often, if not usually true.

In English, we have a saying "never say never".

What 'never'? 'Hardly ever'... to borrow some dialogue.

A man who is hardly ever wrong doesn't use words like 'always' and
'never' much, or imply as much in general statements.

Owen- Ocultar texto de la cita -

- Mostrar texto de la cita -

Hello Owen, good day in Australia I hope!

Sorry, with due respect, your answer throws back the ball out of the
soccer field :)
I like poetry also but would you mind search the web for another
scientific uses of "never" word?, such as in
http://www.upscale.utoronto.ca/PVB/H...y/Entropy.html.

Of course many thanks for your time and your kind reply.

Miguel LU6ETJ

On Jun 12, 8:52*pm, Owen Duffy wrote:
If there was a valid Thevenin equivalent circuit for a transmitter (and
that is questionable), then you can not use that equivalent circuit to
make any inference about the internal dissipation of the source (the
transmitter in this case), or its efficiency. Nevertheless, I see people
trying to do this one way or another in the various threads here.

In his food-for-thought article on forward and reflected power, Roy
(w7el) says: "So we can model a 100 watt forward, 50 ohm nominal
transmitter as a 141.4 volt (100 * sqrt(2)) RMS voltage source in
series with a 50 ohm resistance." He goes on to calculate power
dissipation in the source resistor.
--
73, Cecil, w5dxp.com

Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784-
:

...
OK. Thank you very much. This clarify so much the issue to me. Please,
another question: On the same system-example, who does not agree with
the notion that the reflected power is never dissipated in Thevenin
Rs? (I am referring to habitual posters in these threads, of course)


Thevenin's theorem says nothing of what happens inside the source (eg
dissipation), or how the source may be implemented.
. . .

Cecil has used this fact as a convenient way of avoiding confrontation
with the illustrations given in my "food for thought" essays. However,
those models aren't claimed to be Thevenin equivalents of anything. They
are just simple models consisting of an ideal source and a perfect
resistance, as used in may circuit analysis textbooks to illustrate
basic electrical circuit operation. The dissipation in the resistance is
clearly not related to "reflected power", and the reflected power
"theories" being promoted here fail to explain the relationship between
the dissipation in the resistor and "reflected power". I contend that if
an analytical method fails to correctly predict the dissipation in such
a simple case, it can't be trusted to predict the dissipation in other
cases, and has underlying logical flaws. For all the fluff about
photons, optics, non-dissipative sources, and the like, I have yet to
see an equation that relates the dissipation in the resistance in one of
those painfully simple circuits to the "reflected power" in the
transmission line it's connected to.

Roy Lewallen, W7EL

Roy Lewallen wrote in
:

For all the fluff about
photons, optics, non-dissipative sources, and the like, I have yet to
see an equation that relates the dissipation in the resistance in one
of those painfully simple circuits to the "reflected power" in the
transmission line it's connected to.


I saw the challenge and note the lack of response.

Let me offer a steady state solution.

In the case of a simple source being an ideal AC voltage generator of Vs
and an ideal series resistance Rs of Ro, and that Zo=Ro, for any
arbitrary load, at the source terminals, Vf=Vs/2, Vl=Vf+Vr=Vs/2+Vr, and
the voltage difference across Rs is Vs/2-Vr (noting that Vr is a complex
quantity and can have a magnitude from 0 to Vs/2 at any phase angle),
therfore dissipation in Rs is given by:

Prs=(Vs/2-Vr)^2/Rs where Vs is the o/c source voltage, Vr is the complex
reflected wave voltage equivalent, Rs is the source resistance.

Clearly, dissipation in Rs is related to Vr, but it is not simply
proportional to the square of Vr as believed by many who lack the basics
of linear circuit theory to come to a correct understanding.

Roy, is that a solution?

Owen