On 13 jun, 04:13, lu6etj wrote:
On 13 jun, 03:07, lu6etj wrote:





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 inhttp://www.upscale.utoronto..ca/PVB/Harrison/Entropy/Entropy.html.

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

Miguel LU6ETJ- Ocultar texto de la cita -

- Mostrar texto de la cita -

Sorry I ommited one comment:
The final Thevenin circuit is an idealization built with an ideal
voltage source in series with an ideal resistor. This new idealized
circuit It is a new born entity whose properties are now fully
described for these only two idealized circuit elements. These are the
virtues and the defects of reductionist models :(- Ocultar texto de la cita -

- Mostrar texto de la cita -

R. R. Well... I forget to say the more important = For the sake of
the advance of the topic please do replace "Thevenin circuit" in my
original question for "an ideal constant voltage source in series with
an ideal resistance" equivalent only to itself :)