Re: Question about "Another look at reflections" article.
- From: lu6etj <lu6etj@xxxxxxxxx>
- Date: Tue, 25 May 2010 00:45:36 -0700 (PDT)
On 25 mayo, 03:56, Owen <no...@xxxxxxxx> wrote:
On 25/05/2010 16:10, lu6etj wrote:
...
I think the mixture or combination of models -maybe- it would not be
"elegant" or consistent although it can arrive to the same numerical
results, but I don not dare to advance more than that in my
speculations :>)
Miguel,
My explanation uses standard linear circuit theory, and the RLGC model
of a transmission line (captured in the Telegrapher's equation). It is a
frequency domain model, and it is complete and consistent.
One of the things that creates confusion in some peoples minds is that
they want one foot in the frequency domain (where you can talk about
concepts like reactance, complex impedance, VSWR) and simultaneously,
one in the time domain taking about re-re-reflected waves.
You can work in either domain, and you can transform between domains,
but trying to be in both at the same time creates problems.
BTW, if you think the problem is challenging to solve in the frequency
domain, don't even think about trying to solve it in the time domain.
So, do not worry about re-reflection, it is dealt with as you have
discovered by the steady state solution when you load the source with
the (steady state) impedance seen looking into the line. The resolution
of the wave component voltages and currents with KVL and KCL at the
circuit nodes gives the steady state solution. The Telegrapher's
equation gives you the amplitude and phase relationship of the wave
components for the transmission line, not just for fictitious lossless
lines, but for practical lines as the example demonstrates.
A steady state frequency domain analysis is quite adequate for most ham
problems. You don't see it spelled out as such, but that is how the ham
handbooks describe and solve problems.
As far as the myths about PAs destroyed by absorbing reflected power,
see "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081.
Owen
Hi Richard and Owen
To Richard: What I mean is irrelevant :>) relevant is what Walt
wanted to say in this sentence: "Because of the absorption of the
pad, the generator sees a nearly perfect match for all load conditions
and all reflected power is lost "
Pllease, tell me what in english means "all reflected power is lost"?
I understood (or translate or interpret) that reflected power is
dissipated in the pad: Is it a bad translation/interpretation?
To Owen: Sincerely thanks for your reasons. You can be sure I will
take note about your explanation an take some time tu analize it, but
I am not sure about to arrive at at the right conclusion because what
I read in this newsgroup is a long-standing discussion here.
Miguel
.
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