Walter Maxwell wrote in
:

On Fri, 13 Apr 2007 21:39:22 GMT, Owen Duffy wrote:

Walter Maxwell wrote in
m:

In the thread 'Constructive Interference and Radiowave Propagation',
Owen, on 4-8-07 asserted that my writings in Reflections concerning
the analysis of stub matching procedures using reflection
coefficients are applicable only in cases where the transmission
line is either lossless, or distortionless. I disagree, and in what
follows I hope to persuade those who agree with Owen's position to
reconsider.

Hi Walt,

I did not say that, or in my view, imply that, it is your own
interpretation of what I did say. I did make comment limited to
Chapter 3 of Reflections II, and I stand by that comment.

Chapter 3 does not discuss stub matching at all, though you may apply
principles that you develop in Chapter 3 to your discussion / analysis
in later chapters, including to stub matching.

Owen

Hi Owen,

I'm afraid we both got off the the wrong foot along the way. I'm sorry
if I misinterpreted what you said in the post where we got off track.

Quite possibly the misinterpretation arose in your referencing Chapter
3. When I saw that I assumed you had made a typo, either for 4 or 23,
both of which contain the stub discussions. And I thought I had
earlier referenced Chapter 4. I didn't realize you had actually
reviewed Chapter 3 instead of 4.

Perhaps also you missed my two responses to your post of 4-7-07 in the
earlier thread, in which I accepted your apology (not needed). Anyway,
the issue where I felt you were wrong is my interpretation that you
believed my statements concerning use of reflection coefficients was
wrong because they are applicable for use in analysis only when the
transmission lines are either lossless distortionless.

I hope we can resume on a new footing.

Walt, the last thing I want to do is to upset you.

You have a considerable investment in your publications, and they are a
great service to the amateur community, and a credit to you.

Much of the discussion isn't so much about what happens in the
transmission line, it is about simplified explanations, explanations that
are appealling to learners, and the extension of those simplified
explanations to the more general case. If you look back over the threads,
you and I have both intiated threads where "explanation" was a key word
in the subject line.

My own view is that whilst analysing a simple case that can be seen as
special cases is a good way of introducing the issue that is to be dealt
with (eg showing the inconsistency of the Vf/If=Zo constraint in the
initial wave that travels along a transmission line, and the V/I ratio a
s/c or o/c load), one needs to move on to dealing with the more general
load case, even if in a simplified context (eg lossless line). The
"rules" that are derived have to be clearly qualified with the applicable
limits.

To overemphasis the simple / easy cases and downplay the error of
approximation is at risk of consigning all problem solving to
simplification to a trivial case and applying the solution of that
trivial case to the real problem without appreciation of the leap that
might entail.

Whilst it is no doubt appealing to some to see a virtual s/c or virtual
o/c as an explanation for the single stub tuner example, and it might be
a suitable model for that purpose, it gives the learner a new analysis
tool (without limitations), the virtual s/c or o/c. How perfect does a
virtual s/c need to be to be approximately effective? If I have an
approximately lossless feedline with a VSWR of 100:1, will the virtual
s/c at a current maximum prevent energy propagating in the same way as
the virtual s/c in the stub explanation, or could each virtual circuit
choke of x% of the energy flow? Can you solve a two stub tuner using only
virtual s/c or o/c?

It is a challenge to devise simplified explanations that don't contain
errors that need to be un-learned to develop further. I hate to say to a
learner "throw away what you already know about this, because the
explanation you have learned, understood, and trusted is wrong in part,
and we need to discard it before we move on to a better understanding...
trust me...".

Owen