Wes Stewart wrote:
Johnson says in part, "The first reflected wave will in turn be
reflected when it reaches the sending end. The terminating impedance
is *zero* (emphasis added) at the end....."

Yep, that's why Walter Maxwell calls a Z0-match point a "virtual short"
i.e. a virtual *zero* impedance, because the results are similar. I
call that Z0-match a point of interference because IMO that is a
more accurate description of what is occurring than a "virtual short".

It's quite a leap from a DC situation with zero source impedance to a
RF situation with a matched source.

The source I chose for my example was a *constant power source*.

Assume the source is a 50 ohm signal generator with a circulator load
so Pfwd1 below is a constant 100 watts.

Source----50 ohm lossless coax--+---291.5 ohm lossless twinlead---50 ohm load
Pfwd1-- Pfwd2--
--Pref1 --Pref2

Let time t1 be when the first non-zero Pref2 value arrives back at the '+'
point. tn is steady-state.

Pfwd1 Pref1 Pfwd2 Pref2
t0 100w 0w 0w 0w
t1 100w 50w 50w 25w
tn 100w 0w 200w 100w

If one plots the points between t1 and tn, the diagram will look much like
Johnson's. Pfwd2 steps up to 200w and Pref2 steps up to 100w.
--
73, Cecil http://www.qsl.net/w5dxp



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Jim Kelley wrote:

"Cecil Moore" wrote:
The RF example was out of my head, not out of the reference.

But how does that relate to the topic of multiple reflections?

How does the transient state relate to the topic of multiple
reflections????? Maybe I don't understand your question.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Jim Kelley wrote:

"Cecil Moore" wrote:
The RF example was out of my head, not out of the reference.

But how does that relate to the topic of multiple reflections?

How does the transient state relate to the topic of multiple
reflections????? Maybe I don't understand your question.

Is your assertion that multiple reflections occur only during the
transient period?

73, Jim AC6XG

Jim Kelley wrote:

Cecil Moore wrote:
How does the transient state relate to the topic of multiple
reflections????? Maybe I don't understand your question.

Is your assertion that multiple reflections occur only during the
transient period?

No, but during the transient period, they are visible and measurable.
Sans modulation and noise, they are invisible and unmeasurable during
steady-state. Some people say because they are invisible and unmeasurable
during steady-state, they cease to exist. But that's not me.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:
How does the transient state relate to the topic of multiple
reflections????? Maybe I don't understand your question.

Is your assertion that multiple reflections occur only during the
transient period?

No, but during the transient period, they are visible and measurable.
Sans modulation and noise, they are invisible and unmeasurable during
steady-state. Some people say because they are invisible and unmeasurable
during steady-state, they cease to exist. But that's not me.

Would you assert that what happens during the transient period and what
happens during the steady state are even necessarily the same thing?

73, Jim AC6XG

Jim Kelley wrote:
Would you assert that what happens during the transient period and what
happens during the steady state are even necessarily the same thing?

Does some new particle of physics manifest itself during steady-state?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Jim Kelley wrote:
Would you assert that what happens during the transient period and what
happens during the steady state are even necessarily the same thing?

Does some new particle of physics manifest itself during steady-state?

The two questions are not equivalent. Yours is ludicrous. Sorta like
this:
"Measured near field photons may simply recombine with the antenna's
free electrons and not contribute to far field radiation."

Onward through the fog.

73, Jim AC6XG

Jim Kelley wrote:
Cecil Moore wrote:

Jim Kelley wrote:
Would you assert that what happens during the transient period and what
happens during the steady state are even necessarily the same thing?

Does some new particle of physics manifest itself during steady-state?

The two questions are not equivalent. Yours is ludicrous.

Well, if no new particles manifest during steady-state, why wouldn't
the transient state and the steady-state follow exactly the same laws
of physics? Does something supernatural happen at the transient-state
to steady-state threshold? Or not? (Hint: rhetorical question)

Sorta like this:
"Measured near field photons may simply recombine with the antenna's
free electrons and not contribute to far field radiation."

Hmmmmm, I doubt that Feynman would find that statement to be "ludicrous".
I wonder if "ludicrous" is the term the priests used when they condemned
Galileo to house arrest for agreeing with Copernicus? :-) Photons re-
combining with electrons in the near field is a really simple concept.

On second thought, maybe you are inferring that the measured photons cannot
recombine? I would agree with that but the measured photons are negligible
compared to the total number of photons involved in the near field.
--
73, Cecil http://www.qsl.net/w5dxp



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I started this thread late on, so I don't know what the original issue was.
However, that bit about the reflections from the matched source really threw
me. Its been a long time since I was deep into this stuff in school (it all
made good sense then) & then at work, so I have to really strain the 'ole
brain here. Some of the comments do seem to take a turn off to the side.
With a 5.8:1 with half the power reflected at the load means that the
source'll get warmer to the tune of half the power. The use of a "constant
power" source seems strange to me.
And By the Way, you CAN use a DC circuit to show some of the same
concepts.

Steve, k\9\d\c\i




"Cecil Moore" wrote in message
...
Jim Kelley wrote:
Interesting reference. Wish I had it. He's showing re-reflections from
a Z0-matched source? I don't think I understand all I know about that.

Nope, the reference is a DC transient buildup to steady-state but the
same principles apply to RMS values.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
Well, if no new particles manifest during steady-state, why wouldn't
the transient state and the steady-state follow exactly the same laws
of physics? Does something supernatural happen at the transient-state
to steady-state threshold? Or not? (Hint: rhetorical question)

Given your propensity for hyperbole, if we can't agree that there are
differences between the transient and steady states, I don't think we'll
have too much luck discussing the subject further.

Hmmmmm, I doubt that Feynman would find that statement to be "ludicrous".

Do you really think you're in any postion to be able to speak for
Feynman?

On second thought, maybe you are inferring that the measured photons cannot
recombine? I would agree with that but the measured photons are negligible
compared to the total number of photons involved in the near field.

The photon and the electron were never really "combined" to begin with.
Therefore, the notion that they "recombine" is somewhat off the mark.
Things don't work that way. A photon could on the other hand impart
some or all of its energy to an electron. Certainly the near field can
be seen as affecting the fields within the conductor, thus having an
effect on the charges within that conductor.

73, Jim AC6XG