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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