W. Watson wrote:

Roy Lewallen wrote:

W. Watson wrote:

It seems reasonable that if I have an open ended transmission line
that the current would reflect back and change phase. After all, the
electrons at the end have nowhere to go but back down the line.
However, the voltage is a different matter. There is no phase
reversal (or polarization change) There doesn't seem to be an
intuitive reason for this. However, if one examines the equations for
current and capacitive voltage, then it falls out of the math. Still,
where is the non-math that indicates this is true?

Now suppose instead the line is short circuited. The voltage returns
down the line, and the current does not.



That's not true. Both are totally reflected.

Thanks for the response. Why is any wave reflected at all? In the open
case, I can easily visualize the electrons (drifting cloud) having
nowhere to go when they reach the end of the line, so the current
literally has to go in reverse. Perhaps the shorted line represents a
reactive circuit to the incident wave?
Well, I looked at some physics books that I have access to, Waves by
Crawford, in particular. He spends an entire chapter, called
Reflections(!), and seems to hit every aspect of how all this works in every
conceivable circumstance. One somewhat length section deals with
transmission between different media using a variety of explanations using
dash pots, strings, and so on. He gets all this out of the way by developing
reflection coefficients and other tools, including some boundary analysis, I
believe. Then in about 2-3 pages dispenses with transmission lines by
looking at boundary conditions using what was developed earlier. This is
non-trivial material, and would likely takes many pages of explanation and
diagrams to reduce it to a simpler form.

I think I'll pass on going any further with my question via this thread. I
can probably drag out enough satisfactory info on this from the book and a
few other sources to keep me happy. We could develop a very long thread
otherwise. Nevertheless, thanks for your interest and insights via shedding
some light on boundary conditions.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"I often quote myself - it adds spice to
my conversation." - George Bernard Shaw

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