[SI-LIST] Re: reflection coeficient

  • From: "Kevin G. Rhoads" <kgrhoads@xxxxxxxxxxxx>
  • To: kpsubramani@xxxxxxxxx
  • Date: Mon, 20 Aug 2007 17:48:36 +0000

>I was reading about signal reflections.

It is too bad that most people use clothing dryers and not clotheslines
anymore.  If you've ever "pulsed" a clothesline and watched the pulse
propagate and reflect off the far end as a kid, then when you get to
transmission lines 101 you can visualize just exactly what is going
on phenomenologically.  (So all that time when I was "playing" as
a child was not totally wasted ...)

Absent a clothesline, take a good string or twine and run a taut line
over at least 10 feet, longer if you can.  Ping the line by plucking
it near one end and watch the propagating pulse.  You can literally
see the pulse reflect from the far end.  If one uses the natural 
analogy of displacement <-> voltage and transverse velocity <-> 
current, then a tied end is analogous to a shorted line.  An
opne line would be simulated by having the twine tied to a slip
ring that can freely move up and down, which is much harder to
get working.

There is no substitute for understanding the math -- but good
visualization can be very helpful as well.

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