On 07/07/15 00:36, Dave Platt wrote:
The only case I am aware of that will give total reflection is when
the terminal is open circuit with infinite impedance absorbing *no*
signal.

Also when it is a zero impedance (short circuit).

I'm trying to picture this.

In the case of an open circuit a matched driver drives the transmission
line to 50% of the driving voltage. The wave reaches the open
termination and is reflected with the same polarity resulting in a
return wave that reaches 100% of the driving voltage.

In the same vein, if the wave hits the short circuit the reflected wave
will be the opposite polarity making the reflected wave 0% of the
driving voltage resulting in the short circuit eventually showing to the
drive circuit.

Yup. You can see this happen on a time-domain reflectometer (an
o'scope and a pulse generator will do).

(although, to pick nits, I'd clarify your latter paragraph to read
"will be of the opposite polarity, making the sum of the forward and
reflected wave 0% of the driving voltage...")




There is a good demo on YouTube of this. The presenter built simple
little, rather neat, pulse generator to demonstrate such things. I built
one for demos. It works very well.

It is quite useful for measurements etc.

https://www.youtube.com/watch?v=9cP6w2odGUc