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?

The forward current hits an open-circuit. The net current is zero.
Therefore, the reflected current must be equal in magnitude and
opposite in phase to the forward current at the open-circuit.
Since the net current goes to zero, i.e. the magnetic field goes
to zero, all the energy existing at that point must
migrate into the electric field thus increasing the voltage. And
indeed, the voltage doubles at an open-circuit indicating that
the reflected voltage is equal in magnitude and phase to the
forward voltage. A simple RF voltage measurement at the open-
circuit will prove that the above is true.

Now suppose instead the line is short circuited. The voltage returns
down the line, and the current does not. In this case, there doesn't
seem to be any non-math or intuitive feel for why the short should cause
this--either for voltage or current. Can one clue me in on what's really
happening above (voltage) and here (voltage and current)? Inquiring
minds want to know.

It's (surprise) the reverse of an open-circuit. The net voltage goes
to zero at the short indicating that the electric field is zero at
that point. Therefore, all the energy existing at that point migrates
into the magnetic field. The reflected voltage is therefore equal in
magnitude and 180 degrees out of phase with the forward voltage. And,
indeed, the current at the short is double the magnitude of the forward
current indicating that the forward current and reflected current are
equal in magnitude and phase at a short circuit. RF voltage and current
measurements prove it to be true.
--
73, Cecil, http://www.qsl.net/w5dxp