Keith wrote:
"Those 0 volts and currents can be measured."

The phase of the incident wave at a distance from the generator is the
phase that existed at the generator at an earlier time proportional to
distance.

Take a point on the signal traveling on a transmission line which is
reflected back toward the generator. It encounters the later generated
signal traveling toward the reflection point.

Suppose the reflection is from an open circuit. At the open, incident
and reflected waves have the same amplitude and phase. Their voltages
add arithmetically. Open-circuit reaction reverses the phase of the
reflected current, so incident and reflected currents add to zero.

Back from the reflection, phase of the incident wave advances with
distance. We see a signal which was generated more recently the farther
back toward the generator we look.

Back from the reflection, phase of the reflected wave lags with
distance. We see a signal which was generated farther back in time the
farther back toward the generator we look.

At those fixed points on the transmission line where the incident and
reflected voltages are exactly out-of-phase, they add to zero.

At those fixed points on the transmission line where the incident and
reflected voltages are exactly in-phase, they add to a double of the
incident voltage.

The forward (incident) and reflected waves retain their distinctions.
But it takes a directional coupler to separate them. The pattern of
standing waves is manifested by the sum of the forward and reflected
waves.

The forward wave consists of a voltage everywhere associated with a
current equal to that voltage over Zo.

The nature of the reflected wave is the same, except it travels in the
opposite direction.

Best regards, Richard Harrison, KB5WZI