Richard Harrison wrote:

Someone wrote:
"Instantaneous standing wave current moves."

Current is movement. Standing waves stand still.

Forward (incident) waves move forward. Reverse (reflected) waves move
rearward. Interference between incident and reflected waves makes a
stationary current pattern.

Neither the instantaneous magnitude nor instantaneous phase is constant.
Even at the point where the peak of the current loop occurs, that point
goes through a zero transition twice in every cycle. Yes, instantaneous
standing wave current equals zero all up and down the line twice each cycle.

Consider a lossless open-circuit transmission line with reflections.
At one current loop maximum on the line, the instantaneous current
will be positive, i.e. flowing toward the load. At the next current
loop maximum, the instantaneous current will be negative, i.e. flowing
toward the source. 1/2 cycle later, these values reverse sign and
direction. Assume the following graphic snapshot of a standing wave
is sinusoidal and includes magnitude and phase.
_
/ \
/ \
_/__________\________________
\ /
\ /
\ _ /

1/2 cycle later the snapshot will look like this. Anyone who doesn't
believe it has never seen it on an o'scope.
_
/ \
/ \
______________/__________\_
\ /
\ /
\ _ /

1/4 cycle later the instantaneous standing wave pattern looks like this:

__________________________________________________ _______________________

Here is a dynamic graphic of what a standing wave really looks like.
The black line is the standing wave. Note that neither the magnitude
nor phase is standing still.

http://einstein.byu.edu/~masong/HTMs...newave2EX.html

The positive peaks of the current are flowing toward the load because the
phase angles of both the forward and reflected waves are zero, i.e. at
that point, the instantaneous forward current and instantaneous reflected
current are both flowing toward the load. Remember, half the time, the
instantaneous forward current is flowing toward the source and half the
time, the instantaneous reflected current is flowing toward the load.

The negative peak of the current is flowing toward the source because
the phase angles of both the forward and reflected waves are 180 degrees,
i.e. at that point, the instantaneous forward current and instantaneous
reflected current are both flowing toward the source.

1/2 cycle later, the positive peak will have become negative and the
negative peak will have become positive, i.e. their respective directions
of flow have been reversed.

In our enthusiasm for RMS values, we forget what the AC waveforms are
actually doing. RF forward current reverses its direction every 1/2 cycle.
So does RF reflected current.
--
73, Cecil, W5DXP