Cecil, W5DXP wrote:
"His virtual "center tap to ground" is certainly a valid concept."

Yes. Inertia is a valid idea. A balanced circuit remains balanced unless
something is done to unbalance it.

Work with phone lines and you find center-tapped lines are not required
for balance, or may make balance worse.

Equal exposure and occasional transposition usually maintain balance.

Best regards, Richard Harrison, KB5WZI

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

On Fri, 06 Feb 2004 12:04:36 -0600, Cecil Moore
wrote:
Neither the instantaneous magnitude nor instantaneous phase is constant.
Uh-huh

Richard Clark wrote:

wrote:
Neither the instantaneous magnitude nor instantaneous phase is constant.

Uh-huh

See for yourself at:

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

The only place the instantaneous magnitude of a standing
wave is constant is at a node where it is equal to zero.
Between nodes, magnitude and phase are continually changing.
--
73, Cecil, W5DXP

Cecil Moore wrote:
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.

I think the word you're looking for is *Node*.

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.
_
/ \
/ \
______________/__________\_
\ /
\ /
\ _ /

Right. But the antenna current plots are of the amplitude term of the
standing wave, shown as a function of position. It's not a time plot.
In the equation E*sin(w), E is the amplitude term. The amplitude term
is a contant. It does not vary with time. It varies with position
along the antenna. The solution to E*sin(w) does vary with time because
it is a function of time. You're confusing the two different
functions. Your answer, typically, is that the math is wrong.

73, Jim AC6XG


_
/ \
/ \
______________/__________\_
\ /
\ /
\ /
\ _ /

By the way, here is an I(t) plot where there is a *net* flow of current.

On Fri, 06 Feb 2004 12:35:47 -0600, Cecil Moore
wrote:
Neither the instantaneous magnitude nor instantaneous phase is constant.
Uh-huh
See for yourself at:
Pathetic

Cecil Moore wrote:

Jim Kelley wrote:
The amplitude term is a contant. It does not vary with time.

Uh Jim, please look at this web page and tell me again
that the amplitude is constant and doesn't vary with time.

The amplitude term of an equation, and the one being plotted on an
antenna current plot, is a constant for any given position in a standing
wave. It's the peak amplitude of the time varying function. It's
really not a matter of opinion.

73, Jim AC6XG

Please don't take me for a fool, Cecil. I've done that demo for the
students for 17 years.

At this point you really need to worry less about producing verbal
output, and worry more about being able to properly absorb and utilize
input information. That part seems to be out of order.

Cecil Moore wrote:

Jim Kelley wrote:
The amplitude term is a contant. It does not vary with time.

Uh Jim, please look at this web page and tell me again
that the amplitude is constant and doesn't vary with time.
The standing wave loop looks like a kid's jump rope. Note
that the amplitude of the standing wave is zero everywhere
two times per cycle. How can the amplitude be constant?
It's RF, for goodness sake.

http://einstein.byu.edu/~masong/HTMs...newave2EX.html
--
73, Cecil, W5DXP

Jim Kelley wrote:
The amplitude term is a contant. It does not vary with time.

Uh Jim, please look at this web page and tell me again
that the amplitude is constant and doesn't vary with time.
The standing wave loop looks like a kid's jump rope. Note
that the amplitude of the standing wave is zero everywhere
two times per cycle. How can the amplitude be constant?
It's RF, for goodness sake.

http://einstein.byu.edu/~masong/HTMs...newave2EX.html
--
73, Cecil, W5DXP

Richard Clark wrote:

wrote:
See for yourself at:
http://einstein.byu.edu/~masong/HTMs...newave2EX.html

Pathetic

Discovered why you were confused?
--
73, Cecil, W5DXP