Jim, AC6XG wrote:
"But the impedance "at" such points does not affect the current "at"
such points?"

"At" is a perfectly good preposition. R-F current can`t properly be said
to be "in" the wire due to skin effect.

The point I invoked was that at a certain distance along an antenna or a
transmission line, or at a certain distance from some reference point
there are values which are functions of the location. Often the load is
the reference chosen for a transmission line. Often the tip end of a
standing-wave antenna is used as a reference for distributions along an
antenna. When we know how many degrees a point lies back from the open
end of an ordinary standing-wave antenna a point is, we can predict many
characteristics of that point.

Impedance is a function of position on an antenna or on a transmission
line with reflections. Impedance is a voltage to current imposed on a
point.

On a standing-wave antenna, there are two significant actions which are
related but separate which I want to mention. The first is a somewhat
uniform, but declining due to radiation, incident power flow toward the
open-circuit end of the antenna. The second is a somewhat uniform, but
declining reflected power flow back from the open-circuit end of the
antenna which travels back toward the generator of the power.

Just as in a transmission line, were you to sense the power flowing each
direction alone, via a directional coupler, no standing waves would be
seen. It is only the superposition of the forward (incident) and
reflected waves that produces the familiar display that we might sense
with a slotted (trough) line. The value of standing waves is mainly as
an indicator of mismatch.

A transmission line has an iron-clad Zo due to its construction which
imposes the same voltage to current ratio (Zo) on incident and reflected
waves at every spot along the transmission line. Not so with the surge
impedance (Zo) of the antenna wire. Zo of the antenna wire can be
measured and calculated. It is a function of position along tjhe
antenna. For some calculations an average Zo of an antenna is useful.

I don`t remember everything from my studies over a half century ago.
Even If I did, most readers would either drop off to sleep or find a
more interesting activity.

I have no intention of trying to teach a course in antennas and
transmission lines. My impression is that Cecil is right on target in
this thread.

Best regards, Richard Harrison, KB5WZI

Jim Kelley wrote:
We don't talk about alternating current flowing in only one direction or
another. That would be silly. It's something I've only seen you do.

How about a reference? _Alternating_Current_Circuits_, by Kerchner and
Corcoran, 3rd edition, page 97. It is an AC circuit. There is an arrow
labeled 'I' for the current. The arrow exists in only one direction.
We know the current is not flowing in only one direction in an AC circuit
but the 'I' arrow assigns a convention reference for direction of the AC
current flow. In the accompanying diagram, that 'I' is assigned a value
of I at zero deg. The source voltage is also an arrow labeled 'V' which
points in only one direction. So whadda mean "we" white man?
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Harrison wrote:

Jim, AC6XG wrote:
"But the impedance "at" such points does not affect the current "at"
such points?"

"At" is a perfectly good preposition. R-F current can`t properly be said
to be "in" the wire due to skin effect.

I agree. Cecil doesn't. Perhaps you missed the post where he took
issue with the term.

FB on all the rest. We're on the same page.

My impression is that Cecil is right on target in
this thread.

Even his notion of an alternating current standing wave having a net
"direction" in which current flows?

73, Jim AC6XG

Cecil Moore wrote:

Jim Kelley wrote:
We don't talk about alternating current flowing in only one direction or
another. That would be silly. It's something I've only seen you do.

How about a reference? _Alternating_Current_Circuits_, by Kerchner and
Corcoran, 3rd edition, page 97. It is an AC circuit. There is an arrow
labeled 'I' for the current. The arrow exists in only one direction.
We know the current is not flowing in only one direction in an AC circuit
but the 'I' arrow assigns a convention reference for direction of the AC
current flow. In the accompanying diagram, that 'I' is assigned a value
of I at zero deg. The source voltage is also an arrow labeled 'V' which
points in only one direction. So whadda mean "we" white man?

Ya gotta be kidding, Cecil. Do you really not know that the arrow
simply indicates the direction of positive current flow?

Yikes.

73, Jim AC6XG

Jim Kelley wrote:
I agree. Cecil doesn't. Perhaps you missed the post where he took
issue with the term.

Looks like you missed that post, Jim. I have never taken issue
with skin effect.

Even his notion of an alternating current standing wave having a net
"direction" in which current flows?

Please stop misrepresenting what I posted, Jim. The AC current
in standing waves possesses an instantaneous direction of current
flow which reverses every 1/2 cycle (or 1/2 WL). I have made no
assertions about waves, only about dQ/dt, which is current involving
electron charge carriers. A positive dQ/dt is generally considered
to be flowing toward the load. A negative dQ/dt is generally
considered to be flowing toward the source.

It's pretty sad to have to resort to misrepresentations to try to
save face. You still don't seem to comprehend the difference between
photons (waves) and electrons (charge carriers). Accelerated electrons
launch photon waves but are themselves not much affected by that action.
--
73, Cecil, W5DXP

Jim Kelley wrote:
Ya gotta be kidding, Cecil. Do you really not know that the arrow
simply indicates the direction of positive current flow?

You have been making fun of me for using such an arrow, Jim.
Now it appears that you have cracked open a reference book
and realize how wrong you were. This is what I have been saying
all along. The arrow indicates the direction of current flow
when I* cos(phase_angle) is positive. 1/2 cycle later, the
current is flowing in the opposite direction, i.e. I*cos(phase_
angle) is negative. That's what you have been disagreeing with
and ****ing and moaning about for about a week now. You said
direction of current flow and cos(phase_angle) were unrelated.
--
73, Cecil, W5DXP

Cecil Moore wrote:

Jim Kelley wrote:
Ya gotta be kidding, Cecil. Do you really not know that the arrow
simply indicates the direction of positive current flow?

The arrow indicates the direction of current flow
when I* cos(phase_angle) is positive. 1/2 cycle later, the
current is flowing in the opposite direction, i.e. I*cos(phase_
angle) is negative.

The arrow does not indicate "the direction AC is flowing" - which is
what you've been trying to imply. Moreover, it has nothing to do your
claim that more alternating current flows into one end of an inductor
than flows out of the other. As I have been saying all along, that
particular notion is invalid.

When the value I in the expression i = I*sin(w) for a standing wave
happens to be greater at one end of a transmission line than the
corresponding value of I at the other end of the transmission line, it
is NOT true, or correct to say that more current is flowing into one end
than is flowing out of the other. It's totally bogus electronics. I
wish you would be courageous enough to stand corrected on that point.

73, Jim AC6XG

Jim Kelley wrote:
The arrow does not indicate "the direction AC is flowing" - which is
what you've been trying to imply.

Sorry Jim, I never tried to imply anything of the sort. The arrow,
which is just a convention, indicates the direction of instantaneous
current flow when cos(phase_angle) is positive which is during 1/2 of
the cycle. The instantaneous current flows in the opposite direction
1/2 cycle later when cos(phase_angle) is negative. You have argued loud
and long that current phase has nothing to do with current direction.
That's just simply false. In fact, the current phase and direction of
current flow in the wire are 100% correlated.

Moreover, it has nothing to do your
claim that more alternating current flows into one end of an inductor
than flows out of the other. As I have been saying all along, that
particular notion is invalid.

Tom's and Roy's own measurements proved that the measured current at
the bottom of the coil is greater than the measured current at the top
of the coil. Those currents are not standing still. They are flowing
in and out of the coil and have been proven not to be equal by actual
measurements.

Let's look at one example again. The current at the bottom of the coil
is 0.87 at -1.23 deg and the current at the top of the coil is 0.67 at
-1.57 deg. (Those angles deviate from zero degrees by a negligible
amount.) The cosines of those phase_angles are positive indicating that
we are on the '+' side of the axis (in phase with the feedpoint current)
so we draw the current arrow into the bottom of the coil and out the top
of the coil. Your objection to that commonly accepted convention is noted.

With the positive feedpoint current as our reference, we label the current
arrow pointing into the bottom of the coil as 0.87 amps and we label the
arrow pointing out of the top of the coil as 0.67 amps. So we have:

Source Current at Current at
Current Bottom of coil top of coil
1.0 amp 0.87 amp 0.67 amp
--- ---- coil ---
--------------------------------////////------------------------

At the time in the cycle when the instantaneous source current is
positive, the current into the bottom of the coil is positive and
greater than the current out of the top of the coil which is also
positive.

When the value I in the expression i = I*sin(w) for a standing wave
happens to be greater at one end of a transmission line than the
corresponding value of I at the other end of the transmission line, it
is NOT true, or correct to say that more current is flowing into one end
than is flowing out of the other. It's totally bogus electronics. I
wish you would be courageous enough to stand corrected on that point.

The net current is the phasor sum
of the forward current and reflected current. It can indeed vary from
one point in the transmission line to another and it does exactly that
in a line with reflections. I said long ago that the forward current
in a transmission line is relatively constant and the reflected current
is relatively constant. But their phasor sum, the net current, can vary
from zero to almost double the value of the forward current and anywhere
in between including positive and negative values. By convention, if it
is positive, it is flowing toward the load. If it is negative, it is
flowing toward the source. Non-zero standing-wave current reverses its
direction of flow every 1/2 cycle, i.e. it doesn't just stand still
contrary to its name. With a single inductive pickup, you cannot tell
a standing-wave current from a traveling-wave current. That fact speaks
volumes.
--
73, Cecil, W5DXP

Cecil Moore wrote:

You have argued loud
and long that current phase has nothing to do with current direction.

If that's what you think, then you misunderstood.

Tom's and Roy's own measurements proved that the measured current at
the bottom of the coil is greater than the measured current at the top
of the coil.

I note you using the term AT now. Very good. I agree with it. I also
note that you no longer say the current into the bottom of the coil is
greater than the current our of the top of the coil. That is what I
objected to at the beginning of this mess.

Those currents are not standing still.

Never said current stands still, Cecil. You're the only one whose said
anything about that. What I've said is that alternating current isn't
unidirectional.

They are flowing
in and out of the coil and have been proven not to be equal by actual
measurements.

Exactly what I've been saying - repeatedly, all along. I'm glad you
finally agree.

73, Jim AC6XG

Cecil wrote, among other things,
... With a single inductive pickup, you cannot tell
a standing-wave current from a traveling-wave current. That fact speaks
volumes.
--
73, Cecil, W5DXP

Maybe you can't, but I can. Actually, you can, too. Just move
the probe a little bit, laterally, and observe the amplitude on the O'scope
screen. If it changes, it's not a pure travelling wave.
73,
Tom Donaly, KA6RUH