Cecil Moore wrote:

snip

Kraus says: "It is generally assumed that the current distribution
of an infinitesimally thin antenna is sinusoidal, and that the phase
is constant over a 1/2WL interval, changing abruptly by 180 degrees
between intervals."

Kraus says something quite similar in the second edition of "Antennas". (I
believe you are quoting from the third edition, which was co-authored by someone
else.)

However, Kraus is merely being careless with terminology. (It is likely that he
did not fully anticipate that he would be quoted out of context.) If one studies
the accompanying diagrams it is clear that Kraus is simply referring to the
standard functional form of a sinusoidal curve. For reasons not clear to me he
decides to call the natural progression from positive to negative as the sine
function passes through zero an abrupt 180 degree phase change. This is
misleading at best.

A true phase change would be, for example, an abrupt transition from +1 to -1 in
the sine function. This sort of phase change is used in numerous communication
schemes, such as PSK31.

snip

Consider something even more bizarre. If the coil is exactly 1/2WL and
each end is located at a current node, assuming the forward current is
equal to the reflected current (Kraus' assumption) then zero net current
is flowing in and out of both ends of the coil even though there is a
current maximum point in the middle of the coil. This is how Kraus'
phase-reversing coil works in his collinear array antenna.

Why is this even the least bit bizarre? Your favorite example of an ideal
transmission line with a perfectly reflecting termination shows exactly the same
thing. Are you suggesting that any node on an ideal standing wave cuts off
everything further downstream? If so, then you might want to consider Tom's
suggestion and head back to school.

73,
Gene
W4SZ

Gene Fuller wrote:
Consider something even more bizarre. If the coil is exactly 1/2WL and
each end is located at a current node, assuming the forward current is
equal to the reflected current (Kraus' assumption) then zero net current
is flowing in and out of both ends of the coil even though there is a
current maximum point in the middle of the coil. This is how Kraus'
phase-reversing coil works in his collinear array antenna.

Why is this even the least bit bizarre? Your favorite example of an
ideal transmission line with a perfectly reflecting termination shows
exactly the same thing. Are you suggesting that any node on an ideal
standing wave cuts off everything further downstream?

No, no, no. I'm saying that if Tom finds current flowing into both ends of a
coil at the same time to be a bizarre thought, then a coil with no current
flowing into the ends at all, even though current is maximum at the center
of the coil, would be an even more bizarre thought *FOR HIM*. Tom seems to
have a sacred cow that he doesn't want to barbecue.

Assume a 180 degree phase shifting coil with a current node at each end
as I described above. Also assume one misses the current nodes by 6 degrees
and that the maximum current loop is 1 amp. The current at one end of the
coil will be ~0.1 amp at zero degrees while the current at the other end
of the coil is ~0.1 amp at 180 degrees. That means current is flowing into
both ends of the coil at the same time and then flowing out of both ends
at the same time 1/2 cycle later. Tom calls anyone who believes that
"gullible" and that tells me I should go back to school. I am merely
demonstrating the laws of physics operating outside of Tom's sacred cow box.
--
73, Cecil http://www.qsl.net/w5dxp



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Gene Fuller wrote:
Cecil Moore wrote:
Kraus says: "It is generally assumed that the current distribution
of an infinitesimally thin antenna is sinusoidal, and that the phase
is constant over a 1/2WL interval, changing abruptly by 180 degrees
between intervals."

Kraus says something quite similar in the second edition of "Antennas".
(I believe you are quoting from the third edition, which was co-authored
by someone else.)

However, Kraus is merely being careless with terminology. (It is likely
that he did not fully anticipate that he would be quoted out of
context.)

It is within the context of physics. It is only out of context
when the context is sacred cows and old wives' tales.

If one studies the accompanying diagrams it is clear that
Kraus is simply referring to the standard functional form of a
sinusoidal curve. For reasons not clear to me he decides to call the
natural progression from positive to negative as the sine function
passes through zero an abrupt 180 degree phase change. This is
misleading at best.

Kraus is merely following convention. The sign of the real part of the
current at 89 degrees is positive. The sign of the real part of the current
at 91 degrees is negative. A positive sign indicates current flowing in
one direction. A negative sign indicates current flowing in the opposite
direction. Since there are only two possible directions in a wire, those
two directions are 180 degrees apart, by definition.

A true phase change would be, for example, an abrupt transition from +1
to -1 in the sine function. This sort of phase change is used in
numerous communication schemes, such as PSK31.

A true phase change would also be, a smooth transition from +0.001 through
zero to -0.001. When current equals zero at a standing wave node, the phase
of the real component of current on each side of that zero is 180 degrees
different. For the real component of the current, a 180 degree phase reversal
occurs between 89 degrees and 91 degrees. Cos(89) = +0.017, Cos(91) = -0.017
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,

This is absurd.

The "phase" in the equation y = A sin (x) is the "x", not the "A" or the "y"

There is no standard convention in the world of math, science, or engineering
that claims a sine wave reverses phase as its amplitude ranges through positive
and negative values.

Kraus was careless with his terminology, but I suspect he was not confused.

You appear to be carefully confusing the entire topic.

8-)

73,
Gene
W4SZ

Cecil Moore wrote:
Gene Fuller wrote:

Cecil Moore wrote:

Kraus says: "It is generally assumed that the current distribution
of an infinitesimally thin antenna is sinusoidal, and that the phase
is constant over a 1/2WL interval, changing abruptly by 180 degrees
between intervals."


Kraus says something quite similar in the second edition of
"Antennas". (I believe you are quoting from the third edition, which
was co-authored by someone else.)

However, Kraus is merely being careless with terminology. (It is
likely that he did not fully anticipate that he would be quoted out of
context.)


It is within the context of physics. It is only out of context
when the context is sacred cows and old wives' tales.

If one studies the accompanying diagrams it is clear that Kraus is
simply referring to the standard functional form of a sinusoidal
curve. For reasons not clear to me he decides to call the natural
progression from positive to negative as the sine function passes
through zero an abrupt 180 degree phase change. This is misleading at
best.


Kraus is merely following convention. The sign of the real part of the
current at 89 degrees is positive. The sign of the real part of the current
at 91 degrees is negative. A positive sign indicates current flowing in
one direction. A negative sign indicates current flowing in the opposite
direction. Since there are only two possible directions in a wire, those
two directions are 180 degrees apart, by definition.

A true phase change would be, for example, an abrupt transition from
+1 to -1 in the sine function. This sort of phase change is used in
numerous communication schemes, such as PSK31.


A true phase change would also be, a smooth transition from +0.001 through
zero to -0.001. When current equals zero at a standing wave node, the phase
of the real component of current on each side of that zero is 180 degrees
different. For the real component of the current, a 180 degree phase
reversal
occurs between 89 degrees and 91 degrees. Cos(89) = +0.017, Cos(91) =
-0.017

Gene Fuller wrote:
There is no standard convention in the world of math, science, or
engineering that claims a sine wave reverses phase as its amplitude
ranges through positive and negative values.

Of course there is, Gene. There are only two possible directions of
travel for real current in a wire. Current is either flowing to the
right, zero degrees by convention, or to the left, 180 degrees by
convention. Those are the only two directions possible for the real
part of Imax*e^jwt. The real part of the current has only two phases,
either zero degrees or 180 degrees. Any magnitude of real current
flowing to the right is at zero degrees, by convention. Any magnitude
of current flowing to the left is at 180 degrees, by convention. The
phase of current flow in a wire looks like a digital signal with only
two states possible.

Dang, you guys have really been seduced by your math models. RF current
reverses directions by 180 degrees every 1/2 cycle. In a transmission
line that is multiple wavelengths long, all up and down the same wire,
you have current flowing outward and current flowing inward 1/2WL apart.
Just because you hang an arrow on the direction of current flow
in an AC situation, doesn't mean the AC current always flows in that
direction. That is only a reference corresponding to t=0.
At t=(0+1/2 cycle), the current is flowing in the *opposite* direction
to the arrow.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,

Sorry, I forgot that Wednesday is "no math day" in Texas.

8-)

73,
Gene
W4SZ


Cecil Moore wrote:

Dang, you guys have really been seduced by your math models.

Gene Fuller wrote:
Sorry, I forgot that Wednesday is "no math day" in Texas.

When you can't refute what I say, offer a quip instead? If
you tell me what is wrong with what I said, I will profit
by my mistakes. Otherwise, I will be bound by the same
old laws of physics that I learned in the 50's.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Gene Fuller wrote:
There is no standard convention in the world of math, science, or
engineering that claims a sine wave reverses phase as its amplitude
ranges through positive and negative values.

Of course there is, Gene. There are only two possible directions of
travel for real current in a wire. Current is either flowing to the
right, zero degrees by convention, or to the left, 180 degrees by
convention. Those are the only two directions possible for the real
part of Imax*e^jwt. The real part of the current has only two phases,
either zero degrees or 180 degrees. Any magnitude of real current
flowing to the right is at zero degrees, by convention. Any magnitude
of current flowing to the left is at 180 degrees, by convention. The
phase of current flow in a wire looks like a digital signal with only
two states possible.

Yikes, Cecil. Using that logic, you're basically arguing that every 1/2
WL or 180 degrees, a forward wave turns into a reflected wave. You
oughta think about what Gene's saying a little longer. Phase is the wt
part of the equation, and it varies continuously with time. It doesn't
change abruptly - unless it encounters a discontinuity of one sort or
another.

73, Jim AC6XG








Dang, you guys have really been seduced by your math models. RF current
reverses directions by 180 degrees every 1/2 cycle. In a transmission
line that is multiple wavelengths long, all up and down the same wire,
you have current flowing outward and current flowing inward 1/2WL apart.
Just because you hang an arrow on the direction of current flow
in an AC situation, doesn't mean the AC current always flows in that
direction. That is only a reference corresponding to t=0.
At t=(0+1/2 cycle), the current is flowing in the *opposite* direction
to the arrow.
--
73, Cecil http://www.qsl.net/w5dxp

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Jim Kelley wrote:
Yikes, Cecil. Using that logic, you're basically arguing that every 1/2
WL or 180 degrees, a forward wave turns into a reflected wave.

Nope, but half the time in a horizontal standing wave antenna, the
forward current is flowing toward the left while the reflected current
is flowing toward the right, and vice versa. That's simply a characteristic
of RF current. In a single conductor into your house, half the time, the
current is flowing toward the source. I am absolutely amazed that
you, of all people, would allow yourself to be seduced by a shortcut
DC model applied to an AC problem.

The beauty of AC power transfer is that the same electrons are run back
and forth through the generator. For a UHF transmitter, very few of the
electrons running back and forth through the transmitter reach the
antenna. It is somewhat akin to the bouncing ball bearings. The center
one doesn't move.

You oughta think about what Gene's saying a little longer.

Sorry Jim, but you oughta think, period. At the moment, you are
running on autopilot in a tiny box. Repeat after me until you
understand. AC is NOT DC. AC is NOT DC. AC is not DC. AC is not
DC. ... In any one wire, the direction of AC current changes by
180 degrees every 1/2 cycle. This was taught in detail at Texas
A&M in the 50's. What on earth has happened in the ensuing 50
years?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Jim Kelley wrote:
Yikes, Cecil. Using that logic, you're basically arguing that every 1/2
WL or 180 degrees, a forward wave turns into a reflected wave.

Nope, but half the time in a horizontal standing wave antenna, the
forward current is flowing toward the left while the reflected current
is flowing toward the right, and vice versa. That's simply a characteristic
of RF current.

The point is it's not a reversal in phase, abrupt or otherwise. A
reversal in polarity, maybe. And you can't try to argue that polarity
and phase mean the same thing. This is really common knowledge,
freshman level stuff, Cecil. You really ought to just let it drop.
It's not even pertinent to the topic. But since for you, arguing is an
objective in itself, I'm sure you'll continue to argue about it.

73, Jim AC6XG