Gene, W4SZ wrote:
"Your favorite example of an ideal transmission line with a perfectly
reflecting termination shows exactly the same thing."

Yes. Several readers have available Terman`s 1955 edition of "Electronic
and Radio Engineering". On page 94 is Fig. 4-5, "Phase Relations on a
Transmission Line for Two Typical Conditions".

One of the conditions is for a complete reflection (Rho = 1). The phase
changes are indeed abrupt. Over a distance of 1.25-wavelengths we have 5
abrupt transistions of power factor between 90-degrees lag and
90-degrees lead or vice versa. The similarity between a standing-wave
antenna and a standing-wave transmission line would lead one to expect
abrupt phase reversals on the antenna too, as the open circuit at the
antenna end is an abrupt almost complete reflection maker.

Best regards, Richard Harrison, KB5WZI

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.

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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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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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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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.

Consider a balanced transmission line. When forward current in one wire
is flowing toward the load, the forward current in the other wire is
flowing toward the source. When reflected current in one wire is flowing
toward the source, the reflected current in the other wire is flowing
toward the load.

Moral: Be very, very careful about the when and where of t=0. Is the
top or bottom of an balanced antenna tuner link coil the output path
or the return path?
--
73, Cecil http://www.qsl.net/w5dxp



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On Thu, 15 Jan 2004 13:02:25 GMT, Andy Cowley
wrote:

You also have modelling programs which don't work.

Can you please provide a list of these "non-working" programs?

Danny, K6MHE

"Dan Richardson " wrote:

On Thu, 15 Jan 2004 13:02:25 GMT, Andy Cowley
wrote:

You also have modelling programs which don't work.

Can you please provide a list of these "non-working" programs?

Danny, K6MHE

Dear Dan,

dipole3.exe produces very unlikely values for the 'Input
resistance'(sic) of electrically short dipoles. I assumed that
'Input resistance' was the resistive component of the feedpoint
impedance. I pointed this out to Reg and got insults and bluster
but no meaningful reply.

E.g. a 16.6 m dipole at 1.8 MHz h=6m w=1.5 s=120 gives 44.3 ohms.
That seemed a little high to me. So I reduced the length to
1 metre !!!! the resistance rises ????? to 212.8 ohms. Am I
hitting some boundary condition? or am I misunderstanding the
significance of 'Input Resistance'? I'm pretty sure the radiation
resistance plus loss resistance of a 1 metre antenna on top band
should be much less than 1 ohm.

EZNEC gives values at least an order of magnitude less than the
values obtained from dipole3 for the resistive component of the
feedpoint impedance. I believe EZNEC to be a reliable, well proven
program, which gives accurate (at least in this context) results.
The mathematical basis and assumptions of EZNEC and NEC2 are
publicly available, unlike those of Reg's programs.

As far as I am concerned if one of Reg's programs has errors that
he is unwilling or unable to correct or explain then the results
of any of his programs should be checked by a more reliable method
before they are used.

Let the user beware.

vy 73

Andy, M1EBV