Antenna Loading Coils
 

GENTLEMEN, behave yourselves.

The ONLY way of modelling the effect of a loading coil in an antenna wire is
to consider it to be a section of a continuous-inductance-loaded
transmission line which also has a radiation resistance.


Which, of course, is what it actually is. It can then be incorporated in
the remainder of the system which consists of other radiating transmission
line sections.


As with all other lines it has length and diameter (that of the coil
former).


It has a uniformly distributed capacitance (to the rest of the world) per
unit length.


It has normal distributed inductance per unit length PLUS the MUTCH extra
inductance due to being wound as a coil.


It has the normal RF wire loss resistance.


It has a uniformly distributed radiation resistance according to the length
of the coil former. (NOT of the length of the wire on the coil.)


R, L and C are all calculable, or at least can be estimated, from
dimensions.


So in an antenna system, in general, we have 3 consectutive transmission
lines sections with the loading coil forming the center section.


Because of the high inductance of the loading coil, Zo = Sqrt(L/C) will have
a much higher value than that of a wire of the same straight length.


If a generator (transmitter) is applied at one end then currents, voltages
and phase relationships at any point along the overall length can be
calculated. Mismatches between Zo's of the various sections are
automatically taken into account.


But we are ultimately interested only in input impedance, efficiency and
power radiated. All the intermediate stuff which may be available in the
process is just so much waffle for the old wives to haggle about.


As is well known, the coil alone, a simple helix, if of appreciable former
length relative to a 1/4-wavelength, will radiate.


Download in a few seconds program HELICAL and run immediately. Enter the
following values -


Height = 2.5m
Coil dia = 50mm
Coil turns = 750
Wire dia = 2.5mm
Rod length = 0mm
Rod dia = 0mm
Ground loss = 8 ohms

Computed results are the performance of a Helical 160 meter band antenna
which was popular a few years back amongst UK mobile amateurs.


Its a case of the height being so low and the loading inductance being so
big that it occupies the whole length of the antenna. Why waste the space?
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg Edwards wrote:
So in an antenna system, in general, we have 3 consectutive transmission
lines sections with the loading coil forming the center section.
Because of the high inductance of the loading coil, Zo = Sqrt(L/C) will have
a much higher value than that of a wire of the same straight length.

(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Reg Edwards wrote:
So in an antenna system, in general, we have 3 consectutive transmission
lines sections with the loading coil forming the center section.
Because of the high inductance of the loading coil, Zo = Sqrt(L/C) will have
a much higher value than that of a wire of the same straight length.

(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?
--
73, Cecil http://www.qsl.net/w5dxp

Maybe it's a half wavelength long? ;-)

73, Jim AC6XG

Cecil Moore wrote:

Jim Kelley wrote:
Maybe it's a half wavelength long? ;-)

For a real-world air-core coil to exhibit identical currents at the
input and output, it would have to be one wavelength long, lossless,
and non-radiating. That's a pretty tall order just to support an
old wives' tale. :-)

I happily stand corrected.

73 de jk

Reg wrote,

The ONLY way of modelling the effect of a loading coil in an antenna wire is
to consider it to be a section of a continuous-inductance-loaded
transmission line which also has a radiation resistance.


Another absolutist, fairly assinine statement from across the pond. How do
you know it's the ONLY way, Reg, have you tried any others?

Tom Donaly, KA6RUH

Jim Kelley wrote:
Cecil Moore wrote:
(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?

Maybe it's a half wavelength long? ;-)

Strangely enough, that won't do it, Jim. A coil equivalent to 1/2WL
reverses the phase of the current such that current is flowing into
both ends at the same time. According to some gurus, that violates
Kirchhoff's laws. But Kraus shows how phase-reversing coils are
used in collinear arrays. Reckon Kraus knows he is violating Kirchhoff's
laws?

For a real-world air-core coil to exhibit identical currents at the
input and output, it would have to be one wavelength long, lossless,
and non-radiating. That's a pretty tall order just to support an
old wives' tale. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Reg Edwards wrote:
So in an antenna system, in general, we have 3 consectutive transmission
lines sections with the loading coil forming the center section.
Because of the high inductance of the loading coil, Zo = Sqrt(L/C) will
have
a much higher value than that of a wire of the same straight length.

(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?
--
73, Cecil http://www.qsl.net/w5dxp


An invidious post if ever I saw one. You've got to get out of the
habit, Cecil, of believing the things you think up in your head.
You've got a horrible case of I-think-therefore-it-is syndrome.
Experiment more. Sit at the feet of Richard Clark and learn how
to measure. Learn the truth first and then make up your theories,
knowing beforehand that every theory is an abstraction. Leave the
tunnel vision and its resultant dogmatism to the local baptist
minister. Quit believing that you can win an argument with slippery
evasions and insults, or that there is even any advantage in winning
at all. If they are true, your ideas will fight their own battles, and if
they're false, no amount of bluster and tortured logic will make people
believe them. You've spent countless hours arguing the case for your
interpretation of how waves work, and the only thing you've accomplished
is that you've antagonized a group of people more knowledgeable than
you are.
I'm not asking you to give up, but it would be nice, both for the
benefit of the newsgroup and for your reputation if you would temper
your fanaticism with just a bit of experimentation, dispassionate
reflection and self-doubt.
73,
Tom Donaly, KA6RUH

73,
Tom Donaly, KA6RUH

Tdonaly wrote:
You've spent countless hours arguing the case for your
interpretation of how waves work, and the only thing you've accomplished
is that you've antagonized a group of people more knowledgeable than
you are.

A group more knowledgeable about EM waves than Eugene Hecht? It is
not my interpretation of how waves work, Tom. It is the consensus
of opinions of experts from the field of optics. Non-glare glass
is exactly the same thing as a 1/4WL matching section in a transmission
line and how the interference causes the match is fully understood. If
proven, accepted knowledge from a closely related technical field
antagonizes a bunch of closed-minded ivory tower gurus on this newsgroup,
so be it.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg Edwards, G4FGQ wrote:
"It has a uniformly distributed radiation resistance according to the
length of the coil form."

That may be the case of "treating" radiation resistance as if uniformly
distributed. Radiation resistance may be defined as the resistance which
would take the same power as that radiated when placed at the
high-current point of the antenna.

While a transmission line of uniform cross section may have uniform
inductance and capacitance per unit length, it is unlikely that an
antenna has uniform capacitance per unit length. Electric field lines of
force have a varying concentration along equal small segments of wire
length. It`s usually a function of distance between wires and this
varies in an antenna because the antenna is meant to radiate.

Variation of capacitance along an antenna causes a variation in surge
impedance along the antenna, but a useful average can be used for
calculations. Straight wire or coiled as in a rubber ducky, an antenna
is subject to this variation in capacitance and surge impedance.

Best regards, Richard Harrison, KB5WZI

"Tdonaly"
Reg wrote,

The ONLY way of modelling the effect of a loading coil in an antenna wire
is
to consider it to be a section of a continuous-inductance-loaded
transmission line which also has a radiation resistance.


Another absolutist, fairly assinine statement from across the pond. How do
you know it's the ONLY way, Reg, have you tried any others?

Tom Donaly, KA6RUH

========================

Tom, beware the Green-eyed Technology Goddess.

WE have modelling programs which actually WORK.

And FREE to US citizens.

Is this 'dumping' of shoddy goods?

After gigabytes upon gigabytes of civil war amongst yourselves - YOU
havn't!
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Richard, it's only a model - and it WORKS very well.

"If you know of a better hole then go to it." - Bruce Bainsfather,
newspaper cartoonist, caption of a cartoon in the trenches, mud and
shrapnel, Belgium, WW1. ;o)
----
Yours, Reg.
=============================


"Richard Harrison" wrote in message
...
Reg Edwards, G4FGQ wrote:
"It has a uniformly distributed radiation resistance according to the
length of the coil form."

That may be the case of "treating" radiation resistance as if uniformly
distributed. Radiation resistance may be defined as the resistance which
would take the same power as that radiated when placed at the
high-current point of the antenna.

While a transmission line of uniform cross section may have uniform
inductance and capacitance per unit length, it is unlikely that an
antenna has uniform capacitance per unit length. Electric field lines of
force have a varying concentration along equal small segments of wire
length. It`s usually a function of distance between wires and this
varies in an antenna because the antenna is meant to radiate.

Variation of capacitance along an antenna causes a variation in surge
impedance along the antenna, but a useful average can be used for
calculations. Straight wire or coiled as in a rubber ducky, an antenna
is subject to this variation in capacitance and surge impedance.

Best regards, Richard Harrison, KB5WZI

(Rhetorical Question)
Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?
===============================

(Rhetorical Answer)
It can't. Are you trying to insinuate I've ever said that it could?

But I'm pleased to see you are getting nearer to understanding how to model
a loading coil in an antenna wire. After all, the concept is simplicitly
itself to any electrical engineer worth his salt. And it's intuitively
obvious it's the only way of going about the job. Your 'cosine formula'
automatically comes out in the wash. As Holmes said to Watson. ;o)

Incidentally, from memory, in the 1950's, in the IEEE "Reference Data for
Radio Engineers" there was an article on short helically-wound antennas,
giving number of turns for a given height of 1/4-wave resonance. The author
was on the right track. But there were errors in the formulae which had not
been arrived at by analytical means.
----
Reg, G4FGQ

Reg Edwards wrote:
(Rhetorical Question)

Given that the coil section resembles a high-Zo transmission line with
reflections, how can the current into the coil section be equal in
magnitude and phase to the current out of the coil section?

(Rhetorical Answer)
It can't. Are you trying to insinuate I've ever said that it could?

Nope, but others have asserted such. What would be a ballpark figure
for the Z0 of a bugcatcher loading coil?

Incidentally, from memory, in the 1950's, in the IEEE "Reference Data for
Radio Engineers" there was an article on short helically-wound antennas,
giving number of turns for a given height of 1/4-wave resonance. The author
was on the right track. But there were errors in the formulae which had not
been arrived at by analytical means.

I just happen to have a 1957 copy from college days. Interestingly, it has
a velocity of propagation formula for the helix that includes axial velocity.
Didn't someone say axial velocity doesn't control the speed of propagation
for a loading coil?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Strangely enough, that won't do it, Jim. A coil equivalent to 1/2WL
reverses the phase of the current such that current is flowing into
both ends at the same time. According to some gurus, that violates
Kirchhoff's laws. But Kraus shows how phase-reversing coils are
used in collinear arrays. Reckon Kraus knows he is violating Kirchhoff's
laws?

For a real-world air-core coil to exhibit identical currents at the
input and output, it would have to be one wavelength long, lossless,
and non-radiating. That's a pretty tall order just to support an
old wives' tale. :-)
--
73, Cecil http://www.qsl.net/w5dxp



You need to go back to school, Cecil. Anyone can stick a coil -
or a capacitor for that matter - between two similar antiresonant circuits
and find a frequency where the two circuits are in phase without resorting
to calling the coil - or capacitor - 1/2WL. There's also a frequency where
the two circuits are 180 deg. out of phase, but current isn't flowing into
two ends of the coil - or capacitor - at the same time. I hope
there's no on this newsgroup gullible enough to take your
fractured circuit theory seriously.
73,
Tom Donaly, KA6RUH

Jim Kelly wrote,


Cecil Moore wrote:

Jim Kelley wrote:
Maybe it's a half wavelength long? ;-)

For a real-world air-core coil to exhibit identical currents at the
input and output, it would have to be one wavelength long, lossless,
and non-radiating. That's a pretty tall order just to support an
old wives' tale. :-)

I happily stand corrected.

73 de jk



Pathetic.
73,
Tom Donaly KA6RUH

Tdonaly wrote:
There's also a frequency where
the two circuits are 180 deg. out of phase, but current isn't flowing into
two ends of the coil - or capacitor - at the same time. I hope
there's no one on this newsgroup gullible enough to take your
fractured circuit theory seriously.

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."

If I locate a loading-coil such that the phase change node is
in the middle of the coil, current-in will be 180 degrees out of
phase with current-out. In a two-terminal series circuit, if the
net current-in is 180 degrees out of phase with the net current-out,
those two currents are either flowing into the coil at the same time
or flowing out of the coil at the same time 1/2 cycle later.

Consider a 1.5WL helical dipole. The two net currents at 0.4WL and 0.6WL
are flowing in opposite directions.

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.
--
73, Cecil http://www.qsl.net/w5dxp



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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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Tdonaly wrote:

Jim Kelly wrote,


Cecil Moore wrote:

Jim Kelley wrote:
Maybe it's a half wavelength long? ;-)

For a real-world air-core coil to exhibit identical currents at the
input and output, it would have to be one wavelength long, lossless,
and non-radiating. That's a pretty tall order just to support an
old wives' tale. :-)

I happily stand corrected.

73 de jk



Pathetic.
73,

Pathetic, best regards?

Please elaborate.

73, Jim AC6XG

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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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

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

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.

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?

:-) That explains a lot, Cecil. It points up another Moral: Don't
write an equation and then forget where you put your point of
reference. Your wave is moving a lot faster than your electrons. Don't
worry about your electrons so much - they'll take care of themselves.

73 de jk

Jim Kelley wrote:

Cecil Moore wrote:
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.

There are only two directions possible for real current in a wire so
real polarity and real phase indeed do mean the same thing. Kraus clearly
agrees. Take a look at Figure 14-4 on page 465 of _Antennas_For_All_Applications_,
third edition. The graph of the current phase is a square wave that jumps
from zero degrees to 180 degrees and back. Between you and Kraus, I choose Kraus.

A wire is one-dimensional with two and only two directions. In what dimension
do the extra phases of the current that you allude to exist? The real part of
I*e^jwt is either positive or negative, i.e. binary. The only possible change
of direction is abrupt. The change in magnitude is not abrupt, but the change
in phase is abrupt, just as Kraus says.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
There are only two directions possible for real current in a wire so
real polarity and real phase indeed do mean the same thing.

Non-sequitur, ad absurdum, ad nausium.

Thank you.

73 de jk

Jim Kelley wrote:
Cecil Moore wrote:
There are only two directions possible for real current in a wire so
real polarity and real phase indeed do mean the same thing.

Non-sequitur, ad absurdum, ad nausium.

So that's your opinion of Kraus? In that freshman class you mentioned
they must have taught you that math models dictate reality. Have you
been a case of arrested development ever since? Don't you realize that,
in a one-dimensional environment, the 'j' operator is really imaginary?
There is no dimension in which j1.0 can actually exist in reality.

The current in a wire at a certain point and time is 0 + j1.0.
Among the electron charge carriers at that point, exactly where
does that j1.0 exist? The physical wire is essentially a one
dimensional environment for those free electrons. In one dimension,
polarity and phase are the same thing. For the current on a standing
wave antenna, Kraus clearly indicates there are only two phase
possibilities, zero and 180 degrees. Maybe you should contact Kraus
and tell him that he is wrong.
--
73, Cecil, W5DXP

Jim Kelley wrote:
Non-sequitur, ad absurdum, ad nausium.

I'm going to let you do the math to convince yourself
that Kraus is correct, given his assumptions about thin
wire antennas.

Assume two traveling-wave currents, each with a maximum
magnitude of 1.0 amps, and flowing in opposite directions.
They are a forward current wave and a reflected current wave,
If and Ir. This will set up a classical current standing wave.
Here are five possible superpositions of those two currents.
('+' is the 0,0 origin)

(1)*********************************************** **************

+------- 1.0 +-------
If = 1.0 at zero degrees Ir = 1.0 at zero degrees

What is the phase of the sum of those two phasors? __________

(2)*********************************************** **************

/ +
/ \
/ \
+ \
If = 1.0 at 45 degrees Ir = 1.0 at -45 degrees

What is the phase of the sum of those two phasors? __________

(3)*********************************************** **************

| +
| |
| |
| |
+ |
If = 1.0 at 90 degrees Ir = 1.0 at -90 degrees

What is the phase of the sum of those two phasors? __________

(4)*********************************************** **************

\ +
\ /
\ /
\ /
+ /
If = 1.0 at 135 degrees Ir = 1.0 at -135 degrees

What is the phase of the sum of those two phasors? __________

(5)*********************************************** **************

-------+ -------+
If = 1.0 at 180 degrees Ir = 1.0 at -180 degrees

What is the phase of the sum of those two phasors? ___________

************************************************** ************

When you guys figure it out, you will realize why Kraus shows only
two possible phases for current in standing wave antennas, zero
degrees and 180 degrees. Everyone who doubts the binary nature of
the phase of standing waves, please post your answers.
--
73, Cecil, W5DXP

Cecil, W5DXP wrote:
"Take a look at Figure 14-4 on page 465 of "Antennas For All
Applications---third edition."

Yes. If you don`t have a copy, you are truly deprived.

Kraus corroborates the square phase diagram in the text. On page 463, he
says: For each length the relative amplitude and phase of the current
are presented for omega prime = 10 and omega prime = infinity
corresponding to total length-diameter ratios (l/a) of 75 and infinity"
(a very thin wire).

What Kraus shows is a center-fed 5/4-wave dipole, 5/8-wave per side, for
maximum gain without production of significant extra lobes.

At 1/2-wave back from the open circuit ends of the dipole, phase moves
up a vertical line from the zero-degree level to the 180-degree level.
This is in the case of the extremely thin wire. For the l/a=75 wire, the
phase change is much more gradual.

Please look at Terman`s Fig. 4-5 on page 94 of his 1955 edition of
"Electronic and Radio Engineering".

Fig. 4-5 is: "Phase relations on a transmission line for two typical
conditions. In these curves, the voltage of the incident wave at the
load is used as the reference phase, and the line attenuation is assumed
to be small."

For the case of the complete reflection, the load is an open circuit as
shown. The reflection coefficient is 1 (one) on an angle of zero. The
reflected wave will be just as strong as the incident wave. The
reflection causes the voltages of incident and reflected waves to have
the same phase at an open circuit. They add arithmetically, and the
total voltage across the open circuit (load) end of the line doubles. In
this case the current of the two waves are equal and of opposite phase
at the open circuit. Thus they add to zero at this point.

At a distance of 1/4-wave back from the open circuit, the incident wave
has advanced by 90-degrees from its phase position at the load, while
the reflected wave has dropped back by the same 90-degrees. The line
voltage from the forward (incident) and reflected waves at this point,
one quarterwave back from the open circuit, are now 180-degrees
out-of-phase. Their sum is nearly zero from a complete reflection on a
nearly lossless line. The currents from the forward and reflected waves
which were out-of-phase at the open circuit are now in-phase, at this
point, 1/4-wave back from the open circuit.

FROM Fig. 4-5(c), the phase line representing the case of a complete
reflection, goes from zero-degrees for the voltages at the open circuit,
and abruptly falls to a 90-degree lead with respect to the incident
voltage at the open-circuit (load).

AT 1/4-wave back from the load, the phase shifts instantly from
90-degrees lead to 90-degrees lag.

At 1/2-wave back from the load, the phase shifts instantly from
90-degrees lag to 90-degrees lead. This flip-flop behavior continues
each 1/4-wave of travel back from the reflection point.

For the case shown for the reflection coefficient of 0.4, the phase
oscillates between leads and lags of 40-degrees, not the 90-degree
limits of the complete reflection case.

The phase reversals in Kraus` Figure 14-4 are analogous to those in
Terman`s figs. 4-5 and 4-7. All show abrupt 180-degree phase shifts
alternating at regular intervals.

Best regards, Richard Harrison, KB5WZI

Jim Kelley wrote:

Cecil Moore wrote:
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?

:-) That explains a lot, Cecil. It points up another Moral: Don't
write an equation and then forget where you put your point of
reference. Your wave is moving a lot faster than your electrons. Don't
worry about your electrons so much - they'll take care of themselves.

That's pretty much the point, Jim. The energy in the wave causes electrons
to pile up closer at some places than at other places. Simply knowing the
probability of the location of the physically bunched electron particles
tells us everything about the waves, much as the vertical mass of water
molecules tells us everything about a water wave. I say vertical mass
because water is somewhat incompressible. Phasor math is not the only
valid way of dealing with AC voltages and currents. Some methods don't
even require the concept of "phase".
--
73, Cecil http://www.qsl.net/w5dxp



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Andy there is an old saying " let the buyer beware"
How much did you PAY Reg for using his software
and did you get what you PAID for ?
Cheers mate
Art

"Andy Cowley" wrote in message
...
Andy Cowley wrote:

"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,


An addition to my last post about Reg's dipole3.exe:-

With these settings l=1, h=6, w=1.5, s=0.2, f=1.8, 'Input resistance' is
given
as 248.4 ohms. Even if it is assumed that all the antenna current flows to
the
end of the wire, the wire resistance can't exceed 0.08 ohms, the correct
figure
being closer to 0.04 ohms, assuming linear current distribution. For a
short
antenna it is obvious that the radiation resistance must be less than that
of
a dipole in free space i.e. less than 73 ohms. That leaves a contribution
of
at least 175 ohms for the ground losses. Increasing height to h=1000
(effectively free space) the ground resistance falls to 136 ohms. There
is something very wrong here. Increasing the wire diameter produces big
reductions in the 'Input resistance'. I feel that the RF wire
resistance/wire
losses are being incorrectly calculated.

I'm fully prepared to be corrected if I'm wrong about this but Reg has so
far
failed to give any satisfactory explanation of the results I obtained. If
I am
wrong, I will, of course , make an unreserved apology to Reg.

Perhaps someone with more skill and knowledge than I have can check what
I've
done? I used EZNEC to simulate an identical aerial and got very different
results.



vy 73

Andy Cowley, M1EBV

Art Unwin KB9MZ wrote:

Andy there is an old saying " let the buyer beware"
How much did you PAY Reg for using his software
and did you get what you PAID for ?
Cheers mate
Art


That's exactly why I said 'Let the user beware' and not the
buyer. I paid Reg nothing and got something worth less than
that. I think a program like dipole3, which Reg proclaims to
be accurate and useful, should do what it says on the tin,
even if it is free. There is plenty of free software that
is reliable and correct. There are plenty of free software
authors who are prepared to explain how their stuff works
and to correct malfunctions. Reg is not among them. I paid
for EZNEC and got very good value for money. The free version
of EZNEC is correct and accurate within its stated limits. I'm
not complaining that Reg is trying to rip people off, he
obviously isn't, just pointing out that not all his stuff
does what he claims it does and that users should be aware
of that.

vy 73

Andy, M1EBV