"K7ITM" wrote in message
...
On Oct 22, 9:52 pm, "John KD5YI" wrote:
"Richard Harrison" wrote in message

...



Mike, N3LI wrote:
"Why would the velocity be less at increased (antenna element) width?"

Let B = the phase velocity on the antenna element, in radians per unit
length. 2pi/B = wavelength on the element.
Therefore, 2pi/B=velocity of phase propagation.
Due to the behavior of of open-circuited transmission lines and
open-circuited antennas:
B=2pif times sq.rt. of LC radians / unit length.

2 pi f / B = velocity of propagation.

It is intuitive that a fat antenna element has more L & C than a thin
element and thus a lower velocity of propagation.

Best regards, Richard Harrisob, KB5WZI

Hmmmm... my straight wire inductance equation from the ARRL handbook
indicates smaller wire diameters have larger inductance.

???

73,
John

Not surprisingly, that's what E&M texts say too--or leave as an
exercise. With a larger diameter, there's less net magnetic field for
a given current, so less energy stored, so less inductance.

Cheers,
Tom


So, then, it isn't intuitive (to me, at least) that a fat antenna has more
inductance. Intuitive to me is that the reverse may be true.

Cheers to you, too, Tom.

John

John Wood, N4GGO wrote:
"---or intended such as Andrew`s "Radiax" brand of leaky transmission
line for installation in tunnels and elevator shafts as a convenient
means to extend the reach of over-the-air broadcasts."

Similar results are obtained more cheaply by replacing the Radiax with
300-ohm twin-lead.

Best regards, Richard Harrison, KB5WZI

Mike, N3LI wrote:
"I thought that the inductance tends donward as the diameter of the wire
increases. I can understand your calculation after the wavelength part,
but don`t quite get the increased inductance part."

Good observation.

Wire inductance decreases with the circumference increase as this
effectively places more parallel inductors in place along the surface of
the wire.

Wire capacitance increases proportionally with the square of the
circunference of the wire as it is proportional to the wire`s surface
area.

The fatter wire grows capacitance faster than it changes inductance.

Reactance along a wire antenna element varies quickly near resonant and
antiresonant points so is not uniformly distributed. This complicates
calculations and requires average values for some. Bailey says of surge
impedance: "Nevertheless, this variation in theoretical surge impedance
shall not deter us from setting uup practical "average" values of surge
impedance.
Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Mike, N3LI wrote:
"Why would the velocity be less at increased (antenna element) width?"

Let B = the phase velocity on the antenna element, in radians per unit
length. 2pi/B = wavelength on the element.
Therefore, 2pi/B=velocity of phase propagation.
Due to the behavior of of open-circuited transmission lines and
open-circuited antennas:
B=2pif times sq.rt. of LC radians / unit length.

2 pi f / B = velocity of propagation.

It is intuitive that a fat antenna element has more L & C than a thin
element and thus a lower velocity of propagation.

Best regards, Richard Harrisob, KB5WZI


If B is the 'phase velocity' then surely it's also the 'velocity of phase
propagation' so that's not 2pi/B? The velocity of propagation of an
electromagnetic wave, be it the phase or group velocity, is most-strongly
dependent on the permittivity and permeability of the medium in which the
wave is propagating.

Another clue to resolution of this issue is that the terminal impedance of
an open circuit stub has a slope with respect to frequency that depends on
the characteristic impedance of the stub. For the case of a cylindrical
dipole, the characteristic impedance is not constant but increases
progressively along the lengths of the limbs, but the slope of the terminal
impedance can be related to an 'average characteristic impedance' and the
value of this parameter depends on the average distributed inductance and
capacitance, as has been said here before. Z = sqrt(L/C) in general terms.

The self-inductance of a conducting cylinder has been shown fairly
rigorously by some (e.g. Rosa, and used by Terman) to be inversely
proportional to its radial 'thickness' but this appears to be a contentious
issue and can lead the unwary user into a paradox!

Chris

On Thu, 23 Oct 2008 07:01:18 -0400, (J. B. Wood)
wrote:

In article , Richard Clark
wrote:

Lest there be any confusion: an antenna IS a transmission line.


Hello, and I think one would have to include two antennas and the
intervening medium(s) for the above statement to make sense.
....
Over a range
of frequencies the behavior of this 2-port can easily differ from that of
a transmission line, though.

It would appear your first sentence is contested by your last sentence
in your reply. It follows, then, that changing my statement through a
speculative inclusion introduced a problem not already in the
original. When we withdraw your inclusion to suit your complaint, we
are again left with my original.

What you are arguing is a failure of application, not a failure of the
device. I've seen similar arguments that forced terms of transformer
or transducer into the mix to show how they fail. I find the terms
suitable in a casual discussion, but the new minted failures occur on
the basis of forcing definitions when the casual applications worked
just fine.

One can, by a simple twist of the oscillator's frequency knob, find
failure in all analogues of antennas, lumped circuits, and
transmission lines. Those failures are not exotic perturbations in
the 5th decimal place, but simple and utter refusals to conform to a
general rule (such as my bald statement). For any attempt to refute
my bald statement with "proven concepts" will reveal those challenging
concepts built on a foundation of sand by a similar token of counter
proof.

73's
Richard Clark, KB7QHC

On Oct 23, 10:35*am, (Richard Harrison)
wrote:
Mike, N3LI wrote:

"I thought that the inductance tends donward as the diameter of the wire
increases. I can understand your calculation after the wavelength part,
but don`t quite get the increased inductance part."

Good observation.

Wire inductance decreases with the circumference increase as this
effectively places more parallel inductors in place along the surface of
the wire.

Wire capacitance increases proportionally with the square of the
circunference of the wire as it is proportional to the wire`s surface
area.

The fatter wire grows capacitance faster than it changes inductance.

Reactance along a wire antenna element varies quickly near resonant and
antiresonant points so is not uniformly distributed. This complicates
calculations and requires average values for some. Bailey says of surge
impedance: "Nevertheless, this variation in theoretical surge impedance
shall not deter us from setting uup practical "average" values of surge
impedance. *
Best regards, Richard Harrison, KB5WZI

I know we're talking about linear antennas here, but even in that
case, it's surely not true that capacitance increases as the square of
the wire diameter (or radius or circumference); nor inductance
proportional to 1/diameter. Consider that if both those were true,
doubling the wire diameter would quadruple the capacitance and halve
the inductance, and the propagation velocity along that wire would be
1/sqrt(4*0.5) or about .707 times as great as with the thinner wire.
Clearly things change much more gradually than that.

In the controlled environment of a coaxial capacitor, the capacitance
per unit length is proportional to 1/log(b/a), where a is the inner
conductor diameter and b is the inside diameter of the outer
conductor. If you change b/a from 10000 to 5000 (huge outer diameter,
like a thin wire well away from ground), the capacitance increases by
about 8 percent. Going from b/a = 100000 to 50000, the capacitance
increases by a little over 6 percent. Similarly, inductance in coax
is proportional to log(b/a), so in coax as you change the inner
conductor diameter, the capacitance change offsets the inductance
change exactly and the propagation velocity is unchanged. The
environment of an antenna wire is different than that, but not so
different that doubling the wire diameter has a drastic 30% effect on
the resonant frequency.

Cheers,
Tom

In article , Richard Clark
wrote:

On Thu, 23 Oct 2008 07:01:18 -0400, (J. B. Wood)
wrote:

In article , Richard Clark
wrote:

Lest there be any confusion: an antenna IS a transmission line.


Hello, and I think one would have to include two antennas and the
intervening medium(s) for the above statement to make sense.
...
Over a range
of frequencies the behavior of this 2-port can easily differ from that of
a transmission line, though.

It would appear your first sentence is contested by your last sentence
in your reply.
snip
Hello, Richard, and all. And as I previously pointed out the 2-port model
might not be the equivalent of a line in a broadband sense. Another way
to put it would be that the 2-port could have the electrical
characteristics (characteristic impedance, delay, loss) of a particular
line at one frequency but of a different line at another frequency.

Please excuse my snipping of the remainder of your comments but they sound
more of philosophy than science and quite frankly I have no idea what
you're talking about. You emphatically stated an antenna "IS" a
transmission line without a few words on why this should be so.

My take on a transmission line (or waveguide) is that it is a medium
(ideally lossless) used to convey electromagnetic energy from one place to
another. An antenna (or antenna array) is used to introduce or extract
electromagnetic energy from a medium. Unlike the power available at the
output of a low-loss transmission line, a receiving antenna operating at a
far-field distance from a transmitter can only extract a macimum of 1/2
the power available from an incident electromagnetic wave.

Now, if you meant that antennas and transmission lines share phenomena in
common (e.g. standing waves) that would be a correct statement. And
Maxwell's equations certainly apply to both. But I don't see an
equivalency of a single antenna and a non-radiating (at least intended by
design) transmission line and I don't recall any of my many
electromagnetics texts making such a statement. Sincerely,






What you are arguing is a failure of application, not a failure of the
device. I've seen similar arguments that forced terms of transformer
or transducer into the mix to show how they fail. I find the terms
suitable in a casual discussion, but the new minted failures occur on
the basis of forcing definitions when the casual applications worked
just fine.

One can, by a simple twist of the oscillator's frequency knob, find
failure in all analogues of antennas, lumped circuits, and
transmission lines. Those failures are not exotic perturbations in
the 5th decimal place, but simple and utter refusals to conform to a
general rule (such as my bald statement). For any attempt to refute
my bald statement with "proven concepts" will reveal those challenging
concepts built on a foundation of sand by a similar token of counter
proof.

73's
Richard Clark, KB7QHC

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

K7ITM wrote:
On Oct 23, 10:35 am, (Richard Harrison)
wrote:
Mike, N3LI wrote:

"I thought that the inductance tends donward as the diameter of the wire
increases. I can understand your calculation after the wavelength part,
but don`t quite get the increased inductance part."

Good observation.

Wire inductance decreases with the circumference increase as this
effectively places more parallel inductors in place along the surface of
the wire.

Wire capacitance increases proportionally with the square of the
circunference of the wire as it is proportional to the wire`s surface
area.

The fatter wire grows capacitance faster than it changes inductance.

Reactance along a wire antenna element varies quickly near resonant and
antiresonant points so is not uniformly distributed. This complicates
calculations and requires average values for some. Bailey says of surge
impedance: "Nevertheless, this variation in theoretical surge impedance
shall not deter us from setting uup practical "average" values of surge
impedance.
Best regards, Richard Harrison, KB5WZI

I know we're talking about linear antennas here, but even in that
case, it's surely not true that capacitance increases as the square of
the wire diameter (or radius or circumference); nor inductance
proportional to 1/diameter. Consider that if both those were true,
doubling the wire diameter would quadruple the capacitance and halve
the inductance, and the propagation velocity along that wire would be
1/sqrt(4*0.5) or about .707 times as great as with the thinner wire.
Clearly things change much more gradually than that.

Trying to make a "readers Digest" version here....

If I'm following so far:

The lowered frequency of resonance is due to changes in the velocity factor.

The lowered vf is somewhat due to increased capacitance, and an increase
in inductance - the latter part I'm still trying to grok. I think there
is likely something more going on.

I'm still left with the increased bandwidth phenomenon. None of the
above would seem to account for this.

I've been working with mobile antennas for the past several months, and
I might be going astray, because I keep thinking about increased
bandwidth as a partner of lowered efficiency. Not likely the case here.


Thanks to everyone for the help, while I'm happy to accept the obvious
real results, It is even better if I can understand what is going on.


- 73 de Mike N3LI -

J. B. Wood wrote:


Hello, and I think one would have to include two antennas and the
intervening medium(s) for the above statement to make sense. In any
...
John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

Absolutely, such as two antennas stuck into a superconducting media,
which extends in all directions to the point of seemingly infinite
distances.

A rather unique way of viewing the phenomenon, and rarely presented in
such terms. Yet, quite valid, nonetheless.

Regards,
JS

Tom, K7ITM wrote:
"The environment of an antenna wire is different from that, but not so
different that doubling the diameter has a drastic 30% effect on the
resonant frequency."

Thanks to Tom for his observation. It makes sense to me. I was wrong.

Best regards, Richard Harrison, KB5WZI