On Oct 20, 5:57*pm, Jim Lux wrote:
....
Some might argue, though, that the reason the effective velocity is less
is because the sqrt(1/LC) term is smaller because C is bigger because of
the increased surface area. *And that might not be far from the truth
for a restricted subset of antennas.

On the other hand, the propagation velocity of coaxial cable of
constant outer conductor ID is independent of the inner conductor
diameter, even though the capacitance per unit length increases as the
inner conductor diameter is increased. Clearly one must be careful
about attributing the effect to a single cause like increased
capacitance.

I haven't noticed in this thread any reference to Ronold W. P. King's
work. His writings should give more insight into the subject, if you
can get deeply enough into them. It's discussed empirically in
"Transmission Lines, Antennas and Waveguides," (with lots and lots of
interesting graphs showing the effect from various viewpoints) but you
can probably go deeper into the theory than you need in his other
books and papers on linear antennas.

Cheers,
Tom

K7ITM wrote:
On Oct 20, 5:57 pm, Jim Lux wrote:
...
Some might argue, though, that the reason the effective velocity is less
is because the sqrt(1/LC) term is smaller because C is bigger because of
the increased surface area. And that might not be far from the truth
for a restricted subset of antennas.

On the other hand, the propagation velocity of coaxial cable of
constant outer conductor ID is independent of the inner conductor
diameter, even though the capacitance per unit length increases as the
inner conductor diameter is increased. Clearly one must be careful
about attributing the effect to a single cause like increased
capacitance.

Which was the original intent of my comment. Fat radiators are shorter
at resonance than thin ones, and the details of why are not simply
explained by something like "capacitance effects", although such an
explanation may sort of work over a limited range.

Jim Lux wrote:
K7ITM wrote:
On Oct 20, 5:57 pm, Jim Lux wrote:
...
Some might argue, though, that the reason the effective velocity is less
is because the sqrt(1/LC) term is smaller because C is bigger because of
the increased surface area. And that might not be far from the truth
for a restricted subset of antennas.

On the other hand, the propagation velocity of coaxial cable of
constant outer conductor ID is independent of the inner conductor
diameter, even though the capacitance per unit length increases as the
inner conductor diameter is increased. Clearly one must be careful
about attributing the effect to a single cause like increased
capacitance.

Which was the original intent of my comment. Fat radiators are shorter
at resonance than thin ones, and the details of why are not simply
explained by something like "capacitance effects", although such an
explanation may sort of work over a limited range.

Sorry, been away for a while, but I'm back.

Certainly the capacitance may play some small part. But does added
capacitance increase bandwidth to the extent - or at all - that is
achieved by the cage or very thick dipole?


Richard Harrison's reference to Baily regarding velocity is interesting.
Why would the velocity be less at increased width? And would that
increase the Bandwidth?


- 73 de Mike N3LI -

Michael Coslo wrote:
Jim Lux wrote:
K7ITM wrote:
On Oct 20, 5:57 pm, Jim Lux wrote:
...
Some might argue, though, that the reason the effective velocity is
less
is because the sqrt(1/LC) term is smaller because C is bigger
because of
the increased surface area. And that might not be far from the truth
for a restricted subset of antennas.

On the other hand, the propagation velocity of coaxial cable of
constant outer conductor ID is independent of the inner conductor
diameter, even though the capacitance per unit length increases as the
inner conductor diameter is increased. Clearly one must be careful
about attributing the effect to a single cause like increased
capacitance.

Which was the original intent of my comment. Fat radiators are
shorter at resonance than thin ones, and the details of why are not
simply explained by something like "capacitance effects", although
such an explanation may sort of work over a limited range.

Sorry, been away for a while, but I'm back.

Certainly the capacitance may play some small part. But does added
capacitance increase bandwidth to the extent - or at all - that is
achieved by the cage or very thick dipole?

Nope.. that's why "increased capacitance" is a bad model.



Richard Harrison's reference to Baily regarding velocity is interesting.
Why would the velocity be less at increased width? And would that
increase the Bandwidth?

larger C per unit length makes 1/sqrt(LC) smaller
no for the BW

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

"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

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

"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

Richard Harrison wrote:
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.


I thought that the inductance tends downward 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.


- 73 de Mike N3LI -

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