From page 22.2 of the 2005 ARRL Handbook

"CONDUCTOR SIZE"

"The impedance of the antenna also depends on the diameter of the
conductor in relation to the wavelength. If the diameter of the
conductor is increased, the capacitance per unit length increases and
the inductance per unit length decreases. Since the radiation
resistance is affected relatively little, the decreased L/C ratio
causes the Q of the antenna to decrease so that the resonance curve
becomes less sharp with change in frequency. This effect is greater as
the diameter is increased, and is a property of some importance at the
very high frequencies where the wavelength is small."

Lots of interesting graphs and charts in the ARRL Antenna Handbook as
well.

Roger

wrote in message
ups.com...
From page 22.2 of the 2005 ARRL Handbook

"CONDUCTOR SIZE"

"The impedance of the antenna also depends on the diameter of the
conductor in relation to the wavelength. If the diameter of the
conductor is increased, the capacitance per unit length increases
and
the inductance per unit length decreases. Since the radiation
resistance is affected relatively little, the decreased L/C ratio
causes the Q of the antenna to decrease so that the resonance curve
becomes less sharp with change in frequency. This effect is greater
as
the diameter is increased, and is a property of some importance at
the
very high frequencies where the wavelength is small."

Lots of interesting graphs and charts in the ARRL Antenna Handbook
as
well.
======================================
A nice summary.

But to be more precise, it is the ratio of conductor diameter over
length which matters.

Inductance and capacitance change very slowly with diameter/length.
The changes are hardly noticeable.

L = 0.2 * Length * ( Ln( 4 * Length / Dia ) -1 ) microhenrys.

C = 55.55 * Length / ( Ln( 4 * Length / Dia ) -1 ) picofarads.

Zo = Sqrt( L / C ) = 60 * Ln( 4 * Length / Dia ) -1 ) ohms.

Antenna Q = 2 * Pi * Freq * L / (Distributed Radiation Resistance).

For a half-wave dipole the distributed radiation resistance is 146
ohms, or twice the feedpoint resistance.
----
Reg.

Reg Edwards wrote:
wrote in message
ups.com...

From page 22.2 of the 2005 ARRL Handbook

"CONDUCTOR SIZE"

"The impedance of the antenna also depends on the diameter of the
conductor in relation to the wavelength. If the diameter of the
conductor is increased, the capacitance per unit length increases

and

the inductance per unit length decreases. Since the radiation
resistance is affected relatively little, the decreased L/C ratio
causes the Q of the antenna to decrease so that the resonance curve
becomes less sharp with change in frequency. This effect is greater

as

the diameter is increased, and is a property of some importance at

the

very high frequencies where the wavelength is small."

Lots of interesting graphs and charts in the ARRL Antenna Handbook

as

well.

======================================
A nice summary.

But to be more precise, it is the ratio of conductor diameter over
length which matters.

Inductance and capacitance change very slowly with diameter/length.
The changes are hardly noticeable.

L = 0.2 * Length * ( Ln( 4 * Length / Dia ) -1 ) microhenrys.

C = 55.55 * Length / ( Ln( 4 * Length / Dia ) -1 ) picofarads.


So, if Length / Dia equals e / 4 (about 2.7183), then C = infinite?


Zo = Sqrt( L / C ) = 60 * Ln( 4 * Length / Dia ) -1 ) ohms.

Antenna Q = 2 * Pi * Freq * L / (Distributed Radiation Resistance).

For a half-wave dipole the distributed radiation resistance is 146
ohms, or twice the feedpoint resistance.
----
Reg.



John

John - KD5YI wrote:
Reg Edwards wrote:

wrote in message
ups.com...

From page 22.2 of the 2005 ARRL Handbook


"CONDUCTOR SIZE"

"The impedance of the antenna also depends on the diameter of the
conductor in relation to the wavelength. If the diameter of the
conductor is increased, the capacitance per unit length increases


and

the inductance per unit length decreases. Since the radiation
resistance is affected relatively little, the decreased L/C ratio
causes the Q of the antenna to decrease so that the resonance curve
becomes less sharp with change in frequency. This effect is greater


as

the diameter is increased, and is a property of some importance at


the

very high frequencies where the wavelength is small."

Lots of interesting graphs and charts in the ARRL Antenna Handbook


as

well.


======================================
A nice summary.

But to be more precise, it is the ratio of conductor diameter over
length which matters.

Inductance and capacitance change very slowly with diameter/length.
The changes are hardly noticeable.

L = 0.2 * Length * ( Ln( 4 * Length / Dia ) -1 ) microhenrys.

C = 55.55 * Length / ( Ln( 4 * Length / Dia ) -1 ) picofarads.



So, if Length / Dia equals e / 4 (about .67957), then C = infinite?




Zo = Sqrt( L / C ) = 60 * Ln( 4 * Length / Dia ) -1 ) ohms.

Antenna Q = 2 * Pi * Freq * L / (Distributed Radiation Resistance).

For a half-wave dipole the distributed radiation resistance is 146
ohms, or twice the feedpoint resistance.
----
Reg.




John

So, if Length / Dia equals e / 4 (about .67957), then C = infinite?

====================================
C even goes negative for smaller values of Length/Dia.

I'll let you into a secret - the formulae are approximate and don't
apply when antenna length is less than about 5 times its diameter.

When was the last time you saw an antenna wire only 5 times longer
than its diameter?

Reg Edwards wrote:
So, if Length / Dia equals e / 4 (about .67957), then C = infinite?


====================================
C even goes negative for smaller values of Length/Dia.

I'll let you into a secret - the formulae are approximate and don't
apply when antenna length is less than about 5 times its diameter.

When was the last time you saw an antenna wire only 5 times longer
than its diameter?



You should supply your "secrets" along with your formulae.

You should supply your "secrets" along with your formulae.
=====================================

At my time of life I don't have time to write a book!

You'll just have to read between the lines. ;o)
----
Reg.