Tom Ring wrote:
I don't believe a single bare wire will operate as a transmission line
in free space.

Let's say we have a 1/2WL dipole in free space driven by a
self-contained source at the center. If we float a florescent
light bulb around the ends of the dipole, are you saying the
electric fields won't fire the bulb like it does on earth?
--
73, Cecil http://www.qsl.net/w5dxp

Some more info he http://www.answers.com/topic/goubou-line

If you search for Goubou line AND Goubau line, you can find lots more.
Older editions of "Reference Data for Radio Engineers" had design info
on them.

The losses, as with any good line, are mainly due to I^2*R loss in the
wire. The current is lower than it would be for the same wire in coax,
for a given power, and thus the loss is lower. "YMMV" when it rains,
or when the line gets coated with soot and grime.

I believe I've seen it described as "quasi-TEM". Clearly if you look
immediately next to the wire, you'll find magnetic field symmetrically
encircling the wire, and electric field is always perpendicular to good
conductors so the electric field is radial. That's the same as in
coax, but if you look at the article Tom posted a reference to, you'll
see that the field lines do not remain perpendicular to the wire
further out.

Cheers,
Tom

K7ITM wrote:
Some more info he http://www.answers.com/topic/goubou-line

If you search for Goubou line AND Goubau line, you can find lots more.
Older editions of "Reference Data for Radio Engineers" had design info
on them.

The losses, as with any good line, are mainly due to I^2*R loss in the
wire. The current is lower than it would be for the same wire in coax,
for a given power, and thus the loss is lower. "YMMV" when it rains,
or when the line gets coated with soot and grime.

I believe I've seen it described as "quasi-TEM". Clearly if you look
immediately next to the wire, you'll find magnetic field symmetrically
encircling the wire, and electric field is always perpendicular to good
conductors so the electric field is radial. That's the same as in
coax, but if you look at the article Tom posted a reference to, you'll
see that the field lines do not remain perpendicular to the wire
further out.


According to Goubau's original paper [1] the mode is a surface wave
which is attached to the wire, but decays over a distance of a few
wavelengths sideways from the wire. Unlike a normal TEM wave, the energy
in this surface wave remains confined to its cylindrical near field, and
does not radiate into the far field. Its only direction of long-distance
propagation is along the wire, which is what makes it usable for
transmission-line purposes.

The surface wave also has the rather odd property that on a bare wire of
infinite conductivity, it will not propagate at all! However, it will
propagate successfully if the wire is coated with a magnetic or a
dielectric material, and for practical applications Goubau favoured
various forms of insulated wire.

The practical problem is that the surface wave requires a feedhorn of
several wavelengths in diameter, to selectively excite this particular
mode without also exciting the radiating TEM mode. Out along the wire,
any disturbance to the propagating fields tends to cause mode conversion
back into TEM, which makes the G-line revert to radiating like any
normal wire antenna. When the wire is viewed as a transmission line, any
far-field radiation represents a loss.

To sum up, the G-line surface wave is very different from the normal TEM
waves around an isolated wire. Unless you take specific steps to excite
this particular mode, it won't occur at all, so it isn't relevant to the
main topic under discussion.



[1] Georg Goubau, 'Single-conductor Surface-Wave Transmission Lines'.
Proc IRE, June 1951, pp 619-624.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Tue, 25 Apr 2006 09:06:24 +0100, "Reg Edwards"
wrote:

Richard, your use of the English language is HIGHLY approximate and
therefore prone to errors greater than 59 percent.
----
Reg.

I'm sorry Reggie, Old Son, but being a native speaker does not elevate
your opinion to that of expert. In fact, your being British is the
single most negative mark against you in that respect. Your precision
is merely adequate to conversing with the corner grocer - luckily your
software code does not tolerate such abiquity. We would have far more
intelligent conversations with you if you stuck with Pascal instead.
Even the sewer rats of Rio would notice you had something to say.

73's
Richard Clark, KB7QHC

Cecil Moore wrote:

Tom Ring wrote:

I don't believe a single bare wire will operate as a transmission line
in free space.


Let's say we have a 1/2WL dipole in free space driven by a
self-contained source at the center. If we float a florescent
light bulb around the ends of the dipole, are you saying the
electric fields won't fire the bulb like it does on earth?

Stop acting like an idiot Cecil.

tom
K0TAR

It's a mistake to think that just because an antenna looks like it has
one wire (although it really always has two) that it bears any
similarity to a G line in operation. Whatever mode a G line effects, it
isn't the same as an antenna -- a G line doesn't radiate significantly
unless bent or improperly constructed.

Roy Lewallen, W7EL

Tom Ring wrote:
Tom Donaly wrote:


What is the transmission mode in a single conductor transmission line?

That is a good question. I'd never thought about it. Anyone here have
experience with G Line?

tom
K0TAR

Ian White GM3SEK wrote:
snip
To sum up, the G-line surface wave is very different from the normal TEM
waves around an isolated wire. Unless you take specific steps to excite
this particular mode, it won't occur at all, so it isn't relevant to the
main topic under discussion.


Ian,

Thanks for the explanation. It was very helpful as well as concise.

And I didn't think it had much to do with the main topic when I diverted
to this one, except for the phrase "single wire transmission line", but
that never stopped anyone else here before!

tom
K0TAR

Regarding the use of English, I will interpret your opening line as
excluding Tom and me from the ranks of nitpickers. Thank you for the
comma.

Indeed, we build our world on approximations. Even Maxwell and friends
gave us only approximations, though ones that are far better than we
need for the things we do with our HF or even microwave antennas.

But if I'm given two DIFFERENT ways to approximate the same thing, and
they give me VERY different answers, then I'd like to understand the
situation better. In other words, I'm exactly interested in that art
you mention, and in being able to judge when others claim to know that
art but in fact do not. They can try to lead me astray, but I don't
have to let them.

In other words, if you or anyone else gives me answers, directly or
through graphs or computer programs or whatever, I'd like to be able to
judge the validity of those answers for what I'm trying to accomplish.
I trust that's not a goal you'd disagree with, but perhaps you will.

I also am much more wary of people who just give answers with no
indication of the degree to which they are approximations, than I am of
people who explain that their answers are approximations and to what
degree and why they are.

In this case, I happen to think that it's worthwhile understanding WHY
the DC capacitance isn't very useful in the dynamic situation of an
antenna. Thankfully, for those who can't figure that out for
themselves, there are some decent explanations kicking around.

Cheers,
Tom

Reg, G4FGQ wrote:
"I`m even more certain you will find an equation for inductance of an
isolated wire of length L: and diameter D somewhere in the bibles."

Equation 14 on page 48 of Terman`s 1943 edition of "Radio Engineers`
Handbook is:

Lo = 0.00508 l (2.303 log 4l/d - 1+mu/4) microhenrys

Lo is the (approximate) low-frequency inductance and the dimensions are
in inches.

Terman also gives the (approximate) low-frequency inductance formula of
a single-layer solenoid on page 55 of the same book.

One can find the resonant frequency of the coil when using a known
capacitance to resonate the coil at a low frequency. Maybe a dip meter
could be used. Capacitive and inductive reactances are equal at
resonance. Self and stray capacitances are included with the known value
of capacitance used to resonate the coil at the low frequency. The
resonant frequency is lower than the known capacitance by itself would
produce.

The resonance formula used with the actual inductance of the coil will
give the capacitance of the resonant circuit

The difference between the calculated capacitance and the known
capacitor value is equal to the stray and self-capacitance total, so it
is good to minimise stray capacitance when seeking the self-capacitance
value of the coil.

An ARRL Single-Layer Coil Winding Calculator is a slide rule which makes
things easy.

Best regards, Richard Harrison, KB5WZI

That's all very nice. Let's see if it's useful for anything.

A while back, Cecil posted a model of a base loaded vertical antenna. It
has an inductor which is vertically oriented. The bottom of the inductor
is 1 foot from the ground and the inductor is 1 foot long and six inches
in diameter. Inductance is 38.5 uH and it's self resonant at 13.48 MHz.
(Moving it very far from ground changes the resonant frequency to 13.52
MHz.)

What's it's velocity factor, and how did you calculate it?

Roy Lewallen, W7EL


Richard Harrison wrote:
Reg, G4FGQ wrote:
"I`m even more certain you will find an equation for inductance of an
isolated wire of length L: and diameter D somewhere in the bibles."

Equation 14 on page 48 of Terman`s 1943 edition of "Radio Engineers`
Handbook is:

Lo = 0.00508 l (2.303 log 4l/d - 1+mu/4) microhenrys

Lo is the (approximate) low-frequency inductance and the dimensions are
in inches.

Terman also gives the (approximate) low-frequency inductance formula of
a single-layer solenoid on page 55 of the same book.

One can find the resonant frequency of the coil when using a known
capacitance to resonate the coil at a low frequency. Maybe a dip meter
could be used. Capacitive and inductive reactances are equal at
resonance. Self and stray capacitances are included with the known value
of capacitance used to resonate the coil at the low frequency. The
resonant frequency is lower than the known capacitance by itself would
produce.

The resonance formula used with the actual inductance of the coil will
give the capacitance of the resonant circuit

The difference between the calculated capacitance and the known
capacitor value is equal to the stray and self-capacitance total, so it
is good to minimise stray capacitance when seeking the self-capacitance
value of the coil.

An ARRL Single-Layer Coil Winding Calculator is a slide rule which makes
things easy.

Best regards, Richard Harrison, KB5WZI