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Re: Goubou line, "G-line" (was Tesla Coil RF Transmitter)

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 10:19 AM 9/15/2005, you wrote: 
Original poster: William Beaty <billb@xxxxxxxxxx>

On Wed, 14 Sep 2005, Tesla list wrote:

> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> G-line is not a simple wire.  It has a dielectric coating (usually
> polyethylene) on the outside and the launchers establish a radial
> electric field which then propagates with low loss on the outside of the
> highly conducting center conductor to the receiving "launcher".  Can't
> imagine any such action with the earth because it's so lossy and the
> dielectric constant of the atmosphere is indistinguishable from one.

Heh!  You're wrong, since experiment beats theory: if the wave-guiding
effect was real, wouldn't it be used?  It's used today.  The military
maintains a network <snip>


Uh. AM broadcast also uses vertically polarized radiators and surface wave.

However, neither of those are "guided waves" in the same sense that G-line works. In G-line, the EM propagation is "within" the dielectric. You can guide a wave within anything where there's some boundary that reflects. Fiber optics is a fine example and that same concept (containing a wave within a dielectric immersed in something else with a different epsilon) is used at millimeter waves.
In these cases, the difference in dielectric constant (or index of refraction) results in reflection at shallow enough angles. The practical problem is that the dielectric is lossy. You could also build a waveguide with dielectric walls and do basically the same thing. All you need is the interface.

Then, you can guide a wave through a space defined by conductive surfaces (classic microwave waveguide), or, semiconductive surfaces (VLF signals carried in a "waveguide" between ionosphere and earth's surface). Again, it's the mismatch at the "wall" that makes it work. Here, though, the loss is in power lost into the wall (IR losses in one sense, although you can also look at it as the wall having a reflection coefficient <1, so the transmission coefficient is >0)

There HAS been some work with propagating a wave that is "attached" to the surface of a dielectric.

http://www.nasatech.com/Briefs/Apr01/NPO21001.html

Since it doesn't penetrate the dielectric, it's very low loss. This is different than the evanescent waves familiar to antenna engineers. It's also different than so-called "whispering gallery" modes.



In this G-line stuff, what's important is the wave-guiding "restoring
force" which makes the waves follow the conductor even if the conductor is
slightly curved.  If the "force" was weak, then waves would only follow
the wire if it was curved very gently.  The curve of the earth is only 130
feet of deflection for each 10 miles traveled If Tesla managed to "launch"
some vertically polarized VLF waves out across the earth, would they
follow the earth or fly out into space?  They're KNOWN to bend around the
Earth, at least the 150KHz waves do.

One might be careful here. Just because you receive a signal doesn't mean that a) the wave has actually propagated by the means you suggest or b) that the bending is entirely due to what you suggest. Refractive effects are well known (to the point where when you do microwave path calculations, you assume that the earth is 4/3 its actual diameter).

You can propagate a signal by "surface wave" without any bending going on.



The old articles on UHF/microwave G-line setups showed that the G-line
didn't need to be straight; it could be bent with a many-inches radius
curve over tens of degrees over several feet... But only if they added a
thicker dielectric coating to the cable: a plastic rod about 1" across.
Without the thick plastic rod, only a larger radius bend was allowed. What
happens with no dielectric at all? I received email from an engineer
claming that G-line still works fine if you don't use a plastic coating,
and also claiming the math shows that resistive effects in the metal will
create a wave-guiding effect.  (So a superconductor wire wouldn't work?)
But he didn't quote me any papers that go into this rigorously.




It does make sense though, since any rod which slows the waves below c
will also tend to focus them slightly inwards toward the rod, which keeps
them following the rod.  That's essentially how the "director" elements of
a Yagi antenna work: they absorb and re-radiate the incoming waves but
with phase delay, so the row of "director" elements acts like a dielectric
rod made up of giant resonant atoms all in a row.  Also I've seen articles
about microwave waveguides based on dielectric rods, where the rod is much
thinner than a quarter wavelength, so the microwave field is mostly
outside the rod, yet is still guided by the rod. Sort of like "optical
fiber," but with the fiber thinner than a wavelength of light.