[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

Original poster: Mark Fergerson <mfergerson1@xxxxxxx>

Tesla list wrote: 
Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
Hi Bill,
On 13 Sep 2005, at 22:30, Tesla list wrote:
 > Original poster: William Beaty <billb@xxxxxxxxxx>
 >
 > On Sun, 11 Sep 2005, Tesla list wrote:
 >
 >  > Original poster: Ed Phillips <evp@xxxxxxxxxxx>
 >  >
 >  > 3 -- given the above statements, why is it so hard for anyone to >
 >  believe that Tesla was transmitting by conduction through the earth,
 >  > and not propagation through the air?! Just becuase you CAN transmit
 >  > RF through the air, doesn't mean it is the ONLY way to do it."
 >
 > This isn't quite correct.  RF energy cannot flow through conductors.
 > After all, whenever we send electrical energy down a piece of coax or
 > a length of lampcord, both the coax and the lampcord function as
 > waveguides, and the electromagnetic energy is flowing through the
 > space outside the metal and not flowing inside the conductors.  The
 > current is in the metal, yet the flowing energy is in the space
 > nearby.


  Now we're getting somewhere; Poynting vector-land.

 > If Tesla successfully used the Earth to transmit VLF energy from place
 > to place, the energy had to have flowed through the air, not through
 > the Earth.  Yes, the EM energy was associated with electric currents
 > in the Earth's surface.  And the EM energy would be constrained to
 > follow the Earth's surface.  But electrical energy doesn't move
 > through conductors. Look at microwave waveguides (the hollow
 > rectangular type), where the currents are in the metal surface, while
 > the RF energy is in the hollow center of the pipe.  Coax and twinlead
 > are similar, and they still behave as waveguides regardlesss of
 > frequency.

Since they also confine waves so that their fields self-interact, the direction they carry power in depends on the phase relationship between those interacting waves, which depends (among other things) largely on the guides' physical dimensions.

But AIUI a G-line differs in that the guided waves don't necessarily self-interact the same way.

 > Or in other words, *ALL* electrical energy is the same thing as "radio
 > waves."  Electrical technology is all based on propagating EM fields
 > guided by electric circuits.  The only difference is in our minds:
 > when electromagnetism is guided by some wires, we concentrate on the
 > currents in the wires, ignore the surrounding field, and we call it
 > "electrical energy." But when it flys off an antenna and crosses empty
 > space, we call it "radio waves."  Yet the energy is made of
 > space-filling EM fields in either case.  Similarly, the only
 > difference between a power supply and a radio transmitter is...  the
 > radio transmitter is connected to an antenna. So Tesla's system was
 > using the Earth as a waveguide in somewhat the same way that the
 > electric utility companies use copper wire as waveguides.


 > Here's where it gets weird.  Perhaps Tesla's system did not actually
 > take advantage of the Ionosphere at all.  After all, in the microwave
 > waveguide system called the "Goubou Line" or "G-line," there is an
 > electric current in a single conductor, and the EM waves are guided by
 > that conductor.  A "G-line" system is fed by conventional coax cable,
 > but then the coax shield is flared out into a horn shape called the
 > Launcher, and the center conductor continues on alone.  At the far end
 > is another "horn," the Catcher, which leads to the shield of normal
 > coax.  In between the horns the single wire has no return path, just
 > as there is no return path in optical fibers or in rectangular
 > microwave waveguides.  Or, from an e-field standpoint, the single wire
 > functions as it's own return path, since the fast-moving regions of
 > positive and negative charge on the long "G-line" wire are connected
 > together by electric field lines.


  So basically we're talking vertically-polarized ground waves?

 > An analogy:  if electric circuits are like drive belts wrapped around
 > pulleys, then Tesla's system was sending sound waves along a single
 > length of stretched rope.  When frequency is high, no closed circuit
 > or return rope is neeed.


  Nice analogy; think I'll steal it. ;>)

 > If Tesla's system is similar to microwave G-line, then the Earth's
 > ionosphere plays a less significant role, since the single conductor
 > itself is the only necessary part.  But in that case, the "launching
 > horn" is the important part.  The smaller the horn, the worse the
 > impedance match, and the harder it becomes to send electrical energy
 > along the single wire.


  So the line is effectively as wide as it is long and nonuniformly lossy.

 > Hmmm, I wonder what happens if we actually try sending signals along a
 > couple hundred feel of coax cable, but we strip off the shield braid
 > in a fifty-foot length in the middle of the cable?  Well, I guess it
 > would only be a fair test if we used 100MHz signals or higher, so 50ft
 > is many wavelengths long.  Also use ungrounded signal generator and
 > detector, so there's no earth-return path.  Could we light a light
 > bulb over such a transmission line?  (Of course put a tank circuit on
 > the light bulb to take advantage of resonant matching effects.)

Tesla did this regularly in his lectures, though not at 100 MHz. He noted there were effects on the brilliance of individual lamps as people moved about (nonuniformly lossy dielectric, too; walking persons would analogize to mobile lossy inhomogeneities in the dielectric).

I would argue that a single wire is really just the "centre" conductor
of a two wire transmission line with the "outer" conductor (if one wants
to liken it to coax) having a rather large radius. I don't see any
way of avoiding some coupling to the surroundings, relatively distant
though they may be.

"Relatively distant" is a key point. You're describing coax with infinite shield radius and a dielectric constant averaging unity. What's its cutoff wavelength?

Analyzing (actually, analogizing) Tesla's World Power System as a G-line makes the Wardenclyffe tower's segmented toroid the "launch horn" (except it would launch waves downward, not up as in the ionospheric-conduction scenario; note that the tower was conical, not cylindrical!) and as Bill mentions being small WRT Earth's diameter make a lousy z-match to the "line", the nonuniformly lossy Earth itself. A catcher (Tesla coil in "recieve mode") would necessarily be smaller than the launcher and make an even worse z-match.

An antinode in Wardenclyffe's induced field would be the ideal site for a catcher, but the z-match would still be poor.

  Well, the idea hangs together, but doesn't seem all that practical.


  Mark L. Fergerson