Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 02:20 PM 9/19/2005, you wrote:
> Original poster: "Dan" <DUllfig@xxxxxxxxxxxxx>
>
> Ok, everyone keeps talking about near and far field effects, EM, 
> electrostatics, etc. But in a cable, power is transmitted quite 
> effectively by a current, without the need of any other effect.

In that cable, there are both electric and magnetic fields.  An 
electric field along the length of the cable (which causes the 
current flow) and a magnetic field around the cable.



> As far as I can tell, no one has actually DISPROVEN that currents 
> cannot be conducted through the earth.

Of course current can be conducted through the earth. Single wire 
telegraph is but one example, using the earth as the return 
conductor. Some HVDC transmission links use the earth as a standby 
return in case one wire breaks.

However, *efficiently* transmitting power from "a point" to "a point" 
is pretty difficult, given the resistive and lossy nature of the 
earth (or EM propagation through space for that matter).

The challenge isn't just the moving energy from one place to another 
(radio transmitters and receivers do it with no real problems).  It's 
moving it efficiently (in commercial terms).


> There is a lot of talk of why we THINK it cannot be done, but until 
> someone actually tries it, we won't know for sure. From my reading 
> of Tesla's writings, it looks like a minimum setup to prove one way 
> or the other would be:
>
> tesla coil operating in CW mode, properly grounded, no spark 
> emissions, frequency tuned to a whole multiple of the earth's 
> diameter ( so the earth is in resonance with the transmitter ). 
> Receiver of similar construction, situated so it is not sitting on a 
> node of the standing wave.
>
> Don't forget that all throughout history there have been things that 
> we "knew couldn't be done" until we tried them :)

This isn't that category.  We know it can be done, it IS done on a 
day to day basis, but it's not a particularly economic way to move power.

And, the particular example you cite has been done, numerous times, 
at a whole variety of frequencies, in the course of geophysical 
prospecting, and the loss from transmitter to receiver is tremendous. 
If you can't transmit significant power 100 meters or 10 km, clearly 
you're not going to get to the antipodes.

Also, the earth is hardly a homogenous sphere. The idea of a "nodes" 
or "standing waves" presumes a nice resonant structure with uniform 
propagation speeds.   Such does not exist for the earth.  Perhaps on 
a more homogenous structure?  Jupiter has icy moons (Callisto, 
Ganymede) that are fairly uniform, and very close to spherical.