Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 10:53 AM 9/20/2005, you wrote:
> Original poster: "Dan" <DUllfig@xxxxxxxxxxxxx>
>
> Paul:
>
> Ok, interesting paper. But I have one criticism: I think you give 
> resonance far too little importance. Let me give you an analogy, and 
> see if I can make myself clear.
>
> Suppose you have a flexible beam, solidly held at it's mid point. If 
> you grab one end with your hand, and slowly move one half of the 
> beam back and forth, you will be hard pressed to even detect the 
> slightest motion at the other half of the beam. But if you shake one 
> half of the beam at it's resonant frequency, and the other half has 
> the same resonant frequency, the amplitude of the motion will be 
> nearly identical on both halves, even though nothing is physically 
> shaking the other end.

That flexible beam is actually a pretty high Q resonator, and, 
furthermore, because of its shape, has a limited number of 
vibrational modes that it will support.

The Earth is not even close.


> Let us not forget, Tesla did not even contemplate world power 
> transmission, until he measured standing waves produced by lightning strikes.

Exactly how did he do this?

> Standing waves would mean the EM pulse produced by the lightning 
> strike is being reflected back to the source without much attenuation.

One can have standing waves WITH attenuation (consider a lossy 
transmission line that's not terminated). I measure reflected waves 
that are many 10s of dB below the forward wave all the time at a 
variety of frequencies.  A decent precision RF connector has a VSWR 
of 1:1.01, meaning that it reflects about 1/40,000th of the incident power.

Looking through a 20dB pad into a short would be the same sort of thing.


> This would also mean the EM pulse travels all over the globe before 
> returning. Tesla didn't need the "shaking" in the earth to be 
> particularly strong, he just needed it to travel all over the globe. 
> The only way you can do that is by tuning to the resonant frequency 
> of the earth.

Not true.  Any signal can travel world wide, if it's at a frequency 
where it can propagate.  As a practical matter, this excludes VHF and 
higher. However, the Omega navigation system relied on worldwide 
propagation, as a single mode, of signals around 10-13 kHz.  Typical 
uncertainties in the propagation speed would result in an error on 
the order of one part in 10,000.  HF propagates by skywave 
(reflection of the ionosphere) and is substantially more random.  A 
typical doppler spread in the signal might be 1-5 Hz.

However, it's a long way from world wide propagation to world wide 
transmission of power.


> So I go back to my prior question: Do lightning strikes actually 
> produce standing waves or not ?!

no, they do not.  What lightning does do is put broadband noise into 
a system which has a finite bandwidth.