Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Dan" <DUllfig@xxxxxxxxxxxxx>

Jim:

Two issues to bring up. First, earth as a resonator:

Standing waves are THE definition of resonance in a sphere. There is 
no known mechanism by which a sphere can show increased response to 
certain frequencies, and not have standing waves. When you look at a 
Schumann resonance spectral chart, you see peeks in frequency 
response that correspond very nicely with what would be expected if 
you divide the speed of light by the circumference of the earth. But 
you are saying that these peaks are due to some not-yet-explained 
phenomena. Your implication fails Occam's razor too! ( they don't 
call it "Schumann Resonance" for nothing :)

The only reason you don't want to accept that the earth resonates, is 
that you are not comfortable with the implication: global power 
distribution. You say the attenuation is too great, that the earth 
has a low Q. But if waves don't make it all the way around the earth, 
there are no standing waves. And without standing waves, there is no 
resonance. Without resonance, the earth would have equal frequency 
response to all frequencies, BUT IT DOESN'T!

Second, LC tank circuits as lumped circuits:

There is a tendency to think that just because a formula accurately 
predicts the outcome of an event, that the formula "explains" what is 
going on. This is not so.

Just because lumped circuit calculations can predict the resonant 
frequency of an LC tank circuit, does not mean that an LC tank is a 
lumped circuit. At resonance, the electrical charge is bouncing back 
and forth between the two sides of the capacitor, passing through the 
inductor on its way back and forth. By definition, the voltage HAS to 
be higher at the capacitor plates than it is at the center turn of 
the inductor coil. You admitted as much without even realizing: you 
said that there was uneven current distribution. Lumped circuit 
calculations assume up front even current distribution!

These kind of approximations are done in physics all the time, 
because the difference between an approximation, and an accurate 
description, is so small that the extra effort is a waste of time. 
The formula for the period of a pendulum only holds true for small 
arcs of swing. When we push a car, we figure out acceleration by 
assuming it is going in a straight line, but in fact it is moving in 
a 17500 km circle! An LC tank circuit at resonance is not really a 
lumped circuit, but the lumped circuit calculations give numbers that 
are so close, why bother with more accurate formulas? But never 
forget that lumped circuit calculations are approximations that give 
reasonable numbers, not a description of what is going on.

Dan

----- Original Message -----
From: <mailto:tesla@xxxxxxxxxx>Tesla list
To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
Sent: Sunday, September 25, 2005 2:34 AM
Subject: Re: Tesla Coil RF Transmitter

Original poster: Jim Lux <<mailto:jimlux@xxxxxxxxxxxxx>jimlux@xxxxxxxxxxxxx>

At 12:08 PM 9/24/2005, you wrote:
>Original poster: "Dan" <<mailto:DUllfig@xxxxxxxxxxxxx>DUllfig@xxxxxxxxxxxxx>
>
>Jim:
>
>Any resonant system will exhibit standing waves at certain frequencies.

What standing wave occurs in a lumped LC circuit?  There's reactive
power circulating, but not really a standing wave, which sort of
implies "propagation".

For that matter, is there a standing wave in a standard spark gap
tesla coil?  Nope.. a couple lumped LC circuits (albeit with some
uneven current distribution, etc.), not many waves travelling in that
primary. Yes, one CAN model the system as a complex transmission
line, but it fails the Occam's razor test.

>I have a feeling you are of the oppinion that the earth has no
>resonant mode or frequency. Is this so, and why?

Actually, the point was that just because you observe a bandlimited
phenomena, it's not necessarily because there's a resonance.  It
might be, and it might not. The observation itself does not provide
sufficient information to discriminate.

Sure, the earth has nice low Q resonant modes, but I don't think that
implies a standing wave.  I think the Q is so low that the system is
overdamped.