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Re: Tesla Coil RF Transmitter

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 09:53 AM 9/23/2005, you wrote: 
Original poster: William Beaty <billb@xxxxxxxxxx>

On Tue, 20 Sep 2005, Tesla list wrote:

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

But the finite-bandwidth peaks are caused by standing waves!

One can have a band limited system with no standing waves. A lumped LC is a fine example.
ANother is one where there are frequency selective effects, e.g. dispersion or absorption.
I suppose one could argue that there is some form of standing wave in the molecules causing absorption lines in an optical spectra, but it's not a cavity resonance.


OK...  where Earth's tuned cavity is concerned, can you explain the
difference between a standing wave, versus "broadband noise in a system
which has a finite bandwidth?"

These are simply two ways to describe the same phenomenon: if a tuned
cavity has a Q which is high enough to produce a significantly finite
bandwidth at a fundamental frequency (and at overtone frequencies,)
standing waves must be present.  A standing wave is the same as two waves
propagating in opposite directions, and in a driven tuned cavity we have
waves propagating through each other in opposite directions.

Only if the propagating wave is absorbed as it moves, falling deep into
noise so it never makes a complete trip around the earth, only then would
no standing waves be present.  But then no cavity resonance effects and no
narrowband peaks would be observed either.

If the phenomonon causing the absorption is frequency dependent, then one could observe a peak in the broadband noise without any overall cavity resonance being present.

If I tune across the HF band and record the background noise level, it has peaks and valleys. But the peaks and valleys are not representing resonance modes, but, rather, the geographical distribution of the noise source (lightning) convolved with the propagation paths supported from those locations. Likewise, the increase in background noise level at 7 MHz during the day isn't due to some funky resonance coming and going, but merely that the ionosphere is more ionized and supports propagation from where the lightning is.


Perhaps the original question was about CONTINUOUS standing waves.  A
lightning strike would cause an exponential ring-down, like striking a
bell.  While the cavity was ringing, standing waves would exist, but their
amplitude would be exponentially decreasing with time.

The percentage bandwidth of a bell is substantially higher than the 8 Hz noise data.

In order to have a "resonance", I think you have to have a situation where the energy stored in the system is greater than the energy lost per cycle.