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Re: 7.1Hz, how the heck did Tesla succeed?

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 11:35 AM 7/15/2005, Tesla list wrote: 
Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
  But received power
> depends on receiver Q, and isn't fixed by antenna length.

That is news to me. Energy has to be collected and the bigger the
collector....  I thought received optical power depended on the amount of
light intercepted (e.g. solar cells to put it into an electrical context).

It's the difference between effective aperture and physical aperture. A resonant structure can have an effective aperture larger than it's physical aperture. A straightforward example is a resonant dipole/doublet anntenna made of thin wire. It might be physically 0.5 wavelengths long and 0.001 wavelengths in diameter, but the effective aperture (based on the amount of power it will collect) will be on the order of 1/8 square wavelength, a lot more than the .005 square wavelength the antenna physically occupies.

There IS a limit of course and it's related to the Q of the system.


> Why should it remain fixed?

Tesla considered the earth to be a spherical conductor of "limited
dimensions" and those dimensions do not substantially change. The Schumann
cavity is something I thought wasn't known to Tesla but I may be wrong. In
the context of his considerations nothing should have changed much if at all.

Doesn't even have to be a cavity (in the sense of two nested shells), if you're talking about ground wave propagation (i.e. propagation "attached" to a boundary between materials). The 7-8 Hz bump can be nicely explained by simple propagation time (but, I guess, that's what resonant structures are all about).

By the way, the non-spherical nature (which would tend to kill the Q of the resonance) of the Earth was known in Tesla's time. Clarke developed the standard ellipsoid that is the basis of most maps we use today in 1866. Newton argued for Oblate (flat at the poles). The Cassinis (a whole family of them) argued for Prolate (pointy at the poles) in the late 1600s. The French measured it in the mid 1700s. It's oblate.



  The real question is *how much* does it
> wander (a tiny percentage, or a significant amount?)  I've seen papers
> that mention significant frequency changes over spans of months, so
> these changes are possible.  If there were significant random changes
> over a span of seconds, then this would appear on spectrum
> measurements as an artifact: a falsely wide resonance band, and a
> falsely low Q.  See
> http://www.pupman.com/listarchives/1995/january/msg00002.html

Uhh.. I don't know that you can have a "high Q" resonator with "small random frequency changes". I suppose if you define Q as the energy stored vs the energy lost in one period, it would work. Imagine an oscillator with a rechargeable battery... It could be very crummy spectrally, but still only lose a tiny fraction of the stored energy in each cycle, but this isn't the usual definition of Q as applied to resonators.

There are high Q resonators with small changes in frequency: Cesium beam clocks are a good example.. Very, very stable in the long run, but pretty bad in the short run.