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

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Thu, 14 Jul 2005, Tesla list wrote:

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> Ahem. the earth is not a sphere (eccentricity is about 1 part in 300),
> particularly for an EM wave, and it is quite lossy.  If you send an impulse
> out from a point on the earth, and you sit at the antipodes, it will not be
> a nice narrow pulse. This makes the Schumann resonance quite broad.

Doesn't it affect narrow pulses and high frequencies?   Supposedly the
resonance overtones vanish above 10 to 20 KHz, and Earth eccentricity
would be a good explanation for this.  The low overtones, where wavelength
is nearly the size of the earth, those would essentially ignore the
geographic features which are far smaller than the wavelength.  But I
don't know how to figure the frequency above which these effects start to
ruin the resonance.

> As for the tradeoff between size, efficiency, and bandwidth (Q) etc. of
> antennas, you need to look at the work of Chu in 1948 ("Physical
> Limitations of Omni Directional ANtennas" Journ. App. Phys., v19 Dec 1948),
> as well as the dozens of folks following him, although they are mostly
> refining the theory.  If you take the Chu limit as a order of magnitude,
> you won't be far off.  Essentially, all physically small antennas (i.e.
> small compared to a wavelength) have a narrow bandwidth OR low efficiency.

Yep, and Tesla's high-power system would have to be very narrowband, like
single-freq 60Hz power lines, and unlike voice transmissions with big
sidebands.  The challenge is how to design small high-Q receiving
antennas, and how to keep the narrowband tuning from missing the
narrowband transmissions.



> There's also the variability of the height of the ionosphere to consider.
> Before it was decommissioned, Omega navigation relied on the relatively
> stable propagation of waves at around 10-13 kHz, but even there, the nav
> solution needed to take into account the difference in prop delay along a
> night path and a day path.  But even there, you're looking at uncertainties
> on the order of 1 part in 20,000 (which, I grant you, is a fairly high Q)

Aha, some numerical values!  The uncertainties for lower resonances would
be proportionally smaller, no?  But the lower we go, the smaller the
antennas behave, and the higher the Q needed in order to receive
signficant power.  The system probably won't work at all at 7Hz or at
100KHz. Somewhere in between it might become a feasible proposition, or
might not.


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