Re: SSTC As a transmitter.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Jim wrote:
> as far as radiating power uniformly in all directions (i.e. an
> isotropic radiator) goes, they're equally good...The physically
> small radiator will have a low radiation resistance,

Yes, in the language of charge displacements and dipole moments,
we would say that to maintain the moment q*h as you reduce h, you
must increase q accordingly, thus higher current is needed to
displace the larger q in the same quarter-cycle, in other words
a higher current is necessary for the same radiative effect, so
we say there is a lower radiation resistance.

Perhaps we should try to identify the basic problems and fallacies
which lie behind Tesla's proposals.  Browsing through snippets of
Tesla's writings as posted here and there on the web, the
impression gained is that Tesla was concentrating his attention on
the desired effects of charge displacement to a remote location
brought about by conduction currents forced into the ground at the
transmitter.  He seems to describe the effects that might be
expected of a hypothetical monopole charge source, and so far in
my readings I've not seen him address the consequences of the
source in reality being a dipole.  For example, Tesla wrote

 "From my circuit you can get either electromagnetic waves, 
  90 percent of electromagnetic waves if you like, and 10 percent
  in the current energy that passes through the earth. Or, you can
  reverse the process and get 10 percent of the energy in
  electromagnetic waves and 90 percent in energy of the current
  that passes through the earth."

It must be appreciated that it is the dipole moment which allows
energy to be coupled to the field, which in turn carries it
outwards, some to be captured by the effective areas of the
receivers. It is a clear fallacy to pretend that the ground
currents provide an alternative mechanism for energy transport -
one which can work alone, divorced from the EM field.  In this
case, in order to set the ground currents in motion, an E-field
must be set up, and lo and behold, the energy required to establish
that field is just that which Tesla would rather attribute to his
'current energy'.  In short, 'current' doesn't provide an
alternative to 'field' when it comes to transporting electrical
energy.  Whereas an electrician will prefer to say he has volts 
times amps = watts flowing through his wires, a physicist might
prefer to say that the power is quantified by the integral of 
e-field cross h-field over a surface separating source and 
destination.  Both would give the same answer of course, because
it's just the same energy flow being described in two different
ways.

Tesla wrote:
 "...there being no appreciable diminution of the effect with the
 increase of distance from the transmitter."

This is a curious statement, which suggests that Tesla was 
visualising the whole earth surface being uniformly charged and
discharged in an alternating cycle, so that any point on the
surface will experience the same alternating radial (vertical)
E-field strength.  But such a monopole radiator cannot exist due
to conservation of charge.  The charge must be borrowed from
some place else, which would destroy the spherical symmetry and
create some sort of a dipole.   In Tesla's vision, the receiver
would couple to a monopole field radiating out from the earth,
but that vision is faulty because in reality the receiver would
be responding to a dipole field, and thus the performance of each
receiver would depend on its position and orientation wrt the 
dipole.  In view of this, it seems a whole lot depends on where
you borrow the charge from on each half-cycle. A spherical shell
around the earth would do nicely, eg the ionosphere.  The charge
displacement is then set up between the planet's surface and a
conducting layer of the ionosphere, and if the frequency is low
enough all parts of the earth's surface will experience the same
radial E-field in a common phase.  

We now have an interesting situation.  If the ionosphere is a 
good enough conductor (at the operating frequency) it will
confine all the radiation within it's radius.   If the earth is
a good enough conductor (again at the operating frequency), it
will confine the radiation to outside it's radius.  So we have
a spherical shell cavity being forced into excitation (it is not
resonating).  The field within the cavity is not spherically
symmetric because we must have at least one conducting channel
containing a charge pump connecting earth to ionosphere, located
some place on earth, which thus breaks the symmetry, but this is
not a problem if the frequency is low enough.

So if this earth-ionosphere cavity idea corresponds to Tesla's
intentions for a system of global power distribution, then at least
we have an in-principle mechanism for confining the fields which
could satisfy Tesla's claim to uniform distribution.  Of course,
in practice it all depends on whether the earth and ionosphere
wish to cooperate, in terms of their conductivity at the operating
frequency, which would need to be of the order of 1 Hertz.

BTW, you would not wish to operate at any of the resonances of 
this cavity, because that would violate the requirement for uniform
distribution. 

Leaving aside the ionosphere part of it, the earth is only a 
partial conductor and its skin depth - the effective depth to which
EM waves can penetrate, at these frequencies is very deep. For this
reason they're used for comms to submarines.  That represents a
huge volume of the earth's crust, the resistance of which will
couple effectively to the field, and thus absorb vast amounts
of power.  The total effective area of all the worlds receivers
would be hard pushed to compete with all those millions of cubic
miles of rock, soil, and ocean.  

Tesla also seems not to appreciate the size of a receiver that 
would be necessary to draw useful power from such a field. Consider
the volts/metre at the earth's surface necessary to put a useful
voltage across say a man-portable object.  Just like the
transmitter, a small receiver couples to the field in proportion to
its size, and taps capacitively or inductively into the field.
Note that a resonant receiver such as a TC is absolutely no help
here, the effective area of the receiver is fixed by the geometry
of its electrodes - it doesn't care what you connect to its
terminals.  Does Tesla supply any calculations which estimate the
necessary field strength needed at the reception site in order to
carry out his plans? 

 "... to make the little filament glow, the entire surface of
  the planet, two hundred million square miles, must be strongly
  electrified. This calls for peculiar electrical activities,
  hundreds of times greater than those involved in the lighting of
  an arc lamp through the human body"

It doesn't take much calculation to see that huge field strengths
are needed in order to draw a useful amount of current from the
inevitably small collecting area of any practical receiver.  Did
Tesla believe that a resonant receiver would rescue the situation?
If so, then that represents another fallacy. Huge fields strengths
really would be necessary, and the loss factor becomes apparent
when you picture that field impressed across 200 million square
miles of damp soil and salt water, and that's only the surface! 
You have to dig down to below the skin depth to say you've really
reached earth - a long way at 1Hz, and everything above that layer
has that huge field strength across it.  I haven't yet seen
anything in which Tesla addresses these fairly obvious problems.

Aside from the question of losses, did Tesla actually intend to
use the ionosphere in this way?  Or was that something added later
by others?  I'm not sure.

None of the criticisms and fallacies mentioned above are at all
subtle, they are rather obvious faults which would have been put
to Tesla at the time.  Are these documented anywhere?  Where are
Tesla's responses?  These ideas would not have progressed far
through a peer review process, even in Tesla's time.  I note that
most of his comments that we find on the web are taken from patents
and articles intended for the public.  Did he avoid the scientific
process altogether?  

As a fan of LF and ELF reception, it would be interesting to
build a receiver for the 1Hz band.  A short wip antenna and a
high impedance, low pass front-end, followed by an A/D into a PC
would be all that would be required.  It would be interesting to
look at the background field of the earth at these frequencies.
Anyone know of any good websites for ELF spectra?

It's quite easy to make a real sensitive input stage.  I like to
use op-amps and sensitivity is, as Jim says, limited by the
background noise picked up by the antenna rather than the
receiver's electronic noise.  My dual op-amp receiver easily picks
up the whine of an insect's wings several metres from the whip
antenna, along with all the whistles and groans of the planet. 
The violent and brief alternating dipole moments of lightning
discharges all over the planet inject their ripples into the EM
field, which sweep around the earth to land as 'tweaks' in the
receiver.  You can hear a drain-pipe like resonance imposed upon
the snap of the discharge due to the earth-ionosphere cavity.

Another post from Gary just came in.  Some quick comments,
> You end up with a bipolar Tesla Coil with a small capacitance at
> one end and a very large capacitance at the other.  BTW, unlike
> a symetrical bipolar TC which has a voltage node at the very
> center of the secondary, the node will shift in the direction of
> the larger conducting body.

Right.  The half-wave mode of the symmetric bipolar can be 
continuously deformed into the quarter wave of the asymmetric 
'monopole' by a redistribution of the external capacitance to one
end.  This changes the radiation pattern from that of a 
horizontal torus to an inverted cone, angling the far field 
radiation upwards from the horizontal.  It remains a dipole all
the time.

> Some of Tesla's early experiments involved the transmission of
> electrical energy through a single wire, taking advantage of the
> displacement current phenomenon which you referred to earlier.

He would not be able to force a current through a wire without
first creating a field to drive it. In that sense he cannot avoid
taking advantage of a displacement current.

> As for coil losses these can be minimized in a number of ways
> that we can discuss later on. 

I'll take those for granted.  They're perhaps the least of the
problems.  Perhaps better not to use TCs.  Take a mammoth chunk
of piezo material that mechanically resonates at the operating
frequency.  Mechanically couple it to the ocean surface to 
extract sea wave energy at 1Hz, turning it straight into HV AC.

> I believe it will be found that ground-conduction losses are
> associated primarily with the quality of the local ground
> connections at the transmitter and receiver sites.

Wishful thinking I'm afraid.  A usable field strength must be
available at the receiver site, and unavoidably, that field
strength is impressed across the entire surface, and all the
lossy material in it.  

> The point is that with a Tesla system you can couple your
> receiver directly to the energy source and ignore the EM
> radiation component.

That seems to be the crux of the error. It's really the field
that's doing the business, and the radiation is inevitable and
essential.  You can guide it to your destination with wires or
you can confine it to a volume as I've shown above, or you can
just let the dipole radiation escape.  The last case is obviously
wasteful, the cavity case is also wasteful, because although 
it contains the energy within the enclosed volume, losses go up in
proportion.  Only the wire-guided (transmission line) approach
gives you a usable efficiency because it confines the energy to
narrow channels rather than spreading it over a wide area. 

> I agree, the isotropic cap will have to be big and high to
> acheive the best results.

Yes, but remember, it is not an isotropic cap, it is half of a
dipole.  The earth is the other half.  

Incidentally, nowhere it seems in any of this power transmission
stuff is the phenomena of resonance really necessary.

Ralph Zekelman wrote:
> thank you for your many excellent discussions.

Hey, thanks. Glad some of it makes sense. I can only rattle on as
I do because we can be sure there are several list members who'll
quickly pounce if I make even the slightest mistake.  For that
unique and precious attribute of this list we have others to thank.

Sorry for the long post, but these things seem to need clarifying.
--
Paul Nicholson
--