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>

I wrote:

>> If you want propagation over long distances, then
>> you need to be encouraging radiation, surely?

Gary Peterson wrote:

> Not if you're trying to reproduce the results which Tesla
> reported so assertively.

Except that he never reported any results.  The idea is flawed,
but Tesla couldn't see that. 

Let me try and describe the situation re power transfer.

Tesla wanted to force current through the ground such that to the
earth, it would appear as a monopole radiator, ie a point source of
alternating charge at the earth connection.  This alternating
point source would cause a conduction current to ebb and flow
radially from the earth terminal, thereby inducing alternating
currents in a receiving ground terminal. 

However, conservation of charge means that a monopole radiator
cannot exist in nature (the term 'monopole' used by radio engineers
to describe a vertical radiator is a misnomer).  Wherever a 
collection of say +ve charge is assembled, it must be drawn from
somewhere, which leaves an equal and opposite quantity of -ve
charge behind.  Thus whenever you try to construct a monopole
radiator, you find you actually have a dipole instead.  In this
case, the charge forced into the earth is drawn from the topload,
and when you look at this, you see that the ground current flowing
out from the 'monopole ground terminal' is matched by an equal
displacement current returning from the ground surface back to the
topload.  Thus we have a complete AC circuit which allows energy to
be coupled to some device tapped into this loop, eg a receiver TC.

So far so good.  Real power can be transferred over a distance by
displacing charge in this way.  But displacing charges takes 
energy - the conduction currents in the ground turn some of it 
into heat, and both the conduction current and the displacement
current cause EM energy to be radiated.  Tesla was arguing that a
suitable arrangement of transmitter could be made to stir up the
necessary charge displacements in the ground without loosing
significant power to either EM radiation or to ohmic losses. This
is realistic only for cases in which the transmitter is intended
to deliver power to nearby receivers.

The difficulty becomes apparent when you look at the efficiency of
the transfer.  At short ranges (much less than a free-space
wavelength) the arrangement can be modeled by an equivalent
circuit, such as

     (TX topload)------------||-----------(RX topload) 
           |          |      Cc       |         |
           |          |               |         |
        [TX coil]    ===Ct           ===Cr   [RX coil]
           |          |               |         |
           /          /               /         /
           \Rt        \Rtg            \Rrg      \Rr
           /          /               /         /
           \          \               \         \
           |          |       Rc      |         |
   -----------------------\/\/\/\/\--------------------
   ///////////////////////////////////////////////////////

I've shown various resistances which represent coil losses and
ground conduction losses.  Ct and Cr represent the bulk topload
capacitances of each resonator, and Cc is the coupling capacitance.
Rr is the receiver's loss resistance which includes the useful 
load.  

The coupling coefficient is Cc/sqrt(Ct*Cr) and at ranges greater
than about a topload-height, Cc becomes very small compared with
Ct, so that the receiver only intercepts a small proportion of the
transmitter's circulating current.  Even at these short ranges,
the majority of the input power is dissipated in the transmitter's
loss resistance Rt and the ground losses represented by Rtg. If
at the same time you demand a high loaded Q factor in the receiver
coil, you'll get a similar decimation of efficiency added in there.

The upshot is that the efficiency is lousy, even at very short
range.  This is so, even if the transmitter is small compared
with the wavelength so that there is negligible far field
radiation.   

At longer ranges - a wavelength of more, we can no longer describe
the system by a simple equivalent circuit and it becomes better to
think in terms of the capture area of the receiver coil.  This
area, which might be a few hundred sq metres for a large receiver
will only intercept an amount of power proportional to its capture
area divided by (4*pi*range^2). Thus the coupling coefficient is
very small indeed for any decent range.

So realistically, you must forget power transfer, signals yes, but
useful power no.

However, there are ways around this.  The transmitter could
focus its radiation in the direction of the receiver, eg using
dish antennas, but these are impractical except at high frequency.
For low frequencies, some sort of waveguide can increase the
coupling dramatically.  One way to do this is to string a
conductor between transmitter and receiver.  Currents induced in
this wire guide the waves efficiently to the receiver.  As it
happens if you look at the currents and voltages induced in this
wire, they happen to be exactly what you'd expect from an 
overhead transmission line - it makes no difference if you think
of a line carring power by virtue of its voltages and currents, or
if you regard it as a guide for energy carried in the EM field. 
So it's fine to think of the connecting conductor as a guide to
the radiated energy which concentrates it at the receiver. In a
sense, we are already using Tesla's power distribution scheme,
continent-wide, but with the enhancement of guided waves[*].
Without this or some other mechanism, the coupling at any useful
range is minute and the efficiency almost zero.

Another way to get around the small coupling coefficient is to
enclose the entire system of transmitter and receiver, and the
space in between, inside a lossless cavity.  Then the cavity can
fill with radiation to a point where the tx and rx are in
equilibrium as far as their exchange of energy is concerned. 
Efficient power transfer under these conditions is only possible
with a high-Q cavity, but the sometimes proposed cavity between
earth and ionosphere is far too lossy to qualify, at any frequency.

And as for EM radiation - if you want a transmitting TC to spread
it's displacement current field over a range anything approaching
a wavelength or above, then you cannot avoid significant EM
radiation...

Gary wrote:
> http://www.tfcbooks-dot-com/writings/w_system.htm.

...unless that is you believe in some of the pseudoscience in the
cranky books for sale here?  21st century snake oil! Caveat emptor.

And I wrote:
> And what is meant by a 'slow-wave' resonator?  Does the adjective
> mean anything?

Jim wrote:
> Some structure along which a wave propagates at less than free
> space. 

For EM waves, that applies to all physical structures.  Can you
make a fast-wave helical resonator?  Hence my feeling that the
term is redundant, although it sounds impressive.

Jim wrote:
> Corums used the terminology when describing their (now
> deprecated) theories of TC function (basically a 1/4 wave
> transmission line much shorter than free space 1/4 wave because
> propagation is in a "slow wave structure").. 

I disagree, that's about the only bit they got right in their
'Class Notes' paper.  The rest is worthless or wrong.

> Terry's measurements of voltage and current phase at top and
> bottom of secondary, and your modeling work, have pretty much
> shot that theory down. 

Terry's phase measurements in fact are quite consistent with the
representation of a solenoid as a transmission line, or as a lumped
element - take your pick. They neither confirm nor refute that
part of Corum's theories. The unequivocal confirmation comes from
the existence of a mode spectrum rather than just a single
resonance.

[*] And Tesla wrote:
> you will use a very low frequency so that the loss in these
> electromagnetic waves . . . should be minimized. . . .

which at 50-60Hz we do indeed!
--
Paul Nicholson
--