Re: SSTC As a transmitter.

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

Original poster: "Gary Peterson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <glpeterson-at-tfcbooks-dot-com>

> Maxwell's equations were well established by Tesla's time, and we
> can be sure that he did not want the transmitter to radiate any
> more than necessary beyond the targeted receiver, . . .

Even the slightest amount radiation from the vertical conductor of a
Tesla-type transmitter is undesirable as the wave energy is dissipated into
space and becomes, for the most part, unrecoverable.

> . . . but to avoid
> radiation altogether is to avoid broadcasting power.  What perhaps
> Tesla failed to appreciate is that to send an electric influence
> from one place to another requires radiation.  EM radiation is the
> essential mechanism here, not just an undesirable side-effect.

Tesla

     "Pardon me, you are mistaken."

Counsel

     "That is what I want you to explain.  I must be mistaken,
because my conception does not fit in with your statements."

Tesla

     "All right, I will explain that.

     "In my first efforts, of course I simply contemplated to
disturb effectively the earth, sufficiently to operate instru-
ments.  Well, you know you must first learn how to walk before
you can fly.  As I perfected my apparatus, I saw clearly that
I can recover, of that energy which goes in all directions, a
large amount, for the simple reason that in the system I have
devised, once that current got into the earth it had no chance
of escaping, because my frequency was low; hence, the electro-
magnetic radiation was low.  The potential, the electric
potential, is like temperature.  We might as well call
potential electric temperature.  The earth is a vast body.
The potential differences in the earth are small, radiation is
very small.  Therefore, if I pass my current into the earth,
the energy of the current is stored there as electromagnetic
momentum of the vibrations and is not consumed until I put a
receiver at a distance, when it will begin to draw the energy
and it will go to that point and nowhere else. . . ."

> The TC transmitter is an electrode at height h connected to earth
> through some sort of a charge pump, eg a secondary coil.  If the
> pump displaces a charge q between the earth and topload, then it
> exerts a dipole moment q*h on the EM field.  News about that
> dipole's existence and its subsequent changes of value with time,
> propagate outward from the dipole as variations in the EM field,
> ie EM waves.  It is the history of EM wave output from the dipole
> radiator which establishes the instantaneous E-field gradient at
> any potential receiving point.

That explains what takes place on and around the vertical conductor, but
that's only half of the story.  Let's take a look at an entire Tesla-type
system modeling it as a modified bipolar Tesla coil.  Start with a few
primary turns.  Next add a vertical coil, a vertical conductor and a topload
for one half of the oscillator.  Next envision an open vertical shaft
directly below it with one or more ground rods in the form of iron pipes
driven either horizontally or further downward from the shaft's bottom, and
then connect a vertical conductor from the bottom of the coil down to the
iron-pipe ground connection.  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.  Tesla explained it this way:

    "Consider now the effect of such a conductor of vast dimensions on a
circuit exciting it. The upper diagram of Fig. 6 illustrates a familiar
oscillating system comprising a straight rod of self-inductance 2L with
small terminal capacities cc and a node in the center. . . ."

http://www.tfcbooks-dot-com/writings/images/wireless-06.gif

". . . In the lower diagram of the figure a large capacity C is attached to
the rod at one end with the result of shifting the node to the right, thru a
distance corresponding to self-inductance X. As both parts of the system on
either side of the node vibrate at the same rate, we have evidently, (L+X)c
= (L-X)C from which X = L(C-c/C+c). When the capacity C becomes commensurate
to that of the earth, X approximates L, in other words, the node is close to
the ground connection.  The exact determination of its position is very
important in the calculation of certain terrestrial electrical and geodetic
data and I have devised special means with this purpose in view. . . ."

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.  Here is what Tesla wrote as this
relates to his system:

    "Granted, then, that an economic system of power transmission thru a
single wire is practicable, the question arises how to collect the energy in
the receivers. With this object attention is called to Fig. 5, . . .

 http://www.tfcbooks-dot-com/writings/images/wireless-05.jpg

". . . in which a conductor is shown excited by an oscillator joined to it
at one end. Evidently, as the periodic impulses pass thru the wire,
differences of potential will be created along the same as well as at right
angles to it in the surrounding medium and either of these may be usefully
applied."

The point is that with a Tesla system you can couple your receiver directly
to the energy source and ignore the EM radiation component.  Sky wave or
surface wave eminating from the elevated vertical conductor, who cares? as
long as every single one of your circuits is precisely in tune with the
others.  As for coil losses these can be minimized in a number of ways that
we can discuss later on.  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.

> [regeneration] implies a power source local to the receiver, enabling some
> sort of positive feedback to assist with signal recovery.

Yes, possibly involving a local oscillator as well.

> Without an antenna, a TC has a limited dipole moment and would not
> be expected to broadcast far. . . .

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

> The important factor now is the size of the signal
> at the receiver compared with the background noise at the
> receiver.

I believe the S/N ratio will be found to be quite favorable compared to
short-wave systems.

> We are not discussing two alternative mechanisms here,
> when we talk about radio comms with EM waves, versus TC comms with
> ground/displacement currents, . . .

That's right.

    "It is just like this:  I have invented a knife.  The
knife can cut with the sharp edge.  I tell the man who applies
my invention, you must cut with the sharp edge.  I know per-
fectly well you can cut butter with the blunt edge, but my
knife is not intended for this.  You must not make the antenna
give off 90 percent in electromagnetic and 10 percent in cur-
rent waves, because the electromagnetic waves are lost by the
time you are a few arcs around the planet, while the current
travels to the uttermost distance of the globe and can be
recovered. . . ."

> . . . By comparison with what we
> use nowadays, Tesla's wireless proposals seem primitive and naive.

We'll see.

Gary Peterson