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>

Gary Peterson wrote:
> I believe Tesla knew there would be a surface wave associated
> with the conduction current.  And, he did refer to an EM
> radiation component from the elevated structure as loss.

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, 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.

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.  The size of the transmitting
dipole moment determines how well it couples to the field, and
thus determines the extent to which any receiving structure will
couple to the transmitter. You increase the transmitting dipole
moment by either increasing h (higher topload) or increasing q 
(bigger topload) for a given pressure of charge pump.  If we reduce
the transmitter topload height, the dipole reduces by the same
proportion, but then so does the E-field gradient available at 
all receiver sites. Thus the coupling coefficient to all receivers
is reduced in the same proportion, loss resistances stay the same,
so efficiency goes down. 

However it's done, electrical energy transfer from A to B boils
down to guiding energy in the form of EM waves from source to
destination.  It all a matter of how you direct that energy.  Do
you broadcast it over a wide area (thus wasting most of it) or do
you choose to beam or guide it to its preferred destination -
that's the only real choice you have. 

> a vertical conducting rod extending about 1800 feet above the
> earth's surface and excited at a frequency of 136 kHz would be
> a fairly efficient radiator.

Certainly would.

> a much shorter Tesla-type transmitting structure, say, about 50'
> overall height... would not be as efficient a radiator.

Indeed. 

> It it reasonable to assume the capture area could be increased
> by some technique that would increase RF current flow in the
> receiver coil, such as regeneration?

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

>  I still not convinced the telecommunications application is
> real.

Without an antenna, a TC has a limited dipole moment and would not
be expected to broadcast far.  Note that with signal transmission
rather than power transmission, the criteria is no longer one of
efficiency.  The important factor now is the size of the signal
at the receiver compared with the background noise at the
receiver.  If the former is sufficient wrt the latter, then 
information encoded in the signal can be extracted.  This is a much
easier proposition than trying to deliver useful power to the same
distance.

But remember, you cannot draw any fundamental distinction between
a movement of charge and the EM field which accompanies it.  You
cannot divorce the two and you're perfectly free to regard the 60Hz
power coming out of your wall socket as arriving there as a guided
EM wave.  We are not discussing two alternative mechanisms here,
when we talk about radio comms with EM waves, versus TC comms with
ground/displacement currents, or for that matter, telegraphy  or
power transmission with wires.  In all cases it is a matter of how
much, and by what mechanism, the EM field is confined and guided.

At base level, charges and their fields are indelibly linked.  If
you want to send an electric influence from A to B, then like it
or not radiation must take place (for that is the influence that
carries the energy and information), and it is up to you to
confine it in such a way that most of it arrives where you want it.
Tesla never said how to do this.  He was happy to broadcast power
over a wide area without hope of ever being able to receive more
than a small fraction of it.  We choose instead to guide the EM
waves to their particular destinations using a sophisticated
pattern of conductors - the grid.  By comparison with what we
use nowadays, Tesla's wireless proposals seem primitive and naive.
--
Paul Nicholson
--