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>

> > Tesla liked to use proportionately tall helical resonators when
> > an application required sharpness of tuning.  This would also
> > help get the isotropic cap up into the air without having to use
> > an excessively long vertical conductor, which would be a source
> > of that undesirable electromagnetic radiation.
>
> So the long vertical conductor would radiate but not the tall
> vertical coil :))   In fact the EM radiated from the TC is
> proportional to the amount of charge displaced into the topload
> during each RF half cycle, and the height of the topload.
> Radiation is very little unless the topload height is a non-
> negligible fraction of a free-space wavelength.  At say 150kHz,
> a topload at 100 metres elevation would give you 1/20th of a
> wavelength and you would surely need a license at that point.

I don't know if Tesla was ever able to completely solve the problem EM
radiation emanating from the vertical conductor.  I'm sure he would have
liked to accomplish this.  Read what he had to say in 1916 about his system:

    ". . . the apparatus which I devised was an apparatus enabling one to
produce tremendous differences of potential and currents in an antenna
circuit.  These requirements must be fulfilled, whether you transmit by
currents of conduction, or whether you transmit by electromagnetic waves.
You want high potential currents, you want a great amount of vibratory
energy; but you can graduate this vibratory energy.  By proper design and
choice of wave lengths, you can arrange it so that you get, for instance, 5
percent in these electromagnetic waves and 95 percent in the current that
goes through the earth.  That is what I am doing.  Or, you can get, as these
radio men, 95 percent in the energy of electromagnetic waves and only 5
percent in the energy of the current.  Then you are wondering why you do not
get good results.  I know why I do not get good results in that way.  The
apparatus is suitable for one or the other method.  I am not producing
radiation in my system; I am suppressing electromagnetic waves.  But, on the
other hand, my apparatus can be used effectively with electromagnetic waves.
The apparatus has nothing to do with this new method except that it is the
only means to practice it.  So that in my system, you should free yourself
of the idea that there is radiation, that energy is radiated.  It is not
radiated; it is conserved. . . ." - Nikola Tesla On His Work With
Alternating Currents, pp. 132-133.

> > It would be nice to have a lower frequency allocation, say in
> > the area of 73 kHz
>
> If you're not using EM radiation, you don't need the license. You
> just need to convince the inspector that you're using a non-EM
> radiation :)

True, the intention is to suppress the EM radiation but it's difficult to
eliminate completely.  Even if you view the radiated component as loss and
as being undesirable you will still be aware of its existence.  It now
becomes a matter of debate as to whether you are an intentional radiator.

> During the '70s some radio amateurs were keen on what they called
> 'earth mode' communications, which basically involved pumping lots
> of LF power circa 20kHz into the ground, using two electrodes set
> into the ground quite some distance apart.  The receiver uses
> a similar pair of electrodes to pickup up the differential voltage
> due to the current field in the earth excited by the transmitter.
> As you can imagine the signal strength falls off very rapidly with
> range.

There are people still doing that.  I think 4 or 5 miles is considered a
good result.

> > I'm interested in seeing the results of real-world propagation
> > studies that involve the use of slow-wave helical resonators and
> > elevated capacitances.
>
> If you're interested in power transmission, try measuring the
> coupling coefficient between two TCs as a function of range. The
> coupling will fall away very rapidly (about the same as the earth
> current mode mentioned above).  As the topload is raised, the
> coupling falls away less rapidly, and eventually you end up with
> the topload a quarter-wave above ground and a coupling proportional
> to 1/range^2 at long distances, in which efficient radiation is
> occurring.

My primary interest is in energy transmission for telecommunications
purposes.  Geophysical exploration also rates high on the list.

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

I'm a little vague on that as well.  Perhaps someone else on the list can
explain it?

> > ...that undesirable electromagnetic radiation.
>
> Undesirable?   If you want propagation over long distances, then
> you need to be encouraging radiation, surely?

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

> On the whole, a non self-oscillating CW TC should make quite a
> good exciter for a short (wrt wavelength) wire antenna.  The
> high impedance at the top of the coil is appropriate for the
> high radiation resistance of the short wire.  A low frequency
> antenna tuner correctly set up to match a transmitter into a
> short wire would look a lot like a base-fed TC.

I'm going out on a limb again, but it's my understanding very best results
will be obtained when the transmitting apparatus is configured in such a way
as to absolutely minimize radiation resistance.  Look at the things "radio
men" do to maximize radiation resistance and consider doing the opposite.
The two which come quickly to mind are 1) position the helical resonator
very close to the ground and connect the lower terminal to the very best
ground connection that you can afford, and 2) keep your vertical conductor
electrically short and top load it.

> --
> Paul Nicholson
> --

Gary


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, July 24, 2002 11:35 AM
Subject: Re: SSTC As a transmitter.


>
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
>
> Gary Peterson wrote:
>
> > what impedance does the lower end of a magnifying transmitter's
> > extra coil see, looking towards ground?
>
> Anything from several 10s of ohms up to several hundred ohms.
>
> > Tesla liked to use proportionately tall helical resonators when
> > an application required sharpness of tuning.  This would also
> > help get the isotropic cap up into the air without having to use
> > an excessively long vertical conductor, which would be a source
> > of that undesirable electromagnetic radiation.
>
> So the long vertical conductor would radiate but not the tall
> vertical coil :))   In fact the EM radiated from the TC is
> proportional to the amount of charge displaced into the topload
> during each RF half cycle, and the height of the topload.
> Radiation is very little unless the topload height is a non-
> negligible fraction of a free-space wavelength.  At say 150kHz,
> a topload at 100 metres elevation would give you 1/20th of a
> wavelength and you would surely need a license at that point.
>
> > It would be nice to have a lower frequency allocation, say in
> > the area of 73 kHz
>
> If you're not using EM radiation, you don't need the license. You
> just need to convince the inspector that you're using a non-EM
> radiation :)
>
> During the '70s some radio amateurs were keen on what they called
> 'earth mode' communications, which basically involved pumping lots
> of LF power circa 20kHz into the ground, using two electrodes set
> into the ground quite some distance apart.  The receiver uses
> a similar pair of electrodes to pickup up the differential voltage
> due to the current field in the earth excited by the transmitter.
> As you can imagine the signal strength falls off very rapidly with
> range.
>
> > I'm interested in seeing the results of real-world propagation
> > studies that involve the use of slow-wave helical resonators and
> > elevated capacitances.
>
> If you're interested in power transmission, try measuring the
> coupling coefficient between two TCs as a function of range. The
> coupling will fall away very rapidly (about the same as the earth
> current mode mentioned above).  As the topload is raised, the
> coupling falls away less rapidly, and eventually you end up with
> the topload a quarter-wave above ground and a coupling proportional
> to 1/range^2 at long distances, in which efficient radiation is
> occuring.
>
> And what is meant by a 'slow-wave' resonator?  Does the adjective
> mean anything?
>
> > ...that undesirable electromagnetic radiation.
>
> Undesirable?   If you want propagation over long distances, then
> you need to be encouraging radiation, surely?
>
> > The lowfers use a technique called coherent CW which I think
> > uses WWV to synchronize transmitters and receivers.
>
> Yes, WWV, and in UK, the MSF, can be used to sync both the
> carrier frequencies and modulation phase at each end.  Extremely
> narrow bandwidths can be used to enhance signal/noise ratio, and
> the limitation here tends to be phase distortion during
> propagation, which sets a limit to the minimum reciever bandwidth
> in any given situation.
>
> On the whole, a non self-oscillating CW TC should make quite a
> good exciter for a short (wrt wavelength) wire antenna.  The
> high impedance at the top of the coil is appropriate for the
> high radiation resistance of the short wire.  A low frequency
> antenna tuner correctly set up to match a transmitter into a
> short wire would look a lot like a base-fed TC.
> --
> Paul Nicholson
> --
>
>
>