Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Thu, 6 Oct 2005, Tesla list wrote:

> Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>
> >MIT has a couple of very cool antenna animations which demonstrate
> >part of the idea that short antennas aren't necessarily "short":
> >
> >quarter-wave antenna animation, 2megs
> >http:/web.mit.edu/8.02t/www/802TEAL3D/visualizations/
light/QuarterWaveAntenna/QuarterWaveAntenna.htm
> >
> >short antenna animation, 2megs
> >http:/web.mit.edu/8.02t/www/802TEAL3D/visualizations/
light/dipoleRadiationReversing/DipoleRadiationReversing.htm
>
> The caption associated with the second animation doesn't say anything
> about the antenna being electrically short.

Huh?  Who needs captions!  Just observe details and connect them with EM
physics concepts, then we can write our own accurate captions.

We know that a quarter wavelength is roughly the boundary between
conventional antennas and electrically short antennas (that's what
"electrically short" means.)  Look at the wavelength in the diagrams.
It's the same for both animations.  Now look at the antenna length.  See?
One of the antennas is right on the long/short boundary, while the other
one is considerably shorter.  If an antenna is "short," where its length
is smaller than the nearfield region, then the nearfield region will
exhibit dipole fields which visibly expand and contract.  So look for
expanding/contracting fields in those animations.

Closely observe the two animations, because they depict the main
difference in behavior between a conventional antenna and an electrically
short antenna.


> It looks to me like the
> thing is just drawn to a smaller scale than previously.

Wrong.  The wavelength in the two animations is about the same, but the
antenna length is greatly different, and the field behaviors are greatly
different.  The short-antenna animation clearly depicts a dipole field
that expands and then shrinks again.  The field pattern in the 1/4-W
antenna animation doesn't do this; instead it looks like bubbles coming
through a window.


> Also, these
> animations represent the operation of a dipole "antenna" (in the
> sense used above) in free space. This is an inaccurate representation
> of the launching structure of a Tesla-coil transmitter, which is
> grounded and by my definition is NOT an "antenna."

Wrong.  But I was assuming that everyone knew that the upper half of these
animations is exactly the same as the field pattern of a groundplane
antenna, so the diagrams tell us a lot.

Cover the lower half of the animation with a piece of paper.
In that case the *long* antenna shows the field pattern for a quarter-wave
tower erected above a groundplane.  The short antenna shows the field
patterns for an electrically short grounded-vertical (i.e. a Tesla Coil.)
The Earth's surface isn't a perfect conductor, so we'd expect to see the
fields near the ground be delayed slighty, tilted slightly forwards so
they go slightly downwards.

These animations do show the field patterns and RF radiation for a Tesla
coil, but don't give a good idea of the field intensity.  If the short
antenna was MUCH shorter, then most of the field pattern would consist of
an expanding/contracting blob of dipole fields, with only a tiny bit of
travelling waves escaping.

>
> >. . . There is *always* some radiation from a short transmitting
> >antenna, . . . The question is, how much power gets out?  Or
> >more accurately: what's the SNR [Signal-to-Noise Ratio] at a
> >great distance from the TC?  If your Tesla coil's radio emissions
> >are far weaker than the natural VLF noise at that frequency, then
> >you might as well just collect the natural EM waves as a power
> >source, since your TC doesn't add much.
>
> I notice that you're talking about the Tesla-coil transmitter as if
> it was intended as a source of "radio waves."  The Tesla system does
> not work by the propagation of what are called "radio waves" in the
> narrowest sense of the term,

Right and wrong.  Whenever the transmitter and receiver are separated by
more than a wavelength or two, then there is no direct coupling; no
capacitor connecting the two.  The connection is via waves.  They might be
waves in a waveguide, but that's irrelevant; they're still waves.

> i.e., far-field electromagnetic waves
> that have closed back upon themselves and are no longer associated
> with the launching structure. Operating a 20 watt SSTC transmitter at
> 108 kHz a couple of years ago,

How long an antenna?

(Or do you imagine that Tesla's plans for Wardenclyffe DIDN'T include any
vertical antenna?)

> I found that noise is all that you hear with an LF receiver at 1,000
meters.

You're transmitting DC and expecting to *hear* a signal?!!!!!!!!  That
doesn't make much sense.

Also... what receiver?   What antenna?


> Bring a tuned receiving
> transformer with the secondary removed close to the receiver's
> antenna and the electrostatic noise goes away, to be replaced by
> "dead air" created by the CW Tesla-coil transmitter.

That's not a signal, that's just the receiver's AGC kicking in.


>
> > > 2) If so, at what distance from the TC transmitter can the electrical
> > > disturbance be detected using a receiving transformer of similar size?
>
> >That's a signal-to-noise issue, no?   If there were no noise, then it
> >would be easy to detect the signal by just cranking up the receiver gain.
>
> Yes it is, only you're using the term "signal-to-noise ratio" as it
> applies to "radio wave" reception.

Says who?!!  SNR is about signals, period.   It's not about radio wave
reception.

If the Earth-resonance cavity is full of energy from distant lightning
storms, and if this energy flow is much stronger than the power from your
small Tesla transmitter, then the SNR will be terrible, and your receiver
won't detect any signal no matter how high the gain and no matter whether
it's Tesla longitudinal waves or ducted "radio waves."


> The propagation of electrical
> energy between a Tesla-coil transmitter and a Tesla receiving
> transformer is not by "radio waves."  It is by electrical conduction
> between the ground terminals, and direct and indirect electrostatic
> induction between their respective elevated terminals.

If the two are separated by more than a wavelength, then circuit-concepts
no longer apply, and we have to model it as radio waves travelling in a
waveguide.  That's not radio waves in free space, but neither can you
model it as capacitive coupling.  Weird things occur.  For example, if the
transmitter and receiver are placed into a high-Q resonant waveguide, then
the impedances act VERY different than those for a normal transmitter and
receiver.

Anyone can "prove" that Tesla's ideas don't work:  just eliminate any long
antenna, then run your transmitter at a frequency which is not at one of
the Earth resonances.  Or even better, run your transmitter at frequencies
well above 1KHz.

But that's pseudoscience.  It's dishonest, it's the logical fallacy called
"straw man."

If we want to demonstrate Tesla power transmission, then we MUST include
all the critical parts:

  1  Transmission frequency well below 1KHz
  2  Transmission frequency tuned *exactly* to an Earth resonance.
  3  Very low impedance ground connection
  4  Tall vertical antenna (wire, or UV beam, or x-ray beam)

There may be a 5th requirement.  I've been speculating about it:  a high
operating frequency and a much lower Earth-resonant modulation frequency,
as well as a modulator element consisting of fast-switched power rectifier
on top of the Main Terminal: Tesla's "radiant energy" device; an x-ray or
UV emitter which also rectifies.  It would take in the high freq high
power of the Extra coil, and spit out high-volt pulses at whatever low
frequencies you wished.


>  In a fully
> developed Tesla transmission-reception system the signal-to-noise
> radio is so great that electrostatic noise is essentially
> nonexistent; it's a "static eliminator."

But you were running at 20watts drive!  If your TC had no large capacitive
structure such as UV or X-ray vertical beams, or Tesla's balloon-lofted
vertical wires, then all the drive power would end up heating the
secondary coil, and the actual energy going into the Earth resonance might
have been microwatts.

If you'd modulated your SSTC you might have picked up a signal with
your LF receiver and been able to make measurements of transmitted power
versus TC drive power.



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William J. Beaty                            SCIENCE HOBBYIST website
billb at amasci com                         http://amasci.com
EE/programmer/sci-exhibits   amateur science, hobby projects, sci fair
Seattle, WA  206-789-0775    unusual phenomena, tesla coils, weird sci