Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>


> Original poster: William Beaty <billb@xxxxxxxxxx>

> > Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>

> > I think we can all agree that a grounded Tesla coil without a
> > Marconi-type antenna is a poor source of radio waves, i.e.,
> > electromagnetic waves that have closed back upon themselves and are
> > no longer associated with the antenna.

> Not necessarily.
>
> If we keep making a transmitting antenna smaller, but we also keep
> stepping the voltage up which drives that antenna, then the antenna
> doesn't act smaller.  As long as the strength of the EM field at
> 1/4-wavelength distance is not decreasing, then we can keep making the
> antenna physically smaller.  We only pay for this in wasted power, since
> step-up transformers use coils which get hot. . . . Or in other words,
> it's hard to judge how well a small transmitting antenna works.

While a theoretician might find it difficult to determine how well an 
electrically short antenna might work, in practice it's a simple 
matter.  In using this term "antenna"  I'm referring to a physical 
structure intended for the launching of radio waves, i.e., 
electromagnetic waves that have closed back upon themselves and are 
no longer associated with said launching structure.

> Even the shortest antenna must always radiate SOME
> electromagnetic waves, and if an impedance-matching network is involved,
> then far more energy gets out than one might expect.  To make your small
> antenna act larger, just step up the drive voltage while stepping down the
> current.  Don't forget: if a superconducting Tesla coil was used, with
> superconductor primary and superconductor capacitor plates, hooked to a
> superconducting ground plane, then the Tesla coil would be just as good as
> a humongous quarter-wave antenna.  Of course the voltage would get a bit
> high, and you might have to bury the thing inside a block of solid Teflon
> a mile across.

In using the phrase "a grounded Tesla coil without a Marconi-type 
antenna" I was referring to a Tesla-coil transmitter such as might be 
assembled by someone on this list.  I tend to agree with Chuck when 
he asserts that the "Effective Radiated Power (ERP) would still be 
miniscule, probably undetectable (electromagnetic waves [that have 
closed back upon themselves]) beyond about 500 to 1000m distance I 
would think."

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

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

> > 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.  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.  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."

> William J. Beaty

Gary Peterson