DID TESLA'S WARDENCLYFFE TOWER
W. Beaty 2008
An Odd Relaxation Oscillator
Here's a "lost concept" which I noticed while reading lots of Tesla
material. Suppose we drive a Tesla coil using a low power RF
source which is weakly coupled? And suppose the coil has extremely high
"Q," wound from copper pipe or Litz wire. What happens?
In that case the coil's RF output voltage will ramp up slowly, as if
the oscillating coil was a kind of "capacitor" being charged up. The
Tesla secondary coil is an energy storage component. But it's being
with AC high frequency, not with DC! Doesn't this mean we can treat
our coil much
like a capacitor? We could discharge it with a very short spark-gap placed
across its terminals. If we kept driving it via loose coupling, this
gap should start firing slowly and periodically, since the
coil loses half or more of its stored energy each time it's shorted out by
the arc. It ramps up with AC oscillations, then sparks over. It
should go "snap-snap-snap-snap" just like a DC capacitor spark-gap system,
yet it's entirely AC high-frequency.
Here's another odd concept. In the above AC device, suppose we place
a large capacitor in series with that spark gap. Have the discharge drive
a capacitor. What will happen? Usually nothing strange. The
AC signal just thinks the capacitor looks like a
good conductor. It's
invisible to the capacitor, it just looks like a short circuit for the
However, if next we adjust the spark gap so it quenches quickly, then
whenever the gap fires, it will produce a single pulse of just one
polarity, and it
will deposit a large DC potential across our added capacitor. During the
spark, the oscillating coil dumps a half-cycle of a sine wave. A DC
this mean that we've invented an early type of rectifier? An 1890s-style
AC-to-DC converter? No vacuum tube, no silicon! Yes, but I'm just
getting started! :)
To do this, the spark gap would have to quench fast; quench after a
single half-cycle of the ringing (or more easily done: quench after an odd
number of half-cycles.)
In addition, during the next firing of the gap, the capacitor's DC
polarity should reverse! After all, the gap only fires at a large
potential, and if the capacitor had already been previously charged during
the last arc, the gap-voltage will be at maximum when the instantaneous
coil voltage is opposite to the previous DC polarity left sitting
on the capacitor. So, the gap only fires when the peak-volts of the AC
happens to be backwards.
each slow triggering of the gap, the capacitor DC polarity is reversed.
As the spark-gap slowly goes snap-snap-snap, the capacitor's DC voltage
goes pos-neg-pos-neg. And most important, the output voltage might not be
too much smaller than the Tesla Coil's HV output. If we built a
multi-megavolt Tesla coil, we could use it to create slow, multi-megavolt
square waves. "Slow" here meaning 10x lower than the coil's resonance
so perhaps 10KHz. Or with
high enough Q, and slow AC ramps, maybe much lower than resonance. 1KHz,
or 100Hz, or even 1Hz. (Or 8Hz. Or sixty!)
By taking a conventional Tesla coil and adding two devices to its
output terminal, one spark gap and one H.T. capacitor, perhaps we can STEP
DOWN the coil's output frequency to a very low value. We drive it with
high freq AC as usual, and it outputs such a low frequency ...that Nikola
Tesla might call it "electrostatic." Or, if we look at it from another
viewpoint: we've just built simple a sawtooth relaxation oscillator, but
it's a strange variant where both the power supply and the slow ramp are
made of AC oscillations, and the output is not a sawtooth or a brief
spike, instead it is a square wave.
Nikola Tesla owned no "Tesla Coils"
Where did this idea come from?
Well, think about it: Tesla wasn't working with "Tesla Coils." He didn't
call them that. To us, Tesla Coils are those famous vertical-coil
lightning machines. But to Tesla they were just one more electrical
component, one more useful tool among many he'd invented.
To him they were just power supplies.
If we have an AC high-voltage power supply kicking around our lab, what
might we use it for? Well, if you're Tesla, you can hook it in series
with a spark gap, then route the enormous discharge pulses through a
resonant circuit. That's right, use a Tesla coil as the power supply
for a Tesla coil. Aha, the two frequencies need not be the same.
(But this idea was always there, since classic Tesla Coils are driven by
high-volt sixty-cycle AC resonator: a transformer secondary with a
capacitor across it. Almost using a 60Hz tank-circuit as the main power
supply! Why not just use 200KHz AC to drive your 100KHz primary coil
So what happens if we connect a Tesla Coil as a power supply for a
very low-freq resonator? Use a few-100KHz Tesla Coil to power a low-freq
long wave VLF spark
transmitter? Tesla mentions the parts of the process: when an Extra coil
is driven with CW, its oscillations ramp up over time, and if its output
is suddenly shorted by a spark gap, brief pulses of "inconceivable power"
produced. Initially the TC secondary acts like a tank, like a slowly
charging "capacitor," then it gets periodically "discharged" by the spark
gap. But unlike modern energy-storage caps, this "AC-storing capacitor"
could easily be charged to megavolts, and most important: it could be
recharged over and over again in tiny fractions of a second.
A TC secondary coil probably has enormous power-processing ability far
beyond that of DC energy
storage capacitors ...which is exaclty what Tesla said on numerous
So Tesla figured out a way to build a Tesla coil where the power supply
operated at megavolt output, and then his large coil at Wardenclyffe
stepped it up from there. Aaaaaaand... the output frequency could be
A small experiment
But is this actually real? How about an experiment? OK, I'll take
this 1" diameter long narrow 800KHz T.C. secondary and drive it at
using my old Wavetek sig gen. It's now behaving like the Extra Coil of a
Magnifier: one end of the coil is driven, and the far end is
The Wavetek puts out about 10Vp, and at resonance the far end of the coil
is running at a thousand volts at least. (NE-2 bulbs glow when held
near!) Next I'll
let the extremely tiny sparks from the far end of the coil start leaping
to a "capacitor" in the form of a metal object sitting atop a plastic
block. What happens? Something Very Cool!
A low frequency SQUARE WAVE does appear on the floating metal object.
and high-Z, so I monitor it with a nearby scope probe. It's very noisy
and grungy. The cause of this square wave is obvious:
- The 800KHz Extra-coil's output rises to max volts over about ten
- the gap sparks over
- after quenching, some DC volts are left on the metal object
- the 800KHz HV ramps up again
- because there's now static HV on the metal object, this time the gap
fires on the OPPOSITE POLARITY of the 800KHz wave
- after quenching, opposite polarity of DC HV is left on the metal
So it's bascially a relaxation oscillator much like a NE-2 blinker. But
this one is powered by AC, not DC. The slow-rising "sawtooth" waveform is
an 800KHz modulation rather than a DC ramp. And the output is alternating
positive and negative current spikes, which produce an alternating DC on
a capacitor. Wow! Pretty cool, eh?
OK, what if I harness those "slow" alternating spikes? I can use them
to drive a low-freq resonator. Add a simple tank circuit. I grab an
inductor and capacitor out of the junkbox, connect in parallel, then route
the alternating spikes from the metal object through the resonator and to
Earth connection. Yes! A large slow sine wave appears across this
grounded LC tank. Also, the spark gap's pulses do "phase lock" to the LC
circuit's oscillations, and the signal isn't nearly as grungy as before.
On the scope it remains coherent over more than 50 cycles. It's sort of
like an old hit-and-miss gasoline engine, where the cylinder only fires on
some of the piston/flywheel cycles. Makes sense:
the low-freq AC voltage on the resonator is affecting the spark-gap
timing, and it's forcing the gap to fire at just the right time to dump a
single-polarity pulse, and that pulse kicks the next cycle of the slow
sine wave on the resonator. (It's much like a Marconi Spark Transmitter
powered by DC, but here my power supply is a 0.8MHz tesla coil.
I examine the component values using an LRC meter, and calculate that
coil/capacitor tank circuit should run at 39KHz. Those were randomly
chosen junkbox components. I calculate a better freq: the AC ramp takes
about 10 cycles to rise, and the pulses are half that period, so the ideal
RLC resonator would be... 40KHz?!!!!! But my RLC is 39KHz. Bizarre.
Just by chance those random component values were perfect. I love it when
that stuff happens. (If I'd grabbed different ones ...would I have
failed? and given up?)
So, I now am the owner of a BACKWARDS TESLA COIL. Its CW sine-wave
input drive is
800KHz, and its output is 20x lower: 40KHz. And this step-down factor
depends on the Q of the Extra Coil. If instead the Q-factor of my
coil had been 10x higher, where it took 100 cycles for the AC HV output to
slowly ramp up
to the spark-gap voltage, then I could
have stepped the 800KHz down to 4KHz, which would be within the set of
Schumann absorption lines for Earth-res. (or, hook it to a high-Z piezo
loudspeaker and hear what it sounds like.)
If Tesla had a huge 75KHz coil of very high Q, then the PRF of his
spark gap and his transmitter output could have been far lower: down in
the hundreds of Hz. The output is an alternating spike waveform, and the
"tank circuit" which forms the sine wave is ...the entire Earth. As all
oscillators do, it phase-locks its pulse drive to its tank circuit, so
that any changes to the tank circuit's resonant frequency won't de-tune
the drive pulse-rate. It will just continue oscillating at the changing
frequency. And so a simple Tesla coil should be able to excite the
Earth's very low resonances even though the TC output frequency is tens or
times higher. (But note that this "Earth-res phase-lock" effect would
only occur above a certain threshold of operating kilowatts. Those
returning waves in the sky-fields which are trapped in the Schumann
ionospheric duct, they must be strong enough to bias the next triggering
of the spark gap.
Hmmmm now, did Tesla have any plans for a giant transmitter where
there was a large, CW-driven "Extra coil," but there was also an
unexplained mysterious "Extra Gap" placed in series with the HV output
Yes. Yes he did.
Regarding Tesla's transmitter at Wardenclyffe NJ, it's still an open
question about how he was able to use a tens-KHz system to drive the Earth
resonance frequencies (which are all below 20KHz, and the best ones far
lower.) To excite the Earth, a huge Tesla coil would have to have far
lower resonance than usual, and so be built 20x or 50x taller than the
largest ones ever made. Or, Tesla would have to have some way to step the
frequency down without reducing the enormous output voltage.
Perhaps he connected a spark gap in series with his coil's output,
then used this to charge a capacitor? Yes, according to above unpatented
drawings from his collected works, this is exactly what he was working on
during Wardenclyffe years. But nobody has said why that "Extra Gap" was
placed between the main coil output and the capacitive topload hemisphere.
So maybe a mystery is solved, and the Wardenclyffe tower was the world's
largest square-wave signal generator?
SQUARE WAVES, AND PHASE-LOCK FEEDBACK TOO
Relaxation oscillators are sensitive to environmental e-fields. After
all, they're being triggered when the voltage across a spark gap reaches a
particular threshold. If other external e-fields are present, these extra
can add or subtract from that threshold. They'll cause the oscillator's
pulses to come earlier or later than normal. (This is why a little NE-2
blinker circuit can detect nearby RF sources.)
If we set up Wardenclyffe to be a square wave oscillator, and then we
leave it outdoors where it can be influenced by other e-fields, perhaps
something very useful will happen. Perhaps the pulse-waves sent outwards
by our system will race all the way around the Earth, then concentrate
themselves in contracting ripples back at our location and cause our
oscillator to fire early.
If such things were to occur, what does it mean? It means that our
device will drive just one of the Earth Resonance frequencies. It means
that if the resonance were to slightly wander because of Solar Wind or
changing magnetosphere phenomena... our transmitter would still remain
locked to that frequency. The system would keep oscillating even as the
frequency drifted up and down. And if we attempted to set our transmitter
a much higher frequency, it would leap discontinuously to the
absorption line in the Earth Resonance series. Remember that these
frequencies are all in the audio range. So if the spark gap distance was
made wider and wider, the noise from such a system
would sound like successive notes being struck on a piano keyboard. Or
perhaps sound like an air-raid siren which leaps from note to note. (Well,
actually be buzzing raspy, spark-gap notes!)
Brrrrrrrrrrr-Baaaaaaaaaaaa-BIIIIIIIIII-BEEEEEEEEEEN! That *may* have
been the characteristic sound of Wardenclyffe tower in operation.
This all solves another Tesla mystery: Earth Resonance frequencies are
known to wander around slowly. For this reason it's supposedly impossible
to strongly excite the Earth Resonances. If your VLF transmitter managed
to hit the target frequency, your success would only be temporary, since
the Earth system would slowly change, and you'd lose the resonance. The
solution is found above: stop treating the Earth as a target frequency for
your drive transmitter, but instead make it part of your oscillator. If
the Earth becomes our oscillator's "Tank Circuit," then such an oscillator
will always be on resonance, even if the frequency-determining components
are wandering in value.
Yes, except for my 800KHz coil test, all this stuff is pure speculation.
But it all hangs together SO NICELY, and explains so many mysteries, that
I thought I'd post the whole mess here on my website and let the critics
have at it.