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Re: electromagnetic wave fundamental frequency and harmonic series?

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



Original poster: Vardan vardan01@xxxxxxxxxxxxxxxxxxxxxxx



. . . A better test would be to run the secondary at Fo from a signal
generator in say an open field and use a LF radio receiver.  Just walk
back and find out how far you get. . . . . . . Would it be useful to
actually do this test??
. . .   Terry


I say yes.  Particular attention should be paid to construction of the LF
radio receiver's antenna.  I recommend a tuned vertical monopole, as tall as
possible, that's centered directly above a wire counterpoise elevated, say,
2 or more meters above the ground on insulating supports.  (See
http://www.qsl.net/w9rb/webdoc11.htm for some tips on LF antenna
construction.)  A grounded antenna should be avoided to limit as much as
possible the introduction of propagating ground currents into the receiver's
antenna circuit.

As for the TCT, a high aspect-ratio SSTC, on the order of 9:1 or more,
operated in a CW mode is the way to go.  Good operating frequencies are
71.6-74.4 kHz, 135.7-137.8 kHz, or the bottom of the 160-190 kHz band.  I
suggest running the transmitter directly from a lead-acid battery bank
positioned near the base of the transformer.  Of course the solid-state
circuit controller is positioned there as well.  The pulse generator can be
positioned a few meters away and connected to the transformer with coaxial
cable.

Needless to say, the experiment will not be complete until field strength
measurements are also taken with a well grounded TCR used in conjunction with
the same LF radio receiver.

Gary Peterson



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

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

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Original poster: "Langer Giv'r" <transworldsnowboarding19@xxxxxxxxxxx>



. . .  I am wondering about the frequency of output of my Tesla Coil . .
.



   . . . there is SOME radiation but it will be very small because the
coil is a most inefficient radiator because of its length compared to
the wavelength of the signal in it. . . .



   . . . The coupling from the primary circuit will be much higher at
the fundamental frequency than at any harmonics so there won't be much
harmonic current flowing in the secondary. On the other hand, the
radiation efficiency of a very short antenna increases as the square of
the frequency so any harmonics present will be radiated more efficiently
than will be the fundamental. . . .



If one operates a very large Tesla coil in the non-sparking mode, at say
100 watts, and say that 5% of the energy is dissipated in the form of
electromagnetic radiation, where do you think the remaining 95% goes?



I have done this.

Most of the energy is simply dissipated as heat being burned off in the
Secondary wire resistance.  There are also losses involved with the top
capacitance and it's ground return path.  Some of those losses are
probably RF, but it seems at least 90% of the energy is lost to resistive
heating.



   It's possible to calculate the radiation resistance knowing the coil
geometry and the frequency - the coil acts as a simple helical resonator
and the formulae are in the handbooks and available on the net.  I
suspect the answer will be that more like 99.9%+ is lost in the circuit
and spark gap resistance.  If the gap quenches perfectly all of the
energy would be dissipated in the secondary except for the minute amount
which would be radiated.



The problem is that the circuit from the toroid to the surroundings and
back to the coil's base ground is in series with the winding AC
resistance.  It is hard to tell how much current there is lost just to
heat in the ground return path or might be radiated.  I suspect very
little is radiated, but the type of test I did could not determine that
for sure.

A better test would be to run the secondary at Fo from a signal generator
in say an open field and use a LF radio receiver.  Just walk back and find
out how far you get ;-)

One could probably figure it out pretty well with some thought as to how
to calibrate everything in that simple case.



Would it be useful to actually do this test??  I have a fairly nice (all
digital, so you know it's good ;-)) receiver that has a 144kHz to 288kHz
band.  I can probably get a ~200kHz coil going somewhere.  Perhaps the TCT
could be a signal generator unless somebody's boat has a 120VAC invertor
on it (Gerry??)  Then I could us the HP signal generator.  I just bought a
super nice UPS too...  Perhaps the DRSSTC or DF-DRSSTC could run off the
old UPS...

It could be run in the back yard in suburbia too...  One person out there
with the receiver and GMRS radio...

Maybe not real science, but it would put a stick in the sand...

Cheers,

        Terry