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Re: Tesla Coil RF Transmitter

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


Original poster: Alex Crow alexcrow@xxxxxxxxxxxxxxxx 

. . . I think that there is still experimentation to be done with very
large TCs, but I don't think any of us have the finance to be able
to do it. About the only person I can think of who could at least
come close to the size of coils we'd need is Mr. Leyh, and I'm
not even sure he's got the necessary funding even for the ALF
yet (which is still probably a couple of magnitudes too small
for any real experiment in remote power transmission).

The individual experimenter doesn't need a large high-power Tesla-coil transmitter to learn a lot about the wireless transmission of electrical energy--Tesla style--and to produce meaningful results. Anyone with a small solid-state Tesla coil can do this. Actually smaller may be better because this allows the 'close-in nearfield' demonstrations to be more easily performed inside of a Faraday cage, if so desired. Here are some guidelines.

For the transmitter:
1) Use a 7 : 1 to 9 : 1 aspect-ratio coil form wound with about 1,100 to 1,800 turns of wire.
2) Position the transformer about 25 to 50 feet from a good Earth connection, and connect the two using a piece of insulated #12 or larger cord laying on the ground.
3) Use a well filtered DC power supply in conjunction with a high precision pulse generator to drive a unidirectional switching circuit, i.e., don't use the four-device bridge circuit. Connect the pulse generator to the SSTC driver circuit with about 25 feet of RG 58 coaxial cable. Use optical isolation; the coax could be replaced with fiber optic cable. Start out with the pulse generator set to a 50% duty cycle and tweak.
5) Elevate the topload so it's about 1.5 times the bottom-to-top secondary height above the secondary's top turn.
4) Increase the size of the topload so that streamers do not escape from it when the oscillator is operating at maximum power.
6) Tune the oscillator to its fundamental resonant frequency by observing the reaction of an analog voltmeter set to the lowest scale, with one lead connected to ground and the other connected to a nearby elevated terminal. A neon lamp is good for course adjustment. A frequency counter also helps, as will an oscilloscope.
7) If your SSTC's coefficient of coupling is tight, try loosening it.

For a passive receiver or wavemeter:
1) Construct a coil stand out of 2 1/2" white PVC pipe and 6 pieces of 22" x 1' x 1/2", fastened with 1/4" x 20 brass bolts to form a tripod. (See http://www.teslaradio.com/images/Telluride01.jpg for an example.) This type of stand is great for the TC transmitter as well (see http://www.teslaradio.com/images/Telluride04.jpg.
2) Construct an adjustable topload using piece of heavy-duty aluminum foil, 4' long by 18" wide, wrapped around a 20" wooden dowel, mounted on a small board with end brackets. Before starting the wrap, fold one end of the foil around a piece of bare copper wire, with one end flush and the other extending out 2", and solder it to a copper slip-ring installed on one end of the dowel. (The topload will be connected to the coil with a piece of wire run to a strip of springy metal pressing on this slip ring.) Now roll a few inches of the foil's free end on to a 20" wooden batten and then sandwich it with a second batten, and attach a pull cord of light nylon line. Mount the entire assembly on a vertical section of 1 1/2" black PVC pipe. Use a 1 1/2" to 2 1/2" slip bushing and a 2 1/2 " to 2 1/2" coupling to mate to the 2 1/2" pipe. Tuning is accomplished by pulling the foil out from the roller like a window shade. This arrangement works well, especially if there is little or no wind. One difficulty is the need to tip the whole apparatus to its' side in order to roll back the foil when its adjusted past peak resonance. An alternative arrangement is two telescoping PVC pipes with a cord and pulley arrangement (see http://www.teslaradio.com/images/Telluride02.jpg.) This more robust elevated cap assembly allows a topload of fixed dimensions to be raised and lowered at will. The coil-to-topload connection is with a festoon possibly made with a conductor stripped from a piece of hard elevated telephone drop wire.
3) Obtain a 1.5 : 1 to 3 : 1 aspect-ratio coil form on which to wind the receiver's resonator coil. Fill it with a piece of wire the size and length of which will result in a coil that, with the adjustable topload attached and set at or near its smallest capacity, is resonant at a slightly higher frequency than the transmitter frequency. This is the receiving transformer's primary coil. A higher aspect-ratio primary can also be used. A miniature receiving coil can be created using an empty Al foil tube wound with AWG #40. A removable secondary can be wound on a short section of paper towel roll. Tuning can be accomplished with a moveable ferrite rod, such as used for AM radio loop stick antennas.
4) Ground the resonator using a piece of insulated #12 cord about 25' to 50' in length as is done with the transmitter. Good results can be achieved using a standard ground rod 8' or longer driven into soaking-wet earth. Fire hydrants and steel well casings also work well.
5) Wind a secondary coil around the primary, close to its base. Instead of a solid conductor, it may be better to use a piece of insulated wire from a split-in-two zipcord, or a long piece of test-lead wire. A small low-voltage incandescent Christmas tree lamp is connected to the secondary as a load. A small permanent magnet DC motor can be run through a 4-diode bridge rectifier. Work with this arrangement for a while to hone your tuning skills.
6) For long distance reception the secondary (re: #5) is not used. A conventional long-wave communications receiver is capacitively coupled to the primary circuit instead. This is done by running a lead from the receiver's antenna terminal across and up to a point on or near the PVC pipe, about 2 ft. above the top turn of the resonator. A second lead is run from the receiver's ground terminal to a common grounding point fastened to one of the tripod legs. Tune both the helical resonator and the receiver to the transmission frequency; try adjusting the antenna-to-resonator coupling for effect. Nearby objects such as hillsides, trees and buildings have a noticeable effect on tuning, so get as much out in the open as possible. You'll find that you have to step back from the coil to avoid detuning of the resonator, and to get maximum resonant rise. Watch the "S" meter as you move forward and back, as this helps with fine tuning. Have an assistant sweep the pulse repetition rate through the resonator's center frequency and observe the effects on the signal strength and background noise level. An oscilloscope can be used in place of the receiver. A sensitive e-field probe will also produce good results.

. . .
Non-Hertzian waves may or may not be a myth - but as far as the current
results of Googling go, the promise isn't great, with a large percentage
of results referring to the "aether" or "orgone energy". Sad, because much
of this has brought both amateur and semi-pro HV and HF research in the
public eye into the "crank" realm, eg. conspiracy theories over HAARP, etc.

Because Tesla himself did not use the term "non-Hertzian waves" and the fringe element does, this is not a particularly good search phrase. Try the following: adiabatic plasma, asymmetric capacitor, capacitively coupled discharge plasma, cathode reaction forces, charge, charge displacement, cold plasma model, de Broglie wave, dielectric displacement current, dielectric tensor, electrodynamics, electrostatic induction, electrostatic wave, ion acoustic wave, isotropic capacity, glow discharge, inductively coupled discharge, Langmuir-Tonks plasma oscillation (Langmuir wave), Lorentz gas plasma model (electron gas), magnetohydrodynamic wave, norton surface wave, plasma wave, power factor, quantum vacuum, radiation fields, radiation resistance, resistive magnetohydrodynamics, resonance, space charge, soliton waves, transport in plasmas, voltage standing wave ratio (vswr) , weakly ionized plasma, zenneck surface wave.

Not that I'm any kind of electrical engineer, just trying to preempt a
possible flamewar! Some Things most certainly /can/ be done, it
just takes an awful lot of effort to find out how or "if"; but even us
tinkerers sometimes have a bit-part in all of this!  Alex

"Blessed are the peacemakers, for they will be called sons of God" (Matthew 5:9).