EXPERIMENTS WITH AN ELECTRICAL COUNTERPOISE AND THE FUNCTION OF RF GROUNDING IN HELICAL RESONATORS *************************************************************** Sounds impressive? I assure you it is not! I have been wanting to transcribe some of my lab notes concerning a series of experiments that I happened into quite accidentally in the fall of 1992 while working with a four inch coil system. Before I jump into the simple equipment and instructions required to duplicate these very educational experiments, I want to give a brief history of how I happened onto this line of investigation with Tesla Coil systems. But even before that: The disclaimer! This short paper was written for those interested in Tesla systems who already have a small working coil or two. These experiments, like any high-voltage or Tesla experiments, can be dangerous. In addition, several setups detailed below can produce excessive radio frequency interference (RFI - EMI). It is under- stood among ALL coilers that any adjustments, tuning, or changing of connections in a coil system are done with the power off and with the primary capacitors discharged. It is also understood that setups which may produce excessive RFI - EMI are properly shielded (as in a grounded Faraday cage). A REAL Tesla ground is REQUIRED for some of these experiments. You don't want to set up the transmitter configuration detailed below under "Optional Experiments" and ground it to your house wiring! I was back-tracking down in size from 6 - 8 eight inch coils prior to the construction of a new 10" coil system. I was con- cerned about the expense in time and materials for the new large primary coil that I was beginning to envision. I wanted to have a work table or platform where I could wind and test fire simple primary coil designs. I was looking to resonate several Tesla secondary coils in the 4 - 5 inch diameter range with a variety of temporary "lashed up" primary coil shapes and sizes. Due to space constraints I wanted a rolling platform with a lower shelf where my homemade capacitor tanks could rest, a side shelf for the placement of spark gaps, and some method of making a simple low impedance connection to my heavy, dedicated, RF ground. I went ahead and built a rolling platform from scratch wood. The grounding system on my rolling platform is what led to the following series of experiments with electrical counterpoises and RF grounding. The top of the rolling platform had a hole drilled into the center for a ground wire to come through. For a ground- ing point directly below the secondary coil, a wire is led through the hole and it clamps to a rather solid brass block that was screwed into the underside of the tabletop (junk box find). The brass block has four #6 multi-strand wires soldered to it (scrap wire box, the sections were too short for anything else, so I used all of them). Each wire is insulated with heavy vinyl tubing as it runs down the four legs of the platform (insulation was required here because of the close proximity to the capacitor terminals and the tank circuit wiring). I looked around for some method of tying the four #6 ground cables together at the base of the platform, and settled on what turned out to be an aluminum traffic sign which came out of a sheet aluminum scrap bin. It fit precisely under the base of the platform, and I bolted the four cables to the conductive plate. A heavy ground strap could be brought in from any direction, the conductive plate pried gently with a screwdriver, and a large surface area temporary connection could be made by inserting the ground strap between the conductive plate and the wooden bottom of the platform.... Now I will move on with this paper. **************************************************************** MATERIALS REQUIRED ARE: A well tuned Tesla coil with a 4 - 6 inch ( 10 - 15 cm ) diameter secondary. Some one inch (2.5 cm) high plastic medicine cups, or some pieces of plastic scrap about inch high that can be used for simple light-weight standoff insulators. A section (any shape) of flat sheet metal of at least 2.25 square feet, but not much over 4 square feet (.7 to 1.2 square meters). The exact size to get the best experimental results will depend on the size and efficiency of the coil system you are using. Since this component need have no special characteristics, and any flat conductive material may be used, you might want to get a selection of pieces of various sizes. A low pressure gas tube (neon, florescent) Some sections of braided ground strapping or other flexible conductor with a large surface area. Some simple clamps (clothes pins, large paper clips, etc.) Some thick plastic sheeting may be required in places for insulation. A dedicated RF ground for ground pathing and for grounding HV xfmr cores and Tesla resonators. OPTIONAL MATERIALS: Toroid or sphere discharge terminals of various sizes. These additional dischargers are highly recommended for any degree of experimentation with resonating coils. A separate Tesla secondary just a bit larger than the secondary used in the operating system. The optional experiments do not require a second coil SYSTEM with tank circuit, etc.. Just a bare secondary coil that resonates at a slightly higher frequency than the system used to power these experiments. **************************************************************** Set four or more of the plastic standoff insulators on a concrete, dirt, or metal floor. A wooden floor will not be satisfactory, and may well become a fire hazard during the course of experimentation. A concrete basement or garage floor is ideal. Place the flat sheet of metal on top of the plastic insulators so that the conductor is electrically isolated 1 inch (2.5 cm) above the floor. This forms an insulated capacitance or "counterpoise". Use a clothespin or other small clamp and connect one end of a section of ground strap (or other flexible low impedance conductor) to the piece of sheet conductor. Connect the other end of the ground strap to the base wire of a Tesla secondary coil in a system that has been previously tuned until it will produce at least 6 inches (15 cm) of spark. The secondary coil should NOT be connected to any other ground while experimenting with the counterpoise. Fire the coil using a variac voltage controller on the primary of the step up xfmr, bringing the coil slowly up and down in power levels. --------------------------------------------------------------- 1) Observe the performance of the coil at various power levels. How does spark from the coil when connected to the counterpoise compare to spark from the coil when it is grounded to a low impedance RF ground? Switch the ground connection back and forth between your counterpoise and your low impedance RF ground. 2) Observe the space between the counterpoise and the floor when the coil is in operation at various power levels. a) My lab notes indicate that at low power the Tesla secondary operated normally without a ground connection. The counterpoise alone is all that is required to achieve efficient resonance during low power operation. However, as power levels grew, spark lengths failed to increase, despite significant increases of input power. b) The point at which the coil "stalled" (where additional power into the system caused no increase in spark length) was also the point at which a visible electrical disturbance began in the space between the counterpoise plate and the floor. This disturbance was marked by bright corona and sparking between the counterpoise and the floor. This disturbance increased with the amount of power input into the system, though there was little or no improvement in the output of spark from the top of the coil. c) If you were not able to overwhelm the counterpoise during the experiment to produce any noticeable effect, your counterpoise was too large, or your coil was not processing enough energy. Try a smaller section of flat sheet conductor and re-run the experiment until you are getting visible effects beneath the counterpoise. ---------------------------------------------------------------- 1) With the coil ground wire connected to the counterpoise fire the coil system at various power levels while holding a low pressure tube near the counterpoise plate. Observe the tube brightness. 2) Repeat experiment #1 above with the coil well grounded to a dedicated low impedance RF ground. Hold the low pressure tube near the ground strap. a) My lab notes state that when the coil is working off the counterpoise, a low pressure tube indicates significant standing voltage and current. Since the counterpoise is insulated from the floor, leakage and radiation of energy must be unloading the counterpoise. When the counterpoise is overwhelmed, this leakage is quite visible with the naked eye, and appears in the form of corona and sparks to the floor. This indicates a situation where large amounts of RF interference (RFI) is leaving the system. b) When the coil is grounded to a low impedance RF ground there is only a faint glow from the low pressure tube when it is held near the ground strap. The tube does brighten when one terminal is in direct contact to the ground strap, which shows the ground is energized. This indicates that the RF voltage and current is no longer trapped and radiating, but is going to ground. --------------------------------------------------------------- 1) Connect the base of the secondary coil to the counterpoise. Place the low pressure tube in series between the counterpoise and the RF ground. Fire the coil at various power levels and observe the tube. a) This experiment clearly shows the need of a dedicated RF grounding system on Tesla resonating systems. At very low power the tube glows brightly, at higher power the tube begins to heat from the RF current through the low pressure gas. ---------------------------------------------------------------- OPTIONAL EXPERIMENTS Load the Tesla coil system with a toroid or other discharger that is large enough to prevent spark from breaking out, then retune the system with the new discharger. (hint: without spark, retuning may be done by the glow of a low pressure tube {brighter = closer in tune} or by drawing off spark with a grounded probe) Repeat the experiment series above. a) The first thing that will be noted is that ground current has increased dramatically when spark is no longer allowed to break out of the discharge terminal. The counterpoise is overwhelmed immediately, even at very low power. The energy forced into the secondary is trapped. Due the damped nature of the secondary oscillations, radiation is inefficient. The trapped energy is forced to ground. THIS IS THE BASIS OF TESLA'S WIRELESS POWER TRANSMISSION IDEA. This may now be called a transmitting coil, or transmitting system. Take a second Tesla resonator (just a bare coil, no primary or tank circuit) of slightly higher frequency than the transmitting system used to power these experiments. Load discharger onto the bare secondary until the coil is tuned to match the frequency of the "driver" system. This simple uncoupled tuned coil will now be referred to as the "free" coil. 1) Connect the transmitting Tesla coil system {set up and tuned as detailed under [OPTIONAL EXPERIMENTS]} to the counterpoise. Note: the counterpoise is overwhelmed almost the instant the transmitter coil is energized. Connect the base wire of the "free" coil to the counterpoise, then energize the transmitter coil. 2) Connect the transmitting Tesla coil system to the dedicated RF ground. Run a ground strap or other flexible low impedance conductor from the dedicated ground to the base of the "free" coil. a) The "free" coil is retrieving the RF current from the counterpoise and resonates to spark despite lack of inductive or electrostatic coupling. This coil may be placed quite some distance, even off axis, from the transmitting coil and will still spark well. b) The "free" coil still resonates to spark despite the fact that the transmitter coil is driving into a dedicated low impedance RF ground. This shows the ability of even a small coil system, properly set up and tuned, to "power up" a low impedance RF ground to the point where usable energy may be drawn off. --------------------------------------------------------------- These experiments clearly show the importance and function of RF grounds for the efficient operation of Tesla resonators. The more advanced "Optional Experiments" show the basis of Tesla's wireless power transmission through earth resonate ground currents. Richard Quick ... If all else fails... Throw another megavolt across it!