[TCML] RF Grounding
rtqii at charter.net
Fri Mar 7 08:13:15 MST 2008
Hi all :)
A bunch of people here are getting ready to rehash RF grounding techniques etc... This is an area I feel qualified to comment on.
You can take an ungrounded Tesla coil, place it on a concrete or earthen floor and it will operate just fine. You may toast some wire at the base, arcing will remove the energy, the coil will operate and spark from the discharge terminal just fine. Depending on the construction of the coil, you may, or may not, notice any visible performance variations in the discharge. You can ground a coil with a tiny thin wire, same thing, except arcing from the bottom turns will be prevented.
I noticed a post awhile back where someone stated the coilbld documents are dated and require revision. I stand on that work, as is, still today. I would not change a thing. I clearly stated in the text "these instructions are designed to
produce a highly efficient RF resonator with exceptional electrical strength at the lowest possible cost." You are of course perfectly free to alter, change, experiment, spend additional money, or time, with any design or modification you choose. I would be the last person to offer any resistance to people who want to do things differently.
My understanding of resonator functions is pretty clear. A standard 1/4 wave Tesla coil with a grounded base has a very complex wave form. A coil never ceases to ring electrically, even when the power is off... They are documented radio technology and they are always processing some signal, be it stray EMF, induction from some nearby power source, even cosmic ray impacts will excite them (try explaining this to a patent attorney who insists they can only operate with pulsitile output in a spark gap excited circuit). If you don't believe me, test it with a sensitive scope and a capacitive pickup (like a strip of aluminum foil wrapped as a partial, unshorted, turn around the coil. Connect the strip to a scope and slide it up and down along the length)... There is always signal there, always.
When the tank circuit fires, the coil is pulsed. In 1/4 wave Tesla resonators the pulse causes the coil to respond with a current spike at the base. The continous output (averaged by something like an RF ammeter or visually indicated with a low pressure tube placed in series with the ground) is what you are accustomed to seeing/understanding... But the current spikes are simply enormous. Huge.
It is because of these spikes, and a nearly instantaneous impedance function that is associated with these spikes, that I prodded people to install heavy RF grounding systems. 50% of the energy processed by a Tesla coil is current which must be efficiently removed from the base of the coil in order to achieve optimum performance. This current is continous, it never stops, and traces of it can be detected in a coil even with the power off. In the waveform of that current, there is a train of current spikes when it is excited by a tank circuit... Very, very, heavy current, which spikes for just a microsecond or two. It will flow out and disperse no matter what... If there is no easy, clean, low impedance path for this current, the voltage at the base of the coil will rise as the 1/4 wave current function at the base of the coil will shift away, up into the winding. The voltage will continue to rise at the end of the coil until the impedance at the base matches the impedance of the output path and energy is permitted to escape.
You can test this too... But drawing spark from a bi-polar coil. If you ground one end of a bi-polar coil, it shifts to 1/4 wave function. If you remove the ground lead and draw an arc... The impedance, and the coil wave function will shift back and forth between 1/2 wave operation and 1/4 wave operation as the grounded lead is moved closer to, and farther from one end of the bi-polar coil. You can observe the inverse function on the opposite end of the coil as you do this.
People have the wrong impressions of how a coil operates if they do not understand this. In order to obtain maximum efficiency at high power, you have to keep the coil function from shifting. This means that you have to lower the impedance of the ground path as close as possible to ideal zero. The impedance shifts around with power levels, and with each and every current spike.
Yes, an ungrounded Tesla coil sitting on a concrete or earthen floor will work just fine. You may burn out some lower turns as it will arc (high impedance)... A very fine wire will prevent the arcing... The coil will still work fine.
But I would not post information here today (have I ever?) that I have not personally tested and measured myself. If you want the best possible performance, the safest operation, the lowest possible EMI hash in the surrounding area... You will read, and try to understand there is more going on than meets the casual eye; the time functions are very small, and the current peaks are very hard to detect and measure because of the energy type, and the shifting functions at the base of the coil (measuring it actually and truly changes the values).
I just got another patent application filed. It is my second in a series I am working on. It's a provisional application (no claims at this time) I have a year to file the utility application... The patent office does not publish provisionals, but it is documented, so I can prove priority. I have sent a copy to Gary Peterson
( http://www.tfcbooks.com/ ) and we will offer it for sale as a printed document for a modest fee to cover the processing, printing, and handling. I would expect to make a buck or two. Nobody is ever going to get rich selling Tesla documentation, I sure don't, but it's not free to produce either. This is just an FYI. I am not trying to sell anything to anyone, but there has been interest and so I have cleared this with the patent attorney and Gary Peterson to make this documents available. There is a short list of people who will be getting complementary copies, but it will be available to everybody, soon, for a reasonable fee. We have not finalized pricing, or when print copies would be available... Gary should have more information after this weekend, and you should contact him (not me) next week sometime for more information if you are interested.
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