Tesla Grounding Issue

[Jeg]

Hi@all

I have made a Tesla coil which needs grounding. What i'd like to ask is what about the length of the ground wire from the bottom of the coil up to the ground point. To my understanding, this length is added to the main coil wire length, and affects my overall wave length calculations. How can i get over this factor? My ground which is in my garden is many meters from my coil bottom, and i'd like to cancel this extra cable affection. What is your opinion on this? If i put 2 diodes in parallel to the bottom of my coil, one facing upward and the other facing downward, will this cancel the extra cable length affection to my wavelength calculations?

Thanks
Jeg

[TinselKoala]

You can try it of course but I think you will need some pretty hefty diodes if you don't want them to blow out. Both ends of your TC will be swinging through the same peak relative voltages. The purpose of the ground at the bottom of the secondary is to "pin" the voltage there at ground potential. This doesn't mean nothing is happening there! The ground acts as an infinite source/sink for electron charges, and ultimately the power of the secondary discharge makes a current loop, just like any other current loop. You just can't see most of the TC loop because it is happening through the big capacitor made of the local environment.... and the Earth itself. Draw current from the top of the secondary, and you also "suck" current from the ground into the bottom.

If I were you I'd string a fairly heavy cable conductor out by the shortest path to the real Earth ground. The length of this cable/wire won't matter in terms of being a good ground, as long as the ground end is done properly. Drive a piece of 1/2" copper plumbing pipe, not too expensive, cheaper than copper rod, 3 or 4 feet into soft moist soil and secure the cable to it with a hoseclamp.  Yes, this will affect the tuning of your coils, but the coils will run much better when tuned and grounded like this. It sounds like you already have a good ground like this.

I confronted this issue in several places I have lived. Some of my early work is on YT, where I lived in a small basement apartment; I was actually underground with the entire coil and the Earth ground I used actually ran to a level above me. If you are in a tall apartment building or something like that, you could try the cold water plumbing pipes in your kitchen or bathroom but much newer construction doesn't even have metal pipes, and there may be other things that would make the cold water pipe not usable as well. Whatever you do, don't use the "ground" conductor in the mains wiring! This will cause noise on the line for everyone else and could actually be very dangerous if there is a ground fault in the building's wiring, or if an arc forms between the ground connection and one of the other mains wires.

Also, as you know, the "effective length" of the ground wire can be very different from the actual physical length, so don't be surprised if the calculated frequency differs from the actual resonant freq when the ground is connected. The proper way to compensate is with a LC network that stays connected to the ground wire, and you take your TC ground from that. But that kind of compensation is of course frequency dependent.

[Jeg]

Hey Tins nice to see u again:)

You made a good point about this LC network on ground side. I'll keep it in mind for later consideration. First i'll try the diodes as i hope that they will cut this extra ground cable effectiveness to the system.  Perhaps a few picofarads cap. will do the job either. I just want the system to work on any ground cable without the need of re-calibration!
What is your opinion on RF grounds? I will also try a big metal plate between that bottom of the coil and the ground rod. I hope the coil will 'see' this plate as a ground, with only a meter of cable connecting them together.

Tnks
Jeg

[TinselKoala]

Oh yes, for a full Tesla system the RF ground is important. Most people building small coils neglect this aspect for portability purposes but the "real deal" includes the RF ground plane, the overhead surroundings and more. Take a look at my favorite TC design software, it even gives you a little diagram of your coil and capacity.
http://www.classictesla.com/java/javatc/javatc.html

[Jeg]

It looks great. I'll give it a try..thanks