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RF Ground when living on 7th floor of a building ? pls help

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PhilGood

Wed Apr 06 2011, 03:10PM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Hi all, I'm new to this forum and TC stuff, and I'm wondering what I can
actually run safely regaring EMI/RFI problems.

I live on the 7th floor of a big building:

I have a large terrace:

There's nothing above the terrace, so it's like a roof.
Its covered with flagstones, and under them is a 4" space mainly used to collect rain
The surface under flagstones is partially covered with aluminium-tar:

So I have two questions:

1) Are TC's the only HV devices that requires a good and separated RF ground ?

2) According to what I described above, what would you suggest to make an efficient RF ground or counterpoise for a TC ?

I was thinking to something like putting some metal grids under the flagstones, connect them all together, and have a wire comming up from the center of that big grid as RF ground.

I my opinion that "could" act as a counterpoise, but on an eletrical point of view, it seems that it would be a big capacitor with my terrace beeing the top plate, and the "real" ground (floor -3) beeing the bottom plate... what's gonna happen inside this capacitor where many ppl live

?

(I gotta add that, for now, I'm only willing to build a small SGTC, something like 10" height 200W)

Thanks in advance for your advices and suggestions

Killa-X

Wed Apr 06 2011, 03:35PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Hard to say. No expert here so I would wait for others to respond. I would think it would be best to run a wire all the way down the side of the building to the ground. The reason I say this, is because it's a known fact that a lot of steel buildings are grounded. Part of the NEC says its not require, but you can ground the whole structure, and then use the structure for grounding equipment. So, if your building is consisting of steel framework, I just worrie if you try to make a grounding grid on the roof, and it tries to spark through the roof to a metal part of the frame, it could risk any device plugged into the wall with a 3 prong plug.

Also, Tesla coils do emit a range of RF. When your coil is operating, it makes a rather large magnetic field, which could possibly mess with people below your floor. For example, if I run my SSTC, anywhere in the house, the touch-lamp upstairs will flick on and off. Even when i was outside 50ft from the house with a ground rod, still did it. Computer USB devices often connect/disconnect too. So I would take that into consideration, so if the people below start seeing anything act funny, you can maybe solve it, rather than letting them suffer =)

PhilGood

Wed Apr 06 2011, 05:21PM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Thanks Killa-X for your first advice and recommandations

I understand It's quite a complex and unusual situation with many parameters to take into account...

Unfortunately I know for sure I'll never be allowed to run a wire down to the ground (I'm not owner here, just tenant), and it would be better that no one knows what I'm doing, lol

That's why I'll add a 3rd question:

3) If I have no way to have a proper RF Ground , what is the max Power/Size SGTC I can run without RF ground and without trouble ?

(I've seen many videos with tinny TC's running inside, even on desks close to computers and so on ... don't have the links right now but I'll post some as soon as I find them)

Proud Mary

Wed Apr 06 2011, 05:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

It might be possible to use a counterpoise Earth - an artificial groundplane - tuned to the TC frequency of oscillation.

Killa-X

Wed Apr 06 2011, 09:31PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Cant fully help with question 3, but I will tell you this. I already know my lamp touch sensor is way over sensitive. But, my coil sits in the room below, maybe an agular distance of 50ft away. Even at 10V in, that lamp freaks out. This coil uses no connections to mains ground, and the secondary is connected to a wire that feeds through my window, to earth.

I use to use a metal plate on the floor, which makes the coil work, but then of course you have a lot of RF. Hard to say. Would be crazy to run a wire way down to earth, I'm not sure even how effective it would be at a 7-story length of wire anyways.

Good luck though, Hopefully you can get something figured!

UbuntuNinja

Thu Apr 07 2011, 02:54AM

Registered Member #2677 Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64

You could research Bipolar Tesla Coils. I think a bipolar coil might not need an earth ground because the center of the secondary coil has a potential of zero volts. This is merely speculation, so I would be sure to read up on the topic to see if that is a viable option.

Good luck,
UbuntuNinja

PhilGood

Thu Apr 07 2011, 09:19PM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

This might be a solution ...

I found an interesting configuration designed by Stefan Kluge, where 2 vertical coils (one complete coil + another secondary) act as a bipolar halfwave horizontal coil... Both secondaries bottoms are just connected together.

I think it's quite similar to what you suggested, Proud Mary, but instead of wasting energy in a metal plate we use it to power the tuned 2nd coil.

But this is probly harder to tune, especially for a 1st trial...

_________                _________
 (_________)==^-~-\,-~-`-~(_________)
     I I                      ItI
     I I                      IwI
     I I                      IiI
     I I                      InI
     IcI                      IcI
     IoI                      IoI
   \ IiI /                    IiI
    \IlI/                     IlI
      +-----------o------------+
                  |
                  virtual gnd point
                  (not connected to any real gnd!!!)

Full details: Stefan Kluge's Vitamini Twins

______________

Edit :

I've seen a few VTTC's and it seems evrything (including secondary's bottom) is connected to mains ground ... is that right ?

Crunchy Frog

Fri Apr 08 2011, 01:28PM

Registered Member #2422 Joined: Tue Oct 06 2009, 02:41AM
Location:
Posts: 85

You can, in fact, use a counterpoise ground if it's big enough. Running a wire down the building would be pointless (and potentially dangerous) because the inductance of the wire could cause the 0V point to be somewhere it shouldn't be.

The secondary doesn't need to be grounded per se, it just needs something with sufficient capacitance to the topload to "complete the circuit." Ordinarily this would be earth, but in your case any large connector connected to the bottom of the secondary should work.

However, the primary circuit, at least for an SGTC, should be left floating. This will help protect your mains wiring from hf.

Steve Conner

Fri Apr 08 2011, 01:37PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

[quote]

_________                _________
 (_________)==^-~-\,-~-`-~(_________)
     I I                      ItI
     I I                      IwI
     I I                      IiI
     I I                      InI
     IcI                      IcI
     IoI                      IoI
   \ IiI /                    IiI
    \IlI/                     IlI
      +-----------o------------+
                  |
                  virtual gnd point
                  (not connected to any real gnd!!!)

[/quote]

I've run a DRSSTC like this, it seems to work well.

wrote ...

I've seen a few VTTC's and it seems evrything (including secondary's bottom) is connected to mains ground ... is that right ?

Yes. VTTCs produce less interference because of lower peak power, so it is OK.

Apartment coiling can be tricky, good luck! :) This is my DRSSTC in operation on the table in my 4th floor apartment. The secondary base is just connected to mains ground at the fuse box, where the mains supply enters the apartment. The best way of controlling interference is to do it when the neighbours are out.
Spark0611 S

I've since built a full Faraday cage for public demos.

GeordieBoy

Fri Apr 08 2011, 03:00PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

As others have said, definitely use a Faraday cage, or at least an extensive local ground plane beneath the coil.

The RF current between the base of a TC secondary and ground (earth) can be quite large. If you force this AC current to flow to ground through a long conductor dangling from a 7th floor window it will likely make an effective antenna and radiate interference (>.<)

The idea with the counterpoise or faraday cage is to catch all of the displacement current from the toroid and return it to the base of the secondary with the shortest possible round-trip journey! Large AC currents flowing in long lengths of wire are the best way to produce radio waves!

-Richie,

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