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Re: Some more Questions on RF Interference and others

Hi Human,

At 12:15 AM 5/15/99 -0700, you wrote:
>Hi everyone,
>
>Any info on the following will be much appreciated:
>
>1st here is the particulars of my coil.
>
>NST -at- 12KV, 30mA (240V, 50Hz)
>Secondary: 4" PVC, 1000 turns 0.5mm wire and a 5" Plexiglass about 1050 
>turns 0.5mm wire.
>Primary: flat spiral, about 12 turns of 3.15mm wire (enamel coated). I'm 
>going to get 1/4" tube today to make a new one.
>Cap: 0.02 microfarad, 15KV (got it at a radiaham festival for equivalent of 
>about 4.8US$, the show was held on marconi day a few weeks ago, and they had 
>two tesla coils (and a lot of other high voltage stuff there, 100KV xray 
>machine xfrms etc). They didn't have any special filters etc as far as I 
>could see and the building they had it in was right beside a field full of 
>radio dishes, didn't hear anyone complain about that :). The two guys who 
>presented it worked for a University here in my country and I asked the one 
>guy and he said it wasn't illegal.)
>RSG: 4 electrodes, about 3100 rpm, type of fan engine.
>Toroid: some sponge tube I coated with Al foil.
>
>1) What is the range of the RF Interference of a Tesla coil? I currently 
>have no neighbours around me except across the street.

There is some RFI at the resonant frequency and a lot of high frequency
noise from the spark gap.  Since you are in a low population area these
should not bother anyone since they will not travel far at all.  If the
neighbor across the street has a problem.  Simply run the coil when they
are not using TV or whatever.  If you ground things well, they will never
see a thing.

>2) Can a faraday cage be made out of the wire used for bird cages? or must 
>it be a more fine mesh of wire? Also can the frame be made out of 
>wood/plastic?

Any wire and frame material is fine.  The TC frequencies are so low that
any size mesh will be fine.  Be a bit cautious about fire.

>3)What is the minimum size of a faraday cage for my coil dimensions? Our 
>ceiling is 3 meters high.

3 times the height of the coil will be about the right number for the
height, width, and depth of a cage.  Depends on some things but that is my
best guess.  The cage will affect the resonant frequency a little but that
should not be a problem.  However, you can really go down as far as the
streamers will allow.  If you find the distance where the streamers just
will not arc to ground, that would be a good distance.

>4) Anyone got plans for building one? Especially one that can be dismantled 
>in a few minutes?

I don't.

>
>5) Our ceiling consists of pressed metal plates (patterns), will that act as 
>some kind of block to some of the RFI?

You bet.  The walls would be nice to if they had the same covering.  You
may want to try and ground this ceiling if that is possible.  But even
without grounding, the capacitance of this structure will keep the RF
contained fairly well in the up direction.  Grounding does not really help
RF containment much but will help if it gets hit by a streamer.  You would
not want and big metal things like this getting electrically charged so
grounding is a very good idea.


>
>6) I have this circut for a mains filter (got it somewhere on internet, 
>can't remember where):
>
>AC in  -----CHOKE--------------------------to NST
>                   |   |
>                  --  --
>                  --  --
>                   |   |
>                   --------Ground
>                   |   |
>                  --  --
>                  --  --
>                   |   |
>AC in  -----CHOKE--------------------------to NST
>
>Each choke, 30 turns of 3.15 mm wire on a 1" diameter iron rod (I cut a 
>weightlifting rod for it, couldn't find ferrite cores except small toroid 
>ones)
>Caps: 630V, 220nF each (maybe use bigger caps?)

This looks reasonable.

>
>With this circuit I still get feedback, can this go out of our house wire 
>and into the powerbox that distribute to the rest of the neigborhood? I 
>don't care about our own radios/TV in the house since I unplug the TV and 
>usually only run my coil at odd hours and for short durations.

It can.  High frequencies will not travel far.  By the time any
interference reaches the others, the levels should be low enough.  Use good
grounding and most RFI problems will be eliminated.

>
>7) Can I use the lighning protection unit/surge protector/mains filter of my 
>pc to filter the mains? Must I connect it in reverse for this?

NO!  The PC boxes typically try to short surges to ground.  Unfortunately,
they are not made strong enough to handle TC type surges and they may be
easily damaged.  Go with the normal line filter circuits and leave the box
on the PC.

>
>8) We got suspended wooden floors in our house? Will that make things a bit 
>safer in case of a hit from the secondary?

If you get hit, any insulation like this will help.  Do not depend on it
though.  Humidity could make the floor surprisingly conductive.

>
>9) How do you convert caps rated in nanoJoule to farads?

Those are different units?  1 farad = 1000000 micro farad = 100000000 nano
farad = 1000000000000 pico farad.

Hope this helps!

	Terry


>
>Thanx in advance.
>
>Human Buirski
>Pretoria
>South Africa
>
>
>
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