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Re: [TCML] Maximum Field



Suggest looking up 'radiation resistance of helical antennas' before worrying too much. VHF radiation from leads to gap is a much bigger problem.

Ed

Derek, Extreme Electronics wrote:

Jim,
I agree with your assessment of the radiated energy, but if you design a coil to give a high field without any mitigating sparks you will radiate more RF than usual.

Even if you only radiate 0.01 % of say 5KW, that is enough to interfere with radio communication in a large area, my warning was purely to take this in mind when building such a coil.

Luckily radios tend to use much higher frequencies than most of our coils these days, so this is becoming less of an issue admittedly.

    Derek


On 21/12/2012 14:00, Jim Lux wrote:

On 12/21/12 4:38 AM, Derek, Extreme Electronics wrote:

Cole,
Make a large coil with a large top-load and don't let it break out..

     e.g  Design your coil like an antenna...

     Just a word of warning, what you describe is a radio transmitter.
Tesla coils usually sneak under the radar as their secondries / toploads
make poor RF radiators and a spark / arc kills the emissions further
still. As soon as you create a coil with a maximised field you are
likely to cause interference and be hunted by the authorities.


This isn't actually true.. you can have a very high field in a small space and it doesn't radiate very well. Consider, for example, the field in a spark plug: a gap of 1mm with a voltage of 40kV is a field of 40MV/meter (well above breakdown of air, because the gas inside an engine cylinder is compressed, so it's breakdown is correspondingly higher)

What you're thinking of is "radiated field", and given the incredibly small size (compared to wavelength of, say, 3km) of even a huge tesla coil, it is not an effective *radiator*, even though the field near the coil is quite high.

While the near field near a coil can be quite intense, it's pretty well contained and doesn't radiate.


     Put it in a Faraday cage to protect yourself from a knock on the
door..



I would venture to say that no tesla coiler has ever gotten a "knock on the door" from the FCC or comparable radio regulatory authority.

Angry neighbor, perhaps, but more because of acoustic noise or fear of sparks, than because of EMI.


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