On 4/13/11 6:02 AM, dave pierson wrote:
Electrically it would help a lot. Aesthetically it would suck bigtime. If you could leave off the side toward the audience it would still be a big help. You could hoke the cage up to make it look like some kind of lab walls.An open sided 'cage' will catch SPARKS/ARCs only. EMI/RFI will propagate freely.
ANd, for the frequencies of interest in a TC (at the fundamental, at least) a cage isn't going to do all that much good. The cage is in the "near field" of the coil (RF wise, considering it as an antenna) so a significant amount of the power is carried in the magnetic field, and a wire cage only stops that part of the field parallel to the wires, and not very well at that.
For the VHF/UHF (radiated from TC wiring near spark gap, for instance) (or from the spark from the top load), a wire cage "might" work if it's pretty well constructed (no gaps between walls, small enough holes, no wires penetrating the cage). I'll bet most TC Faraday cages are actually pretty darn poor at shielding for radiated emissions.
I think one of the mechanisms for TC interference is actually a form of conducted emissions: conducted by the capacitance between coil and victim equipment. Yes, the field is sort of radiated, but I think of radiated emissions as being in the sense of propagating waves (not strictly true), but since the TC wavelength is very much longer than the physical size of the things, I think you could consider the path as a lumped component rather than as a antenna propagating a wave to another antenna.
My guess is that TC cages work because they contain where the sparks physically go, and more importantly, they provide a low impedance return path to the coil for the spark current. That is, the E field from the spark doesn't penetrate the cage very much, so there's not much capacitive coupling from the sparks or coil to things in the surrounding (mic cables, power cords, etc.).
It's like putting a grounded electrostatic shield in the middle of a capacitor.
And if this is the case, then whether your cage has 6 sides or 5 or 3 doesn't make as much difference as whether you have something conductive between source and victim.
(didn't one of the long-time list members do some stuff with a semiconductive sheet hung horizontally above their coil to prevent "roof strikes"... In Switzerland, I think, but maybe Germany.
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