On 5/9/13 6:03 AM, dave pierson wrote:
Actually, there is a potential powerful EMI source that exists only when a secondary is in place and sparking. That's the magnetic field formed by the current flowing in the loop from secondary topload through spark to ground and back to secondary. Very fast rise/fall time (di/dt), large area of the loop, and pretty high peak currents makes for a potent transient source.I'm not sure how the house is wired, if that's what you're asking. The coil and the computer are plugged into neighboring outlets, maybe six feet apart. I can definitively say they're on the same circuit, possibly in parallel, but I can't say for sure.Assuming this involves a 'primary' including a coil and gap (or solid state driver): Yes. Once the circuitry starts to oscillate: the primary, all leads, etc, RADIATE. There is nothing particular to a secondary, with or without discharge that causes 'radiation' to only happen once a secondary is in place. The secondary may improve 'efficiency' of radiation.
And a cage or strike rod doesn't really help with reducing this source, since the issue is the magnetic field, not the electric field. The rapidly changing magnetic field induces a voltage in any other loop nearby.
One could probably reduce the effects on a particular piece of victim equipment by a)making sure the victim doesn't have an inadvertent loop that is large and b) orienting the sparks by moving the strike electrode and/or breakout point so that the loop that radiates is oriented properly.
Unless contained (eg carefully debugged Faraday Cage) the
RF field clutters up everything nearby.
A typical faraday cage won't do anything for the magnetic fields radiated by the primary. Cages are all about E field and electrostatics. The only easy way to reduce H field is by layout.
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