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Re: faraday cages (II)

Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
> Original poster: "Ray von Postel by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <vonpostel-at-prodigy-dot-net>
> Bill:
> Glad you joined this thread. You are preceded by your reputation.
> >From what I can find out, there is little SPECIFIC information available
> relating to the output of a Tesla coil.  I hope you can point me
> to a source.  There is an old saying: "You don't really know until you
> can write an equation."  (that should produce a flame).

	This may have originated with Faraday (? Or is his name on
	my mind?) as:

		Knowledge, without measurements is very unsatisfactory.

	(or close to that...).

>>The equations are there for the design of the coil itself, but almost
>>everything else seems to be anecdotal.

	Equations are nice.  Some phonomena are a bit too complex for
	equations.  A good set of measurements may lead to equations.

	EMI (RFI, RFI call it what one will) can get that way.

> Tesla list wrote:

> > Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <wysock-at-ttr-dot-com>

> > To Ray, et. al.

> > (Terry, my apologies for not "snipping" this thread, but I felt
> > it was a necessary addendum to this discussion).

> > All good shielding techniques aside, the *real* problem has
> > been (and continues to be), at least in my experience, how to
> > attenuate the *very broad-band* RFI emitted by the SPARK
> > DISCHARGE ITSELF, from a medium to high powered
> > Tesla Coil.  It turns out, that the R.F. spectrum from the
> > spark discharge (itself), can (and will be), the *main* culpret
> > in mitigating RFI issues of any given installation.

	Decades (literally) ago i did some rough work (since
	lost) with arc welders, in fact, RF stabilizd arc welders.
	There was relatively little out put from the arc, per se.
	In that case, the welders were on a thr ground floor, with offices
	(and 'puters) above.  Copper Screen was laid on the fllor above, no
	problems were seen.

	On The Other Hand, the RF fromt he welding arc was indcidental,
	and that from the RF generator was Just Enough to stabilize the
	arc, so the situation is different...

> You speak of attenuation of  a "very broad band" of RFI.
> RFI to me means an annoyance rather than a real problem. Stopping
> it is usually as much public relations as technical skill.  It is
> often messy, tedious and time consuming and can involve such little
> things as a ground wire touching a rusty tomato can. What I  am
> concerned about is sufficient electrical energy at what ever power and
> at what ever frequency and wave shape sufficient to cause physical
> damage such as burning out transistors.

	In general EMI work there is 'principal':
		Attenuate and isolate as close to the source
		as possible.

	In this case, how practial would it be to build a 'doghouse'
	around the gap.  Leads in and out (AND the motor shaft shaft
	if rotary) would require filtering, any grounds being tied
	together and to the doghouse.
> When I spoke of the "output" spectrum of a Tesla coil, it was not my
> intent to limit the problem to the SPARK DISCHARGE ITSELF.  By that
> I assuming you mean the fixed or rotary gap.  I take it as a given
> that every Tesla coil system is a very dirty r.f. source.  However, I
> don't know if anyone has taken the time to measure it in terms of
> frequency and amplitude.   i.e. How many microvolts per meter, at
> what frequencies,  at some specified distance from the coil and
> how many decibels above or below some recognized standard power.

	I rather suspect this would vary widely (one might say wildly)
	from each to each.

> Developing a field pattern for  the radiation from a Tesla
> coil would at best be difficult because of the almost infinite number
> offrequencies.  Not only that, but such a pattern would be unique to
> that particular installation just as it is for radio transmitters in
> general.  You can engineer a radio installation and hope
> you get the coverage you want, but the result still has to be proven
> experimentally.

> If EMP is generated, how much?    What, if any thing is the problem?
> Have you or do you know of any one who has attempted these measurements on
> a Tesla coil?


> > Best regards,
> > Bill Wysock. 

> Perhaps my interest in this is related to the fact that I would rather
> design something on paper first, then build and test it, with some
> assurance that what I am working on has a reasonable chance of doing
> what I want it to.

	One of the distinctions between science and engineering...
	(The line is by no means absolute....)

> But then, as Dr. Terman was quoted as saying:
>>  "You can design something, but in the end, you often find yourself
>> tinkering."

> Tinkering is fun but it is cheaper to waste paper.

	Sometimes (I believe this is one of them) tinkering is the only
	approach.  Good advice (as has been proposed here) can guide the
	tinkering.  There is much knowledge which may or may not
	be generally available, which is, no the less there for the taking.

	My personal impression is that (nukes, lightning, and gummint
	exercises aside) most of the 'threat' here is electomagnetic
	rather than magnetic.  as electromaginetic, it can be (relatively)
	predictably shielded.  IF.  If attention is paid to the details.
	If the details are missed and an Assumption is made about the
		O  It is Magnetic and hence hard to handle
	It can lead away from the useful fix of getting the electromagnetic
	shielding right...

	dave p