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Re: Faraday cage

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

Tesla list wrote:

> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Tesla list wrote:
>>Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"

> <jimlux-at-earthlink-dot-net>
>>----- Original Message -----
>>From: "Tesla list" <tesla-at-pupman-dot-com>
>>To: <tesla-at-pupman-dot-com>
>>Sent: Saturday, May 11, 2002 11:34 AM
>>Subject: Re: Faraday cage

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


>>>>Was very effective in keeping high energy RF/arcs away
>>>>from me.  Cut off frequency is 1/2 wavelength of longest
>>>>opening if memory is right,

>>>Single longest dimension _is_ key:
>>>Thus a door, 2' by 6' is about as leaky as
>>>an 'unlaced' corner, 1" by 6".

>>For what it's worth, all the dimension stuff is totally irrelevant if you're
>>nowhere near the wavelength of the EM radiation you're trying to stop... So,
>>unless you're worried about 100 MHz  (3 meter wavelength) noise from your

> 	When I run my little 3" x 15" coil at 600 watts input I don't get much
> BCI at all.  However, it does cut up the TV pictures.  I disconnected
> everything but the capacitor and the gap and found that the TVI didn't
> change much, so assume all of the interference (at least in this case)
> is coming from the gap/capacitor leads, as you hypothesize.

> 	If you think about the circuit formed there, it's not much different
> from what Hertz used in his pioneering experiments.


	Two points:
	Hertz (& early Marconi) was in the hundreds MHz.  Initially
	little understood (especially, apparently) by Marconi,
	Freq control got tighter, better understood, and drifted
	down, as transmission distances are longer.

	Also:  Illustrates the broadband nature of spark
	oscillators:  MANY freqs are in the output.

	(OK:  Third point  8)>>)
	'stuff' can couple by radiation OR BY RIDING THE WIRES.
	cf my rant about how to do the filtering of a cage
	properly.  MUST deal with any wires in or out.

	And: while I'm in here, from another subthread:
	Grounding of the cage to ground, as several have
	pointed out correctly IS Not Relevant.
	(maybe helps with mag field???).  So long as 'the cage'
	is complete, what its tied to makes no difference.

	(There is a Lovely Quote I've posted before from an
	1880s book on lightning protection:

		...mesh, even so large as i commonly used
		for poultry is sufficient...


> Ed