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Re: EMI Shield Beads
From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent: Sunday, September 14, 1997 9:21 AM
To: Tesla List
Subject: Re: EMI Shield Beads
On Friday, September 12, 1997 1:54 PMWilliam Noble
[SMTP:William_B_Noble-at-classic.msn-dot-com] wrote;
> at the risk of disagreeing with the more experienced members of the list,
> consider the following - most installations have some length of wire from the
> transformer to the primary coil/gap/capacitor area. If this wire were to run
> through these EMI beads, then its inductance would be increased. These beads
> are really cheap - surplus stores sometimes have bags of them. I suppose,
> lacking beads, you could use nuts (like a #10/24 nut) on the wire to increase
> inductance.
Perhaps a little description of what happens inside a choke at the
molecular level will clarify. Any magnetic substance is composed og
domains, these act like small magnets. In core material designed for
high frequency work these domains can move very freely, thus they can
flid in unision with the rapidly alternating current passing through
the surounding coils. In core material designed for low frequency
work, especialy chokes, these domains do not move as freely thus
affording great resistance to higher frequencies. The EMI beads are
designed for high frequency and thus will offer little or no
resistance to the lower frequencies of a Tesla Coil. Material like
carbon steel or silicon steel is far better for R.F. chokes in the
frequency range that the typical Tesla coil is operated at. If you
still doubt, then take an R.F. signal generator and a Scope and take
an EMI bead and loop a wire through it and observe how it responds
over a frequency range from say 50 Khz on up to 200 MHz and you will
see it offers little or no resistance untill up in the 200 Mhz range,
which is above any spark driven Tesla coil I have ever seen or heard
of.
Sincerely
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Alfred A. Skrocki
Alfred.Skrocki-at-CyberNetworking-dot-com
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