[TCML] RFI EMI Filter question and PC survivability
jimlux at earthlink.net
Wed Jan 28 15:45:14 MST 2009
>That is a really nice and educational summary!
>All monitors should have at the very least a sizeable Ferrite barrel clipped
>around the shielded cable. I remember a fix that was sent out by let us say
>Viewsonic which was a large ferrite clip on barrel. I don't know how many
>VGA adapters failed or got flaky before the kits were retrofitted. Now that
>was presumably without a poorly grounded Tesla coil just running near
>breakout running in the neighborhood ;-)
The ferrite will do almost no good in the TC world. For the fundamental at several hundred kHz, the ferrite has very low loss. For the fast transient, it might help, because it adds a bit of series inductance to the loop that's "receiving" the magnetic field transient, that will slow down the rise time of the pulse on the loop (e.g. on the ground wires) which would reduce the amplitude of a coupled transient to other wires. On the other hand, the increased RF resistance from the ferrite will make the voltage difference between the ends of the wire greater, possibly aggravating the transient.
>I guess RF though gets around anything though that's not isolated in a
>Faraday cage. Hole size of course even becomes an issue at the really short
>wavelengths. We used to have a big, very elaborate fine copper screened one
>when I worked for a science company in Illinois doing microvolt stuff. Even
>the door seals are impressive.
A Faraday cage only helps for E field, and doesn't do much for the magnetic field, except for components that happen to be parallel to the cage walls. Only if the cage is complete enough that it forms a "shorted turn" would it actually do anything.
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