[SI-LIST] Re: Gigabit fiber transceivers, EMI, trace lengths, and... antennas.

  • From: "Doug McKean" <dmckean@xxxxxxxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 9 Aug 2001 14:46:27 -0700

"Kolstad, Joel (EIP)" wrote:
>
> So, we have a fix, but I'm curious -- how does a 318.75MHz
> signal radiate from a hole in the rear bracket that's ~.4"x.3" wide?

You'd be surprised at how little energy is needed to
violate emissions testing levels.  I did a little informal
experiment with various length stub antennas starting
at 1 inch on up to 6 inches and found high levels of
emissions from 30MHz to 1GHz with something like
a -20dB/decade rolloff.  Not bad for a piece of wire
1 inch long.

And it most likely isn't the hole that's radiating.   It's
probably the bracket by way of a slot effect.  Slots
are electrical duals of wires, but their directivity is
roughly 10 times that of a simple wire.

- Doug McKean


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