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Posted by Charles Marslett on 02/24/07 22:07
On Mon, 19 Feb 2007 08:56:07 +0100, Martin Heffels
<goofie@flikken.net> wrote:
>On Mon, 19 Feb 2007 01:57:39 -0500, "Smarty" <nobody@nobody.com> wrote:
>Yeah, the software radios are quite nice. It's amazing how they can keep
>out the RF generated by the computer, while some of them are crammed inside
>the computer :-)
>
>-m-
At first glance it's true, but then you think a bit about the way
those cheap boxes are designed (at least at Dell, I work there!) -- to
minimize the shielding (cost) you do a lot to balance the radiation.
In a previous life (before VLSI was bought by Philips) I worked on a
project to eliminate most of the shielding requirements entirely --
just make sure that every signal was balanced with one very nearby. It
works really well at GHz frequencies and it saved on wires as well.
You just run 20 wires from here to there (< 1/2 inch of board width
even with a 4 layer board) and make sure that any H/L transition is
balanced with a L/H transition, make sure there are enough to power an
A/C to D/C converter in the second chip and you wind up with no power
plane (or power plane radiation) and no signal RFI. And very little
conducted EMI.
At a couple of inches you could do decent RF without much (or any)
shielding. Of course, computers are getting smaller every year, so it
might be a bit more challenging now to find any spot 2 inches from the
CPU and memory.....
--Charles
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