At 15.34 2005.10.01 +1200, you wrote:
>I know a couple of people on the list have mentioned having
>their products tested for EMI interference and what they did
>to stop it, hopefully they'll be able to give you some advice
>
>> Used an old ATX power supply metal box,
>
>Does this box have any holes in it ? If it's like every other
>PC supply I'm guessing it does. The noise will find its way
>in through those holes. Try blocking all the holes with
>aluminium foil, see if that makes a difference. Ideally you
>want an unbroken metal barrier all around the circuit, which
>includes the wires

Only signals with wavelength smaller than the holes will go
through, like a low-pass filter. Thus many small holes are
better than one big hole (considering equal surface). That's
why it's typical to see many small holes for venting than
fewer bigger ones, expecially where high frequences can be
a problem.

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