Re: [SI-LIST] : Noise Voltage levels vs. EMI levels

Douglas McKean (dmckean@corp.auspex.com)
Tue, 27 Jul 1999 15:32:42 -0700

At 01:03 PM 7/26/99 -0400, Spencer, David H wrote:
>
>My questions:
> Is there is an absolute noise voltage level that should never be exceeded?

There are times when S/N levels were critical.
In the telco industry depending upon the
technology. A former company that made CATV
equipment for TCI and other companies was
absolutely fanatic about it.

> Is there a way to "accurately" quantify the impedance's of the PCB ground
> plane and cables?

I don't know.

>Can noise voltage become a PCB design specification?

Again, at a former telco company, S/N level
was specified as a design criteria. That's about
as close as I've seen of a noise voltage being
a PCB design specification.

>Most importantly, when all is said and done, is there an "accurate"
>correlation between noise voltage and EMI levels?

No. I have spent a large part of time trying to correlate
actual near field E-probe measurements to the far field.
It doesn't work. The variables are just too many.

There are some special cases where you can blindly predict.
I've seen it done with cables.

But, otherwise, it can only be done as long as there
is already some history with the product.

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