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[SI-LIST] Re: EMC Analysis

From: "Hassan O. Ali" <hassan@xxxxxxxx>
To: darshanmehta2k@xxxxxxxxx, si-list@xxxxxxxxxxxxx
Date: Mon, 13 Mar 2006 11:34:13 -0500
Nobody knows :-)

Seriously, for EMC purposes, the electric (E) field radiation levels are 
measured in the 
far-field e.g. at a distance of 10 meters from the radiation source. If you 
have two (or 
more) electromagnetic field radiation sources, the sum of their radiated 
E-field at a 
far-field point is a spacial and temporal vector sum which depends on many 
things. 

For example, if the two radiation sources have orthogonal radiation patterns 
e.g. the 
point of maximum radiation of one source lies along the x-axis and the other 
along the y-
axis, if the far-field point where you measure the E-field is along the x-axis, 
the 
total measured E-field will probably be just the maximum E-field of the first 
source 
(certainly not the linear sum of the two maxima).

You also mentioned "system level" - and I'm sure you know that all systems are 
not 
created equal! A system can have other factors that affect field interactions 
making it 
so difficult to determine the best way to aggregate radiated E-field from 
multiple 
sources. A printed circuit board with many nets, operating at various 
frequencies, is a 
very complex radiation system by itself. When you have many of those boards, 
say in a 
shelf, you've compounded the problem even more. That's why I said at the 
beginning, 
nobody would know how to sum the radiated fields unless you're very specific on 
many 
things. 

In the 90's there were many tools that were claiming that they could predict 
radiated 
emission levels from printed circuit boards. Those tools failed primarily 
because of the 
prediction complexity that I've mentioned above.

Best regards.

Hassan.



On Mar 13, Darshan Mehta <darshanmehta2k@xxxxxxxxx> wrote:
> 
>   Hello Everybody,
>  
>  I have one very basic question about EMC Analysis. If we have 2 nets in 
> design, CLK1 
and CLK2, both switching at 200 MHz. If we see Electro-Magnetic radiation of 
100 dB from 
CLK1 and 105 dB radiation from CLK2, what will be the EMI radiation level at 
System 
level? Thanks in Advance!
>  
>  Best Regards,
>  Darshan Mehta
>   
>               
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[SI-LIST] Re: EMC Analysis

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