[RFI] Server switching power supplies

[Jim Brown]

On Mon,6/26/2017 10:59 PM, Martin Kratoska wrote:
> Which RFI/EMI options should be added?

Hi Martin,

Without going inside the box, the best things to do are the fundamentals.

1) Use twisted pair for the current carrying conductors on both mains 
and DC wiring.

2) Make certain that the protective earth goes STRAIGHT to the chassis 
at the point of entry, NOT through the chassis to interior wiring and 
then to the chassis (the Pin One Problem)

3) Put SERIOUS common mode chokes on the mains cable and the DC 
cable(s), following the guidelines in k9yc.com/RFI-Ham.pdf

4) Add RF bypass caps across the DC line and the mains line

These measures attack the components of the noise conducted to external 
wiring and radiated by it. They won't help with interior design issues 
related to poor circuit layout, construction, and shielding. If you've 
done your best with these (get very serious with the chokes, aim for at 
least 5K ohms choking Z at the frequencies of interest) and the noise is 
still there, you're stuck with serious interior design issues that can 
turn into a major science project. :)

If you don't already own it, the latest (3rd) edition of Henry Ott's 
classic text on EMC is a great reference. It includes chapters on 
switch-mode power supplies and printed circuit layout. Henry is a ham 
with a WA2 call.

73, Jim K9YC