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Re: [RFI] Server switching power supplies

To: rfi@contesting.com
Subject: Re: [RFI] Server switching power supplies
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 27 Jun 2017 10:44:30 -0700
List-post: <mailto:rfi@contesting.com>
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

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