Shielding components from EMI/RFI... Help please


A recent experiment with a product designed to reduce EMI/RFI left me curious about other ways to reduce EMI/RFI in my system. In the past ten days, I've stepped onto a slippery slope, at the bottom of which is surely some kind of insanity...

I've been experimenting with copper plates in an effort to absorb, deflect, diffract, and block EMI/RFI. I've tried copper plates under components, on top of components, and inside components.

This is the point where you tell me I don't know what I'm doing and I'm likely to short circuit something and/or electrocute myself. Consider me duly warned. This is also the point where you tell me to get some balanced interconnects, or at least to get some shielded interconnects for Chrissake. Consider me duly informed. Moving on...

I'm hoping you can help me make the most of this experiment, and help me avoid killing a component or myself. My strategy so far has been to:

1. Place copper plates at locations that generate a lot of EMI/RFI, e.g., components with switching mode power supplies or high frequency clocks. The system has a total of 3 SMPS and 3 clocks.

2. Place copper plates at locations that are vulnerable to EMI/RFI, e.g., under the amp, near the transformer.

3. Place copper plates inside noisy components -- in particular, my Meridian G68 preamp/processor. I've begun to build 2 partial Faraday cages, one for the SMPS, and one for the analog output stage.

4. Ground the copper plates either to the component chassis (when plates are used inside a component) or to an independent ground point (when plates are used above/below a component).

Has anyone tried this sort of thing?

Bryon
bryoncunningham
The plate is directly under the switch. I placed it there to keep the braided ground strap as short as possible, to minimize any antenna effect. Out of curiosity, is there another reason why it should be directly under the switch?
Just my vague intuitive feeling that placing it there might enhance the effectiveness of the switch's internal ground plane, perhaps reducing the amount of digital noise generated within the switch that might end up coupling or radiating to points downstream.

With regard to the well thought out summary you presented in your last post, my only comment is that it would seem to make sense that the best results were obtained via a configuration that does not provide any paths that bypass the reclocker and its galvanic isolation. As you noted, such a path previously existed, via the ground wire from the switch to the conditioner, and from there via power cords to the downstream components.

Well done! Best,
-- Al
I agree that the current configuration seems to maximize the benefit of the reclocker's galvanic isolation.

I have a follow up question for you, Al, about the dissipation of noise in an equipment's chassis... Is the dissipation potential of a chassis determined by its surface area, its mass, its material, its conductivity, its magnetism...? Several of the above?

bc
Is the dissipation potential of a chassis determined by its surface area, its mass, its material, its conductivity, its magnetism...? Several of the above?
Excellent question, but I have no particular knowledge of what the answer might be. I suspect, however, that the answer will be a combination of those factors, and that the optimal combination will vary as a function of the frequency components of the noise. And unfortunately digitally-induced noise will typically have spectral components covering a huge range of frequencies.

If you are feeling particularly ambitious at some point, I suspect that some good answers can be found in "Electromagnetic Compatibility Engineering", by the distinguished expert Henry W. Ott.

Best,
-- Al
Thanks, Al. That looks like a great reference guide, though much of it is over my head. I think at some point I'll take a course in electronic engineering, to get a firmer grasp on some of the more difficult concepts.

I read a few of Ott's articles and tech tips on his website. I particularly enjoyed this one.

bc
I particularly enjoyed this one.
LOL! I hadn't seen that before. Thanks!

Best regards,
-- Al