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A few months ago, I switched to T-Mobile for an android phone. Upon doing so, I learned that T-Mobile's service tends to be interrupted (drop to no connection randomly) by EMI from a computer. I've tried my SIM in several phones, and all show the same results. Looking at the network providers in Cincinnati on my phone, when near my computer, shows both AT&T and Cincinnati Bell, and T-Mobile will be missing.

So to solve this situation, I'd like to know what are the best ways to reduce EMI from my computer? I've unplugged all devices from the computer to determine the EMI is coming from the case itself. Unfortunately, the side and front of the case are plastic, instead of metal (with the front door removed).

I'm using a Core i7 in my desktop. I've enabled Spread Spectrum, when does seem to help at times, but the problem still exists. The problem is also only bad while Windows is running, even if the wireless card has been disabled, which I'm guessing is due to the CPU being in use more than during BIOS boot-up.

Should I be looking at replacing the case with a full metal enclosure to help reduce EMI further?

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up vote 5 down vote accepted

The only way to stop electromagnetic radiation from the machine is to encase it in a Faraday Cage.

Just make sure you leave any wireless antennae outside the cage.

It may seem like overkill, but it doesn't have to be a perfect cage, you could try using fine mesh chicken wire for example, it just has to block 80% (say) of the radiation.

Wrapping your PC in aluminium foil would also work - as long as you left enough gaps for the cooling airflow.

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For some reason, I see this as overkill for a small desktop. I'm less concerned about stopping all radiation, and more concerned about just reducing it to lessen my issues. – Will Eddins Oct 28 '09 at 18:08
+1 for being thorough. – Tyler Oct 28 '09 at 18:40
GG for taking my aluminum foil answer. :( – Thomas Owens Oct 28 '09 at 18:53

From Computer EMI:

If the computer has a metal case, EMI tape can be used to seal any slots or seams in the case (be sure you don't cover ventilation holes, however!).

If the case is plastic, a drastic step is to use EMI spray on the inside of the case. EMI spray is a conductive paint that can add shielding. Several words of warning are in order! Changing shielding is not a simple matter. Adding metal shielding to a design often changes the thermal characteristics. Components that operated safely in open air can overheat when surrounded by metal. EMI tapes can also come loose, causing short circuits. EMI spray is paint! If the surface being painted is not clean, the paint can flake, sending metal flakes all over the place. This will cure the EMI problem by killing the computer.

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+1 for including the last sentence. – Travis Oct 28 '09 at 18:49

Expanding on ChrisF's answer - wrap your computer as much as possible in aluminum foil.

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Should I be looking at replacing the case with a full metal enclosure to help reduce EMI further?

Yes, a full-metal case will help your computer in two ways:

1) Any EMI/RFI radiating from within your case will hit the metal sidewalls and should theoretically go out thru the ground. (Make sure the ground on your outlet is actually grounded. I have seen places where the ground is not actually grounded...)

2) Prevent radiation from entering the computer case and interfering with the operation of your computer.

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Seriously though, I would make sure that the computer is grounded properly.

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