FAQ: EMI / RF Interference

aoLhaTer · 06-08-2005, 02:22 AM

EMI (Electronomagnetic Interference) is emitted by all computers no matter the type. RF (radio frequency) interference can be synonymous with EMI and in the computer environment is caused by oscillating clock cycles at a certain frequency (your front side bus). The reason the interference occurs is not important though as we are just looking at how to stop it.

RF interference will cause problems with AM/FM signal, GPS signal or stock or aftermarket alarm remotes. If once your computer is turned on, your AM/FM radio signal or alarm remote signal degrades then your computer is causing RF interference
I personally had a problem with my computer degrading the signal of the FM band, GPS and my alarm keyfob. Below I will list what I did to correct my problem.

To correct my interference problem I scrapped my computers old wood and fiberglass case and switched to a basic (custom made) aluminum box with mounts for my M10000, Opus and a 2.5" HD. The case has several holes on it for cables to go through but the more sealed the case is the better. The case will also shield better the thicker it is. I then mounted the case directly against the body of my car so all of the metal was in contact; this was done in the trunk area next to the spare tire. Mounting flat against the body of the car will create a good ground plane. Locating the computer further down in the trunk area also distanced it more from the radio and GPS antenna.
These simple steps completely eliminated my problems.

Further measures to eliminate RF interference include using cables that are well shielded and with ferrite ends. You can also relocate the computer even farther from any antennas; the more distance the better. Computer and electronic stores also sell EMI tape which supposedly will help stop EMI but I have personally not tried it

As well as your computer, your LCD or any other electronic device may be radiating interference. If you have an RF interference problem and are unsure of the source, eliminate the source possibilities by powering one thing at a time.

Change · 06-08-2005, 03:12 AM

You can also try adding a ferrite choke to a device's power connection (as close to the device as possible), this will stop signals from getting in/out of the device by the power cable route.

Something like this: http://www.radioshack.com/product.as...t%5Fid=273-105

Bugbyte · 06-10-2005, 03:56 PM

Thanks for the FAQ! Added to the FAQ to the FAQ

Black98Cobra · 05-19-2007, 02:06 AM

Quote: Originally Posted by aoLhaTer

Further measures to eliminate RF interference include using cables that are well shielded and with ferrite ends. You can also relocate the computer even farther from any antennas; the more distance the better. Computer and electronic stores also sell EMI tape which supposedly will help stop EMI but I have personally not tried it

After nearly having my ears (and speakers) blown out by an errant police officer overmodulating his radio while driving next to me on the freeway, I opted to wrap my audio cables and speaker wires with 3M copper adhesive tape. There spiral wrapped from end to end and the end nearest the signal origination is grounded through a copper braid and ring terminal. This is similar to the RF hardening the military used to do

kazzxtrismus · 10-02-2007, 04:54 PM

there are various types of copper and lead and "anti" RF plates, tapes, soft sheet metals, and so on available on the market.

some paints even contain RF sheilding...although I have never heard of any really good protection coming from it...maybe some only need a slight improvement?

ground ground ground, keep power (+) lines from signal (RCA etc) and BUY GOOD CABLES....with RF you WILL see / hear the difference...really no joke.

Lithoss · 10-13-2007, 03:57 PM

As long as you have shielded wire, ground your cases, and keep signal cables away from high current and high frequency wires, you'll be fine.
Monster wire etc is overkill and a waste of money.

eastvolt · 11-05-2007, 04:24 AM

EXTREMELY IMPORANT:

Just a note when using shielded cables.

To be used properly, you only terminate the shield on *ONE* end of the cable. Very important since if you terminate the shield at both ends, electrical current will be able to flow through the shield contributing to any noise that may exist.

TTLLOGIC · 02-05-2008, 11:44 AM

Aluminum foil also works quite well and is cheap