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Joined: Jul 2002
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Let's not go down that road, Greg. whistle

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Sorry Mike I thought this was a topic about noise on AM radio. My apologies.
Rush is fine as long as you understand it is just entertainment ... like Jon Stewart (Daily show), Letterman or the Roadrunner.
Rush will point that out


Greg Fretwell
Joined: Mar 2005
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The source of EMI from PCs is the PC itself. With speeds faster than 1GHz, and bus speeds ranging from 100-200MHz and cables and copper interconnects (read: antennas) all through the PC with speeds of MHz to GHz, there is all sorts of broadband radiation just waiting to escape. There's very little you can do about it.

PC monitors can also give out tons of EMI. This is easy to check- just turn off the monitor and see if it stops. I had a huge argument with one of my coworkers once due to high-audio frequency EMI interference. The problem was that I was the youngest in the office by 10 years and nobody else could hear it! Was this ultra-high-pitched squeal that was driving me nuts, and he was insistive I was making it up and refused to do anything about it, until a team of fire inspectors came through and the youngest of the group, a 20-something new hire, commented on it, too.

In this case, all we had to do was change the refresh rate of the monitor from 60Hz to 70Hz and it pushed the EMI out of my audible range where it was no longer annoying. I swear it still gave me headaches, though.

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Well, the question is moot now but...here goes a long ramble...

Turns out it is defiantly not on the power line it self. Couple days after my original post I had a chance to stop and think about the radio again. Didn't have 6 D batteries handy so I grabbed a 100' extension cord. Plugged into the same receptacle as my computer and took a walk. the reception on the radio cleared up about half way into the parking lot. So my computer radiates noise for about 50' - 60' from the actual tower. It is definitely the PC itself. Monitor, printer, ect makes no difference. Everything is good as far as the slot covers, grounding, ect.

In the mean time the boss is back in the country and was able to get AT&T to fix our DSL so I am streaming AM now and can once again work without having to listen to myself think.

What direction would I go if I wanted to squash this noise? I'm curious how you would go about preventing the PC from radiating such noise. I'll guess one option would be lining the tower in a material that blocks/absorbs the RF radiation. What other methods could I try?

And for those AM radio pundits in the crowd...I listen to Armstong and Getty in the mornings from 6 to 10. Some times I Listen to Clark Howard from 10 to 12. Other then that AM radio in my area drives me crazy. 12 to 6 is split between Dr Laura and Michale Savage they both grate on me a bit and I only listen if I'm really in the mood or my MP3 player is dead. Weekends are really hit or miss. Some good gardening shows occasionally and one tech show. I like click and Clack on NPR but that's only because I used to read their newspaper column as a kid. Happy now? I admit I'm a little off but FM radio just really pisses me off. If I want music I'll fire up my MP3 player and listen to what I want.

Thanks Guys the responses were great!




The more I work on the office side of the business the more I realize how good I had it in the field. So much easier running work and even easier being "just" an installer. I really long for the days of being an apprentice when everything was new and exciting. Such is life...grass being greener on the other side of the fence.haha

Last edited by Local; 07/15/08 11:30 PM.
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You could try overclocking (or underclocking) the main system clock of your computer. It'll most likely be in BIOS as the front side bus frequency- try shifting it up or down 1-2% and see if that changes your radio at all. This won't eliminate the EMI, but will change the fundamental frequency and possibly shift it to a channel you don't care about. Then again, you don't know what's causing the EMI, and changing the system clock should change the ram, FSB, PCI and AGP busses, won't necessarily effect all the other components.

Double-check the case grounding, too. If it's good, try a supplemental grounding electrode of some sort, connected to a good grounding electrode with as short a cable as possible. Conventional ground wires are extra-especially lousy at dissipating ground voltages much above 60Hz since impedance at higher frequencies is so high, and if it's a long path to ground, it may just be harmonics and noise building up on the case.

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Sometimes the shielding on the computer case itself is adequate, but a lot of noise is escaping by way of radiation from the cables connected to it (keyboard, monitor, USB leads, etc.).

A turn or two through a ferrite toroid as close as possible to the computer can sometimes help, although you need to be prepared for a lot of experimentation.

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