Computer causing radio interferance

[Sylvanas]

This has only happened recently since I installed a my new Quadcore 955 CPU about a month or two ago. What happens is that when I turn on my computer downstairs, the (older) radios upstairs have huge audible interference and it makes listening to the radio impossible. I have the computer listed in my sig that is watercooled by 2 radiators and 6 fans. Am I right in thinking it's the PSU? In that installing my new Quadcore somehow increased the power draw and is somehow exhibiting or exacerbating the interference with the radio? I'm sure someone here has a more in depth knowledge on the subject so please let me know

 

[Modelworks]

The majority of radio noise off a pc comes from the CPU , GPU , and other circuits. All that switching at high MHZ puts out a lot of RF. That is why pc case are suppose to be designed with enough metal to block RF from those areas. Unfortunately more and more cases have plastic windows and such that let the RF pass right through.


An easy test is to find an old handheld radio with a telescoping antenna and move the antenna around the pc components to find the worst offenders.

 

[Sylvanas]

Thanks Modelworks, so what can be done to alleviate the issue? Some sort of grounding cable?

 

[Modelworks]

Originally posted by: Sylvanas
Thanks Modelworks, so what can be done to alleviate the issue? Some sort of grounding cable?

Once you know what the source is you an try a couple things. Move the pc around. Replace cables that do not have ferrite chokes with ones that do, those are the large round parts on some cables, they are there to block RF from using the wire as an antenna. The other way to block it is using something like aluminum foil. Placing the foil over unused fan ports or plastic windows in a case can block quite a bit of the RF. You could use a hot glue gun to tack it in place and then connect a wire from the ground on the case to the foil .

 

[SergeC]

Is it interference in your power lines, or over the air? If it's power, a UPS or line filter should do the trick.

 

[Zepper]

AM radios generally have very little resistance to interference. As others have said, it helps to locate the problem (noise waves thru the air or fed back into the house wiring or both to find out what needs to be done) sometimes it could be as easy as rotating the radio to minimize the noise. Try running it on battery if possible to rule out coming over the power wiring, etc. Just moving the radio as far away from the confuser as possible can help. Sometimes bringing the radio closer can help pinpoint the source of the leak - just bring it close to the various sides of the computer, etc. can give a better idea of the source. Use the radio as a leak detector... If fate gives you lemons, make lemonade... And another said above that computer cases used to be designed more for preventing escape of radio frequency interference as the mfr was required to design to FCC standards. Now it is up to the owner to assure that his computer doesn't interfere with other equipment. Worse to worse, you may have to get a windowless case with few extraneous openings and some cables (AC, video, etc.) with RFI/EMI suppression filters. Good luck.

..bh.

 

[Sylvanas]

Thanks for the input everyone. I have used the advice given and used a portable radio to identify the cause of the interference. It was the strangest of things, this Antec Spotcool fan which I picked up as a multi-purpose fan I can stick anywhere in the case was the culprit. As soon as I disconnected it from a power source the buzzing went away back to normal and the FM radio sounded as clear as per normal. I have it screwed into one of the PCI slot brackets fastened to the case itself and will leave it disconnected for now.

Mystery solved, but for my own interest- how would a fan be the cause of this? I was under the impression it would be a component on the motherboard.

 

[Zepper]

Little expense is spared in the design of some of these junky add-ons. Perhaps it's only the one you have or maybe the whole run of the things. In any case, I don't see them for sale much, whereas if they were any good, they'd be all over the place. When it comes to computers, Antec sells some decent cases and has some decent PSUs made for them and that's about it. For other stuff, it pays to look elsewhere. I don't think any of their fans are considered top notch. If your spot fan is still in warranty, you may have a shot at getting a replacement. Not worth the cost of shipping it back though, so if they require that, just chalk it up to experience.. I was thinking about picking up one of those - now I'm glad I didn't - another good idea perhaps poorly executed.. Let us know if you find out it was a fluke and not a design flaw in the product.

I have one of those Zalman fan brackets onto which one can hang any fan that'll fit the application; and some other company (perhaps Sunbeamtech) made an all-purpose, adjustable bracket for hanging anything where you need it inside a case (hard drive, fan, etc). Double sided, foam, mounting tape can also mount a low-flow fan into tight spots or even a dab of silicone seal or hot glue...

.bh.

 

[Modelworks]

Fans like that one and the ones in most pc don't use motors like the ones in a ceiling fan or or house fan. Instead they use a system of rapidly switching current through several coils . If it isn't designed right what you get is a fan that is really a radio transmitter sending out a signal at the fans switching rate..

Here is a link that explains how a pc fan motor works and the schematic on how the pins are wired.
http://www.industrial-embedded.com/articles/id/?3726