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Unknown interference from computer

I wasn't sure where to post this, but anyway I just had a baby and I bought a baby monitor. When I have the receiver in the same room as my brother in law's computer it goes crazy and all I can hear is static. We thought it could have been his wireless router but we unplugged it and it didn't help. We unplugged everything in the room except his computer with a keyboard and mouse, and the interference is definitely coming from his tower. What the heck could be transmitting a signal? I tried enabling the CPU Spread Spectrum in the BIOS because I know it has something to do with EMI but it didn't help. Any suggestions?
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  1. Best answer
    Congrats on your baby! Anyway, what kind of monitor does the computer use? An old CRT can emit RF noise from the flyback transformer when it's on its last legs. If an LCD, then probably not the problem, but you could turn it on by itself and see if it does.

    A poorly shielded computer can radiate a lot of RF noise. I'd check for loose connections on the computer and monitor, make sure the video card and PCI cards are fully seated, and then try reorienting the case so that there's mainly metal between your receiver and the mobo (i.e., if there's a case window, face it away from where you sit). If the PC has CCFL lighting, try turning that off - the 12V to 400V inverter is generally a cheap unshielded circuit. Another thing to try is selectively disabling the case fans one at a time, to see if one is causing noise.

    Also, as a last resort to either leaving the PC off or moving it to another room or buying a new one, plus it would likely look ugly as hell, but you could try making a Faraday shield to encase the computer - basically a ventilated metal box to fit over it, with aluminum or copper (not plastic) screened vent holes for the intake and exhaust fans to do their thing.

    Finally, most baby monitors have an A/B switch to avoid interference with another monitor. I'd try switching channels to see if that helps. If not, then maybe look for a monitor that uses FM instead of AM.
  2. fazers_on_stun said:
    Congrats on your baby! Anyway, what kind of monitor does the computer use? An old CRT can emit RF noise from the flyback transformer when it's on its last legs. If an LCD, then probably not the problem, but you could turn it on by itself and see if it does.

    A poorly shielded computer can radiate a lot of RF noise. I'd check for loose connections on the computer and monitor, make sure the video card and PCI cards are fully seated, and then try reorienting the case so that there's mainly metal between your receiver and the mobo (i.e., if there's a case window, face it away from where you sit). If the PC has CCFL lighting, try turning that off - the 12V to 400V inverter is generally a cheap unshielded circuit. Another thing to try is selectively disabling the case fans one at a time, to see if one is causing noise.

    Also, as a last resort to either leaving the PC off or moving it to another room or buying a new one, plus it would likely look ugly as hell, but you could try making a Faraday shield to encase the computer - basically a ventilated metal box to fit over it, with aluminum or copper (not plastic) screened vent holes for the intake and exhaust fans to do their thing.

    Finally, most baby monitors have an A/B switch to avoid interference with another monitor. I'd try switching channels to see if that helps. If not, then maybe look for a monitor that uses FM instead of AM.


    Yes, he has a CRT monitor at the moment, and we have checked all of the connections in his tower, I will try disconnecting things and see if I can figure it out. And switching bands doesn't make a difference. Thanks.
  3. Best answer selected by Andon48.
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