DVI cable is interfering with my cell phone

radio1911

Junior Member
Jan 5, 2015
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This may not be the exact forum for this question but this but the question relates to the DVI specification and I figure you guys would be the most knowledgeable on DVI clock speeds and bitrates:

A while back I ran into a weird EMI interference issue between my cell phone and a new custom built PC inside of a Cooler Master CM690 KKN2 case. When the PC booted to Windows calls would drop on all cell phones nearby, whether 3G, LTE, on Verizon or AT&T and they could not connect to any mobile networks. (Nobody in my office has T-Mobile, so we don’t know if they would have been affected too)

I spent a lot of time googling and couldn’t find any solutions. I eventually figured out what was causing it and wanted to post something here in case others are having the same issue. I assumed the high airflow case meant it was poorly shielding EMI from inside the case. It also has a painted interior and I don’t think the shell was grounded. I tried swapping out every single component and cable inside and even swapped out the case, but It turns out all that was completely unrelated.

There was some kind of interaction between my PC’s DVI cable and the NEC monitor it was connected to, and only at a refresh rate of 59 Hz. When I switched to 60 Hz or if I plugged into a different monitor the problem went away completely.

What I still don’t understand is how can a low frequency DVI signal (max clock rate at 165 Mhz) interfere with multiple high frequency cell phone bands (800Mhz to 1700Mhz). I’d love to hear from someone with hardware knowledge of the DVI spec if they have any theories on why this was happening. If anyone’s interested in more details about the machine or setup I wrote a full description about the problem and the frustrating debug process here: http://provare.com/news/cognitive-bias-as-an-impediment-to-effective-troubleshooting
 

razel

Platinum Member
May 14, 2002
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It could also be the graphics card or the NEC monitor. Have you tried the NEC monitor and DVI cable on another computer?
 

radio1911

Junior Member
Jan 5, 2015
3
0
0
I did try the monitor on a good PC with a good cable, and the problem followed the monitor. I tried the suspected DVI cable on a good PC and a good monitor, but the problem didn't follow the cable. I could get the faulty monitor to work by changing the refresh rate. I think the DVI cable is acting as an antenna and whatever problem the monitor is having was radiating through the cable.
 

razel

Platinum Member
May 14, 2002
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My fellow workers at the IT hardware department here on their last PC upgrades, installed 400 computers using DVI cables instead of VGA because that's what was included in the monitor box. Not one issue.

I do remember some video cards in the past, like ones from ATI that came with ferrite cores for you to put on your video cables. Did you try other cables with heartier cores? If so, you probably just got a winning? lottery combination. 60hz is the normal refresh rate. Unless that 59hz is really TV 59 which could be 59.9.

Regardless I guess you could have fun with it. Wrap the cable up with alumumin foil see if that helps.