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A very Strange Failure Mode.

sythen

sythen

sythen

Associate
Joined
3 Mar 2008
Posts
6
Good morning/afternoon/evening all!

So i just had a very interesting afternoon.

We had OFCOM sniffing around the area today looking for a Strong source of interference in the area. As i licenced HAM, i was kinda worried about my radio gear, I invited em in, they checked it out, no issues were found with any of it.

But they did find that the source of the interference WAS coming from my place.

So we start killing devices left right & center, no change.

Until we got to my housemates bedroom.

We found that the source of the interference was coming from his PC (A build i did years ago on the 1366 platform <3)

So we start unplugging keyboards, mice, controllers, USB hard drives, still no change...

Then we started unplugging the video cables, SUDDENLY, the interference drops off like a rock, sorted right? Bad cable?....Nope...

We started testing cables on my test bench, no issues there, changed for different cables (DVI, HDMI) It comes back.

We change his graphics card for one of the spares we keep around (A trusty GTX 660)

BOOM!

Problem is gone, I start scratching my head, confused, so i drop his card in my rig....BANG! Source of interference appears once again!

Turns out that the card, when a video output is plugged it, is radiating a strong 800mhz signal up the cable, using it as an antenna, and Effecting the local Vodafone coverage!

The card in question is an MSI GTX 970 Twin Frozr, bought in 2015, Luckily the card is still in warranty, cause in its current condition, its illegal to use it.

Thank you for reading my re-telling of the haunted video card, movie comes out in 2020 ;)
 
The video controller will be switching in the MHz range but don't think it would be 800MHz unless its somehow generating 2 pulses or something let alone how that would be emitting enough power to interfere with something to any significant degree beyond 1-2 meters away or so.
 
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Also a radio ham, It can be the video out put is oscillating at 800mhz causing interference. I had a new Sky Q box fitted and it caused massive interference across the HF band. I had them remove it. went with the solo 4K system and no interference at all. just goes to show, you never know where it comes from.

M0VPL
 
That is possible. I heard that is a common problem with those sky Q boxes. Would explainot why my 20/40m reception is bad these days.

Anyway. Good news is that the card is still under warranty. MSI accepted the rma. Just waiting for an RMA number now.

2E0DHY

73
 
Yup. Easy peasy. In our case. They pulled up in a van marked ofcom. They wore hig-vis with ofcom on it. In this case. They were walking around with a spectrum analyser and a directional horn antenna.

It's not like the TV licencing agency. These 2 were pretty good folk. And did appreciate that we helped em find the issue.
 
Just got the readings back from Ofcom, my mind is still blown.....

TTaShGR.png
 
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