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GTX 680 - GPU under load causes wireless connection to drop

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post #1 of 11 (permalink) Old 05-14-2013, 02:47 PM - Thread Starter
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Alright, put your thinking hats on because this one's interesting (and a bit long, sorry). smile.gif

I just returned from college last week and recently noticed that whenever my GPU is under a significant load, my wireless PCI card basically stops functioning. Before I went off to college, everything was working fine (only change to hardware was the addition of the Samsung 840 Pro, physical location of PC and router is exactly the same), and I didn't notice the problem at college because I was using wired ethernet.

Hardware details to start (most relevant components bolded):
Antec 902
ASRock X58 Extreme
Intel Core i7-920 Bloomfield @ 3.2Ghz
ARCTIC COOLING Freezer 7 Pro Rev.2
EVGA GeForce GTX 680 @ +110/+220
A-DATA Gaming Series 12GB DDR3 1600G
Samsung 840 Pro 256GB SSD (OS drive)
OCZ Vertex 2 120GB SSD (Games & Data)
WD Caviar Blue 640GB
Corsair TX750W power supply
Windows 7 Home Premium 64-bit
D-Link WDA 2320 PCI Rangebooster G Desktop Adapter

To confirm the problem I ran the Heaven Unigine Benchmark 4.0 on the Extreme preset while having inSSIDer open and pinging google.com in a command prompt for the duration of the test. Here are the results:



As you can see from the screenshots, as soon as the test starts the ping requests to Google start failing, and inSSIDer shows a complete loss of signal. Note that the inSSIDer graph isn't an indicator of connection strength, it's an indicator of signal strength - even if you're not connected to a given network the graph will still show the received signal strength for that network. The fact that the RSSI indicator drops off completely means that not only is the active connection to the network lost, but the adapter can't see the router's signal at all. This clearly indicates it's a hardware problem and not a software one.

I've eliminated processor load (or general loading of the PSU) as the cause by running Prime95 at full load for a good several minutes - connection strength as reported by inSSIDer stayed constant and there was no significant change in ping times.

I've Googled around looking for this type of problem and have only found two other cases: A Tom's Hardware forum thread from last year (here) and an ancient thread from 2007, which is notable because he has the same wireless PCI card that I do (here). Neither of these found a solid cause or solution to the problem.

It seems to me there are 3 possible causes to this:

(1) Heat from the 680 is affecting the WDA 2320 and pushing it out of it's operating temperature range, causing it to lose signal. This seems pretty unlikely to me, given that the cards are separated by 2 slots, my case is pretty well ventilated, GPU temps are pretty normal, and the problem never manifested itself a year ago with the same combination of hardware.

(2) The 680 under load is drawing too much power, starving the wireless PCI card of power and causing it to stop functioning. Also seems unlikely, given that I haven't seen any other problems with the PC lately, my power supply is of good quality, and placing other components of the system under load doesn't seem to affect anything. And a year ago, I wasn't having any power problems - the only hardware addition between now and the last time everything was working was a Samsung 840 Pro SSD, and SSD's don't exactly draw tons of power (I although I guess it could be theoretically possible that it was a "tipping point" for the limit of the PSU).

(3) EMI interference from the GPU is spitting noise all over the WiFi frequency range, causing the adapter to drop signal. Honestly this seems least likely at first but it's what I'm most concerned about. If I run a test to put the GPU under load and hold my Galaxy Nexus up to the back of the PC (near the antenna of the PCI adapter), guess what? The wireless connection on the phone drops. This seems to be pretty damning evidence that there is indeed some sort of strong EMI from the 680.

Theoretically, though, this may actually make sense. My wireless router is on channel 1 in the 2.4 Ghz spectrum, which is 20 Mhz wide channel centered on precisely 2412 Mhz. Guess what? With my current overclock, my 680 core boosts to 1201 MHz under load. The second harmonic of this frequency is 2402 Mhz, which is very, very close to that 2412 Mhz of the 2.4 Ghz Channel 1 spectrum.

It's also worth noting that before I went to college, we had a different wireless router (Linksys WRT54GS) than we do now (Apple Airport Extreme 5th gen), which I believe was on channel 11, while the current router is on channel 1 (due to lots of other networks on channels 6 and 11 in our area). Perhaps this small (~72 MHz) difference in frequency was enough to be the difference between interfering and not interfering.

I'm going to run a few more tests to try to confirm this (like resetting my overclock and changing the channel of the router), but it's impossible to confirm without a WiFi spectrum analyzer like this, and I'm not about to go out and spend $200 on hardware that I'm probably only going to use once.

So it seems like my GTX 680 is spitting out enough EMI to completely block out the wifi signal from my router with noise. I guess I'm asking: is this a problem? Should I be concerned? If the EMI is powerful enough to completely **** up my wireless adapter, how do I know it's not spilling all sorts of other EMI in other frequencies all over the rest of my delicate hardware?

And does anyone have any other ideas about what may be causing this issue?

Thanks in advance, sorry for the length! smile.gif
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post #2 of 11 (permalink) Old 05-14-2013, 03:11 PM
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I would like to start out by stating this, Very, Very nice analysis. You must be majoring in a technical field.

You would be correct in the assumption that some EMI is being generated by the 680. This and the fact that the router is tuned to channel 1 is my hypothesis of the problem!

I have not researched the tuning characteristics in depth of the current generation of routers and wireless PCI cards but with personal experience, they seem to not like channels other then 6 and 11 for consistent reception. The crystal tuning tolerances must be extremely tight or the cost of crystals outside of these narrow range must be imperative.

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post #3 of 11 (permalink) Old 05-14-2013, 04:46 PM - Thread Starter
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Quote:
Originally Posted by Electroneng View Post

I would like to start out by stating this, Very, Very nice analysis. You must be majoring in a technical field.
Thanks. Electrical Engineering, so yeah. smile.gif
Quote:
Originally Posted by Electroneng View Post

You would be correct in the assumption that some EMI is being generated by the 680. This and the fact that the router is tuned to channel 1 is my hypothesis of the problem!
Would this be considered normal, though? Or is something wrong with my 680 that is causing it to spew EMI and I should get it RMA'ed?

I swapped out my PCI card with a USB wireless N adapter (this one) and ran the same test - still dropping packets but I don't get a complete signal loss like before (probably because of the increased distance from the 680 - inSSIDer also shows a stronger baseline RSSI compared to the previous adapter). I don't want to have to sacrifice my precious overclock, so I guess I'll try changing the channel on the router now (unfortunately channel 11 is pretty busy in my immediate neighborhood, but I guess we'll have to make it work).
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post #4 of 11 (permalink) Old 05-14-2013, 07:05 PM
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In my experience, channel 6 and channel 11 are the most reliable frequencies. A lot of routers, when powered off or during a power blip, will assign a different channel that can cause a lot of connection issues.

Maybe you can call technical support with Netgear, Trendnet, etc.. and ask this question. I have witnessed it across all manufacturers.

In my home, I have a main router and two extenders. This happens even with the new AC protocol. thumb.gif

There is nothing wrong with the 680, you are just communicating precariously on the wireless channel fringes. It takes very little to disrupt the channel. The small EMI frequency increase by a fully loaded GPU is all it may take.

Sys #2,: A10-7700K @ 4.6Ghz, ASRock FM2A88X Extreme6+( FM2+) ,4gb GSkill Ripjaws @2133Mhz, Corsair 300R, Samsung P2770 HD-1080p, R7 250, Crucial C300 64GB Boot + Samsung F3 500Gb, NOCTUA NH-D14, Antec 620C Neo


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post #5 of 11 (permalink) Old 05-14-2013, 07:15 PM - Thread Starter
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Alright, so a little more testing and it looks like I've confirmed the cause. Here are the results of some throughput tests I did using Speedtest.net with my router configured for channels 1, 6 and 11. These are with my new USB adapter, which I plugged in and adjusted the location/orientation while looking at an RSSI graph of the two antennas to find the best possible configuration (it has a cool stiff bendable USB extension thing which allows you to point it in any direction and keep it there).

Average throughput for Speedtest.net speed test with same server
Control, no GPU load: 30.20 Mbps (this was consistent across all 3 channels in multiple tests, within a margin of error)
Channel 1, GPU loaded: 1.2 Mbps
Channel 6, GPU loaded: 19.85 Mbps
Channel 11, GPU loaded: 20.43 Mbps

So it looks like I'll be switching my router to channel 6 or 11, probably 11 in order to stay as far away from the 680's harmonic as possible.

Problem solved, I guess. I'm still wondering whether I should be concerned that the 680 is emitting this much EMI in the first place - if anyone could contribute on that, it would be much appreciated. (Electroneng edited his post and answered this.)

Hopefully this thread can help someone else in the future with the same problem - it's definitely pretty obscure and if I hadn't had a hunch that it might be EMI I would have had no idea how to solve it. smile.gif
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post #6 of 11 (permalink) Old 05-14-2013, 07:24 PM - Thread Starter
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Quote:
Originally Posted by Electroneng View Post

There is nothing wrong with the 680, you are just communicating precariously on the wireless channel fringes. It takes very little to disrupt the channel. The small EMI frequency increase by a fully loaded GPU is all it may take.

Alright, many thanks for your help! Now to convince all my neighbors to move to channel 1 so it isn't so damn crowded on 6/11. biggrin.gif

Thanks again.
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post #7 of 11 (permalink) Old 05-14-2013, 08:10 PM
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I have several workstations and about 18 HD 7970's in a close space and, if I go near it, both my wireless signal AND 4G drops to nothing. It is a complete deadzone.

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post #8 of 11 (permalink) Old 05-14-2013, 08:48 PM
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Interesting observations.
I've recently experienced sporadic wireless dropout on my Desktop PC. I'll have to take a deeper look at it now although I'm not sure if mine can be remedied as easily as yours - I use a mobile phone hot-spot and wireless USB dongle for internet access. I'm unsure if I can set channels.

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post #9 of 11 (permalink) Old 05-15-2013, 08:19 PM
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I'd suggest looking into flashing your wireless router with dd-wrt. You can select which channel is the least crowded and change your router to broadcast on it. Hopefully this solves your problem. I couldn't load all the comments as I'm on my phone.

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post #10 of 11 (permalink) Old 01-21-2014, 06:52 PM
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I know this thread is ancient but I wanted to say thank you to the Electroneng and especially the thread creator. I google searched high and low for the same exact problem and stumbled upon this thread. Changing the channel on my router has fixed my problem. I was getting 50% uptime internet connection when my 4 gigabyte 270x's were under load.
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