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Tracking Down Wi-Fi Interference?
Nicros writes "Almost every evening, between 8:30 and 10:00, my Wi-Fi just dies. This, in itself, could be explained by a crappy Wi-Fi source or some hardware failure, except that I know both of my neighbors are experiencing the same loss of signal at the same time. While the Wi-Fi is down, the LAN is OK, and anything plugged into Cat5 can access the Internet just fine. One possibility comes to mind — perhaps some other neighbor arrives home and turns on their router from 8:30 to 10:00? And something in their signal is hosing our Wi-Fi? I have tried looking around for software to help identify the source of interference, but either the programs are ridiculously expensive for a home user, or else my card (Intel Link 1000 BGN) isn't supported. (Netstumbler is an example of the latter.) Any suggestions on how I can track this down?"
Once he got a 5 GHz phone all was well.
Long story, short: lots of things use the 2.4 GHz spectrum. It may not have anything to do with WiFi.
An associate of mine reported the same issue. In his case it was a failed security lamp that was trying to come on at sunset and failing; it was only when the ballast gave up after an hour and a half that his wifi -- and his AM radio -- came back. Note that many security lights are sodium arc or mercury vapor arc; not much is as hard on RF in general as a big fat arc.
inSSIDer
I've been pretty happy using that to help find the best channel for my WAPs in congested areas. If you really believe it might be a neighbor jumping online from 8:30 to 10, that could help. I haven't yet found a card it doesn't work with under windows (assuming you are running windows...)
Happens the same whether you're on channel 1, 6, or 11? (the only b/g channels that don't overlap)
I know in my high-rise apartment, almost everyone is on channel 6, and I wouldn't be surprised if peak usage was mid-evening.
Did you double-check that some rule didn't accidentally get selected, which filters you out (either in the router interface... of you're using software that has scheduling...)
If you're using a radio type that is using the 5Ghz channel, someone's old beastly cordless phone might be affecting it too. If you're using a dual-band radio on your router, try using the other band and see what happens.
Running Wireshark (free) might not tell you what specifically is causing the problem, but you can narrow it down to see if packets are timing out, or getting filtered. Maybe there's traffic you didn't expect to be there? http://www.wireshark.org/download.html
I will add my 2c and say it is the increased usage of cordless 2.4GHz phones during those hours. Some of the (cheap) units don't behave particularly well with WiFi and I've personally seen just one phone cause a complete outage of all WiFi in a house.
Chances are that one of your neighbours with a teenage daughter bought some cheap but funky looking cordless phone off eBay and uses it every night during your outage window.
Dan. -- So what if it's spelt wrong, nobody's perfect
Netstumbler did not support my wifi card but came across InSSIDer which is free, and allowed me to easily see channel usage in the neighbourhood. They also sell USB spectrum analyzers for non wifi interference which is what you may need. http://www.metageek.net/products/inssider
This is exactly the problem we had with our apartment neighbor's teenage daughter. 8:30pm -10:00 pm fits the high school homework phone schedule.
A gift of 5 GHz wireless phones to the neighbors (in exchange for their old phones of course) cleaned up our mutual WiFi problems.
Took the old phones and dumped them into ATT Wireless Store's recycle bin.
Get either the USB stick or one of the 2.4Ghz supported AP's from Ubiquiti. [www.ubnt.com]
The newest firmware supports a Spec analyzer mode - quite good, IMO - and it's not limited to WiFi equipment - anything in the radio spectrum is "seen."
Their wireless bridges in the 5Ghz spectrum using N tech (dual spacial streams) are seriously killer too - if you've got a wireless bridge, or WISP type situation, it's really, really cheap stuff. I'm likely to end up with 2.4 ghz and 5Ghz units just for spec analysis on the cheap. The units then double as AP's / routers / Bridges. (And at around $100 each, they're pretty awesome - Bullet M5, and Nano Station M5's for example.Find a wireless N bridge that will hold links over miles that are that cheap anywhere else!)
For around $100 you could have a nice AP and a spec unit in the same hardware. Antenna, unless built into the unit is a bit more difficult/pricey, but still do-able.
Anyway, I've got a setup using them in a PtMP setup, and though it's not miles, I'm seriously impressed - and the cost factor is simply *insanely* cheap.
http://www.ubnt.com/
-Greg
You realize that N doesn't spec frequency, right?
802.11n can run in 5Ghz spectrum, but can also run in 2.4 spectrum. So, simply saying "use N" doesn't mean anything in terms of frequency.
In fact, most of the "consumer-grade" 802.11n equipment is 2.4Ghz exclusively.
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I'd mostly agree that 5Ghz spectrum will be less cluttered, but I'd also guess that decent equipment using the tech in the N standard will do a lot better in 2.4 than b/g will. Multiple spacial streams, and (when implemented beam-forming) as well as beneficial use of "multi-path" etc will probably make N a lot better in most environments regardless of spectrum.
I don't know if they'll come and check things out, but they do care about unlicensed bands - if you're way outside the power envelope allowed, I'm sure they'll whack you upside the head just as bad as if you were doing it in licensed spectrum.
Given the symptoms, I wouldn't be surprised to find something in the spectrum being used that IS outside the allowed power-limits.
However, I think you're more likely to get results if you find out what the offending device/person/entity is and asking them to help resolve the conflict. If they don't then you can move on to a complaint with the FCC based on power-output.
...enter the FCC. That's kinda what they do....
Here's a cheap build-it-yourself spectrum analyzer: http://hackaday.com/2010/03/17/im-me-spectrum-analyzer/ The IM-ME can be had for about $15 or so, and is purportedly very hackable.
John
That device only covers 281 - 361, 378 - 481, and 749 - 962 MHz bands. It will not be useful for debugging the 2.4ghz spectrum.
There are likely some other options for a cheap analyzer around. I had some friends in a wireless shop convert an AP to a spectrum analyzer via a firmware update . However, those AP's were intended for commercial use and the price was a bit too steep.
"You should always go to other people's funerals; otherwise, they won't come to yours." -- Yogi Berra
You can do the same issue with dd-wrt, but that only if the signal also conforms to the 802.11b specification.
A burst of noise or device using the spectrum differently will not display using such techniques. The spectrum is open and there are a number of protocols today that rely on those frequencies.
I had a friend with a 2.4ghz phone which would completely and utterly destroy our wireless reception.
"You should always go to other people's funerals; otherwise, they won't come to yours." -- Yogi Berra
It may in fact be a ham that is legally operating in the 2.4GHz band. Hams are licensed users of this spectrum, and have priority. They could be causing the interference (if in fact they are), and if so you just have to live with it, if it can't be resolved. Hams are also protected from interference (by law) from the unlicensed users of the spectrum.
And by the way, end users increasing the power output of a WiFi transmitter is not a good idea. It can cause interference on nearby spectrum, and increased noise levels in the band, which can defeat the purpose of the increase in the first place. This is not something that should be hacked.
Heisenberg may have been here.
A quick clarification: The top of the AM dial (around 1500) is 1500kHz, or 1.5MHz. This is not close to the 2400MHz, or 2.4GHz at which WiFi operates.
The ability to identify the origin of the interference using an AM radio relies on the fact that the interference is produced from a source (often an electrical spark or arc) which generates RF noise on the entire spectrum. The spark plugs in car engines are a notorious cause of this sort of interference. If the spark plug wiring in a car is not shielded properly, you will hear a whining sound on an AM radio which changes pitch as the engine RPM changes.
AM radios happen to be easy to find and are very good at "hearing" the noise produced by an arc. If the noise is something like a microwave oven, which produces RF energy only at about 2.4GHz, then the AM radio will not help you find the problem.
I hope this helps to clarify the issues.
-Todd
p.s. As an interesting experiment. If you have WiFi and a microwave oven in your house/apartment, start downloading a large file. Look at the download rate (300kB/sec. or whatever). Then, start the microwave and look at the download rate. Mine drops to about 10-20kB/sec., because the microwave interferes with the WiFi signal.
Omne ignotum pro magnifico.
+1 - we were given a baby monitor that transmits live video and source temperature. It destroys our WiFi capability - but only within 20 metres or so.
airodump-ng --showack -w output mon0
take note that all your idiotic neighbors all use channel 6 for everything.
decrypt WEP/WPA keys for router.
connect to router, login using default (never changed) credentials.
upload notepad.exe to router as a firmware upgrade.
no wireless devices running in range of your equipment.
A couple of days ago, I was using my microwave oven while watching a MythTV stream over the Wi-Fi network from a laptop three feet away. Not even a hiccup.
The whole point of the design of a microwave is that the holes in its Faraday cage are much smaller than the wavelength of the signal generator within. If your microwave is wrecking your Wi-Fi connection, don't grumble about it. Get a newer microwave oven.
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