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Wireless Networking

Tracking Down Wi-Fi Interference? 499

Posted by kdawson
from the hello-fcc-i'd-like-to-report-hello?-hello? dept.
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?"
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Tracking Down Wi-Fi Interference?

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  • report it to the fcc (Score:2, Interesting)

    by Surt (22457)

    Let them track it down for you, it's their job. Have your neighbors report the problem also. For 3 reports they'll be there next day with triangulation equipment.

    • by Anonymous Coward on Tuesday June 29, 2010 @05:24AM (#32727848)

      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.

      • by fuzzyfuzzyfungus (1223518) on Tuesday June 29, 2010 @07:00AM (#32728390) Journal
        For shame, man! There is no way that your neighbor's router is licensed to run a copy of Genuine Microsoft Notepad.exe

        Just use the first four megabytes that come out of /dev/random. Odds are that those 4 megabytes violate somebody's software patent; but at least the BSA won't be after you.
      • by nametaken (610866) * on Tuesday June 29, 2010 @12:04PM (#32732166)

        I wouldn't ever brick someones router, especially since they'd just go get a new one and we'd be back where we started. What I have occasionally done is survey from a friends living room, then connect to all the open and default pw'd ap's around their house and adjust what channels everyone is on. I mostly consider it a service to the neighborhood, but no, I do not go over to the neighbors houses and survey again to find out if they don't have a more distant neighbor that they're now banging heads with.

        I kinda hate consumer wifi. I sometimes wish there were something governing its use that prevented there from being 300 routers for 300 tenants in one apartment building. It's especially nasty that AT&T rolls out their ewire devices everywhere for home dsl and doesn't care about their configuration other than to lock them down.

  • by originalhack (142366) on Monday June 28, 2010 @11:36PM (#32726160)

    First thing to try is setting your AP to a different channel.

    If that doesn't set you right, get a USB Wifi device that is supported under Linux and fire up Kismet and identify any strong signals nearby.
    • by Cylix (55374) * on Tuesday June 29, 2010 @01:06AM (#32726738) Homepage Journal

      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.

      • Re: (Score:3, Insightful)

        by clone53421 (1310749)

        My parents had a wireless phone that killed the wifi every time it rang.

        I changed the wifi channel. Problem solved.

    • by Z00L00K (682162) on Tuesday June 29, 2010 @01:52AM (#32726976) Homepage

      That is assuming that the interfering signal is something other than noise.

      Do you someone around that does a lot of welding? That's a lot of sparks flying around and it causes interference. Bad microwaves does too, but considering the time it's unlikely.

      Radar is also a factor. Commercial and military communication as well.

      Of course - it may also be someone's TV that's radiating interference. Especially old TV:s can be suspect. And other older equipment since RF filters may degrade by time - or the fact that they weren't tested for interference at the high frequencies that WiFi are using. 2.4GHz was something very exotic during the 70's.

    • Re: (Score:3, Informative)

      by X0563511 (793323)

      You are all assuming it's another Wifi device.

      By the exact timing, it sounds more like ordinary unexciting EM interference.

    • Re: (Score:3, Informative)

      by hpa (7948)

      Indeed... I put my 2.4 GHz AP on channel 1, because *all* the APs I could see from my house was on channels 6 and higher. It turns out to be a reason for that -- something that *isn't* 802.11 is interfering with the lower channels. Bumping it to channel 11 and all the interference problems went away.

      Wifi operates in the ISM bands - the scrap heaps of the radio spectrum. There is tons of crap, and 802.11 is just a small part of that.

    • Re: (Score:3, Informative)

      by cjb658 (1235986)

      1. Download a Ubuntu Live CD [ubuntu.com].
      2. Open a terminal and type "sudo apt-get install aircrack-ng"
      3. If aircrack-ng installs successfully (you may need to connect an ethernet cable to get an internet connection), type "sudo airmon-ng start wlan0".
      4. Type in "sudo airodump-ng mon0" and you'll get a nice list of all the wireless access points in your area (even the hidden ones).
      Aircrack-ng (and airodump-ng) documentation can be found here [aircrack-ng.org].

      You can also try NetStumbler [netstumbler.com], which runs on Windows, but it much less powerful

  • by IANAAC (692242) on Monday June 28, 2010 @11:36PM (#32726162)
    I had a neighbor that had an old 2.4 GHz cordless phone that used to interfere with my WiFi signal.

    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.

  • by BabaChazz (917957) on Monday June 28, 2010 @11:36PM (#32726166)

    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.

    • by e4g4 (533831) on Tuesday June 29, 2010 @01:00AM (#32726700)
      This is very interesting - I've been experiencing extreme wifi interference issues since I moved to my new place (about a year ago) in Brooklyn. My neighborhood is not known as one of the more crime free boroughs in the city, and presumably as a result of that reputation, the neighboring building's backyard has an always-on sodium light at the ground floor (of the brightness and sickening color of your typical street-side sodium lamp). My bedroom (also on the ground floor, facing the backyard) experiences the worst effects of a very obvious latent interference in the area, that is lesser (but not gone) in the 5GHz range, but renders wifi nearly unusable in the 2.4GHz band (with the added interference of several other networks in that frequencey range close by - though there is 3 channel free band). I wonder if the sodium lamp is the issue...
  • by javaguy (67183) on Monday June 28, 2010 @11:36PM (#32726170)

    ...put a sign in your front window or building lobby asking if anyone else is having the same problem, or uses electrical equipment only between those times. Make it a friendly note, with smiles, rainbows, and unicorns, so you don't offend anyone or make it look like a witch. As a bonus you get to know your neighbours.

  • by millisa (151093) on Monday June 28, 2010 @11:37PM (#32726176)

    If you are finding your fancy wifi card isn't supported by stumbler and other free channel overlap type tools . . . why not buy a cheap wifi card to use with those apps? You could always drop it back on craigslist/ebay (or even return it to the store claiming it doesn't match your curtains).

    • Also, InSSIDer (Score:5, Informative)

      by millisa (151093) on Monday June 28, 2010 @11:40PM (#32726228)

      inSSIDer [metageek.net]
      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...)

      • Re: (Score:3, Informative)

        by noc007 (633443)

        Third this. It's a great app and gives you a simple easy to understand view of the APs that are in range. If it's a bunch of APs turning on at once, you may be able to pick a channel that will work better.

        If it's annoying enough, MetaGeek has their Wi-Spy [metageek.net] line of Spectrun Analyzers that will give you a better detailed view of the spectrum and not just a map of the APs in your area.

        If your WiFi card supports 802.11a (5GHz), an investment in a new AP may be the way to go. The 5GHz band isn't utilized as much

  • by Anonymous Coward on Monday June 28, 2010 @11:37PM (#32726186)

    That's the same time I microwave up all my hotpockets for the next day's raiding Ice Crown Citadel...

  • Are you using Wireless a/b/g or Draft-n?

    Are you still able to view broadcasted SSIDs?

  • What trace information do you have? For example I run netbsd on my wife router and if the wifi interface goes down or stops working I would look in /var/log for trace information.

    How close are your neighbors? Do you live on a farm? Or in a block of small apartments? Maybe you have a channel space issue.

  • by crath (80215) on Monday June 28, 2010 @11:38PM (#32726196) Homepage

    Talk to someone in your local ham radio club and see if they have a member with a spectrum analyzer and a directional antenna. Have them come out to the house and do some direction finding to determine who is transmittin on the WiFi freqeuncies in your neighbourhood.

    Be polite. Ask nicely. Buy them pizza and beer to say thank you.

    Hams are nice guys and gals and they will probably be happy to help out.

    The ARRL website can probably provide a contact for your local ham radio club.

    • Re: (Score:2, Redundant)

      ^That right there, is just plain old good idea.

    • by bezenek (958723) on Tuesday June 29, 2010 @12:01AM (#32726396) Journal

      First try what is suggested by BabaChazz in his comment above and is what most Hams would do to start. Listen for the noise on an AM radio. You do not want FM, as one of the characteristics of FM is to block this noise.

      Take your (preferably hand-held) radio and tune it somewhere on the dial where there is no station. Then, you can try moving it around your computer to hear all of the RF interference your motherboard, etc. are giving off. If you cannot hear this noise, something is wrong with the radio--be sure it is set to AM. :-)

      Leave the radio on, and you might hear the noise start at the time your WiFi drops. If you do not, the interference is not covering the AM frequencies (an arc will cover everything), and it is probably time to call in a Ham.
      It is likely you will hear it.

      If you hear it, you can walk around inside and outside your house listening for where the noise gets stronger. Often this will be tracked down to a phone pole or something else.

      Once you find it, contact the appropriate person (electric distribution supplier, city, etc.) Convincing someone to fix a problem like this is not always easy.

      -Todd

      • Re: (Score:3, Informative)

        by mcrbids (148650)

        I would add only one detail: tune the AM radio up near the "high end" of the radio spectrum, around 1500 or so. That's the part of the AM spectrum that's closest to 2400 Mhz, and thus most likely to pick up the interference.

        • by bezenek (958723) on Tuesday June 29, 2010 @01:51AM (#32726972) Journal

          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.

          • Re: (Score:3, Informative)

            by Thelasko (1196535)

            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.

            Here is another one. Put your cell phone in the microwave, and close the door. DON'T TURN THE MICROWAVE ON. After a few seconds, your cell phone should say, "no signal," or "out of network," etc. If your cell phone still has signal after 10 seconds, it's time to get a new microwave. The housing of your microwave is no longer acting as an effective faraday cage, [wikipedia.org] and is leaking dangerous amounts of radiation.

    • by adolf (21054)

      Seconded.

      I haven't met a ham yet that wasn't a proper thinking sort of fellow, with a willingness to help other folks solve problems (especially if the problems are interesting to them).

      Sometimes, though, it's not something so complicated that outside help is needed.

      I once troubleshot a WiFi link that spanned two buildings, a block or two apart. Things had been stable since we installed it a year or two prior, but suddenly it would drop out completely a few minutes at a time, between 11:45 and 12:30.

      The li

    • by APL bigot (606126) on Tuesday June 29, 2010 @01:51AM (#32726966)
      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.
      • Re: (Score:3, Interesting)

        by Anonymous Coward
        Yes, we have priority, but we're not pricks. If someone came to my house to ask if my radio equipment is causing WiFi signal dropping from area houses, of course I'd be happy to help by solving the problem. Helping my neighbours change the WiFi channels or installing directional indoor antennas for them ($10 from DealExtreme) could help in this issue...
  • Hey Nicros (Score:5, Funny)

    by Anonymous Coward on Monday June 28, 2010 @11:39PM (#32726208)

    I'd help you buddy, but every night between 8:30 and 10:00pm I'm working on my microwave disruptor beam. If it happens any other time, let me know and I'll be glad to pop over and take a look.

    • by Anachragnome (1008495) on Tuesday June 29, 2010 @05:21AM (#32727830)

      "I'd help you buddy, but every night between 8:30 and 10:00pm I'm working on my microwave disruptor beam. If it happens any other time, let me know and I'll be glad to pop over and take a look."

      Mike, that you?

      In all seriousness, I knew a guy up in Alaska that was trying to do exactly that.

      He lived on some undeveloped property, raised pigs and collected old cars--his neighbor prided himself on his carefully manicured yard. They did not get along. Things got tense until one day the neighbor called the cops on him during a BBQ...and the war started.

      One day, I'm over at his place and he takes out this finely-crafted, solid brass gizmo with all sorts of gears and worm screws in it, about 4 inches to a side. Barely concealing his excitement, he explained that he got it from a buddy that used to work at the local Airforce base, and that it was used by aircraft landing in the dark or on aircraft carriers. It was the core of a device he was constructing--a microwave cannon...to be used in the war.

      Apparently he had managed to obtain a device that directed microwaves into a tight, adjustable beam. I guess it was used as part of a microwave guidance system for aircraft. Anyways, he had also had a large section of copper pipe silvered and polished on the inside and had fitted a microwave generator from a commercial-grade microwave oven onto the device. Amazingly, the generator fit PERFECTLY into the beam focuser, almost as if it was Destiny guiding his hands (or the industry has standards for such things).

      I moved out of the state before he finished it. As far as I know, his girlfriend had convinced him not to finish it. To be honest, the guy was starting to scare me as I began to think he might actually be on to something usable for it's intended purpose.

      I told him that if it actually worked, and he settled matters with his neighbor in a more civilized manner, he could always mount the thing on a lazy-susan, put it in the middle of his yard, get a clock motor to spin it slowly in circles, and he could simply turn it on to mow his yard. Flatest mow-job in town.

  • During a remodel of one of my employer's stores, we have trouble with our RF gun (laser scans bar codes, then prints price labels, runs off of 802.11whatever). When I went to troubleshoot it, near as I could figure, the contractors working upstairs has something that was putting out so much RF interference, the gun wouldn't boot because it couldn't read the flash memory soldered to the circuit board. Once the contractors left, it was all back to normal.

  • have you tried... (Score:5, Informative)

    by uniquegeek (981813) on Monday June 28, 2010 @11:42PM (#32726240)

    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 [wireshark.org]

  • hard to solve (Score:2, Interesting)

    by Anonymous Coward

    I used to work several military trade shows at m last job, bringing in all kinds of weird stuff we were doing with wireless tablets and iphones and junk, just to show off what we could do... would stay up till 3am getting everything looking right, would show up 7:30am to make sure the morning of everything was good to go, then boom 8:30am rolled around and everyone fired up there demo hardware and all wireless in the building stopped working, it was ridiculous, happened at three different shows, we kept buy

  • InSSIDer (Score:4, Informative)

    by whoisrich (1194797) on Monday June 28, 2010 @11:47PM (#32726290) Homepage
    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 [metageek.net]
  • 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/ [ubnt.com]

    -Greg

    • Re: (Score:3, Informative)

      by pcjunky (517872)

      They sell a USB module for 2.4GHz that costs around $38.

      A friend got us a suriund sound system for our entertainment setup that included wireless rear speakers. Couldn't use hte rear speakers as it clobbered the WIFI. These things transmit a constant stream a really do a good job jamming WIFI. Sounds like something like this may be happening to you. Would explain the time frame.

  • If you got an iPhone or a Driod, you can get WiFi-Fo-Fum. Go into your router settings and make sure you're broadcasting your SSID and lock on to it on the smartphone. I've found dead spots in my rowhome (3 stories) where there were just Faraday-like dead spots in my house and one was near my basement PC. Repositioned the antenna and all was back to normal. I also can't walk near the spots when I'm using my mobile or the calls cut off, too.

  • Part 15 devices... (Score:3, Interesting)

    by sillivalley (411349) <[sillivalley] [at] [comcast.net]> on Monday June 28, 2010 @11:52PM (#32726318)
    As a Part 15 device, you have to put up with what other devices are doing.

    My first guess would be a non-802.11 device such as a video or audio sender. They can take out many 2.4GHz channels at once, where a microwave oven usually only knocks out a couple.

    One workaround is to go to 5GHz -- you're still under Part 15 and susceptible to interference, but there's less of it, a lot more channels, and you can find a 40 MHz channel for 802.11n.

    Without something that acts like a spectrum analyzer (such as a real spectrum analyzer -- but some modern access points and other 802.11n devices offer spectrum analysis/FFT capabilities), it's going to be difficult to identify your interference source.

    Using a simple reflector such as a parabolic reflector or a corner reflector, you might have a better chance at establishing a direction for your interference source.
    • by darrylo (97569)

      My first guess would be a non-802.11 device such as a video or audio sender. They can take out many 2.4GHz channels at once, where a microwave oven usually only knocks out a couple.

      This, or, as others have said, an old cruddy analog 2.4GHz wireless phone. A microwave is also unlikely due to the long interference period, unless someone is trying to cook everyone around him ....

  • by Anonymous Coward

    Keep an open mind to ANY device which could be turning on and off during the problem times.
    I also had this problem and after weeks found it to correspond with the watering schedule for my garden - the water pump was on the other side of the wall to my router and was causing the interference.

  • by Anonymous Coward on Tuesday June 29, 2010 @12:00AM (#32726390)

    Baby monitors. One of the few devices that can completely trash all wi-fi frequencies in an area, not just for 1-20 minutes like a microwave but for years on end. Especially older models which use an analog signal.

    • Re: (Score:3, Informative)

      by eyrieowl (881195)

      it's the years on end part which kind of rules that one out, i think. op says it only happens for a couple hours each night. unlikely that's the only time when the baby monitor would be in use....

  • by sdavid (556770)
    I think it is caused by an analog 2.4 ghz phone, and someone chats during that time period. I had one of those phones and found that when I used it it hosed most of the available channels. Replacing the phone solved the problem and doubtless made my neighbors' lives easier. After a move, the same pattern showed up. The solution was a dual-band router.
  • by djupedal (584558) on Tuesday June 29, 2010 @12:22AM (#32726504)
    Check for any satellites that track overhead at that time.

    I remember when they used to open electric garage doors around the neighborhood....
  • RF shielding paint? (Score:3, Interesting)

    by MikeFM (12491) on Tuesday June 29, 2010 @12:23AM (#32726506) Homepage Journal

    Tried http://www.safelivingtechnologies.ca/rf/Products_RF_Shielding_Paint_HSF54.htm [safeliving...ologies.ca] RF Shielding paint? I always wondered if such paint would help. Of course it might kill your cell reception. If so, might be fun to paint your apartment in it before you move or maybe your bosses office when he is away.

  • by bassman998 (922503) on Tuesday June 29, 2010 @12:30AM (#32726534)
    Metageek [metageek.net] has a few products in their Wi-Spy USB Spectrum Analyzer family. The cheapest one (the 2.4i [metageek.net]) is $99, and the next model up (2.4x [metageek.net]) is $199. It analyzes the entire 2.4GHz spectrum using your laptop and lets you see potential sources of interference. The 2.4x version allows you to use their more advanced software which also has device signatures -- you can overlay signal patterns of various types of devices (microwave, cordless phone, wireless baby monitors, etc.) on top of the signal density graph in order to identify what's causing the interference. I use the DBx version (2.4 + 5GHz) at work, and it's great for helping to find problems.
  • by Dynamoo (527749) on Tuesday June 29, 2010 @04:22AM (#32727638) Homepage
    If you have an Android phone, you can download a free application called WiFi Analyzer by Kevin Yuan which scans signal strength and can identify possibly interfering networks, pretty much like NetStumbler but in a more convenient package. If you are patient enough then you can map out signal strengths in various locations when you have GOOD reception, and then compare them to what happens when you have BAD reception and see where the interference is worse.. if it's a rival WiFi network then it should be even easier! But as others say.. the source of interference could be one of so many things in the 2.4 GHz band including DECT phones, baby monitors, microwaves or even just plain old fault equipment
  • Look for antenna's (Score:4, Informative)

    by Taelron (1046946) on Tuesday June 29, 2010 @05:50AM (#32728012)
    Growing up a friend of mine had a CB base station and a Ham radio, not satisfied with the range on his CB Base station he added boosters to his system. Any time he fired up his Base station to full power, TV's for a block or so went out everytime he key his mic. Look around and see if you see any radio antenna's around the neighborhood. Could be an overpowered CB or Ham Radio operator that gets on at that time every night.

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