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Wireless Abrupt Change to Severe Inteference

Discussion in 'Tomato Firmware' started by liquidzyklon, Feb 3, 2013.

  1. liquidzyklon

    liquidzyklon LI Guru Member

    Hi all, I haven't really followed Tomato firmware in a couple of years because the router and firmware is so stable I have no issues until now.

    Hardware & Firmware:
    Router = ASUS RT-N16
    Firmware version by filename = tomato-K26USB-1.28.9054MIPSR2-beta-vpn3.6
    Kernel and Wireless Drivers from About = Linux kernel and Broadcom Wireless Driver updates

    Home Setup:
    Detached house
    3 Laptops with built-in wireless
    2 Android phones
    Wireless Settings was:
    Wireless Mode = Access Point
    Wireless Network Mode = Auto
    Radio = Enabled
    SSID = red
    Security = WPA Personal (PSK) + AES
    Channel = 6 - 2.437 GHz
    Channel Width = 40 MHz --> Required to get the most out of 802.11n speeds up to 300 Mbps
    Interference Level = Acceptable

    Everything has been working for months now with no issues. Today all of a sudden the Interference Level went from Acceptable to Severe and disconnected all of my devices. I've tried disabling the wireless and re-enabling it, channel scanned to change channels from 6 to 1 with less interference, rebooted the router, unplugged microwaves, cordless phones (DECT 6.0 and 900 Mhz models only) but nothing worked. Wireless Interference remained at Severe.

    Temporary fix, I changed the Channel Width from 40 Mhz down to 20 Mhz and Wireless Interference returned to Acceptable. Now all of my devices can reconnect back to the router but at half of the maximum 300 Mbps.

    My question is why the "sudden" change in Wireless Interference from Acceptable to Severe? I am trying to find a logical explanation / root cause for this change. Then I can try to rectify the problem and restore my Channel Width back to 40 Mhz.

    Any help is welcome.
  2. Mangix

    Mangix Networkin' Nut Member

    Probable Cause: Your Neighbors.

    Also, Nobody should ever run 40MHz on 2.4GHz. Just saying.
  3. OldTimeCoder

    OldTimeCoder Addicted to LI Member

    Well, besides the generic "neighbors" issue, you can see what's out there by pulling up the wireless survey on the router:= Tools >Wireless Survey
    (BTW Mangix. 40 Mhz is good to mess up bad neighbors, thus saith the WiFi Troll :cool: )
    Other possibilities occur to me also -
    • Usual suspects:= cordless phones & microwave ovens
    • New suspects:= Wifi hotspots from 4G phones
    • Less likely suspect:= Bluetooth
    And, since you have a couple of Androids, try the WiFi Analyzer application:= https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer
    I use it periodically to walk around the neighborhood to see who is where with what in wireless.
    /s/ O.T.C.
  4. koitsu

    koitsu Network Guru Member

    I should note this will not show you what's causing interference entirely -- this will just show you surrounding APs. There are many non-wifi devices that live in the 2.4GHz and 5GHz spectrums that can cause interference. The only way to see these is to get a hardware analyser and have it break everything down.
  5. Toastman

    Toastman Super Moderator Staff Member Member

    One thing that has suddenly started to become more obvious is USB3.0 hard disks - these generate a hell of a lot of crap,
  6. liquidzyklon

    liquidzyklon LI Guru Member

    1) I thought living in a detached house will help alleviate the problem of interference from neighbours since their house has brick walls and my house has brick walls. After doing a wireless scan show wireless networks at about -85 dBm compared to -99 dBm noise floor.
    2) As stated, everything within my house has not changed in terms of cordless phones (1.9 Ghz and 900 Mhz models only) or microwave. I'll take a look if any of our Android phone somehow turned on Wifi hotspots.
    3) I actually do have external hard drives connected through USB. But this setup has been there for months and not problems prior. The problem just abruptly started on which got me puzzled.
  7. Monk E. Boy

    Monk E. Boy Network Guru Member

    Your neighbors could have bought new equipment. WiFi doesn't understand these things called walls, it passes right through them.

    Try running inSSIDer on a WiFi-equipped PC and see if you can spot any 40Mhz equipment. It's free and works with Windows.

    However, unless you get some piece hardware that can detect non-WiFi networks, it's still only half the picture. Your neighbor(s) could have gotten a new set of wireless security cameras, or baby monitors, or...
  8. Mangix

    Mangix Networkin' Nut Member

    If you want your walls to not pass wifi through them, paint them with lead. Partially serious.

    I have a friend with lead-painted walls, horrible reception from one room to another.
  9. koitsu

    koitsu Network Guru Member

    Or consider that anti-wifi paint. Or that anti-wifi wallpaper. Google is your friend.
  10. mvsgeek

    mvsgeek Addicted to LI Member

    There's also an Android smartphone version of InSSIDer if you'd prefer not to lug a PC around the neighbourhood:)
  11. Toastman

    Toastman Super Moderator Staff Member Member

    Also remember that for every AP you see there will be many associated clients that don't show up. Example - anyone sitting outside my building will see a few AP's but not the 167 clients!
  12. Monk E. Boy

    Monk E. Boy Network Guru Member

    That's one feature I miss from Kismet (and it's OSX port, Kismac), it not only showed you all the APs but also the wireless clients associated with those APs. Still wouldn't show me a microwave or baby monitor, though.

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