Utilities to scan for wireless interference?

Discussion in 'Home Networking' started by Dr Zoidberg, Sep 26, 2006.

  1. Dr Zoidberg

    Dr Zoidberg Guest

    Does anyone know of any utilities (preferably free) that will let you scan
    the relevent frequencies for sources of interference. This may be other
    people's access points or it may be other electrical equipment generating
    noise.
     
    Dr Zoidberg, Sep 26, 2006
    #1
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  2. Dr Zoidberg

    Conor Guest

    ROFLMAO...and just how do you expect this to work?

    Priceless...


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    Conor, Sep 26, 2006
    #2
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  3. Dr Zoidberg

    Dr Zoidberg Guest

    Because wireless cards are a radio receiver.
    They take meaningful patterns on the required frequency and convert that to
    data for the PC.

    Some of them will report signal to noise ratios depending on the card and
    software and they are very obviously capable of picking up random signals on
    the same frequency.

    All I want is a utility to report just the noise on various channels.
    I know some access points can do this but they aren't portable. I already
    have a cisco site survey tool that will do a similar job , but would like a
    choice of them if possible.

    What's so hard about that?

    Nowhere did I say that I want it to identify sources of intereference , just
    to say if it's there or not.



    --
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    Hermes: "We can't afford that! Especially not Zoidberg!"
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    Dr Zoidberg, Sep 26, 2006
    #3
  4. Dr Zoidberg

    Tiny Tim Guest

    Netstumbler will seek out other APs and report the channel number, signal
    strength and encryption type. So you can see if you might have an
    interfering channel nearby. You need 5-6 channels of separation - not sure
    which - as the channels spread and overlap each other. So if you're on
    channel 6 and find another network nearby on the same or close channel
    number than change your channel to 1 or 13 to move away from the
    competition.
     
    Tiny Tim, Sep 26, 2006
    #4
  5. Dr Zoidberg

    Clint Sharp Guest

    Http://www.thinkgeek.com/gadgets/electronic/80ce/

    Not all software so not free, something buried in the jumble of
    information I call a memory makes me think there's a free/cheaper
    version of this as it's a fairly standard USB WiFi adapter.
     
    Clint Sharp, Sep 26, 2006
    #5
  6. Dr Zoidberg

    Dr Zoidberg Guest

    Excellent.
    Thats exactly the sort of thing I'm after.

    Still laughing Conor?
     
    Dr Zoidberg, Sep 27, 2006
    #6
  7. Dr Zoidberg

    Conor Guest

    Yup...because it's a USB device and not one utilising the Wifi gear you
    already have.

    I'm still winning.


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    Conor, Sep 27, 2006
    #7
  8. Dr Zoidberg

    Conor Guest

    Yes...

    Only does anything on 2.4GHz. Doesn't pick up electrical interference.

    As well as being an additional piece of hardware and not using what you
    already got.



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    Conor, Sep 27, 2006
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  9. Dr Zoidberg

    Dr Zoidberg Guest

    It's close enough , and all their device is is a normal USB wireless adaptor
    with their own drivers , and it sounds like there may be a version using
    generic cards.
     
    Dr Zoidberg, Sep 27, 2006
    #9
  10. Dr Zoidberg

    Dr Zoidberg Guest

    But thats all I care about when checking for interference on 802.11b/g
    radios.
    It's only $99 , hardly a fortune when compared to the amount we charge for a
    proper site survey
     
    Dr Zoidberg, Sep 27, 2006
    #10
  11. Dr Zoidberg

    Conor Guest

    Oh dear.
    It has **** all range and very limited functionality and reporting.
    It's about as much use outside of home use as a chocolate fireguard.
    --
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    I'm really a nice guy. If I had friends, they would tell you.

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    Conor, Sep 27, 2006
    #11
  12. Dr Zoidberg

    Dr Zoidberg Guest

    I have legs , I can walk around
    Seems to be enough for what we need.
     
    Dr Zoidberg, Sep 27, 2006
    #12
  13. In true pantomime fashion - "Oh no you're not!".

    Airmagnet will scan for interference and supports a wide range of
    wireless cards and adaptors:
    <http://airmagnet.com/products/cards.htm>

    WLanExpert (free) will scan each channel in turn and present a graph of
    signal strength per channel, allowing you to find the channel with the
    least interference (not quite what the OP was after, but still).

    Accept that you were wrong gracefully, Conor. I know it's not in your
    irascible nature, but it'd be a nice change.
     
    Gareth Halfacree, Sep 28, 2006
    #13
  14. Dr Zoidberg

    MED Guest

    On a b or g network, you need 3 channels of separation. Therefore you can
    have 5 networks working in close proximity:

    On channels 1,4,7,10 and 13. (in Europe).

    Mike.
     
    MED, Sep 28, 2006
    #14
  15. Dr Zoidberg

    Dr Zoidberg Guest

    Nope , 6 channels is what's needed ideally.
    If you check for interference you will see quite a bit of signal from 1
    leaking into 4.
    It may work fine , but it's just as likely not to
     
    Dr Zoidberg, Sep 28, 2006
    #15
  16. Dr Zoidberg

    Dr Zoidberg Guest

    Spot on , and it works with some of the cards I have available.
    Thanks.
    Is that airborne bacon?
     
    Dr Zoidberg, Sep 28, 2006
    #16
  17. Dr Zoidberg

    MED Guest

    Agreed - there are 3 non-overlapping networks in the 2.4GHz band. But if
    you have a high number of clients in close proximity, AND you want to have a
    reasonably high bandwidth, then a 3 channel separation is (or I suppose 'can
    be') acceptable.

    It depends on what you want to do, and how many clients you have per
    channel.
     
    MED, Sep 28, 2006
    #17
  18. Dr Zoidberg

    stephen Guest

    this is packet networking - so interferences "pulses" with the traffic, and
    interference gets worse as the traffic levels increase on the set of
    "overlapping" channels.

    what you really need is interference below a given level - and other things
    besides separation can help, such as choosing the antenna type to give you
    non uniform radiation patterns, and tweaking power levels (down usually) to
    reduce interfence between your APs.
    The thing to remember is this is radio and radio is not that precise.

    filtering, sidebands and related effects do not suddenly stop at a
    particular frequency, they just get smaller as you get further from the base
    frequency. Similarly the reciever filter gets better as frequency separation
    increases.

    What this means in practice is that a big enough interference source can
    cause problems even if it is more than the 5 channels away from the one you
    try to use. What is supposed to happen is that the power limits for users in
    the 802.11 band limit the effect.

    The 3 "non overlapping" channels is for a specific definition of "not enough
    signal spills across to be a problem at the power levels used and with the
    filters specified, etc etc"

    if you really want more "non overlapping" channels try 802.11a where there
    are 8 available.
    Agreed - radios always have some interference. The big issue is can you get
    the "good" signal thru without a sufficiently low error rate.
     
    stephen, Sep 28, 2006
    #18
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