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Thread: signal shape

  1. #1

    Default signal shape

    Hi,

    Using Inssider, I see that my WRT54GL with dd-wrt displays a Gauss shaped curve, channel 11 centered. I don't understand from where does this shape comes from, when I was used to watch rather "square" shapes (see joined file).

    Thanks,

    Olivier
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  2. #2

    Default

    Insider uses you wifi card to get the signal strength, channel and some other data that helps ID the type of wifi signal eg: 802.11a/b/g/n. Since the wifi card simple hands back packets and not real data about the signal structure, insider uses different shapes to show different types of wifi signals seen.

  3. #3

    Default

    Quote Originally Posted by olivier57 View Post
    Hi,

    Using Inssider, I see that my WRT54GL with dd-wrt displays a Gauss shaped curve, channel 11 centered. I don't understand from where does this shape comes from, when I was used to watch rather "square" shapes (see joined file).
    Olivier: Hi!

    The InSSIDer display shape approximates the physical spectrum.

    The square shape (eg inconnu in your attached graphic) is a signal with OFDM (Orthogonal frequency division multiplexing). The Gaussian curve (eg dd-wrt_vap in your attached graphic) is a signal with a DSSS (Direct sequence spread spectrum).

    802.11b (and predecessors) use DSSS modulation.

    802.11a, g, and n use OFDM modulation.

    802.11a, g, and n Access Points may also broadcast a DSSS modulated signal when they are idle (ie no clients connected) and then switch to an OFDM signal shape when transferring data. 802.11a, g, and n Access Points may also broadcast a DSSS modulated signal when they are communicating with a 802.11b client and operating at slow transfer speeds.

    So your dd-wrt_vap might be 802.11b. Or it might be 802.11a, g, or n that is idle and in beacon mode.

    V
    Last edited by vmq6695; 07-16-2011 at 09:16 PM. Reason: correct typo, add to explanation

  4. #4

    Default

    Hi,

    Thanks for your answers and thanks for this detailed explanation V !

    Knowing those modulations, I understand much better what happens now.

    Olivier

  5. #5

    Default shape depending on card used also?

    Hi,

    I am using multiple machines, and on some, a certain signal shows up in a rectangular shape, in others in a bell shape. Based on other comments in other threads, I guess this is probably due to the capabilities of the adapter, as the one showing the bell shape I think does support n (its a used model I recently purchased, with unclear specs about adapter capabilities), while the others definitely don't.

    Is my guess correct?

    Thanks!

  6. #6

    Default

    Yes, if an access point shows up differently on different machines, it would be because of the capabilities of the adapters used in the machines.

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