Re: PIR interfering with wireless network

Discussion in 'Wireless Networking' started by Lem, Jan 30, 2009.

  1. Lem

    Lem Guest

    Peter Hucker wrote:
    > We have a wireless network at work which appears to have gone downhill since the workmen installed PIRs for the burglar alarm. One of them in particular appears to cause dropped packets the closer a laptop is to it. Is this possible?? It's not a wireless PIR as far as I know, as I can see some leftover cable he was using which is a multicore (about 10 cores) type similar to phone systems, so I assume this is for the signal aswell as power. The person in that office swears blind that there were absolutely no problems until the PIR was installed above her desk, and now when I check, about 60% of the packets are being dropped. Moving her laptop to the opposite side of the room it drops only 5% of packets. PIRs used to just pick up infrared of your bodyheat, but I think now they are also motion sensors? Perhaps this means they are sending out a signal and bouncing it off you? Perhaps this could interfere with wireless networking?
    >


    1. You have a device on the wall that works with your security system
    but you don't really know what it is. If it really is a "PIR" then by
    definition, it is a "Passive InfraRed" detector, which means that it
    receives signals but doesn't send them out ("passive"). And yes, a PIR
    is typically used as a motion detector:
    http://en.wikipedia.org/wiki/Passive_infrared_sensor

    2. Just because the installers left some cable behind doesn't mean that
    *all* of the devices they installed are wired to the alarm electronics.
    Very often, a security system installed in an already-built location (as
    compared to one installed during construction) will be a combination of
    wired and wireless detectors.

    3. Ask the company that installed the security system. Are some of the
    sensors wireless, and if so, what frequency band do they use? (AFAIK,
    if you're in the UK, as suggested by one of the groups you posted to,
    wireless security systems are *supposed* to use 868 MHz, but you never
    know). Even if the devices are nominally supposed to use 868 MHz, their
    transmitters may be poorly designed and cause interference in the 2.4GHz
    band of 802.11G.

    --
    Lem -- MS-MVP

    To the moon and back with 2K words of RAM and 36K words of ROM.
    http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
    http://history.nasa.gov/afj/compessay.htm
     
    Lem, Jan 30, 2009
    #1
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  2. Lem

    Bob Willard Guest

    Peter Hucker wrote:
    > On Fri, 30 Jan 2009 19:37:05 -0000, Lem <lemp40@unknownhost> wrote:
    >
    >> Peter Hucker wrote:
    >>> We have a wireless network at work which appears to have gone downhill since the workmen installed PIRs for the burglar alarm. One of them in particular appears to cause dropped packets the closer a laptop is to it. Is this possible?? It's not a wireless PIR as far as I know, as I can see some leftover cable he was using which is a multicore (about 10 cores) type similar to phone systems, so I assume this is for the signal aswell as power. The person in that office swears blind that there were absolutely no problems until the PIR was installed above her desk, and now when I check, about 60% of the packets are being dropped. Moving her laptop to the opposite side of the room it drops only 5% of packets. PIRs used to just pick up infrared of your bodyheat, but I think now they are also motion sensors? Perhaps this means they are sending out a signal and bouncing it off you? Perhaps this could interfere with wireless networking?
    >>>

    >> 1. You have a device on the wall that works with your security system
    >> but you don't really know what it is. If it really is a "PIR" then by
    >> definition, it is a "Passive InfraRed" detector, which means that it
    >> receives signals but doesn't send them out ("passive"). And yes, a PIR
    >> is typically used as a motion detector:
    >> http://en.wikipedia.org/wiki/Passive_infrared_sensor

    >
    > It looks cheap and cheerful with one red LED coming on when I walk about. I've seen others (in our temporary huts) with THREE different coloured LEDs that come on seperately when I walk in different directions, which I assume are multi-detection ones. Those don't cause problems with wireless.
    >
    >> 2. Just because the installers left some cable behind doesn't mean that
    >> *all* of the devices they installed are wired to the alarm electronics.
    >> Very often, a security system installed in an already-built location (as
    >> compared to one installed during construction) will be a combination of
    >> wired and wireless detectors.

    >
    > The building is being completely refurbished (everything except the main supporting walls basically). The section with the problem is an extension, a completely new building.
    >
    >> 3. Ask the company that installed the security system. Are some of the
    >> sensors wireless, and if so, what frequency band do they use?

    >
    > He wasn't there when I was testing, but he was when the user noticed a problem. When she asked him if the PIR he'd installed could have caused the problem, he said "don't be rediculous, they don't do that". I've told the project manager to get him to disconnect it for the time being, so I'll see.
    >
    >> (AFAIK, if you're in the UK, as suggested by one of the groups you posted to,

    >
    > Yes, UK.
    >
    >> wireless security systems are *supposed* to use 868 MHz, but you never
    >> know). Even if the devices are nominally supposed to use 868 MHz, their
    >> transmitters may be poorly designed and cause interference in the 2.4GHz
    >> band of 802.11G.

    >
    > I once bought a wireless video camera which stated it used 2.4GHz. That had channel settings and only interfered with wireless if on the same channel as the wireless access point.
    >


    If it is difficult to remove that PIR, then just cover it up with
    something made of iron or copper or tin to present a shield between the
    PIR and the wireless laptops.

    --
    Cheers, Bob
     
    Bob Willard, Jan 30, 2009
    #2
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  3. Lem

    Lem Guest

    Peter Hucker wrote:
    > On Fri, 30 Jan 2009 20:14:31 -0000, Bob Willard <> wrote:
    >
    >> Peter Hucker wrote:
    >>> On Fri, 30 Jan 2009 19:37:05 -0000, Lem <lemp40@unknownhost> wrote:
    >>>
    >>>> Peter Hucker wrote:
    >>>>> We have a wireless network at work which appears to have gone downhill since the workmen installed PIRs for the burglar alarm. One of them in particular appears to cause dropped packets the closer a laptop is to it. Is this possible?? It's not a wireless PIR as far as I know, as I can see some leftover cable he was using which is a multicore (about 10 cores) type similar to phone systems, so I assume this is for the signal aswell as power. The person in that office swears blind that there were absolutely no problems until the PIR was installed above her desk, and now when I check, about 60% of the packets are being dropped. Moving her laptop to the opposite side of the room it drops only 5% of packets. PIRs used to just pick up infrared of your bodyheat, but I think now they are also motion sensors? Perhaps this means they are sending out a signal and bouncing it off you? Perhaps this could interfere with wireless networking?
    >>>>>
    >>>> 1. You have a device on the wall that works with your security system
    >>>> but you don't really know what it is. If it really is a "PIR" then by
    >>>> definition, it is a "Passive InfraRed" detector, which means that it
    >>>> receives signals but doesn't send them out ("passive"). And yes, a PIR
    >>>> is typically used as a motion detector:
    >>>> http://en.wikipedia.org/wiki/Passive_infrared_sensor
    >>> It looks cheap and cheerful with one red LED coming on when I walk about. I've seen others (in our temporary huts) with THREE different coloured LEDs that come on seperately when I walk in different directions, which I assume are multi-detection ones. Those don't cause problems with wireless.
    >>>
    >>>> 2. Just because the installers left some cable behind doesn't mean that
    >>>> *all* of the devices they installed are wired to the alarm electronics.
    >>>> Very often, a security system installed in an already-built location (as
    >>>> compared to one installed during construction) will be a combination of
    >>>> wired and wireless detectors.
    >>> The building is being completely refurbished (everything except the main supporting walls basically). The section with the problem is an extension, a completely new building.
    >>>
    >>>> 3. Ask the company that installed the security system. Are some of the
    >>>> sensors wireless, and if so, what frequency band do they use?
    >>> He wasn't there when I was testing, but he was when the user noticed a problem. When she asked him if the PIR he'd installed could have caused the problem, he said "don't be rediculous, they don't do that". I've told the project manager to get him to disconnect it for the time being, so I'll see.
    >>>
    >>>> (AFAIK, if you're in the UK, as suggested by one of the groups you posted to,
    >>> Yes, UK.
    >>>
    >>>> wireless security systems are *supposed* to use 868 MHz, but you never
    >>>> know). Even if the devices are nominally supposed to use 868 MHz, their
    >>>> transmitters may be poorly designed and cause interference in the 2.4GHz
    >>>> band of 802.11G.
    >>> I once bought a wireless video camera which stated it used 2.4GHz. That had channel settings and only interfered with wireless if on the same channel as the wireless access point.
    >>>

    >> If it is difficult to remove that PIR, then just cover it up with
    >> something made of iron or copper or tin to present a shield between the
    >> PIR and the wireless laptops.

    >
    > Aha! Wish I'd thought of that! So it has to be iron copper or tin? Not just any metal? The first metal thing I can think of that would be to hand is the lid of a tin of chocolates. Cadbury's Roses I think, not sure what they use.
    >

    Covering the sensor with the Cadbury's lid (mainly, the shield needs to
    be made of an electrically conductive material; copper works best
    (unless you want to use silver); aluminum foil would probably work just
    as well) may help your wifi problem, but it will also make it rather
    useless for the security system. If you can find the main control box
    for the security system, perhaps there is make/model info there that
    will help you determine if some of its sensors are wireless and if so,
    on what frequency.

    I've also seen 2.4GHz security cams, but from a quick Google search, it
    seemed that the wireless sensors used in UK security systems were all
    supposed to be 868 MHz. I don't know how to reconcile those facts (I'm
    neither in the UK nor particularly knowledgeable about security systems).

    --
    Lem -- MS-MVP

    To the moon and back with 2K words of RAM and 36K words of ROM.
    http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
    http://history.nasa.gov/afj/compessay.htm
     
    Lem, Jan 30, 2009
    #3
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