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speed cameras on police vehicles

Discussion in 'Hobby Electronics' started by Phil, Sep 30, 2006.

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  1. Phil

    Phil Guest

    Hi all,

    I had a good look at a speed detector on a police car the other day.

    The unit said it operates on 24 Ghz. (not 2.4Gig but 24Gig)

    My knowledge of frequencies thus leads me to believe that the signal would
    be extremely narrow, and even if one did make a speed camera detector, the
    moment it detects the signal, it's probably too late, as the copper is
    already pointing the gun at you.

    Do you concur?
     
  2. Just because it's got a 12.5mm wavelength doesn't mean it's got a
    narrow beamwidth, though you can make a narrow beam with a smaller
    antenna if you use a higher frequency. If the unit you saw was fixed
    and not hand-held, it'd need at least a 45 degree beamwidth, since
    it's not steerable, and would have to cover 20-ish degrees left and
    right.

    Whether handheld or car-mounted, it's probably only got a frontal
    dimension of a few cm (how big was it, 5cm?), which means the antenna
    is not likely to have much forward gain, maybe 2-3x - which agrees
    with a beamwidth in the range of 20-50 degrees.

    Just my opinion...

    Clifford Heath.
     
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