speed cameras on police vehicles

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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?




Re: speed cameras on police vehicles


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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.

Re: speed cameras on police vehicles



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In the UK most traps are laser, which is even narrower beam! For radar, as
long as your detector is twice as sensitive as theirs you should get a
warning before they get a readable return pulse, but radar is used for all
sorts of things, in the UK they are often used on temporary traffic lights
and fixed non reporting speed warning signs - so you could be getting lots
of false alarms.



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