speed cameras on police vehicles

[Phil]

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?

 

[Clifford Heath]

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,

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.