Radar - was: Another speeding ticket question

[Charlie Smith <charlie@elektro.cmhnet.org>]

Earlier, Bob Rossato wrote:
> 
> My understanding of moving RADAR is that it takes a reading from a
> stationary object, e.g. the road, to determine the speed of the cruiser and
> compares it to the reading from the moving object, the victim, to determine
> it's speed.  They are not hooked into the vehicles speedometer.

Bob's right.

The radar unit determines target speed by figuring the difference between
background returned signals (stationary objects) and the returned signal
from the target.

I'm a volunteer police officer in Columbus Ohio, so every now and then
I get a chance to practice / experiment with radar units.

A few other interesting facts worth considering -

    When the cruiser is moving, moving radar will only clock vehicles
    coming toward the cruiser.  While you are moving, it will not clock 
    vehicles moving away from you.

    Radar units work through a small "horn" that transmits and receives
    the microwave signals.  This will only measure speeds on moving
    objects that are "in front of the horn".   If the cruiser is parked,
    it will show speeds of both vehicles coming toward the cruiser and
    vehicles going away from the cruiser.

    MOST cruisers running radar have only one radar horn.  That means
    when they are parked, they will only be able to clock cars that
    are in the direction the horn is pointing - eg: in front or behind
    of the cruiser.  Here's the catch:  it is possible to equip a
    cruiser with two horns, one pointing out the front and one pointing
    out the back ...  these type radar units have a flip switch on the
    hand control so the officer can pick which horn is used at any
    given instant.   My guess is it's the cost factor that keeps this
    setup from being used more widely, that and the "calibrate it twice"
    time needed every time a different person uses it.  In Columbus,
    only the freeway cars usually have two horns.


Charlie Smith   charlie@elektro.cmhnet.org  614-471-1418  
 http://elektro.cmhnet.org/~charlie/  Columbus Ohio   USA


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