They are usually mounted on the rear left window of the police car facing toward the rear. The officer reads your speed on a small console mounted on or under the dash. The unit has a digital readout that displays the highest speed read during the second or two your vehicle passes through the beam. This means that once you go through the radar beam, slowing down does no good.
These units also have a “speed set†switch that can be set to the speed at which the officer has decided a ticket is appropriate. This allows the officer to direct his attention elsewhere while your car travels through the beam. If the speed reading exceeds the “speed set†value, a sound alarm goes off. The officer looks at the readout, then at your car, and takes off after you.
Most modem police radar units can also operate in a “moving mode,†allowing the officer to determine a vehicle’s speed even though her own patrol vehicle is moving. In moving mode, the radar receiver measures the frequency of two reflected signal the one reflected from the target vehicle‑as in the stationary mode‑and another signal bounced or reflected off the road as the patrol vehicle moves forward. The frequencies of these two signals indicate the relative speed between the officer’s vehicle and the target, and the officer’s speed relative to the road. The target vehicle’s speed is then calculated by adding or subtracting these two speeds, depending on whether the two vehicles are moving in the same, or opposite, directions. This calculation is done automatically, by the electronics in the radar unit.
10. What are hand‑held radar units?
Hand-held radar guns are used most often by motorcycle officers. A radar gun is simply a gun‑shaped plastic mold containing the transmitter, receiver, and antenna. The antenna is normally mounted at the front of the gun, and a digital speed readout is mounted on the back. A trigger is included, allowing the officer to activate the radar beam only when she sees a car that appears to be traveling fast enough to spark her interest.
11. How can radar readings fail?
Contrary to many boastful municipal prosecutors, new technology has not completely ironed out problems known to cause radar malfunctions. Most screw ups result from the radar’s operation in real-world conditions, which are often far less than ideal. Moreover, human error can also cause radar devices to fail.
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