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The unit may becalibrated manually and electronically

10/22/2019

　　Living With Police RadarPolice use hand-held or vehicle mounted radar units tomonitor the speed of vehicles for the purpose of traffic lawenforcement. The units are "low power" and have a range of onlyabout Liquid sulfur dioxide one-half mile. The range may be more or less depending uponterrain, weather, and the size of the target vehicle. Officers must usually be trained and certified to operate aradar unit and to testify in court concerning readings obtainedwith it.Traffic radar may be operated in the stationary mode or themoving mode. Radar units are designed either for stationary useonly, or may have a switch to select stationary or movingoperation. In the stationary mode the officer parks the policevehicle at an advantageous location and directs the radar antennain the direction of the target vehicle. The target vehicle may beeither moving toward the radar unit or away from it.

If thetarget is large enough or close enough to reflect the radar signalback to the radar unit, the target's speed will be recorded.In the moving mode, the officer's vehicle must be in motionand can monitor the speed of targets approaching from the oppositedirection. The radar unit measures the speed of the officer'svehicle and the speed of the oncoming target vehicle. The twospeeds are added to each other by the radar's computer. Then thepolice vehicle speed is subtracted from the total of the two thusgiving the target speed. The readout is obtained in a fraction ofa second.The radar unit must be calibrated at the beginning of eachshift. Some jurisdictions may require that the unit be calibratedbefore and after each radar traffic stop is made.

The unit may becalibrated manually and electronically by the officer. Manualcalibration is done by striking a small tuning fork "cut" for acertain speed and holding the fork in front of the radar antenna.If properly calibrated, the radar will indicate the same speed asstamped on that particular tuning fork. The unit is also checkedby pressing a "calibrate" button on the radar and observing thecorrect electronic responses indicating that the unit isfunctioning properly.Traffic radar is prone to a few errors if not operated byproperly trained personnel. Radar units operated inside thevehicle may read the speed of the spinning ac/heater fan. Thiserror is obvious because of the constant "speed" readout in theabsence of targets.