Common Errors Encountered in Operating Police Radar

Radar is an advanced technology, and most people, including the police do not understand how the gadget works. The police commonly uses two types of radar, and they include stationary radar and moving radar. The most common type of stationary radar used by the police is the hand-held radar gun. The federal government has developed standards to ensure accuracy and reduce radar errors. Most states governments have used the guidelines provided by the federal government to train the police in radar operations. This article discusses some of the common errors encountered in operating police radar.

1. Antenna Positioning Error

Radars work by projecting a beam that travels in a straight line and cannot bend around curved and hilly terrains. Failure to position the antenna correctly may make it to record the speed of another car in the background instead of the oncoming one.

2. Look-Past Error

Even in cases police officers position the radar correctly, it can still be affected by the “look-past” error. The error occurs when a radar foregoes a small reflection from a smaller object in the foreground to capture a bigger reflection behind. This error is the most difficult to detect because poorly trained radar operators believe that it cannot happen. However, in some traffic conditions, the closest vehicle to the radar antenna may fail to send the strongest signal.

For instance, in a study dubbed “Car and Drive” done in 1979, the look-past error was identified. The researcher was interested in finding out the range at which the Kustom Signals KR11 radar would still be effective in measuring the speed of different vehicles. The radar failed to detect most small sedans until they were less than 1200 feet from the antenna. However, the same radar was able to detect a Ford 9000 semi when the vehicle was still 7600 feet away from the radar. This is evidence that most vehicles reflect microwaves at different rates.

3. Vehicle Interference Error

The vehicle interference error is commonly experienced with moving radars because they register readings using complicated mechanisms compared to stationary radars. This error occurs when a moving radar is used in heavy traffic. For instance, the traffic ahead can make the radar register wrong patrol speeds. Moving radars work by obtaining target speed from the difference between patrol speed and closing speed of the target vehicle. Hence, any problem that results in a low evaluation of the patrol speed will consequently generate a high speed for the targeted vehicle. The problem becomes more pronounced when the difference between the patrol speed and interference speed is 5 to 10 Mph. This means that a target vehicle doing 61 Mph may be registered at 66 to 71 Mph. This close-range speed difference is difficult to tell with the eye.

4. Cosine Error

Cosine errors generate the same reading problems as those generated by the interference error, except moving traffic is not needed. Stationary objects located on the roadside, for example, buildings and road machinery may act as efficient reflectors compared to the horizontal pavement. This means that the radar will use reflections from these objects to calculate the patrol speed.

In cases where the reflective objects are located straight ahead of the radar path, the estimated patrol speed is close to the real speed. On the contrary, if the objects were located off the radar antenna, the estimated patrol speed would be lower. This error is a caused by a simple trigonometry problem based on the cosine of the angle formed between the targeted reflector and the ground reflector. In most cases, the cosine error makes the patrol speed to be lower than the real speed, and this increases the target speed.

5. Double-Bounce Error

This error is caused by the fact that microwaves are reflected easily. In fact, the ease at which microwaves are reflected is the reason they are used in radars. Nevertheless, radar operators should know how to differentiate ordinary reflections, from bounce reflections. Huge objects, for example, trucks are very good reflectors, and the radar beam can bounce off a couple of moving tracks at the same time. This results in the production of erroneous readings.

6. Beam-Reflection Error

The ease at which microwaves are reflected require the police to be extra cautious when fitting the radar antenna on the patrol car. It is possible for the rear-view mirror to create a reflection path, even if the mirror is set facing forward in the patrol car. This means that the radar will record the speed of the vehicles behind the patrol car, and this includes coming vehicles and ongoing ones because the radar cannot distinguish between the two.

7. Radio-Interference Error

It has been noted that the UHF radio waves can make radars read different numbers when transmission is made. Public radio transmission in the patrol car can generate ghost or false readings. Police officers are advised to refrain from making radio transmissions when approaching the target vehicle.

8. Fan-Interference Error

When the police fit radar antennae inside patrol cars, the radar is more likely to pick readings from heaters, fan motor, defroster and air conditioner among others. The fun readings are likely to disappear when a target vehicle approaches; this means that the fan is less likely to interfere with the readings. However, when the police use moving radars, a fan running at a steady speed is likely to override the speed of the patrol car reflected from the road. This means that the radar will substitute the patrol speed with false speed coming from the fan when calculating the target speed. The radar calculates the target speed by obtaining the difference between the patrol speed and the closing speed. If the speed of the fan is lower than the patrol speed, it leads to a higher reading for the speed of the target vehicle.

9. Road-Sign Error

Microwaves are reflected easily and this means that road signs can also generate errors.

Apart from the nine common errors encountered in operating police radar discussed above, radars do have other limitations. For example, it is impractical to use them on highways with heavy traffic.

About the Author: Danny Williams

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