Radar guns are used to measure the speed of moving objects. An acronym for Radio Detection and Ranging, these sensors produce microwaves, electromagnetic radio waves or infrared laser light so the user can measure the reflections for specific purposes like location, presence, speed, and motion.
Law enforcers use this Doppler radar device also referred to as a speed gun to measure the speed of moving cars and enforce speed limit guidelines. It can be handheld, mounted on a car or stationed to a location.
Aside from law enforcement, different professional sports also use a similar device to measure the speed of a ball being pitched or track the bowling speeds. These radar guns have certainly come a long way since its first use in the year 1947 to issue speed tickets in the state of Connecticut.
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How Do Radar Guns Work?
Since radar guns follow the principle of a Doppler effect, it is best to have a good understanding of this first. Basically, this is the increase of decrease of the frequency of light and sound as it moves towards you or away from you.
The Doppler Effect will cause a noticeable change in pitch. Say for example a car is running towards you, the pitch would be compressed and higher in pitch whilst a car moving past you, the sound waves are being stretched so the pitch tends to go on lower frequency signal and a lower pitch.
With this principle explained, here’s how police radar guns can calculate and measure the speed of the cars cruising and zooming in the highways.
- Squeeze the trigger so a radio wave can be sent out of the antenna to the specific direction of the target which at this point is a car. The car will then reflect the wave back to the radar gun and that wave will be detected by the radar gun. Note that this back and forth volleying of radio waves all happen at the speed of light.
- The frequency will then change depending on the speed of the car and its direction, if it is moving towards you or away from your location. The radar gun will then calculate the change in frequency and convert the change of frequency to speed.
- The radar gun calculates the change of frequency by getting the difference between the reflected frequency and the original frequency. The unit used is Hertz.
- The difference is then converted to speed following a formula of change in frequency divided by the original frequency being transmitted. This is then multiplied by the velocity of light which is a constant 6.71 x 10^8.
- The speed will then be reflected at the radar gun. Depending on the radar gun’s features, the direction can also be included on the display and if the speed is a positive number, it would indicate that the car is moving towards you and if it is a negative figure, then the vehicle is moving away from you.
What kind of radar guns do police use?
The police force usually use radar and lidar guns to measure the speed of the cars. The main difference between these two are radars depend on microwaves while lidar utilizes pulsed infrared or IR laser light radiation. Also, police radars are usually set to two configurations, fix mounted or hand-held.
Hand held radars usually operate from a position that is stationary and its transmission can either be on command or continuous. Depending on the model and series, some of these radars can measure both the receding and approaching traffic at the same time.
Meanwhile, fixed mounted radars can both have moving and fixed modes and it can also do its transmission on command or continuously. It can be set inside the patrol car and would usually have a front or rear antenna for better broadcast.
How accurate are radar guns?
Radar guns are accurate to a plus or minus 1 mile per hour (± 1 MPH). Radars that are set to moving mode has an accuracy of plus or minus 2 miles per hour (± 2 MPH).
How the speed gun has changed over time?
It was in February 1949 when the Connecticut State Police adopted the radar speed measurement started issuing speed tickets based on radar measurements. Garden City, New York also adopted the same practice and issued speed tickets and to help the force come up with a revenue.
These early radar systems operate at 2.455 Ghz under the S-ban are deem not to be that reliable as it is only accurate to within a couple of miles per hour and it only has a range of 150-500 ft. The emergence of speed guns also gave birth to radar detectors so the police force became more determined to make their speed guns be more effective.
Fast forward to 2000 and today, the police force is now using digital radar guns that boasts high levels of accuracy that helps a lot of communities make their highways and roads safer. Right now, there are different speed guns that are being used.
It can range the from the traditional Ka-band Dopplers, directional radars and the more advanced LIDAR guns that utilizes pulse light instead of radar that can help police target individual cars. Some radars now can also take pictures of a specific car’s license plate which makes identification so much easier.
Additionally, to battle those speed detectors that also improved, most of the speed guns now comes with anti-jamming features so it would very difficult for would-be violators to evade the laws of the road.
How to request radar gun calibration records?
Requesting for the radar gun calibration records is one of the ways of disputing a speeding ticket. Usually, aside from the gun calibration records, the notes of the law enforcer also come in handy. For those who want to get a copy of the radar gun’s calibration records, you can directly make your request and address it to the law enforcement agency.
This is under the Freedom of Information. Depending on your state, there might be an additional step or two but you should be able to get your request done in obtaining the maintenance and calibration records of the radar gun that was used for your alleged road violation.
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