Inter-Tech Overload

How Radar Guns Measure Speed

February 7, 2014 by · Leave a Comment 

Radar is a directed radio frequency transmission that is projected to an object and bounced back, allowing users to send and receive information. The information may include an object’s location, size, shape, composition, and velocity. First developed during WWII as a means of locating enemy ships and aircraft, radar is now used by a number of devices for an array of reasons, including police radar guns meant to deter speeding.

Radar Guns Explained

Radar uses a phenomenon known as the Doppler Shift to measure the speed of objects. Similar to sound waves, radio waves have their own specific frequency, or the number of oscillations made for each unit of time. When a car and a speed gun are both standing still, the echo and original signal will have the same wave frequency, creating a perfect mirror of the original signal.

However, when a car is moving, different parts of a radio signal are reflected at various points in space, which causes fluctuations in the wave pattern. When a car is traveling away from a radar gun, the signal’s second segment must travel farther to reach the car than its first segment. This stretches out a wave and produces a lower frequency. Conversely, when cars approach radar guns, the second segment of each signal travels shorter than the first prior to being reflected. This is how fixed points like radar speed limit signs help to measure speed and distance travelled.

Radar guns are able to calculate the speed of cars, trucks, motorcycles, and other vehicles as they approach or drive away from the device. However, if police radar guns are used when a police car is moving, the movement of the cruiser must be factored into the equation. For example, if a police cruiser is traveling at 40 miles per hour and the gun says the target is moving away at a speed of 15 miles per hour, then the target is driving 55 miles per hour.

Common Radar Errors

There are many errors that can negatively affect the accuracy of a radar reading. The most common problem, cosine error, occurs when the radar beam hits the path of a target vehicle at an angle. The more pronounced the angle, the greater the error will be. This results in a reading that is slower than a car is actually traveling. However, some speed guns compensate for this error simply by allowing users to input an angle. Errors also come from frequency drift caused by fluctuating voltage, temperature changes, and so on.

Radar guns must be recertified and calibrated periodically, and if a driver contends a speeding ticket, the certifications of the radar operator and the radar device may be called into question in court. Radar guns sold by manufacturers like Radar Gun Sales have many safeguards in place to ensure the proper use of radar, and that the information they provide is both accurate and correctly interpreted.


Radar Gun Sales offers a variety of radar guns, including police radar guns and speed guns. To order a radar gun online, visit Radar Gun Sales.

Speak Your Mind

Tell us what you're thinking...
and oh, if you want a pic to show with your comment, go get a gravatar!