How Radar Detectors Work

Driving slightly over the posted speed limit is the norm these days. Most of us will bend this particular traffic law at some point, or perhaps regularly, and radar detectors are able to alert you if a police officer has their eye on you.  The eye, in this case, would be a radar gun.

Radar guns have been used by traffic police for decades to catch drivers with a lead foot, and modern radar guns are still using the same fundamental technology. The gun is essentially a radio transmitter and receiver combined in one device. A strong, focused radio signal is projected by the radar gun, and then it awaits an echo of the signal. Radio signals travel through the air at the speed of light which is constant, therefore a radar gun is able to accurately determine the distance of a vehicle. Telling distance isn’t quite enough though, and that’s where Doppler shift comes into play.

Radio waves have a very specific frequency, and when the radar gun and the targeted object are both standing still the echo will have the same frequency as the original signal. However, if the vehicle is in motion away from the radar gun then the radio signal is reflected at a different point in space as the vehicle moves forward. The second segment of the radio signal has to travel just a bit farther to reach the vehicle than the first segment, which results in an echo with a “stretched” or lowered frequency. IF the vehicle is moving toward the radar gun, the second segment of the radio signal will travel a shorter distance than the first, which means the frequency increase.

A radar gun can use this information to tell how quickly a vehicle is moving toward or away from it, based in the amount of change in frequency. If a police vehicle is in motion, the radar gun must take the speed of the vehicle into account when calculating the speed of another vehicle. For example, if a police cruiser is travelling 30 miles per hour and the radar gun detects a target vehicle moving away at 20 miles per hour, they know the target is actually traveling 50 miles per hour (the combined speed of the police vehicle and target vehicle).

The Brains Behind the Detector

Now that we’ve covered how a radar gun works, let’s dive into how a radar detector is able to alert you that one is operating nearby. A detector is actually very similar to a radar gun in that it is a radio receiver, just not a transmitter. After all, it has no reason to send radio signals, but to detect other incoming radio signals within a specific frequency spectrum used by radar guns. Should the frequency range used by police equipment expand, you will likely need a new detector that is capable of picking up the new frequencies.

Police normally leave radar guns on for periods of time, rather than turning them off and on whenever they need a speed reading from a vehicle. While the radar gun is on, the electromagnetic wave emitted by the antenna of the gun quickly spreads out over a wide area, however the gun can only track one specific target at a time, which means detectors can often pick up the signal before the vehicle is tracked and allow the driver a few precious seconds to slow down. This situation isn’t full-proof however; if your vehicle happens to be the first one targeted by the radar gun, your detector will not have time to warn you before the police have the info they need.

There are radar detectors on the market that are more elusive, equipped with their own radio transmitter design to obstruct (jam) the police radar signals, however radar jammers are not legal in North Carolina.

DeDona Tint & Sound offers several options if you’re interested in a radar detector, including products from Escort including the 9500ix, with GPS learning technology that will find and remember non-police signal sources, stores the location of those signals, and silences audible alerts for those sources in the future so you only get audible alerts that are important. You can even connect it to your PC with a USB cable and easily download software updates over an internet connection.

For more information on our available radar detectors and pricing options, call us at (336) 851-1300, or contact us directly through our website.

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5212 W Market St.


DeDona Tint & Sound

5212 W. Market St. | Greensboro, NC 27409

(336) 851-1300

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