Police Radar Information Center and Consulting

Police radars use the Doppler Effect to measure speed. The radar transmits a microwave signal and receives reflections simultaneously. The microwave transmission radiates in a cone shaped beam that varies with model from 9° - 15°. Reflections from moving objects have a slight frequency difference (Doppler Effect) from the transmit frequency. The frequency difference is based on target speed, and can be calculated in MPH. Target vehicle range can be up to a mile or more depending on circumstances.
Optimum Setup
Radar close to road with the 12° beam angled 6° to traffic.

Doppler Effect
Doppler Effect Frequency Shift
Reflections from stationary objects, including the ground, have no change in frequency.

Police lidars transmit pulses of infrared (IR) laser radiation to measured range. The IR pulse travel time between lidar and target and back is used to determine range. The target change in range during 0.3 seconds (or more) is used to calculate speed. Lidars have very narrow beams, just under 0.2°. Practical range is limited to about 500 feet.
Laser Pulse

Lidar Laser Pulse
Transmits 100 to 500 pulses per second depending on model.

Police radars and lidars are not just point (at target) and click (transmit) devices. There are some basic setup limitations and operating procedures that must be observed. Too often procedures are not properly followed in order to save a little time or hide from motorists, resulting in speed errors. Additionally, far too many operators don't remember, or don't use, what they were taught in radar training.
NEW -- Police Radar Basics (Table of Contents) -- NEW
Everything Every Driver, and the Police, should know about Traffic Speed Radar
Book | Kindle
Police Radar Operator Error (Table of Contents)
Microwave and Laser Radar Protocols and Results of Improper Use
Book | Kindle | iPad
Police Radar Handbook (Table of Contents)
A Comprehensive Guide to Speed Measuring Systems
Book | Kindle

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Police Radars Do Make Mistakes

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