bjones
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Radar, more properly RADAR, was invented during WWII. The name stands for Radio Detection and Ranging. It was originally developed to spot flying aircraft. Early on, it was also discovered that radar could detect speed. Radar guns emit radio waves at a specific frequency which strike objects and reflect back to the gun, where differences are measured and converted into standard units, such as miles per hour. Early radar emitted radio waves at the frequency of 2.455 GHz in the S-band. In the 1960s the X-band began to be used at 10.525 GHz. In 1976, the K-band began to be used at 24.125 GHz and 24.150 GHz. K-band is absorbed by heavy rains and high humidity so, today, police radar covers 13 channels on the Ka-band that range from 33.4 GHz to 36.0 GHz.
Most people believe that radar guns work by bouncing the radio waves off of objects and measuring the time it takes for them to get back to the gun. This, however, is not exactly true. Speed radar uses a phenomenon called the Doppler effect. The Doppler effect is the name for a shift in frequency a wave makes due to motion. This can be illustrated by sound waves. When a train approaches you, the sound of the train suddenly drops to a lower pitch once it passes you. The wave changes frequency because the distance between the peaks of the wave is affected by the speed of the object. As the object moves toward you, the distance is less. As the object moves away from you, the distance increases. Police radar measures the change in the frequency of the radio waves to determine the exact speed of the object.
 Posted 5138 day ago
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