Radar gun
From Wikipedia, the free encyclopedia
A radar gun is a small Doppler radar used to detect the speed of objects. A radar gun does not return information regarding the object's position. It relies on the Doppler Effect applied to a radar beam to measure the speed of objects it is pointed at.
Radar guns may be hand-held or vehicle-mounted. They can be used as a tool in the regulation of traffic speed by law enforcement and also to measure speeds in sports.
Most of today's radar guns operate at X, K, Ka, and (in Europe) Ku bands. An alternative technology, LIDAR, uses pulsed laser light.
The radar gun was invented by Bryce K. Brown of Decatur Electronics in March 1954, and was first used in Chicago, Illinois by Patrollman Leonard Baldy in April 1954.
There are radar detectors on the market which can detect most police radar and laser systems. Conversely, in the spirit of electronic warfare, some police radars are equipped with detectors of operating radar detectors.
[edit] How radar guns work
Radar guns are, in their most simple form, radio transmitters and receivers. They send out a radio signal, then receive the same signal back as it bounces off the objects. However, the radar beam is different when it comes back and from that difference the radar gun can calculate vehicle speed.
A radar beam is similar to the beam of a flashlight as it spreads out as the distance from the signal origin increases. The signal then bounces off objects in the path of the beam and are reflected back to the gun. The gun uses the doppler effect to calculate the speed of the object in the beam's path.
All bands of radar work the same way; they simply operate on different frequencies. X band guns are becoming less common due to the fact the beam is strong and easily detectable. Also, most automatic doors utilize radio waves on X band and can possibly affect the readings of police radar. As a result K band and Ka band are most commonly used by police agencies.
[edit] Problems with radar guns
Although radar is an effective tool to acquire an object's speed, there are problems with it. Today's technology is relatively effective and error free so most inaccurate speed measurements are caused by the user.
For speed to be accurately calculated, the object whose speed is desired should be the only moving object in the beam of the radar. If this is not the case, as in a police officer monitoring speed on a stretch of busy road, more articulation is needed in testifying to a particular vehicle's speed. As such, most police officers are trained in the practice of visual estimation of speed, and the radar is thus used as a verification of the visual estimation. In addition, it is easy enough to testify that the vehicle in the left lane was passing vehicles in the right lane, and is therefore the vehicle whose speed is showing on the readout as traveling above the posted limit. The angle in which the object is in relation to the radar source can also affect the reading. This includes angles on a horizontal and vertical plane. This is referred to as Cosine Error, but this effect generally causes the displayed speed to be lower than actual speed, in actuality benefitting the violator.
