The Physics
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Frequency of a Police Radar Gun

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Miller, Rex. Electronics The Easy Way. Hauppauge, NY: Barron's Educational Series, 1988: 284-285. "That X band radar for police use and for others in the experimental band is 10.525 gigahertz (GHz) or 10,525 MHz. They also use the K band (hand held unit) which is in the gigahertz range. Police radar operates on 24.15 GHz." 10.525 GHz
(X band)
24.15 GHz
(K band)
"Radar Applications by Frequency." Encyclopedia Britannica. Chicago: Encyclopaedia Britannica, 1997. "X band (8 to 12 GHz). This is a band frequently used for shipboard civil marine radar, tracking radar, airborne weather avoidance radar, systems for detecting mortar and artillery projectiles, and police speed meters. 8–12 GHz
(X band)
"Radar Wars: Upping the Ante." Car and Driver. 38, 4. (October 1992): 153. "The granddaddy of systems is X band radar… X band operates on the narrow channel from 10.500 to 10.550 gigahertz (GHz)… K band appeared in the seventies and quickly became popular in its deadliest form: a hand held gun featuring an instant on switch. K band operates on a higher-frequency channel from 24.050 to 24.250 GHz… In 1989, photo radar appeared on the scene, and it was bad news for motorists--it operated on a frequency that was undetectable by existing radar detectors. The FCC set up a channel for photo-radar from 34.200 to 34.400 GHz, which lies within the wide Ka band… Which brings us to the Stalker, the latest wrinkle in hand-held radar guns. It operates on the Ka band anywhere from 34.200 to 35.200 GHz." 10.500–10.550 GHz
(X band)
24.050–24.250 GHz
(K band)
34.200–34.400 GHz
34.200–35.200 GHz
("The Stalker")
Markus, John. Modern Electronic Circuits Reference Manual. New York: McGraw Hill, 1980: 82. "10.5 GHz RADAR DETECTOR- Picks up CW Doppler traffic signals in X band region at 10.525 GHz and alerts speeding driver with audio tone." 10.5 GHz
(X band)
Hitzeroth, Deborah. Radar: The Silent Detector. Murray Hill, NJ: Lucent, 1990: 62-63. "Police use two frequencies of radar, K band and X band. K band operates at a frequency of twenty four Gigahertz (one Gigahertz is equal to one billion Hertz). X band radar operates at a frequency of 10 Gigahertz." 10 GHz
(X band)
24 GHz
(K band)
Lotz, W. Gregory & Robert A. Rinsky. Occupational Exposure of Police Officers to Microwave Radiation From Traffic Radar Devices. Occupational Safety and Health Administration, June 1995. "The early traffic radar devices were designed to operate at 10.525 gigahertz (GHz), in which electromagnetic energy wave oscillatesat a frequency of 10.525 billion cycles per second." 10.525 GHz
Service of Police Radars. Vizma, 1998. "Working frequency of radiation at measurement of speed (10525 +-30 EHz [sic].)" 10.525 GHz

The branch of law enforcement that regulates traffic on highways and other roads where a certain speed limit must be met uses a radar gun to calculate the speed of the vehicles. Radar is an acronym which stands for radio detection and ranging. Radar works by transmitting electromagnetic energy in the form of waves into the environment and detecting the energy reflected by objects. Radar picks up this "echo"and calculates its Doppler shift. Radar is based on the Doppler effect which describes the increasing frequency of waves on a stationary observer as the moving source heads toward the observer, and likewise a decrease in frequency as the source moves away. The frequency shift that this radar gun picks up from the "echo"is directly proportional to the velocity of the moving object that reflects the "echo".

Law enforcement radar guns became popular and set to daily use in the early 1970s. Though they emit microwave radiation they are relatively harmless because they emit only 15 to 50 milliwatts of microwave power which is a considerably small amount since power is energy per time. In addition to being low-power devices, radar guns emit waves in a continuous fashion and are known as continuous wave (CW) systems. The frequency of the electromagnetic waves emitted by the police radar gun is determined by the Federal Communications Commission (FCC) and is designated in the X band or K band. The most common was the radar gun mounted inside the squad car window or dashboard and lies in the X band frequencies of 10.500-10.550 GHz. A handheld version of this radar gun utilizes the K band frequencies between 24.050-24.250 GHz.

The X band and K band radar guns soon became vulnerable to radar detectors that pick up these frequencies and alert drivers of upcoming radar guns. This fact made research of this topic extremely difficult considering the fact that nobody would want to give away the frequency of these radar guns so that radar detectors could be created in light of this research. When these devices became open to the public at a cheap price, radar gun designers started creating radar guns which utilized the Ka band from 34.200 to 35.200 GHz. This frequency band is currently undetectable by existing radar detectors and thus makes devices like the Stalker and photo-radar very useful. They are very expensive though and they won't be seen in your local highway trooper's hands any time soon.

Max Lipkin -- 2000
with additional references from Pak Nin Lui -- 1996

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