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Radar Guns FAQ (Frequently Asked Questions about Radarguns)
Radar Guns FAQ
- (Q)What are the different types of radar?
- (A)There are 2 basic types of radar (such as Police Radar Guns or Sports Radar Guns), microwave transmitters and laser (ladar or lidar) transmitters.
- (Q)How do microwave radar speed sensors work?
- (A)Microwave radars use the Doppler principle to measure speed. Doppler radar uses the fact the return echo from a moving target (vehicles, baseballs, hockey pucks, golf balls, etc.) is frequency shifted (off the transmit frequency) proportional to the target speed. The greater the target speed, the greater the frequency shift (change) also referred to as the Doppler shift.
- (Q)What frequency do microwave radar guns operate?
- (A)In the United States most radars transmit on a single frequency in X band (10.525 GHz), K band (24.150 GHz), or Ka band (between 33.4 - 36 GHz).
- (Q)How do laser radar speed sensors work?
- (A)Laser radars transmit a narrow infrared laser pulse to measure the time it takes to reflect off an object. Knowing the speed of light (186,000 miles per second) target range can be calculated. If the object is moving the range changes with time -- target speed equals change in target range divided by time.
- (Q)Why is laser radar sometimes referred to as "lidar" or "ladar"?
- (A)Lidar stands for "Light Detection And Ranging". Ladar stands for Laser Detection And Ranging. A laser light beam is a pure color of light (red, green, blue, etc.). Police laser radar transmits in the infrared (IR) region at a wavelength of about 905 nanometers (invisible to the eye). The term lidar really does not apply to police laser radar, but is used because of the stigma associated with radiation.
- (Q)How do sports radars work?
- (A)Sports radars are usually microwave transmitters that operate much like a police radar. Sports radar usually have shorter sample times (shorter detection range), wider beams, and sometimes less radiated power.
- (Q)Speed of what object can cheap radar gun such as Bushnell Speedster measure?
- (A)The Bushnell Speedster can measure objects as small as a golf ball to as large as a truck. I have measured rain speed with the Bushnell (through a window from inside a dry structure).
- (Q)Can I measure the speed of a baseball bat swing / golf club? Tennis ball? Bowling ball? Golf Ball?
- (Q)How important is it to stand in front or behind the object when measuring its speed?
- (A)Somewhat important. The less the radar is directly in front of or directly behind the target object, the lower the measured speed (the Cosine Effect). The error is directly proportional to the angle off the direction of the target object. An angle error of about 25 degrees equates to about a 10 percent error (reading low by 10%).
- (Q)Are radar guns a potential threat to civilians?
- (A)Unknown. Anyone targeted by a radar (probably) has nothing to worry about (the time and energy levels are just too small). Cellular phones are a greater concern, much more power transmitting close to users head (sometime for hours). Some have concerns about long term use (by police) of police radars.
- (Q)Can a Police Radar Gun be fried by a Transmitter?
- (A)It is possible but unlikely, and probably would not happen by accident.
- (Q)Are radar guns calibrated?
- (A)Radars are calibrated in (and when they leave) the factory, after that the units are typically checked that they operate within design specifications (calibration check) once or twice per year.
- (Q)Can private citizens own radar guns?
- (A)Yes. Radar units may be used, under FCC Rules and Regulations Part 90, by anyone with a legitimate need to measure the speed of objects or vehicles.
- (Q)What is Radar Gun Jamming ?
- (A)By definition a jammer is intended to prevent a radar from obtaining a speed measurement and/or spoof the radar by forcing a false reading.
- (Q)Is radar jamming legal?
- (A)Microwave jamming is against FCC Rules and Regulations, laser radar jamming is not illegal (except in Illinois and Tennessee as of July 2006).
- (Q)What does it mean - radar gun locked the car at speed XX MPH?
- (A)When an officer observes a speeding violation the officer can
"lock" the speed -- freeze the reading on the radar display, sometimes in a separate window.
- (Q)What other means of measuring a speed of a speeding car besides a Doppler radar gun?
- (A)Other speed measuring systems include across the road laser (2 laser beams), inductive loops (in road), Piezo Ceramic road sensors, road cables (2 or more), aerial clocking (from an aircraft), distance/time computer, a stopwatch, and pacing (with patrol car).
- (Q)How to record data measured by a radar gun?
- (A)Some radars record, at a minimum, measured speed and date/time, for download to a personal computer.
- (Q)How accurate are radars?
- (A)Most stationary radars are accurate to ±1 mph (±2 km/hr). Moving radars are accurate to ±2 mph (±4 km/hr).
- (Q)Why is moving radar less accurate than stationary radar?
- (A)Moving mode radar measures 2 echoes, the target speed (closing or opening speed relative to the moving radar) and the ground echo (radar speed). Each measurement has an accuracy of ±1 mph (±1 mph x 2 = ±2 mph).
- (Q)Why does moving radar require 2 measurements?
- (A)Vehicles measured from a moving radar have a Doppler shift of the combination of the patrol car speed (radar) and the target vehicle speed. The radar measures it's own speed to calculate target vehicle actual speed.
- (Q)How do tuning forks test radar accuracy?
- (A)A radar can measure a vibrating tuning fork, registered speed is proportional to fork resonance. An accurate radar should register a certain speed knowing the fork resonance. For example a tuning fork that resonates at 2000 Hertz (Hz) should register a speed of 64 mph on an X band radar. Note 2000 Hz should register 28 mph on a K band radar.
Note 2 tuning forks (that resonate at different frequencies) are required to test moving mode radar. One fork for ground speed and one for target speed.
- (Q)Does weather effect radar?
- (A)Yes. Weather mainly effects radar detection range. X band radars operate better than K or Ka band radars in bad weather. Water in the atmosphere (humidity and rain) effects K band radars the most, Ka band radars transmissions are also effected. X band radars to a lesser degree.
- (Q)What is the maximum range a police radar can measure speed?
- (A)Radar range varies widely with radar, target (size/shape), and weather conditions. Maximum detection range can be as little as 100 feet, or greater than 1 mile.
- (Q)What is the "Cosine Effect"?
- (A)The Cosine Effect is a radar measured speed error due to the angle between the radar and target vehicle or object.
- (Q)How does the Cosine Effect influence measured speed?
- (A)The Cosine Effect causes a stationary radar to measure speeds low, the greater the angle the lower the measured speed. Moving mode radar may measure target speed HIGH in some situations.
- (Q)Which angle is the Cosine Effect angle?
- (A)The Cosine Effect angle (from the target vehicle's point of view) is the angle between the direction of the target vehicle and the radar. If the target vehicle is traveling directly toward (or away) from the radar, the Cosine Effect angle is 0 degrees (no error).
- (Q)How large or small is the Cosine Effect error?
- (A)The greater the angle, the greater the error. The error is a function of the cosine of the angle, thus Cosine Effect error. Measured speed = actual speed multiplied by the cosine of the angle.
- (Q)Can a stationary radar measure other vehicle speeds from a moving patrol car?
- (A)No. A stationary radar operating from a moving vehicle will measure the ground echo (the patrol car speed). The ground echo is huge compared to other moving vehicles. Moving radars are designed to distinguish the ground echo and the target vehicle echo.
- (Q)What is the difference between radar "transmit power", "power density", and EIRP specifications?
- (A)Transmit power is the power delivered to the antenna. Antenna specifications (gain and efficiency) are required to determine the radiated power from power delivered to the antenna. Power Density is a measure of radiated power per area. Typically radars are specified in milliwatts per square centimeters (mW/square centimeter) at a specific range (usually 3 meters). The greater the range the lower the power density. ERIP (Effective Radiated Isotropic Power) or just ERP (Effective Radiated Power) also measures radiated power compared to a perfect isotropic radiator in Watts (W), milliwatts (mW), or dBm (decibels above or below 1 mW).
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