Originally posted by sisteve+Oct 16 2003, 04:30 PM-->Originally posted by sleepergtx@Oct 15 2003, 10:55 PM
Green92HatchDX@Oct 16 2003, 03:26 AM
how is that?
Radar reflects off the reflective material the plates are painted/made with easier than they do paint. That's also why if you see a picture with a bright flash the plates turn out to be bright white.
actually, radar guns view a light source (headlight, foglights etc) before bouncing off every other thing. Thats why you see a lot of cops doing radar traps at night.
It all depends on the Radar gun.
Source of this upcoming quote:
The Speedchek Speed Sport Radar Gun works by using Doppler Signal Processing to clock speeds. The internally located antenna, when activated, sends out a radio frequency (RF) signal at a specific frequency (10.525 GHz). The signal projects from the unit like a flashlight beam, decreasing in strength with distance. If a moving object, like a thrown ball, enters the device's transmitted signal, the frequency of the reflected signal off the ball is changed or "shifted". This frequency change, or "Doppler Shift", is proportional to the ball's speed, and the Speedchek Speed Radar Gun's internal circuits instantly process the return signal to display speed in your choice of either MPH or km/h.
The Speedchek Speed Sport Radar Guns' projected signal is able to pass, unaffected, through certain materials, such as netting, wire mesh fencing, tarps or backdrops, and Plexiglas. This allows you to put a protective barrier between the moving target object and your Speedchek Speed Radar Gun without affecting speed measuring performance (a recommended precautionary procedure).
The Speedchek unit is designed to clock objects that move directly in line with (or facing) the direction of target travel. The device is designed to measure and display the speed of objects;
1 Approaching the unit;
2 Moving away from the unit;
3 Passing over or under the unit;
4 Passing beside the unit.
The most effective clocking range is within 30 feet. The unit is not designed to clock moving objects from long ranges. In motorized sports applications, it is best to go in a direction towards the unit. The unit will not be accurate for side-to-side measurements.
Safe Use Recommendations and safety information
The manufacture strongly recommends the following:
Regardless of the activity you have planed to use the Speedchek Speed Sport Radar Gun for, be sure that you have selected a safe, open area and that people, personal property, or your Speedchek Speed Sports Radar Gun cannot be inadvertently injured, struck, or damaged.
ALWAYS warm up properly before performing physical activities with the Speedchek Speed Sport Radar Gun. If you have been injured or strained previously in other activities, performing a physical activity with the Speedchek Speed Sports Radar Gun could aggravate your condition and injure you further. If this is the case, consult your doctor before using the Speedchek Speed Sport Radar Gun.
Your Speedchek Speed Sport Radar Gun should never be hand-held during any coaching, training, or speed trial use. Never allow any other person to hold or stand near unit while in use. Any person holding the Speedchek during use puts themselves at risk of severe personal injury or possible death by accident. The handle position feature is only intended for use to carry to area of use, and the stand position feature is intended to place the unit on a level surface during use.
The Speedchek Speed Sport Radar Gun is a form of radio transmitter. When it is turned on, the unit's internal antenna sends out a very low level radio frequency (RF) signal at a specific frequency (10.525 GHz). In addition to the low energy level, and as the user is not required to be in close proximity to the unit, any exposure to RF energy is virtually eliminated when operating the Speedchek Speed Sport Radar Gun. The device also features an "Auto Power Shut-Off" function that turns the unit off following five minutes of inactivity to reduce unnecessary RF output.
Edit: more information from howstuffworks.com.
Radar Basics:
To understand how radar detectors work, you first have to know what they're detecting. The concept of measuring vehicle speed with radar is very simple. A basic speed gun is just a radio transmitter and receiver combined into one unit. A radio transmitter is a device that oscillates an electrical current so the voltage goes up and down at a certain frequency. This electricity generates electromagnetic energy, and when the current is oscillated, the energy travels through the air as an electromagnetic wave. A transmitter also has an amplifier that increases the intensity of the electromagnetic energy and an antenna that broadcasts it into the air.
A radio receiver is just the reverse of the transmitter: It picks up electromagnetic waves with an antenna and converts them back into an electrical current. At its heart, this is all radio is -- the transmission of electromagnetic waves through space (see How Radio Works to learn more).
Radar is the use of radio waves to detect and monitor various objects. The simplest function of radar is to tell you how far away an object is. To do this, the radar device emits a concentrated radio wave and listens for any echo. If there is an object in the path of the radio wave, it will reflect some of the electromagnetic energy, and the radio wave will bounce back to the radar device. Radio waves move through the air at a constant speed (the speed of light), so the radar device can calculate how far away the object is based on how long it takes the radio signal to return.
Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the number of oscillations per unit of time. When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal. Each part of the signal is reflected when it reaches the car, mirroring the original signal exactly.
But when the car is moving, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the car is moving away from the radar gun, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. As you can see in the diagram below, this has the effect of "stretching out" the wave, or lowering its frequency. If the car is moving toward the radar gun, the second segment of the wave travels a shorter distance than the first segment before being reflected. As a result, the peaks and valleys of the wave get squeezed together: The frequency increases.
Based on how much the frequency changes, a radar gun can calculate how quickly a car is moving toward it or away from it. If the radar gun is used inside a moving police car, its own movement must also be factored in. For example, if the police car is going 50 miles per hour and the gun detects that the target is moving away at 20 miles per hour, the target must be driving at 70 miles per hour. If the radar gun determines that the target is not moving toward or away from the police car, than the target is driving at exactly 50 miles per hour.
Police officers have been catching speeders this way for more than 50 years. Recently, many police departments have added a new sort of speed detector, one that uses light instead of radio waves. In the next section, we'll see how these cutting edge devices work.
