X/K/Ka Super Wideband (220-1648) Speed Detection Faxback Doc. # 3411 Radar Detector A RADAR (Radio Detecting And Ranging) device can bounce a radio signal off of a moving object, such as a car. The reflected signal is picked up by a receiver. Traffic radar receivers measure the frequency difference between the original and reflected signals. This frequency difference is converted into a speed, which appears on the receiver's display. Radar signals, like other types of radio signals, travel in straight lines until they hit an object that either absorbs, reflects, or refracts the signal. Radar receivers cannot see around curves or over hills, so a vehicle must be in sight for traffic radar to get a speed measurement. IS RADAR ALWAYS ACCURATE? Usually, yes. A well-maintained, properly-tested radar receiver, used by a professional operator, can be accurate to within 1/10 of a mile per hour. The radar signal spans all traffic going in both directions. Aimed at an object less than 1/4 mile away, the beam can be as wide as six or eight lanes of traffic. The radar receiver reports on the strongest signal it picks up. Vehicle size and shape can make a difference (a big truck reflects a stronger signal than a motorcycle or small car). This means that the radar receiver can sometimes pick up a reading from a vehicle other than the one intended by the operator. RADAR SPEED DETECTION SYSTEMS Technical advances have yielded several radar speed detection systems you should be aware of. Continuous Wave (CW) - This standard speed radar system transmits constantly. The detector receives and alerts you up to several miles from the radar source. Continuous Wave Low Power - This speed radar operates like CW radar, but uses a much lower power level. The detector can alert you up to a mile or more from the radar source. Triggered CW, Stationary - This speed radar system uses a burst method Mode (also known as of transmitting radar signals, and requires Instant-On, Laser Pulse, less than 1 second to lock in a speed reading. or Hawk) The detector senses the radar signal pulse and alerts you with a special alert signal up to several miles away from the radar source. However, since the traffic radar gun only transmits the radar signals when the operator triggers it, the alert range depends on how often the operator triggers the traffic radar gun. Triggered CW, Moving Mode - This speed radar system uses signal pulses to determine the police vehicle's speed. Then, when the operator triggers it, it transmits a signal burst to determine the speed of oncoming traffic. The detector senses both the police vehicle speed pulses and the triggered signal. CONDITIONS THAT AFFECT RADAR ALERTS If you feel the detector is not alerting you properly, keep in mind that the following conditions can influence the intensity or duration of an alert. * If the police are using instant-on/pulsed radar, the officer does not trigger the unit to send a signal until he has a clear view of the vehicle. To detect this signal, you must rely on reflected signals from radar directed at the traffic traveling ahead of you. * If the police radar unit is positioned perpendicular to the road, around a curve, or just over the crest of a hill, the possible reception range is significantly reduced. * Traffic between the vehicle and the police radar source both blocks and reflects transmitted signals. The presence of several large trucks between you and the police radar unit could also significantly reduce reception. * Rain and humid weather conditions can absorb transmitted signals before they reach the vehicle, again reducing the detection range. * If the police traffic radar equipment is misaligned, it might be transmitting outside the allocated X-, K-, and Ka-bands. NON-RADAR SPEED DETECTION SYSTEMS Police agencies use several other methods to determine vehicle speed without using traffic radar. If these non-radar methods are used, no detector can warn you. VASCAR - VASCAR is nothing more than a stopwatch. The (Visual Average Speed time a vehicle takes to travel a known distance is Computer and Recorder) translated into miles per hour. Pacing - A vehicle follows behind the car and matches the driving speed to determine how fast you are driving. Aircraft - If aircraft warnings are posted, the method of speed calculation is normally a VASCAR approach. An observer in the aircraft measures the time it takes a car to travel between two predetermined points on the road, computes the speed, and radios a chase vehicle. You can usually identify the points at which the aircraft starts and stops measuring by watching for a painted stripe on or across the shoulder of the road. LIDAR - This is the so-called LASER radar systems. This (Laser Infrared type of speed detection system bounces a narrow Detection and Ranging) beam of infrared light off of the vehicle to determine its speed. LIDAR detection requires a laser detector. You can purchase a laser detector to use with the radar detector at the local Radio Shack store. TYPICAL FALSE ALERTS Ideally, a detector should only alert in the presence of police radar. However, because other devices share the X-band with police radar, false alerts sometimes occur. Generally, a false signal produces only a short audio and visual alert. Since they are most often weak, it is possible to drive out of the signal's range very quickly and receive only a brief alert. Although many times you can easily identify the probable source of the false signal (supermarket, bank, commercial building, and so on), you should exercise caution until you can verify the source. The X-band alert pattern caused by non-police source can look like the first alert caused by actual police radar. For this reason, you should always take the appropriate action whenever the detector sounds an alert. DRIVE SAFELY The detector is intended to keep you alert and aware of all traffic conditions. It is not a license to speed. Always drive safely and always wear your seatbelt. (CJD/all-12/05/94)