RADAR'S INTERACTION WITH IT'S ENVIRONMENT - The trained radar operator has to view the operation of his unit in the context of the total environment. Unfortunately, that environment includes both electrical and mechanical sources of Interference with the radar unit's operation. Radar reads the speed at which objects move, and in a traffic environment we find that many things, including wind-blown trees and signs may be moving. The officer is also under constant electronic bombardment, with ambient electronic interference being emitted by his own radio, CB radios, cellular phones, intrusion alarms, Amateur Radio operators, air traffic radar, telephone microwave links, traffic signal controllers, satellite communications, radar altimeters, gate controllers, pipe locators, level sensing devices. All or these can create "ghost" readings, but are readily identifiable as such in the presence of a valid target with proper operating techniques. These ghost readings will disappear and be replaced by the target reading when the actual target vehicle gets close enough, and will not affect the accuracy of the target reading.
EXTERNAL MECHANICAL INTERFERENCE - This is one of the most common types of radar effect, and has been demonstrated on national television. Typically, the radar is picking up a signal from some mechanical device, frequently from fans or ventilators. The radar may either be reading the actual speed of the fan blades, or may be picking up the electrical signals generated by the fan motor. This type of reading is distinguishable primarily through the use of the audio Doppler tone. Unlike the rising or falling tones of an automobile, the fan will generally be heard at a constant pitch.
RFI NOISE EFFECTS AND SOURCES - As mentioned above, there is a constant flow of radio signals in our environment no matter where the patrol vehicle is positioned. Under certain circumstances, that ambient "noise" may be read by the radar unit. We'll discuss specific sources of radio frequency interference below .
INTERFERENCE INSIDE OF THE PATROL VEHICLE - Even within the patrol car, there are a surprising number of devices, which may interact with a radar unit. These Include the ignition system, heater or air conditioning blowers, the police radio, cellular phone, CB radio, handy-talkies, A.M. radios, the alternator and even the buzzers for the seat belts. One of the keys to locating and eliminating this type of interference lies with the recurrence of such readings under similar conditions. If you start receiving 'ghost" readings in the 50-60 MPH range every time you run the air conditioner you can learn to either run without the air conditioner or reject all readings under those conditions. None of these sources of interference will sound like a car on the audio Doppler, and the audio remains the key to valid interpretation of the radar unit.
RFI INTERFERENCE THROUGH POWER AND ANTENNA LEADS - The power connection between the radar unit and the vehicle is a major potential source of interference. Electrical devices on the vehicle all produce a certain amount of feed-back into the system which may be read by the radar unit, much the same as a blender or vacuum cleaner will affect a nearby television. A poor connection through a dirty cigarette lighter socket may interrupt the unit's power, causing "ghost" readings because of the power surge. Connecting the radar unit directly to the vehicle battery can easily eliminate this type of effect, using the equipment available from any of a number of manufacturers.
Particular care should be taken with how the cable is routed in the patrol car. Keep the cable away from all radios and other electrical devices and avoid intertwining the antenna and power leads.
RFI INTERFERENCE - CB RADIOS - A CB radio operated within the same vehicle as the radar unit will almost always result in swamping the radar signal, frequently resulting in an erroneous display. Therefore, officers should never transmit on CB equipment while the radar is in operation. Radar may also be affected by CB equipment broadcasting in other vehicles. The range of this effect is generally limited to 100 feet, more if an illegal linear amplifier is in use. Again, Interpretation of the audio Doppler will prevent the officer from misinterpretation of this reading. Both the quality and tone of the signal will change as radar unit shifts from reading the automobile to reading the RFI from the CB radio.
RFI INTERFERENCE - POLICE AND BUSINESS RADIO, CELLULAR PHONES - Police and business radios (often as powerful as 100 watts) will cause the same types of interference as CB radio. Because of this, officers should disregard any readings, which occur while they are broadcasting on the radio, or when another unit is broadcasting in close proximity. Cellular Phones will cause interference – even when not in use. This is because the cell phone transmits to the towers automatically when driving along to relay information on your location.
RFI INTERFERENCE - LIGHTS - Neon and fluorescent lights are another potential source of radio interference. Radar units tend to be affected not only by devices operating at or near their assigned frequencies, but also by devices operating at multiples of that frequency. For instance, a fluorescent lamp operating at 60 cycles/sec will generate a speed reading of around 23 MPH on an X-band radar unit. This is because 60 cycles/second taken to the 11th power is very close to the X-band frequency. Officers can avoid this by parking their patrol units well away from illuminated areas, and again, by carefully listening to the tone.
RFI INTERFERENCE - POWER LINES - The humming, buzzing and crackling of high-tension power lines (particularly in moist weather) is a familiar sound to most people. Those sounds are produced because the lines are emitting power (and RFI) across a broad spectrum. The interference produced by these lines will sound very similar in the audio Doppler to those sounds heard directly from the lines. To avoid this type of error, officers should refrain from working radar anywhere near these lines, and ignore readings received while in proximity to power lines and power generating facilities.
HARMONlC SIGNAL INTERFERENCE - A harmonic is simply a multiple of a basic frequency, For example, a device operating at 500 HZ can create signal interference at 1000 HZ, 1500 HZ or even 10,000,000 HZ. Again, such false readings created by harmonics can be identified by the tone, which will be substantially different from that of a bona fide target.
OWN SPEED CAPTURE EFFECT - In some moving radar systems, the unit will read the ground simultaneously for both the target speed and the ground speed. The same speed will then be displayed in both of the unit's windows. The officer should reject any reading on a moving radar where the patrol and target speeds match.
PULSATING SIGNAL AMPLITUDE EFFECT - When radar encounters an irregular surface, the beam reflected back to the unit may also become irregular. When that object has a regular pattern, such as a chain-link fence, the signal may be reflected back in pulses, which can be read by the radar as a Doppler shift. The audio tone is the key to the correct interpretation of any such reading, and officers should use particular care when using moving radar alongside evenly placed structures such as fences, walls or guard railings.
FEEDBACK EFFECT - The counting unit of the radar unit is generally very sensitive to any signal, and may receive feedback directly from the antenna, causing very high-speed readings and a very strong audio tone. This is particularly true if the radar antenna is swung to face the counting unit, although the side and rear lobes of the antenna's pattern may also disrupt the counting unit. As a matter of practice, the antenna and counting units should be mounted as far apart as is possible.
EFFECTS OF AUDIO INTERFERENCE - Noise, such as that coming from an A.M. radio, is simply vibration, and vibration is movement which the radar can read. This may occur by the radar antenna itself being vibrated, by the radar reading vibrations of the windshield, or reflecting off the windshield and reading the speaker's oscillations directly. On one radar unit, Barbara Streisand gets clocked consistently around 35 MPH. Officers should refrain from listening to anything other than the Doppler tone while working radar.
EFFECTS OF ANTENNA VIBRATION - Radar reads the speed of objects relative to the antenna. If the antenna itself is in motion, a false speed reading may occur. Such vibration may occur when the antenna is vibrated, which may be caused by an out-of-balance wheel, a rough road surface, or any of a variety of factors. Some units will even generate Doppler tones merely when the outer case is touched.
MOTORCYCLE APPLICATION CONSIDERATIONS - Any experienced motor officer can tell you that all of the equipment on a bike takes a tremendous beating, even to the point where the rivets of metal ticket-book holders are vibrated out of place. As a result, radar units used in these applications will require extra care and maintenance. Special care should be taken that the unit is handled gently and carried in a padded enclosure. The radar should never be left on in a metal saddlebag, as this may cause the Gunn-effect diode to fail.
EFFECTS OF DENTED ANTENNA HORNS - It has been found that dented or misshaped antenna horns have misshaped patterns. These antennas are carefully designed and engineered for the optimum beam pattern. Antennas, which are damaged in any way, should be replaced immediately.
EFFECTS OF WINDSHIELDS AND OBSTRUCTIONS - Just as a windshield reflects, distorts and refracts light, it will change the nature of the radar beam. The radar signal may be reflected down the defroster openings, it may be bent and distorted by the curvature of the glass, or it may be blocked by the presence of the windshield wipers. Care should be taken in mounting the radar unit behind the straightest section of windshield, where it has a clear, undistorted view of the roadway.
BEAM REFLECTION CONSIDERATIONS - Officers should be aware of the fact that the radar signal will reflect off many objects. A unit parked with the antenna facing a reflective surface, such as a highway sign or metal-sided truck, may well be reading traffic in the opposite direction. Officers can check this by carefully monitoring the activities of cars in both directions, and avoiding parking in locations, which are near such reflective objects.
WEATHER EFFECTS OF TRAFFIC RADAR - Poor weather conditions require officers to be extra alert to their radar units. Fog, snow and rain all tend to reduce the range of the radar unit. A driving rain may show on the unit as a "ghost" reading. Also, the slick pavement may make it difficult for the radar to read a patrol speed, so special care should be taken in avoiding moving cosine angle error.
EFFECTS OF HEAT BUILD-UP - Electronic components in radar units are generally not designed to withstand changes in temperature below freezing or above 140 F. However, even on an 80 F day the temperature of a radar unit on a patrol car's dash may climb to well over 145. As the temperature changes, the values of the components change and the unit may drift. Frequent calibration checks are in order on exceptionally warm or cold days. Generally, heat failures in radar units are catastrophic. Special care should be taken to keep radar units protected from any extremes of temperature.
"POP" OR POWER SURGE EFFECT - Many radar units experience a power surge (similar to the "pop" heard when first turning on an A.M. radio) when the unit is first turned on, or when it is taken off the detector defeat mode. This momentary effect does not present a problem unless automatic lock functions are in use, which might lock onto this erroneous speed.
AUTO LOCK AND AUTO ALARM EFFECTS - Automatic lock and automatic alarm systems may lock onto any of the errors mentioned in this text. Without continuous readings and audio Doppler, there is no way for the officer to interpret false readings by the unit. Such functions should not be used under any conditions. Where possible, these features should be removed or disconnected from existing units.
AUTOMATIC GAIN CONTROL - Most radar units have an automatic gain control, which automatically increases the sensitivity of the unit when there is no signal present. As a result, "ghost" readings are far more likely to occur when there is no other traffic evident. These readings generally disappear as soon as a legitimate target comes into the beam.
PANNING EFFECT - As stated before, the radar unit reads the motion of objects relative to the antenna. If you swept a radar antenna across the front of a wall, it would show a speed, based on its relative speed. This type of error is particularly prevalent when the patrol car sweeps through a U-turn, or when hand-held radar units are used to follow traffic in a sweeping or panning movement. The radar antenna should never be moved while speeds are being clocked by the radar unit, and if it is moved any resultant readings should be rejected.
BATCHING EFFECT - Batching errors occur when the patrol car changes speed while using moving radar. Many of the older radar units take samples of both the patrol and violator speeds, but not necessarily at the same instant. Thus, if the patrol car speed changes prior to the next sample, and erroneous speed reading may occur. While using moving radar, it is very important that the patrol speed be kept at a constant, steady rate.
SHADOWING EFFECT - Shadowing errors occur when the ground speed (patrol speed) side of a moving radar unit locks onto a moving object rather than the ground. The most common example is when patrolling at lower speeds, the radar’s patrol speed locks onto an oncoming vehicle rather than the ground and the radar reads the sum of the patrol car and the oncoming vehicle in the patrol window. This is the reason the patrol speed window cuts off at 69 MPH
(59 MPH for City Units on K-55 radar units)(79 or 89MPH on some models). The radar will not lock onto an oncoming vehicle as ground speed as long as the sum of the patrol speed and the oncoming vehicle’s speed is higher than 69 MPH (59 MPH for City Units). This effect can be reduced by aiming the antenna more down toward the road, and if necessary slightly to the right away from the oncoming traffic.
Another example is when the patrol car overtakes a large truck travelling at 45 MPH. As the patrol car travelling at 55 MPH overtakes the truck, it suddenly reads the patrol speed as 10 MPH. (It “thinks” it is passing a stationary object at 10 MPH) It then subtracts 10 MPH instead of 55 MPH from the closing speed of a violator and indicating speeds of 100 MPH or more for the violator. The alert operator readily rejects such indications. This error may be easily prevented by always comparing the radar-indicated patrol speed against the speedometer for verification.
MULTI-PATH SIGNAL EFFECT - This type of error is very rare, but is one, which the operator should be aware of. Under certain circumstances, radar may bounce off the target, strike another vehicle or object and bounce off the target a second time before returning to the radar unit. Under such conditions there is usually a very rapid shift in the Doppler tone and a very high speed is indicated which will not agree with the operator's visual estimate.