Radar 101
IMPORTANT: Radar 101 is only for offering some general knowledge of speed
monitoring devices and clear up any possible misunderstandings of how an
officer can get your speed.
RADAR
Q: How does police radar work?
A: A police radar gun operates by transmitting radio waves at certain frequencies which reflects
off objects (your vehicle) and are then picked up by the radar gun's receiving section. When
radar waves reflect off a moving target, a measurable frequency shift occurs. The radar unit
converts this shift into miles per hour to determine the target's speed.
Two basic types of radar are used - stationary and moving. Stationary radar must be used from a
static site, typically a patrol car parked along side the road (See above figure). But with a single
antenna moving radar, an officer can clock approaching vehicles while driving on patrol. Moving
radar with two antennae - one facing forward, the other aimed out the back of the cruiser - can
also clock vehicles even after they have passed by, headed in the opposite direction.
Q: How does a radar detector work?
A: A detector is a radio receiver tuned to specific frequencies used by police radar. It is
extremely sensitive, often able to hear radar from over a mile away, far beyond the range at
which radar can clock a vehicle's speed. In evaluating a detector, the two most important
performance criteria are sensitivity and selectivity. Sensitivity is a measure of a units detection
range. Selectivity refers to a unit's ability to reject non-police microwave signals and is an
important feature because of the many sources of "electronic pollution". (Note: Automatic door
openers and some burglar alarms operate on X-band, which is a police band. A radar detector
cannot tell if a store is opening a door or a police officer is checking speed.)
Q: How common is the use of police radar?
A: Since the mid-seventies radar has served as the tool of choice for speed enforcement. Over
100,000 radar units are in service by police in all 50 states and account for over 37,000,000
speeding tickets each year. In fact, there are so many radar guns on the road today, your speed
may be radar monitored more than fifteen times during a single trip from New York to Los
Angeles.
Q: What Frequencies are used?
A: Except for a few early units, X band (10.525 GHz) was the only frequency used for police
radar until the mid 1970's. In 1976 radar guns using K band (24.150 GHz) were introduced; this
led to the development of the first dual band (X/K) radar detectors. A proliferation of radar guns
using Ka band frequencies began in 1987 with the introduction of photo radar (34.3 GHz) and
was followed by the Stalker (34.2 - 35.2 GHz) in 1991 and the BEE 36A (33.4-34.4 GHz) in
1992.
Q: Why are radar detectors described as dual band, triband, wideband or superwideband?
A: Early detectors needed only to listen for X band radar. When K band arrived, dual band
models able to receive both frequencies (X and K) were required. The introduction of Ka band
photo radar (34.3 GHz) led to the development of triband models able to detect X, K, plus a
small portion of Ka band. A fourth category of radar receivers called wideband, with X, K and
"wideband" Ka (34.2 - 35.2 GHz) detection capabilities reached the market following the
introduction of Stalker radar. And finally, in response to the BEE 36A a new generation of radar
detectors were developed termed superwideband, which cover all radar guns operating on X, K
or "superwideband" Ka (33.2- 36.0 GHz).
Q: What is a false alert?
A: A number of transmitting devices are also allowed to operate on the same frequencies used by
police radar. These are not considered false signals. For example, the automatic door openers
commonly used by business are low powered X band transmitters. They produce signals that
appear legitimate to a radar detector and cause it to alarm. Other sources produce "harmonics"
signals, ghosts or look-alike K or Ka band radar signals which make a radar detector give a false
alert. A better radar detector reduces these types of false alarms.
Q: What is "pulse" or "instant on" radar?
A: When radar detectors proved easily capable of sniffing out radar from miles away, radar gun
manufactures responded by producing instant-on radar. In the instant-on mode, the radar's
transmitter is placed on hold, ready to fire but not yet producing a signal for detectors to hear.
The officer waits until his target is very close (brings a new meaning to "wait till you see the
whites of their eyes") releases the radar from stand by mode and gets a speed reading within a
second or so. In this situation, no detector offers much warning. TIP - When traveling in
unknown highways always try to find a vehicle which is traveling at the same rate or faster than
you are and keep several car lengths behind them. This way the other vehicle can "flush out the
radar".
LASER
Q: How do laser speed guns work?
A: Laser speed guns transmit short bursts of invisible light which bounce off a target vehicle and
return to the laser gun. By timing the outgoing and return trips of the light bursts, it can compute
the target's speed. The laser's biggest selling point is its narrow beam-only about six feet wide at
a distance of 1,000 feet-a feature that provides nearly foolproof target identification. (In
comparison, a radar's beam is about 250 feet wide at 1,000 feet.) Laser guns must be used from a
stationary position and are most effective at short range, usually when targeting traffic at 700 to
1,200 feet.
Q: How does a laser detector work?
A: Since laser guns use a specific light frequency, it is possible to detect a laser's signature light
pulses. Keep in mind that laser detectors act differently than radar detectors. Since the narrow
laser beam produces very little "scatter"-random bits of electromagnetic energy bouncing down
the road- it is much harder to detect than a powerful radar gun that blankets the countryside with
easily detectable microwave signals. Laser guns operate exclusively in instant-on mode and
usually target vehicles at short range. The result is your laser detector usually will offer less
advance warning. Similar to instant on radar, if you are the target vehicle don't expect much
warning.
Q: How common is the use of laser for speed monitoring?
A: Less than 1,000 laser guns are in service in 45 states at present. Most are used by city police
on urban multi-lane roadways although some state highway patrols-Illinois and Ohio to name
two- have dozens of units spread throughout the state. The use of laser guns for speed monitoring
is expected to increase, but will remain limited due to their high cost-four times that of a moving
radar-and limited attractiveness to agencies that favor the convenience, offered by conventional
moving radar. Currently, laser guns account for less than 5% of the total number of speed
monitoring guns (radar and laser) sold in the U.S. annually; during the next five years, this figure
is expected to remain under 8%. Laser guns will likely be in service in every state within a few
years.
Q: Will laser guns replace radar?
A: No. Their premium price, limited applications (compared to moving radar), and more
complex operation will keep sales of laser guns at a much lower level than radar.
Q: Do laser detectors "false" like radar detectors?
A: Top selling detectors use sophisticated signal processing and optical filtering to almost totally
eliminate laser falsing. Because of the design's incredible accuracy, assume any laser alert
received as valid.
RADAR DETECTOR DETECTORS
Q: What is a radar detector detector?
A: A radar detector detector (RDD) is a microwave receiver used by police to detect signals
radiated by the local oscillator of a radar detector. The trade name of the only RDD currently
manufactured is Interceptor VG-2, most often simply referred to as VG-2. An officer using a
VG-2 typically parks next to a busy freeway and aims the device at a 45 degree angle across the
traffic stream. The VG-2 acts just like a radar detector when it hears an approaching radar
detector, increasing its audio alert rate and progressively lighting more LED's in its visual
display. By observing the traffic and watching how the VG-2 responds, the officer can make an
educated guess as to which vehicle is using a radar detector. Some detectors are "noisier" than
others and can be detected by the VG-2 from as far away as 4,000 feet.
In Virginia, the largest user of the VG-2, officers are not empowered to search a vehicle unless
visible signs are present to support the RDD's guess that a radar detector is in the targeted
vehicle. A missing cigarette lighter plug, dangling power cord, Velcro on the dash, a mounting
bracket on the windshield or visor will tip the officer as to the possible presence of a detector and
allow him to search for it. If found, the detector isn't confiscated; the officer notes its serial
number, checks to see if it's operational, then hands it back to the driver- along with a citation for
having used it.
Q: Where is the VG-2 used?
A: At present the police in Virginia, New York, Illinois and the five eastern Canadian provinces
employ VG-2s. Because of the recent FHwA regulation which prohibits nationally the use of
radar [and laser) detectors in commercial vehicles, interest in the use of VG-2 by law
enforcement agencies has increased.
Q: Can an officer detect my undetectable radar detector?
A: Big YES! There is a new receiver that the officers can use, its called Spectre! It's designed to
receive the signal that all radar detectors emit. These undetectable radar detectors were designed
to only out smart the VG-2. Currently, with the new Spectre model, no radar detector is safe.
Just don't take my word on it, check out speedzones.com
NON RADAR
Q: What is VASCAR?
A: VASCAR (Visual Average Speed Computer and Recorder) is a time/distance computer that
determines a vehicle's average speed by timing it between two reference points, usually white
stripes painted on the roadway. Used both by ground units and aircraft, VASCAR uses no radio
waves and therefore is not detectable. Officers typically sit at the top of a freeway on-ramp or
other vantage point, timing traffic between the two reference points. It is rarely used at night.
Watch for the telltale white stripes across the road that will reveal I you're in VASCAR country.
Q: What is "pacing"?
A: Pacing is the granddaddy of all speed measuring techniques. The officer typically drives up
behind the target, accelerating until his speed matches the speed of the target vehicle. His
calibrated speedometer then verifies the target vehicle's speed. Although pacing also works when
the police cruiser is in front of the target vehicle, some courts consider this approach unreliable
and won't allow it. Pacing is especially effective at night, but rarely works when the drivers
maintain a close watch in their rear view mirror.
Q: How are aircraft used to monitor speed?
A: Using white reference marks on the road, the airborne officer simply times the target between
two of the marks to establish average speed. Most states use VASCAR (a few use stopwatches),
first programming in the known distance between the marks, then operating the time switch to
determine target speeds. Cruisers waiting below stop the violator and write the ticket. Contrary to
popular belief, radar cannot be used from aircraft.
LEGALITIES
Q: Are detectors legal?
A: Laser detectors are completely legal in every state when used in automobiles or light trucks
(under 10,000 lbs.). Similarly, when used in automobiles or light trucks, radar detectors are legal
in almost every state. Exceptions are Virginia and Washington DC, which have local regulations
restricting the use of radar receivers in any vehicle.
Concerning trucks over 10,000 lbs., the Federal Highway Administration (FHwA) issued a
regulation, effective January 19, 1994, which prohibits nationally radar and laser detector use in
these types of vehicles.
Prior to the FHwA regulation, laws existed in the state of New York restricting the use of radar
detectors in trucks over 18,000 lbs. and in Illinois in trucks over 26,000 lbs. These laws remain
in effect. In Canada, radar detectors and laser detectors are illegal to use in Manitoba, New
Brunswick; Newfoundland, Ontario, Prince Edward Island, and Quebec.
Q: What can I do to keep radar and laser detectors legal?
A: Fight for your rights. Specifically, watch for news stories about any legislation in your state
that seeks to ban the use or sale of detectors and let your elected representatives know your
feelings. Don't ignore such legislation even if it targets only heavy trucks. A favored tactic of the
anti-detector forces-primarily large insurance companies who benefit immensely from slapping
surcharges on ticketed drivers-is to first go after truckers' rights to use detectors. If successful in
banning detector use in trucks, you can bet their efforts will turn to banning in cars.
SAFETY RADAR
This relatively new radar is not for speed detection at all, it is used to keep you informed of
highway safety. Transmitters are installed and programmed (for example: in emergency vehicles)
to make you aware of possible situations that may require your attention, such as: ambulance
vehicles that are moving or stationary, road hazards ahead, road construction delays or detours,
etc. At present safety radar transmitters are few. To check if safety radar is in your area, click
here.
These safety radar transmissions are received by all radar detectors because they transmit on Kband frequency, however, only newer radar detectors with safety radar capability can identify
them.