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Radar Detector Information - Glossary of Terms
This section will help guide you through some of the features of radar
detectors and also explain some of the technical specifications given
throughout the site. If you need more information on radar detectors
and their role in helping to make our roads a safer place, why not
visit our FAQ Section?
Audio/Visual Alerts - The most common audio warning
is a series of "beeps" or "braps" that grow
faster as you near the radar source (ie a Gatso Speed Camera). Visible
alarms can be either a digital display of signal strength or a series
of LEDs.
Auto-Muting - Replaces a continuous audio alert
with a single alert followed by clicking. This can preserve your
sanity during extended radar encounters while continuing to notify
you of the presence of radar.
City Mode/Highway Switch - This function helps
to eliminate false alarms from non-police X-band emissions sometimes
encountered in built-up areas (such as a busy city). This is usually
accomplished by reducing the detector's sensitivity since the ability
to "see" long distances is not critical on city streets.
Cosine Effect on Moving Radar: Moving Radar measures
closing speed between the radar and target. The radar also measures
patrol car speed (from the ground echo) to calculate the target
speed. (Target speed=closing-patrol car). This introduces additional
sources of cosine error. In most situations the angle between the
radar and target is the major error source and favours the target
(measure too low). However if the antenna is misaligned (off patrol
car direction) the patrol car speed may measure low resulting in
target speed measured too high.
Dash Mount - Velcro strips usually serve to keep
the detector in place.
Dim Control - Drivers sometimes find that the
level of brightness on a detector's display, although perfect during
the daylight hours, can be a distraction when driving during the
night. This is why most radar detectors have a built-in Dim Control
that allows you to adjust the brightness according to the lighting
conditions and your personal preferences.
Doppler Principle: Everyday life has a multitude
of examples of the doppler effect with sound. The whistle from a
train is a good example. As the train approaches a stationary listener,
the pitch (frequency) of the whistle sounds higher than when the
train passes by, at which point the train and the person standing
are technically stationary.
Electromagnetic waves radiated by the traffic radar obey the same
principle, although electromagnetic waves travel at the speed of
light and audio waves at the speed of sound. The Doppler Effect
that enables police radar to work is a frequency shift that results
from relative motion between a frequency source and the listener.
The Doppler shift is proportional to speed between source and listener,
frequency of source, and the speed the waves travel at (speed of
light for electromagnetic waves).
GATSO - is the name given to the Dutch made "photographic
trap" system used in the UK and Europe. Most GATSO traps are
unmanned and take a photo of the rear of the speeding vehicle. GATSO
traps operate on K band and are therefore detectable by most good
detectors. The majority of GATSO cameras are inactive - the average
ratio is one "live" camera site for every ten boxes. Even
"inactive" sites will appear to take photographs of passing
vehicles by flashing at them, but since no photographic equipment
is installed no photographs can be taken. If the GATSO system is
fully loaded it is transmitting K band signals constantly monitoring
the speed of every vehicle that passes.
GPS - Global Positioning System.
GPS notifies you your position using satalite technologies.
How Do Laser Guns Work? - The word Laser actually
stands for "Light Amplification by Stimulated Emission of Radiation."
It is a form of electromagnetic radiation the same as radio and
microwaves. The difference is that light has a much higher frequency
than radio or microwaves.
The light emitted by a laser is no different than any other source
except that it has a unique method of generating light. The type
of laser used is an infrared semiconductor laser diode. The generated
light energy has a wavelength of approx. 900 nanometers, with a
beam divergence of 3 millenarians, equal to a beam width of about
3 m (or ft) at 1000 m (ft). Target acquisition times range from
0.3 to 0.7 seconds.
This laser is completely eye safe, meeting FDA Class 1 specifications.
This means that you could stare directly into the laser for 3 hours
without any harm to your eyesight. The radiated light power on MOST
lasers is in the order of 50 microwatts, or in other terms, it outputs
only one twentieth the light power of a typical TV remote control,
and far less than a flashlight.
This is why laser jammers using industry standard laser LED diodes
are effective against laser guns. The products calculate distance
by measuring the time of flight of very short pulses of infrared
light. This method is different from the traditional surveying instrument
method of measuring phase shifts by comparing the incoming wavelength
with the phase of the reflected light. Any solid object will reflect
back a certain percentage of the emitted light energy - it need
only be small for the sensitive detector to pick it up. The guns
measure the time it takes a laser pulse to travel to the target
and back with a precision, crystal-controlled time base. Knowing
the speed of light, you then calculate the distance travelled. To
increase accuracy, the laser measures as many as sixty pulses, utilizing
a least squares method of determining the range. Sophisticated error
trapping algorithms are in place to ensure a reliable reading.
However laser jammers generate an off phase pulse which infills
the phasing cycle of the laser guns making them easy to defeat.
Instant ON (Pulse Radar) - Intended to defeat
radar detectors. Instant ON radar allows the operator to control
the radar transmission. The operators only transmit after selecting
the target, and only long enough to get a speed-reading. In practice
most police find this a difficult mode to operate in and are more
likely to have the radar on all the time unless two officers are
present in the car, one driving and one working the radar.
K Band Radar - Frequency Tolerance 24.150 GHz100Mhz
Frequency Range 24.050-24.250 GHz. K Band radars have been around
since the 1970s and operate on a single frequency. With K Band operating
in the limits of the water vapour absorption band (centred at about
22.24 GHz) signals in the absorption band tend to become absorbed
by moisture in the atmosphere and do not have the range that other
frequency bands offer. Primarily this is why the FCC allocated this
frequency for short range Police use. The most well known Radar
devise operating on this frequency is the HAWK.
Ka Band Radar - The available bandwidth allocated
to Ka Band traffic radar is 2.6 GHz operating between 33.4GHz-36GHz.
Most Ka traffic radar has a frequency tolerance of 100Mhz (200MHz
band width). Therefore 2.600 MHz (available band width) divided
by 200MHz (Channel Bandwidth) equals 13 channels. Traffic radars
in the Ka band with a frequency tolerance of 100MHz may have more
channels, but some or all the channels will overlap. Some models
transmit on a single frequency only. Others may allow the operator
to select one of the several fixed frequencies. Some can hop from
one frequency to the next in a Phase Loop.
Laser speed Detection System uses a gun that emits infrared light
pulses just outside the range of visible light. Each pulse measures
the distance to any object that reflects the laser. The speed of
the object coming towards the gun is measured using a very narrow
beam of light so it can pinpoint a speeding car in the traffic.
A radar detector will pick up the signal due to "splattering"
caused by the beam hitting warm and cold pockets this "splattering"
makes the beam appear much wider.
Laser - Front Detection - Laser emits a narrow
beam that is highly directional and therefore can be difficult to
detect. Radar detectors with Front Detection have the ability to
detect laser when in use in front of the car. Detectors listed as
having Front Detection in our compare grids may also have Rear and
even 360° Detection. See also: 360° Detection and Rear Detection.
Laser - Rear Detection - Radar detectors with
rear detection functionality will always have the ability to detect
laser when in use both in front of and behind the vehicle.
Legal Notice - In most states in America it is
legal to purchase and use a laser detector, although in some states
(such as Virginia), it is a criminal offence. In England and Wales,
laser detectors are perfectly legal to use. Other European countries
have varied policy on the use or purchase of such devices, for a
more in-depth report, please visit our Radar Detectors and the Law
section.
It is legal to purchase and use radar detectors in 49 of the 52
states of the US. Please be advised that it is NOT legal to use
a radar detector in the state of Virginia, and therefore illegal
for us to sell them to Virginia residents.
LIDAR - Laser Radar as it's sometimes called.
(LIght Detection And Ranging). These systems radiate in the upper
infrared 9IR) band and have extremely low beams compared to radar.
You should avoid products without Laser detection built in (Q4000
Whistlers and old two band radar detectors). Competent Radar and
Laser detectors can detect laser up to 3 km away in the right circumstances.
Operational effective range for laser is around 800 metres. It's
just too hard for an operator to stabilise a target much beyond
this distance.
Moving Radar Variables - Target speed will only
measure higher than true speed when the target is approaching the
patrol car AND the cosine angle between radar and target are small,
(typically less than 5%) AND the angle between the patrol car and
the ground is large, (typically greater than 5%). Patrol car and
target speeds are significant; patrol car speed greater than target
speed increases the error.
Mounting/Fitting - Radar Detectors must be able
to "see" radar and laser to detect it, they must be mounted
in place that will allow them to do so, normally on the inside of
the windshield. Every radar detector is supplied with the necessary
equipment so it can be mounted where it will be most effective.
Mute or Volume Control - Allows you to turn down
or turn off a detector's audible alerts, while keeping the visual
alerts.
Photo Radar - Automatic unattended photo radar
started appearing in the late 80s and came to U.K. in 1993. With
Photo radar systems a human operator does not observe any speeding
violation, but is replaced by electronic circuits and a photo-recording
device. No one has to see the alleged violation; the process is
automatic. The registered owner of the vehicle usually receives
a ticket in the mail. Photo radar is across the road radar and designed
to point a narrow beam of radar (typically 5 degree horizontal beam
width) across the road at an angle of 22.5 degrees. Speed measurement
is then adjusted for the angle.
Some units operate with an amber (orange) flash filter. This is
not as bright to the human eye and causes minimum disruption to
a driver even at night.
Power output is very low (2.5mW typically) which makes detection
for radar detectors difficult, but not impossible.
Radar - (Radio Detecting And Ranging.)
Radar operates by transmitting radio waves at certain frequencies,
which reflect off objects and are picked up by a receiver. When
the beam reflects off a moving object, a measurable frequency shift
occurs which is then converted into miles per hour to determine
the object's speed.
There are 3 main sets of frequencies used by the manufacturers
of speed trap apparatus. These are known as X, K & KA. The majority
of traps use K band (e.g. GATSO cameras and most hand held guns).
X band is the oldest and is mainly used by the older gun based systems;
it is also the band where most false alarms occur since other pieces
of equipment use this frequency range. KA band is used by the new
'Stalker' radar guns and is one of the most popular, having been
extended twice since 1991.
Safety Alert - Many parts of the country have
systems that transmit signals designed to alert you to changing
or potentially dangerous road conditions such as accidents and construction
on the roadway. These signals contain both a warning tone and text
messages; the kind of radar detector you have determines the type
of signal you are able to receive. Radar detectors that can pick
up these signals can not only keep you informed, but also help you
stay out of harm’s way altogether by allowing you to take
alternate routes to avoid the situation. See also: Safety Warning
System
Shadowing - Radars identify ground echoes as
the strongest signal (most of the time). The ground echo cosine
angle is a function of the radar antenna alignment and beam width.
More reflective terrain in only part of the beam could change the
angle of the ground return (shadowing), which can change the measured
speed of the patrol car. Large and or reflective objects such as
overpasses or billboards and road signs may have a momentary effect
on radar. Guardrails, bridge trusses and construction zones may
have a longer effect.
Signal Strength - Radar detectors will alert you
to the presence of radar and indicate (through a progressive lighting
of a series of LEDs (lights) or sound), the strength of the signal
to let you know how close you are to the source of the signal.
VASCAR is an acronym for Visual Average Speed
Computer And Recorder. This is little more than a glorified stopwatch,
whereby the vehicle is timed over a set distance (for example over
two white markings in the road surface or over two bridges) an average
speed is then automatically calculated. No radio waves or beams
of light are emitted and thus this system is unable to be detected
by any form of electronic detector.
VG-2 is a microwave receiver used by some police
forces to detect signals radiated by the local oscillator of a radar
detector, because of this VG-2 has become known as a 'radar detector'
detector. It is primarily used to identify radar detector equipped
vehicles, as, in the past drivers faced losing their detector if
caught. VG-2 immunity prevents electronic detection of your unit.
X Band Radar - Frequency tolerance 10.525 GHz25
Mhz Frequency range 10.500-10.550 GHz. X band radars have been around
since the 1960s and operate on a single frequency. Typically their
operational range was 20 mph- 90 mph or more. U.K. and Australia
ceased using X Band Radar many years ago when the frequency was
licensed out to other industries that required access to Microwave
transmitters (alarm systems etc).
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