Technical Details
20
How Radar Works
Traffic radar, which consists of microwaves,
travels in straight lines and is easily reflected
by objects such as cars, trucks, even
guardrails and overpasses. Radar works by
directing its microwave beam down the
road. As your vehicle travels into range, the
microwave beam bounces off your car, and
the radar antenna looks for the reflections.
Using the Doppler Principle, the radar
equipment then calculates your speed by
comparing the frequency of the reflection
of your car to the original frequency of the
beam sent out.
Traffic radar has limitations, the most
significant of these being that it typically can
monitor only one target at a time. If there is
more than one vehicle within range, it is up
to the radar operator to decide which target
is producing the strongest reflection. Since
the strength of the reflection is affected by
both the size of the vehicle and its
proximity to the antenna, it is difficult for
the radar operator to determine if the signal
is from a sports car nearby or a semi-truck
several hundred feet away.
Radar range also depends on the power
of the radar equipment itself. The strength
of the radar unit’s beam diminishes with
distance. The farther the radar has to travel,
the less energy it has for speed detection.
Because intrusion alarms and motion
sensors often operate on the same
frequency as X-Band radar, your STi will
occasionally receive non-police radar
signals. Since these X-Band transmitters are
usually contained inside of a building, or
aimed toward the ground, they will
generally produce much weaker readings
than will a true radar encounter. As you
become familiar with the sources of these
pseudo alarms in your daily driving, they
will serve as confirmation that your STi’s
radar detection abilities are fully
operational.
How “POP” Works
“POP” mode is a relatively new feature for
radar gun manufacturers. It works by
transmitting an extremely short burst,
within the allocated band, to identify
speeding vehicles in traffic. Once the target
is identified, or “POPPED,” the gun is then
turned to its normal operating mode to
provide a vehicle tracking history, (required
by law).
21
How Laser (Lidar) Works
Laser speed detection is actually LIDAR
(Light Detection and Ranging). LIDAR guns
project a beam of invisible infrared light.
The signal is a series of very short infrared
light energy pulses, which move, in a
straight line, reflecting off your car and
returning to the gun. LIDAR uses these light
pulses to measure the distance to a vehicle.
Speed is then calculated by measuring how
quickly these pulses are reflected given the
known speed of light.
LIDAR (or laser) is a newer technology
and is not as widespread as conventional
radar, therefore, you may not encounter
laser on a daily basis. And unlike radar
detection, laser detection is not prone to
false alarms. Because LIDAR transmits a
much narrower beam than does radar, it is
much more accurate in its ability to distin-
guish between targets and is also more
difficult to detect.
AS A RESULT, EVEN
THE BRIEFEST LASER ALERT SHOULD
BE TAKEN SERIOUSLY.
There are limitations to LIDAR equip-
ment. LIDAR is much more sensitive to
weather conditions than RADAR, and a
LIDAR gun’s range will be decreased by
anything affecting visibility such as rain, fog,
or smoke. A LIDAR gun cannot operate
through glass and it must be stationary in
order to get an accurate reading. Because
LIDAR must have a clear line of sight and is
subject to cosine error (an inaccuracy,
which increases as the angle between the
gun and the vehicle, increases) police
typically use LIDAR equipment parallel to
the road or from an overpass. LIDAR can be
used day or night.
STi Manual 3/28/05 3:39 PM Page 23
