Radar, Laser, Speedtrap
Police Radar Units use an unmodulated continuous
wave and measure reflections or echoes of the original signal, there will
be a difference in the returning signal from the original signal, the
speedtrap measuring device will calculate this difference and present
it in the format of a speed reading. Radar Speedtraps work on the Doppler
Shift priciples. This relies on the fact that an object moving relative
to a wave source will alter that wavelength by either increasing the wavelength
(lower pitch) if it is receding from the source or decreasing it (higher
pitch) if it is moving towards the source. If you have ever had an aircraft
fly close overhead or a car travel past at high speed you may have noticed
that as the vehicle approaches, the pitch of the noise is higher and gets
lower as it moves away, this is doppler effect.
Police Laser units or Lidar ( Light detection and
ranging ) use an infra red wavelength. They send out a beam of light which
will travel at about 30cm ( 1ft ) per nanosecond then will reflect off
a vehicle back to the speed gun. The time ( in nanoseconds ) it takes
for this to happen ( divided by 2 ) gives the gun the distance from the
vehicle, this can be done hundreds of times in half a second so the difference
between the distance readings over a very short period of time can be
used to calculate the speed of the vehicle, and they are very accurate.
First used in 1947 on 2.455 GHz these consisted of multiple pieces of
equipment including a separate transmitter and receiver, a pen recorder
and a needle type speedometer, so a very cumbersome and unwieldy unit
to operate. Detection range was only 150 to 500 feet. Now obsolete.
Developed during the 1950s and in use since about 1965. X Band ranges
between 10.5 and 10.55 GHz (10.525 with a tolerance of 0.025), compared
to other bands it has low frequency and high output. This makes it particularly
easy to detect, in fact it is possible to detect at up to 4 miles away
although it's own useful range is obviously a lot less than this. Unfortunately
because intrusion alarms, radio masts, and door openers use a similar
signal these can be the cause of a lot of false alarms.
This came into use in 1976-8 firstly for mobile units and uses 24.150
plus or minus 100 MHz (to give 24.050 to 24.250 GHz), or 24.125 plus or
minus 100MHz (to give 24.025 to 24.225 GHz). Because water will absorb
wavelengths around 22.24 GHz it can be absorbed more easily by water in
the atmosphere so a rainy day may give a weaker signal. K Band can be
detected anything upto 2 miles away on a good clear day. Traffic light
sensors and some automatic door openers use K Band transmitters so a false
alarm may result when approaching these devices.
Ka Band / Ka WideBand
Came into force in 1983-7 and uses 34.2-35.2 GHz, Ka Wide Band detection
range is upto 1/2 mile.
Ka Super Wide Band
1992 Developed from Ka Wideband, Superwide Band can use any frequency
between 33.4-36.0 GHz.
13.45 GHz Has been tested in the UK and is used on the continent.
Laser 904 nM
A mobile unit the laser gun can pinpoint a target in a lane of traffic,
it takes less than half a second to get a reading wheras a radar can take
2-3 seconds. It can't be used from behind glass, requires a very steady
hand, and at 1000 feet the beam is 3 feet wide, at 1 and 1/2 miles the
beam is 2 lanes wide.
VG2 radar detector
VG-2 is a technology which allows the police to detect the use of a radar
detector, with added technology radar detectors can be made immune to
this. As radar detectors are not illegal in the UK this may not be necessary
but is a good feature to have anyway.
| Typical Radar and Laser Speed
|| Typical Band
| Hand held radar guns.
|| K Band radar,
X Band radar (non UK)
| Gatso cameras.
|| K Band radar
Hand held or tripod mounted Pro Laser 2,
LTI 20/20 laser gun
| Mini Gatso cameras
|| K Band radar,
Ku Band radar (non UK)
| Multanova 6F portable
speed monitoring systyem.
|| Ka Band (non UK)