What is a Radar Detector?
A radar detector in general terms is a device which
has the capability to detect or recognise a radar signal.
What does that mean to you, well if you are a motorist then this is quite
significant. On UK roads(and in other countries) there are devices known
Speedtraps are designed to record the speed of vehicles that may be travelling
above the local speed limit posted for that road.
The speedtraps can use various forms of speed recording and one of these
types of speedtrap is called Gatso
and uses radar. The radar is transmitted by the speedtrap which also has
a receiver. When the signal is sent out from the speedtrap it will have
a particular wavelength. When the signal is reflected back by a vehicle
if the vehicle is moving in relation to the transmitter,the wavelength
will have changed this is known as Doppler Effect.
The receiver picks up this altered signal and reads it's wavelength, the
difference between the transmitted wavelength and received wavelength
will give an indication of the speed of the vehicle.
If the speed is above the threshold that the speedtrap has been set to
then the speedtrap will initiate the action of a camera which is built
into the Gatso speedtrap. The camera will take 2 images in quick succession.
As there are lines painted onto the road surface (equally spaced apart)
the 2 pictures can be used as further evidence that the vehicle was speeding,
as speed is calculated from distance travelled over time elapsed. e.g.
metres per second, kilometres per hour or miles per hour.
If a driver could identify areas where a radar signal
is being used then it could help the driver to be reminded to check their
speed before they drive into the radar operated speedtrap. A radar detector
is usually able to do this and give up to 100 metres warning depending
on the quality and sensitivity of the particular detector, the conditions
around the Gatso camera and the amount of traffic already going through
the speedtrap itself.
Problems with radar detectors are :
- False alarms, these occur when a signal similar to a radar signal
is being detected and confuse the detector. Radar is a microwave radio
signal and there are many devices which use microwave radio signals
such as mobile phones, some types of car alarms, automated doors on
shops etc. So common false alarms come from these sorts of equipment.
- Although Gatso cameras still use radar to detect speed not all speedtraps
are Gatso cameras. There are now Truvelo and SPECS and other types which
do not use radar and so a radar detector would give no warning of these
types of speedtrap and may give the driver a false sense of security.