Radar is also used to calculate the speed of an object using a scientific occurrence called Doppler shift. Police officers have been able to nab many speedsters in this manner over this past 50 years.
Picking up signals:
Speedsters commonly use radar detectors to evade the police using the comparatively easy to track traditional radar gun systems. The most basic radar detector comprises of a simple radio receiver, exactly like the one used to catch radio stations.
If the receiver must be effective, then it must only receive signals within a particular frequency. Just as a radio receives signals in the AM and FM band, the one in a radar detector is able to pick up the signal range of radar guns used by cops. However, the police keep widening their equipment’s frequency range to make life difficult for speedsters.
A simple radar gun would be of no use to the speedster if he is already caught by the radar gun of the police by the time his radar detector warns him. However, on many occasions speedsters get away as these detectors are able to track the signal in advance as the police frequently switch on their guns for longer durations instead of turning them on when they are much closer to the car.
Radar guns are equipped with a dish or cone shaped antenna that converges the signal, however the signal extends rapidly over a greater area. The gun is constructed in such a way that it focuses only on the speed of a specific object, so the probability of the detector being able to catch the signal earlier than the radar gun does it is quite high. However, these types of detectors are not fool proof as if the police pursues you first then you shall be caught. Present day radar detectors come with more features that help speedsters evade the cops.
How are signals jammed?
Apart from the basic receiver, the newer versions of radar detectors have a built in radio transmitter, which produces a jamming signal. The purpose of this is to duplicate the original signal emitted from the police radar gun, but after adding radio noise to it. The police radar gun then receives a perplexing echo signal, which does not allow the police to note the vehicle’s speed correctly. It must be noted however that even this system is not infallible, with the police coming up with more sophisticated equipment regularly.