Transmitted
Frequency 24,150,000,000 cycles per sec.
+ 4,321 cycles per sec.
Vehicle Receding at 60 mph
Reflected
Frequency
24,149,995,679 cycles per sec.
Transmitted
Frequency 24,150,000,000 cycles per sec.
– 4,321 cycles per sec.
Note again how the reflected frequency is greater than the transmitted as the vehicle approaches and less than the
transmitted as it recedes, yet the difference, the Doppler shift, remains constant for this particular vehicle speed.
Stationary radar theory and ranging technology
Most stationary radars cannot detect what direction a target is moving. In both of the previous examples, a
“normal” stationary radar would detect a Doppler shift of 4321 cycles per second and convert that to 60 mph.
They cannot tell if the true Doppler shift was +4321 or - 4321 cycles per second.
In addition to telling the operator the exact distance of the target vehicle, MPH’s ranging technology also allows
the radar to tell the direction a target is moving relative to the radar. So in the two examples above, the radar
would see two different Doppler shifts: +4321 and – 4321` cycles per second respectively. +4321 cycles per
second would be converted to +60 mph, meaning that the target is approaching at 60 mph. - 4321 cycles per
second could be converted to -60 mph, meaning that the target is moving away at 60 mph.
This allows the Ranger EZ to do something that many traffic radars cannot do. The operator can select to only
have the radar monitor targets in a particular lane of traffic while completely ignoring traffic in the other lane.
This is particularly important when a “Jersey barrier” is present, preventing the officer from pursuing traffic in the
other lane.
Moving radar theory
Moving traffic radar refers to units that have the ability to function while the patrol vehicle itself is in motion.
They have this ability in addition to their standard stationary capabilities. When being used as moving traffic
radar, the MPH Ranger EZ will simultaneously display both the patrol vehicle speed and the target vehicle speed.
Like the stationary radar, the moving radar is based on the Doppler theory. However, with moving radar, the
signal processing is more involved than with stationary. The radar receives reflected signals from both the target
and the roadway. The target signal contains information on the combined speed of the two vehicles while the
patrol signal has the information concerning the speed of the police vehicle. The receiver (mixer diode) in the
antenna provides all of this information.
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