THE HOW AND WHY OF PATROL SPEED SHADOWING
Traditional radar units exclude patrol speed tracking below 20 mph. One of the unique features of S DSR 2X is that it allows
patrol speed tracking below 5 mph, when the low-end patrol speed is set to 5. This feature is very popular and is excellent for
enforcing school zones. However, with this setting, S
DSR 2X is more prone to "shadowing." Shadowing occurs when a
strong same lane target in the radar beam captures the patrol speed, instead of the weaker passing ground reflection.
The following is an example of the shadowing effect: A patrol vehicle traveling 30 mph is following a pickup traveling
42 mph. The pickup is pulling away from the patrol vehicle at 12 mph. The radar, in error, thinks this 12 mph speed is the correct
ground speed and displays 12 mph in the patrol window, instead of the correct value of 30 mph.
S
DSR 2X has three options for eliminating the shadowing effect: 1) make the unit re-acquire the correct patrol speed by
pressing the PS BLANK key, 2) change the low-end patrol speed from 5 mph to 20 mph (see Page 22 for instructions), 3) operate the
radar using the optional VSS mode. To eliminate the shadowing effect in the city, Option 1 is recommended. Option 2 is
recommended for highway radar use. Option 3 eliminates all shadowing and is achieved by installation of VSS cabling in the patrol
vehicle.
USING THE STOPWATCH MODE
S DSR 2X offers Stopwatch mode, which can be disabled or enabled through the Options Menu (See Page 46). Stopwatch
mode is used to measure target speeds using the traditional time-distance method. All of the timing and computing is performed in the
S
DSR 2X counting unit. The length (in feet or meters) of the measurement zone must first be entered into the counting unit
using the remote control Ï or Ð keys. The maximum length of the measurement zone is 9999 feet or 9999 meters.
Since the electronic timer is started (by pressing START/STOP) when the target vehicle enters the measurement zone and stopped
(by pressing START/STOP again) when the target vehicle exits the measurement zone, the time to traverse the measurement zone is
measured and displayed on the counting unit. After the completion of each start/stop timing interval, the counting unit displays the
calculated target speed in the patrol window.
NOTE: IT IS REQUIRED THAT THE FRONT ANTENNA BE CONNECTED DURING STOPWATCH MODE. THE
COUNTING UNIT USES THE ANTENNA INTERNAL CRYSTAL FOR START/STOP TIMING DURING STOPWATCH
MODE.
Stopwatch Principle
The counting unit calculates speed by measuring how much time it takes the vehicle to pass through the pre-set distance and then
calculates and displays the speed in MPH or KPH. The known distance is divided by the measured time and multiplied by a
conversion factor to obtain target speed.
Example: 1/2 mile (2640 feet) of distance over 30 seconds of time = 60 mph
1/4 mile (1320 feet) of distance over 15 seconds of time = 60 mph
1/4 mile (1320 feet) of distance over 11.9 seconds of time = 75 mph
The speed (mph) formula is: mph = 0.682 x Distance (in feet)
Time (in seconds)
To easily convert feet/sec into mph, there is a 0.682 conversion factor that is used. Multiplying feet/sec by the 0.682 conversion factor
will provide speed in miles per hour.
No hard and fast rule can be established concerning the minimum distance over which a vehicle should be monitored. However,
several factors enter into the equation which does establish the fact, that the farther the distance, the less the chance of impact of an
error. Three factors that can influence the calculation include:
1. Human error in activating the START/STOP key
2. The distance measured
3. The speed of the vehicle
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