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Example:
Distance Set to:
440m (0 .4 km)
Time Measured:
150 (15 .0 seconds) ( .00416 hours)
Calculated Speed:
96 km/h
To make use of the stopwatch mode, you need a road surface
that is marked with known distance intervals, or you will need to
independently make a measurement between two visible points
on the road in which you can time motor vehicles passing between
those points (for example a bridge underpass and a road sign) with
some precise distance measuring equipment .
Once you have an established measurement area, use the "-" or "+"
side of the RANGE button to enter the distance of the measurement
area in yards . Quickly press and release the (-) or (+) side of the
button to cycle up or down one single distance unit . By holding one
side of the RANGE button, the units will cycle up or down by tens,
and then later by hundreds .
When the correct distance is set, you can time motor vehicles as they
cross between the markers in your measurement area . Use the LOCK
button to start and stop the timer . The time will be counted and
displayed in the LOCKED window . Each sequential number represents
a tenth of a second (there is no decimal point displayed between the
right two digits) . For example 150 represents 15 .0 seconds .
After you have started and stopped the timer, a calculated speed
will be displayed in the TARGET window . The speed shown will be in
km/h .
The accuracy of the stopwatch mode will be limited by the precision
in which the distance measurement was made and the precision in
which the timer start and stop was activated . Press the MODE button
to exit the Stopwatch mode .
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6. Performance Tips
Understanding potential radar interference and what to do when it
occurs can greatly improve your results .
6.1 How Radar Works
Determining a motor vehicle's speed begins with the radar antenna
transmitting and directing a beam of microwave energy (radio
waves) at an approaching (or receding) target motor vehicle . When
energy from this beam strikes a moving motor vehicle, a small
amount of the beam is reflected back to the antenna .
The reflected signal frequency shifts by an amount proportional to
the speed of the target motor vehicle . This is known as the Doppler
Effect . The radar device then determines the target motor vehicle
speed from the difference in frequency between the reflected and
transmitted signal .
6.2 Interference Sources and Remedies
When properly installed and operated, Doppler radar technology
is accurate and reliable . However, variations in the environment
can cause situations and circumstances, which can cause spurious
responses which are readily identified by a qualified operator . Signs
that a speed is spurious can include the following characteristics:
25/Aug/2010
• A valid target motor vehicle speed in the operational range will
always override the source of interference and will be confirmed
by the audio component .
• The Doppler tone will lack the pitch and clarity component .
• Speeds are irregular .
• Speeds appear to track with the engine speeds .
6.2.1 Angular Interference (Cosine Effect)
When operating in the Stationary Mode, the cosine effect causes
the radar unit to display a speed, which is always lower than the
actual target motor vehicle speed . This condition exists when the
25/Aug/2010
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