Performance Tips; How Radar Works; Interference Sources - Decatur Electronics GHD User Manual

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7. Performance Tips

Understanding potential radar interference and what to do when it occurs
can greatly increase the radar's performance.

7.1 How Radar Works

Determining a vehicle's speed begins with the radar gun transmitting
a beam of microwave energy (radio waves) at an approaching or
departing target vehicle. When energy from this beam strikes a
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 vehicle. This is known as the Doppler effect.
The radar device then determines the target vehicle speed from the
difference in frequency between the reflected and transmitted signal.

7.2 Interference Sources

When properly installed and operated, Doppler radar technology
is extremely accurate and reliable. However, variations in the
environment can cause situations and circumstances which can cause
spurious (erratic and unusually low or high) speeds to display. Signs
that a speed is spurious can include the following characteristics:
• A reading appears when no target vehicle is in the operational
range of the antenna.
• A target vehicle entering the operational range overrides the
interference signal, causing the display speed to change suddenly
to the vehicle's speed.
• The Doppler tone is corrupted with noise.
• Speeds are irregular and do not provide a valid traffic history.
• Erroneous speeds appear to track with the engine speeds.
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USER'S MANUAL
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