Interference Information and Precautions
There are several factors that can influence the operational behavior of Doppler radar. These influences can be
natural or man-made. A knowledgeable operator will not be confused by these external influences.
1. Natural
Influences
Driving rain or blowing dust can cause a scattering effect, or diffusion, which can decrease the effective
range. A driving rainstorm may affect the patrol display. Close observation of the patrol vehicle speed is
recommended.
Terrain can affect the range. If the patrol car is on a slight decline, the antenna could be shooting short of
the target vehicle. If on a slight incline, it could be shooting over the target vehicle. The distance at
which the radar can detect vehicles may be shortened in either case.
Strong reflectors can cause target readings that are the same as the patrol speed when in the moving
mode. To avoid this problem, the Ranger EZ detects these harmonics and inhibits their display.
Note
: The harmonic detection feature may cause occasional blanking of legitimate target speeds when it
is the same as the patrol speed, or a multiple of it. If the operator suspects this is the case, he can change
his speed. In any case, the range of any other target is not changed; for example, if the closest target is
blanked due to the coherence detector, the Ranger EZ will not acquire and display a weaker, more distant
target in its place.
2. Man-made
Influences
These influences are normally the most troublesome because they generally involve electronic signals that
may cause spurious displays, or they may lessen the effective range.
Power transformers, radio transmitters, neon lights, etc. generate electronic noises. These influences
generate a phenomenon that can cause radar to display a false reading or lessen the effective range. The
RFI indicator will show the presence of strong RF fields caused by local transmitters. To prevent
possible readings caused by the interference, no target speed will be displayed when this indicator is on.
Intermittent signals may also be caused by electrical noise produced by the vehicle’s ignition system or by
vehicles with noisy alternators. The RFI detection circuitry will recognize this noise as well and suppress
the speed readings. However, the officer needs to be aware that these sources of electrical noise may
affect the operation of the radar.
All radar speed measurement devices are sensitive to objects that move or vibrate in front of the antenna.
In instances where the antenna is pointed in the general direction of the fan, or where the radar beam is
reflected by the glass towards the heater/defroster fan, the radar may read the speed of the fan. Reading
the fan speed is annoying and, in some cases, can reduce the effective range of the speed measurement
device.
Ranger EZ includes a fan-defeat mode in which the radar will ignore targets that are within 10 yards of
the radar. This effectively inhibits readings from the defroster fan.
Intermittent readings need not be confusing if the officer is familiar with the operation of the Ranger EZ.
MPH Industries suggests the following if fan interference is suspected:
42
