22
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. Should the patrol car be 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. Range 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 PYTHON III 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
PYTHON III
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, which 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 speed readings. However, the officer needs to be aware that these
sources of electrical noise may affect the operation of the radar.
Intermittent readings need not be confusing if the officer is familiar with the operation of
the PYTHON III. For example, if the radar is pointed at the dashboard of the patrol
vehicle, it may read the speed of the defroster/heater fan, because most dashboards are
now made of plastic. The PYTHON III comes equipped with specially designed mounting
brackets that will help to eliminate intermittent readings from fan pickup.
