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8 Pathfinder Radar Scanners
• Access: The scanner unit site should be easily accessible to allow
maintenance to be carried out safely.
• Magnetic compass: Mount the scanner unit at least 1 m away
from a magnetic compass.
• Cable run: The maximum length of cable between the display
unit and the scanner unit should not normally exceed 20 m (60 ft)
for radome scanners, or 15 m (45 ft) for open array scanners. If
you need to use a longer cable power cable lengths must be con-
sidered, refer to Section 1.4 Cable Runs to determine appropriate
lengths.
• Shadow sectors and false echoes: Mount the scanner away from
large structures or equipment, such as the fly bridge, large engine
stacks, searchlights, horns, or masts. It is particularly important to
avoid shadow sectors near the bow. Raising or even lowering the
scanner may help to reduce these effects.
In shadow areas beyond the obstruction there will be a reduction
of the beam intensity, although not necessarily a complete cut-off;
there will be a blind sector if the subtended angle is more than a
few degrees.
In some shadow sectors the beam intensity may not be sufficient
to obtain an echo from a very small object, even at close range,
despite the fact that a large vessel can be detected at a much
greater range. For this reason the angular width and relative bear-
ing of any shadow sector must be determined at installation.
Sometimes shadowing can be seen by increasing the radar gain
until noise is present. Dark sectors indicate possible shadowed
areas. This information should be posted near the display unit and
operators must be alert for targets in these blind sectors.
It should also be noted that wet sails create shadow areas and thus
sail boat operators should be aware that radar performance may
reduce in rain.
If you mount the scanner on a mast, echoes from the mast may
appear on the radar display. These can be minimized by placing
absorbing material, such as a block of wood, between the scanner
and mast.
• Platform rigidity/stability: The scanner platform should not
twist (causing bearing errors) or be subject to excessive vibration.
• Heat/fumes: Mount the scanner away from the top of exhaust
stacks, since the scanner and cables can be damaged by excessive
heat and the corrosive effects of exhaust gases.
154_4.book Page 8 Wednesday, October 25, 2000 3:02 PM