Bearing Accuracy; Range Measurement; False Echoes - Furuno FAR-2218-BB Operator's Manual

2.1.5

Bearing accuracy

One of the most important features of the radar is how accurately the bearing of a tar-
get can be measured. The accuracy of bearing measurement basically depends on
the narrowness of the radar beam. However, the bearing is usually taken relative to
the ship's heading, and thus, proper adjustment of the heading line at installation is an
important factor in ensuring bearing accuracy. To minimize error when measuring the
bearing of a target, put the target echo at the extreme position on the screen by se-
lecting a suitable range.
2.1.6

Range measurement

Measurement of the range to a target is also a very important function of the radar.
Generally, there are two means of measuring range: the fixed range rings and the vari-
able range marker (VRM). The fixed range rings appear on the screen with a prede-
termined interval and provide a rough estimate of the range to a target. The variable
range marker's diameter is increased or decreased so that the marker touches the in-
ner edge of the target, allowing the operator to obtain more accurate range measure-
ments.
2.2

False Echoes

Occasionally echo signals appear on the screen at positions where there is no target
or disappear even if there are targets. They are, however, recognized if you under-
stand the reason why they are displayed. Typical false echoes are shown below.
Multiple echoes
Multiple echoes occur when a transmitted pulse returns from a solid object like a large
ship, bridge, or breakwater. A second, a third or more echoes may be observed on the
display at double, triple or other multiples of the actual range of the target as shown
below. Multiple reflection echoes can be reduced and often removed by decreasing
the gain (sensitivity) or properly adjusting the A/C SEA control.
Target
Your ship
True
echo
Multiple
echo
2. RADAR OBSERVATION
2-3