Bearing Accuracy; Range Measurement; False Echoes; Multiple Echoes - Furuno FR-8045 Operator's Manual

2.1.3

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 depends on the narrow-
ness of the radar beam. The bearing taken is relative to the heading of the ship.
Correct adjustment of the heading line at installation is important to get accurate bear-
ings. To minimize the error when you measure the bearing of a target, put the target
echo at the extreme position on the screen by selecting a suitable range.
2.1.4

Range measurement

Measurement of the range to a target is important function of the radar. There are
three methods to measure range: the fixed range rings, the Variable Range Marker
(VRM), and the cursor (if the cursor is set to measure range and bearing). The fixed
range rings appear on the screen with a given interval and provide a rough estimate
of the range to a target. The diameter of VRM is increased or decreased so that the
marker touches the inner edge of the target (see paragraph 1.15.2). The VRM is a
more accurate range measurement than the fixed range rings. For cursor, see
section 1.13.
2.2

False Echoes

The echo signals can appear on the screen at positions where there is no target or
disappear when there are targets. These false echoes are shown below.
2.2.1

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 can be seen on the dis-
play at double, triple or other multiples of the actual range of the target as shown be-
low. You can reduce and remove the multiple reflection echoes with the A/C SEA
control.
Target
Your ship
Multiple echoes
2. DESCRIPTION OF RADAR
True
echo
Multiple
echo
2-3