Furuno FCR-2107 series, Operator'S Manual

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3. Radar Observation
3-2
Bearing resolution
Bearing resolution is the ability of the radar to display as separate pips the echoes received from two targets which
are at the same range and close together. It is proportional to the antenna length and reciprocally proportional to the
wavelength. The length of the antenna radiator should be selected for a bearing resolution better than 2.5° (IMO
Resolution). This condition is normally satisfied with a radiator of 1.2 m (4 ft) or longer in the X-band. The S-band
radar requires a radiator of about 12 feet (3.6 m) or longer.
Range resolution
Range resolution is the ability to display as separate pips the echoes received from two targets which are on the
same bearing and close to each other. This is determined by pulse length only. Practically, a 0.08 microsecond pulse
offers the discrimination better than 40 m as do so with all FURUNO radars.
Test targets for determining the range and bearing resolution are radar reflectors having an echoing area of 10 m
2
.
Bearing accuracy
One of the most important features of the radar is how accurately the bearing of a target 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 selecting a suitable range.
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 variable range marker (VRM). The fixed range rings appear on the
screen with a predetermined 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 inner edge of the target, allowing the
operator to obtain more accurate range measurements.