Radar Resolution; Bearing Accuracy; Range Measurement - Furuno FR-2125V Operator's Manual

X-band and S-band
In fair weather, the above equation does not give a significant difference between X- and
S-band radars. However, in heavy precipitation condition, an S-band radar would have
better detection than an X-band radar.

2.1.2 Radar resolution

There are two important factors in radar resolution (discrimination): bearing resolution and
range resolution.
Bearing resolution
Bearing resolution is the ability of the radar to display as separate pips the echoes re-
ceived 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 chosen for a bearing resolution better than 2.5 (IMO Resolu-
tion). 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
pulselength only. Practically, a 0.08 microsecond pulse offers the discrimination better
than 35 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 .

2.1.3 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 nar-
rowness 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.

2.1.4 Range measurement

Measurement of the range to a target is also a very important function of the radar. Gener-
ally, 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 diam-
eter is increased or decreased so that the marker touches the inner edge of the target,
allowing the operator to obtain more accurate range measurements.
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