Furuno FAR-21 7-BB Series, Operator'S Manual

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2. RADAR OBSERVATION
2-7
2.3.3 General remarks on receiving SART
SART range errors
When responses from only the 12 low frequency sweeps are visible (when the
SART is at a range greater than about 1 nm), the position at which the first dot is
displayed may be as much as 0.64 nm beyond the true position of the SART.
When the range closes so that the fast sweep responses are seen also, the first
of these will be no more than 150 meters beyond the true position.
Radar
b
andwidth
This is normally matched to the radar pulselength and is usually switched with
the range scale and the associated pulselength. Narrow bandwidths of 3-5 MHz
are used with long pulses on long range scales and wide bandwidths of 10-25
MHz with short pulses on short ranges.
A radar bandwidth of less than 5 MHz will attenuate the SART signal slightly, so
it is preferable to use a medium bandwidth to ensure optimum detection of the
SART.
Radar side lobes
As the SART is approached, side lobes from the radar antenna may show the
SART responses as a series of arcs or concentric rings. These can be removed
by the use of the anti-clutter sea control although it may be operationally useful
to observe the side lobes as they may be easier to detect in clutter conditions
and also they will confirm that the SART is near to own ship.
Note:
SART information excerpted from IMO SN/Circ 197 OPERATION OF
MARINE RADAR FOR SART DETECTION.