Furuno FR-1500 MARK-3 Series User Manual page 83

General remarks on receiving SART
Radar range scale
When looking for a SART it is preferable to use either the 6 or 12 nautical mile range scale. This is
because the total displayed length of the SART response of 12 (or 24) dots may extend
approximately 9.5 nautical miles beyond the position of the SART and it is necessary to see a
number of response dots to distinguish the SART from other responses.
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 mush 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 bandwidth
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.
Detuning the radar
To increase the visibility of the SART in clutter conditions, the radar may be detuned to reduce the
clutter without reducing the SART response. Radar with automatic frequency control may not
permit manual detune of the equipment. Care should be taken in operating the radar in the
detuned condition as other wanted navigational and anti-collision information may be removed.
The tuning should be returned to normal operation as soon as possible.
Gain
For maximum range SART detection the normal gain setting for long range detection should be
used, i.e., with a light background noise speckle visible.
A/C SEA control
For optimum range SART detection, this control should be set to the minimum. Care should be
exercised as wanted targets in sea clutter may be obscured. Note also that in clutter conditions the
first few dots of the SART response may not be detectable, irrespective of the setting of the
anti-clutter sea control. In this case, the position of the SART may be estimated by measuring 9.5
nautical miles from the furthest dot back towards own ship.
Some sets have automatic/manual anti-clutter sea control facilities in which case the operator is
advised to use manual control initially until the SART has been detected. The effect of the auto sea
control on the SART response can then be compared with manual control.
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