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2. RADAR OBSERVATION
2-6
2.3.2 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 bandwidth
This is normally matched to the radar pulse length and is usually switched with the range scale
and the associated pulse length. 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.
2.4 RACON
A RACON is a radar beacon which emits radar receivable signals in the radar frequency spectrum
(X- or S-band). There are several signal formats; in general, the RACON signal appears on the
radar screen as a rectangular echo originating at a point just beyond the position of the radar
beacon. It has a Morse coded pattern. Note that the position on the radar display is not accurate.
RACON
RACON