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2. RADAR OPERATION
2-50
A/C SEA control
For optimum range SART detection, this control should be set to the minimum.
Care should be exercised as wanted target 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 nm from the
furthest dot back towards own ship.
Some sets have automatic/manual anti-clutter sea control facilities in which case
the operator should switch to manual.
A/C RAIN control
This should be used normally (to break up areas of rain) when trying to detect a
SART response which, being a series of dots, is not affected by the action of the
anti-clutter rain circuitry. Note that racon responses, which are often in the form
of a long flash, will be affected by the use of this control.
Some sets have automatic/manual anti-clutter rain control facilities in which case
the operator should switch to manual.
Note: This SART information is excerpted from IMO SN/Circ 197 Operation of
Marine Radar for SART Detection.
2.27.4 Racon (Radar Beacon)
A racon is a radar transponder which emits a characteristic signal when triggered
by a ship’s radar (usually only the 3 centimeter band). The signal may be emitted
on the same frequency as that of the triggering radar, in which case it is
superimposed on the ship's radar display automatically.
The racon signal appears on the PPI as a radial line originating at a point just
beyond the position of the radar beacon or as a Morse code signal (see figure
below) displayed radially from just beyond the beacon.
Racon
Appearance of racon signal on the radar display