User Manual
Reference number: 4111A-RADAR4600-GBD-R1.1
Date: 27 February 2018
Page 125 of 149
False image of a far distant target as second trace echo
Depending on weather conditions, skip appear caused by the temperature inversion layer of air, etc. In this
case, the unusual propagation of the radio wave may reach distant targets out of the radar range. A target
at more than the maximum range may appear as an image target, and may be displayed as a false image
closer than an actual distance.
This phenomenon will be suppressed in modern radar systems by jittering the send pulses, so that such kind
of targets will be received in shifting positions. Furthermore the IR function and/or ASC Sea1 can be used to
eliminate such false targets.
7.10
Target enhancer
Objects which are equipped with RACON or SART transponders start to transmit radar pulses when they are
hit by radar waves. These transmitted pulses are received and shown in a special manner on screen like
radial stretched targets.
7.10.1
RACON targets
RACON signals appears on the radar screen as radial
directed flashes with a beam width of about 1° to 2°. The
stretched image starts short behind of the carrying
beacon, which is shown as normal target. The length
depends on the duration of the RACON pulse, which is
specified by IMO to have a length of about 20% of
maximum range but not more than 5NM. Normally they
will have a length of about 1.5 to 3NM.
RACON signals may have a coding by showing short and long pulses as a morse code. Especially in areas
with more than one with RACON equipped beacons this is used to get clear identification.
7.10.2
SART targets
SARTs (Search And Rescue Transponders) have a
similar characteristic like RACONs. But they react
only on X-band radar within a distance of about
5NM. The SART is activated by radar pulses from a
vessel and transmits a series of 12 short radar
pulses on same frequency. The regarding image
will be like the left shown screen example, if the
transponder is far away. When the distance
becomes shorter, the image changes in a way like
in right shown example.
A SART-Transponder separated from the
belonging ship is mostly not visible on radar
screen. But it will be positioned just in front of the
first echo point