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3-3
3.3 SART (Search and Rescue
Transponder)
A Search and Rescue Transponder
(SART) may be triggered by any X-Band
(3 cm) radar within a range of approxi-
mately 8 nm. Each radar pulse received
causes it to transmit a response which is
swept repetitively across the complete ra-
dar frequency band. When interrogated, it
first sweeps rapidly (0.4 µs) throught the
band before beginning a relatively slow
sweep (7.5 µs) through the band back to
the starting frequency. This process is re-
peated for a total of twelve complete
cycles. At some point in each sweep, the
SART frequency will match that of the in-
terrogating radar and be within the pass
band of the radar receiver. If the SART is
within range, the freguency match during
each of the 12 slow sweeps will produce a
response on the radar display, thus a line
of 12 dots equally spaced by about 0.64
nautical miles will be shown.
When the range to the SART is reduced
to about 1 nm, the radar display may show
also the 12 responses generated during
the fast sweeps. These additional dot re-
sponses, which also are equally spaced
by 0.64 nm, will be interspersed with the
original line of 12 dots. They will appear
slightly weaker and smaller than the origi-
nal dots.
General procedure for detecting
SART response
1. Use range scale of 6 or 12 nm as the
spacing between the SART responses
is about 0.6nm (1125 m) to distinguish
the SART.
2. Turn off the automatic clutter suppres-
sion.
3. Turn off the Interference Rejector.
4. Turn off the Echo Average.
is a false echo which is caused by the mir-
ror effect of a large object on or close to
your ship as shown in the figure below. If
your ship comes close to a large metal
bridge, for example, such a false echo may
temporarily be seen on the screen.
True
echo
False
echo
Own
ship
Target ship
Mirror image
of target ship
Shadow sectors
Funnels, stacks, masts, or derricks in the
path of the antenna block the radar beam.
If the angle subtended at the scanner is
more than a few degrees, a non-detecting
sector may be produced. Within this sec-
tor targets can not be detected.
Radar
antenna
Radar
mast
Blind zone