3 sart (search and rescue transponder), General procedure for detecting sart response, Shadow sectors – Furuno FR-2805 Series User Manual
Page 84
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
µ
s) throught the
band before beginning a relatively slow
sweep (7.5
µ
s) 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
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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