Furuno FAR-1416, Operator'S Manual

Page: 87 / 226

2. RADAR OBSERVATION
2-5
Shadow sectors
Funnels, stacks, masts, or derricks in the path of the antenna block the radar beam. If
the angle subtended at the antenna is more than a few degrees, a non-detecting sec-
tor may be produced. Within this sector targets can not be detected.
2.3 SART (Search and Rescue Transponder)
2.3.1 SART description
A Search and Rescue Transponder (SART) can be triggered by any X-Band (3 cm)
radar within a range of approximately 8 nm. Each radar pulse received causes it to
transmit a response which is swept repetitively across the complete radar frequency
band. When interrogated, it first sweeps rapidly (0.4
P
s) through the band before be-
ginning a relatively slow sweep (7.5
P
s) through the band back to the starting frequen-
cy. This process is repeated for a total of twelve complete cycles. At some point in
each sweep, the SART frequency will match that of the interrogating radar and be
within the pass band of the radar receiver. If the SART is within range, the frequency
match during each of the 12 slow sweeps will produce a response on the radar dis-
play, thus a line of 12 dots equally spaced by about 0.64 nautical miles will be shown.
When the radar to the SART is reduced to about 1 nm, the radar display my show also
the 12 responses generated during the fast sweeps. These additional dot responses,
which also are equally spaced by 0.64 nautical miles, will be interspersed with the orig-
inal line of 12 dots. They will appear slightly weaker and smaller than the original dots.
Wharf and its echo
Large ship
Size of blind sector depends
on size of obstruction and range.
Radar position
Radar position
Wharf and its echo
Shadow sector occurs
because obstruction
(like mast) is in path
of radar beam.
Shadow sector
occurs because
wharf is hidden
behind ship.
Radar antenna
beamwidth
Screen A: When SART is distant Screen B: When SART is close
Echo from SART
Position of
SART
Your ship
position
Your ship
position
SART mark
length
24 NM
1.5 NM
Position of
SART
Echo from
SART
Lines of 12 dots are displayed in
concentric arcs.