Furuno Marine Radar - Manual (Page 16)

A/C Sea (STC): Sea control, also called STC
(Sensitivity Time Constant), suppresses reflections
from waves near own ship. In rough seas the
reflected echoes from wave crests are very strong,
producing a mass of echoes which cover the central
part of the display. This is called sea clutter. Any
echoes within the clutter will be partially or totally
obscured. Adjust this control to reduce the clutter
and distinguish echoes. The proper setting should be
such that the clutter is suppressed and echoes become
distinguishable. If the control is set too high, both sea
clutter and echoes will disappear from the display.
When there is no sea clutter visible on the display,
turn the control fully counterclockwise.
Brill: This control adjusts the display brilliance.
Range: Press the [+] and [-] keys to raise and lower
the range respectively. When you change ranges,
the number of range rings and range ring interval as
well as pulselength are automatically changed. For
confirmation, the range and range ring interval appear
on the display.
Rings: Press this key to show or hide the range
rings. Range rings provide an estimate of the range
to a target. The number of range rings and range ring
interval automatically change with the range. Ring
interval (distance between rings) appears on the
display.
VRM: The VRM (Variable Range Marker) measures
the range to targets. To measure range, press the key
to display the VRM. It appears as a dashed circle.
Adjust the VRM so that it touches the inner edge of
the target. The range to the target appears in a data
box on the display. Some Radars may display two
VRM’s; the length of the dash of the #2 VRM is
longer than that of the #1 VRM.
EBL: The EBL (Electronic Bearing Line) measures
bearing to targets in degrees. To measure bearing,
press the key to display the EBL. It appears as a
dashed line. Adjust the EBL so that it bisects the
target. The bearing to target appears in a data box on
the display. Some Radars can display two EBL’s; the
length of the dash of the #2 EBL is longer than that of
the #1 EBL.
Offset EBL: This EBL can be shifted to any
location on the display. This allows you to predict
other ships’ course (to avoid collision) and measure
the range and bearing between two targets.
Plot: This function plots the movement of all ships
relative to own position. Press the key to start plotting.
The positions of all targets at the end of the preset
time are marked on the display.
Echo Trails: This feature continuously shows the
movements of other ships in afterglow. It is useful for
assessing target movement and collision possibility.
Display Mode: The display mode determines target
position and movement on the display. There are two
types of display mode: Relative and True.
Relative Bearing Display: • This mode is also
known as Head-up, since own ships heading is
always at the top of the display. The position of
own ship is fixed and echoes of all other objects
therefore move relative to own ship. This is the
usual form in small Radar sets.
True Bearing Display:
• This mode is sometimes
called North-up since the display is oriented
North. This mode is suitable for long -range
observation since it is somewhat like looking at a
nautical chart.
Off Center: This key shifts the display center
to location desired. The off-center display allows
the operator to view the situation around own ship
without changing the range. Set the cursor where you
want the center position to be, and then press the key.
To cancel the off-center display, press the key again.
X2 Zoom: The X2 ZOOM feature allows you to
take a closer look at a target of interest. Set the cursor
near the object you want to zoom and press the key.
To cancel zoom, press the key again.
Index Lines: Index lines are useful for maintaining
a constant distance between own ship and the
coastline or a partner ship. Press the key to toggle
index lines on and off.
Multiple Echoes
Multiple echoes can occur when a strong, short-range
echo is received from a target. A second, third or more
target may be observed on the display at double, triple
or other of the actual range of the target. Multiple
reflection echoes may be reduced or often eliminated
by decreasing the sensitivity.
Blind and Shadow Sectors
Funnels, stacks, masts or derricks in the path of the
antenna may hide Radar targets which are behind
them. If the angle subtended at the scanner is more
than a few degrees a blind sector may be produced.
Within the blind sector small targets at close range
may not be detected while larger targets at much
greater range may be detected.
Side Lobe Echoes
Every time the scanner rotates, some radiation escapes
from each side of the beam. This energy is referred to
as side lobe energy. If a target exists where it can be
detected by the side lobes as well as the main lobe,
the side lobe echoes may be represented on both
sides of the true echo at the same range. Side-lobes
usually only show at short ranges and from strong
targets. They can be reduced through careful reduction
of sensitivity or proper adjustment of the A/C SEA
control.
14 7
Radar Interference
Radar Interference occurs when in the vicinity of
another Radar operating on the same frequency
band, normally 9GHz; 3GHz for large Radars. It
is usually seen on the display as large numbers of
bright dots either scattered at random or in the form
of dotted lines extending from the center to the edge
of the display. The interference effects are easily
distinguishable from normal echoes because they do
not appear at the same places on successive rotations
of the scanner. You can reduce the interference effects
by turning on the interference rejection.
Figure 13 - Example of Sidelobes