Raymarine RL70C, Owner'S Handbook Manual

Page: 73 / 218

Chapter 3 Standard Radar Operations 59
On shorter ranges, you may wish to reduce the gain slightly to reduce the
speckle and therefore improve target definition.
Sea Clutter Control
Radar returns from waves around your vessel can clutter the centre of the radar
picture, making it difficult to detect real targets. Such
sea clutter usually
appears as multiple echoes on the display at short range scales, and the echoes
are not repetitive or consistent in position. With high winds and extreme
conditions, echoes from sea clutter may cause dense background clutter in the
shape of an almost solid disc.
D3968-1
The Sea control reduces the gain level in the areas near your vessel, extending
up to 3 to 5nm depending on the wave and sea conditions. This has the effect of
reducing the sea returns to intermittent small dots, while small targets are still
visible. Gain levels further from your vessel remain unchanged.
You can use the gain and Sea control to help minimise the effects of side lobes
(see
Identifying False Echo Returns above).
Note: O n short range scales, do not set the Sea control so high that all clutter is
removed, since this could stop you seeing echoes from close targets.
Tuning the Receiver
The TUNE control is used to fine tune the receiver in the scanner for maximum
target returns on the display. In Auto mode, the radar tunes itself automatically
on all range scales.
We recommend that you leave the
TUNE TUNE TUNE TUNE TUNE
control in Auto
mode.
If you do set the TUNE control to Manual, you will need to adjust it about 10
minutes after you have turned on the radar, since the required setting changes
once the magnetron has warmed up.
If you cannot tune the radar successfully, refer to Section 7.5 for information on
the Tune Preset function.
Adjusting Gain,
Sea Clutter and
Rain Clutter
SEA
MANUAL
75%
TUNE
A
U
T
O