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17.11.1
STC (Sensitivity Time Control)
The STC function attenuates echos from surface down to the specified STC depth by
changing the sensitivity of the receiver, decreasing it near the surface and gradually
increasing it as the depth increases.
STC impacts bottom finding so can be particularly useful i.e. to better track a rock sea
bottom distinguishing it from the mud in suspension over it for example when close to rivers
outlet to the sea (consider to use at same time also Dual Frequency mode and White Line
for an easier identification of real sea bottom), as well as to solve issues in false bottom
detection when in presense of significant surface clutter.
Its default value is SHORT for the 200kHz frequency and MID for the 50kHz frequency. Such
values are good in most conditions. However when navigating in very Shallow Waters it may
be necessary to switch it to OFF, while in very deep waters with a lot of Surface Clutter it
may be better to increase it to MID or LONG.
In some situations it may be necessary to adjust the STC so the sounder can read through the
surface noise and show the bottom. One indication that the STC needs to be changed is when the
display intermittently changes the depth from the correct depth to a very shallow depth.
The STC can be changed from Short, Mid, Long and Custom.
· STC Length
This is the depth range which the STC operates. In custom mode it can be varied from
0Ft to 1000Ft (60Ft or 255Ft on previous software versions). In preset mode it's value
is reported in the following table.
· STC Strength
It is the starting attenuation value of the STC. It acts by attenuating the Gain of the given
percentage value. In custom mode it can be varied from 0% to 100%. The STC effect
is maximum near the surface, to mitigate the Surface Clutter and it progressively
diminishes to 0 at the selected STC depth.
· Preset values table
When in shallow water and the Fish Finder display is showing a bottom or digital
readout deeper than the actual depth this situation may occur if STC is set to LONG
or MID when the bottom is shallow. This issue may be resolved by adjusting the STC
value to SHORT or even to OFF in very Shallow Waters.
CP390i and CPF390i
NOTE
Figure 17.11.1 - STC - Surface Clutter
Figure 17.11.1 - STC Preset values table
Page 127
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