Furuno FSV-75, Operator'S Manual

Page: 83 / 235

3. VERTICAL SLANT MODE
3-5
3.5 How to Eliminate Weak Echoes
Echoes from targets such as bottom and fish return to the transducer in order of dis-
tance to them, and when we compare their intensities at the transducer face, those
from nearer targets are generally stronger due to little propagation attenuation and lit-
tle absorption. If these echoes are displayed directly on the screen, the size of the dis-
played echo from the same school of fish may change with distance, making it difficult
to judge the actual size of the school of fish. To overcome this inconvenience use the
TVG curve function. It compensates for propagation loss of sound in water; amplifica-
tion of echoes on short range is suppressed and gradually increased as range increas-
es so that similar targets are displayed in the similar intensities irrespective of the
ranges to them.
3.5.1 How to set the TVG curve
You can adjust the gain change for the TVG curve, do as follows.
1. Open the menu.
2. Select [2 Gain Setting], then left-click.
3. Select [1 TVG Curve], then left-click.
4. Left-click the S or T button to select the desired setting.
The smaller the number, the gentler the gain change over distance.
5. Select [Quit], then left-click.
6. Close the menu.
The TVG is also used to suppress unwanted echoes (sea surface reflections,
cruising noise, etc.) on near ranges. If the selected curve does not provide satis-
factory results, try to adjust [TVG-Near], [TVG-Medium] or [TVG-Far], as shown in
section 3.5.2.