Furuno FSV25S, Operator'S Manual

Page: 81 / 163

3. VERTICAL MODE
3-7
3.7 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.
3.7.1 Change sensitivity of TVG curve
Four TVG curves are available and they vary the gain from large to small.
1. Press the MENU/ESC key to open the main menu.
2. Click [Gain Setting].
3. Press the
H/V/S key to select the [V] tab.
4. Click [TVG Curve].
5. Click
S or T to select a suitable Log value.
The smaller the number, the gentler the gain changes over dis-
tance.
6. Click [Quit] on the setting box to close the box.
7. Long-push the
MENU/ESC key to close all menus.
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
satisfactory results, see section 3.7.2 for how to adjust near gain and far gain.
Gain Setting Quit
H1 P1
H2 P1
TVG Curve : 15Log
Near Gain : 5.0
Near Gain Distance : 400m
Far Gain : 5.0
Far Gain Distance : 400m
AGC : 5.0
Noise Suppress : 2.0
V P1
Quit
Cancel
2
(0.0~10.0)