1. OPERATION
1-42
1.26.2
How to erase weak echoes for external echo sounders where
"External Fish Finder Window" is set to "On" at installation
1. Place the cursor inside the external fish finder screen, then right-click to show the
[External Fish Finder] menu.
2. The [Sounder] menu is already selected.
3. Select the [Color Erase] setting. The drop-down options box appears at the far
right-side of the window.
4. Click the drop-down box, then select the appropriate color erasure level. As the
setting increases, reflections are removed in order, from weakest to strongest.
5. Click [Apply] to save the current changes and change or adjust other settings.
Click [OK] to save the current changes and close the menu window.
Click [Cancel] to abort all changes and close the menu window.
1.27
How to Adjust TVG (Time Varied Gain)
A school of fish at a deep depth is displayed in weak colors even if it is equal in
strength to one in shallow waters. This is due to propagation attenuation of the ultra-
sonic wave. To compensate for this difference, use TVG. TVG automatically adjusts
the gain with depth so that echoes of the same strength and different depths are
shown in the same colors regardless of their depths. The gain is increased with depth
to display echoes of equal strengths in the same colors. In the figure below, for exam-
ple, the TVG is set for 100 m and the TVG level is adjusted. Then, unwanted echoes
at a distance less than 100 m are deleted and echoes at depths greater than 100 m
are not affected.
0 m
100 m
0 m
100 m
TVG OFF:
Schools of fish of equal strengths
shown in different sizes and colors.
TVG adjusted:
Schools of fish of equal strengths
shown in same sizes and colors.
Unwanted echoes
appear.
Unwanted echoes
suppressed.
