Furuno CSH-8L - Manual (Page 30)

2. FINE TUNING THE SONAR PICTURE
2-2
8. On a long range, locate a fish school which is approaching own ship. Note
that the tilt should be kept adjusted so that the fish school is always placed in
the center of the sonar beam, i.e., so that the fish school is displayed in
strongest colors possible. Check that the fish echo is displayed in the same
color while it approaches. If the color changes suddenly to weaker colors as
the fish echo enters FAR and NEAR areas, the TVG is improperly set. Adjust
the TVG to correct it. If this again produces sea surface reflections and noise,
try to remove them with the AGC and noise limiter as described later on.
9. Press the [MENU] key to close the menu.
2.2 Displaying Surface Fish Clearly
When you are searching for surface fish with the tilt set to a narrow angle, sea
surface reflections may disturb or mask wanted fish echoes. In this case, in
addition to the TVG adjustment described earlier, adjust AGC on the SONAR
menu. Normally set it between “0” and “3.”
2.3 Suppressing Bottom Tail
As noted earlier, fish schools (echoes) located near the bottom are sometimes
difficult to detect because you have to discriminate them from the bottom
reflections. AGC, PULSE LENGTH and 2ND AGC in the SONAR menu, if used
properly, decrease the tail of bottom reflections, making it easier to discriminate
bottom fish.
2.3.1 AGC
The AGC functions to automatically reduce the receiver gain only against strong
echoes such as the bottom or a large fish school. Since weak echoes remain
unaffected, a small fish school becomes easier to detect. Adjust the AGC so it
works only on bottom reflections.
1. Press the MENU key.
2. Use the [RANGE] control to choose [MENU MODE] at the top of the screen.
3. Use the [GAIN] control to choose SONAR to display the SONAR menu.
4. Use the [RANGE] control to choose AGC.
5. Use the [GAIN] control to set AGC value. The setting range is 0-10 and the
higher the setting the stronger the AGC effect.
6. Press the [MENU] key to close the menu.