Furuno CHS-5LMARK-2-55, Operator'S Manual

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2. FINE TUNING THE SONAR PICTURE
2-2
proaches. 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.
10. 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, schools of fish (echoes) located near the bottom are sometimes dif-
ficult 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, de-
crease 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 school of fish. Since weak echoes remain unaf-
fected, a small school of fish 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.