Power, pulse length, TVG and AGC decide how strong each echo looks at each distance. Set them well and a school keeps the same color as you close on it.
At a glance
- Lower TX OUTPUT, not gain, over shallow hard bottom
- Longer pulse for surface and midwater fish; shorter to separate fish from the bottom
- Reduce TVG NEAR by 1 to 2 to clear surface clutter
- AGC 0 to 3 and 2ND AGC 1 to 4 for the bottom tail
About 8 minutes. Part of Tune the picture in the CSH-8L MK2 course.
Power and pulse
For long range, use TX OUTPUT 10. Over shallow, hard bottoms, lower the output rather than the gain: it quiets the strong bottom echo while weak fish echoes stay visible. Pulse length runs from 0.5 to 20 ms and is tied to the range. A shorter pulse separates fish from the bottom; the longest pulse suits fish near the surface or in midwater. For close targets, Furuno USA notes that reducing power and pulse gives a better size reading.
TVG near and far
TVG NEAR sets sensitivity within about 300 m and TVG FAR beyond. Two rules from Furuno: reduce NEAR by one or two to kill surface clutter and plankton, and set the pair so that a school keeps the same color as it moves from the far zone into the near zone. If the school brightens or fades as it crosses the boundary, the two settings are out of balance.
AGC and 2ND AGC
Furuno suggests 0 to 3 for AGC and 1 to 4 for 2ND AGC to deal with the bottom tail. Furuno USA's starting preset uses AGC 1 and 2ND AGC 2.
Gain, last
Gain is usually between 3 and 7. If you reach for more gain to see a weak echo, check TX OUTPUT, TVG and the noise limiter first. In shallow water with old echoes, Furuno also suggests setting TX CYCLE to 7 or 8.
Check yourself
Three questions
Sources
- CSH5LMK2 CSH8LMK2 Operator's Manual: Sections 1.4, 2 and 6
- CSH8LMK2 Base Settings Guide: Settings
- CSH5LMK2 CSH8LMK2 Operator's Manual: Appendix 1
This lesson summarizes Furuno's public documents in our own words. Limits and settings differ by model and software version, so your own manual and your installer have the last word. OmniCSH is an independent project, not a Furuno program.