Adjust Sonar Sensitivity Manually
All fish finders include a feature that allows to sonar unit to automatically set the sensitivity (gain). The effectiveness of the feature varies widely based on the manufacturer, water conditions (temperature, salinity, etc.), speed, other manual settings, and the type/placement/quality of the transducer. To ensure the best results the angler needs to learn how to manually adjust sonar sensitivity.
The following steps will ensure the best fish finder performance:
- Bring your boat to a depth you commonly fish (preferably more than 20ft). Do not attempt to do this in shallow water. The cone of bottom coverage from even the best transducers in shallow water is so small that the sonar unit is only good for showing the depth.
- Turn off the auto-sensitivity (gain) feature and turn off the auto-range feature (you can turn that back on later). Be sure that both auto-features are off! If your fish-finder is equipped with a fish ID feature, turn it off and NEVER turn it on again (see How to Understand Your Sonar).
- Manually adjust the range to more than twice the depth. If you are in 20ft of water you need to adjust your range to 50ft (40ft will not work). You can even set the range to three times the depth and get the same results.
- Adjust the sensitivity (gain) so that you can just see a faint second bottom echo. If your depth is approximately 20ft, you will see this echo at 40ft. The second echo occurs because your sonar signal is hitting the bottom and being reflected back up to the transducer. Some of that signal reflects off the surface of the water back to the bottom and up to the transducer again. The presence of the second echo ensures that the full signal is being picked up at the transducer. If your sensitivity (gain) is too high then the signal will be distorted and you will have trouble distinguishing bait from fish.
- Re-adjust the range to your desired depth or turn on your auto-range feature. Leave the auto-sensitivity and fish ID features off (indefinitely).
Periodically re-adjust the sensitivity of your sonar unit especially when moving the boat to an area when one or more environmental factors have changed. The optimal sensitivity (gain) depends on the following factors:
- Water depth
- Water temperature/density
- Water clarity
- Salinity (critical around outflows and river mouths)
Boat speed can also change the optimal desired setting. Less gain is required when a boat is drifting slowly in calm water than when the boat is trolling or cruising. The signal loss can be so significant that at higher speeds, full gain is required just to get a consistent bottom reading. In those situations the auto gain feature is probably the best bet (you are not going to mark any fish anyway).
When you are confident that you can properly adjust your fish finder, then you need to learn how to understand what you are seeing on your sonar.
The following video demonstrates the concepts for manually adjusting fish finder sensitivity.
Click to view on YouTube or share this link http://youtu.be/O9YTM5PTumU