How to Stop Interference Between Two Depth Finders

Depth-finder interference is often caused by the trolling motor.

The most common cause of interference between depth finders on a boat is the trolling motor. The interference usually causes flicker or a black-out of the depth finder screen. Wiring of the depth-finder transducer, which converts the sonar signal to visual information on the screen, can also cause interference if the wire is mounted along the shaft of the trolling motor, as is common practice.

Instructions

1. Dial down the sensitivity on the depth finders to between 50 and 75 percent, which should immediately eliminate some or most of the interference. Keeping the sensitivity at 50 percent in summertime is a good idea anyway, since algae and aquatic flora will be in full growth and will affect the depth finder's readings. During the summer months, a high sensitivity setting isn't necessary.

2. Turn the trolling motor to the high-bypass setting. If interference on the depth finder suddenly stops, the problem is probably the speed-control knob on the foot pedal of your trolling motor. Adjust the knob to gauge how much improvement you can see on the depth finder screen.

3. Install the transducer wire for the depth finder on the outside of the trolling motor, not on the power cable or the foot pedal that activates the motor. The idea is to reduce electrical impulses getting to the depth finder and interfering with the screen readout.

4. Visit MotorGuide (see Resources), a resource for boaters and anglers. The company sells a product called an RF Choke, which attaches to the outside of the depth finder's power cable. The RF Choke is a filter that blocks unwanted electrical signals from the trolling motor and other devices that can cause interference on the depth finders.

Tips & Warnings

• Disconnect the trolling motor from the power source before rewiring the depth finder transducer wire.

References

• Depth finder information

Resources

• MotorGuide: Boating and angling resource