Eliminate Trolling motor Interference from Lowrance HDS Sonar
This is the way I routed the transducer wire on my Ultrex. There are 2 wires because I included the transducer built into
the trolling motor with the one from the HDI transducer mounted on the motor.
A Fortrex TM mount is the same as the Ultrex so you should be able to route cables the same way. I tapped holes and
used cable clamps to secure the cables to the bracket but zip ties work just as well.
The reason you don’t want the transducer cable run down the cable sheath is that the interference is generated in the
motor controller located in the foot pedal and travels up the wires inside the cable sheath making it an antenna.
One other place where interference is generated is the commutator plate inside the motor housing. Minn Kota tries to
deal with this by providing a wire that routes the noise to the negative battery circuit. This wire has a 3 amp fuse in the
trolling motor head. You need to check that the fuse is not blown. Just remove the 4 screws on the back of the trolling
motor head and the top comes off. The fuse holder should be visible.
There is a way to determine if the noise is coming from the motor controller in the foot pedal. The physics of the circuit
will cause the interference to be worse at slower speeds, get better as you move up the dial and almost if not
completely disappear at 100%. This simple on water test helps to isolate the source.
In addition to trying to keep the interference away from the HDS unit, there are some settings on the sonar that will
help:
Ping Speed – MAX
Scroll Speed – NORMAL
Surface Clarity – MEDIUM
Noise Rejection – MEDIUM
Hope these simple steps solve your problem.
Bill Reynolds