Interference

[Hawker]

While fishing last weekend with a buddy in his boat, I noticed some strange interference on his locator when the trolling motor was either turned on or off. No interference when speed or course corrections were made, only when turned on or off. He is running four batteries for the trolling motor, isolated completely from the dual cranking/accessories batteries. He is running a M/C Terrova trolling motor and a new Lowrance HDS unit with all the bells and whistles. He is stumped as am I what can be causing the interference, and how since the batteries that run the TM are isolated in no close proximity to the batteries that run the electronics and other accessories. It's pretty weird, any suggestions as to a cure??

[yarcraft91]

Try re-locating some of the wires- either TM power or sonar power and transducer cables. Turning the TM on and off creates radio frequency interference and the wiring can work like an antenna. The greater the distance separating the wires, usually the less problem you'll have. Another possibility is to put a ferrite on the sonar power wires near the sonar- chasing down RF interference is sort of a guessing game without the right equipment.

[ferriswheel]

You can also try looking for ground loop issues. Check your charging system to ensure nothing is connected. As previous poster mentioned, check wire routing.

A simple test is hooking your sonar to an independent battery temporarily (try an alarm battery as your source). If that fixes you know it is the on board batteries or wiring.

[Hombre Robusto]

My buddy was getting weird lines on his HDS when someone would communicate on the VHF radio (didn't have to be in his boat). He bought some wire loom/shield, and shielded the radio and HDS wires with it, and all interference went away.

[Hawker]

I guess I shouldn't have bugged my fishing partner so much about the interference that I noticed, he's going bonkers looking for it now! ha The four batteries for the trolling motor are under the console and the batteries for the big motor and electronics and accessories at at the back of the boat, but do pass into and through the console to his electronics. He runs a Minn Kota Terrova and uses the wireless remote exclusively for it's operation. The boat is a center console 23' Predator which he uses almost exclusively for guiding, so the console has a ton of room under it. I am sort of leaning to the idea that it is RF interference coming from the wireless remote, but I really don't know for sure. I told him about the shielded wire, so he may be looking into that. Appreciate the thoughts and ideas from ya'll and I'll keep passing them onto to him!

[yarcraft91]

I have a Minnkota Co-pilot, operate the remote within 1' of an LMS-527 and have never seen interference while doing that, so I'm inclined to doubt that's your friend's problem (but, anything's possible). My TM wiring and console wiring are at least 3' from each other.

Sounds like the TM and console wiring on your friend's boat are closest to each other under the console. Have your friend look for places where the two sets of wiring lie parallel to and close to each other and change that so the console wires cross the TM wires at close to right angles- that can also reduce noise pickup.

Probably not the cause, but your friend might try cleaning and tightening all the TM battery connections. A loose connection in a high-current circuit can be a significant source of RF, but symptoms are usually different than what you've described. Whether it solves his problem or not, not a bad maintenance item to do once in a while. :)